Immediate effects of increased blood pressure on pattern of resting discharge in renal postganglionic neurons

In experiments performed on anaesthetized rabbits the pattern of resting activity in renal postganglionic neurons during sustained increase in blood pressure (BP) was investigated. Resting discharge was recorded in 39 single units. Sustained increases in BP by about 20 mm Hg were evoked by i.v. infusion of phenylephrine (15 μg/kg/min). From interspike-interval histograms accumulated for each neuron, the shortest, preferred and longest interspike-intervals were calculated. The mean discharge rate was also measured. During elevation of BP the shortest interspike-intervalengthened from control value of 7.2 ± 0.2 ms (± S.E.) to 17.4 ± 8 ms, preferred interval increased from 28.3 ± 5.7 ms to 80.7 ± 12.9 ms, and longest interval lengthened from 6440 ± 396 to 7431 ± 387 ms. The discharge rate decreased from 1.437 ± 0.2 to 0.973 ± 0.2 spikes/s. All changes were statistically signifi cant (P < 0.05). Elevated BP lowered correlation coeffi cient between the shortest interval and discharge rate from r = -0.347 (P = 0.03) to r = -0.186. Immediate eff ects of elevated BP on pattern of discharge of single renal neurons most probably resulted from the central eff ect of phenylephrine on altered interactions between cells generating activity in vasomotor neurons