Abstract
The present study investigated the regulation of substantia nigra pars compacta (SNc) dopamine neuronal activity by pedunculopontine (PPT) cholinergic neurons. Changes in dopamine efflux following chemical activation or blockade of muscarinic acetylcholine receptors in the PPT were measured at stearate-carbon paste electrodes in the striatum of urethane (1.5 g/kg) anaesthetized male rats using in vivo chronoamperometry (30 s sampling rate). Intra-PPT infusions of a mixed muscarinic/nicotinic (carbachol 8 microg/microl) or M2/4-selective muscarinic (oxotremorine 0.5 microg/microl) receptor agonist attenuated striatal dopamine efflux, whereas a non-selective (scopolamine 100 microg/microl) or M2/4-selective (methoctramine 50 microg/microl) muscarinic receptor antagonist enhanced striatal dopamine efflux. These results suggest that M2/4 muscarinic receptors in the mesopontine tonically influence SNc basal dopamine cell activity and striatal dopamine release.
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