Neonatal methamphetamine-induced long-term acoustic startle facilitation in rats as a function of prepulse stimulus...

Neonatal exposure to methamphetamine (MA) has previously been shown to induce acoustic startle facilitation when the animals were tested as adults. The present experiment sought to replicate and extend this effect using a lower dose of MA and to determine if the effect varied as a function of prepulse stimulus intensity. Sprague-Dawley CD rat offspring were culled on the day after birth to eight (preferentially retaining females). On days 1-10, progeny were injected SC with either 20 mg/kg of d-MA twice per day (doses spaced at least 8 h apart) or distilled water. On postnatal day 50, offspring were administered 51 acoustic startle trials followed by 36 prepulse trials. Prepulse intensities were 0, 70, 75, 80, 85, or 90 dB. MA progeny showed augmented startle response amplitudes on both paradigms but the effect was most pronounced on the prepulse trials. Prepulse intensity interacted with MA treatment in that significant facilitation in the MA animals occurred on 0 and 70 dB prepulse trials but was only a trend (p < 0.10) on 75, 80, 85, and 90 dB trials. This implies that the effect of MA is most likely upon the basic startle reflex and not upon inhibitory pathways that modify startle reactivity.