Expression and distribution of novel peptidehormones in memory and learning system of cephalopod brain

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An orphan receptor homologous to gonadotropin-releasing peptide (GnRH) was cloned from the brain of octopus (Octopus vulgaris). The receptor expressed in Xenopus oocyte caused Cl^--current by application of oct-GnRH, however, vertebrate GnRHs failed to trigger the current. Using this assay system, the octopus brain extract was fractionated by HPLC, then, the purified material was identified to oct-GnRH. Thus, the cloned receptor was deorphaned to be the oct-GnRH receptor (oct-GnRHR). Oct-GnRHR mRNA was widely expressed in the central and peripheral nervous system, the tissues such as buccal muscle, salivary gland, crop, rectum, aorta, heart, ovary, testis, etc. Oct-GnRH caused contractions of buccal muscle and exhibited the synthesis and release of sex steroids from the ovary and testis. These results suggested that oct-GnRH is a multifunctional peptide with important central roles in neurotransmission and neuromodulation in addition to the peripheral role as a hormone.The distribution of oct-GnRH in the brain was further studied. Oct-GnRH-immunoreactive neurons and fibers were distributed in the anterior subesophageal mass (movement of arms), posterior subesophageal mass (visceral movement and siphon movement), optic tract lobe and basal lobe (posture control), olfactory lobe, superior buccal lobe (higher center of taste and touch), inferior frontal lobe (higher center of touch), superior frontal lobe (higher center of vision), and vertical lobe (higher center of vision and touch). These higher centers are believed to be homologous to hippocampus and cerebral cortex. Octopressin, an octopus peptide in the oxytocin/vasopressin-superfamily, was also immunoreactive in the vertical lobe. It can be proposed that these peptides have important roles, including feeding, memory, learning, movement, and autonomic functions.