A distinct distribution of functional presynaptic 5-HT receptor subtypes on GABAergic nerve terminals projecting to single hippocampal CA1 pyramidal neurons.
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.
Katsurabayashi
S
S
Cellular and System Physiology, Graduate School of Medical Sciences, Kyushu University, 812-8582, Fukuoka, Japan.
Kubota
H
H
Tokutomi
N
N
Akaike
N
N
D000818:Animals; D005071:Evoked Potentials; D006624:Hippocampus / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D066298:In Vitro Techniques; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism / Q000502:physiology*; D017966:Pyramidal Cells / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017661:Receptors, Presynaptic / Q000378:metabolism / Q000502:physiology*; D011985:Receptors, Serotonin / Q000378:metabolism / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D044406:Receptors, Serotonin, 5-HT3; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D017661:Receptors, Presynaptic; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D044406:Receptors, Serotonin, 5-HT3; D005680:gamma-Aminobutyric Acid