Effect of ventromedial hypothalamic procaine injections on feeding, lever pressing, and other behavior in rats.

Rats were given bilateral injections of 1-2 mul procaine HCl solution (50 mug/mul) in the region of the ventromedial hypothalamus. Normal-sized meals occurred reliably with a latency of 16-120 sec, indicating that this region has the function of inhibiting onset of eating, not just the function of stopping a meal. Food-rewarded fixed-ratio-of-one (FR 1; continuous reinforcement) lever pressing was elicited by 2-mul but not by 1-mul procaine. The FR 64 pressing appeared to be disrupted during a period of increased activity following procaine injection, although visual observations indicated that the pressing which did occur was normal in topography and was significantly associated in temporal sequence with approaches of the food magazine.     

Memory of conditioned food aversion follows a U-shape function in rats

Rats drinking saccharin solution for the first time were poisoned by injection of lithium chloride and then offered saccharin solution 90 min, 1, 2, 3, 7, 10 or 14 days later. The memory function was U-shaped with 90-min and 14-day groups retaining the most aversion to saccharin. Intervention with an anticholinesterase (physostigmine) failed to produce a disruption or enhancement of memory, as might have been expected from theories that the laying down of memories depends on modification of cholinergic synapses.     

Effects of gastric loads and food deprivation on subsequent food intake in suckling rats.

Suckling rats were subjected to deprivation periods of 6-8 hr. Intake following deprivation was greater in deprived than in nondeprived sucklings, but did not increase with increasing deprivation. Gastric loads of NaCl solutions depressed subsequent intake; 3% NaCl was more effective than .9% NaCl. Other gastric loads of varying osmotic and caloric value also depressed subsequent intake. In order of increasing effectiveness in depressing intake, the gastric loads were protein hydrolystate, heavy cream, water, milk, lactose, glucose, and corn oil. Effectiveness was unrelated to osmotic or caloric value of the load. Gastric fill and, possibly, some property of carbohydrate appear to be important determinants of satiety in the suckling rat.