Article
Immunoreactivity for GAD and Three Peptides in Somatosensory Cortex and Thalamus of the Raccoon

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Abstract

Immuno-cytochemical methods were used to determine the distributions of glutamic acid decarboxylase (GAD), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), and somatostatin (SOM) in the primary somatosensory cortex and somatosensory thalamus of adult raccoons. The cortex showed extensive immunoreactivity for GAD, revealing a large population of GABAergic neurons. GAD-labeled cells were numerous in all cortical layers, but were most concentrated in laminae II–IV. The cells were nonpyramidal and of varying morphology, typically with somata of small or medium size. GAD-immunoreactive puncta, presumably synaptic terminals, were widespread and often appeared to end on both GAD-negative and GAD-positive neurons. Immunoreactivity for the peptides was much less extensive than that for GAD, with the number of labeled neurons for VIP > CCK > SOM. Peptidergic cells were preferentially located in the upper and middle cortical layers, especially laminae II and III. The cells were nonpyramidal, often bitufted or bipolar in morphology, and small to medium in size. Their processes formed diffuse plexuses of fibers with terminal-like varicosities that occasionally surrounded nonpeptidergic neurons. The thalamus showed a clearly differentiated pattern of immunoreactivity for GAD, but little or no labeling for the three peptides. Nuclei adjoining the ventral posterior lateral (VPL)/ventral posterior medial (VPM) complex—including the reticular nucleus—contained many GAD-positive neurons and fibers. In contrast, the VPL and VPM nuclei displayed considerably less GAD immunoreactivity, somewhat surprising given the raccoon's highly developed somatosensory system. However, the ventral posterior inferior (VPI) nucleus revealed rather dense GAD labeling, perhaps related to a specialized role in sensory information processing. Thus, the primary somatosensory cortex of the raccoon showed patterns of immunoreactivity for GAD and peptides that were similar to those of other species; the somatosensory thalamus revealed a distinctive profile of GAD immunoreactivity, with labeling that was light to moderate in the VPL/VPM complex and relatively extensive in VPI.

References (42)

  • M.O. Miceli et al.

    Differential distributions of cholecystokinin in hamster and rat forebrain

    Brain Res.

    (1987)
  • K. Mizukawa et al.

    The distribution of somatostatin-immunoreactive neurons and fibers in the rat cerebral cortex: Light and electron microscopic studies

    Brain Res.

    (1987)
  • M. Molinari et al.

    Distributions of certain neuropeptides in the primate thalamus

    Brain Res.

    (1987)
  • J.H. Morrison et al.

    The distribution and morphological characteristics of the intracortical VIP- positive cell: An immunohistochemical analysis

    Brain Res.

    (1984)
  • H.L. Obata-Tsuto et al.

    Distribution of the VIP-like immunoreactive neurons in the cat central nervous system

    Brain Res. Bull.

    (1983)
  • E. Rinvik et al.

    Gamma-aminobutyrate-like immunoreactivity in the thalamus of the cat

    Neuroscience

    (1987)
  • T. Sugimoto et al.

    Coexistence of neuropeptides in projection neurons of the thalamus in the cat

    Brain Res.

    (1985)
  • A. Yamashita et al.

    Ontogeny of somatostatin in cerebral cortex of macaque monkey: An immunohistochemical study

    Dev. Brain Res.

    (1989)
  • K.D. Alloway et al.

    Responses of neurons in somatosensory cortical area II of cats to high-frequency vibratory stimuli during iontophoresis of a GABA antagonist and glutamate

    Somatosens. Motor Res.

    (1988)
  • P. Ciofi et al.

    Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

    J. Comp. Neurol.

    (1990)
  • G.S. Doetsch et al.

    Intracortical connections of two functional subdivisions of the somatosensory forepaw cerebral cortex of the raccoon

    J. Neurosci.

    (1988)
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