The CRF1 receptor antagonist, R121919, attenuates the severity of precipitated morphine withdrawal

https://doi.org/10.1016/j.ejphar.2007.05.041Get rights and content

Abstract

Corticotropin-releasing factor (CRF) regulates the hypothalamic–pituitary–adrenal axis, coordinates the mammalian stress response, and acting primarily via the CRF1 receptor, has been strongly implicated in the pathophysiology of depression and anxiety. Furthermore, the behavioral and autonomic activation that occurs following withdrawal in drug dependent animals resembles the mammalian stress response. Concordant with this view is evidence of enhanced CRF transcription, release and activity following withdrawal from several drugs of abuse. Conversely, CRF receptor antagonists have been demonstrated to reduce the severity of many drug withdrawal symptoms, implicating a specific role for activation of CRF neurons in mediating the anxiogenic and stress-like reactions observed during withdrawal. To extend these findings, we investigated whether pretreatment with a selective CRF1 receptor antagonist, R121919, is capable of similarly decreasing the autonomic, behavioral and neuroendocrine activation observed following precipitation of morphine withdrawal in dependent rats. The results indicate that pretreatment with R121919 attenuates the global severity of the precipitated morphine withdrawal syndrome as measured by the Gellert–Holtzman scale. In addition, rats pretreated with R121919 prior to precipitation of morphine withdrawal demonstrated decreased hypothalamic–pituitary–adrenal axis activation, as measured by plasma ACTH concentrations, and decreased early expression of the CRF gene in the paraventricular nucleus of the hypothalamus, as measured by CRF heteronuclear RNA. These findings suggest that activation of CRF neuronal systems via the CRF1 receptor may be one element of the neurobiological mechanisms activated during drug withdrawal and that CRF1 receptor antagonists may have a potential therapeutic role in the treatment of human drug withdrawal syndromes.

Introduction

The neuropeptide, corticotrophin-releasing factor (CRF), mediates the endocrine response to stress via its actions as the major physiological regulator of the hypothalamic–pituitary–adrenal axis. Substantial evidence has accumulated to support the hypothesis that CRF additionally functions as a neurotransmitter in extrahypothalamic limbic structures and brainstem nuclei, and serves to mediate the behavioral and autonomic arms of the stress response in coordination with the endocrine response. In addition to this key role, there is a considerable evidence implicating CRF in the pathophysiology of mood and anxiety disorders (Risbrough and Stein, 2006).

Significant data has also accrued to indicate that activation of CRF neuronal systems is involved in the withdrawal syndromes from a variety of drugs that produce physiological dependence, as this well-studied phenomenon is characterized by anxiety and autonomic activation that in many ways resembles a mammalian stress response. After the chronic administration of benzodiazepines, cocaine, ethanol, or morphine is discontinued there is evidence of heightened hypothalamic–pituitary–adrenal axis activity, as measured by plasma adrenocorticotropic hormone (ACTH) and corticosterone concentrations, CRF mRNA expression in the paraventricular nucleus of the hypothalamus, or c-fos mRNA induction in CRF-containing neurons in the paraventricular nucleus of the hypothalamus (Keith et al., 1983, Owens et al., 1991, Roberts et al., 1992, Milanes et al., 1998, Hamlin et al., 2004). In addition to stress-induced activation of the neuroendocrine axis, findings of increased CRF mRNA transcription and/or peptide release within the amygdala (Pich et al., 1995, Rodriguez de Fonseca et al., 1997, Richter and Weiss, 1999, McNally and Akil, 2002, Maj et al., 2003, Zhou et al., 2003), and/or increased CRF concentrations in the cerebrospinal fluid (CSF; Adinoff et al., 1996) following withdrawal from cannabis, cocaine, ethanol, or morphine indicate increased central CRF neuronal activity.

These results suggest that activation of CRF neuronal systems may be common to withdrawal from drugs of abuse. If this elevated CRF activity is a causal element in the affective and autonomic symptoms of drug withdrawal, then blocking CRF neurotransmission with a CRF receptor antagonist should diminish the withdrawal syndrome. This hypothesis is supported by reports that withdrawal-induced anxiety, following chronic cocaine or ethanol administration, is diminished by pretreatment with a CRF receptor antagonist or CRF antiserum (Baldwin et al., 1991, Rassnick et al., 1993, Sarnyai et al., 1995, Basso et al., 1999). Recent data from our laboratory has indicated that pretreatment with the CRF1-selective receptor antagonist, 2,5-dimethyl-3-(6-dimethyl-4-methylpyridin-3-yl)-7-dipropylaminopyrazolo[1,5-a]pyrimidine (R121919), attenuates hypothalamic–pituitary–adrenal axis activation, induction of CRF heteronuclear RNA expression in the paraventricular nucleus of the hypothalamus, and behavioral evidence of anxiety following withdrawal from the benzodiazepine, lorazepam (Skelton et al., 2007).

Following morphine withdrawal, in particular, there is significant evidence that pretreatment with CRF receptor antagonists (both non-selective and CRF1-selective) reduces many of the behavioral and autonomic signs of precipitated morphine withdrawal in rats (Brugger et al., 1998, Iredale et al., 2000, Lu et al., 2000, Funada et al., 2001, McNally and Akil, 2002). Further, Contarino and Papaleo (2005) demonstrated that mice bred to lack the CRF1 receptor did not develop conditioned place aversion associated with the negative affective state of spontaneous morphine withdrawal. Conversely, pretreatment with a peptidergic CRF2-selective receptor antagonist was found to be largely ineffective (Lu et al., 2000). These findings imply a specific role for activation of CRF, acting via the CRF1 receptor, in mediating the aversive behavioral and autonomic states produced during withdrawal from drugs of dependency, such as benzodiazepines, cocaine, ethanol and morphine. Based on this hypothesis, we sought to expand our previous findings on benzodiazepine withdrawal, by examining the efficacy of the selective CRF1 receptor antagonist, R121919, in attenuating the morphine withdrawal syndrome as analyzed by a standardized rating system that incorporates behavioral and autonomic measures. In addition, we investigated the utility of R121919 in decreasing activation of the hypothalamic–pituitary–adrenal axis induced by morphine withdrawal, as measured by ACTH and corticosterone concentrations, as well as CRF heteronuclear RNA expression in the paraventricular nucleus of the hypothalamus, never before studied after morphine withdrawal.

Section snippets

Animals

Male Sprague–Dawley rats (225–250 g on arrival; Charles River Laboratories, Raleigh NC) were individually housed in an environmentally controlled animal facility on a 12 h light/dark cycle (lights on at 0730 h) with food and water available ad libitum. All animals were handled daily throughout the course of the experiment.

All animal protocols were approved by the Emory IACUC, and the “Guide for Care and Use of Laboratory Animals” (Institute of Laboratory Animal Resources, National Academy

Gellert–Holtzman scale for precipitated withdrawal signs

As expected, behaviors rated as withdrawal signs were observed primarily in the rats treated with naltrexone to precipitate withdrawal. The Gellert–Holtzman score increased from 2.5 ± 0.7 in the total vehicle-treated rats to 35.3 ± 2.6 (P < 0.001) in the total naltrexone-treated rats. The low, but measurable, score in the non-withdrawn rats was due to the occasional observation of an abdominal contraction or wet dog shake, as well as the sporadic appearance of facial fasciculations, ptosis, genital

Discussion

The results of this experiment indicate that pretreatment with the CRF1 receptor antagonist, R121919, significantly attenuates many of the behavioral signs of naltrexone-precipitated morphine withdrawal in Sprague–Dawley rats. In addition, withdrawal-induced activation of the hypothalamic–pituitary–adrenal axis was diminished by R121919, as evidenced by reductions in ACTH release and CRF heteronuclear RNA expression in the paraventricular nucleus of the hypothalamus. Taken together with the

Conflict of interest statement

Kelly Skelton, M.D. Ph.D., serves on the Speakers' Bureau of AstraZeneca, Bristol-Myers-Squibb, and Pfizer.

Michael J. Owens, Ph.D., has received speakers' honoraria from GlaxoSmithKline, has research grants from Pfizer, GlaxoSmithKline, Merck, Lundbeck, Cyberonics, and Johnson & Johnson, has served (or continues to serve) as consultant for Bristol-Myers-Squibb, Pfizer, Lundbeck, Sepracor, Johnson & Johnson, Sanofi-Avent, and Forest Labs, and has the following patent — “A method to estimate

Acknowledgments

This work was supported by the National Institutes of Health Grants MH42088 and MH58299.

In addition, the authors wish to thank Donna O'Brien, PhD, for her assistance with conducting aspects of the experiments described in this manuscript.

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