sign in sign up
<<
Home , Basal forebrain, Magnocellular cell, Nucleus basalis, Substantia innominata

Neuroscience 184 (2011) 1–15

COMPARATIVE ANALYSIS OF THE OF MEYNERT AMONG PRIMATES

M. A. RAGHANTI,a,b* G. SIMIC,c S. WATSON,a overall number of subcortical that provide that C. D. STIMPSON,d P. R. HOFe AND C. C. SHERWOODd innervation. Published by Elsevier Ltd on behalf of IBRO. aDepartment of Anthropology, Kent State University, Kent, OH 44242, USA Key words: , choline acetyltransferase, Ch4, , nucleus subputaminalis. bSchool of Biomedical Sciences, Kent State University, Kent, OH 44242, USA cDepartment of Neuroscience, University of Zagreb Medical School, It was Theodor Meynert who first performed histological Croatian Institute for Brain Research, Zagreb, 10000, Croatia analyses of the human basal in 1872. In his work, dDepartment of Anthropology, The George Washington University, he described situated within the paleocortical Washington, DC 20052, USA part of the telencephalon and named this group of nuclei eFishberg Department of Neuroscience and Friedman Brain Institute, that “extends from the level of to the level Mount Sinai School of Medicine, New York, NY 10029, USA of lateral geniculate body” as the nucleus ansae lenticu- laris (Meynert, 1872). The well-known eponym “nucleus Abstract—Long projection axons from the Ch4 cell group basalis of Meynert” (nbM) was given by Kölliker (1896), of the nucleus basalis of Meynert (nbM) provide cholin- although Meynert’s work does not exactly show this cell ergic innervation to the neurons of the cerebral cortex. group (as later shown by Mettler, 1968). Along with the This cortical innervation has been implicated more detailed analysis of magnocellular groups of nuclei in behavioral and cognitive functions, including learning and memory. Recent evidence revealed differences among between the and optic tract, Kölliker primate species in the pattern of cholinergic innervation (1896) introduced the term “basal telencephalon” and also specific to the . While macaques dis- suggested cytological criteria to differentiate these neu- played denser cholinergic innervation in layers I and II rons from others within this region. These criteria require relative to layers V and VI, in chimpanzees and humans, that neurons be clearly larger than others by four to six layers V and VI were as heavily innervated as the supra- times when measuring their longer axis; neurons be hy- granular layers. Furthermore, clusters of cholinergic axons were observed within the prefrontal cortex of both humans perchromatic (i.e. a more pronounced “reaction” upon and chimpanzees to the exclusion of macaque monkeys, Nissl stain than for other neurons); the staining be more and were most commonly seen in humans. The aim of the pronounced at the periphery of the perikaryon; and that present study was to determine whether the Ch4 cell group nuclei of these cells be pale and the nucleolus easily seen. was modified during evolution of anthropoid primates as a By using these criteria, one group of such neurons situated possible correlate of these changes in cortical cholinergic mostly below the lateral part of the was named innervation. We used stereologic methods to estimate the total number of choline acetyltransferase-immunoreactive and described in the human and chimpanzee brains as the magnocellular neurons within the nbM of New World mon- nucleus subputaminalis (NSP) by Giuseppe Ayala (Ayala, keys, Old World monkeys, apes, and humans. Linear re- 1915, 1924; Simic et al., 1999) (see Fig. 3L, M at all levels), gression analyses were used to examine the relationship whereas Foix and Nicolesco (1925) were the first to de- of the Ch4 cell group with neocortical volume and brain scribe these magnocellular neurons within the internal and mass. Results showed that total nbM numbers hy- external medullary laminae and the (see poscale relative to both neocortical volume and brain mass. Notably, the total number of nbM neurons in humans Fig. 3M at the intermediate level). Finally, Brockhaus real- were included within the 95% confidence intervals for the ized that the magnocellular neurons in Meynert’s nucleus prediction generated from nonhuman data. In conclusion, are only one component of the whole complex of the basal while differences in the cholinergic system exist among forebrain magnocellular cell groups. Therefore, he included primate species, such changes appear to involve mostly nuclei of the and the olfactory tuber- axon collateral terminations within the and, with cle into the complex of the basal telencephalon nuclei—the the exception of the relatively small group of cholinergic cells of the subputaminal subdivision of the nbM at the “Basalkernkomplex” (Brockhaus, 1942). By describing not anterointermediate and rostrolateral levels, are not accom- only magno- but also microcellular nuclei, Andy and panied by a significant extra-allometric increase in the Stephan provided the most precise description of the nuclei as delineated by classic Nissl-staining *Correspondence to: M. A. Raghanti, Department of Anthropology, 750 Hilltop Drive, 226 Lowry Hall, Kent State University, Kent, OH (Andy and Stephan, 1968). 44242, USA. Tel: ϩ1-330-672-9354; fax: ϩ1-330-672-2999. The development of new histochemical and immuno- E-mail address: [email protected] (M. A. Raghanti). cytochemical methods that allowed detection of cholinergic Abbreviations: Ach, acetylcholine; ChAT, choline acetyltransferase; ChAT-ir, ChAT-immunoreactive; nbM, nucleus basalis of Meynert; neurons in the late 1970s and early 1980s provided evi- NSP, nucleus subputaminalis; PBS, phosphate-buffered saline. dence that the nbM is a major source of long projection 0306-4522/11 $ - see front matter. Published by Elsevier Ltd on behalf of IBRO. doi:10.1016/j.neuroscience.2011.04.008

1 2 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 neurons that provide cholinergic innervation to the neurons haus (1942, based on Nissl staining), the following conclu- of the cerebral cortex and the (Hong and Jang, sions can be derived: the Ch4am group mainly corresponds 2010; Johnston et al., 1979; Mesulam et al., 1983, 1986; to the pars diffusa, and the Ch4i to the of Mesulam and Geula, 1988b; Mesulam and Van Hoesen, Brockhaus. The posterior group (Ch4p) of Mesulam and col- 1976; Pearson et al., 1983). Specifically, it was demon- leagues corresponds to the cell clusters that were designated strated that more than 90% of the neurons in the nbM are by Kostovic (1986) as the pars aggregata. cholinergic in that their perikarya and axons contain cho- The nbM has been implicated in numerous behavioral line acetyltransferase (ChAT) (German et al., 1985; Mesu- and cognitive functions, including attention, learning and lam and Geula, 1988a; Mesulam et al., 1983; Nagai et al., memory, and cortical plasticity (Cabrera et al., 2006; Con- 1983; Pearson et al., 1983; Saper and Chelimsky, 1984). ner et al., 2010; Gold, 2003; Hasselmo, 1999; Ramana- Based on the topographical distribution of ChAT-immuno- than et al., 2009; Sarter and Bruno, 2000; Sarter and reactive (ChAT-ir) cell bodies in the rhesus macaque brain, Parikh, 2005). Specifically, neurons within the Ch4 cell a new nomenclature proposed by Mesulam and col- group respond to novel stimuli (Santos-Benitez et al., leagues (1983) was established. This has become the 1995; Wilson and Rolls, 1990), triggering the release of most widely accepted terminology for the primate magno- acetylcholine (ACh) within the cerebral cortex. ACh pro- cellular basal forebrain. Although the human nbM is rela- motes long-term potentiation and synaptic plasticity via an tively larger and more complex, the same terminology has inhibition of potassium conductance that enhances re- been adopted for the . According to this no- sponsiveness to further excitatory inputs. These effects menclature, the main part of the human magnocellular are mediated mainly by the muscarinic M1 receptor sub- forebrain, nbM, is designated as the Ch4 cell group and is types that are preferentially expressed within the cerebral further divided into six sectors: the anterior part (Ch4a) is cortex (von Bohlen und Halbach and Dermietzel, 2006). divided by vasculature into the anteromedial (Ch4am) and The Ch4 cell group is a target for human-specific neu- the anterolateral (Ch4al) sectors; the anterointermediate ropathological processes and several reports indicate that division (Ch4ai) that spans the anterior and intermediate it is affected early and progressively with cognitive impair- parts (and is not well-developed in nonhuman primates); ment (e.g. Grothe et al., 2010; Iraizoz et al., 1999; Mesu- the intermediate part (Ch4i) is divided by the ansa pedun- lam et al., 2004; Mufson et al., 1989b; Zaborszky et al., cularis into the intermediodorsal (Ch4id) and the interme- 2009), although other reports indicate that the cholinergic dioventral (Ch4iv) sectors; the posterior division occupies system is not affected until cognitive impairment is estab- a sector designated as Ch4p. Comparing the terminology lished (Davis et al., 1999; DeKosky et al., 2002; Gilmor et of Mesulam and collaborators (1983, based on ChAT im- al., 1999). A decrease in nbM total neuron number has munostaining) with the classification provided by Brock- been associated with a number of neurodegenerative dis- Table 1. Specimens used in this study

Group Species Common name Sex Age Fixation* Total neurons in nbM

Humans Homo sapiens Human M 24 5 231,214 Homo sapiens Human F 56 5 201,901 Apes Pan troglodytes Chimpanzee M 25 Ͻ60 161,978 Pan troglodytes Chimpanzee F 45 Ͻ60 153,407 Symphalangus syndactylus Siamang M 33 14 151,987 Old World monkeys Macaca nemestrina Pigtailed macaque F 9 7 96,051 Macaca nemestrina Pigtailed macaque F 6 7 97,854 Macaca nemestrina Pigtailed macaque F 15 7 121,067 Macaca nemestrina Pigtailed macaque M 3 7 91,730 Cercopithecus kandti Golden guenon M Adult Ͻ60 104,808 Cercocebus agilis Golden mangabey F 19 7 81,285 New World Monkeys Saguinus oedipus Cottontop tamarin M 11 18 18,955 Saguinus oedipus Cottontop tamarin F 10 45 20,563 Aotus trivirgatus Owl monkey M Ͼ18 Ͻ60 28,308 Aotus vociferans Owl monkey M 18 Ͻ60 41,536 Aotus vociferans Owl monkey F 5 7 29,614 Alouatta caraya Howler monkey M 21 Ͻ60 24,378 Alouatta caraya Howler monkey M 3 15 20,712 Saimiri boliviensis Squirrel monkey F 9 35 40,262 Saimiri boliviensis Squirrel monkey F 9 8 95,074 Pithecia pithecia White-faced saki F 1.5 Ͻ60 60,221 Cebus apella Brown capuchin M 16 7 108,760 Cebus apella Brown capuchin F 12 7 141,514 Ateles fusciceps Spider monkey F 16 45 117,868 Ateles belzebuth Spider monkey F 36 14 134,835

* Duration of time in fixation is given in days. M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 3 eases, such as Alzheimer’s disease and Parkinson’s dis- Association for Assessment and Accreditation of Laboratory Ani- ease (Arendt et al., 1983; Cullen and Halliday, 1998; Klein mal Care (AAALAC)-accredited. The animals died of natural et al., 2010; Lehéricy et al., 1993; Mufson et al., 1991; causes or were humanely euthanized for reasons independent of this research. The golden guenon brain was provided by the Office Teipel et al., 2005). Furthermore, progressive decline in Rwandais du Tourisme et des Parcs Nationaux and the Mountain numbers correlates with the worsening Gorilla Veterinary Project in compliance with CITES regulations. of in Alzheimer’s disease (Iraizoz et al., 1999) Brain specimens from adult, nongeriatric humans were provided with total numbers of neurons decreasing with duration of by the Cuyahoga County Coroner’s office. All human brains were disease (Mufson et al., 1989b). devoid of gross and microscopic neuropathologic lesions. Table 1 Gorry (1963) compared the nbM among a variety of provides details on the individuals included in this analysis. phylogenetic groups, reporting an absence of a definable All samples for this study were derived from the left hemi- sphere. In many cases, the right hemisphere was not available for Ch4 nucleus in the taxonomic orders Marsupialia, Insec- analysis and previous studies reported no differences in neuron tivora, and Chiroptera. Among the other taxonomic orders density or volume of the nbM between hemispheres or sexes in investigated (including Primates, Lagomorpha, Rodentia, humans (Halliday et al., 1993; Zaborszky et al., 2008). The sample Cetacea, Carnivora, Sirenia, Perissodactyla, and Artiodac- was limited to specimens that were sectioned continuously tyla), Gorry reported phylogenetic variation in the extent throughout the nbM and for which the entirety of the nbM was and differentiation of the nbM that correlated with the over- available. all size of the cerebral cortex, with the greatest differenti- Tissue processing ation of the nbM in Primates and Cetacea. Among primates, the nbM has been described in Old All brains were collected postmortem and were immersion-fixed in World monkeys (e.g. Ghashghaei and Barbas, 2001; Me- 10% buffered formalin. Brain mass was recorded for each speci- sulam et al., 1983, 1986; Smiley and Mesulam, 1999), New men prior to histological processing. Once fixed, the brains were transferred to a 0.1 M phosphate-buffered saline (PBS, pH 7.4) World monkeys (Everitt et al., 1988; Kordower et al., 1989; solution containing 0.1% sodium azide and stored at 4 °C to Wu et al., 2000), apes (Gorry, 1963), and humans (Halli- prevent bacterial growth and further tissue shrinkage and antigen day et al., 1993; Kostovic, 1986; e.g. Mesulam and Geula, blockade. Prior to sectioning, samples were cryoprotected by 1988a; Mesulam, 2004; Perry et al., 1984; Selden et al., immersion in a series of sucrose solutions (10%, 20%, and 30%). 1998). The anatomical descriptions of the nbM among Samples were frozen on dry ice and cut to 40 ␮m-thick sections primates are in general agreement with one another (Me- using a Leica SM2000R sliding microtome (Leica, Bannockburn, IL, USA). Individual sections were placed into eppendorf tubes sulam and Geula, 1988a; Mufson et al., 1989a; Selden et containing freezer storage solution (30% each distilled water, al., 1998), although the distribution of cholinergic cortico- ethylene glycol, and glycerol and 10% 0.244 M PBS) and num- petal cells in the human nbM has been described as more bered sequentially. Sections were stored at Ϫ20 °C until immu- extensive relative to that of macaques (Mesulam and nohistochemical or histological processing. Geula, 1988a; Mesulam et al., 1983, 1986; Mufson et al., 1989a; Simic et al., 1999). Species-specific differences in the neurochemical phenotype of the Ch4 neurons have also been observed (Melander and Staines, 1986; Wu et al., 2000). In addition, differences in the pattern of cholin- ergic innervation within the prefrontal cortex occur among human and nonhuman primate species (Raghanti et al., 2008a). In areas 9 and 32 of the prefrontal cortex, ma- caques have denser cholinergic innervation in layers I and II relative to layers V and VI. In contrast, layers V and VI are as heavily innervated as the supragranular layers in humans and chimpanzees. Furthermore, clusters of cho- linergic axons that may be involved in cortical plasticity (Mesulam et al., 1992) were observed within the prefrontal cortex of both humans and chimpanzees but not in ma- caque monkeys, and this morphology appears to be more common in humans. The goal of the present study was to assess the evolution of the Ch4 cell group among anthro- poid primates in the context of the role of cortical cholin- ergic innervation in cognition.

EXPERIMENTAL PROCEDURES Specimens

This study included brain specimens from 23 individuals repre- senting 12 anthropoid species. Postmortem nonhuman brains were obtained from zoological or research institutions where an- imals were housed according to each institution’s guidelines. All institutions were either American Zoo and Aquairium (AZA) or the Fig. 1. Primate phylogeny used for independent contrasts analyses. 4 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15

A one-in-10 series for all samples was stained for Nissl sub- Triton X-100, and 5% bovine serum albumin. Sections were then stance with a 0.5% solution of Cresyl Violet to reveal cell somata. incubated in primary antibody (goat anti-ChAT polyclonal anti- Nissl-stained sections were used to identify the cytoarchitectural body, AB144, Millipore, Billerica, MA, USA) at a dilution of 1:500 boundaries of the magnocellular neurons within the basal fore- in PBS for 48 h at 4 °C. Following this, sections were incubated in brain. Once delineated, a series of equidistant sections spanning a biotinylated secondary antibody (1:200) in a solution of PBS and the nbM was selected for immunohistochemical processing. Each 2% normal serum. The sections were then incubated in an avidin- series included sections that were rostral and caudal to the nbM to peroxidase complex (PK-6100, Vector Laboratories, Burlingame, ensure full representation of the Ch4 cell group. CA, USA) followed by a 3,3’-diaminobenzidine-peroxidase sub- The Ch4 cell group has been described in humans (Halliday strate with nickel enhancement (SK-4100, Vector Laboratories). et al., 1993; Mesulam and Geula, 1988a; Perry et al., 1984; Saper Omission of the primary or secondary antibodies resulted in a and Chelimsky, 1984; Zaborszky et al., 2008), macaque monkeys complete absence of staining. (Mesulam et al., 1983, 1986; Smiley and Mesulam, 1999), capu- chins (Kordower et al., 1989), owl monkeys (Melander and Data collection and analysis Staines, 1986), and marmosets (Everitt et al., 1988; Wu et al., 2000). These descriptions were used to inform the boundaries of Quantitative data were collected using an Olympus BX-51 photo- the nbM within the species studied here. microscope equipped with a Ludl XY motorized stage, Heidenhain z-axis encoder, StereoInvestigator software (MBF Bioscience, Immunohistochemistry Williston, VT, USA, version 8), and a digital camera that projects images onto a 24-inch LCD flat panel monitor. The Ch4 cell group Free-floating tissue sections were immunostained for choline was outlined in each section at low magnification (4ϫ). The Ch2 acetyltransferase (ChAT) using the avidin-biotin-peroxidase group was readily distinguishable from Ch4 by the more vertical method, as described previously (Raghanti et al., 2008a). Briefly, orientation of neurons. The outline included the entirety of the Ch4 sections were pretreated for antigen retrieval by incubating in a 10 group, including interstitial elements and the outline was reduced mM citrate buffer (pH 8.5) at 86 °C for 30 min. Sections were to a line between clusters of cells. The optical fractionator (West, rinsed and endogenous peroxidases were quenched using a so- 1999) was used to determine total neuron number at high mag- lution of 75% methanol, 2.5% hydrogen peroxide (30%), and nification (60ϫ). A guard zone of at least 2 ␮m was employed at 22.5% distilled water for 20 min at room temperature. Sections the top and bottom of the sections and section thickness was were preblocked in a solution of PBS with 4% normal serum, 0.6% measured at every fifth sampling site. Stereology parameters

Fig. 2. The extent and distribution of the NSP in human (A–C) and chimpanzee (D–F). The panels represent anterior, intermediate, and posterior levels, respectively. Black arrows point to neurons that constitute the nucleus subputaminalis. Scale barsϭ500 ␮m. M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 5 were variable depending on brain size. Counting frames were set the brain, the logarithm (base 10) of total neuron number was at 100ϫ100 ␮m2 with an optical disector height of 10 ␮m. The regressed on the logarithm of brain mass. The brain mass from sampling grid area ranged from 40,000 to 360,000 ␮m2. There each specimen used in this study was measured prior to his- was an average of 253Ϯ155.21 sampling sites per individual tological sectioning. We also analyzed the relationship between (range 81–608) and an average of 229Ϯ144.41 neurons counted total neuron number and neocortical volume (data taken from per individual (range 46–629). Stephan et al., 1981) to explore the scaling relationship be- All subsequent analyses used species mean values, with tween the Ch4 cell group and, specifically, the major region that the exception of the genera Aotus and Ateles in which individ- it innervates. Because not all the same species are represented uals from different species were grouped because of limited in the Stephan et al. (1981) dataset and the current study, we sample sizes. To examine the scaling of nbM neurons within used neocortical volumes from the closest relatives that were

Fig. 3. Distribution of ChAT-ir corticopetal cells within the anterior (left panel), intermediate (middle panel), and posterior (right panel) divisions of the Ch4 cell group in tamarin (A), owl monkey (B), howler monkey (C), squirrel monkey (D), white-faced saki (E), capuchin (F), spider monkey (G), macaque (H), golden guenon (I), golden mangabey (J), siamang (K), chimpanzee (L), and human (M). Abbreviations: ac, anterior commissure; cc, corpus callosum; C, caudate; CP, cerebral peduncle; ic, internal capsule; GP, ; EGP, ; IGP, ; oc, optic chiasm; ot, optic tract; P, putamen; Th, . Arrows point to neurons of the nucleus subputaminalis in chimpanzee and human. 6 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 available. Although this is not ideal, it is notable that our scaling Regression coefficients and associated standard errors were analyses against brain mass were similar to those obtained for also generated using phylogenetic independent contrasts (Gar- neocortical volume. Because both brain mass and neocortical land et al., 1992). We used Mesquite version 2.74 (mesquitepro- mass have been shown to scale linearly with the total number ject.org) to perform these analyses, based on a Bayesian estimate of neurons that they contain in primates (Gabi et al., 2010), the of phylogeny and associated branch lengths downloaded from the scaling exponents derived from analyses of nbM neuron num- 10k Trees website (http://10ktrees.fas.harvard.edu/; see phylog- ber against these variables are expected to reflect proportional eny in Fig. 1). A least-squares linear prediction of human values changes in the population of neurons in each structure relative based on nonhuman data was performed to determine if human to one another. nbM neuron number deviates significantly from allometric expec-

Fig. 3. (Continued). M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 7 tations for neocortex volume and brain mass. Predictions based tion of the nbM was ventral and anterior to the anterior on independent contrasts were calculated according to the commissure. The nucleus extended caudally until it grad- ␣ method described in Garland and Ives (2000).An level of 0.05 ually disappeared lateral to the optic tract, approximately at was set for all statistical tests. the level of the lateral geniculate nucleus. Overall, the distribution of ChAT-ir magnocellular neurons within the RESULTS nbM was relatively similar among species. A notable ex- The nbM was identifiable in all species examined, with the ception, however, was found in the New World howler anterior, intermediate, and posterior divisions readily ap- monkey (Alouatta). While the nbM occupied similar ana- parent. The magnocellular neurons within the Ch4 cell tomical levels as in the other primates, the neurons were group were large and multipolar, with variable orientation markedly limited in dispersion and in numbers (see Fig. and dendritic arborization patterns throughout the extent of 3c). Somewhat comparably, the tamarin and owl monkey the nucleus in all species analyzed. The most rostral por- (both small, New World primates) displayed relatively lim-

Fig. 3. (Continued). 8 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 ited dispersion of the anterior division of the Ch4 cell absent in all other species and although present in the group, but not to the extent observed in Alouatta. Interest- chimpanzee, it contained fewer neurons that were rela- ingly, Alouatta is the only folivorous species in this sample tively dispersed compared to the dense clusters that com- and it possesses one of the lowest encephalization quo- prise the human NSP, a difference that was pronounced at tients among primates (Jerison, 1973). the anterior level (see Fig. 2A, D). At the anterior, antero- The most notable qualitative difference in the cholin- intermediate, and intermediate levels, the NSP is defined ergic groups of cells in the basal forebrain was the pres- by the presence of very large (cholinergic) cells below the ence of the rostrolateral and anterointermediate part of the putamen (i.e. between the ventral caudate and the anterior subputaminal nucleus of Ayala (NSP) in the human and perforated substance) and lateral to the anterior commis- chimpanzee brains (Fig. 2). This group of neurons was sure. At the posterior part, the NSP is again situated below

Fig. 3. (Continued). M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 9

Fig. 3. (Continued).

the putamen, but medial to the anterior commissure. Con- A hypometric scaling relationship was also observed be- sidering the absence of a distinct NSP in the siamang, a tween total neuron numbers and neocortex volume (contem- lesser ape, it will be interesting to ascertain the status of porary species data: Fϭ21.2, Pϭ0.001, RMA slopeϭ0.557, the NSP in other hominid species, such as gorillas and R2ϭ0.658; independent contrasts: Fϭ9.158, Pϭ0.012, RMA orangutans. slopeϭ0.654, R2ϭ0.454; Fig. 7). The 95% prediction interval As expected for a sample of species spanning a 131- generated using the nonhuman data included the human fold range in total brain size (minimum—Saguinus, maxi- mean, but the observed human value was lower than the mum—Homo), phylogenetic variation was evident in the point estimate derived from the nonhuman least-squares re- total number of cholinergic neurons within the Ch4 cell gression (contemporary species data–log observed human group (see Table 1). The total number of Ch4 neurons point: 5.34; log predicted point: 5.64, 95% prediction interval: varied by 11-fold, with humans having the largest number 4.95Ͻ6.03; observed total neuron number: 216,558, pre- of neurons. The total neuron estimates generated for the dicted total neuron number: 441,124; independent contrasts– nbM in humans were consistent with the value of 200,000 log predicted point: 5.49, 95% prediction interval: 4.62Ͻ6.36; previously reported by Arendt et al. (1985). The distribution predicted total neuron number: 309,430). of ChAT-ir cells in the anterior, intermediate, and posterior divisions of the Ch4 cell group is illustrated in Fig. 3A–M. DISCUSSION For Fig. 3, photo montages of the basal forebrain were obtained at 4ϫ and markers were placed over ChAT-ir Comparative neuroanatomical studies of the mammalian neurons using Adobe Photoshop. Photomicrographs of basal forebrain have demonstrated phylogenetic variation ChAT staining for all species are presented in Fig. 4. in the size and cytoarchitectonic complexity of the magno- Additional images of the tamarin, howler monkey, and cellular basal complex (Divac, 1975; Gorry, 1963). For siamang are provided in Fig. 5. example, humans and apes (gibbon, chimpanzees, and There was a hypometric scaling relationship between gorillas) possess a different localization of galanin-ir within total nbM neuron numbers and brain mass (contemporary the basal forebrain relative to monkeys (brown capuchins species data: Fϭ20.9, Pϭ0.001, RMA slopeϭ0.593, and rhesus macaques). Specifically, monkeys display co- R2ϭ0.655; independent contrasts: Fϭ9.368, Pϭ0.011, localization of galanin in basal forebrain magnocellular RMA slopeϭ0.674, R2ϭ0.460), indicating that the number neurons whereas apes and humans do not (Benzing et al., of neurons in the nbM increase at a slower rate than 1993). Rather than colocalization, apes and humans have increases in brain mass across species (Fig. 6). The 95% a dense plexus of galanin-ir fibers that appeared to inner- prediction interval for total neuron number within the nbM vate the magnocellular neurons. In addition, carnivores generated from nonhuman data included the human mean, have a less extensive nbM with more elaboration of its however, the observed mean total neuron number in hu- medial part (Kimura et al., 1981; St-Jacques et al., 1996; mans was lower than expected (contemporary species Steriade et al., 1987), while rodents have only medial, data–log observed human point: 5.34, log predicted point: subpallidal, and peripallidal equivalents of the nbM (Arm- 5.66, 95% prediction interval: 4.95Ͻ6.03; observed total strong et al., 1983; Bigl et al., 1982; Cuello and Sofroniew, neuron number: 216,558, predicted total neuron number: 1984; Fibiger, 1982; Johnston et al., 1979; Rye et al., 454,106; independent contrasts–log predicted point: 5.46, 1984). By comparison with primates, it could be concluded 95% prediction interval: 4.61Ͻ6.31; predicted total neuron that the lineage-specific specializations of the magnocel- number: 289,953). lular chain of nuclei within the basal forebrain has been 10 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15

Fig. 4. ChAT-ir neurons and axons within the nbM of each species included in this study. Images were taken ventral to the anterior commissure, at the level of the posterior anterior commissure (corresponding to the intermediate division of the Ch4 cell group). In panels (A–L), the anterior commissure is visible in the upper left corner. Pictured are (A) tamarin, (B) owl monkey, (C) squirrel monkey, (D) white-faced saki, (E) howler monkey, (F) capuchin, (G) spider monkey, (H) golden guenon, (I) golden mangabey, (J) macaque monkey, (K) siamang, (L) chimpanzee, and (M) human. Scale barsϭ250 ␮m for panels (A–M). High magnification photomicrographs show ChAT-ir neurons and axons in chimpanzee (N) and human (O), scale barϭ50 ␮m.

“directed” mostly towards the expansion of its rostrolateral the hypothesis that the evolution of cognitive functions in part. The prominence of the nbM in the primate brain may the primate lineage might have entailed a significant alter- be therefore explained by the remarkable expansion of the ation of this neurochemical system. cerebral cortex that represents its main innervation target When the basal forebrain cholinergic system is com- (Bigl et al., 1982; Divac, 1975; Everitt et al., 1988; Gorry, pared among a larger range of mammals, the expansion of 1963; Johnston et al., 1979; Jones et al., 1976; Kievet and its rostrolateral subdivision is remarkable in humans and Kuypers, 1975; Mesulam and Geula, 1988a; Mesulam et some hominoids, considering that these species are the al., 1983; Mesulam and Van Hoesen, 1976; Pearson et al., only ones noted to have all rostrolateral groups of the nbM 1983; Saper, 1987, 1990; Struble et al., 1986). Our earlier cells. Moreover, at the most rostral and anterointermediate research identified differences in the patterning of cortical levels of the nbM complex, only humans and chimpanzees cholinergic innervation among humans, chimpanzees, and possess a subputaminal subdivision, with the human sub- macaque monkeys (Raghanti et al., 2008a). Due to the putaminal division being more cell dense and extensive role that cortical cholinergic innervation plays in learning, (see Fig. 2)(Ayala, 1915; Simic et al., 1999). The larger memory, and cognitive flexibility, the current study tested size of the subputaminal subdivision of the nbM within the M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 11

Fig. 4. (Continued).

left hemisphere of the human brain (Halliday et al., 1993; with neurodegenerative conditions. Sharma et al. (2010) Simic et al., 1999), the ascension of subputaminal cholin- reported that the number of tyrosine hydroxylase-immuno- ergic fibres through the (Kostovic, 1986) reactive neurons within the human falls towards the perisylvian language areas (Simic et al., within predicted ranges based on nonhuman primate data, 1999), and its most protracted development among all the and that the human total is lower than the predicted value. magnocellular aggregations within the basal forebrain Surprisingly, while this subcortical neuron population re- (Kracun and Rosner, 1986), suggest that, although rela- tains a scaling relationship with the areas it innervates, the tively small in size, this part of the nbM may have human- pattern and density of tyrosine hydroxylase-immunoreac- specific contributions to cognitive functions (Simic et al., tive axon collaterals within the cerebral cortex itself also 1999). Therefore, the pathological changes of these hu- displays significant variation among species (Hof et al., man-specific parts of basal forebrain may be particularly 2000; Raghanti et al., 2008b). important in the context of human-specific diseases, such We predicted that the human nbM would possess a as (Heimer, 2000), Alzheimer’s disease, significantly higher total number of neurons to support and primary progressive aphasia (Boban et al., 2006). alterations in the patterning of prefrontal cortical cholin- Interestingly, the quantitative allometric scaling pat- ergic innervation and associated cognitive specializations. terns reported here are similar to what was found for the However, humans actually had fewer nbM neurons than locus coeruleus in humans and nonhuman primates expected based on nonhuman data predictions for both (Sharma et al., 2010). Long projection neurons of the locus brain mass and neocortical volume. In conclusion, while coeruleus provide the noradrenergic innervation to the differences in prefrontal cortical cholinergic innervation neocortex and have also been implicated in learning and were reported among humans and other catarrhine pri- memory processes (Gaspar et al., 1989; Morrison and mates (Raghanti et al., 2008a), these changes were not Foote, 1986). Loss of these neurons is also associated supported by significant alterations in the subcortical cell 12 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15

Fig. 5. Low power (4ϫ) image montages in tamarin (A, B), howler monkey (C, D), and siamang (E, F). Scale barsϭ500 ␮m. population that supplies that innervation. Primates pos- diversity of -immunoreactive axon densi- sess a disproportionately large neocortex relative to other ties and distributions, there is demonstrable plasticity in the species and it is possible that there are significant devel- patterning of axon collaterals within the cortical mantle, opmental constraints on basal forebrain systems relative to which is independent of variation in the number of neurons the neocortex. However, as evidenced by phylogenetic

Fig. 7. Total neuron number within the nbM regressed on neocortical Fig. 6. Total neuron number within the nbM regressed on brain mass. volume. Data points for New World monkeys are dark grey; Old World Data points for New World monkeys are dark grey; Old World monkey monkey data points are white; lesser and great ape data points are data points are white; lesser and great ape data points are light grey. light grey. M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 13 that give rise to these projections. Thus, evolutionary mod- Davis KL, Mohs RC, Marin D, Purohit DP, Perl DP, Lantz M, Austin G, ifications in the anatomy and function of such diffuse neu- Haroutunian V (1999) Cholinergic markers in elderly patients with romodulatory systems in the brain may involve decoupling early signs of Alzheimer’s disease. JAMA 281:1401–1406. of terminal axon patterns and the distribution of neurons in DeKosky ST, Ikonomovic MD, Styren SD, Beckett L, Wisniewski S, Bennett DA, Cochran EJ, Kordower JH, Mufson EJ (2002) Upregu- the basal forebrain nuclei themselves. lation of choline acetyltransferase activity in and frontal cortex of elderly subjects with mild cognitive impairment. Acknowledgments—This work was supported by the National Sci- Ann Neurol 51:145–155. ence Foundation (BCS-0921079, BCS-0827531, BCS-0639180) Divac I (1975) Magnocellular nuclei of the basal forebrain project to and the James S. McDonnell Foundation (22002078). G.S. was neocortex, brainstem and . Review of some func- supported by the Croatian Ministry of Science, Education, and tional correlates. Brain Res 93:385–398. Sports grant no. 108-1081870-1942. Brain materials used in this Everitt B, Sirkia T, Roberts A, Jones G, Robbins T (1988) Distribution study were loaned by the Great Ape Aging Project (NIH grant and some projections of cholinergic neurons in the brain of the AG14308, “A Comparative Neurobiology of Aging Resource,” Dr. common marmoset, Callithrix jacchus. J Comp Neurol 271:533– Joseph Erwin, PI), the Cleveland Metroparks Zoo, the Michale E. 558. Keeling Center for Comparative Medicine and Research at the Fibiger HC (1982) The organization and some projections of cholin- University of Texas M.D. Anderson Cancer Center, the National ergic neurons in the mammalian forebrain. Brain Res Rev 4:327– Primate Research Center at the University of Washington (NIH 388. RR00166), the Comparative Pathology Department at the New Foix C, Nicolesco J (1925) Les noyaux gris centraux et la région England Regional Primate Research Center (Division of Research mésencéphalique optique, suivi d’un appendice sur l’anatomie Resources, grant RR00168), the Foundaton for Comparative and pathologique de la maladie de parkinson. Anatomie cérébrale. Conservation Biology, Office Rwandais du Tourisme et des Parcs Paris: Masson & Cie. Nationaux (Dr. Antoine Mudakikwa), and the Cuyahoga County Gabi M, Collins CE, Wong P, Torres LB, Kaas JH, Herculano-Houzel Coroner’s Office (Dr. Andrea McCollum). S (2010) Cellular scaling rules for the brains of an exxtended number of primate species. Brain Behav Evol 76:32–44. Garland T, Harvey PH, Ives AR (1992) Procedures for the analysis of comparative data using phylogenetically independent contrasts. REFERENCES Syst Biol 41:18–32. Andy OJ, Stephan H (1968) The septum in the human brain. J Comp Garland T, Ives AR (2000) Using the past to predict the present: Neurol 133:383–410. confidence intervals for regression equations in phylogenetic com- Arendt T, Bigl V, Arendt A, Tennstedt A (1983) Loss of neurons in the parative methods. Am Nat 155:346–364. nucleus basalis of Meynert in Alzheimer’s disease, paralysis agi- Gaspar P, Berger B, Febvret A, Vigny A, Henry JP (1989) Catechol- tans and Korsakoff’s disease. Acta Neuropathol 61:101–108. amine innervation of the human cerebral cortex as revealed by Arendt T, Bigl V, Tennstedt A, Arendt A (1985) Neuronal loss in comparative immunohistochemistry of tyrosine hydroxylase and different parts of the nucleus basalis is related to neuritic plaque dopamine-beta-hydroxylase. J Comp Neurol 279:249–271. formation in cortical target areas in Alzheimer’s disease. Neurosci- German DC, Bruce G, Hersh L (1985) Immunohistochemical staining ence 14:1–14. of cholinergic neurons in the human brain using a polyclonal anti- Armstrong DM, Saper CB, Levey AI, Wainer BH, Terry RD (1983) body to human choline acetyltranferase. Neurosci Lett 61:1–5. Distribution of cholinergic neurons in rat brain demonstrated by the Ghashghaei HT, Barbas H (2001) Neural interaction between the immunocytochemical localization of choline acetyltransferase. basal forebrain and functionally distinct prefrontal cortices in the J Comp Neurol 216:53–68. rhesus monkey. Neuroscience 3:593–614. Ayala G (1915) A hitherto undifferentiated nucleus in the forebrain Gilmor ML, Erickson JD, Varoqui H, Hersh LB, Bennett DA, Cochran (nucleus subputaminalis). Brain 37:433–438. EJ, Mufson EJ, Levey AI (1999) Preservation of nucleus basalis Ayala G (1924) Weitere untersuchungen über den Nucleus subputami- neurons containing choline actyltransferase and the vesicular ace- nalis. J Psychol Neurol 30:285–299. tylcholine transporter in elderly with mild cognitive impairment and Benzing WC, Kordower JH, Mufson EJ (1993) Galanin immunoreac- early Alzheimer’s disease. J Comp Neurol 411:693–704. tivity within the primate basal forebrain: evolutionary change be- Gold PE (2003) Acetylcholine modulation of neural systems involved tween monkeys and apes. J Comp Neurol 336:31–39. in learning and memory. Neurobiol Learn Mem 80:194–210. Bigl V, Woolf NJ, Butcher LL (1982) Cholinergic projections from the Gorry JD (1963) Studies on the comparative anatomy of the ganglion basal forebrain to frontal, parietal, temporal, occipital and cingulate basale of Meynert. Acta Anat 55:51–104. cortices: a combined fluorescent tracer and acetylcholinesterase Grothe M, Zaborszky L, Atienza M, Gil-Neciga E, Rodriguez-Romero analysis. Brain Res Bull 8:727–739. R, Teipel SJ, Amunts K, Suarez-Gonzalez A, Cantero JL (2010) Boban M, Kostovic I, Simic G (2006) Nucleus subputaminalis: ne- Reduction of basal forebrain cholinergic system parallels cognitive glected part of the basal nucleus of Meynert. Brain 129:E42. Brockhaus H (1942) Vergleichend-anatomische untersuchungen über impairment in patients at high risk of developing Alzheimer’s dis- den Basalkernkomplex. J Psychol Neurol 51:57–95. ease. Cereb Cortex 7:1685–1695. Cabrera S, Chavez C, Corley S, Kitto M, Butt A (2006) Selective Halliday G, Cullen K, Cairns M (1993) Quantitation and three-dimen- lesions of the nucleus baslais magnocellularis impair cognitive sional reconstruction of Ch4 nucleus in the human basal forebrain. flexibility. Behav Neurosci 120:298–306. Synapse 15:1–16. Conner JM, Kulczycki M, Tuszynski MH (2010) Unique contributions of Hasselmo ME (1999) : acetylcholine and memory distinct cholinergic projections to motor cortical plasticity and learn- consolidation. Trends Cogn Sci 3:351–359. ing. Cereb Cortex 20:2739 doi:10.1093/cercor/bhq022. Heimer L (2000) Basal forebrain in the context of schizophrenia. Brain Cuello AC, Sofroniew MV (1984) The anatomy of the CNS cholinergic Res Rev 31:205–235. neurons. Trends Neurosci 7:74–78. Hof PR, Glezer II, Nimchinsky EA, Erwin JM (2000) Neurochemical Cullen K, Halliday G (1998) Neurofibrillary degeneration and cell loss and cellular specializations in the mammalian neocortex reflect in the nucleus basalis in comparison to cortical Alzheimer pathol- phylogenetic relationships: evidence from primates, cetaceans, ogy. Neurobiol Aging 19:297–306. and artiodactyls. Brain Behav Evol 55(6):300–310. 14 M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15

Hong JH, Jang SH (2010) Neural pathway from the nucleus basalis of Mesulam MM, Geula C (1988b) Acetylcholinesterase-rich pyramidal Meynert passing through the cingulum in the human brain. Brain neurons in the human neocortex and hippocampus: absence at Res 1346:190–194. birth, development during the life span, and dissolution in Alzhei- Iraizoz I, Guijarro JL, Gonzalo LM, de Lacalle S (1999) Neuropatho- mer’s disease. Ann Neurol 24:765–773. logical changes in the nucleus basalis correlate with clinical mea- Mesulam MM, Hersh LB, Mash DC, Geula C (1992) Differential cho- sures of dementia. Acta Neuropathol 98:186–196. linergic innervation within functional subdivisions of the human Jerison HJ (1973) Evolution of the brain and intelligence. New York: cerebral cortex: a choline acetyltransferase study. J Comp Neurol Academic Press. 318:316–328. Johnston MV, McKinney M, Coyle JT (1979) Evidence for a cholinergic Mesulam MM, Van Hoesen GW (1976) Acetylcholinesterase projec- projection to neocortex from neurons in basal forebrain. Proc Natl tion from basal forebrain of the rhesus monkey to neocortex. Brain Acad SciUSA76:5392–5396. Res 109:152–157. Jones EG, Burton H, Saper CB, Swanson LW (1976) Midbrain, dien- Mettler FA (1968) Anatomy of the . In: Handbook of cephalic and cortical relationship of the basal nucleus of Meynert clinical neurology (Vinken PJ, Bruyn GW, eds), pp 1–55. Amster- and associated structures in primates. J Comp Neurol 167:385– dam: North-Holland Publiching Company. 420. Meynert T (1872) Vom Gehirn der Saugetiere. In: Handbuch der lehre Kievet J, Kuypers HGJM (1975) Basal forebrain and von den geweben des menschen und tiere (Stricker S, ed), pp connections to frontal and parietal cortex in the rhesus monkey. 694–808. Leipzig: Engelmann. Science 187:660–662. Morrison JH, Foote SL (1986) Noradrenergic and serotonergic inner- Kimura H, McGeer PL, Peng JH, McGeer EG (1981) The central vation of cortical, thalamic, and tectal visual structures in old and cholinergic system studied by choline acetyltransferase immuno- new world monkeys. J Comp Neurol 243:117–138. cytochemistry in the cat. J Comp Neurol 200:151–201. Mufson EJ, Bothwell M, Hersh L, Kordower J (1989a) Nerve growth Klein JC, Eggers C, Kalbe E, Weisenbach S, Hohmann C, Vollmar S, factor receptor immunoreactive profiles in the normal, aged, hu- Baudrexel S, Diederich NJ, Heiss WD, Hilker R (2010) Neurotrans- man basal forebrain: colocalization with cholinergic neurons. mitter changes in dementia with lewy bodies and parkinson dis- J Comp Neurol 285:196–217. ease dementia in vivo. Neurology 74:885–892. Mufson EJ, Bothwell M, Kordower JH (1989b) Loss of nerve growth Kölliker A (1896) Handbuch der Gewebelehre des menschen. Für factor receptor-containing neurons in Alzheimer’s disease: a quan- ärzte und studirende. Nervensystem des menschen und der thiere. titative analysis across subregions of the basal forebrain. Exp Leipzig: Engelmann. Neurol 105:221–232. Kordower J, Bartus R, Marciano F, Gash D (1989) Telencephalic Mufson EJ, Presley L, Kordower J (1991) receptor cholinergic system of the New World monkey (Cebus apella): immunoreactivity within the nucleus basalis (Ch4) in Parkinson’s morphological and cytoarchitectonic assessment and analysis of disease: reduced cell numbers and co-localization with cholinergic the projection to the amygdala. J Comp Neurol 279:528–545. neurons. Brain Res 539:19–30. Kostovic I (1986) Prenatal development of nucleus basalis complex Nagai T, Pearson T, Peng G, McGeer EG, McGeer PL (1983) Immu- and related fiber systems in man: a histochemical study. Neuro- nocytochemical staining of the human forebrain with monoclonal science 17:1047–1077. antibody to human choline acetyltransferase. Brain Res 265:300– Kracun I, Rosner H (1986) Early cytoarchitectonic development of the 306. anlage of the basal nucleus of Meynert in the human fetus. Int J Pearson RCA, Gatter KC, Brodal P, Powell TPS (1983) The projection Dev Neurosci 4:143–149. of the basal nucleus of Meynert upon the neocortex in the monkey. Lehéricy S, Hirsch E, Cervera-Pierot P, Hersh L, Bakchine S, Piette F, Brain Res 259:132–136. Duyckaerts C, Hauw J, Javoy-Agid F, Agid Y (1993) Heterogeneity Perry RH, Candy JM, Perry EK, Thompson J, Oakley AE (1984) The and selectivity of the degeneration of cholinergic neurons in the substantia innominata and adjacent regions in the human brain: basal forebrain of patients with Alzheimer’s disease. J Comp Neu- histochemical and biochemical observations. J Anat 138:713–732. rol 330:15–31. Raghanti MA, Stimpson CD, Marcinkiewicz JL, Erwin JM, Hof PR, Melander T, Staines WA (1986) A galanin-like peptide coexists in Sherwood CC (2008a) Cholinergic innervation of the frontal cortex: putative cholinergic somata of the septum-basal forebrain complex differences among humans, chimpanzees, and macaque mon- and in acetylcholinesterase-containing fibers and varicosities keys. J Comp Neurol 506:409–424. within the hippocampus in the owl monkey (Aotus trivirgatus). Raghanti MA, Stimpson CD, Marcinkiewicz JL, Erwin JM, Hof PR, Neurosci Lett 68:17–22. Sherwood CC (2008b) Cortical dopaminergic innervation among Mesulam M, Geula C (1988a) Nucleus basalis (Ch4) and cortical humans, chimpanzees, and macaque monkeys: a comparative cholinergic innervation in the human brain: observations based on study. Neuroscience 155:203–220. the distribution of acetylcholinesterase and choline acetyltrans- Ramanathan D, Tuszynski MH, Conner JM (2009) The basal forebrain ferase. J Comp Neurol 275:216–240. cholinergic system is required specifically for behaviorally medi- Mesulam M, Mufson E, Levey A, Wainer B (1983) Cholinergic inner- ated cortical map plasticity. J Neurosci 29:5992–6000. vation of cortex by the basal forebrain: cytochemistry and cortical Rye DB, Wainer BH, Mesulam MM, Mufson EJ, Saper CB (1984) connections of the , diagonal band nuclei, nucleus Cortical projections arising from the immunohistochemical localiza- basalis (substantia innominata) and hypothalamus in the rhesus tion of choline acetyltransferase. Neuroscience 13:627–643. monkey. J Comp Neurol 214:170–197. Santos-Benitez H, Magariños-Ascone CM, Garcia-Austt E (1995) Nu- Mesulam M, Mufson E, Wainer B (1986) Three-dimensional represen- cleus basalis of Meynert cell response in awake monkeys. Brain tation and cortical projection topography of the nucleus basalis Res Bull 37:507–511. (Ch4) in the macaque: concurrent demonstration of choline acetyl- Saper CB (1987) Diffuse cortical projection systems: anatomical orga- transferase and retrograde transport with a stabilized tetramethyl- nization and role in cortical function. In: Handbook of physiology— benzidine method for horseradish peroxidase. Brain Res 367:301– the nervous system (Plum F, ed), pp 169–210. Bethesda: Ameri- 308. can Phyiological Society. Mesulam M, Shaw P, Mash D, Weintraub S (2004) Cholinergic nu- Saper CB (1990) Cholinergic system. In: The human nervous system cleus basalis taupathy emerges early in the aging-MCI-AD contin- (Paxinos G, ed), pp 1095–1114. San Francisco: Academic Press. uum. Ann Neurol 55:815–828. Saper CB, Chelimsky TC (1984) A cytoarchitectonic and histochemical Mesulam MM (2004) The cholinergic innervation of the human cere- study of nucleus basalis and associated cell groups in the normal bral cortex. Prog Brain Res 145:67–78. human brain. Neuroscience 13:1023–1037. M. A. Raghanti et al. / Neuroscience 184 (2011) 1–15 15

Sarter M, Bruno JP (2000) Cortical cholinergic inputs mediating Struble RG, Lehmann J, Mitchell SJ, McKinney M, Price DL, Coyle JT, , attentional processing and dreaming: differential afferent DeLong MR (1986) Basal forebrain neurons provide major cholin- regulation of the basal forebrain by telencephalic and brainstem ergic innervation of primate neocortex. Neurosci Lett 66:215–220. afferents. Neuroscience 95:933–952. Teipel SJ, Flatz WH, Heinsen H, Bokde ALW, Schoenberg SO, Sarter M, Parikh V (2005) Choline transporters, cholinergic transmis- Stockel S, Dietrich O, Reiser MF, Moller H-J, Hampel H (2005) sion and cognition. Nat Rev Neurosci 6:48–56. Measurement of basal forebrain atrophy in Alzheimer’s disease Selden N, Gitelman D, Salamon-Murayama N, Parrish T, Mesulam M using MRI. Brain 128:2626–2644. (1998) Trajectories of cholinergic pathways within the cerebral von Bohlen und Halbach O, Dermietzel R (2006) hemispheres of the human brain. Brain 121:2249–2257. and neuromodulators. Handbook of receptors and biological ef- Sharma Y, Xu T, Graf WM, Fobbs A, Sherwood CC, Hof PR, Allman JM, fects, 2nd ed, p 386. Weinheim, Germany: Wiley-VCH Verlag Manaye KF (2010) Comparative anatomy of the locus coeruleus in GmbH & Co. humans and nonhuman primates. J Comp Neurol 518:963–971. West M (1999) Stereological methods for estimating the total number Simic G, Mrzljak L, Fucic A, Winblad B, Lovric H, Kostovic I (1999) of neurons and synapses: issues of precision and bias. Trends Nucleus subputaminalis (Ayala): the still disregarded magnocellu- Neurosci 22:51–61. lar component of the basal forebrain may be human specific and Wilson FAW, Rolls ET (1990) Neuronal responses related to novelty- connected with the cortical speech area. Neuroscience 89:73–89. and familiarity of visual stimuli in the substantia innominata, diag- Smiley J, Mesulam M (1999) Cholinergic neurons of the nucleus onal band of Broca, and periventricular region of the primate basal basalis of Meynert receive cholinergic, catecholaminergic and Gabaergic synapses: an electron microscopic investigation in the forebrain. Exp Brain Res 80:104–120. monkey. Neuroscience 88:241–255. Wu C, Hersh LB, Geula C (2000) Cyto- and chemoarchitecture of St-Jacques R, Gorczyca W, Mohr G, Schipper HM (1996) Mapping of basal forebrain cholinergic neurons in the common marmoset (Cal- the basal forebrain cholinergic system of the dog: a choline acetyl- lithrix jacchus). Exp Neurol 165:306–326. transferase immunohistochemical study. J Comp Neurol 366: Zaborszky G, Atienza M, Gil-Neciga E, Rodriguez-Romero R, Teipel 717–725. SJ, Amunts K, Suarez-Gonzalez A, Cantero JL (2009) Reduction Stephan H, Frahm HD, Baron G (1981) New and revised data on of basal forebrain cholinergic system parallels cognitive impair- volumes of brain structures in insectivores and primates. Folia ment in patients at high risk of developing Alzheimer’s disease. Primatol 35:1–29. Cereb Cortex 20:1685–1695. Steriade M, Parent A, Pare D, Smith Y (1987) Cholinergic and non- Zaborszky L, Hoemke L, Mohlberg H, Schleicher A, Amunts K, Zilles K cholinergic neurons of cat basal forebrain project to reticular and (2008) Stereotaxic probabilistic maps of the magnocellular cell mediodorsal thalamic nuclei. Brain Res 408:372–376. groups in human basal forebrain. Neuroimage 42:1127–1141.

(Accepted 6 April 2011) (Available online 13 April 2011)