Two-component arterial blood pressure conditional response in rat

The objective of these experiments was to quantify the pattern of change in arterial blood pressure (BP) during a discriminative aversive classical conditioning paradigm in rat using a new "high resolution" computer analysis. Sprague-Dawley rats (n = 5) were restrained in a soft, conical cloth pouch and conditioned using a 6 sec. pulsed tone (CS+) followed by a 0.5 sec. tail shock; a steady tone, never followed by shock, served as a CS-. BP peaked at 16.4 +/- 6.5 mm Hg (mean +/- SD) above control at 1.5 +/- 0.1 sec. after onset of CS+. This "first component" ("C1") also occurred during CS- (12.1 +/- 3.8 mm Hg), although the magnitudes of the two were significantly (p < 0.05) different. Another group of rats (n = 8) was treated identically except the tones were 15 seconds long. The conditional BP response consisted of two components. C1 was reminiscent of that seen using the short tone: for CS+ a peak of 13.6 +/- 5.6 mm Hg at 1.5 sec. or, for CS-, of 10.0 +/- 4.3 at 1.3 sec. (p < 0.05). In CS+ trials BP peaked again ("C2," 7.4 +/- 2.5 mm Hg) at 8.3 +/- 1.2 sec. There was no statistically significant C2 for CS- trials, clearly demonstrating discrimination between tones. The unconditional BP response in both groups consisted of two large, closely spaced peaks in BP. Respiration was recorded in 3 additional rats. After shock delivery these subjects often showed a sudden shift between (1) a regular respiratory pattern with moderate chest excursion and (2) apneic episodes interspersed with single, deep breaths. This latter pattern was associated with large, low frequency fluctuations in BP. Continued development of the rat conditioning paradigm is especially warranted because of the ability to record sympathetic nerve activity in intact, awake subjects and the large number of readily available genetic strains, which model human pathological states.