The corticotropin-releasing factor receptor-1 pathway mediates the negative affective states of opiate withdrawal

Abstract

The negative affective symptoms of opiate withdrawal powerfully motivate drug-seeking behavior and may trigger relapse to heroin abuse. To date, no medications exist that effectively relieve the negative affective symptoms of opiate withdrawal. The corticotropin-releasing factor (CRF) system has been hypothesized to mediate the motivational effects of drug dependence. The CRF signal is transmitted by two distinct receptors named CRF receptor-1 (CRF1) and CRF2. Here we report that genetic disruption of CRF1 receptor pathways in mice eliminates the negative affective states of opiate withdrawal. In particular, neither CRF1 receptor heterozygous (CRF1+/-) nor homozygous (CRF1-/-) null mutant mice avoided environmental cues repeatedly paired with the early phase of opiate withdrawal. These results were not due to altered associative learning processes because CRF1+/- and CRF1-/- mice displayed reliable, conditioned place aversions to environmental cues paired with the kappa-opioid receptor agonist U-50,488H. We also examined the impact of CRF1 receptor-deficiency upon opiate withdrawal-induced dynorphin activity in the nucleus accumbens, a brain molecular mechanism thought to underlie the negative affective states of drug withdrawal. Consistent with the behavioral indices, we found that, during the early phase of opiate withdrawal, neither CRF1+/- nor CRF1-/- showed increased dynorphin mRNA levels in the nucleus accumbens. This study reveals a cardinal role for CRF/CRF1 receptor pathways in the negative affective states of opiate withdrawal and suggests therapeutic strategies for the treatment of opiate addiction.

Fig. 1.

Lack of negative affective states in opiate-withdrawn CRF₁ receptor-deficient mice. Place aversion scores of control and opiate-withdrawn wild-type, , and mice. For each mouse, a place-aversion score was calculated as described in Materials and Methods. Values represent mean ± SEM. n = 11-14 per group. *, P < 0.01 versus all other groups.

Fig. 2.

Opiate-withdrawn CRF₁ receptor-deficient mice do not show increased dynorphin gene expression in the nucleus accumbens. (A) Dynorphin mRNA levels in the shell portion of the nucleus accumbens of control and opiate-withdrawn wild-type, , and mice. Results are expressed as silver grain density (silver grains per 100 μm²) by neuron density (labeled neurons per 0.5 mm²). Values represent mean ± SEM. n = 8-10 per group. *, P < 0.0005 versus all other groups. (B) Negative images of Biomax-MR films (Upper) and high-magnification silver grains photomicrographs (Lower) of some representative brain sections illustrating dynorphin mRNA levels in the nucleus accumbens shell (S) of control and opiate-withdrawn wild-type, , and mice. (Scale bars: Upper, 0.8 mm; Lower, 10 μm.)

Fig. 3.

Opiate withdrawal does not affect dynorphin gene expression in the nucleus accumbens core. Shown are dynorphin mRNA levels in the core portion of the nucleus accumbens of control and opiate-withdrawn wild-type, , and mice. Results are expressed as silver grain density (silver grains per 100 μm²) by neuron density (labeled neurons per 0.5 mm²). Values represent mean ± SEM. n = 8-10 per group. Overall, mice showed lower dynorphin mRNA levels than wild-type and mice (P < 0.01).

Fig. 4.

Unaltered CPA abilities in CRF₁ receptor-deficient mice. Shown are place aversion scores of control and U-50,488H-treated wild-type, , and mice. For each mouse, a place aversion score was calculated as described in Materials and Methods. Values represent mean ± SEM. n = 6-11 per group. *, P < 0.0001 versus control mice.