VIP-like and GFAP-like immunoreactivities in the chicken brain stem. II. The pons and the tegmentum of the mesencephalon.

An immunocytochemical analysis was performed on the chicken pons and mesencephalon (except the optic tectum) according to the PAP-DAB procedure, to study the distribution here of the neurons reacting to anti-VIP antibodies and the gliocytes reacting to anti-GFAP antibodies. Positive and negative controls were carried out in both the immunoreactions. The VIP-immunoreactive neurons showed a distribution essentially corresponding to that observed in other species by various Authors. They appeared scattered mainly in 3 sites: (a) the subventricular grey between pons and mesencephalon; (b) the periaqueductal grey, up to the diencephalon; (c) the rostro-ventral portion of the mesencephalic tegmentum, up to the diencephalon. Furthermore, some perivascular VIP-immunoreactive neuronal processes were seen. No differences have so far been detected as regards the GFAP-like immunoreactivity distribution, in comparison with the data reported by the authors in the chicken medulla and by others in in the brain stem of some other species