Chronic Morphine Sensitizes the Brain Norepinephrine System to Corticotropin-Releasing Factor and Stress

Abstract

Chronic opiate use produces persistent changes in brain neurons that are expressed as adverse effects, including physical dependence and compulsive drug-seeking behavior. Dysregulation of the hypothalamic-pituitary-adrenal response to stress also occurs with chronic opiate administration and has been implicated as a contributing factor to continued substance abuse. This study provides the first evidence for dysregulation of the central noradrenergic response to stress by chronic opiates. Chronic morphine selectively sensitized locus ceruleus (LC)-norepinephrine (NE) neurons to corticotropin-releasing factor (CRF), an integral mediator of the stress response. CRF doses that were inactive in vehicle-treated rats produced a near-maximal activation of LC neurons of rats chronically administered morphine. LC sensitization to CRF was not solely a pharmacological phenomenon but was expressed as hyperresponsivity to physiological stress. Finally, opiate-induced LC sensitization translated to a change in the behavioral repertoire in response to environmental stress (swim stress) such that NE-mediated hyperactive behaviors predominated. The opiate-induced sensitization of the central NE response to stress predicts that chronic opiate administration increases vulnerability to certain stress-related symptoms (e.g., hyperarousal, attentional dysfunction), and this may contribute to the maintenance of opiate-seeking behavior.

Ultrastructural evidence for co-localization of corticotropin-releasing factor receptor and μ-opioid receptor in the rat nucleus locus coeruleus

“…CRF produced a near maximal-activation of LC neurons of rats chronically treated with morphine compared to vehicle-treated rats. Moreover, the chronic opiate-induced LC sensitization altered the behavioral repertoire in response to swim stress, a form of environmental stress [34]. In light of these findings and the expression of CRFr and μOR immunoreactivities in the LC in independent studies [15,29,34], we hypothesized that CRFr and μOR are co-localized in the same dendritic processes in LC neurons.…”

“…Moreover, the chronic opiate-induced LC sensitization altered the behavioral repertoire in response to swim stress, a form of environmental stress [34]. In light of these findings and the expression of CRFr and μOR immunoreactivities in the LC in independent studies [15,29,34], we hypothesized that CRFr and μOR are co-localized in the same dendritic processes in LC neurons.In an effort to further elucidate cellular substrates for interactions between CRF receptor type 1 (CRFr) and μOR, the present study used combined immunofluorescence and dual immunoelectron microscopy. Triple immunocytochemical labeling for CRFr, μOR and tyrosine hydroxylase (TH) was conducted on the same section of tissue.…”

“…The CRF-opioid convergence in the LC-norepinephrine (LC-NE) system is shown to be involved in the neural circuitry underlying stress responses [22] and opiate actions [12]. We have shown that chronic but not acute morphine treatment selectively sensitized LC-NE system to CRF [34]. CRF produced a near maximal-activation of LC neurons of rats chronically treated with morphine compared to vehicle-treated rats.…”

“…The procedures in this study were approved by the Institutional Animal Care and Use Committee of Thomas Jefferson University and conformed to NIH guidelines. All efforts were made to utilize only the number of animals necessary to produce reliable scientific data, and attempts were made to minimize animal distress.Using immunohistochemical analysis, the characterization and specificity of the goat antiserum against CRFr and the rabbit antiserum against μOR have been previously described [15,29,34]. The goat polyclonal CRFr was raised against the C-terminus of CRFr that recognizes both CRFr1 and CRFr2 [15,34].…”

“…Likewise, using immunodotblot analysis, the antiserum recognizes amino acid sequences within μOR, however, it does not recognize either sequence of δ-and κ-opioid receptors [4]. Mouse antiserum against TH specifically recognizes the catecholamine synthesizing enzyme [34].Perfusion, sectioning and immunohistochemical protocols for tissue sections intended for immunofluorescence have been previously described [15,16]. Every fourth coronal tissue section (30 μm thick) of LC from four rats were incubated in goat anti-CRFr (C-20; 1:1,000; Santa Cruz Biotechnology, Santa Cruz, CA), rabbit anti-μ-OR antiserum (1:2,500; Chemicon, Temecula, CA) and mouse anti-TH (1:1,000; Immunostar Inc., Hudson, WI) for 15-18 h in 0.1 M tris-buffered saline (TBS; pH 7.6) with 0.1% bovine serum albumin (BSA) and 0.25% Triton X-100.…”