Effects of acute “binge” cocaine on mRNA levels of μ opioid receptor and neuropeptides in dopamine D1 or D3 receptor knockout mice

Impact of OPRM1 (Mu-opioid Receptor Gene) A112G Polymorphism on Dual Oxycodone and Cocaine Self-administration Behavior in a Mouse Model

The use of mu-opioid receptor (MOP-r) agonists such as oxycodone together with cocaine is prevalent, and deaths attributed to using these combinations have increased.

RATIONALE

It is unknown if functional single nucleotide polymorphisms (SNPs), such as the OPRM1 (MOP-r gene) SNP A118G, can predispose individuals to more dual opioid and psychostimulant intake. The dual self-administration (SA) of MOP-r agonists and cocaine has not been thoroughly examined, especially with regard to neurobiological changes.

OBJECTIVES

We examined oxycodone SA and subsequent dual oxycodone and cocaine SA in male and female A112G (A/G and G/G, heterozygote and homozygote, respectively) mice, models of human A118G carriers, versus wild-type (A/A) mice.

METHODS

Adult male and female A/G, G/G and A/A mice self-administered oxycodone (0.25 mg/kg/infusion, 4hr/session, FR 1.) for 10 consecutive days (sessions 1-10). Mice then self-administered cocaine (2 hr) following oxycodone SA (4 hr, as above) in each session for a further 10 consecutive days (sessions 11-20). Message RNA transcripts of 24 reward-related genes were examined in the dorsal striatum.

RESULTS

Male and female A/G and G/G mice had greater oxycodone SA than A/A mice did in the initial 10 days and in the last 10 sessions. Further, A/G and G/G mice showed greater cocaine intake than A/A mice. Dorsal striatal mRNA levels of Pdyn, Fkbp5, Oprk1, and Oprm1 were altered following oxycodone and cocaine SA.

CONCLUSIONS

These studies demonstrated that this functional genetic variation in Oprm1 affected dual opioid and cocaine SA and altered specific gene expression in the striatum.

Cocaine self-administration in dopamine D₃ receptor knockout mice

The dopamine D₃ receptor has received attention over the last two decades as a target for medications development for substance abuse disorders. Results have remained mixed. Despite emergence of more D₃-selective ligands, possible attribution of observed effects to D₂ receptors remains a concern. Knockout mice may help shed light on mechanisms. Here we evaluated the effect of constitutive D₃ receptor inactivation ("knockout") on the reinforcing effects of cocaine. We tested D₃ wild-type (WT), heterozygous (D₃⁺/⁻), and knockout (D₃⁻/⁻), mice in acquisition and maintenance of intravenous self-administration across a broad range of cocaine doses, using a fixed ratio (FR) 1 and a progressive ratio (PR) schedule of reinforcement, along with parallel food-reinforced studies. Generally, D₃⁻/⁻ mice showed cocaine self-administration comparable to WT controls across assays. Moderate and nonsignificant trends toward lesser reinforcing effects of a low cocaine dose (0.32 mg/kg) were apparent in acquisition and PR studies, consistent with the idea that the D₃ receptor may play a subtle role in the reinforcing effects of low cocaine doses under low FR conditions. However, those effects with cocaine self-administration were more subtle than the lower responding of D₃ knockout mice observed with food-maintained behavior. In addition, the D₃ antagonist PG01037 failed to affect cocaine self-administration under an FR 1 schedule in WT mice. The present data do not support a necessary role for the D₃ receptor in the direct reinforcing effects of cocaine.

The effects of pramipexole on prepulse inhibition and locomotor activity in C57BL/6J mice

Pramipexole (PRA) is a preferential D3R agonist that, in rats and humans, modifies prepulse inhibition (PPI) of the acoustic startle reflex, an operational measure of sensorimotor gating. The ability to use similar PPI measures across species, and the relative ease of genetic manipulations in mice, suggests that molecular studies of the D3R regulation of sensorimotor gating might be best pursued in mice. Here, we evaluate the effects of PRA on PPI and locomotion in C57BL/6J mice, the background strain for many gene knockout mouse models. Male C57BL/6J mice were tested for PPI and locomotor activity after injection of PRA. No significant effects of PRA on PPI were observed at any dose (0.1-10.0 mg/kg), but a significant reduction in startle magnitude was observed after 10 mg/kg PRA. In contrast, the D1/2 agonist, apomorphine (5 mg/kg) significantly reduced PPI in these mice. At doses of PRA that did not alter startle magnitude (0.3, 1, 3 mg/kg), significant decreases in the amount of locomotor and investigatory behavior were observed. Distinct from findings in rats and humans, it seems that either: (i) PRA does not activate D3Rs in C57BL/6J mice, or (ii) D3R agonists are not sufficient to alter PPI in this mouse strain.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Bidirectional translational research: Progress in understanding addictive diseases

The focus of this review is primarily on recent developments in bidirectional translational research on the addictions, within the Laboratory of the Biology of Addictive Diseases at The Rockefeller University. This review is subdivided into major interacting aspects, including (a) Investigation of neurobiological and molecular adaptations (e.g., in genes for the opioid receptors or endogenous neuropeptides) in response to cocaine or opiates, administered under laboratory conditions modeling chronic patterns of human self-exposure (e.g., chronic escalating "binge"). (b) The impact of such drug exposure on the hypothalamic-pituitary-adrenal (HPA) axis and interacting neuropeptidergic systems (e.g., opioid, orexin and vasopressin). (c) Molecular genetic association studies using candidate gene and whole genome approaches, to define particular systems involved in vulnerability to develop specific addictions, and response to pharmacotherapy. (d) Neuroendocrine challenge studies in normal volunteers and current addictive disease patients along with former addicts in treatment, to investigate differential pharmacodynamics and responsiveness of molecular targets, in particular those also investigated in the experimental and molecular genetic approaches as described above.

Opioids, dopamine, stress, and the addictions

The articulated goals of Dialogues in Clinical Neuroscience are to serve as "an interface between clinical neuropsychiatry and the neurosciences by providing state-of-the-art information and original insights into relevant clinical, biological, and therapeutic aspects." My laboratory the Laboratory of the Biology of Addictive Diseases at The Rockefeller University, has for years been focused on "bidirectional translational research," that is, learning by careful observations and study in patient populations with the disorders under study, in this case primarily specific addictive diseases, and then using that knowledge to create improved animal models or other laboratory-based research paradigms, while, at the same time, taking research findings made at the bench into the clinic as promptly as that is appropriate and feasible. In this invited review, therefore, the focus will be on perspectives of our Laboratory of the Biology of Addictive Diseases and related National Institutes of Health/National Institute on Drug Abuse research Center, including laboratory-based molecular neurobiological research, research using several animal models designed to mimic human patterns of drug abuse and addiction, as well as basic clinical research, intertwined with treatment-related research.

Preprodynorphin mediates locomotion and D2 dopamine and mu-opioid receptor changes induced by chronic 'binge' cocaine administration

Evidence suggests that the kappa-opioid receptor (KOP-r) system plays an important role in cocaine addiction. Indeed, cocaine induces endogenous KOP activity, which is a mechanism that opposes alterations in behaviour and brain function resulting from repeated cocaine use. In this study, we have examined the influence of deletion of preprodynorphin (ppDYN) on cocaine-induced behavioural effects and on hypothalamic-pituitary-adrenal axis activity. Furthermore, we have measured mu-opioid receptor (MOP-r) agonist-stimulated [(35)S]GTPgammaS, dopamine D(1), D(2) receptor and dopamine transporter (DAT) binding. Male wild-type (WT) and ppDYN knockout (KO) mice were injected with saline or cocaine (45 mg/kg/day) in a 'binge' administration paradigm for 14 days. Chronic cocaine produced an enhancement of locomotor sensitisation in KO. No genotype effect was found on stereotypy behaviour. Cocaine-enhanced MOP-r activation in WT but not in KO. There was an overall decrease in D(2) receptor binding in cocaine-treated KO but not in WT mice. No changes were observed in D(1) and DAT binding. Cocaine increased plasma corticosterone levels in WT but not in KO. The data confirms that the endogenous KOP system inhibits dopamine neurotransmission and that ppDYN may mediate the enhancement of MOP-r activity and the activation of the hypothalamic-pituitary-adrenal axis after chronic cocaine treatment.