Characterization of cardiovascular and behavioral responses to alerting stimuli in rats

Freely moving rats exhibit complex motor and cardiovascular responses to tactile stimulation (12.5 psi air puff, 100-ms duration). In naive Wistar-Kyoto rats, the behavioral response is characterized by a short-latency (25 +/- 1 ms) jumping event, the magnitude of which habituates to repeated stimuli. In a paradigm of consecutive tactile stimuli, each delivered at 30-s intervals, the arterial pressure (AP) response is consistent in profile (36.4 +/- 1.7 mmHg, initial stimulus) and habituates rapidly (15.4 +/- 2.2 mmHg, at 20th stimulus). Rates of habituation of the jumping behavior and AP increase are similar and significantly correlated (P less than 0.01), suggesting partial common mediation. Heart rate changes are bimodal and highly dependent on stimulus number. Initial stimuli elicit bradycardia (-42 +/- 7 beats/min), habituating to extinction by stimulus 10. A temporally delayed tachycardia becomes evident by trial 5 (19 +/- 5 beats/min) and persists unchanged throughout the remainder of the 30-stimulus session. Delayed tachycardia may represent activation of secondary autonomic mechanisms. The nature of cardiovascular responses elicited by the tactile stimulus suggests a somatomotor reflex mediated through the ventrolateral medulla. Adrenal enucleation exaggerated the magnitude of transient bradycardia and abolished extinction of bradycardia with repeated stimuli. Adrenal medullary secretion has only minor importance in direct mediation of the response, but this study suggests that adrenal function plays an important role in tonically setting the level of cardiac responsiveness to parasympathetic vs. sympathetic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)