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The present study has examined the influence of the central nucleus of the amygdala (Ce) and the basolateral nucleus of the amygdala (BL) on the baroreceptor heart rate (HR) reflex in conscious, unrestrained rats. Baroreceptor HR reflex activity was examined in rats with bilateral excitotoxin (N-methyl-D-aspartate; 40 nmol/side)-induced lesions of the Ce or the BL and in control rats (artificial cerebrospinal fluid). After lesioning, the reflex HR responses were recorded following intravenous bolus doses of the pressor agent phenylephrine and the depressor agent sodium nitroprusside. Baroreceptor reflex parameters were determined by sigmoidal computerized curve-fitting. Lesions of either the Ce or the BL failed to affect resting mean arterial pressure (MAP) or HR. However, the Ce lesion reduced the maximum and average gain (sensitivity) of the baroreceptor reflex, and diminished the range of the reflex by altering the minimum, but not the maximum HR plateau. The upper and lower reflex thresholds and the MAP value corresponding to the midpoint of the HR range were not affected. Bilateral lesions of the BL failed to modify any baroreceptor reflex parameters. These results suggest that despite previous evidence for the involvement of the BL in cardiovascular regulation this nucleus does not exert a tonic influence on vasomotor neurons nor does it influence the baroreceptor HR reflex. In contrast, neurons projecting from the Ce appear to provide excitatory input to medullary neurons involved in baroreceptor reflex are regulation. |
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