Fig. 9

a, b Comparisons of changes in mean arterial pressure (ΔMAP) and heart rate (ΔHR) in response to electrical stimulation of the bilateral masseter muscles before and at 10 min after hexamethonium chloride administration (1, 10 mg kg⁻¹, each n = 8). Decreases in basal MAP in response to hexamethonium administration were compensated to control levels by the continuous infusion of phenylephrine hydrochloride (see “Methods”). c, d Comparisons of MAP and HR following phenylephrine hydrochloride (40 μg ml⁻¹, 0.1 ml) injection before and at 10 min after hexamethonium chloride (10 mg kg⁻¹) administration, and the comparisons of ΔMAP and ΔHR at the peak pressor response in six rats (the vasomotor response test). Decreases in basal MAP in response to hexamethonium administration were compensated to control levels by the continuous infusion of phenylephrine (see “Methods”). PE additional test administration of phenylephrine hydrochloride, Ф peak of the pressor response following phenylephrine hydrochloride injection, *p < 0.05, **p < 0.01, N.S. not statistically significant (paired Student’s t test)