Final Activity Report Summary - EIF-2003-ET/RS (Role of neurosteroids in a novel mechanism modulating the nociceptive system through ATP and GABA receptors) Transmission of pain signals is essential to maintain the integrity of an organism. Certain diseases however generate chronic, pathological pain, which is detrimental to this integrity. The initial objective of this proposal was to improve our comprehension of the generation of pathological pain and define the role of neurosteroids, i.e. a class of steroids synthesised by the nervous system, in the initiation and transmission of pain signals. Gamma-aminobutiric acid (GABAA) receptor, the major inhibitory receptor in the nervous system, is involved in the control of the transmission of pain signals. We stimulated the production of neurosteroids in cultured sensory neurons with diazepam. Flumazenil was used to block the concurrent binding of diazepam to the benzodiazepine modulatory site located on GABAA receptors. Flumazenil was not considered to have an intrinsic effect on GABAA responses. Surprisingly, the sustained application of flumazenil alone inhibited GABAA responses. This atypical inhibitory effect suggested that our experimental conditions could unveil either: 1. an undescribed pharmacological property of flumazenil, or 2. the presence of an unknown endogenous molecule that stimulated GABAA receptors. Flumazenil could displace this unknown constitutive stimulator, thereby inducing an apparent inhibition of the GABAA response. The project has been refocused on the analysis of the pharmacology of flumazenil in order to analyse this atypical effect. However, despite the use of optimised standardised protocols, the initially reproducible inhibitory effect of flumazenil was lost in later experiments. This raised the probability that physiological parameters, such as the stress level of the organisms, might affect the presence of the unknown modulator or modify the sensibility of cells to flumazenil. This work provided a new view on the pharmacology of flumazenil and its clinical use as a drug reversing the effects of benzodiazepines. In addition to the main project, I participated in a collaborative work studying the mechanisms of the generation of inflammatory pain. We analysed the regulatory factors of the FOS family and the neuronal nitric oxide signalling pathway in the spinal cord and evaluated their synergistic interaction during inflammatory pain. This novel mechanism might constitute a target for innovative therapeutic strategies in the management of chronic or neuropathic pain.
