The development of behavioral changes following either neural isolation or DC lesion of the ventromedial hypothalamus in rats

Abstract

This experiment was designed to compare ventromedial hypothalamic damage as a result of dc lesions to ventromedial hypothalamic damage as a result of isolating knife-cuts on a variety of behavioral measures known to be sensitive to such damage. It was further designed to assess developmental changes in the measures which are typical of the hypothalamic hyperphagic syndrome. Finally, it was designed to make an evaluation of the effects of hypothalamic damage on food motivation which was independent of specific deprivation conditions. Thirty-one female albino rats underwent a six-day series of tests once pre-operatively and four times post-operatively. The final test series began eight weeks following surgery. The tests consisted of measures of water and food consumption, quinine finicky behavior, spontaneous activity, and willingness to bar press for food rewards. The Ss receiving knife-cuts, although gaining great amounts of weight immediately following surgery, were lighter at the end of the experiment than Ss receiving dc lesions. The development of quinine finickiness closely paralleled relative changes in body weight. The knife-cut group became finicky much sooner following surgery than the lesion group, although there were no differences at the end of the experiment. On all other measures there were no statistically reliable differences between the lesion and knife-cut groups. Both groups were reliably polydipsic and hyperphagic, and they expressed a dramatic and permanent hypoactivity. Furthermore, both experimental groups displayed a willingness to work on a FR8 schedule to obtain as great a proportion of their exaggerated daily food intake as normal animals would obtain under such conditions of their normal daily food intake. The results were discussed in connection with the hypothesis that measures producing similarities between the experimental groups could be traced to neural connections, while measures producing differences must be related to biochemical differences known to exist between the two experimental groups.