Gonadotropin-releasing hormones modulate electrical activity of vasotocin and isotocin neurons in the brain of rainbow trout

Gonadotropin-releasing hormone (GnRH) is widely distributed in the vertebrate brains; however, its significance in the brain function is poorly understood. Both GnRH and vasopressin-family hormones are involved in control of reproductive behavior. Anatomical evidence indicated the possible action of GnRH on classical neurosecretory neurons. In the present study, we examined whether GnRH modulates electrical activity of vasotocin (VT) and isotocin (IT) neurons in the brain of rainbow trout (Oncorhynchus mykiss). Two forms of GnRH, salmon GnRH and chicken GnRH 11, are present in the rainbow trout brain, and their fibers are localized in the close vicinity of VT and IT neurons. Applications of both GnRH forms elevated the frequency of cell-type-specific synchronous Ca2+ pulses in VT and IT neurons that are blocked by a GnRH-receptor antagonist. Our results showed facilitatory actions of GnRHs on VT and IT neurons, suggesting that GnRH neurons modulate classical neurosecretory neurons to control reproductive behavior. (C) 2003 Elsevier Ireland Ltd. All rights reserved.