Dc. Randall et al., SYMPATHETIC NERVOUS ACTIVITY AND ARTERIAL BLOOD-PRESSURE CONTROL IN CONSCIOUS RAT DURING REST AND BEHAVIORAL STRESS, American journal of physiology. Regulatory, integrative and comparative physiology, 36(5), 1994, pp. 1241-1249
The object of this experiment is to analyze the neural control of arte
rial blood pressure (BP) during rest and a sudden behavioral stress. S
prague-Dawley rats were classically conditioned by following a 15-s to
ne (CS+) with a 0.5-s tail shock. Bipolar renal nerve electrodes and a
caudal artery catheter were implanted. Two days later BP and sympathe
tic nervous activity (SNA) were recorded in the behaviorally trained a
nimals. The CS+ evoked a large initial increase in BP (peak, 14 +/- 5
mmHg, mean +/- SD; n = 12) that lasted 3.9 +/- 0.8 s. An abrupt (laten
cy = 0.16 +/- 0.03 s), short (duration = 0.58 +/- 0.12 s), and intense
(4.09 +/- 1.02 times average control) burst in sympathetic activity p
receded this first component (C-1) of the BP conditional response. The
size of C-1 was related to the magnitude of the SNA burst. SNA then f
ell below control; this quiet period preceded a fall in BP after the C
-1 peak. Pressure rose again (Ct; peak = 6 +/- 3 mmHg, average increas
e = 3 +/- 3 mmHg) for the remainder of the CSS. SNA increased to 1.24
+/- 0.14 of control during this second component of the BP conditional
response. Ganglionic blockade eliminated the BP and SNA conditional r
esponse (n = 3). The C-1 pressure increase appears to result from an '
'open-loop'' process in which a brief barrage of nerve activity govern
s BP changes lasting several seconds. The quiet period probably result
s from a negative feedback (i.e., baroreflex) relationship between SNA
and BP. Finally, the baroreflex may be reset to regulate BP at a high
er level during the remainder of the conditional response, perhaps bec
ause of altered central drive.