Behavioral suppressant effects of clonidine in strains of normotensive and hypertensive rats

Abstract

The behavioral effects of orally administered clonidine were investigated in Long—Evans (LE), Sprague—Dawley (SD) or Kyoto Wistar (KW) rats assumed to be normotensive and in NIH spontaneously hypertensive (SH)_ rats. Although clonidine (0.05–1 mg/kg) resulted in the same quanlitative effects, i.e., depression of motor activity, the dose of clonidine required to depress motor activity to 50% of control levels (ED 50) tended to vary according to strain. An analysis of variance of the dose response curves for the foru strains of rats indicated a significant strain effect. When the effects of clonidine on food-reinforced operant responding were investigated, it was observed that SD and SH rats differed with regard to rate and temporal patterning of IRT > 20 sec responding. Although oral administration of clonidine (0.006–.01 mg/kg) procedure similar percentage decreases from control in SH and SD rats, an analysis of the temporal patterning of responding indicated differences in responsiveness to the behavioral effects of clonidine. These studies demonstrate strain-related differences in responsiveness to the behavioral suppressant effects of clonidine. Marked between genetically hypertensive rats and rats assumed to be normotensive were not evident.