Cocaine addiction is thought to involve persistent neurobiological changes that facilitate relapse to drug use despite efforts to abstain. But the propensity for relapse may be reduced by extinction training--a form of inhibitory learning that progressively reduces cocaine-seeking behaviour in the absence of cocaine reward. Here we show that extinction training during withdrawal from chronic cocaine self-administration induces experience-dependent increases in the GluR1 and GluR2/3 subunits of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate) glutamate receptors in the nucleus accumbens shell, a brain region that is critically involved in cocaine reward. Increases in the GluR1 subunit are positively associated with the level of extinction achieved during training, suggesting that GluR1 may promote extinction of cocaine seeking. Indeed, viral-mediated overexpression of both GluR1 and GluR2 in nucleus accumbens shell neurons facilitates extinction of cocaine- but not sucrose-seeking responses. A single extinction training session, when conducted during GluR subunit overexpression, attenuates stress-induced relapse to cocaine seeking even after GluR overexpression declines. Our findings indicate that extinction-induced plasticity in AMPA receptors may facilitate control over cocaine seeking by restoring glutamatergic tone in the nucleus accumbens, and may reduce the propensity for relapse under stressful situations in prolonged abstinence.

Both D(1) and D(2) receptors in the NAc play a prominent, and perhaps cooperative, role in regulating cocaine-taking and cocaine-seeking behaviors.

The endocannabinoid system has been suggested to elicit signals that defend against several disease states including excitotoxic brain damage. Besides direct activation with CB 1 receptor agonists, cannabinergic signaling can be modulated through inhibition of endocannabinoid transport and fatty acid amide hydrolase (FAAH), two mechanisms of endocannabinoid inactivation. To test whether the transporter and FAAH can be targeted pharmacologically to modulate survival/repair responses, the transport inhibitor N-(4-hydroxyphenyl)-arachidonamide (AM404) and the FAAH inhibitor palmitylsulfonyl fluoride (AM374) were assessed for protection against excitotoxicity in vitro and in vivo. AM374 and AM404 both enhanced mitogen-activated protein kinase (MAPK) activation in cultured hippocampal slices. Interestingly, combining the distinct inhibitors produced additive effects on CB 1 signaling and associated neuroprotection. After an excitotoxic insult in the slices, infusing the AM374/AM404 combination protected against cytoskeletal damage and synaptic decline, and the protection was similar to that produced by the stable CB 1 agonist AM356 (R-methanandamide). AM374/ AM404 and the agonist also elicited cytoskeletal and synaptic protection in vivo when coinjected with excitotoxin into the dorsal hippocampus. Correspondingly, potentiating endocannabinoid responses with the AM374/AM404 combination prevented behavioral alterations and memory impairment that are characteristic of excitotoxic damage. The protective effects mediated by AM374/AM404 were (1) evident 7 d after insult, (2) correlated with the preservation of CB 1 -linked MAPK signaling, and (3) were blocked by a selective CB 1 antagonist. These results indicate that dual modulation of the endocannabinoid system with AM374/AM404 elicits neuroprotection through the CB 1 receptor. The transporter and FAAH are modulatory sites that may be exploited to enhance cannabinergic signaling for therapeutic purposes.

The endocannabinoid system's biological significance continues to grow as novel endocannabinoid metabolites are discovered. Accordingly, a myopic view of the system that focuses solely on one or two endocannabinoids, such as anandamide or 2-arachidonoyl glycerol, is insufficient to describe the biological responses to perturbations of the system. Rather, the endocannabinoid metabolome as a whole must be analyzed. The work described here is based on liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry. This method has been validated to quantify, in a single chromatographic run, the levels of 15 known or suspected metabolites of the endocannabinoid system in the rat brain and is applicable to other biological matrixes. We have obtained an endocannabinoid profile specifically for the frontal cortex of the rat brain and have determined anandamide level differences following the administration of the fatty acid amide hydrolase inhibitor AM374.