Hierarchic organization of blood pressure responses during the expression of natural behaviors in rat: Mediation by sympathetic nerves

We quantitatively assessed, through computer-assisted recording techniques, the magnitude and variability of changes in arterial pressure (AP) and heart rate (HR) associated with the performance of natural behaviors in the rat. The AP and HR were recorded during 1-h sessions in awake, unrestrained rats (N = 8) fitted with an indwelling aortic cannula. During recording sessions, an observer encoded the performance of five behaviors (eating, drinking, grooming, exploration, and rest) and signalled their onset and termination to the computer, which stored the behavioral and cardiovascular data for later analysis. The behaviors were unequally distributed, with eating accounting for 42%, resting for 27%, grooming and exploration each for 13%, and drinking for 4% of total encoded time, on the average. Average AP during behavior was hierarchically organized. The AP (in millimeters Hg) during eating (118 ± 3) and drinking (117 ± 6) was higher (P < 0.01) than during grooming (109 ± 4) and exploration (109 ± 5) and during each of these was higher (P < 0.01) than during rest (95 ± 5). The variability of the AP was less (P < 0.01) during rest than during each of the other behaviors. The HR was lower (P < 0.01) during rest than during the other behaviors, and its variability was greater (P < 0.05) during grooming and exploration than during the other behaviors. Chemosympathectomy through systemic injection of 6-OHDA (N = 5) abolished the rank ordering of blood pressure changes. The average magnitude of the AP during eating (83 ± 5), drinking (85 ± 5), grooming (77 ± 11), exploration (75 ± 9), and rest (83 ± 7) was not different in 6-OHDA-treated animals. The data demonstrate (a) that changes in the magnitude and variability of AP and HR during the performance of each of several natural behaviors were relatively constant within and across animals; (b) that the changes in AP during behavior were hierarchically organized, with the consummatory behaviors, eating and drinking, accounting for the greatest elevations of AP above resting baseline; and (c) that the sympathetic nerves mediate the hierarchic control of blood pressure during natural behavior.