VASOACTIVE INTESTINAL POLYPEPTIDE (VIP)-CONTAINING NEURONS - DISTRIBUTION THROUGHOUT THE BRAIN OF THE CHICK (GALLUS-DOMESTICUS) WITH FOCUS UPON THE LATERAL SEPTAL ORGAN

The distribution of VIP-like perikarya and fibers was determined throu ghout the chick brain. The most rostral immunoreactive perikarya were found to be cerebrospinal fluid-contacting neurons in the pars mediali s of the lateral septal organ. Additional data were presented supporti ng the idea that the lateral septal organ is another circumventricular organ within the brain of birds (Kuenzel and van Tienhoven 1982). A l arge group of immunoreactive perikarya was found in the lateral hypoth alamic area and appeared continuous with immunoreactive neurons in the anterior medial and ventromedial hypothalamic nuclei (n). A few perik arya were located in the paraventricular hypothalamic n. A number of i mmunoreactive neurons were found within and about the infundibular and inferior hypothalamic n., none however was immunoreactive cerebrospin al fluid-contacting neurons. Immunoreactive perikarya were found predo minantly in laminae 10-11 of the stratum griseum et fibrosum superfici ale. A few scattered perikarya were found ventromedial to the n. tegme nti pedunculo-pontinus pars compacta and locus ceruleus. Some of the i mmunoreactivity was unusual, being very homogeneous within the cell bo dy with little evidence of the material in the axon or dendrites. Peri karya were found in the central gray, n. intercollicularis, and area v entralis of Tsai. The most caudal structure showing immunoreactive neu rons was the n. reticularis paragigantocellularis lateralis. Brain are as containing the most abundant immunoreactive fibers, listed from the rostral-most location, were found in the ventromedial region of the l obus parolfactorius and the lateral septal n. Continuing caudally, the re were immunoreactive fibers within the periventricular hypothalamic n.; some of the fibers were found to travel for some distance parallel to the third ventricle. Dense immunoreactive fibers were found in the tractus cortico-habenularis et cortico-septalis, medial habenular n. and posterior and dorsal n. of the archistriatum. A number of areas ha d what appeared to be baskets of immunoreactive fibers (perhaps immuno reactive terminals) surrounding non-reactive perikarya. Brain areas co ntaining terminals included the piriform cortex, area ventralis of Tsa i, interpeduncular n., and specific regions of the stratum griseum et fibrosum superficiale. A very dense immunoreactivity occurred within t he external zone of the median eminence, the dorsolateral parabrachial n., and n. tractus solitarii. Vasoactive intestinal polypeptide appea rs to be a useful peptide for defining the neuroanatomical constituent s of the visceral forebrain in birds.