Origin and propagation of spontaneous electrographic sharp waves in the invitro turtle brain: a model of neuronal synchronization

Objectives: Neuronal synchronization is a basic feature in the generation ( of epileptiform discharges. Spontaneous large sharp waves (LSWs) can be rec orded in the turtle brain in vitro, indicating the synchronous activation o f large neuronal populations. The aim of this study was to analyze the spat ial and temporal distribution of LSWs within the brain; the participation o f glutamate in LSWs generation was also investigated. Methods: Extracellular field potentials were recorded in vivo (n = 4) and i n vitro (n = 36). LSWs were recorded from cerebral cortex, optic tectum, an d thalamus. Results: LSWs were recorded from cerebral cortex, optic tectum and thalamus . No LSWs were observed in cerebellum and brain stem. In some experiments, LSWs could be recorded only from medial cortex. Latency studies demonstrate d that, within each hemisphere, medial cortex led the generation of LSWs; i n addition, isolated medial cortex could sustain LSWs. Intracortical lamina r field potentials in medial cortex indicated that LSWs generate mainly in the molecular layer, probably at pyramidal cell dendrites. Pharmacological experiments demonstrated that NMDA and non-NMDA glutamate receptors are inv olved in LWSs generation. Conclusions: These results suggest that turtle medial cortex is the pacemak er area for LSWs generation and it can be a useful model to study cellular and circuital mechanisms of neuronal synchronization. (C) 1999 Elsevier Sci ence Ireland Ltd. All rights reserved.