[Effect of monoamines on motoneurons of isolated rat spinal cord]

Superfusion of isolated hemisected spinal cord of 9-13 day old rats by solution containing noradrenaline induced de- or hyperpolarization of motoneurons depending on amine concentrations. Both effects resulted from a direct influence of amine upon motoneurons since they remained in the medium with abundance of Mg++ions and deficit of Ca++ions. Depolarization and hyperpolarization of motoneurons induced by noradrenaline was depressed by alpha-adrenoblockators. Depolarization of motoneurons induced by dopamine was suppressed in medium with abundance of Mg++ions. Hyperpolarization of motoneurons induced by dopamine was suppressed by haloperidol but remained unchanged under phentolamine. Depolarization of motoneurons induced by serotonin and its metabolities-mexamine, kynurenine and 3-oxyanthranilic acid-remained in the medium with abundance of Mg++ions and deficit of Ca++ions and was depressed by deseril and BAS. Hyperpolarization effect of serotonin appearing in some experiments under high concentration of serotonin (10(-4)-10(-3) M) was suppressed in medium with abundance of Mg++ions and in the presence of morphine.