Attenuation of opioid tolerance by antisense oligodeoxynucleotides targeting neurogranin

Neurogranin in the nucleus accumbens regulates NMDA receptor tolerance and motivation for ethanol seeking

Dysfunction of N-methyl-d-aspartate receptor (NMDAR) signaling in the nucleus accumbens (NAc) has been implicated in the pathophysiology of alcohol use disorders (AUD). Neurogranin (Ng), a calmodulin-binding protein, is exclusively expressed in the post-synapse, and mediates NMDAR driven synaptic plasticity by regulating the calcium-calmodulin (Ca²⁺-CaM) pathway. To study the functional role of Ng in AUD, we administrated behavior tests including Pavlovian instrument transfer (PIT), operant conditioning, and rotarod test using Ng null mice (Ng^-/- mice). We used adeno-associated virus (AAV)-mediated Ng expression and pharmacological manipulation to validate behavioral responses in Ng^-/- mice. The results from our multidisciplinary approaches demonstrated that deficit of Ng increases tolerance to NMDAR inhibition and elicit faster cue reactivity during PIT without changes in ethanol reward. Operant conditioning results demonstrated that Ng^-/- mice self-administered significantly more ethanol and displayed reduced sensitivity to aversive motivation. We identified that ethanol exposure decreases mGluR5 (metabotropic glutamate receptor 5) expression in the NAc of Ng^-/- mice and pharmacological inhibition of mGluR5 reverses NMDAR desensitization in Ng^-/- mice. Together these findings specifically suggest that accumbal Ng plays an essential role in the counterbalance between NMDAR and mGluR5 signaling; which alters NMDAR resistance, and thereby altering aversive motivation for ethanol and may ultimately contribute to susceptibility for alcohol addiction.

Curcumin attenuates opioid tolerance and dependence by inhibiting Ca2+/calmodulin-dependent protein kinase II α activity

Chronic use of opioid analgesics has been hindered by the development of opioid addiction and tolerance. We have reported that curcumin, a natural flavonoid from the rhizome of Curcuma longa, attenuated opioid tolerance, although the underlying mechanism remains unclear. In this study, we tested the hypothesis that curcumin may inhibit Ca(2+)/calmodulin-dependent protein kinase II α (CaMKIIα), a protein kinase that has been previously proposed to be critical for opioid tolerance and dependence. In this study, we used state-of-the-art polymeric formulation technology to produce poly(lactic-co-glycolic acid) (PLGA)-curcumin nanoparticles (nanocurcumin) to overcome the drug's poor solubility and bioavailability, which has made it extremely difficult for studying in vivo pharmacological actions of curcumin. We found that PLGA-curcumin nanoparticles reduced the dose requirement by 11- to 33-fold. Pretreatment with PLGA-curcumin (by mouth) prevented the development of opioid tolerance and dependence in a dose-dependent manner, with ED50 values of 3.9 and 3.2 mg/kg, respectively. PLGA-curcumin dose-dependently attenuated already-established opioid tolerance (ED50 = 12.6 mg/kg p.o.) and dependence (ED50 = 3.1 mg/kg p.o.). Curcumin or PLGA-curcumin did not produce antinociception by itself or affect morphine (1-10 mg/kg) antinociception. Moreover, we found that the behavioral effects of curcumin on opioid tolerance and dependence correlated with its inhibition of morphine-induced CaMKIIα activation in the brain. These results suggest that curcumin may attenuate opioid tolerance and dependence by suppressing CaMKIIα activity.

Ca2+/calmodulin-dependent protein kinase II alpha is required for the initiation and maintenance of opioid-induced hyperalgesia

Repeated administration of opioids not only leads to tolerance and dependence, but also results in nociceptive enhancement called opioid-induced hyperalgesia (OIH). Nociceptive mediators involved in OIH generation remain poorly understood. In the present study, we tested the hypothesis that Ca(2+)/calmodulin-depent protein kinase II (CaMKIIalpha) is critical for OIH. Opioid-induced hyperalgesia was produced by repeated morphine administration or pellet implantation in mice. Correlating with the development of tactile allodynia and thermal hyperalgesia, spinal CaMKIIalpha activity was significantly increased in OIH. KN93, a CaMKII inhibitor, dose- and time-dependently reversed OIH and CaMKII activation without impairing locomotor coordination. To elucidate the specific CaMKII isoform involved, we targeted CaMKIIalpha by using small interfering RNA and demonstrated that knockdown of spinal CaMKIIalpha attenuated OIH. Furthermore, morphine failed to induce OIH in CaMKIIalpha(T286A) point mutant mice, although wild-type littermate mice developed robust OIH after repeated treatments with morphine. These data implicate, for the first time, an essential role of CaMKIIalpha as a cellular mechanism leading to and maintaining opioid-induced hyperalgesia.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 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 neurological 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).

Disruption of acute opioid dependence by antisense oligodeoxynucleotides targeting neurogranin

Neurogranin has been suggested to serve as a common regulator synchronizing the activities of PKC and CaMKII in acute opioid tolerance. To examine if a similar mechanism exists in acute opioid dependence, we directly targeted neurogranin using antisense oligodeoxynucleotides. Male ICR mice were pretreated with neurogranin antisense or mismatch oligodeoxynucleotides (2 microg/day, i.c.v.) for 3 consecutive days. On Day 4, morphine (100 mg/kg, s.c.) was used to induce dependence, as revealed by naloxone-precipitated withdrawal in saline or mismatch-pretreated mice. Antisense-pretreated mice showed decreased neurogranin expression, lack of morphine-induced phosphorylation of neurogranin and activation of CaMKII and CREB, and absence of naloxone-induced withdrawal jumping. Taken together, these data suggest that neurogranin plays an essential role in acute opioid dependence, possibly by affecting the CaMKII and CREB signaling pathway.