RESUMEN
The lateral hypothalamus (LH) sends neural pathways to structures involved on predatorrelated defensive behaviours, escape and antinociception. The aim of this study was to investigate the role played by µ-opioid receptors located on LH neurons in defensive behaviour and unconditioned fearinduced antinociception elicited by electric stimulation of LH. To achieve the goals, the µ1-opioid receptor selective antagonist naloxonazine was administered at different concentrations in the LH, and the defensive behaviour and fearinduced antinociception elicited by electrical stimulation of LH were evaluated. The electrical stimulation of LH caused escape behaviour followed by defensive antinociception. Microinjections of naloxonazine in a concentration of 5.0 µg/0.2 µL in the LH decreased the aversive stimulusinduced escape behaviour thresholds, but diminished defensive antinociception. These findings suggest that µ-opioid receptors of LH can be critical to panic attackrelated symptoms and facilitate the unconditioned fearinduced antinociception produced by LH neurons activation.