Browsing by Author "Varas, R"

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    Dopamine modulates carotid nerve responses induced by acetylcholine on the cat petrosal ganglion in vitro
    (1999) Alcayaga, J; Varas, R; Arroyo, J; Iturriaga, R; Zapata, P
    We have recently reponed that application of acetylcholine (ACh) or nicotine to the petrosal ganglion-the sensory ganglion of the glossopharyngeal nerve-elicits a burst of discharges in the carotid nerve branch, innervating the carotid body and sinus, but not in the glossopharyngeal branch, innervating the tongue and pharynx, Thus, the perikarya of sensory neurons for the carotid bifurcation exhibit selective cholinosensitivity. Since dopamine (DA) modulates carotid nerve chemosensory activity, we searched for the presence of DA sensitivity at the perikarya of these neurons in the cat petrosal ganglion superfused in vitro. Applications of DA in doses of up to 5 mg to the ganglion did not modify the rate of spontaneous discharges in the carotid nerve, However, if DA was applied 30 s before ACh injections, ACh-evoked reactions were modified: low doses of DA enhanced the subsequent responses to ACh, while high doses of DA depressed the responses to ACh. This depressant effect of DA on ACh responses was partially antagonized by adding spiroperone to the superfusate. Our results show that the response to ACh of petrosal ganglion neurons projecting through the carotid nerve is modulated by DA acting on D-2 receptors located in the somata of these neurons. Thus, dopaminergic modulation of cholinosensitivity could be shared also by the membranes of peripheral endings and perikarya of primary sensory neurons involved in arterial chemoreception. (C) 1999 Elsevier Science B.V. All rights reserved.
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    Electrophysiological characterization of nicotinic acetylcholine receptors in cat petrosal ganglion neurons in culture
    (2006) Varas, R; Valdés, V; Iturriaga-Vásquez, P; Cassels, BK; Iturriaga, R; Alcayaga, J
    Petrosal ganglion neurons are depolarized and fire action potentials in response to acetylcholine and nicotine. However, little is known about the subtype(s) of nicotinic acetylcholine receptors involved, although alpha 4 and alpha 7 subunits have been identified in petrosal ganglion neurons. Cytisine, an alkaloid unrelated to nicotine, and its bromo derivatives are agonists exhibiting different affinities, potencies and efficacies at nicotinic acetylcholine receptors containing a4 or 0 subunits. To characterize the receptors involved, we studied the effects of these agonists and the nicotinic acetylcholine receptor antagonists hexamethonium and alpha-bungarotoxin in isolated petrosal ganglion neurons. Petrosal ganglia were excised from anesthetized cats and cultured for up to 16 days. Using patch-clamp technique, we recorded whole-cell currents evoked by 5-10 s applications of acetylcholine, cytisine or its bromo derivatives. Agonists and antagonists were applied by gravity from a pipette near the neuron surface. Neurons responded to acetylcholine, cytisine, 3-bromocytisine and 5-bromocytisine with fast inward currents that desensitized during application of the stimuli and were reversibly blocked by 1 mu M hexamethoniurn or 10 nM alpha-bungarotoxin. The order of potency of the agonists was 3-bromocytisine >> acetylcholine congruent to cytisine >> 5-bromocytisine, suggesting that homomeric alpha 7 neuronal nicotinic receptors predominate in cat petrosal ganglion neurons in culture. (c) 2005 Elsevier B.V. All rights reserved.