Intratrigeminal and thalamic projections of nucleus caudalis in the squirrel monkey (Saimiri sciureus): A degeneration and autoradiographic study,

Donald Ganchrow*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

In order to test the hypothesis that thalamic efferents of trigeminal nucleus caudalis (NC) are the cranial analogue of the spinothalamic system, lesion and autoradiographic studies were carried out in the squirrel monkey, and the terminal projection fields in thalamus were noted. Results showed that NC, including lateral reticular formation (LRF), projects to contralateral VPM, the VPM‐VPL border and medial VPL, and a region dorsal to ventroposterior nucleus (VP) proper which contains cells larger than those in VPM yet which stain as darkly as VPL neurons; this latter zone of termination may be homologous with VPLo (Vim) in other species, which is that area receiving lemniscal and cerebellar afferents (Mehler, '71; Walsh and Ebner, '73; Boivie, '74). In addition, a small projection is noted in an area intercalated between dorsomedial MG, limitans nucleus and posterior VP which closely agrees with the medial division of Posterior nucleus (Po) described in rhesus and squirrel monkey (Burton and Jones, '76). No terminations were observed in the gustatory nucleus medial to VPM. Bilateral, terminal projection fields were observed in posterior mediodorsal nucleus (MD), and a paralaminar area (PL) which lies in the ventrolateral strip of MD and is particularly prominent in primates; other bilateral fields were noted in CL, particularly the more medial segment of the nucleus. A sparse projection was noted in contralateral CM. Ipsilateral, intratrigeminal connections between NC and main sensory nucleus (MSV) also were observed. We conclude that, in the squirrel monkey, NC efferents, probably including LRF, may be considered analagous to the spinothalamic system by virtue of terminations in older medial and newer ventroposterior thalamus. Terminations in posterior MD may be specific to Primates. Moreover, projections to an area just dorsal to VP proper in squirrel monkey may be included within the broader definition of a neo‐spinothalamic area as reflected in spinothalamic tract projections to the ventrolateral complex in cat (Boivie, '71b; Jones and Burton, '74). The small NC projection to a part of Po is consistent with spinothalamic terminations to a “posterior” thalamic area in other primates (Mehler, '69), and with the suggestion that medial Po transmits pain information (Burton and Jones, '76).

Original languageEnglish
Pages (from-to)281-311
Number of pages31
JournalJournal of Comparative Neurology
Volume178
Issue number2
DOIs
StatePublished - 15 Mar 1978
Externally publishedYes

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