The Study On The Mechanism Of Neurosteroids Modulated By Morphine In The Rat Brain

Morphine is one of the most effective central analgesics. However,chronic exposure to opiate develops the dependence and tolerance, which havelimited its clinical use. Meanwhile, dependence of opiate abuse has alsoresulted in serious social problems. The study on the mechanism of opiatedependence and tolerance remains a challenge for all the scientists so far. The term neurosteroids applies to those steroids that are synthesized in thenervous system, from cholesterol or other blood-borne steroidal precursors,and that accumulate in the nervous system to levels that are at least in partindependent from steroidogenic gland secretion. Neurosteroids areendogenous modulators of neuronal functions responsible for many biologicaland pathophysiological effects. Recent studies have demonstrated that thedevelopment of tolerance and dependence of morphine can be inhibited byconcomitant chronic administration of neurosteroids such as AP, PREGS orPROG. Moreover, they can influence the form of conditioned positionpreference and have preference or aversion actions. Some neurosteroidscould increase dopamine (DA) release in the rat nucleus accumbens andenhance the dopaminergic response to morphine. These results suggested thatendogenous neurosteroids have related with the process of drug addition.Thereby, we investigated the effects of morphine dependence, withdrawal andrelapse on the concentrations of endogenous neurosteroids in male rat braintissues by GC/MS. It is important to find out the effects of morphine on theneurosteroids. This will be helpful to clarify the mechanism of drugaddiction and design some new therapeutical drugs against the opiatedependence and tolerance. 6英 文 摘 要 The presence of steroidogenic enzymes in rat brain has been detectedusing immunohistochemistry, in situ hybridization and RT-PCR. Thepathway of neurosteroid synthesis in the brain tissue has been clarifiedbasically. However, little is known about the expression of a variety ofsteroidogenic enzymes in pathological conditions. Recent studies haveshown that acute alcohol treatment affected the mRNAs expression ofsteroidogenic enzymes such as StAR,P450scc,3β-HSD,P45aro and 3α-HSD. It remains unclear whether the expression levels of steroidogenicenzymes can be affected by chronic morphine treatment. It is still unknownwhether the changes of neurosteroids levels are related with the mRNAsexpression of steroidogenic enzymes if chronic morphine administrationaffected the levels of neurosteroids in rat brain. It is known there is brainregion dependence about the expressions of steroidogenic enzymes, andwhether or not this brain region specificity is related with the neural circuits ofmorphine addiction. It is important to clarify the mechanism of morphinedependence and tolerance, thereby to develop relative therapeutic principles. In this study a simplified method has been established bygas-chromatography-mass spectrometry (GC-MS), to simultaneously detectdifferent type of neurosteroids in rat brain. The levels of neurosteroids wereinvestigated in morphine dependence and relapse rats using GC-MS.Expression of the messenger mRNAs encoding for three key enzymes,P450scc, P450c17 and 3-HSD in the rat brain regions were examined usingRT-PCR analysis. The principal results were as follows: 1. Quantification of neurosteroids in rat brain tissue by gaschromatography-mass spectrometry A simplified method has been established by gas-chromatography-massspectrometry (GC-MS), to simultaneously detect different neurosteroids in ratbrain tissues. Neurosteroids were isolated in a two-step procedure usingethyl acetate in the first step to extract the unconjugated steroids (PREG, 7英 文 摘 要PROG, DHEA and AP) and chloroform/2-butanol (50/50,v/v) in the secondstep to extract sulfated stero...