Neuropeptidergic control of the optic gland ofOctopus vulgaris: FMRF-amide and GnRH immunoreactivity

Abstract

In cephalopods, the endocrine optic glands on the optic tract control the maturation of the gonads. The glands are innervated by the optic gland 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-Arg-Phe-NH2 (FMRF-amide)-like and gonadotropin releasing homone (GnRH)-like peptides were examined in the central nervous system and optic gland by immunohistochemistry. For GnRH immunodetection, antibodies against four different forms of GnRH were used: cGnRH-I, cGnRH-II, sGnRH, and mGnRH. The optic gland nerve provides direct and indirect signals coming from the centres of integration of chemical, visual, and olfactive stimuli to modulate the glandular activity. In these centres, the subpedunculate area, the olfactory and optic lobes, and FMRF-amide-like and GnRH-like immunoreactivities were detected. The subpedunculate area seems to be the source of the FMRF-amide-like peptide, whereas the posterior olfactory lobule is the source of the GnRH-like peptide. The immunoreactive fibres for both neuropeptides leave their sources and directly enter the optic gland nerve. FMRF-amide- and GnRH-immunoreactive nerve endings are seen on the glandular cells. The evidence of a possible neuropeptidergic control of optic gland activity reinforces the analogies and the functional parallels in the octopus, insect, crustacean, and vertebrate hormonal systems.

First visualization of cholinergic cells and fibers by immunohistochemistry for choline acetyltransferase of the common type in the optic lobe and peduncle complex of Octopus vulgaris

“…Our findings extend current knowledge on the optic gland as an endocrine organ involved in the sexual maturation and reproduction (Young, 1971;Di Cosmo and Di Cristo, 1998). Varicose cChAT-positive fibers and terminals were often situated close to endocrine cells, mimicking the axosomatic synapses.…”

“…Some of these peptides are proposed to exist in the octopus. These include somatostatin (Feldman, 1986), FMRF-amide (Di Cosmo and Di Cristo, 1998;, gonadotropin-releasing hormone (Di Cosmo and Di Cristo, 1998;Iwakoshi-Ukena et al, 2004), galanin (Suzuki et al, 2000), neuropeptide Y (Suzuki et al, , 2003, calcitonin gene-related peptide , and corticotropin-releasing factor (Suzuki et al, 2003). These peptides have been localized in octopus by immunohistochemistry, mostly using antibodies against vertebrate-type peptides.…”

Molecular cloning, expression pattern, and immunocytochemical localization of a gonadotropin-releasing hormone-like molecule in the gastropod mollusk, Aplysia californica

“…Its presence was once thought to be restricted to members of Phylum Chordata, but increasing evidence suggests otherwise. A large number of studies reported the presence of GnRH-immunoreactivity (ir) and bioactivity in the gastropods (Goldberg et al, 1993;Young et al, 1999;Zhang et al, 2000;Tsai et al, 2003), bivalves (Pazos and Mathieu, 1999;Nakamura et al, 2007), polyplacophorans , cephalopods (Di Cosmo and Di Cristo, 1998;Di Cristo et al, 2002), cnidarians (Anctil, 2000;Twan et al, 2006), and platyhelminthes (Anctil and Tekaya., 2005). Importantly, a dodecapeptide containing the structural core of chordate GnRH was isolated from the central nervous system (CNS) of the common octopus (Iwokoshi et al, 2002).…”

Sperm-attractant peptide influences the spermatozoa swimming behavior in internal fertilization in Octopus vulgaris

“…Very uncommonly for cephalopods, O. vulgaris has an internal fertilization that takes place in the oviducal gland. The secretory activity of the oviducal gland is under the control of neuropeptides and sex steroid hormones (Di Cosmo and Di Cristo, 1998;Di Cosmo et al, 2001;Di Cristo et al, 2002;Di Cristo et al, 2005;Di Cristo et al, 2008). An octopus male introduces a large amount of spermatozoa in the female oviducts through a hectocotylized arm; these cells are enveloped in spermatophores.…”