The Effects of General Anesthetics on Norepinephrine Release from Isolated Rat Cortical Nerve Terminals


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Abstract

Intravenous and volatile general anesthetics inhibit norepinephrine (NE) release from sympathetic neurons and other neurosecretory cells. However, the actions of general anesthetics on NE release from central nervous system (CNS) neurons are unclear. We investigated the effects of representative IV and volatile anesthetics on [3H]NE release from isolated rat cortical nerve terminals (synaptosomes). Purified synaptosomes prepared from rat cerebral cortex were preloaded with [3H]NE and superfused with buffer containing pargyline (a monoamine oxidase inhibitor) and ascorbic acid (an antioxidant). Basal (spontaneous) and stimulus-evoked [3H]NE release was evaluated in the superfusate in the absence or presence of various anesthetics. Depolarization with increased concentrations of KCl (15–20 mM) or 4-aminopyridine (0.5–1.0 mM) evoked concentration- and Ca2+-dependent increases in [3H]NE release from rat cortical synaptosomes. The IV anesthetics etomidate (5–40 μM), ketamine (5–30 μM), or pentobarbital (25–100 μM) did not affect basal or stimulus-evoked [3H]NE release. Propofol (5–40 μM) increased basal [3H]NE release and, at larger concentrations, reduced stimulus-evoked release. The volatile anesthetic halothane (0.15–0.70 mM) increased basal [3H]NE release, but did not affect stimulus-evoked release. These findings demonstrate drug-specific stimulation of basal NE release. Noradrenergic transmission may represent a presynaptic target for selected general anesthetics in the CNS. Given the contrasting effects of general anesthetics on the release of other CNS transmitters, the presynaptic actions of general anesthetics are both drug- and transmitter-specific.

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