Involvement of Noradrenergic Transmission in the PVN on CREB Activation, TORC1 Levels, and Pituitary-Adrenal Axis Activity during Morphine Withdrawal

Fátima Martín,M Teresa Marín,M Victoria Milanés,Cristina Núñez,Krisztina J Kovács,M Luisa Laorden,Andrew Jenkins

doi:10.1371/journal.pone.0031119

Abstract

Experimental and clinical findings have shown that administration of adrenoceptor antagonists alleviated different aspects of drug withdrawal and dependence. The present study tested the hypothesis that changes in CREB activation and phosphorylated TORC1 levels in the hypothalamic paraventricular nucleus (PVN) after naloxone-precipitated morphine withdrawal as well as the HPA axis activity arises from α1- and/or β-adrenoceptor activation. The effects of morphine dependence and withdrawal on CREB phosphorylation (pCREB), phosphorylated TORC1 (pTORC1), and HPA axis response were measured by Western-blot, immunohistochemistry and radioimmunoassay in rats pretreated with prazosin (α1-adrenoceptor antagonist) or propranolol (β-adrenoceptor antagonist). In addition, the effects of morphine withdrawal on MHPG (the main NA metabolite at the central nervous system) and NA content and turnover were evaluated by HPLC. We found an increase in MHPG and NA turnover in morphine-withdrawn rats, which were accompanied by increased pCREB immunoreactivity and plasma corticosterone concentrations. Levels of the inactive form of TORC1 (pTORC1) were decreased during withdrawal. Prazosin but not propranolol blocked the rise in pCREB level and the decrease in pTORC1 immunoreactivity. In addition, the HPA axis response to morphine withdrawal was attenuated in prazosin-pretreated rats. Present results suggest that, during acute morphine withdrawal, NA may control the HPA axis activity through CREB activation at the PVN level. We concluded that the combined increase in CREB phosphorylation and decrease in pTORC1 levels might represent, in part, two of the mechanisms of CREB activation at the PVN during morphine withdrawal.

Highlights

Opiate withdrawal is associated with central noradrenergic neurons hyperactivity, and it has been proposed that noradrenergic afferents to the extended amygdala and to the hypothalamic paraventricular nucleus (PVN) are critically involved in the aversive properties as well as in the somatic symptoms of opiate withdrawal [1,2,3]
The second aim of the present study was to assess the possibility that the activation of the cAMP Response Element Binding protein (CREB) coactivator, TORC1 in the PVN arises from activation of a1- and/or b-adrenoceptor
NA caused a marked increase in the frequency of postsynaptic potentials of the parvocellular neurons of the PVN [29]

Summary

Introduction

Opiate withdrawal is associated with central noradrenergic neurons hyperactivity, and it has been proposed that noradrenergic afferents to the extended amygdala and to the hypothalamic paraventricular nucleus (PVN) are critically involved in the aversive properties (such as conditioned place aversion) as well as in the somatic symptoms of opiate withdrawal (teeth chattering, piloerection, lacrimation, rinorrhea and ptosis) [1,2,3]. Altered neuronal activity has been found in the PVN after naloxone-induced opiate withdrawal, as evidenced by increased activation of the immediate early gene product c-Fos and enhanced hypothalamus-pituitary-adrenocortical (HPA) axis response (as reflected by plasma levels of corticosterone, a marker for the HPA axis activity). These alterations were markedly decreased by systemic adrenoceptor antagonists [2,12]. Pretreatment with adrenoceptor antagonists attenuated heroin self administration in rats [13], suggesting that noradrenergic system may contribute to mechanisms that promote dependence

Objectives

Methods

Results

Conclusion