Molluscan gonadotropin-releasing hormone

Abstract A peptide with structural features similar to those of chordate GnRHs was originally isolated from the central nervous system of the Japanese common octopus, Octopus vulgaris. It was named oct-GnRH, and was the first GnRH-related peptide in mollusks. Oct-GnRH has also been characterized from the central nervous systems of the common cuttlefish Sepia officinalis, and the swordchip squid Uroteuthis edulis. Oct-GnRH induces gonadal maturation and oviposition by regulating sex steroidogenesis and a series of egg-laying behaviors, as a key peptide in the octopus analog of the hypothalamo-hypophysial-gonadal axis. The localization of oct-GnRH mRNA expression and immunoreactive fibers in the brain, and the distribution of the oct-GnRH receptor in the brain and the peripheral tissues, suggest that oct-GnRH acts as a multifunctional modulatory factor in higher brain functions such as feeding behavior, the touch and visual memory system, cardiac control, arm movement, postural regulation, and sensory and autonomic functions. Molluscan GnRHs including the octopus, sea hare, and yesso scallop increase the Ca2 +-level but not cAMP production via their receptors.