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Auditory thalamus bursts in anesthetized and non-anesthetized states: contribution to functional properties.

Over the last 10 years, high-frequency bursts of action potentials have been the subject of intense researches to understand their potential role in information encoding. Based on recordings from auditory thalamus neurons (n = 302) collected during anesthesia (pentobarbital, urethan, or ketamine/xylazine), waking (W), and slow-wave sleep (SWS), we investigated how bursts participate to frequency tuning, intensity-function, response latency (and latency variability), and stimulus detectability. Although present in all experimental conditions, bursts never dominated the cells mode of discharge: the highest proportion was found during ketamine/xylazine anesthesia (22%), the lowest during waking (4.5%). In all experimental conditions, bursts preferentially occurred at or around the cells best frequency (BF), thus increasing the frequency selectivity. This effect was observed at both the intensities producing the highest and the lowest evoked responses. Testing the intensity-functions indicated that for most of the cells, there was no systematic relationship between burst proportion and responses strength. Under several conditions (W, SWS, and urethan), when cells exhibited bursts >20%, the variability of their response latency was reduced in burst mode compared with single-spike mode. During W, this effect was accompanied by a reduction of the response latency. Finally, a receiver operating characteristic analysis indicated no particular relation between bursts and stimulus detectability. Compared with single-spike mode, which is present for broader frequency ranges, the prominence of bursts at the BF should contribute to filter information reaching the targets of medial geniculate cells at both cortical and subcortical levels.

Acoustic Stimulation↗

[Poisoning caused by chronic exposure to volatile anesthetics. Molecular mechanisms and risk anesthetics].

The possible molecular mechanisms potentially inducing occupational disease among operating room personnel were examined; and the really dangerous anaesthetic agents were identified. As concerns the molecular mechanisms of parenchymatous injury, we surveyed: those connected with free radicals and biological reactive intermediates produced during halothane and nitrous oxide biotransformation; those coming from inorganic fluoride produced during biotransformation of any halogenated anaesthetic agent, and from inorganic bromide released during halothane metabolism; and, finally, those linked to vitamin B12 inactivation from nitrous oxide. Halothane and nitrous oxide can be considered as really dangerous anaesthetic agents for operating room personnel, and enflurane as an agent with marginal toxic power. On the contrary, isoflurane is a safe, useful compound, totally devoided of viscerotoxic effects. From data examined it is possible to conclude that an isoflurane-oxygen-air anaesthesia is safe for operating room personnel more than a balanced anaesthesia with intravenous drugs and nitrous oxide as maintenance.

Air Pollutants, Occupational↗