Kanbar R, Oréa V, Barrès C, Julien C. Baroreflex control of renal sympathetic nerve activity during air-jet stress in rats. Am J Physiol Regul Integr Comp Physiol 292: R362-R367, 2007. First published September 14, 2006; doi:10.1152/ajpregu.00413.2006.-The effects of acute emotional stress on the sympathetic component of the arterial baroreceptor reflex have not yet been described in conscious animals and humans. Arterial pressure (AP) and renal sympathetic nerve activity (RSNA) were simultaneously recorded in 11 conscious rats before and during exposure to a mild environmental stressor (jet of air). Baroreflex function curves relating AP and RSNA were constructed by fitting a sigmoid function to RSNA and AP measured during sequential nitroprusside and phenylephrine administrations. Stress increased mean AP from 112 Ϯ 2 to 124 Ϯ 2 mmHg, heart rate from 381 Ϯ 10 to 438 Ϯ 18 beats/min, and RSNA from 0.80 Ϯ 0.14 to 1.49 Ϯ 0.23 V. The RSNA-AP relationship was shifted toward higher AP values, and its maximum gain was significantly (P Ͻ 0.01) increased from 9.0 Ϯ 1.3 to 16.2 Ϯ 2.1 normalized units (NU)/mmHg. The latter effect was secondary to an increase (P Ͻ 0.01) in the range of the RSNA variation from 285 Ϯ 33 to 619 Ϯ 59 NU. In addition, the operating range of the reflex was increased (P Ͻ 0.01) from 34 Ϯ 2 to 41 Ϯ 3 mmHg. The present study indicates that in rats, the baroreflex control of RSNA is sensitized and operates over a larger range during emotional stress, which suggests that renal vascular tone, and possibly AP, are very efficiently controlled by the sympathetic nervous system under this condition. arterial pressure; baroreceptor reflex; gain; sympathetic nervous system IN LABORATORY ANIMALS AND human subjects, emotional stress evokes parallel increases in arterial pressure (AP), heart rate (HR), and sympathetic nerve activity (SNA) (1, 2, 17). In sleeping or quiet resting subjects, pharmacologically induced increases in AP result in reflex decreases in HR and SNA. From this simple observation, it is logical to hypothesize that emotional stress inhibits or even suppresses the arterial baroreceptor reflex. Support to this hypothesis came initially from studies performed on anesthetized animals. Specifically, electrical stimulation of the hypothalamic defense area of cats, which mimics the cardiovascular and autonomic effects of emotional stress (8), was shown to inhibit baroreceptive neurons in the nucleus tractus solitarius (22). In the latter study, however, it could not be excluded that electrical stimulation had activated fibers of passage. Therefore, the question was recently revisited by using a pharmacological approach. It was found that in urethane-anesthetized rats, disinhibition of neurons of the defense area with a GABA A receptor antagonist induced a rightward shift of the renal SNA (RSNA) baroreflex function curve and increased its sensitivity (20).It is amazing that the effects of emotional stress on the characteristics of the sympathetic baroreceptor reflex have not yet been reported. Howe...