Neuropeptidergic Control of the Optic Gland of Octopus vulgaris : FMRF-Amide and GnRH Immunoreactivity ANNA DI COSMO 1 * AND CARLO DI CRISTO 1,2 1 Department of Zoology, University of Naples, 80134 Naples, Italy 2 Department of General and Environmental Physiology, University of Naples, 80134 Naples, Italy 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-NH 2 (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 subpeduncu- late 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. J. Comp. Neurol. 398:1–12, 1998.  1998 Wiley-Liss, Inc. Indexing terms: cephalopods; invertebrate neuroendocrinology; reproduction; LHRH; immunohistochemistry The optic glands of cephalopods are endocrine organs on the optic tracts that control the maturation of the reproduc- tive system. In Octopus vulgaris, cutting the optic tract results in hypertrophy of the optic gland and gonadal maturation (Boycott and Young, 1956). Wells and Wells (1959) found that the optic glands secrete a gonadotropic hormone, and they clarified the relationship between the gland and the central nervous system (CNS; Wells and Wells, 1959). They were able to demonstrate that cutting the optic gland nerve or a surgical lesion in the subpedun- culate area produces an enlargement of the gland and subsequent hypertrophy of the gonads. A similar response, although weaker, was produced by cutting the optic nerves or removing the optic lobes. On the basis of these experi- ments, they proposed that the CNS exerts an inhibitory control on the optic glands through the optic gland nerve. However, it is not yet known how hormone production by the optic gland is induced under normal conditions. The optic glands have been examined several times at ultra- structural levels (Bjo ¨rkman, 1963). In the immature optic gland, two types of synapses, the axoaxonal and the axoglandular, exist, whereas only one type, the axoglandu- lar, is known in the mature gland (Froesch, 1974). Conse- quently, the axoaxonal synapse may inhibit the axoglandu- lar synapse, according to the widespread pattern of presynaptic inhibition (Froesch, 1974). This idea is sup- ported by the absence of axoaxonal synapses in the gland of adult animals, which is supposed to be active only in the absence of inhibition. The Phe-Met-Arg-Phe-NH 2 (FMRF-amide) is a tetrapep- tide of a family of FMRF-like peptides (Greenberg et al., Grant sponsor: MURST; Grant number: 60%. *Correspondence to: Dr.Anna Di Cosmo, Department of Zoology, Univer- sity of Naples, via Mezzocannone 8, 80134 Naples, Italy. E-mail: dicosmo@unina.it Received 12 June 1997; Revised 11 March 1998; Accepted 12 March 1998 THE JOURNAL OF COMPARATIVE NEUROLOGY 398:1–12 (1998)  1998 WILEY-LISS, INC.