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Willim R. Kcnler Supported. By: NASA Task No. 5202-06-~ Nucleus ol'@uys -c_- Willim R. Kcnler 3ieuro-Dioiogy 3ranc11 Office of Life Sclences A.zes 3esearcii Center - . I N U ITHRUI .. L.. ea (CODE1 Supported. by: NASA Task No. 5202-06-~ GPO PRICE !§ CFSTI PRICE(S) $ t Hard copy (HC) *w Microfiche (MF) *sQ? ff 653 July 65 W. R. Mehler __l' ---_cI- "Tee number ofbhalamic nucl5)has increased in the last I"ew years. To the four classical centers that were described by Burdach one shbuld add the Centre median of Luys and the semi-lunar of Flechsig. Finally, von Monakow and Nissl have subdivided each pincipl nucleus into a large number of secondary Pleiades on me basis of the relative volume 02 cells and the number of mye- l-zeted fibers of the inzerstltial plexus. It is our belief tket i.ic individuality of ti;e na2arnic cenic;s should not -02 based uaon the aspect of such centers'c; TY.NiTs1 or-Weigert sections, but upon ?;'ne study of their fine+nato-$,as it appears in silver chromate smlnecl scctions acd, above all, upon tke specificity of their ~o:~~.~ctLons.A nucleus shodd only be considered as an individual cLLAUerwrien besides having peculiar stxc-cural features, its h;i'erent and efferent fibers are spec:fic .'I Santiago Raymori y Caial l9Oi lkth International Medical Congress Translation by Enrique Ramon-Moliner ._ 1;: 1931 3ioch added a "note" to his then definitive studies on the cii.rAiCc._,:idlonor' the Carnivora (Rioch,l929 a,b, 1931a). This I addendum 1 at-cer;rptzd to rectify his earlier incluslon of the nucleus centre median , of LL.J, In ;Le region 'he -identifie$-as tne nucleus parafascicularis. Follo.;rLriz susplemental studies in a series of re-?vsluztioa of the parafascicular region in Carnivora, Rioch delineated a razker lir:.i.zed median nucleus in the cat and dog as a nuclear enti'q homoli;=ous with the centre medlan exhibited in higher species. He _- described thrs small-celled centre median as contiguous with, but separable frorL, tA,ephmfascicularis caudally and continuous witn the pracentral and zc:--cral Lateral intralarrinar nbclei at its rostral pole. His observations I in lo~r~rrrorGisys (Rioch, 1931b), together with Le Gros Clarks (1929, 1930) corresporidinL comparative studies, presented data suggesting a progressive L;A-ylo;enz4i.ic mvelopment of the nucleus centre r.edian. 2. W. R. Mehler overlooked, misla'oelled or included wltiiin 'ck linitr, 02 adJaccn'i nuclei. Mow recently, there has been a reverse tendency on the prt of mtliors to tirut --A? ce~trex36ian and adjacent cell groups in the region of the internal .-. - ., -c>c7 -'-3A-LK- , .L,u-, 19654 . -- . .. z-Lb-grimate studies, Rioc?L (1931 a,b) called attention to the f Ancci-,x ZL ;2r:y 1959). It a2-p?ars, thereYore, that in rrany cases the limited cytolo;L:a1 i2v;zlopr;;ent or fibrous obscuratiorL of tile centre median has frequently lcci SOLE Lnve,tigators to improger identification of the centre nedian or to ifi-G?;-,--z-c ascending fibers of passage as cosnections with the nucleus. 3. W. R. Kehler Cytoarchitectural studies of the thalarrus led Le Gros Clark (1929,1930) to suggest that the centre cledian (CN) represents a caudal elaboration of intra- * cell gro-~psbecause its cells reser;ble certsin srrall-celled elements +* i-, e 1-c C1s-G2 & - iiyternsl r;:-,&Klicry lcriTrLa. Szv;~,~~--srly,1 Its phylogenetically R' ccns'hx? relationship with the nuclc~sp,rafzscicularis prorrpted Papez (1932) associater; -c~s<cally subscribe to Ceclle and Oskar Vogt 's (1941) subdivision of 'ihc cxlcus in man. En extensive studies ol r,ormz1 and pathological material the TE!::~:~ 2x5 a larger-celled doi-soiq:ediai region adjacent to the internal mdullary cori-csLo:<s TO t;;c sars la-Geraiis of -,he prafasciwlar nucleus which appears to st.c~.e;. a? Ci: In tix hunan fetus, Nih,l and associates then conclcded that probably .. 4. W. R. Mehler Coniparative anatomical studies of the afferent and efferent connections of the ! CM-Pf complex and adjacent intrahinar region are being continued. Data suggested 4 by current studies indicate that experimental means are now available to objectively establish the homologues of these and other thalamic nuclei by delineating than from adjacent cell groups on the basis corticofugal or other afferent projections r3ccntly established (see, recent findings). We believe that judicious use of the selective silver impregnation method o€ Nauta (1957) should---like the 3rudent application of the Marchi method by LeGros Clark (1936) and Walker (l938a, b) ---allow for significant advancement in our understanding of the neural organization of the thalamus and lead us to a. more realistic knowledge of its function. In as much as the identification of the true nuclear homologue of CM in many subprimate species is still a matter of speculation, the present report will be limited principally to those species in which sufficient experimental data have accumulated to meet Cajal' s (1904) criteria for the confirxistion of the individuality of a fiucleus. W. R. Mehler -The efferent projections of the centre median (CM) were the topic of much I' controversy during the past three decades. During the 1930's, however, experimental studies of thalamo-cortical relationships in monkeys revealed that CM was not a cortically dependent nucleus (Walker, 1935, 1938b). Le Gros Clark and Russell's (1939) study appeared to experimentally rule out the insular cortex, suspected by DejerLne (l9Ol), which was not studied in detail by Walker. Their conclusion was confirmed in Roberts and Akert's (1963) recent re-evaluation of the thalamic projections to the insular region. Included in Le Gros Clark8and Russell's report were observations on a human case with a large lesion in the ventrolateral part of the putamen. They noted that CM in this case was almost totally degenerated except for a number of cells in its dorsomedial extremity. In 1941, Cecile and Oskar Vogt demonstrated that the ventrolateral, small-celled subdivlsion of CM preferentially projects to the putamen and the larger-celled dorsomcdial region of thelr subdivision of CM projects naainly to the caudate. Their analyses of cases of status marmoratus clearly established these connections in the !;urnan brain and subsequent neuropathological studies by McLardy (1948) and Simma (1951) confirmed the CM-striatal relationships Experimental confirmation of the Vogts findings appear in Powell and Cowan's (1956) studies in the monkey. For a nore cornprehensive review of the literature dealing with retrograde cell de&eneration studies, the reader is referred to Powell and Cowan's narrative or to Powell ' s (1958) subsequent review. .I- -.. 6. W. R. Mehler Antegrade degeneration studies in the monkey confirm the predominantly putamina1 distribution of the CM projections demonstrated by Nauta and Whitlock (1954) in studies in the cat. The lesion shown in figures 1 and 2 was produced i by a stereotaxically directed electrode introduced from behind, 4 mm lateral to c the midline, at an angle of 30 degrees from the horizontal plane. Figures 1 and 2 ---- about here 2/3 - 3/4 page The fiber degeneration issuing from the lesion is tripartite in distribution. Ventrolaterally, the intranuclear neuropil of CM is disrupted by fine-fibered degeneration which is confined within the limits of the nucleus up to its dense fibrous border with the pulvinar and ventral posterior medial complex. Ventro- medially degenerating fine-fibered fascicles course caudomedially and terminate primarily within the limits of the parafascicular nucleus (Pf). The fiber caliber and fasciculation of this degeneration projecting upon Pf suggests interruption of -twwe&i-al. corticofugal connections which descend through the region of the k-.. -. _--4- --- lesion (see; corticofugal projections). Dorsad to the lesion, dense fiber degeneration courses dorsolaterally in the internal medullary lamina upon which the lesion impinges. Terminal degeneration, dorsal and lateral to the lesion, Zccci-CLiiig clszewski 'a \17JLIflnco) tcr;;.,ificlcgJr, c?istrib~testo the ~-rsm~lt.if~c-fs b of the medialis dorsalis (MDmf'), nucleus centralis lateralis (Cl) and adjacent regions of the ventral lateral (VL) nucleus. The pattern and density of these intra-thalamic connections primarily duplicate the distribution of medially coursing (i.e., via an intralaminar route) cerebello-fuga1 fiber paojections repeatedly observed by us in other studies in the monkey (Mehler et a1 1958, Mehler 1965) Scattered degeneration observed in the pulvinar and lateral 7. W. R. Mehler posterior nuclei relates to incidental occipita-- or tecto-thalamic projections interrupted by the insertion of the lesion electrode. The regional distribution of projections to the striatum exhibited in this case, (fig. 3) corresponds remarkably well with basic topological organization demonstrated in the monkey by Powell and Cowan (1956). The trans-thalamic passage exhibited by these projections similarly confirms and extends both Nauta and Whitlock’s (1954) and Powell’s (1958) observations that the CM-striatal projections . describe a wide path through the ventral anterior (VA) and rostro-lateral reticular nuclei of the thalamus. With the exception of the intra-thalamic connections that resemble the distribution of ascending fiber degenerations which pass through the lesion region, the dense fine-fibered fascicles of the CM efferent projections do -not appear to distribute terminal connections in their passage through the lateral region of the nucleus ventralis.anterior. As these degenerating fascicles interdigitate with the normal fibers of the external medullary lamina, some terminal-like axo-dendritic ramifications appear in relation to reticularis thalami cells encountered in the region of passage. In other words, these connections with the reticularis thalami do not present the more obvious axo-somatic type of termination and their distribution appears limited to the region of passage of the projections to the striatum similar to that described in the-cat by Nauta and Whitlock (1954).
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