NEUROPEPTIDERGIC CONTROL OF THE OPTIC GLAND OF OCTOPUS-VULGARIS - FMRFAMIDE AND GNRH IMMUNOREACTIVITY

In cephalopods, the endocrine optic glands on the optic tract control the maturation of the gonads. The glands are innervated by the optic g land nerve, which originates in the central nervous system. To explore the involvement of neuropeptides in the nervous control of the optic gland of Octopus vulgaris, the presence and distribution of Phe-Met-Ar g-Phe-NH2 (FMRF-amide)-like and gonadotropin releasing homone (GnRH)-l ike peptides were examined in the central nervous system and optic gla nd by immunohistochemistry. For GnRH immunodetection, antibodies again st four different forms of GnRH were used: cGnRH-I, cGnRH-II, sGnRH, a nd mGnRH. The optic gland nerve provides direct and indirect signals c oming from the centres integration of chemical, visual, and olfactive stimuli to modulate the glandular activity. In these centres, the subp edunculate area, the olfactory and optic lobes, and FMRF-amide-like an d GnRH-Like immunoreactivities were detected. The subpedunculate area seems to be the source of the FMRF-amide-like peptide, whereas the pos terior olfactory lobule is the source of the GnRH-like peptide. The im munoreactive fibres for both neuropeptides leave their sources and dir ectly enter the optic gland nerve. FMRF-amide- and GnRH-immunoreactive nerve endings are seen on the glandular cells. The evidence of a poss ible neuropeptidergic control of optic gland activity reinforces the a nalogies and the functional parallels in the octopus, insect, crustace an, and vertebrate hormonal systems. J. Comp. Neurol. 398:1-12, 1998. (C) 1998 Wiley-Liss, Inc.