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Neural Plasticity
Volume 2009 (2009), Article ID 730902, 8 pages
http://dx.doi.org/10.1155/2009/730902
Review Article

Progesterone Withdrawal-Evoked Plasticity of Neural Function in the Female Periaqueductal Grey Matter

Department of Physiology, University of Birmingham, Birmingham B15 2TT, UK

Received 30 May 2008; Accepted 30 July 2008

Academic Editor: Robert Adamec

Copyright © 2009 T. A. Lovick and A. J. Devall. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Cyclical changes in production of neuroactive steroids during the oestrous cycle induce significant changes in receptor expression in female rats. In the periaqueductal grey (PAG) matter, upregulation of GAB receptors occurs as progesterone levels fall during late dioestrus (LD) or during withdrawal from an exogenous progesterone dosing regime. The new receptors are likely to be extrasynaptically located on the GABAergic interneurone population and to mediate tonic currents. Electrophysiological studies showed that when GAB receptor expression was increased, the excitability of the output neurones in the PAG increased, due to a decrease in the level of ongoing inhibitory tone from the GABAergic interneurones. The functional consequences in terms of nociceptive processing were investigated in conscious rats. Baseline tail flick latencies were similar in all rats. However, acute exposure to mild vibration stress evoked hyperalgesia in rats in LD and after progesterone withdrawal, in line with the upregulation of GAB receptor expression.