The effects of dopamine and serotonin on rat dorsal root ganglion neurons: an intracellular study.

The effects of bath application of dopamine and serotonin (10(-10)-10(-8) M) were studied in the superfused dorsal root ganglia of 30-36-day-old rats by means of the intracellular technique. In the majority of cells, dopamine and serotonin caused depolarization (60% and 64% of the tested cells, respectively). In other cells hyperpolarization, biphasic reactions or absence of responses have been observed. All reactions were dose dependent and reversible. Depolarization was accompanied by a decrease of input membrane resistance and hyperpolarization by its increase. Some cells did not show these alterations. Monoamines were also capable of modulating spikes. In some cases dopamine (10(-8)-10(-7) M) decreased the amplitude of the action potential and increased its duration, but the same concentration of serotonin produced the opposite effect on these parameters. The correlation between the electrophysiological properties of the dorsal root ganglion neurons and their responses to monoamines were discovered. Neurons with high input membrane resistance, prolonged action potential and slow conduction velocity (small cells) were influenced much more by monoamines than neurons with low input membrane resistance, "fast" action potential and rapid conduction velocity (large cells). (1) Small cells had lower threshold to monoamines (10(-8)-10(7) M) than large ones, some of which did not respond even to 10(-6) M. (2) The amplitude and duration of monoamine-induced depolarization in small cells were on average about two to three times higher than those in large cells. These data provide evidence for the modulatory role of monoamines in spinal afferent sensory functions.

Different action of ethosuximide on low- and high-threshold calcium currents in rat sensory neurons.

The effects of ethosuximide on calcium channels were studied on dorsal root ganglion neurons from one-day-old rats using the patch-clamp technique. Bath application of ethosuximide induced dose-dependent and reversible suppression of calcium currents without affecting their time-course. Substantial differences between the effects of ethosuximide on the low-threshold and high-threshold (T- and L-) currents were observed. Ethosuximide reduced the T-current with greater potency than the L-current (Kd for T-current is 7 microM vs 15 microM for L-current). This relative specificity of its action still remained if applied at concentrations up to 1 mM. These data support the hypothesis according to which the anti-epileptic action of ethosuximide is related to reduction of the low-threshold calcium currents in sensory neurons.

[The action of dopamine and serotonin on the cells of an isolated spinal cord ganglion of the rat]. / Deistvie dofamina i serotonina na kletki izolirovannogo spinno-mozgovogo gangliia krys.

The effect of bath application of dopamine (DA) and serotonin (HT) was studied in the isolated perfused dorsal root ganglia (DRG) of 30-36 days old rats by means of intracellular technique. 92% of investigated cells responded to the application of DA and 87%--to HT. DA and HT evoked depolarization in most of cells (64.6 and 73.7% of cells, respectively). Responses were dose-dependent and reversible. Depolarization caused by the DA and HT application was accompanied by a decrease in the input resistance (Rm) and alteration of the action potential shape. Hyperpolarization was followed by an increase of Rm. It was demonstrated that both DA and HT influenced predominantly DRG neurons with membrane biophysical characteristics inherent in small cells. Possibility of modulation of the afferent impulsation on the level of the primary sensory neurons is supposed.

[Effect of oxytocin on rat dorsal root ganglia in vitro]. / Vliianie oksitotsina na neirony spinno-mozgovogo gangliia krysy in vitro.

The influence of bath application of oxytocin (OT) was investigated on the isolated dorsal root ganglion (DRG) cells by means of intracellular recording. The results showed that OT evoked depolarization in most cells and affected predominantly the DRG neurons with biophysical+ characteristics inherent in small neurons.

[Effect of vasopressin on the somatic membrane of spinal ganglion neurons]. / Vliianie vazopressina na somaticheskuiu membranu neironov spinal'nykh gangliev.

The application of vasopressin (VP) in the isolated perfused dorsal root ganglia of 22-36 days old rats was studied by means of intracellular technique. 86.76% of cells have responded to the VP application. Depolarization was observed in 67.8% responded cells, the mixed response--in 16.95% cells, hyperpolarization--in 15.25% cells. All responses were dose-dependent and reversible. Input resistance (Rm) of the cell membrane decreased during depolarization and increased during hyperpolarization. The VP-evoked depolarization was accompanied by an increase in the action potential (AP) duration and decrease in the AP amplitude and after-hyperpolarization. Neurons with slow conduction velocity, high Rm and prolonged AP (small cells) had the lowest threshold of the sensitivity to VP (1.10(-11) M) and prolonged high-amplitude responses. Cells with the rapid conduction velocity, low Rm and rapid AP (large cells) responded to 1.10(-8) M, but sometimes even 1.10(-6) M had no effect. Depolarization in these neurons had smaller duration and low amplitude: sometimes hyperpolarization was observed. These results confirm the possibility that VP has effect on small neurons predominantly.