title: Regulation of extracellular potassium in the developing hippocampus.
abstract: It has long been felt that one of the reasons that the immature brain has an increased propensity to seize is due to an inability to regulate the extracellular potassium ([K+]o). However, the data supporting this hypothesis is controversial. Here, we tested the regulation of [K+]o in urethane-anesthetized juvenile and adult rats during and after synchronized epileptiform activity induced by 20 Hz stimulus trains to the CA3 region. The regulation of [K+]o in CA3 was compared to the same measurements in CA1. Across all age groups, there was no difference between CA1 and CA3. There was a slight decrease in the peak level of [K+]o reached during stimulation only in the youngest age groups tested (PN9-11). There was an age-dependent change in the rate of recovery of [K+]o from the elevated levels. This recovery was slowest in the PN9-11 age group. In all the animals in the PN9-11 group and 3/7 animals in the PN14-15 group, there was a secondary increase in the [K+]o during the afterdischarge. This secondary rise was never observed in animals over 15 days of age. These data confirm that there is altered regulation of [K+]o in the developing brain that takes two forms: (1) the ability to recover from elevated [K+]o levels, suggesting maturation of regulatory, or uptake, mechanisms; and (2) that which is related to mechanisms of synchronization and initiation of afterdischarges and the level of [K+]o that is produced during the discharge.
authors.affiliation: Department of Pharmacology and Division of Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. janets@bcm.tmc.edu
authors.forename: J L
authors.initials: JL
authors.lastname: Stringer
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation; D004622:Embryo, Mammalian; D005110:Extracellular Space / Q000502:physiology; D005865:Gestational Age; D006624:Hippocampus / Q000254:growth & development / Q000502:physiology*; D008564:Membrane Potentials; D009474:Neurons / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D011188:Potassium