Role of the laterodorsal tegmental nucleus in scopolamine- and amphetamine-induced locomotion and stereotypy.

Scopolamine (1.5 mg/kg; i.p.) or amphetamine (3 mg/kg; i.p.) increases locomotion and stereotyped behavior patterns in rats. Previous studies suggest that scopolamine acts via muscarinic receptors near the midbrain-pons border. In this study, unilateral microinjections in N-methyl-scopolamine (2.5-10 microg) into the laterodorsal tegmental nucleus (LDT) increased locomotion. Bilateral ibotenate lesions of the LDT attenuated scopolamine-induced locomotion by 68% 7 days postlesion, and by 35% 28 days postlesion. LDT lesions reduced scopolamine-induced stereotypy less than locomotion. The sensitization to amphetamine observed on repeated tests was attenuated by LDT lesions for stereotypy, but not for locomotion. These findings suggest that scopolamine induces locomotion largely, but not exclusively, by blocking muscarinic receptors in LDT.

Prepulse inhibition of acoustic or trigeminal startle of rats by unilateral electrical stimulation of the inferior colliculus.

Transient electrical stimulation of the inferior colliculus (IC) of adult male rats had a strong and long-lasting inhibitory effect on startle responses elicited by either intense noise bursts or unilateral electrical stimulation of the principal trigeminal nucleus. Startle elicited by noise bursts was inhibited over a wide range of interstimulus intervals (ISIs) with the maximum inhibition at ISIs between 15 and 30 ms. Startle elicited by trigeminal stimulation was inhibited more sharply than acoustic startle, with the maximum inhibition at ISIs between 20 and 35 ms. These data support the view that the IC is a critical part of the pathway mediating prepulse inhibition (D. S. Leitner & M. E. Cohen, 1985). More important, the data reveal the time course of the inhibitory influence of the IC on startle and indicate that the inhibitory effects of IC stimulation have higher temporal resolution on trigeminal startle than on acoustic startle.