The influence of ethanol on learned and reflexive heart rate responses of rats during classical aversive conditioning.

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Abstract
Heart rate (HR) responses of rats during aversive classical Pavlovian conditioning were examined in a factorial design involving 2 concentrations of ethanol (0.8 or 2.4 g/kg of body wt) and 2 unconditioned stimulus intensities (0.6 or 1.2 mA electric shock). The animals were 129 naive female, Long-Evans hooded rats, 90-120 days of age. They were conditioned in a sound-isolation chamger with a white noise sound pressure of 75 dB. The conditioned stimulus (CS) was a 6.5 s, 2.9 kHZ tone at 85 dB sound pressure. The uncoditioned stimulus (US) was a 0.5 s, 60 Hz AC electric shock to the base of the tail in a delayed conditioning paradigm where the CS occurred for 6.5 s and the US occurred from 0.5 s during the end of the CS. The smaller dose of ethanol reduced the overall magnitude of the HR orienting response to the CS, but had no effect on the conditioned response. The larger dose prevented the occurrence of both orienting and conditioned changes. The unconditioned response produced by the electric shock in the presence of the higher dose was a biphasic deceleration-acceleration, instead of the monophasic acceleration that occurred with saline. Base-line HR was elevated by the smaller dose and lowered by the larger dose. High doses of ethanol may increase vagal output, resulting in cardiodeceleration.