Hypoalgesia in response to sensitization during acute noise stress.

Three experiments examined the antinociceptive response shown by rats (N?=?103) during exposure to loud noise. Noise exposure resulted in a time-dependent elevation of radiant heat tailflick latency that varied as a function of stimulus intensity. Noise stress hypoalgesia in response to a 90-dB stimulus was blocked by pretreatment with the opioid antagonist naltrexone (0.1–7.0 mg/kg). Systemic administration of midazolam (2 mg/kg) prior to exposure to the stressor attenuated the elevation in tailflick latency. Because topographically similar antinociceptive responses may be elicited with a low intensity noise stimulus that has served as a Pavlovian CS for shock, the use of this paradigm may permit direct comparisons of associative and nonassociative fear responses using qualitatively similar auditory stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)