Heart rate reactivity in HAD and LAD rats during Pavlovian fear conditioning

Abstract

Recently, we reported that High-Alcohol-Drinking (HAD) rats exhibited selective deficits in active avoidance learning under alcohol-naive conditions, and that administration of moderate doses of alcohol (0.5 and 1.0 g/kg) facilitated learning in these rats (Blankenship et al., 2000; Rorick et al., 2003b). We hypothesized that the deficits resulted from excessive fear in the aversive learning context and that the anxiolytic properties of alcohol may have contributed to the improved learning that was observed after alcohol administration. This hypothesis was supported by a recent study in which prolonged freezing in HAD rats was seen after a classical fear conditioning procedure (Rorick et al., 2003a). To provide additional evidence that HAD rats indeed exhibit behaviors consistent with the expression of increased fear in aversive learning contexts, we employed a Pavlovian fear conditioning task to measure heart rate in HAD and Low-Alcohol-Drinking (LAD) rats. In this study, HAD (HAD-1 and HAD-2) and LAD (LAD-1 and LAD-2) rats were assigned to one of three pre-exposure conditions: Context Only, Context/Tone, or Sequential (Context Only followed by Context/Tone) Pre-Exposure. Following pre-exposure, fear conditioning acquisition and extinction procedures were identical for all groups. Results indicated that although no baseline differences were observed between HAD and LAD rats, HAD rats receiving Context-Only pre-exposure exhibited excessive heart rate reactivity to the tone conditional stimulus during fear conditioning acquisition, compared to LAD rats receiving the same pre-exposure conditions. These findings support the hypothesis that HAD rats exhibit behaviors consistent with increased fear in aversive learning contexts, as measured by autonomic conditioning.

Alcohol-Preferring P Rats Exhibit Elevated Motor Impulsivity Concomitant with Operant Responding and Self-Administration of Alcohol

“…Salimov () ultimately characterized the P rats as having “alcohol drive with novelty seeking and persistence,” while the HAD rats have “alcohol drive with timidity and meekness.” Similarly, HAD2s, but not P rats, have been seen to possess an avoidance (but not appetitive) learning deficit that may be due to increased anxiety (Blankenship et al., , ). This view is supported by findings that the HAD2s avoidance learning deficit is decreased with moderate levels of alcohol, presumably via its anxiolytic effects (Rorick et al., ), and the HAD2s have increased heart rate reactivity in a Pavlovian fear conditioning paradigm (Rorick et al., ). When also considering recently demonstrated differences in decision making (Beckwith and Czachowski, ) and the present findings of action cancelation impulsivity, greater number of overall trials completed (Table ), and greater responding for EtOH and persistence in the face of response requirement increases, the P rats appear to be prone to emit behavior, and by contrast, the HADs are perhaps more anxious and/or controlled.…”