Autonomic control of heart rate and blood pressure in spontaneously hypertensive rats during aversive classical conditioning.

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Abstract
An examination was made of the heart rate (HR) and blood pressure (BP) responses of 7- to 9-wk old spontaneously hypertensive rats (SHR) and genetical control Wistar/Kyoto (WKY) rats during aversive classical conditioning. Subsequent to the development of conditioned responding (CRs), assessments were made of the effects of selective autonomic blockade by methyl atropine (10 mg/kg), phentolamine (2 mg/kg) and propranolol (2 mg/kg). The CR complex in the 2 strains consisted of pressor BP CR in conjunction with vagally mediated decelerative HR CR in the SHR strain and sympathetically mediated accelerative HR CR in the WKY strain. The decelerative SHR HR CR did not appear to be secondary to baroreceptor reflex activity, although such activity did appear to be involved in the pressor BP and decelerative HR orienting response (OR) and unconditioned response (UR) complex of the SHR on the initial application of the CS and the US. Augmented pressor BP OR, CR and UR in the SHR relative to the WKY and differential drug effects on BP and HR baselines of the 2 strains suggested the presence of enhanced sympathetic activity in the SHR that was not reflected in the SHR decelerative HR CR. Phentolamine unmasked evidence of reflex .beta.2-vasodilation deficiency in the SHR that could have contributed to the enhancement of their BP OR and CR.

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