Effects of micromolar and nanomolar calcium concentrations on non-synaptic bursting in the hippocampal slice.
To determine how [Ca2+]0 affects non-synaptic epileptogenesis in the CAI area of hippocampal slices, we compared the extracellularly recorded hyperactivity induced by ACSF containing either micromolar ('low-Ca2+, LC-ACSF) or nanomolar concentrations of Ca2+ ('zero-Ca2+, ZC-ACSF). Both solutions effectively blocked chemical synaptic transmission but spontaneous bursts developed more quickly and consistently in ZC-ACSF and were longer in duration and more frequent than those recorded in LC-ACSF Antidromically evoked bursts were less epileptiform, i.e., they exhibited fewer population spikes (PSs), in ZC-ACSF. Increasing [Mg2+]0 or decreasing [K+]0 suppressed spontaneous LC-ACSF bursting but only decreased the intensity and frequency of bursting in ZC-ACSF. Either manipulation increased the epileptiform nature of the antidromically evoked field potential, thereby mimicking the effect of increasing [Ca2+]0 from nanomolar to micromolar levels. Bath application of 250-500 microM GABA commonly arrested spontaneous bursting in LC-ACSF. In ZC-ACSF, GABA decreased the burst frequency but paradoxically superimposed high amplitude PSs on each burst. These effects were reversed by the GABAA receptor antagonists bicuculline methiodide or picrotoxin (50-100 microM). These results indicate that simply lowering [Ca2+]0 from micromolar to nanomolar concentrations increases the burst propensity and intensity of the CA1 population and can dramatically alter responses to pharmacological agents.
Watson
P L
PL
Department of Anatomy and Cell Biology, Faculty of Medicine, Queen's University, Kingston, Ont. Canada.
Andrew
R D
RD
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004827:Epilepsy / Q000503:physiopathology; D005071:Evoked Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008832:Microchemistry; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D005680:gamma-Aminobutyric Acid; D008274:Magnesium; D011188:Potassium; D002118:Calcium