Stereotyped behavioral responses to an auditory stimulus in the course of repeated treatment with methamphetamine plus scopolamine and methamphetamine in rats.

The present experiment was designed to study the effects of an auditory stimulus with 300 Hz, 100 dB on gradual emergence of behavioral sensitization in the course of repeated administration of methamphetamine (MAP) in combination with scopolamine (SCOP) and MAP. Repeated intraperitoneal injection of MAP (4.0 mg/kg) plus SCOP (0.5 mg/kg) induced significantly progressive and enduring enhancement of stereotyped behavior, resulting in intense, focussed stereotypy intermingled with gnawing and licking compared to repeated MAP treatment. Vigorous stereotyped behavior induced by repeated MAP plus SCOP was progressively attenuated by the tone, resulting in attenuation of the development of behavioral sensitization. Conversely, the tone had no invariable effects on behavioral sensitization induced by repeated MAP treatment. The present findings indicate that repeated MAP plus SCOP treatment progressively induced attenuating effects of tone as low as 300 Hz on MAP plus SCOP-induced intense stereotypy and vigorous behavioral sensitization. These findings suggest that a reciprocal balance between dopaminergic and cholinergic inhibitory systems may be involved in producing behavioral sensitization, and in the attenuating effects of the tone on MAP plus SCOP-induced vigorous behavioral sensitization.