Muscarine Reduces Calcium-Dependent Electrical Activity in Substantia Nigra Dopaminergic Neurons

1 Department of Anatomy and Neurobiology, Health Science Center, University of Tennessee, Memphis, Tennessee 38163; and 2 Morehouse School of Medicine, Neuroscience Institute, Atlanta, Georgia 30310 Scroggs, Reese S., Carla G. Cardenas, Joseph A. Whittaker, and Stephen T. Kitai. Muscarine Reduces Calcium-Dependent Electrical Activity in Substantia Nigra Dopaminergic Neurons. J. Neurophysiol. 86: 2966-2972, 2001. The effect of muscarine on Ca 2+ dependent electrical activity was studied in dopamine (DA) neurons located in the substantia nigra pars compacta (SNc) in brain slices from young rats, using sharp electrodes. In most DA neurons tested, muscarine (50 µM) reduced the amplitude of spontaneous oscillatory potentials and evoked Ca 2+ -dependent potentials recorded in the presence of TTX. Muscarine also reduced the amplitude of the slow afterhyperpolarization (sAHP) following action potentials in most DA neurons. These data suggest that muscarine reduces Ca 2+ entry in SNc DA neurons. The reduction of the amplitude of the sAHP by muscarine in DA neurons may facilitate bursting initiated by glutamatergic input by increasing the frequency at which DA neurons can fire. The reduction of the sAHP via activation of muscarinic receptors in vivo may provide a mechanism whereby cholinergic inputs to DA neurons from the tegmental peduncular pontine nucleus could modulate dopamine release at dopaminergic targets in the brain.