前庭神経内側核ニューロン活動に対するｄｅｈｙｄｒｏｅｐｉａｎｄｒｏｓｔｅｒｏｎｅ ｓｕｌｆａｔｅの作用

Abstract

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.