POSTNATAL NEUROGENESIS OF THE HYPOTHALAMIC PARAVENTRICULAR AND SUPRAOPTIC NUCLEI IN THE BRAZILIAN OPOSSUM BRAIN

We have used bromodeoxyuridine (BrdU) single and BrdU-arginine vasopre ssin-oxytocin (BrdU-AVP-OT) double and triple label immunohistochemist ry to characterize postnatal neurogenesis of the supraoptic and parave ntricular nuclei in the Brazilian opossum, Developing pups received a single injection of BrdU between days 1 and 11 postnatally. All brains were collected on day 60 of postnatal life (60 PN). Single label BrdU immunohistochemistry revealed that an injection at 1 PN resulted in h eavy labelling in the hypothalamus including the area of the paraventr icular nucleus, whereas only approximately one third of the cells in t he supraoptic nucleus were labelled. Analysis of data indicated that n eurogenesis of the supraoptic and paraventricular nuclei is completed by days 5 and 7 PN, respectively. Double and triple label immunohistoc hemistry demonstrated that following BrdU injection on day 1 or 2 PN, few of the AVP and OT secreting cells in the supraoptic nucleus were d ouble labelled with either peptide and BrdU, and no double labelled ce lls were seen following BrdU injection on day 5 PN. Similarly, in the paraventricular nucleus most of the AVP and OT secreting magnocellular cells were not double labelled with either peptide and BrdU. Whereas several double labelled cells were observed in the parvicellular part following BrdU injection on day 1 or 2 PN. No double labelled cells we re present in any component of the paraventricular nucleus following i njection on day 7 PN or later. These results indicate that the majorit y of the AVP and OT secreting magnocellular neurons are born prenatall y and the OT and AVP parvicellular group of neurons are born during po stnatal life. Our results also demonstrate that in contrast to that of eutherian rodents such as the rat and mouse, neurogenesis in the opos sum hypothalamus continues into the postnatal period and provides a un ique opportunity to study the neuroanatomical development of diverse r egions such as the paraventricular nucleus.