Effects of spatial memory on morphine CPP and locomotor sensitization in mice

1H Nuclear Magnetic Resonance (NMR)-Based Metabolic Changes in Nucleus Accumbens and Medial Prefrontal Cortex Following Administration of Morphine in Mice

INTRODUCTION

It is well known that opiate addiction is a neurobiological disease associated with dysregulation of multiple neurotransmitters and neurochemicals. Previous ex-vivo 1H nuclear magnetic resonance (NMR) studies have yielded mixed findings concerning opiate-induced neurometabolic changes at key reward-addiction sites. Whether such changes reflect the conditions in a live animal remains unknown. The present study was therefore designed to fill this knowledge gap by determining the effects of morphine-induced neurometabolic changes under in-vivo conditions.

METHODS

In-vivo 1H NMR spectroscopy (SA Instruments, Stony Brook, NY) was used to measure neurochemical changes in nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) of mice, subjected to twice-daily injections of morphine (10 mg kg-1 s.c.) for five days.

RESULTS

Morphine induced significant changes in the concentrations of a number of metabolites in both mPFC and NAc. The glutamine component of the glutamine-glutamate-GABA excitatory-inhibitory cycle, increased in both mPFC and NAc. Significant increase in glutamate was also observed at mPFC, but not in NAc. The phosphocreatine, marker for energy metabolism, and the N-acetylaspartate marker for neuronal viability and energy metabolism decreased significantly in both mPFC and NAc. Glycerophosphocholine + phosphocholine, markers for cell membrane integrity, increased significantly in both NAc and mPFC after morphine. The antioxidant neurometabolites taurine and glutathione increased significantly in NAc; however, taurine decreased, and glutathione was unchanged in mPFC after morphine. Inositol, a marker for neuroinflammation, increased significantly in NAc.

CONCLUSION

The present study is the first in-vivo 1H NMR spectroscopy in mice to demonstrate morphine-induced dysregulation of multiple metabolites and neurochemicals within the reward-addiction neurocircuitry.

Zebrafish models relevant to studying central opioid and endocannabinoid systems

The endocannabinoid and opioid systems are two interplaying neurotransmitter systems that modulate drug abuse, anxiety, pain, cognition, neurogenesis and immune activity. Although they are involved in such critical functions, our understanding of endocannabinoid and opioid physiology remains limited, necessitating further studies, novel models and new model organisms in this field. Zebrafish (Danio rerio) is rapidly emerging as one of the most effective translational models in neuroscience and biological psychiatry. Due to their high physiological and genetic homology to humans, zebrafish may be effectively used to study the endocannabinoid and opioid systems. Here, we discuss current models used to target the endocannabinoid and opioid systems in zebrafish, and their potential use in future translational research and high-throughput drug screening. Emphasizing the high degree of conservation of the endocannabinoid and opioid systems in zebrafish and mammals, we suggest zebrafish as an excellent model organism to study these systems and to search for the new drugs and therapies targeting their evolutionarily conserved mechanisms.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 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, drug abuse and alcohol, 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.

CCR5 mediates HIV-1 Tat-induced neuroinflammation and influences morphine tolerance, dependence, and reward

The HIV-1 regulatory protein, trans-activator of transcription (Tat), interacts with opioids to potentiate neuroinflammation and neurodegeneration within the CNS. These effects may involve the C-C chemokine receptor type 5 (CCR5); however, the behavioral contribution of CCR5 on Tat/opioid interactions is not known. Using a transgenic murine model that expresses HIV-1 Tat protein in a GFAP-regulated, doxycycline-inducible manner, we assessed morphine tolerance, dependence, and reward. To assess the influence of CCR5 on these effects, mice were pretreated with oral vehicle or the CCR5 antagonist, maraviroc, prior to morphine administration. We found that HIV-1 Tat expression significantly attenuated the antinociceptive potency of acute morphine (2-64 mg/kg, i.p.) in non-tolerant mice. Consistent with this, Tat attenuated withdrawal symptoms among morphine-tolerant mice. Pretreatment with maraviroc blocked the effects of Tat, reinstating morphine potency in non-tolerant mice and restoring withdrawal symptomology in morphine-tolerant mice. Twenty-four hours following morphine administration, HIV-1 Tat significantly potentiated (∼3.5-fold) morphine-conditioned place preference and maraviroc further potentiated these effects (∼5.7-fold). Maraviroc exerted no measurable behavioral effects on its own. Protein array analyses revealed only minor changes to cytokine profiles when morphine was administered acutely or repeatedly; however, 24 h post morphine administration, the expression of several cytokines was greatly increased, including endogenous CCR5 chemokine ligands (CCL3, CCL4, and CCL5), as well as CCL2. Tat further elevated levels of several cytokines and maraviroc pretreatment attenuated these effects. These data demonstrate that CCR5 mediates key aspects of HIV-1 Tat-induced alterations in the antinociceptive potency and rewarding properties of opioids.