Elsevier

Neuroscience

Volume 228, 3 January 2013, Pages 235-242
Neuroscience

Opiate-induced changes in brain adenosine levels and narcotic drug responses

https://doi.org/10.1016/j.neuroscience.2012.10.031Get rights and content

Abstract

We have very little information about the metabolomic changes that mediate neurobehavioral responses, including addiction. It was possible that opioid-induced metabolomic changes in brain could mediate some of the pharmacodynamic effects of opioids. To investigate this, opiate-induced brain metabolomic responses were profiled using a semi-targeted method in C57BL/6 and 129Sv1 mice, which exhibit extreme differences in their tendency to become opiate dependent. Escalating morphine doses (10–40 mg/kg) administered over a 4-day period selectively induced a twofold decrease (p < 0.00005) in adenosine abundance in the brainstem of C57BL/6 mice, which exhibited symptoms of narcotic drug dependence; but did not decrease adenosine abundance in 129Sv1 mice, which do not exhibit symptoms of dependence. Based on this finding, the effect of adenosine on dependence was investigated in genetically engineered mice with alterations in adenosine tone in the brain and in pharmacologic experiments. Morphine withdrawal behaviors were significantly diminished (p < 0.0004) in genetically engineered mice with reduced adenosine tone in the brainstem, and by treatment with an adenosine receptor1 (A1) agonist (2-chloro-N6-cyclopentyladenosine, 0.5 mg/kg) or an A2a receptor (A2a) antagonist (SCH 58261, 1 mg/kg). These results indicate that adenosine homeostasis plays a crucial role in narcotic drug responses. Opiate-induced changes in brain adenosine levels may explain many important neurobehavioral features associated with opiate addiction and withdrawal.

Highlights

► Morphine decreased brainstem adenosine in morphine-dependent mice. ► Withdrawal was diminished in genetically engineered mice with reduced adenosine tone. ► Opiate-induced changes in adenosine may explain addiction-associated behaviors.

Introduction

Efforts to improve the care of patients with chronic pain conditions have led to a marked increase in the use of opioid medications. Unfortunately, prescription opioid analgesics are more commonly misused than all other illicit drugs combined, including marijuana [reviewed in (Dodrill et al., 2011)]. New approaches and a re-evaluation of our current understanding of the mechanisms involved in narcotic drug addiction are urgently needed. To develop new strategies for addressing this public health problem, we have been analyzing a murine model of opiate dependence. Mice can be made physically dependent upon morphine, and inbred strains dramatically differ in the extent to which they manifest various features of narcotic drug addiction, which resemble those observed in humans (Liang et al., 2006a, Liang et al., 2006b, Chu et al., 2009). By analyzing these inter-strain differences, we identified four genes affecting opioid responses (Liang et al., 2006a, Liang et al., 2006b, Smith et al., 2008), including the Htr3a/5-HT3 serotonin receptor (Chu et al., 2009). We also demonstrated that administration of a commonly used 5-HT3 antagonist (ondansetron) reduced narcotic drug withdrawal symptoms in mice and in normal human subjects (Chu et al., 2009, Liang et al., 2011).

In addition to genetic data, metabolomic analysis can reveal a great deal about the physiological state of a tissue. We have very little information about metabolomic changes mediating neurobehavioral responses or diseases. It is likely that clinically important opiate responses could be mediated (at least in part) by metabolomic changes that are induced by opiates. However, the extreme differences in physicochemical properties make it impossible to accurately measure changes in all cellular metabolites with a single analytic method. Therefore, we coupled a recently developed Dansyl [5-(dimethylamino)-1-napthalene sulfonamide] derivatization method (Guo and Li, 2009) with LC/MS analysis to analyze changes in a large number of metabolites in brainstem after opiate administration. Dansylation increases metabolite detection sensitivity by 10–1000-fold, and improves metabolite retention and separation on reversed phase columns. It enables changes in many metabolites that have primary or secondary amino or other groups, to be evaluated in an unbiased fashion. This semi-targeted method was used to characterize opiate-induced metabolomic changes in a brain region that is critical for opiate responses in two inbred mouse strains, which exhibit extreme differences in the extent of physical dependence developing after opiate administration. Metabolomic changes in the brainstem were analyzed, since this region has been shown to regulate narcotic drug dependence (Gulati and Bhargava, 1989, Costall et al., 1990, Tao et al., 1998).

Section snippets

Animal studies

All experiments were performed according to protocols that were approved by the Institutional Animal Care and Use Committee at the Veterans Affairs Palo Alto Healthcare System. Male C57BL/6J and 129/SvlmJ mice strains (7–8 weeks old) were obtained from Jackson Laboratories (Bar Harbor, MA) and kept in our facility for a minimum of 1 week prior to initiation of the experiments. Mice with genetically engineered alterations in adenosine kinase (Adk) expression (which are referred to as Adk-tg and

Results

C57BL/6J mice become morphine-dependent after 4 days of administration of increasing doses of morphine; the morphine-dependent mice develop signs of withdrawal within 18 h of their last morphine dose, and naloxone administration rapidly induces substantial withdrawal symptoms (Chu et al., 2009). To characterize opiate-induced metabolomic changes, brainstem tissue was prepared from C57BL/6J mice placed into 4 treatment groups (n = 8 per group) (Fig. 1A): (1) Dependence: tissue was harvested 1 h after

Discussion

This study demonstrates that semi-targeted metabolomic profiling data can provide important insight into neurobehavioral responses. It also provides the first demonstration that systemic opiate administration decreases adenosine abundance in brainstem. The decrease in narcotic drug withdrawal behavior in mice with genetically engineered changes in brainstem adenosine levels or after administration of pharmacologic agents acting on adenosine receptors demonstrates the importance of this

Acknowledgements

G.P. was partially supported by funding from a transformative RO1 award (1R01DK090992) provided by the NIDDK.

References (46)

  • A. Salem et al.

    Role of endogenous adenosine in the expression of opiate withdrawal in rats

    Eur J Pharmacol

    (1999)
  • J. Sawynok

    Adenosine receptor activation and nociception

    Eur J Pharmacol

    (1998)
  • F.E. Studer et al.

    Shift of adenosine kinase expression from neurons to astrocytes during postnatal development suggests dual functionality of the enzyme

    Neuroscience

    (2006)
  • M.R. Zarrindast et al.

    Effects of adenosine receptor agents on the expression of morphine withdrawal in mice

    Eur J Pharmacol

    (1999)
  • T. Beswick et al.

    Major disruptions of sleep during treatment of the opiate withdrawal syndrome: differences between methadone and lofexidine detoxification treatments

    Addict Biol

    (2003)
  • T.E. Bjorness et al.

    Adenosine and sleep

    Curr Neuropharmacol

    (2009)
  • R.M. Brown et al.

    Adenosine A(2A) receptors and their role in drug addiction

    J Pharm Pharmacol

    (2008)
  • R.M. Brown et al.

    A differential role for the adenosine A2a receptor in opiate reinforcement vs opiate-seeking behavior

    Neuropsychopharmacology

    (2009)
  • A. Castane et al.

    Behavioural and biochemical responses to morphine associated with its motivational properties are altered in adenosine A(2A) receptor knockout mice

    Br J Pharmacol

    (2008)
  • L.F. Chu et al.

    From mouse to man: the 5-HT3 receptor modulates physical dependence on opioid narcotics

    Pharmacogenet Genomics

    (2009)
  • A.K. Dixon et al.

    Tissue distribution of adenosine receptor mRNAs in the rat

    Br J Pharmacol

    (1996)
  • C.L. Dodrill et al.

    Prescription pain medication dependence

    Am J Psychiatry

    (2011)
  • T.V. Dunwiddie et al.

    The role and regulation of adenosine in the central nervous system

    Annu Rev Neurosci

    (2001)
  • Cited by (0)

    View full text