Heart rate changes in partially restrained rats during behaviorally and pharmacologically evoked emotional states

The effect of fear and relief from fear on heart rate (HR) was studied in p artially restrained adult male rats. The emotional state was influenced beh aviorally with the use of Pavlovian aversive conditioning procedure, and ph armacologically by injections of the selected anxiolytics and anxiogenics. A signal of danger (DS) - light or tone, preceded tail-shock (excitatory tr ials), while a signal of safety (SS), respectively tone or light, overlappe d last 3s of 5s DS and predicted an omission of this expected aversive even t (inhibitory trials). To assess the stability of HR changes to DS and SS w e analyzed whether and how the experimental conditions (modality and positi on of signals, the ratio of numbers of excitatory to inhibitory trials in t he session) influenced HR. HR changes to DS were different in pattern, stab ility and direction when compared to HR changes in response to SS. Reaction s to DS, although accompanied mainly by conditioned bradycardia, were not c onsistent and depended on experimental conditions. However, the SS always e voked conditioned tachycardia. Anxiolitycs - benzodiazepines (diazepam and midazolam) and buspirone influenced HR in nonconsistent manner. Anxiogenics - PTZ and FG7142 were without significant effects on HR. HR could not be t rusted therefore as direct index of pharmacologically induced emotional sta tes. The results are discussed in the context of possible biobehavioral mea ning of HR changes in response to danger and safety and their reliability a s' fear/relief correlates.