Guinea pig medial vestibular nucleus neurons in vitro respond to ACTH4-10 at picomolar concentrations.

The responses of single guinea pig medial vestibular nucleus (MVN) neurons in vitro to adrenocorticotropic hormone, fragment 4-10 (ACTH4-10) were recorded extracellularly. In coronal slices and in the isolated MVN, neurons were found which responded to ACTH4-10 at picomolar concentrations (10(-12)M), indicating that ACTH4-10 acts directly on MVN neurons and suggesting the possibility that ACTH4-10 may act as a neurotransmitter in the MVN. In most cases where neurons responded to ACTH4-10 (37/74 neurons), the effect was a decrease in firing. Whether or not the depressive action of ACTH4-10 on the firing rate of MVN neurons in vitro is related to the acceleration of behavioral recovery from unilateral labyrinthectomy (vestibular compensation), which has been reported previously (Flohr and Luneburg 1982; Igarashi et al. 1985), is unclear.