Intrinsic bursting of immature CA3 pyramidal neurons and consequent giant depolarizing potentials are driven by a persistent Na+ current and terminated by a slow Ca2+ -activated K+ current.
The CA3 area of the mature hippocampus is known for its ability to generate intermittent network activity both in physiological and in pathological conditions. We have recently shown that in the early postnatal period, the intrinsic bursting of interconnected CA3 pyramidal neurons generates network events, which were originally called giant depolarizing potentials (GDPs). The voltage-dependent burst activity of individual pyramidal neurons is promoted by the well-known depolarizing action of endogenous GABA on immature neurons. In the present work, we show that a persistent Na+ current, I-Nap, accounts for the slow regenerative depolarization that triggers the intrinsic bursts in the neonatal rat CA3 pyramidal neurons (postnatal day 3-6), while a slow Ca2+ -activated K+ current, sI-K(Ca), is primarily responsible for the postburst slow afterhyperpolarization and consequent burst termination. In addition, we exploited pharmacological data obtained from intracellular recordings to study the mechanisms involved in network events recorded with field potential recordings. The data as a whole indicate that I-Nap and sI-K(Ca) are involved in the initiation and termination, respectively, of the pyramidal bursts and consequent network events underlying GDPs.
Sipilä
Sampsa T
ST
Department of Biological and Environmental Sciences, University of Helsinki, FIN-00014 Helsinki, Finland. Sampsa.Sipila@Helsinki.Fi
Huttu
Kristiina
K
Voipio
Juha
J
Kaila
Kai
K
D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology* / Q000254:growth & development; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D019216:Metals, Heavy / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010672:Phenytoin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D019216:Metals, Heavy; D024681:Potassium Channels, Calcium-Activated; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D010672:Phenytoin; D011188:Potassium