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Thalamic projections from the whisker‐sensitive regions of the spinal trigeminal complex in the rat
Author(s) -
Veinante Pierre,
Jacquin Mark F.,
Deschênes Martin
Publication year - 2000
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/(sici)1096-9861(20000501)420:2<233::aid-cne6>3.0.co;2-t
Subject(s) - zona incerta , superior colliculus , pretectal area , thalamus , biotinylated dextran amine , biology , tectum , anatomy , neuroscience , midbrain , antidromic , diencephalon , geniculate , nucleus , axon , stimulation , central nervous system
This study investigated the axonal projections of whisker‐sensitive cells of the spinal trigeminal subnuclei (SP5) in rat oral, interpolar, and caudal divisions (SP5o, SP5i, and SP5c, respectively). The labeling of small groups of trigeminothalamic axons with biotinylated dextran amine disclosed the following classes of axons. 1) Few SP5o cells project to the thalamus: They innervate the caudal part of the posterior group (Po) and the region intercalated between the anterior pretectal and the medial geniculate nuclei. These fibers also branch profusely in the tectum. 2) Two types of ascending fibers arise from SP5i: Type I fibers are thick and distribute to the Po and to other regions of the midbrain, i.e., the prerubral field, the deep layers of the superior colliculus, the anterior pretectal nucleus, and the ventral part of the zona incerta. Type II fibers are thin; branch sparsely in the tectum; and form small‐sized, bushy arbors in the ventral posterior medial nucleus (VPM). Accordingly, a statistical analysis of the distribution of antidromic invasion latencies of 96 SP5i cells to thalamic stimulation disclosed two populations of neurons: fast‐conducting cells, which invaded at a mean latency of 1.23 ± 0.62 msec, and slow‐conducting cells, which invaded at a mean latency of 2.97 ± 0.62 msec. 3) The rostral part of SP5c contains cells with thalamic projections similar to that of type II SP5i neurons, whereas the caudal part did not label thalamic fibers in this study. A comparison of SP5i projections and PR5 projections in the VPM revealed that the former are restricted to ventral‐lateral tier of the nucleus, whereas the latter terminate principally in the upper two tiers of the VPM. These results suggest a functional compartmentation of thalamic barreloids that is defined by the topographic distribution of PR5 and type II SP5i afferents. J. Comp. Neurol. 420:233–243, 2000. © 2000 Wiley‐Liss, Inc.