title: Threshold extracellular concentration distribution of penicillin for generation of epileptic focus measured by diffusion analysis.
abstract: The tissue volume required to produce a penicillin-induced interictal discharge in the local EEG was estimated. A pair of microelectrodes were lowered into the motor cortex of anaesthetised and artificially ventilated rats. One double-barrelled electrode was used to release tetramethylammonium (TMA+) by iontophoresis or to pressure eject a solution containing penicillin (PEN-) and TMA+ concentration. The extracellular distribution of PEN- was defined using diffusion analysis of the TMA+. From these data the spatial distribution of PEN- was estimated at the times of first interictal spikes in the EEG. The critical mass of active nerve cells was calculated from the threshold concentration of PEN- needed to elicit paroxysmal depolarisation shifts in neocortical slices and found to lie within a tissue sphere with a radius of ca. 150 microns.
authors.affiliation: Institut für Physiologie, Westfälische-Wilhelms-Universität Münster, F.R.G.
authors.forename: A
authors.initials: A
authors.lastname: Lehmenkühler
authors.forename: C
authors.initials: C
authors.lastname: Nicholson
authors.forename: E J
authors.initials: EJ
authors.lastname: Speckmann
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism / Q000503:physiopathology*; D004058:Diffusion; D004569:Electroencephalography / Q000187:drug effects; D004827:Epilepsy / Q000139:chemically induced / Q000503:physiopathology*; D005071:Evoked Potentials / Q000187:drug effects; D007478:Iontophoresis; D008297:Male; D009044:Motor Cortex / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D010406:Penicillins / Q000493:pharmacokinetics* / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010406:Penicillins; D000644:Quaternary Ammonium Compounds; C027917:tetramethylammonium