Some Properties of Nicotinic Cholinergic Receptors in Medial Habenular Nucleus of the Guinea Pig

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Pharmacological properties of nicotinic cholinergic receptors in the medial habenular nucleus (MHN) were studied in thin brain sections prepared from the guinea pig. In response to single stimulation of the stria medullaris, a field potential consisting of an initial biphasic potential and a subsequent mainly negative potential (N-wave) was recorded. The biphasic potential seems to represent action potentials of stria medullaris and the N-wave, excitation of postsynaptic MHN neurons. Nicotine suppressed the N-wave at 1-2 µM. Single neuron discharges were recorded spontaneously as well as in response to stria medullaris stimulation. Administration of nicotine at 1-2 µM increased the frequency of spontaneous firing. Similar excitatory action of carbamylcholine was observed at concentrations more than 12.5 µM in the presence of 10 µM atropine. D-tubocurarine (50 µM), hexamethonium (50 µM) and mecamylamine (20 µM) blocked the action of 2.5 µ M nicotine, whereas decamethonium (100 µM) was without effect. These results indicate that the nicotinic receptor in the MHN is akin to that of ganglion type.

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