NPY-, SOM- and VIP-containing interneurons in postnatal development of the rat claustrum.

A growing body of evidence indicates the common origin of the claustrum, endopiriform nucleus, and the basolateral nuclear complex of amygdala from the lateral and ventral parts of the pallium, as the claustroamygdaloid complex. It seems very probable that at least some of the claustral interneurons derive from subcortical sources. The postnatal development of neuropeptide Y-, somatostatin- and vasoactive intestinal polypeptide-containing interneurons was studied during the 4 postnatal months (P0-P120; P, postnatal day). The study was conducted on 45 Wistar rats of both sexes. Our results indicate that neuropeptide-containing interneurons are not morphologically mature at the moment of birth. The characteristic features of neuronal bodies and the relatively long period of postnatal development may indicate their migration from the subcortical neurogenetic centers. Morphological changes in the neuropil are also reported. Although developmental patterns differ between various neuropeptide-containing neuronal subpopulations, two phases of development can be distinguished in each of them: the early phase (P0-P4) during which undifferentiated neurons and neuropil dominate, and the late phase (P7-P28) during which the characteristic features of an adult-like structure gradually appear. Later these observed developmental changes are terminated. The postnatal development of neuropeptide-containing interneurons is completed after 4 weeks of life. This period, which is important for the structural and functional development of the claustrum, must be taken into account in future studies on this structure.