IDENTIFICATION OF HYPOTHALAMIC NUCLEI INVOLVED IN OSMOREGULATION USING FOS IMMUNOCYTOCHEMISTRY IN THE DOMESTIC HEN (GALLUS-DOMESTICUS), RING DOVE (STREPTOPELIA-RISORIA), JAPANESE-QUAIL (COTURNIX JAPONICA) AND ZEBRA FINCH (TAENOPYGIA-GUTTATA)

Domestic hens were injected intraperitoneally with hypertonic or isoto nic saline and killed 0.5, 1, 2, 6, 12 and 24 h later. Japanese quail, Ring doves and Zebra finches were treated in the same way and killed 2 h later Using fos immunocytochemistry, fos-positive cells were visua lized in the preoptic-anterior hypothalamus. In all species, two hours after treatment with hypertonic but not with isotonic saline, a promi nent cluster of fos-positive cells was seen close to the mid-line, dor sal to the anterior part of the third ventricle, in and around the nuc leus commissurae pallii. The cell cluster was associated with the dors al region of the organum vasculosum laminae terminalis and passed caud o-dorsally above the anterior commissure into the area of the subforni cal organ, spreading diffusely into the nucleus septalis medialis and the nucleus dorsomedialis anterior thalami. The maximal expression of c-fos was seen 2 h after treatment with hypertonic saline: weak fos im munoreactive product was seen at 0.5, 1 h and 6 h but not after 12 and 24 h. In all birds, 2 h after treatment with hypertonic but not with isotonic saline, fos-positive cells were also seen in the nucleus para ventricularis and nucleus supraopticus. Double immunocytochemistry in the domestic hen with an antibody to vasotocin showed that these fos-p ositive cells were classical magnocellular vasotocinergic neurones. Th is study extends earlier studies in birds using lesioning and electrop hysiological techniques to identify the precise cellular-localization of the avian ''osmoreceptive complex'' projected onto a stereotaxic at las.