Effects of dopamine-depleting brain lesions on experimental hyperphagia in rats

Dopamine (DA)-depleting brain lesions of various sizes were produced in rats either by intracerebroventricular injections of 6-hydroxydopamine (6-HDA) or by electrolytic lesions of the lateral hypothalamic (LH) area. Among 30 animals that became aphagic and adipsic for at least four days after large LH or 6-HDA-induced brain lesions, only three developed hyperphagia after electrolytic lesions of the ventromedial hypothalamus (VMH) or daily injections of long-acting protamine-zinc insulin (PZI). In 20 rats with smaller LH or 6-HDA-induced lesions, which had not shown marked initial behavioral dysfunctions, only three gained as much weight after VMH lesions as the control animals. Similarly, 6 of 10 rats with smaller LH lesions could not tolerate a 15-day series of PZI treatments, although 14 of 17 rats with smaller 6-HDA-induced lesions increased their food intake and gained weight during the PZI treatments as did control animals. These results indicate that hypothalamic hyperphagia can be blocked by DA-depleting brain lesions that neither produce an initial period of aphagia and adipsia nor involve hypothalamic tissue. They further indicate that even small LH lesions may prevent the development of hyperphagia elicited by PZI, whereas only very large 6-HDA-induced lesions consistently have this effect.