NEUROPEPTIDE-Y RELEASE FROM THE PARAVENTRICULAR NUCLEUS INCREASES IN ASSOCIATION WITH HYPERPHAGIA IN STREPTOZOTOCIN-INDUCED DIABETIC RATS

We tested the hypothesis that the hyperphagia observed in streptozotocin (STZ)-induced diabetic rats is due to increased release of neuropeptide Y (NPY) in the paraventricular nucleus (PVN) of the hypothalamus. In the first experiment, male rats were injected with STZ or vehicle (control) via the tail vein and 18-20 days later, NPY levels in seven hypothalamic sites and release in vitro from selected hypothalamic sites were evaluated. The results showed that in association with STZ-produced marked hyperglycemia and hyperphagia, NPY concentrations were increased in four hypothalamic sites, including the PVN. Evaluation of NPY release in vitro showed that both basal and KCl-induced release was significantly higher from the microdissected PVN of STZ-treated than control rats. A similar augmentation in the NPY efflux in vitro was detected from the median eminence-arcuate nucleus, but not from the neighboring ventromedial nucleus of STZ-treated rats. In the second experiment, rats were treated with STZ or vehicle and received permanent push-pull cannula (PPC) in the PVN for evaluation of NPY release in vivo 18-21 days after STZ treatment. The results showed that mean NPY levels in the perfusates collected from the PVN of diabetic rats were significantly higher as compared to control rats. Since NPY is the most potent naturally occurring orexigenic signal and the PVN is an important initial site of NPY action in the stimulatory pathway regulating feeding, our findings of augmented PVN NPY release in vivo and in vitro are in accord with the hypothesis that increased NPY secretion in the PVN may be responsible for hyperphagia in diabetic rats.