It was established, in experiments on isolated spinal ganglia of adult rats in conditions of intracellular recording, that dopamine (1 microM/liter) elicits depolarized responses in 61% of neurons, hyperpolarized in 20% of neurons, and depolarized-hyperpolarized in 19% of neurons. The depolarized responses are associated with the activation of D1 dopamine receptors, and are governed by the shift of cAMP-dependent cation (sodium) channels to the conducting state. The hyperpolarized responses are triggered by the activation of D2 dopamine receptors, which by means of HTP-binding protein convert the potassium channels to the conducting state. The change in the polarization of neurons with the action of dopamine influences their electrical excitability variously.

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Electrophysiological and biochemical experiments on slices of the rat dorsal hippocampus demonstrated that dexamethasone (100 nM) augmented and prolonged the depressive effect of noradrenaline on synaptic transmission in the СА1 zone; this effect is related to weakening of the uptake of noradrenaline by neurons. The effect of dexamethasone is mediated by glucocorticoid receptors. Inhibitors of presynaptic translocase of noradrenaline, cocaine and imipramine, increased, similarly to dexamethasone, the effects of noradrenaline; an additive synergism was observed upon combined applications of dexamethasone and cocaine. The effect of dexamethasone decreased with an increase in the extracellular concentration of glucose, but increased upon application of the Nа/K-ATPase inhibitor strophantin. The potentiating influence of dexamethasone on the effects of noradrenaline was weaker in slices obtained from rats with behavioral depression induced by social isolation or chronic introduction of dexamethasone. We hypothesize that glucocorticoids stabilize noradrenergic neurotransmission in the brain under the action of stressogenic influences. The role of glucocorticoid mechanisms in the development of depression is discussed.

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