LITTLE OR NO RESPONSE TO 24-HR WATER-DEPRIVATION OF FOS-LIKE IMMUNOREACTIVITY IN VASOPRESSINERGIC MAGNOCELLULAR NEURONS IN THE HYPOTHALAMUSOF HEREDITARY MICROPHTHALMIC RATS

In normal rats, 24-hr water-deprivation was found to cause a significa nt increase in the plasma concentration of arginine vasopressin (AVP), and marked induction of Fos in the AVP-positive magnocellular neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus. On the other hand, 24-hr water-deprivation also caused a significant increase in the plasma AVP concentration in hered itary microphthalmic rats, but much less than in normal rats. Consiste nt with this, the extent of induction of Fos in the nuclei of the PVN and SON of these rats was lesser than in normal rats. These results su ggest that hereditary microphthalmic rats have a defect or decrease in the response to water-deprivation of vasopressinergic magnocellular n eurons in the PVN and SON.