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Cholinergic modulation of medial vestibular nucleus neurons of the gerbil in vitro Belzile, Denise
The actions of various cholinergic agonists on 135 medial vestibular nucleus (MVN) neurons were investigated in in vitro brainstem preparations from young gerbils (p10-p15). Changes in conductance and membrane potential were determined using the whole cell patch clamp technique. Both muscarinic agonists (oxotremorine at concentrations of 5-20 µM) and mixed cholinergic agonists (acetylcholine and carbachol at concentrations of 10-20 µM) produced complex responses in the neurons. The membrane responses persisted on blockade of action potentials by application of 0.3 µM TTX. Increases and decreases in conductance with depolarizations and hyperpolarizations of the membrane potential were observed with all three drugs. There was no correlation between the changes in conductance and the changes in membrane potential. In order to examine the nicotinic responses of MVN neurons, the effects of acetylcholine and carbachol were studied during blockade of muscarinic receptors with the antagonist scopolamine (10 µM). Once again, a variety of membrane changes were observed, indicating a nicotinic response in these neurons. Acetylcholine applied simultaneously with the nicotinic blocker, mecamylamine (10 µM), also produced a mixed response in these neurons, indicating the presence of muscarinic receptors in this nucleus. The simultaneous application of scopolamine and mecamylamine failed to completely block the response of MVN neurons to acetylcholine. Both antagonists were found to have direct effects on MVN neurons, suggesting that endogenous acetylcholine is present within the slice preparation, and may affect the MVN in vivo. The results of these studies imply a more complex role for acetylcholine in the MVN than previously imagined. In addition, we have demonstrated a significant nicotinic response within these cells.
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