EFFECTS OF PROPRANOLOL, PHENTOLAMINE AND METHYL ATROPINE ON CARDIOVASCULAR FUNCTION IN THE SQUIRREL MONKEY DURING BEHAVIORAL EXPERIMENTS

Findings suggest that in the squirrel monkey a relatively high degree of sympathetic nervous system tone persists during behavioral experiments.

Abstract

Systemic mean arterial blood pressure and heart rate were measured in squirrel monkeys trained under a fixed-ratio schedule to press a key that turned off a light associated with the delivery of electric shocks. The mean blood pressures were above values previously recorded in untrained squirrel monkeys. Episodic increases in blood pressure and heart rate commonly were associated with schedule-controlled key-pressing behavior. Phentolamine decreased blood pressure and increased heart rate. The episodic increases in blood pressure persisted even when phentolamine markedly lowered blood pressure. There was little change in blood pressure after propranolol, which markedly decreased heart rate, or after methyl atropine, which increased heart rate. After either drug, the episodic increases in blood pressure persisted. None of these drugs consistently affected key-pressing behavior over the range of doses that markedly affected blood pressure or heart rate. Atropine, which had cardiovascular effects similar to methyl atropine, decreased rates of key pressing. Combinations of propranolol and methyl atropine had effects similar to propranolol alone; these findings suggest that in the squirrel monkey a relatively high degree of sympathetic nervous system tone persists during behavioral experiments.