GENERAL ANAESTHETIC MODIFICATION OF SYNAPTIC FACILITATION AND LONG-TERM POTENTIATION IN HIPPOCAMPUS

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Abstract
The synaptic integrative properties of facilitation and potentiation are important determinants of cortical neurone excitability. The present study measured the effects of halothane and methoxy-flurane on synaptic facilitation, paired-pulse potentiation, and long-term potentiation (LTP) in CA 1 pyramidal neurones of rat hippocampal slices. Methoxyflurane 0.16vol% and halothane 1.2 vol% depressed population spike amplitudes by approximately 100%, but halothane did so with relatively little (< 10%) depressant effect on the field excitatory postsynaptic potential (EPSP). Both agents enhanced EPSP facilitation, halothane more than methoxyflurane. Halothane consistently enhanced paired-pulse population spike potentiation; methoxyflurane sometimes diminished it. Halothane reduced the probability of LTP induction to an extent correlated with block of population spike responses in the inducing stimulus train (r = 0.92); methoxyflurane did not block LTP. The results suggest that these agents affect cortical excitability by multiple actions, the distribution of actions being specific to each agent.