Physiological regulation of hypothalamic neuropeptide Y release in lean and obese rats.

The paraventricular nucleus (PVN) of the hypothalamus is an important site for the regulation of feeding behavior. Neuropeptide Y (NPY) injected into this nucleus strongly stimulates food intake. In the current study, we measured NPY release in the PVN of unrestrained rats through the push-pull technique. The rats were placed in their habitual environment and conditions of life. NPY release was augmented by >40% ( P < 0.01) in Long-Evans rats deprived of food for 12 h. It returned to the baseline as measured in ad libitum-fed rats 90 min after food access. Its stimulation by 55 mM KCl in refed animals indicated that the whole stock of NPY was not used during a short fast. During the light-dark transition, when feeding behavior is initiated, NPY release in lean Zucker rats showed a peak 20 min after lights off and then declined. It corresponded well with the first feeding episodes. In the obese Zucker rats, this peak was absent. NPY release was totally anarchic but at a high level. The feeding behavior of the obese rats was not as time delimited as in the lean rats. This study performed in very physiological conditions therefore indicates that NPY release could drive feeding behavior in the normal life. Its dysregulation in obese rats could participate in overeating and absence of feeding rhythm measured in these rats and speed up the development of their obesity.