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Topographical Organization of the Entorhinal Projection to the Dentate Gyrus of the Monkey

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Topographical Organization of the Entorhinal Projection to the Dentate Gyrus of the Monkey The Journal of Neuroscience, January 1989, 9(l): 216-228 Topographical Organization of the Entorhinal Projection to the Dentate Gyrus of the Monkey M. P. Witter,’ G. W. Van Hoesen, and D. G. Amara13 ‘Department of Anatomy and Embryology, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands, ‘Departments of Anatomy and Neurology, University of Iowa, College of Medicine, Iowa City, Iowa 52242, and 3The Salk Institute for Biological Studies, San Diego, California 92128 The topographic organization of the projections from the The results of the present study indicate that rostrocau- entorhinal cortex to the dentate gyrus in the macaque mon- dally oriented zones of cells that cut across several cytoar- key was studied with anterograde and retrograde tracing chitectonic subdivisions of the entorhinal cortex give rise to methods. Injections of WGA-HRP or the fluorescent retro- topographically organized projections to the dentate gyrus. grade tracers, Fast blue and Diamidino yellow, were placed Cells located laterally in the entorhinal cortex project to cau- at various levels along the rostrocaudal axis of the dentate dal levels of the dentate gyrus, whereas progressively more gyrus and hippocampus. In 5 experiments the fluorescent medially situated cells project to progressively more rostra1 dyes were injected at 2 rostrocaudal levels of the same parts of the dentate gyrus. dentate gyrus. Labeled neurons were observed mainly in layers II and Ill of the entorhinal cortex, though some were also seen in layers V and VI. The labeled layer II cells re- Behavioral data in primates, including man, indicate that the sulting from each of the tracer injections were located hippocampal formation plays an important role in memory pro- throughout much of the rostrocaudal extent of the entorhinal cesses(Scoville and Milner, 1957; Mishkin, 1978; Zola-Morgan cortex, though they tended to have a more limited distribu- and Squire, 1986; Zola-Morgan et al., 1986). While the precise tion in the transverse or mediolateral axis. Injections of retro- mechanismby which it contributes to the long-term storageof grade tracers located caudally in the dentate gyrus resulted information is not known, it is clear that the hippocampal for- in a rostrocaudally oriented zone of labeled cells that was mation is not the solerepository of memory. Information from situated laterally in the entorhinal cortex adjacent to the human amnesiccases (Scoville and Milner, 1957; Zola-Morgan rhinal sulcus. The zone of labeled cells was not oriented et al., 1986) in fact, indicates that hippocampal dysfunction strictly parallel to the rhinal sulcus since at caudal levels it contributes primarily to an anterograde memory impairment extended medially to encompass the full transverse extent with substantially preserved premorbid or retrograde memory. of the most caudal portion of the entorhinal cortex. When The implication of thesedata is that the hippocampalformation injections were placed more rostrally in the dentate gyrus hasaccess to cortically processedsensory information, performs and hippocampus, the rostrocaudally oriented zone of la- some operations with the information, and then interacts with beled cells was situated more medially in the entorhinal cor- storagesites in other brain regions, including the cortex. tex. Anterograde tracing experiments using 3H-amino acid Anatomical studies in a variety of mammals have demon- injections into different rostrocaudal and mediolateral po- strated that most of the cortical sensoryinformation that reaches sitions of the entorhinal cortex confirmed the organization the hippocampal formation enters via the entorhinal cortex. In demonstrated by the retrograde tracers and further indicated the rat, cat, and monkey, the entorhinal cortex receives inputs that the entorhinal fibers terminate in the outer two-thirds of primarily from polysensory cortical areaseither directly or by the molecular layer of the dentate gyrus. Unlike in the rat, way of the adjacent perirhinal cortex (Jonesand Powell, 1970; where the entorhinal termination zone in the molecular layer Van Hoesenand Pandya, 1975a; Van Hoesenet al., 1975; Dea- is clearly bilaminate, projections from all portions of the en- con et al., 1983; Room and Groenewegen,1986; Insausti et al., torhinal cortex appeared to terminate more diffusely 1987).This highly processedsensory information is subsequent- throughout the outer two-thirds of the molecular layer. ly transmitted to the dentate gyrus and hippocampusby way of the “perforant pathway” (Van Hoesen and Pandya, 1975b; Steward, 1976; Van Hoesen, 1982; Witter et al., 1986; Insausti Received Feb. 19, 1988; revised May I I, 1988; accepted May 13, 1988. et al., 1987). We would like to thank Ms. Janet Weber for her help in preparing much of the histological material, Mr. Dirk de Jong, Mr. P. Reimann, and Mr. Kris Tulock The perforant pathway projection to the dentate gyrus in the for help with the illustrations, and Mrs. N. Nauta-Kaat for help in typing the cat and the rat hasbeen studied in detail (Steward, 1976; Wyss, manuscript. This work was supported by NIH Grants NS 16980 to D.G.A. and 1981; Witter and Groenewegen, 1984). This projection arises 14944 to G.W.V.H. M.P.W. was supported by grants from the Van Coeverden Adriani Foundation and the Netherlands Organization for the Advancement of primarily from layer II cells of the entorhinal cortex while pro- Pure Research (ZWO). jections to the hippocampus and subiculum originate in layer Correspondence should be addressed to Menno P. Witter, Department of Anat- omy and Embryology, Vrije Universiteit, van der Boechorststraat 7, 1081 BT III and deeper layers (Steward and Scoville, 1976; Witter and Amsterdam, The Netherlands. Groenewegen, 1984). Earlier studies of the perforant pathway Copyright 0 1989 Society for Neuroscience 0270-6474/89/010216-13$02.00/O projection in the monkey (Van Hoesenand Pandya, 1975b; Van The Journal of Neuroscience, January 1989, 9(l) 217 Hoesen,1982) indicated that its generalorganization resembles some of the dye injections were placed with a 1 ~1 Hamilton syringe. that in the rodent. However, more recent studiesin the rat and For the dye injections, solutions of 2% DY or 3% FB were used. At each injection site, 200 nl of the dye was dispensed over 20 min (2 the cat have provided new insights into the topographic orga- injections of 100 nl were placed with 1 mm vertical separation). For nization of the perforant pathway (Ruth et al., 1982; Witter and the experiments in which 2 injections were made into different levels Groenewegen, 1984; Van Groen and Lopes da Silva, 1985). of the dentate gyrus (n = 5), the FB was placed at the more rostra1 of These studiesindicate that cells in different mediolateral zones the 2 sites, and the procedure was then repeated with the DY at the more caudal site. Animals were allowed to survive for 7-14 d and were of the entorhinal cortex project to different septotemporallevels then deeply anesthetized and perfused transcardially with 4% paraform- of the dentate gyrus. Layer II cells located near the rhinal sulcus aldehyde in 0.1 M phosphate buffer. After 3-5 d of postfixation in the (in both the medial and lateral subdivisions of the entorhinal same fixative and cryoprotection with 20% glycerol in 0.1 M phosphate cortex) project predominantly to the septal part of the dentate buffer, the brains were sectioned at 50 pm on the freezing, sliding mi- gyrus, whereascells located progressively more medially in the crotome. Two adjacent l-in-5 series of sections were immediately mounted on slides and stored dessicated at 4 and 20°C until analyzed entorhinal cortex project to more temporal parts of the dentate with a L.&z Dialux-20 microscope equipped for fluorescence micros- gyrus. copy. An adjacent l-in-5 series of sections was stained with thionin to The entorhinal cortex of the macaque monkey has recently allow the determination of cytoarchitectonic boundaries of the ento- been parcelled into 7 cytoarchitectonically distinguishablesub- rhinal cortex. In addition to the experiments using the fluorescent re- trograde tracers, injections of either WGA-HRP or HRP were made divisions (Amaral et al., 1987). Theseare arrangedfrom rostra1 into the dentate gyrus and hippocampus of 6 animals, either unilaterally to caudal in the entorhinal cortex. In the present studies we (n = 5) or bilaterally (n = 1). These injections consisted of 50-100 nl sought to determine whether the monkey perforant pathway of either a 1% solution of WGA-HRP or 30% HRP. Animals were projection to the dentate gyrus is organized in relation to the allowed to survive for 2 d, and the brains were processed according to cytoarchitectonic subdivisionsof the entorhinal cortex (i.e., do the procedure of Mesulam (1976) as previously described (Amaral and Cowan, 1980; Insausti et al., 1987). different subdivisions give rise to different perforant pathway The 3H-amino acid injections into the entorhinal cortex consisted of components?)or in a manner similar to the rostrocaudally ori- a single injection of 50-100 nl of a 1: 1 mixture of ‘H-leucine and 3H- ented zones describedpreviously in the cat (Witter and Groe- proline (concentrated to 100 pCi/Nl). Animals were allowed to survive newegen,1984) (i.e., does the origin of the perforant pathway for 7-l 4 d and then deeply anesthetized and perfused as above. Sections were cut at 30 pm and processed according to the protocol of Cowan projection to different portions of the dentate gyrus encompass et al. (1972) for the autoradiographic demonstration ofthe anterogradely portions of several cytoarchitectonic divisions?). Since there is transported isotope. no detailed analysisof the topography of the monkey perforant Analysis of material and preparation of summary diagrams of the pathway currently available, we have conducted a seriesof retro- entorhinal cortex and dentate gyrus. The distribution of retrogradely grade and anterogradeexperiments to define its organization. labeled cells in the entorhinal cortex was analyzed for each experiment using a computer-aided X- Y plotting system.
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