Muscarinic modulation of calcium dependent plateau potentials in rat neostriatal neurons

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Abstract
Intracellular recording from neostriatal neurons in rat brain slices revealed effects of the acetylcholine (ACh) agonist carbachol (Cch, 1–10 μmol/l), of the anticholinesterase physiostigmine (10 μmol/l) and of the muscarinic antagonist atropine (10 μmol/l) on plateau potentials elicited in the presence of K-blockers were Cadependent, elicited in the presence of K-blockers were Cadependent, since they persisted in Na-free solution, were resistant to tetrodotoxin (TTX, 3 μmol/l) and blocked by Cd (0.1–0.5 mmol/l). Cch reduced the duration of the plateau potentials and made them more susceptible to fatigue. These effects were antagonized by atropine (1–10 μmol/l), but not by Ba (100–200 μmol/l) or 4-aminopyridine (4-AP, 0.5 mmol/l). Physostigmine (10 μmol/l) had the same atropine-sensitive effects as Cch on the plateau potential. Atropine (10 μmol/l), by itself, prolonged the duration of the plateau potential. High concentrations (100 μmol/l) of Cch did not further reduce the duration of the plateau potential, instead, the duration re-increased with prolonged exposure. The re-increase of the plateau-spike duration was later masked by bursting activity. The opposing effects of low and high concentrations of Cch on the plateau potential duration corresponded to effects of this drug on intrastriatally evoked EPSPs in that low concentrations of Cch reduced the EPSP amplitude, but high concentrations re-increased it after a transient decrease. It is concluded that the muscarinic effect of Ach in the neostriatum is to modulate Ca-influx and that this effect is exerted in a tonic manner.