Ageing potentiates anaesthetic-induced synaptic depression in hippocampal slices

The effects of the volatile anaesthetic isoflurane on dendritic field excitatory postsynaptic potentials (fEPSP) were compared in hippocampal 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 concentration depressed field responses obtained from old hippocampal slices by 42 +/- 6.8% compared with baseline values. Such increased sensitivity to anaesthetic action in the old slices was consistently observed with administration of higher isoflurane concentrations. The presynaptic afferent volley was unaffected by application of low or high anaesthetic 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. Other synaptic sites are probably involved in the mechanisms of age-dependent potentiation of anaesthetic suppression of synaptic transmission.