FOREBRAIN AND HINDBRAIN INVOLVEMENT OF NEUROPEPTIDE-Y IN INGESTIVE BEHAVIORS OF RATS

Neuropeptide Y (NPY) is an extremely potent orexigenic agent. These studies demonstrate that the effect of NPY:on food and water intake are seen after infusion into either the third (3V) or fourth (4V) ventricle and that this is a specific effect, as it was not seen with the deaminated form. There was a nonsignificant tendency for lateral midbrain knife cuts to increase food intake. Both 3V and 4V NPY infusions showed an attenuated increases in food intake at 1 but not 2 h following NPY infusion in the lateral knife cut rats compared to the sham controls. Medical knife cuts resulted in significantly greater food intake in the basal state and a lesser increase in food intake in response to NPY infused into the 3V. These midbrain data suggest a role for both medical and lateral fibers in mediating the effects of NPY on food intake. Lateral fibers appear to be more important, but their transection only delays the time of onset of the stimulating effect of NPY to the second hour. Lateral knife cuts virtually abolish the effect of 4V NPY on stimulating water intake. 3V NPY in the presence of NPY has a less clear effect at 1 h, but mildly attenuated the NPY effect on water intake at 2 h in lateral knife cut rats. Medial knife cuts slightly attenuate the effect of 3V NPY on water intake. However, medial knife cuts markedly increased basal water ingestion. These studies demonstrate the importance of neuronal communications between third and fourth ventricle associated structures in the modulation of ingestive behavior. Further, it appears that NPY, when infused either into the 3V or 4V, stimulates more than one pathway to modulate ingestive behavior.