Effects of the neurosteroid dehydroepiandrosterone sulfate on medial vestibular nucleus neurons.

Neurosteroids increase in concentration under conditions of stress and produce behavioral effects. An electrophysiological investigation was undertaken to determine whether dehydroepiandrosterone sulfate (DHEAS), a neurosteroid, influences the neuronal activity of medial vestibular nucleus (MVN) neurons in alpha-chloralose-anesthetized cats. Single neuronal activities in MVN were recorded extracellularly using a glass-insulated silver wire microelectrode attached along a seven-barreled micropipette. Each pipette was filled with DHEAS, GABA, muscimol (a GABA[A] receptor agonist) and baclofen (a GABA[B] receptor agonist), which were applied microiontophoretically to the immediate vicinity of the target neurons. 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 of type I neurons, but dose-dependently blocked GABA-induced inhibitory effects on type I neurons. In addition, both muscimol- and baclofen-induced inhibitions of firing were blocked by DHEAS. These results suggest that DHEAS suppresses GABAergic inhibitory effects on MVN neurons through both GABA(A) and GABA(B) receptors, presumably resulting in disturbance of control of neuronal activity in the vestibular nucleus and consequent development of vertigo.