Parallel anxiolytic-like and antinociceptive actions of diazepam in the anterior basolateral amygdala and dorsal periaqueductal gray

Abstract

Rationale: The antinociceptive actions of diazepam and other benzodiazepines are partly due to their anxiolytic-like properties. Objective: This study was conducted to analyze the relationship between the anxiolytic-like and antinociceptive effects of diazepam when injected into the anterior basolateral amygdala (ABLA) and the dorsal periaqueductal gray (dPAG). These areas were selected because of their important participation in the regulation of anxiety and defensive responses. Methods: The anxiolytic-like effect of diazepam was evaluated with the rat burying behaviour test. The pain-induced functional impairment in the rat (PIFIR) model was used to study the effects of diazepam on nociception. Nociception was induced by intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Results: Sole exposure to the burying behaviour test produced a slight non-significant hyperalgesic effect. Diazepam injection (2.0 μg/0.4 μl) into the ABLA or dPAG produced a reduction in cumulative burying behaviour – an anxiolytic-like effect – together with an increase in burying behaviour latency. Such reduced experimental anxiety was paralleled by an antinociceptive response (i.e., increased use of the uric-acid-injected limb). Reduced experimental anxiety was correlated with antinociception after diazepam infusion into both brain structures. Conclusions: Diazepam-reduced experimental anxiety was paralleled by antinociceptive effects.