Distribution of vasoactive intestinal polypeptide in the rat and mouse brain.

The distribution of cell bodies and nerve fibers that combine with antisera to vasoactive intestinal polypeptide (VIP) was studied by immunohistochemistry in combination with radioimmunoassay in the brain of rat and mouse. The highest concentrations (60pmol/g wet wt) of immuno-reactive VIP were found in the cerebral cortex and in certain limbic structures, whereas the concentrations in the basal ganglia, thalamus, lower brain stem, cerebellum and spinal cord were low (<15pmol/g). VIP-immunoreactive cell bodies were found mainly in the cerebral cortex and the limbic system, with the great majority of them in neo- and allocortical areas. In the neocortex the VIP-containing cell bodies were found in layers II-V in all areas. The cells were fusiform or stellate shaped, resembling intracortical and corticocortical association neurones. In the pyriform and entorhinal cortex the cell bodies were located mainly in layer II. In the hippocampal complex VIP-containing cell bodies occurred in both the subiculum, areas CA1 and CA3 and the dentate gyrus. Most of the cells had the appearance of interneurones, some of them probably being identical with basket cells. Of subcortical areas, the amygdala had the largest number of VIP-containing cell bodies; they were numerous in all amygdaloid nuclei except in the central nucleus. Non-cortical areas where there were cell bodies containing VIP included the anterior olfactory nuclei, the bed nucleus of stria terminalis, lateral septum, suprachiasmatic nucleus, superior colliculus, and the mesencephalic periaqueductal gray.VIP-immunoreactive fibres had a distribution which on the whole paralleled that of the cell bodies, suggesting that many of the VIP-containing cells project locally. VIP-containing fibres were numerous in the following areas: the entire neocortex, the pyrifom cortex, the entorhinal cortex, the hippocampal complex, the amygdala (the central nucleus in particular), the anterior olfactory nuclei, the nucleus accumbens, ventral pallidum, bed nucleus of stria terminalis, suprachiasmatic nucleus, medial preoptic nucleus, median eminence, lateral geniculate body, pretectum, superior colliculus, periaqueductal gray, and the lateral parabrachial nucleus. Only few, scattered fibres were seen in other parts of the brain stem, in the striatum, thalamus and spinal cord. The cerebellum was devoid of VIP-containing fibres. VIP-containing neurones seem to form predominantly local projections. In addition, some VIP-containing neurones probably also form long projections, such as descending and transcallosal projections from the cortical cells, and projections from the amygdala to preoptic, hypothalamic and basal forebrain areas.The characteristic telencephalic distribution of the neurones that contain VIP suggests a role for this peptide in cortical and limbic functions.