PubMed · 3140566
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J F Nunn. 1988. Ventilation-perfusion mismatching.. https://pubmed.ncbi.nlm.nih.gov/3140566/
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Homosynaptic long-term depression (LTD) is reported to occur in field CA1 of hippocampal slices collected from immature brains. Because the effect has been postulated to be a memory storage mechanism, it is of interest to test for its presence in adult, awake animals. Unfortunately, not only has hippocampal LTD proved difficult to obtain reliably in vivo, but the few successful studies vary with respect to protocols and evidence that the depression is input-specific. The present study tested for input-specific (homosynaptic) LTD in field CA1 after application of various stimulation protocols to the Schaffer collateral/commissural projections in freely moving, adult rats. The results indicate that although low-frequency trains do induce decrements in synaptic transmission lasting for hours to several days, the success rate of eliciting input-specific LTD in the awake rat is very modest compared with the ease with which stable potentiation is obtained in the same synapses. Moreover, it is questionable that the effective protocols represent patterns of activity likely to occur during behavior. The stronger the afferent activation during low-frequency stimulation, the greater was the probability of eliciting LTD accompanied by persistent heterosynaptic depression. Clear evidence for the occurrence of LTD, irrespective of stimulation protocol and current intensity, could not be obtained in rats under barbiturate anesthesia. In all, the results do not accord with the suggestion that LTD occurs routinely in the hippocampus in vivo as part of memory encoding.
Awareness is a traumatic unintentional event during general anaesthesia. Awareness during anaesthesia is a condition which ranges from a state of alertness to deep anaesthesia with partly preserved senses. Awareness can be divided into four groups, depending on the state of alertness and accessibility of the memories after anaesthesia. Diagnostics and follow-up is complicated when awareness with an impaired recall occurs. We conclude that the incidence of awareness has decreased during the last three decades from approximately 1.5% to 0.2% during general surgery. In clinical practice there is no method for the detection of depth of anaesthesia and no anaesthetic technique that prevents awareness during anaesthesia. Guidelines to further reduce the incidence are suggested. Instant treatment of the condition may relieve the acute trauma and reduce the sequelae. We suggest a postoperative visit to ensure quality development for recording and treatment of awareness during anaesthesia.
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