Effects of acute ethanol or amphetamine administration on the acoustic startle response and prepulse inhibition in adolescent and adult rats

Adolescents differ from adults in their sensitivity to a variety of psychoactive drugs. For example, adolescent rats are less sensitive to locomotor stimulant and stereotypic effects of amphetamine as well as to motor-impairing and hypnotic effects of ethanol while more sensitive to ethanol-induced disruption of brain plasticity. The current study further explored age differences in psychopharmacological sensitivity by examining the effects of d-amphetamine (1.0 and 4.0 mg/kg) or ethanol (0.5, 1.0 and 1.5 g/kg) given interperitoneally on the acoustic startle response (ASR) and prepulse inhibition (PPI) in male adolescent and adult Sprague-Dawley rats. The animals were given five startle trials (120 dB for 40 ms) before semi-randomized presentation of 12 startle trials interspersed with ten trials at each prepulse intensity (40 ms pulse of 5, 10, or 20 dB above background; 100 ms before the startle stimulus). Adolescent controls showed significantly less PPI than adults, replicating previous ontogenetic findings. The higher dose of amphetamine disrupted PPI in adult but not in adolescent animals, extending previous reports of an adolescent insensitivity to amphetamine to include this measure of sensorimotor gating. Ethanol exposure failed to alter PPI at either age, although both the 1.0 and 1.5 g/kg doses of ethanol significantly suppressed the magnitude of the ASR at both ages, potentially reflecting sedative or anxiolytic effects. These data provide further evidence of the relative insensitivity of adolescent animals to amphetamine, although no age effects were found in terms of ethanol sensitivity using these measures of startle and sensorimotor gating.