title: Tetrodotoxin abruptly blocks excitatory neurotransmission in mammalian CNS.
abstract: The present study utilised a 'synaptic bouton' preparation of mechanically isolated rat hippocampal CA3 pyramidal neurons, which permits direct physiological and pharmacological quantitative analyses at the excitatory and inhibitory single synapse level. Evoked excitatory and inhibitory postsynaptic currents (eEPSCs and eIPSCs) were generated by focal paired-pulse electrical stimulation of single boutons. The sensitivity of eEPSC to tetrodotoxin (TTX) was higher than that of the voltage-dependent Na(+) channel whole-cell current (INa) in the postsynaptic CA3 soma membrane. The synaptic transmission was strongly inhibited by 3 nM TTX, at which concentration the INa was hardly suppressed. The IC50 values of eEPSC and INa for TTX were 2.8 and 37.9 nM, respectively, and complete inhibition was 3-10 nM for eEPSC and 1000 nM for INa. On the other hand, both eEPSC and eIPSC were equally and gradually inhibited by decreasing the external Na(+) concentration ([Na]o), which decreases the Na(+)gradient across the cell membrane. The results indicate that TTX at 3-10 nM could block most of voltage-dependent Na(+) channels on presynaptic nerve terminal, resulting in abruptly inhibition of action potential dependent excitatory neurotransmission.
authors.affiliation: Research Division for Clinical Pharmacology, Medical Corporation, Jyuryokai, Kumamoto Kinoh Hospital, 6-8-1 Yamamuro, Kitaku, Kumamoto, 860-8518, Japan; Research Division for Life Science, Kumamoto Health Science University, 325 Izumi-machi, Kitaku, Kumamoto, 861-5598, Japan.
authors.forename: Masahito
authors.initials: M
authors.lastname: Wakita
authors.affiliation: Research Division of Neurophysiology, Kitamoto Hospital, 3-7-6 Kawarasone, Koshigaya, 343-0821, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kotani
authors.affiliation: Research Division for Clinical Pharmacology, Medical Corporation, Jyuryokai, Kumamoto Kinoh Hospital, 6-8-1 Yamamuro, Kitaku, Kumamoto, 860-8518, Japan; Research Division for Life Science, Kumamoto Health Science University, 325 Izumi-machi, Kitaku, Kumamoto, 861-5598, Japan; Research Division of Neurophysiology, Kitamoto Hospital, 3-7-6 Kawarasone, Koshigaya, 343-0821, Japan. Electronic address: akaike@kumamoto-hsu.ac.jp.
authors.forename: Norio
authors.initials: N
authors.lastname: Akaike
mesh_terms: D000818:Animals; D002490:Central Nervous System / Q000187:drug effects* / Q000378:metabolism; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D020128:Inhibitory Concentration 50; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013779:Tetrodotoxin / Q000633:toxicity*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D015222:Sodium Channels; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid
keywords: External Na(+); Focal electrical stimulation; Neurotransmission; Tetrodotoxin; ‘Synaptic-bouton’ preparation