| Summary: | 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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