Electrophysiological characterization of nicotinic acetylcholine receptors in cat petrosal ganglion neurons in culture: Effects of cytisine and its bromo derivatives

Laboratorio de Neurobiología, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Santiago, Chile.
Brain Research (Impact Factor: 2.84). 02/2006; 1072(1):72-8. DOI: 10.1016/j.brainres.2005.12.006
Source: PubMed


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 alpha4 and alpha7 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 alpha4 or alpha7 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 microM hexamethonium or 10 nM alpha-bungarotoxin. The order of potency of the agonists was 3-bromocytisine > acetylcholine approximately = cytisine > 5-bromocytisine, suggesting that homomeric alpha7 neuronal nicotinic receptors predominate in cat petrosal ganglion neurons in culture.

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Available from: Rodrigo Iturriaga
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    • "Agonist and antagonist sensibility indicate the presence of both α7 and α4β4 (Shirahata et al., 2000; Varas et al., 2006) or α4β2 nAChRs (Shirahata et al., 2000), in concordance with immunohistochemical evidence (Shirahata et al., 1998, 2000). "
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    ABSTRACT: The petrosal ganglion is a peripheral sensory ganglion, composed of pseudomonopolar sensory neurons that innervate the posterior third of the tongue and the carotid sinus and body. According to their electrical properties petrosal ganglion neurons can be ascribed to one of two categories: i) neurons with action potentials presenting an inflection (hump) on its repolarizing phase and ii) neurons with fast and brisk action potentials. Although there is some correlation between the electrophysiological properties and the sensory modality of the neurons in some species, no general pattern can be easily recognized. On the other hand, petrosal neurons projecting to the carotid body are activated by several transmitters, with acetylcholine and ATP being the most conspicuous in most species. Petrosal neurons are completely surrounded by a multi-cellular sheet of glial (satellite) cells that prevents the formation of chemical or electrical synapses between neurons. Thus, petrosal ganglion neurons are regarded as mere wires that communicate the periphery (i.e., carotid body) and the central nervous system. However, it has been shown that in other sensory ganglia satellite glial cells and their neighboring neurons can interact, partly by the release of chemical neuro-glio transmitters. This intercellular communication can potentially modulate the excitatory status of sensory neurons and thus the afferent discharge. In this mini review, we will briefly summarize the general properties of petrosal ganglion neurons and the current knowledge about the glial-neuron communication in sensory neurons and how this phenomenon could be important in the chemical sensory processing generated in the carotid body.
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    • "It is composed of lobules, separated by connective tissue, containing two different populations of cells: chief or type I cells, which are neuron-like cells and primary oxygen sensors in the CB, in turn separated into light, dark, and pyknotic (Verna, 1979; Pallot et al., 1986) and subtentacular or type II cells which have a supporting role (Porzionato et al., 2005; Pardal et al., 2007). Type I cells making synaptic contact with nerve terminal, mediate an increase in chemosensory discharges in the carotid sinus nerve in response to hypoxia, hypercapnia, and acidosis (Iturriaga and Alcayaga, 2004; Varas et al., 2006; Del Rio et al., 2011). Due to these particular functions, and its high blood flow and metabolism, the CB represents an experimental model suitable for studying hypoxia-related processes such as aging and intake of opiates like heroin (Di Giulio et al., 2003; Porzionato et al., 2005). "
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    • "However , the responses evoked by ACh in the rabbit presented little or no temporal desensitization, and the duration of the responses were dose-dependent. These differences suggest that the nicotinic receptors expressed by PG neurons (Varas et al., 2006) may differ between species. The application of a muscarinic cholinergic agonist to the rabbit PG in vitro had no effect on the basal ongoing activity, but reduced the responses evoked by further applications of ACh to the ganglion. "
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