Postnatal development of a new type of epileptiform activity in the rat hippocampus.
Long-term application of Cs(+) (5 mM) induces an epileptiform field potential (Cs-FP) in area CA1 of the rat hippocampus, which is independent of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors and gamma-aminobutyric acid (GABA)(A) receptors. To gain insight into possible mechanisms for the induction of the Cs-FP, we investigated the postnatal development of the response. In brain slices prepared from rats at different ages, the Cs-FP was evoked by stimulation of the Schaffer-collateral-commisural pathway. We found that expression of this potential was clearly dependent on the postnatal age. Thus, the Cs-FP was completely absent at 1 week of age. By 2 weeks, a reduced form of the response was observed, whereas slices taken from 3-week-old rats, displayed full Cs-FP, which were indistinguishable in size and shape from the adult form. In the presence of 4-aminopyridine, potentials resembling the Cs-FP were evoked. These potentials showed a similar age-dependency as the Cs-FP. The Na(+)/K(+) pump inhibitor dihydroouabain (DHO), when present during wash-in of Cs(+), gave a partial block of the Cs-FP in adult slices. This effect was not seen when DHO was applied after development of the Cs-FP. The data indicate that the processes necessary for expression of the Cs-PF are absent at birth and develop during the second postnatal week. We propose that the Cs-FP depends on Cs(+) entry into presynaptic neurons, and that the Na(+)/K(+) pump contributes to this transport of Cs(+). The observed age-dependency could therefore, in part, reflect the delayed development of the Na(+)/K(+) pump.
Skov
Jane
J
Institute of Physiology and Biophysics, Department of Physiology, University of Aarhus, Denmark.
Andreasen
Mogens
M
Nedergaard
Steen
S
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000375:Aging / Q000502:physiology; D000818:Animals; D002586:Cesium / Q000494:pharmacology; D004594:Electrophysiology; D004827:Epilepsy / Q000503:physiopathology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005110:Extracellular Space / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000254:growth & development* / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D026902:Potassium Channel Blockers; D017470:Receptors, Glutamate; D002586:Cesium; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D015761:4-Aminopyridine; D000254:Sodium-Potassium-Exchanging ATPase