DISTRIBUTION OF SMALL VASOPRESSINERGIC NEURONS IN GOLDEN-HAMSTERS

In rats, small (diameter: ca. 10 mu m) vasopressinergic neurons have b een localized in the forebrain, including extrahypothalamic sites, suc h as the bed nucleus of the stria terminalis (BST) and the medial amyg dala (MeA). In golden hamsters, no such neurons have ever been describ ed in extrahypothalamic sites, while their presence in some hypothalam ic sites, such as the paraventricular nucleus (PVN), remains controver sial. The present studies were carried out to confirm the existence of small vasopressinergic neurons in the forebrain of golden hamsters, u sing rats as a positive control. The presence of small vasopressinergi c neurons in these sites was first tested by immunocytochemistry in co lchicine-treated animals. The resulting distribution was corroborated by in situ hybridization for vasopressin (AVP) mRNA. While a large num ber of small AVP-immunoreactive (AVP-ir) neurons was found in the BST and MeA of colchicine-treated rats, none was found in the same locatio ns in hamsters. Interestingly, as a few large (diameter: 20-25 mu m) A VP-ir neurons were found in the BST just medial to the small neurons i n rats, the same area contained a few large and small AVP-ir neurons i n hamsters. In the PVN, large and small AVP-ir neurons were found in r ats and hamsters. However, three to four times more neurons were count ed in rats. These data were confirmed by in situ hybridization. Indeed , in hamsters, no labelling for AVP mRNA was detected in small neurons within the BST and MeA. Furthermore, the PVN of rats contained more l abelling for AVP mRNA, as compared to hamsters. These results confirm that the distribution of vasopressinergic neurons in rats cannot be ge neralized to other species without a detailed analysis. (C) 1995 Wiley -Liss, Inc.