AGING POTENTIATES ANESTHETIC-INDUCED SYNAPTIC DEPRESSION IN HIPPOCAMPAL SLICES

THE effects of the volatile anaesthetic isoflurane on dendritic field excitatory postsynaptic potentials (fEPSP) were compared in hippocampa l slices taken from young mature and old Fisher 344 rats. Application of isoflurane (1% v/v) to young brain slices produced minimal effects on the recorded fEPSPs. On the contrary, the same anaesthetic concentr ation depressed field responses obtained from old hippocampal slices b y 42 +/- 6.8% compared with baseline values. Such increased sensitivit y to anaesthetic action in the old slices was consistently observed wi th administration of higher isoflurane concentrations. The presynaptic afferent volley was unaffected by application of low or high anaesthe tic concentration, suggesting that age-induced changes in nerve fibre conduction and probably nerve ending excitability are not involved in the increased vulnerability of old synapses to anaesthetic action. Oth er synaptic sites are probably involved in the mechanisms of age-depen dent potentiation of anaesthetic suppression of synaptic transmission.