Eating and drinking induced by cerebral-ventricular injections in rats with lesions in the lateral hypothalamus

Pentobarbital-induced drinking does not rely on a renal dipsogen

Injections of pentobarbital have been shown to produce drinking in both deprived and nondeprived rats and a number of other studies have shown that pentobarbital is a potent renin releasor. Since renin has been shown to be involved in thirst regulatory mechanisms and since the dipsogenic actions of other renin-releasing agents have been blocked by nephrectomy, we sought to determine whether or not pentobarbital-induced drinking relies on a renal dipsogen. Rats were either "sham" operated or nephrectomized under ether anesthesia. Five to six hours later, animals in each group were injected with either 9.5 mg/kg pentobarbital sodium or vehicle, and intakes were measured 60 minutes later. Statistical analysis of water intakes indicated that pentobarbital produced significant drinking in both control operated and in nephrectomized rats, and that the intakes in these two groups did not differ. These results indicate that pentobarbital-induced drinking is not secondary to increased plasma renin activity and may suggest the involvement of central mechanisms in the drinking response.

Feeding following intraventricular injection of CA++, MG++ or pentobarbital in pigs

The effects on food intake, of injections into the lateral ventricle of Ca++, Mg++ or equimolar mixtures of the 2 ions have been studied in pigs. The chloride salts were made up in normal saline which together with 1.35 percent NaC1 was used as a control injection. Dosages of 12.5 mumoles, 25 mumoles, or 50 mumoles either Ca++ or Mg++ elicited increased food intake in the 30 min following the injection and there was a predominantly linear feeding response to increasing concentration of the two ions. Ca++ was more effective in eliciting increased food intake than Mg++. Equimolar mixtures of Ca++ and Mg++ of 6.5 + 6.5 mumoles, 12.5 + 12.5 mumoles or 25 + 25 mumoles also increased food intake linearly and the mixture of ions was more effective than equivalent concentrations of Ca++ or Mg++ alone. No antagonism between Ca++ and Mg++ was seen with respect to food intake. Intraventricular injections of 16 mumoles of sodium pentobarbital also elicited increased food intake in the 30 min following injection. It is suggested that the ions and the barbiturate probably act by deression of periventricular neurons, particularly in the medial hypothalamus which is adjacent to the third ventricle.