Quantitative analysis of corticotropin-releasing factor and arginine vasopressin mRNA in the hypothalamus during chronic morphine treatment in rats: an in situ hybridization study

Suppression of hypothalamic-pituitary-adrenal axis by acute heroin challenge in rats during acute and chronic withdrawal from chronic heroin administration

It is known that heroin dependence and withdrawal are associated with changes in the hypothalamic-pituitary-adrenal (HPA) axis. The objective of these studies in rats was to systematically investigate the level of HPA activity and response to a heroin challenge at two time points during heroin withdrawal, and to characterize the expression of associated stress-related genes 30 min after each heroin challenge. Rats received chronic (10-day) intermittent escalating-dose heroin administration (3 × 2.5 mg/kg/day on day 1; 3 × 20 mg/kg/day by day 10). Hormonal and neurochemical assessments were performed in acute (12 h after last heroin injection) and chronic (10 days after the last injection) withdrawal. Both plasma ACTH and corticosterone levels were elevated during acute withdrawal, and heroin challenge at 20 mg/kg (the last dose of chronic escalation) at this time point attenuated this HPA hyperactivity. During chronic withdrawal, HPA hormonal levels returned to baseline, but heroin challenge at 5 mg/kg decreased ACTH levels. In contrast, this dose of heroin challenge stimulated the HPA axis in heroin naïve rats. In the anterior pituitary, pro-opiomelanocortin (POMC) mRNA levels were increased during acute withdrawal and retuned to control levels after chronic withdrawal. In the medial hypothalamus, however, the POMC mRNA levels were decreased during acute withdrawal, and increased after chronic withdrawal. Our results suggest a long-lasting change in HPA abnormal responsivity during chronic heroin withdrawal.

Peptidomics of Cpefat/fat mouse hypothalamus and striatum: effect of chronic morphine administration

Chronic morphine administration is known to affect several neuropeptide systems, and this could contribute to the behavioral effects of opiates. To quantitate global changes in neuropeptide levels upon chronic morphine administration, we took advantage of a method that allows selective isolation of neuropeptides from brains of mice lacking carboxypeptidase E (Cpefat/fat mice), a critical enzyme in the generation of many neuroendocrine peptides. We used a differential labeling procedure with stable isotopic tags and mass spectrometry to quantitate the relative changes in a number of hypothalamic and striatal peptides in Cpefat/fat mice chronically treated with morphine. A total of 27 distinct peptides were detected in hypothalamus and striatum. Of these, 27 were identified by mass spectrometry-based sequencing, 1 was tentatively identified by the mass and charge, and 9 were not identified. The identified peptides included fragments of proenkephalin, prothyrotropin-releasing hormone, secretogranin II, chromogranin Aand B, protachykinin B, provasopressin, promelanin concentrating hormone, and pro-SAAS. Upon morphine administration, although the levels of most of the peptides were unaltered (within a factor of 1.3 to 0.7 compared with saline control), the levels of a small number of peptides did show consistent changes (increased or decreased by 1.3-fold or more) in hypothalamus and/or striatum. Taken together, these results provide interesting insights into endogenous neuropeptide systems that are modulated by morphine and suggest further experiments to link candidate peptides with long-term effects of morphine.

Opioid abuse and brain gene expression

Opiate addiction is a central nervous system disorder of unknown mechanism. Neuronal basis of positive reinforcement, which is essential to the action of opioids, relies on activation of dopaminergic neurons resulting in an increased dopamine release in the mesolimbic brain structures. Certain aspects of opioid dependence and withdrawal syndrome are also related to the activity of noradrenergic and serotonergic systems, as well as to both excitatory and inhibitory amino acid and peptidergic systems. The latter pathways have been recently proven to be involved both in the development of dependence and in counteracting the states related to relapse. An important role in neurochemical mechanisms of opioid reward, dependence and vulnerability to addiction has been ascribed to endogenous opioid peptides, particularly those acting via the mu- and kappa-opioid receptors. Opiate abuse leads to adaptive reactions in the nervous system which occur at the cellular and molecular levels. Recent research indicates that intracellular mechanisms of signal transmission-from the receptor, through G proteins, cyclic AMP, MAP kinases to transcription factors--also play an important role in opioid tolerance and dependence. The latter link in this chain of reactions may modify synthesis of target genes and in this manner, it may be responsible for opiate-induced long-lasting neural plasticity.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).