ORIGINAL ARTICLE Conservative Nature of Oestradiol Signalling Pathways in the Brain Lobes of Octopus vulgaris Involved in Reproduction, Learning and Motor Coordination E. De Lisa*, M. Paolucci and A. Di Cosmo* *Department of Structural and Functional Biology, University of Napoli ‘Federico II’, Napoli, Italy.  Department of Biological, Geological and Environmental Sciences, University of Sannio, Benevento, Italy. Octopus vulgaris demonstrates sophisticated behaviours as a result of two main evolutionary events. First, advanced encephalisation of the ganglionic masses associated with hierarchical organisation of function and, second, the development of advanced cognitive capa- bilities (1). The central nervous system (CNS) comprises a central part, encircling the oesophagus, and paired optic lobes laterally connected by a distinct optic tract. The central part is divided into suboesophageal and supraoesophageal lobes, linked by the perio- esophageal magnocellular lobes. A combination of anatomical, imaging, electrical and chemical stimulation, lesioning and neuro- physiological recording techniques have demonstrated the hierar- chical organisation of the Octopus CNS and regionalisation of functions (2,3). The degree of encephalisation and functional orga- nisation of the Octopus CNS shows similarities to the mammalian and insect brains, and the convergence in the organisation of the brain areas associated with learning is remarkable (4,5). In addition, the demonstration of the conservative nature of molecular mecha- nisms underlying learning and memory across phyla has led recently to the proposal of a general theory of chronic pain, according to which the mechanisms of learning based on neuronal plasticity are similar to the molecular mechanisms of chronic pain (6). The mounting evidence that oestradiol modulates chronic pain in vertebrates (7) and the demonstration of the antinociceptive effects of neuroactive steroids in the land snail, Cepaea nemoralis, strongly support the existence in mollusks of modulatory mechan- isms analogues to analgesia in vertebrates (8). In O. vulgaris, our group has demonstrated the conservative nature of neural and neuroendocrine control mechanisms. Indeed, the olfactory lobes control sexual maturity through gonadotrophin-releasing hormone (GnRH) neurones (9); in the olfactory lobes, NMDA stimulation increases GnRH mRNA levels, probably through a gluta- mate ⁄ NMDA ⁄ nitric oxide signal transduction pathway (10); NMDA Journal of Neuroendocrinology Correspondence to: A. Di Cosmo, Department of Structural and Functional Biology, University of Napoli, ‘Federico II’, via Cinthia, 80126 Napoli, Italy (e-mail: dicosmo@unina.it). Oestradiol plays crucial roles in the mammalian brain by modulating reproductive behaviour, neural plasticity and pain perception. The cephalopod Octopus vulgaris is considered, along with its relatives, to be the most behaviourally advanced invertebrate, although the neurophysiologi- cal basis of its behaviours, including pain perception, remain largely unknown. In the present study, using a combination of molecular and imaging techniques, we found that oestradiol up- regulated O. vulgaris gonadotrophin-releasing hormone (Oct-GnRH) and O. vulgaris oestrogen receptor (Oct-ER) mRNA levels in the olfactory lobes; in turn, Oct-ER mRNA was regulated by NMDA in lobes involved in learning and motor coordination. Fluorescence resonance energy transfer analysis revealed that oestradiol binds Oct-ER causing conformational modifications and nuclear translocation consistent with the classical genomic mechanism of the oestrogen receptor. Moreover, oestradiol triggered a calcium influx and cyclic AMP response element bind- ing protein phosphorylation via membrane receptors, providing evidence for a rapid nongenomic action of oestradiol in O. vulgaris. In the present study, we demonstrate, for the first time, the physiological role of oestradiol in the brain lobes of O. vulgaris involved in reproduction, learn- ing and motor coordination. Key words: neurosteroids, GnRH, learning, Octopus vulgaris, motor coordination, fluorescence resonance energy transfer. doi: 10.1111/j.1365-2826.2011.02240.x Journal of Neuroendocrinology 24, 275–284 ª 2011 The Authors. Journal of Neuroendocrinology ª 2011 Blackwell Publishing Ltd Journal of Neuroendocrinology From Molecular to Translational Neurobiology