Effects of Dehydroepiandrosterone Sulfate on Neuronal Activity in the Medial Vestibular Nucleus.

To determine whether neurosteroids suggested to be present in the brain act on MVN neurons, we electrophysiologically examined the effects of dehydroepiandrosterone sulfate (DHEAS), a neurosteroid, on the neuronal activity of the medial vestibular nucleus (MVN) in cats anesthetized with α-chloralose. Single neuronal activity in the MVN was extracellularly recorded using a glass-insulated silver wire microelectrode attached to a seven-barreled micropipette. Each micropipette was filled with DHEAS (5 mM), γ-aminobutyric acid (GABA 1 M) or NaCl (5 mM). These chemicals were microiontophoretically applied to the immediate vicinity of the target neuron being recorded. The effects of these chemicals were examined on type I neurons, identified by responses to horizontal and sinusoidal rotations.Microiontophoretic application of DHEAS did not affect the spontaneous and rotation-induced firings, but reduced rotation-induced inhibition, which is known as commissural inhibition, in 8 of 15 type I neurons examined. Moreover, microiontophoretically-applied DHEAS in dose of 100 nA decreased GABA-induced inhibition on type I neurons. These findings suggests that DHEAS reduced the commissural inhibition to type I neurons by attenuation of GABA effects.