N-methyl-d-aspartate lesions of the lateral hypothalamus do not reduce amphetamine or fenfluramine anorexia but enhance the acquisition of eating in response to tail pinch in the rat

These experiments examine the acquisition of tail pinch-induced eating and responses to the anorectic agents d-amphetamine and d,l-fenfluramine by rats bearing N-methyl-d-aspartate (NMDA) lesions of the lateral hypothalamus. Lesioned rats lost weight following surgery but had no significant eating or drinking difficulties in the home cage (Clark et al. 1990). The acquisition of eating in response to tail pinch was enhanced in lateral hypothalamic-lesioned rats: they ate on earlier test sessions than controls and less pressure was required to elicit eating. Home cage food intake over the period when tail pinch was being examined was not affected by the lateral hypothalamic lesions. There were no significant differences between lateral hypothalamic-lesioned and control rats in terms of their anorectic responses to either d-amphetamine or d,l-fenfluramine, though the lesioned rats had a lower baseline intake. These data suggest that the lateral hypothalamus is not an important site for the mediation of amphetamine or fenfluramine anorexia but is involved in the acquisition of tail pinch-induced eating. The disinhibition of responding to tail pinch by lateral hypothalamic lesions is discussed in terms of the possible role the lateral hypothalamus plays in regulating cortical activity. The role of the medial hypothalamus and nonhypothalamic systems in the response to anorectic drugs and tail pinch is discussed.