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.