ALTERATION OF HIPPOCAMPAL EXCITABILITY AFTER HYPERTHERMIA-INDUCED SEIZURES IN INFANT RATS
Abstract number :
1.041
Submission category :
Year :
2004
Submission ID :
4142
Source :
www.aesnet.org
Presentation date :
12/2/2004 12:00:00 AM
Published date :
Dec 1, 2004, 06:00 AM
Authors :
Min-Lan Tsai, and L. Stan Leung
Febrile seizures are the most common seizure type in children between 3 months and 6 years old. It is unclear whether febrile seizures are detrimental to the developing or adult brain. The main goal of this research is to investigate changes in synaptic transmission and excitability in the hippocamus following febrile seizures. We hypothesized that neuronal inhibition in hippocampus is altered following a hyperthermia-induced seizure in immature rats. Febrile seizures were induced by hyperthermia given by a heat lamp in rats of postnatal day 15, and control rats were separated from the dam but not heated. Eleven or 30 days following the hyperthermia-induced seizure, extracellular synaptic responses in the hippocampus were assessed in urethane-anesthetized rats. Laminar field potentials were recorded by 16-channel silicon probes in CA1 and dentate gyrus (DG), in response to the paired-pulse stimulation of CA3 and medial perforant path. Current source density analysis revealed population excitatory postsynaptic potentials (pEPSPs) at the dendrites and population spikes (PS) at the cell layer. The ratio of the 2nd PS (P2) to the 1st PS (P1), and of the 2nd pEPSP slope (E2) to 1st pEPSP slope (E1), were analyzed. The ratios of P2/P1 and E2/E1 were decreased with age in CA1 and DG, for both control and seizure rats. When recorded at 11 days but not 30 days after seizures, P2/P1 ratio was increased in CA1, at 150 to 200 ms IPIs, as compared to control rats (P[lt]0.01, ANOVA following posthoc Newman-Keuls test). P1 was not significantly different between seizure and control rats. E2/E1 ratio in CA1, and P2/P1 (or E2/E1) in DG were not different between seizure and control rats at any time after seizures. Paired-pulse inhibition in CA1 was decreased for about 10 days after a single hyperthermia seizure in immature rats, suggesting a short-term alteration of GABAergic inhibition that normalized with time after the seizure or with age. Alteration of paired-pulse inhibition at 150 to 200 ms suggests a difference in GABA[sub]B[/sub] receptor mediated inhibition. (Supported by CIHR MOP-64433)