Calcium influx through presynaptic 5-HT3 receptors facilitates GABA release in the hippocampus: in vitro slice and synaptosome studies.
Serotonin 5-hydroxytryptamine type 3 receptors (5HT3R) are Ca2+-permeant, non-selective cation channels that have been localized to presynaptic terminals and demonstrated to modulate neurotransmitter release. In the present study the effect of 5-HT on GABA release in the hippocampus was characterized using both electrophysiological and biochemical techniques. 5-HT elicited a burst-like, 6- to 10-fold increase in the frequency of GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) measured with whole-cell voltage-clamp recordings of CA1 neurons in hippocampal slices. When tetrodotoxin was used to block action potential propagation, the 5-HT-induced burst of IPSCs was still observed. Stimulation of hippocampal synaptosomes with 5-HT resulted in a significant increase in the amount of [3H]GABA released by hyperosmotic saline. In both preparations, the 5-HT effect was shown to be mediated by 5HT3Rs, as it was mimicked by the selective 5HT3R agonist m-chlorophenyl biguanide and blocked by the selective 5HT3R antagonist 3-tropanylindole-3-carboxylate hydrochloride. The 5HT3R-mediated increase in GABA release was blocked by 100 microM cadmium or by omitting Ca2+ in external solutions, indicating the Ca2+-dependence of the effect. The high voltage-activated Ca2+ channel blockers omega-conotoxin GVIA and omega-conotoxin MVIIC and 10 microM cadmium had no significant effect on the 5-HT3R-mediated enhancement of GABA release, indicating that Ca2+ influx through the 5-HT3R facilitates GABA release. Taken together, these data provide direct evidence that Ca2+ entry via presynaptic 5HT3Rs facilitates the release of GABA from hippocampal interneurons.
Turner
T J
TJ
Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
Mokler
D J
DJ
Luebke
J I
JI
D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000031:analogs & derivatives* / Q000494:pharmacology; D001645:Biguanides / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008564:Membrane Potentials; D009433:Neural Inhibition / Q000187:drug effects / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3 / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D058831:Serotonin 5-HT3 Receptor Antagonists; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D014316:Tritium / Q000378:metabolism; D000077526:Tropisetron; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D001645:Biguanides; D002121:Calcium Channel Blockers; D018756:GABA Antagonists; D007211:Indoles; D017661:Receptors, Presynaptic; D044406:Receptors, Serotonin, 5-HT3; D058831:Serotonin 5-HT3 Receptor Antagonists; D017366:Serotonin Receptor Agonists; D002104:Cadmium; D014316:Tritium; D012701:Serotonin; C017069:bicuculline methiodide; D005680:gamma-Aminobutyric Acid; D013395:Sucrose; D000077526:Tropisetron; C065734:1-(3-chlorophenyl)biguanide; D002118:Calcium; D001640:Bicuculline