Conservative Nature of Oestradiol Signalling Pathways in the Brain Lobes of Octopus vulgaris Involved in Reproduction, Learning and Motor Coordination (original) (raw)

2012, Journal of Neuroendocrinology

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 capabilities (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 perioesophageal magnocellular lobes. A combination of anatomical, imaging, electrical and chemical stimulation, lesioning and neurophysiological recording techniques have demonstrated the hierarchical organisation of the Octopus CNS and regionalisation of functions (2,3). The degree of encephalisation and functional organisation 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 mechanisms 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 mechanisms 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 glutamate ⁄ NMDA ⁄ nitric oxide signal transduction pathway (10); NMDA