Depression of early and late monosynaptic inhibitory postsynaptic potentials in hippocampal CA1 neurons following prolonged benzodiazepine administration: Role of a reduction in Cl driving force
✍ Scribed by Xu Zeng; Elizabeth I. Tietz
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 120 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0887-4476
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✦ Synopsis
GABAergic synaptic responses were studied by direct, monosynaptic activation of GABAergic interneurons in the CA1 region of in vitro hippocampal slices from rats made tolerant to the benzodiazepine, flurazepam. Monosynaptic IPSPs were elicited in CA1 pyramidal neurons, following 1 week oral flurazepam administration, by electrical stimulation at the stratum oriens/stratum pyramidale or stratum radiatum/ stratum-lacanosum border # 0.5 mm from the recording electrode plane. Excitatory input to pyramidal cells and interneurons was eliminated by prior superfusion of the glutamate receptor antagonists, APV (50 µM) and DNQX (10 µM). GABA A receptormediated early IPSPs were further isolated by perfusion of the GABA B antagonist, CGP 35348 (25 µM) or by diffusion of Cs 1 from the recording electrode. GABA B receptormediated late IPSPs were pharmacologically isolated by perfusion of the GABA A antagonist, picrotoxin (50 µM). There was a significant decrease in the amplitude of pharmacologically isolated early and late IPSPs in FZP-treated neurons without a change in passive membrane properties. A shift of the early IPSP, but not the late IPSP, reversal potential in FZP-treated neurons suggested that a change in the driving force for anions, presumably Cl 2 , in CA1 neurons was one important factor related to the decreased early IPSP amplitude after prolonged activation of GABA A receptors by flurazepam. A decreased early IPSP amplitude accompanied by a decreased late IPSP amplitude suggested that presynaptic GABA release onto FZP-treated pyramidal cells may also be reduced. We conclude from these data that an impairment of GABAergic transmission in CA1 pyramidal neurons associated with the development of tolerance during chronic benzodiazepine treatment may be related to the regulation of both preand postsynaptic mechanisms at the GABA synapse.