Fixed-ratio performance following ventromedial hypothalamic lesions in rats

Abstract

Rats with ventromedial hypothalamic lesions were trained preoperatively to respond for food reward on a FR 64 schedule of reinforcement. Postoperative comparisons with similarly trained unoperated control rats showed no differences when both groups were maintained at 8070 or 90% of their preoperative baseline weights. Lesioned rats responded at a much higher level. however. at 100~ body weight and at a prefeeding condition run at lOW body weight. These results suggest that rats sustaining such iesions overeat and become obese because these lesions increase their hunger motivation. Miller. Bailey, and Stevenson (I950) and Teitelbaum (I 957) rep orted that hyperphagic ventromedial hypothalamic (VMH) lesioned rats were "less hungry" than nonlesioned rats. More recent data. however, suggest that this interpretation originated, in part, from inappropriate testing procedures and between-group comparisons. Kent and Peters (1973) found that VMH-lesioned rats outperformed control rats on both operant and straight alley tasks when the groups were compared at identical moderate deprivation conditions defined in terms of preoperative free-feeding weights. Operant performance was assessed using a variable-interval (VI) reinforcement schedule rather than a progressively increasing fixed-ratio (FR) schedUle. The latter procedure was used by Teitelbaum (1957), and subsequently by others (Sclafani, 1971; Singh, 1970), to obtain the data that, in part, define the VMH paradox: increased food intake and decreased hunger motivation. The purpose of the present experiment was to compare the performance of VMH-les:oned and control rats on a FR schedule of reinforcement. The discrepancies between the operant data reported by Kent and Peters (1973) and that obtained using progressively increasing FR schedules may partially reflect an interaction with either the schedule of reinforcement or the deprivation conditions and comparison procedures used in the different experiments. On a progressively increasing FR schedule, rats are typically trained to barpress initially on a continuous reinforcement schedule. The number of barpresses required to obtain food reward is subsequently increased to 4, 16, 64, and 256, in ascending order. The rats are usually tested for 2 or 3 days at each ratio, and each rat's entire food ration is obtained during daily 12-h sessions. Since VMH-Iesioned rats often perform at higher levels than control rats on *Requests for reprints should be sent to

Temporal analysis of appetitive behavior following VMH lesions in conscious rats

“…These results are consistent with the recently reported data that indicate that rats with VMH lesions overeat and become obese because the lesion increases the rat's hunger motivation (Kent & Peters, 1973;Peters, Sensenig, & Reich, 1973;Wampler , 1973). Although rats barpress at low levels when essentially sated (Days 10-12), 2 h after lesions have been made (Day 13), they respond at much higher levels, as they did under conditions of food deprivation (Day 5).…”

The effects of preoperative ingestive events on feeding and drinking behavior following brain damage

“…Preoperative weight reduction, without the operant training, does not produce this phenomenon (King & Gaston, 1976). This operant effect on rats has been found by others (Beatty, 1973;Beatty, Vilberg, Shirk, & Siders, 1975;King & Gaston , 1973, 1976Peters, Sensenig, & Reich , 1973;Porter & Allen , 1977), and, in an earlier study , was also found with monkeys (Hamilton & Brobeck, 1964).…”

Comparison of septal and ventromedial hypothalamic lesion effects on discrete trial DRL behavior

“…Preoperative training may attenuate the hyperemotionality displayed by the VMH subjects and therefore account for the improved operant performance displayed by preoperatively trained rats (Peters, Sensenig, & Reich, 1973;Singh, 1973b). Flynn, Schirer, and Mitchell (1980) and Peters et al (1973) have reported that extensive preoperative handling reduces VMH emotionality. However, both septal and VMH rats showed a reduction in emotionality during testing on DT-DRL, indicating that this does not account for operant performance differences.…”