Control of GnRH expression in the olfactory lobe of Octopus vulgaris

In the cephalopod mollusk Octopus vulgaris, the gonadotropic hormone released by the optic gland controls sexual maturity. Several lobes of the central nervous system control the activity of this gland. In one of these lobes, the olfactory lobe, a gonadotropin releasing hormone (GnRH) neuronal system has been described. We assume that several inputs converge on the olfactory lobes in order to activate GnRH neurons and that a glutamatergic system mediates the integration of stimuli on these neuropeptidergic neurons. The presence of N-methyl-d-aspartate (NMDA) receptor immunoreactivity in the neuropil of olfactory lobes and in the fibers of the optic gland nerve, along with the GnRH nerve endings strongly supports this hypothesis. A distinctive role in the control of GnRH secretion has also been attributed, in vertebrates, to nitric oxide (NO). The lobes and nerves involved in the nervous control of reproduction in Octopus contain nitric oxide synthase (NOS). Using a set of experiments aimed at manipulate a putative l-glutamate/NMDA/NO signal transduction pathway, we have demonstrated, by quantitative real-time PCR, that NMDA enhances the expression of GnRH mRNA in a dose-response manner. The reverting effect of a selective antagonist of NMDA receptors (NMDARs), 2-amino-5-phosphopentanoic acid (D-APV), confirms that such an enhancing action is a NMDA receptor-mediated response. Nitric oxide and calcium also play a positive role on GnRH mRNA expression. The results suggest that in Octopusl-glutamate could be a key molecule in the nervous control of sexual maturation.