Electrophysiological characterization of 5-HT receptors on rat petrosal neurons in dissociated cell culture

• Published in: Brain research Vol. 816; no. 2; pp. 544 - 553
• Main Authors: Zhong, Huijun, Zhang, Min, Nurse, Colin A
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 23.01.1999; Amsterdam Elsevier; New York, NY
• Subjects: 5-HT 3 receptors; Animals; Biological and medical sciences; Cells, Cultured; Chemosensory neurons; Coculture Techniques; Electric Conductivity; Fundamental and applied biological sciences. Psychology; Ganglia - cytology; Ganglia - physiology; Isolated neuron and nerve. Neuroglia; Kinetics; Ligand-gated channels; Membrane Potentials - physiology; Neurons, Afferent - physiology; Patch clamp; Patch-Clamp Techniques; Rats; Receptors, Serotonin - physiology; Vertebrates: nervous system and sense organs; Patch clamp; Ligand-gated channels; Chemosensory neurons; 5-HT 3 receptors; Characterization; Vertebrata; Mammalia; Neuron; Rat; Rodentia; Electrophysiology; Patch clamp method; Petrous ganglion; Serotonine receptor; In vitro
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(98)01232-3

The petrosal ganglion supplies chemoafferent pathways via the glossopharyngeal (IXth) nerve to peripheral targets which release various neurotransmitters including serotonin (5-HT). Here, we combined rapid 5-HT application with patch clamp, whole-cell recording to investigate whether 5-HT receptors are expressed on isolated petrosal neurons (PN), cultured from 7–12 day-old rat pups. In responsive cells, the dominant effect of 5-HT was a rapid depolarization associated with a conductance increase in ∼43% of the neurons (53/123); however, in a minority population (∼6%; 8/123), 5-HT caused membrane depolarization associated with a conductance decrease. In the former group, 5-HT produced a transient inward current ( I 5-HT) in neurons voltage-clamped near the resting potential (∼-60 mV); the effect was mimicked by the 5-HT 3 receptor-specific agonist, 2-methyl-5-HT, suggesting it was mediated by 5-HT 3 receptors. Further, I 5-HT was selectively inhibited by the 5-HT 3 receptor-specific antagonist MDL72222 (1–10 μM), but was unaffected by either 5-HT 1/5-HT 2 receptor antagonist, spiperone, or by 5-HT 2 receptor-specific antagonist, ketanserin (50–100 μM). I 5-HT displayed moderate inward rectification and had a mean reversal potential (±S.E.M.) of −4.3±6.6 mV ( n=6). Application of 5-HT (dose range: 0.1–100 μM) produced a dose–response curve that was fitted by the Hill equation with EC 50=∼3.4 μM and Hill coefficient=∼1.6 ( n=8). The activation phase of I 5-HT (10 μM 5-HT at −60 mV) was well fitted by a single exponential with mean (±S.E.M.) time constant of 45±30 ms ( n=6). The desensitization phase of I 5-HT was best fitted by a single exponential with mean (±S.E.M.) time constant of 660±167 ms ( n=6). Fluctuation analysis yielded an apparent mean single-channel conductance (±S.E.M) of 2.7±1.5 pS ( n=4) at −60 mV. In the minority (∼6%) population of neurons which responded to 5-HT with a conductance decrease, the depolarization was blocked by the 5-HT 2 receptor antagonist, ketanserin (50 μM). Taken together, these results suggest that 5-HT 3 receptors are the major subtype expressed by rat petrosal neurons, and therefore are candidates for facilitating chemoafferent excitation in response to 5-HT released from peripheral targets.