A distinct distribution of functional presynaptic 5-HT receptor subtypes on GABAergic nerve terminals projecting to single hippocampal CA1 pyramidal neurons

• Published in: Neuropharmacology Vol. 44; no. 8; pp. 1022 - 1030
• Main Authors: Katsurabayashi, S., Kubota, H., Tokutomi, N., Akaike, N.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2003; Elsevier
• Subjects: 5-HT 1A, 5-HT 3; Animals; Biological and medical sciences; Evoked Potentials; Focal stimulation; GABA release; gamma-Aminobutyric Acid - metabolism; Hippocampus - metabolism; Hippocampus - physiology; Hippocampus - ultrastructure; In Vitro Techniques; Medical sciences; Patch-Clamp Techniques; Presynaptic Terminals - metabolism; Presynaptic Terminals - physiology; Pyramidal Cells - metabolism; Pyramidal Cells - physiology; Rats; Rats, Wistar; Receptors, Presynaptic - metabolism; Receptors, Presynaptic - physiology; Receptors, Serotonin - metabolism; Receptors, Serotonin - physiology; Receptors, Serotonin, 5-HT1; Receptors, Serotonin, 5-HT3; Single bouton; Synaptic modulation; Focal stimulation; Synaptic modulation; GABA release; 5-HT 1A, 5-HT 3; Single bouton; 5-HT3; GABA release; Single bouton; Focal stimulation; Synaptic modulation; 5-HT1A
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/S0028-3908(03)00103-5

5-HT is known to modify the excitability of GABAergic interneurons projecting to hippocampal CA1 neurons. In this study we investigate the presence and functionally characterize the 5-HT receptor subtypes found on the presynaptic nerve terminals of these GABAergic neurons. Using conventional whole-cell patch recording, we confirmed that the 5-HT 1A agonist, 8-hydroxy-2-dipropylaminotetralin, presynaptically decreased electrically evoked GABA release while the 5-HT 3 agonist, m-chlorophenylbiguanide ( mCPBG), presynaptically facilitated release. Using the ‘synaptic bouton preparation’, where CA1 neurons are acutely isolated with functional nerve terminals/boutons remaining adherent, we next showed that these receptor subtypes are found presynaptically. We next used the technique of focal stimulation of a single bouton in this preparation to further investigate the distribution of these 5-HT receptor subtypes. We found that all boutons contained inhibitory 5-HT 1A receptors while a subset of boutons showed both 5-HT 1A and excitatory 5-HT 3 receptors. No boutons were detected which contained only 5-HT 3 receptors. Our studies show that presynaptic 5-HT receptor subtypes are found presynaptically and are not uniformly distributed. This provides another potential mechanism whereby 5-HT can modulate GABA release and hence the excitability of hippocampal neurons.