Evidence for a relationship between recovery from anaesthesia, modified state of consciousness and striatal voltammetric levels of ascorbic acid.

The effects of various procedures which modify consciousness were studied on the extracellular concentration of ascorbic acid (AA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5HIAA) in rat striatum, as measured by differential pulse voltammetry (DPV) with electrically pretreated carbon fibre micro-electrodes (CFE). Recovery from anaesthesia (produced by 500 mg/kg i.p. chloral hydrate) was accompanied by a six-fold increase in extracellular striatal AA levels, while negligible changes in DOPAC and 5HIAA occurred. Following complete recovery from anaesthesia, the animals were re-injected with the same dose of anaesthetic which specifically reduced AA levels by 90% (DOPAC levels were unchanged and 5HIAA concentrations slightly reduced). In conscious rats, the neuroleptic haloperidol (1 mg/kg i.p., n = 5) and the minor tranquillizer diazepam (10 mg/kg i.p., n = 5), both considered as behaviourally depressant drugs, reduced extracellular AA levels to 50% of controls. The psychomotor stimulant D-amphetamine (1 mg/kg i.p., n = 5) increased AA levels by 90% over controls. Stress activation of animals (handling for 10 min, n = 10) also produced a transient, significant increase (180% of control values) in this striatal parameter. Taken together with previous reports, our results suggest a close relationship between the state of consciousness and extracellular AA levels in the rat striatum and that this relationship appears to be more correlated to AA as no such clear interdependence was noted between the levels of consciousness and extracellular striatal DOPAC or 5HIAA.