AN IN-SITU HYBRIDIZATION AND IMMUNOHISTOCHEMICAL STUDY OF VASOTOCIN NEURONS IN THE HYPOTHALAMUS OF WATER-DEPRIVED CHICKENS

The distribution of immunoreactive vasotocin (IR-AVT) and AVT mRNA in the hypothalamus of White Leghorn cocks was determined by immunohistoc hemistry and in situ hybridization, respectively. In control birds tha t were provided with water ad lib, AVT mRNA was distributed in the per iventricular and lateral regions of the hypothalamus in clusters of ne urons that correspond structurally with the mammalian paraventricular (PVN) and supraoptic (SON) nuclei. Although the distribution of AVT, i dentified by immunohistochemistry of adjacent serial sections within t he hypothalamus, was similar to the distribution of AVT mRNA, the poss ibility that some positive staining was due to mesotocin neurons was n ot excluded. Water deprivation for 2 and 4 days resulted in both an in crease in levels of AVT mRNA per neuron and the number of AVT mRNA-con taining cells. Additionally, water deprivation resulted in a decrease in the amount of IR-AVT per neuron. The results indicate that osmotic stimulation increases AVT gene expression not only in individual neuro ns but also by activating subpopulation of neurons that are not observ ed in normally hydrated birds.