Depression of glutamate and GABA release by presynaptic GABAB receptors in the entorhinal cortex in normal and chronically epileptic rats.
Presynaptic GABA(B) receptors (GABA(B)R) control glutamate and GABA release at many synapses in the nervous system. In the present study we used whole-cell patch-clamp recordings of spontaneous excitatory and inhibitory synaptic currents in the presence of TTX to monitor glutamate and GABA release from synapses in layer II and V of the rat entorhinal cortex (EC)in vitro. In both layers the release of both transmitters was reduced by application of GABA(B)R agonists. Quantitatively, the depression of GABA release in layer II and layer V, and of glutamate release in layer V was similar, but glutamate release in layer II was depressed to a greater extent. The data suggest that the same GABA(B)R may be present on both GABA and glutamate terminals in the EC, but that the heteroreceptor may show a greater level of expression in layer II. Studies with GABA(B)R antagonists suggested that neither the auto- nor the heteroreceptor was consistently tonically activated by ambient GABA in the presence of TTX. Studies in EC slices from rats made chronically epileptic using a pilocarpine model of temporal lobe epilepsy revealed a reduced effectiveness of both auto- and heteroreceptor function in both layers. This could suggest that enhanced glutamate and GABA release in the EC may be associated with the development of the epileptic condition.
Thompson
Sarah E
SE
Department of Pharmacy and Pharmacology, University of Bath, Bath, UK.
Ayman
Goher
G
Woodhall
Gavin L
GL
Jones
Roland S G
RS
D000818:Animals; D017660:Autoreceptors / Q000187:drug effects / Q000378:metabolism; D002908:Chronic Disease; D003292:Convulsants / Q000494:pharmacology; D004195:Disease Models, Animal; D018728:Entorhinal Cortex / Q000378:metabolism* / Q000503:physiopathology; D004833:Epilepsy, Temporal Lobe / Q000378:metabolism* / Q000503:physiopathology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018755:GABA Agonists / Q000494:pharmacology; D058786:GABA-B Receptor Agonists; D018698:Glutamic Acid / Q000378:metabolism*; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D036881:Long-Term Synaptic Depression / Q000502:physiology; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018080:Receptors, GABA-B / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D009435:Synaptic Transmission / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D017660:Autoreceptors; D003292:Convulsants; D018755:GABA Agonists; D058786:GABA-B Receptor Agonists; D018080:Receptors, GABA-B; D026941:Sodium Channel Blockers; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid