Antinociception elicited by aversive stimulation of the inferior colliculus.

摘要: Abstract We have shown that the inferior colliculus is involved in integration of defensive reactions. Electrical and chemical stimulation this structure elicits fear escape behavior, expressed respectively by immobility (freezing) wild running, followed jumps. In study, we analyzed whether behavior integrated at level midbrain tectum also antinociception its mediation. addition, further addressed or not aversive states stress-induced analgesia share same neural substrates colliculus. To end, animals chronically implanted with a chemitrode, an electrode glued to guide cannula, were injected naltrexone, methysergide, ketanserin, midazolam. The submitted gradual increases electrical colliculus, which allowed measurement thresholds for responses—vigilance, freezing, escape. Following induction behavioral responses tail-flick test. results obtained show midazolam was only treatment changed thresholds. On other hand, while naltrexone did affect fear-induced analgesia, it inhibited microinjections serotonergic blockers, methysergide ketanserin. These emphasize previous data demonstrating nonopioid nature unconditioned brain-aversive stimulation. Because nonspecific antagonist 5-HT receptors, ketanserin acts high degree specificity 5-HT2/5-HT1C present suggest activation receptors may be implicated induced Moreover, indicate reactions from can pharmacologically dissociated.