Innervation of VIP-immunoreactive neurons by the ventroposteromedial thalamic nucleus in the barrel cortex of the rat

Jochen F. Staiger, Karl Zilles, T. Freund

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

We investigated the synaptic terminals of fibers originating in the ventroposteromedial thalamic nucleus (VPM) and projecting to the main input layers (IV/III) of the rat posteromedial barrel subfield. It was our aim to determine whether or not the subpopulation of vasoactive intestinal polypeptide (VIP)-immunoreactive neurons in these layers are directly innervated by the sensory thalamus. Anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) and immunohistochemistry for VIP were combined for correlated light and electron microscopic examination. Columns of cortical tissue were well defined by barrel-like patches of PHA-L-labeled fibers and boutons in layers IV and III. Within these columns VIP- immunoreactive perikarya were located mainly in supragranular layers. Marked perikarya were also seen in infragranular layers, but their immunoreactivity was often weaker. Granular layer IV, which is the main terminal field for thalamic fibers, contained fewer VIP neurons than supragranular layers. In the light microscope, however, PHA-L-labeled fibers appeared to contact the somata or proximal dendrites of 60-86% of the layer IV VIP neurons. By contrast, only 18-35% of the VIP neurons in the supragranular layers, which receive a moderately dense projection from the VPM, appeared to be contacted. PHA-L-labeled boutons were seen close to 13-25% of infragranular VIP-positive cells. Electron microscopy showed that thalamic fibers formed at most four asymmetric synapses on a single layer IV, VIP-positive neuron. Although the proportion of VIP-positive neurons with labeled synapses was lower in supragranular layers, most of them shared multiple asymmetric synapses with labeled thalamic fibers. Up to six labeled synapses were seen on individual VIP neurons in layer III. We conclude that subpopulations of VIP- immunoreactive neurons, located in layers IV, III, and II are directly innervated by the VPM. These neurons may be involved in the initial stages of cortical processing of sensory information from the large, mystacial vibrissae. Since VIP is known to be colocalized with the inhibitory transmitter GABA, it is likely that VIP neurons participate in the shaping of the receptive fields in the barrel cortex.

Original languageEnglish
Pages (from-to)194-204
Number of pages11
JournalJournal of Comparative Neurology
Volume367
Issue number2
DOIs
Publication statusPublished - Apr 1 1996

Fingerprint

Thalamic Nuclei
Vasoactive Intestinal Peptide
Neurons
Synapses
Light
Vibrissae
Presynaptic Terminals
Carisoprodol
Dendrites
Thalamus
Automatic Data Processing
gamma-Aminobutyric Acid
Electron Microscopy

Keywords

  • asymmetric synapses
  • interneurons
  • laminar organization
  • somatosensory cortex
  • thalamocortical connections

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Innervation of VIP-immunoreactive neurons by the ventroposteromedial thalamic nucleus in the barrel cortex of the rat. / Staiger, Jochen F.; Zilles, Karl; Freund, T.

In: Journal of Comparative Neurology, Vol. 367, No. 2, 01.04.1996, p. 194-204.

Research output: Contribution to journalArticle

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