Effects of diazepam and phenobarbital on self-stimulation in posterior hypothalamic and preoptic regions and on the thermoregulatory responses to rewarding brain stimulation

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The effects of diazepam and phenobarbital on body temperature changes induced by self-stimulation behaviour were investigated to determine the relationship between the actions of the drugs on behaviour and on thermoregulation. The drugs were tested at two doses, each representative of doses causing one of two effects; a low dose causing a stimulant effect and a high dose producing sedation. Diazepam was tested at 1·25 and 35 mg/kg intraperitoneally and phenobarbital at 12·5 and 70 mg/kg intraperitoneally. Self-stimulation was produced with stimulation of the posterior lateral hypothalamic region in one group of rats and of the preoptic region in another group of rats. After 10 and 15 min of self-stimulation, the body temperature of the subjects responding for posterior lateral hypothalamic and for preoptic stimulation rose. The increase was of the same magnitude in both groups. The rate of responding and the amount of total brain stimulation taken during this period was higher for the group rewarded with hypothalamic stimulation than for the preoptic group, but the duration of the stimulus-trains was greater for the preoptic group than for the hypothalamic. In control subjects, diazepam and phenobarbital at the low dose increased the body temperature and at the high dose decreased it. In both groups of self-stimulators, the drugs at the low dose failed to potentiate the increases in body temperature induced by self-stimulation behaviour itself, although the drugs increased the rate of self-stimulation or the total time with brain stimulation or the mean duration of the stimulus-trains. At the high dose, both drugs caused the increases in body temperature induced by hypothalamic self-stimulation behaviour to be smaller, but only slightly so. On the other hand, at the high dose, diazepam blocked the increase in body temperature by preoptic self-stimulation behaviour. Phenobarbital was not similarly effective during preoptic self-stimulation. At the time of these effects on body temperature the total amount of brain stimulation received during the sessions and the duration of the stimulus-trains increased. The findings indicate a dissociation between the effects of diazepam on body temperature and on self-stimulation behaviour when reward was in the preoptic region, but not when reward was in the posterior lateral hypothalamic region.