title: Potassium-induced changes in excitability in the hippocampal CA1 region of immature and adult rats.
abstract: Orthodromic and spontaneous population spike activity was measured in vitro in the CA1 region of rat hippocampal slices to determine maturational differences in excitability and susceptibility to K(+)-induced seizures. Several indices of excitability in the CA1 region changed in a non-monotonic fashion during maturation, in response to step-wise increases in bath [K+]. Slices from rats 18-22 days old, showed a greater probability of both spontaneous epileptiform activity and episodes of seizure-like activity followed by spreading depression, and more prolonged durations of evoked seizure-like events. Elevation of [K+] in the bathing medium increased these indices in a similar manner in older rats but not to the same degree as in 18- to 22-day-old rats. However, the threshold level of bath [K+] resulting in evoked bursts of population spikes was lower in adult and 28- to 32-day-old rats than in 18- to 22-day-old rats, suggesting that excitability is not uniformly greater at any given age. In 10- to 15-day-old rats, elevation of bath [K+] either produced persistent blockade of population responses, or increased the amplitude of the initial population spike, without producing bursts. Basal levels of [K+] in the interstitium of the slices corresponded to the various levels of [K+] placed in the bathing medium and there were no differences among age groups. Therefore, differences in basal [K+]o cannot account for the maturational changes in excitability and seizure activity. The period from 18-22 days of age in the rat is a useful focal point for investigating mechanisms underlying maturational changes in propensity to develop seizures.
authors.affiliation: Department of Physiology, Tulane University School of Medicine, New Orleans, LA 70112-2699.
authors.forename: N R
authors.initials: NR
authors.lastname: Kreisman
authors.forename: M L
authors.initials: ML
authors.lastname: Smith
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects* / Q000254:growth & development; D066298:In Vitro Techniques; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012640:Seizures / Q000139:chemically induced*
chemical_list: D011188:Potassium