NEONATAL METHAMPHETAMINE-INDUCED LONG-TERM ACOUSTIC STARTLE FACILITATION IN RATS AS A FUNCTION OF PREPULSE STIMULUS-INTENSITY

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 eff ect using a lower dose of MA and to determine if the effect varied as a function of prepulse stimulus intensity. Sprague-Dawley CD rat offsp ring were culled on the day after birth to eight (preferentially retai ning females). On days 1-10, progeny were injected SC with either 20 m g/kg of d-MA twice per day (doses spaced at least 8 h apart) or distil led water. On postnatal day 50, offspring were administered 51 acousti c 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 pronounc ed on the prepulse trials. Prepulse intensity interacted with MA treat ment 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, 8 5, 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 m odify startle reactivity.