The effect of two anesthetic agents on norepinephrine and dopamine in discrete brain nuclei, fiber tracts, and terminal regions of the rat.
Catecholaminergic neurons have been implicated in the mechanism of general anesthesia, but previous attempts at measuring changes in adrenergic neuron function during anesthesia have been limited by techniques to whole brain. Microdissection techniques and sensitive radioisotopic-enzymatic assays were used to measure levels of catecholamines in 20 different nuclei, fiber tracts or nerve terminal regions in brains of rats anesthetized for 90-105 min with 1% halothane or 18% cyclopropane. These two anesthetics were chosen because of their diverse effects on the electroencephalogram and on the cardiovascular and respiratory systems. Of the areas examined, significant increases in norepinephrine content with both anesthetic agents were found only in the nucleus accumbens, locus coeruleus and central gray catecholamine areas. Only in the nucleus accumbens was the dopamine level increased by both anesthetics; cyclopropane, but not halothane anesthesia, also increased the dopamine content of the caudate nucleus, while halothane, but not cyclopropane anesthesia, significantly decreased the dopamine level of the ventral nucleus of the thalamus. Changes in levels of transmitters do not distinguish cause from effect of anesthesia, and further experiments are needed to delineate what role, if any, the specific areas play in muscle relaxation, analgesia, sleep or anesthesia. This study shows that a drug can affect one nucleus or region without significantly affecting other regions that contain the same transmitter substance, and that changes in transmitter levels can occur selectively in different regions of brain even if the nerve endings are derived from contiguous cell bodies.
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002421:Caudate Nucleus / Q000187:drug effects; D002552:Cerebral Ventricles / Q000187:drug effects; D003521:Cyclopropanes / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D013787:Thalamic Nuclei / Q000187:drug effects
D003521:Cyclopropanes; D006221:Halothane; D004298:Dopamine; D009638:Norepinephrine