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)

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Domestic hens were injected intraperitoneally with hypertonic or isotonic 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 visualized in the preoptic-anterior hypothalamus. In all species, two hours after treatment with hypertonic but not with isotonic saline, a prominent cluster of fos-positive cells was seen close to the mid-line, dorsal to the anterior part of the third ventricle, in and around the nucleus commissurae pallii. The cell cluster was associated with the dorsal region of the organum vasculosum laminae terminalis and passed caudo-dorsally above the anterior commissure into the area of the subfornical 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 immunoreactive 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 paraventricularis and nucleus supraopticus. Double immunocytochemistry in the domestic hen with an antibody to vasotocin showed that these fos-positive cells were classical magnocellular vasotocinergic neurones. This study extends earlier studies in birds using lesioning and electrophysiological techniques to identify the precise cellular localization of the avian “osmoreceptive complex” projected onto a stereotaxic atlas.