Neuropathic pain is a clinical manifestation of nerve injury difficult to treat even with potent analgesic compounds. Here, we used different lines of genetically modified mice to clarify the role played by CB 2 cannabinoid receptors in the regulation of the central immune responses leading to the development of neuropathic pain. CB 2 knock-out mice and wild-type littermates were exposed to sciatic nerve injury, and both genotypes developed a similar hyperalgesia and allodynia in the ipsilateral paw. Most strikingly, knock-outs also developed a contralateral mirror image pain, associated with an enhanced microglial and astrocytic expression in the contralateral spinal horn. In agreement, hyperalgesia, allodynia, and microglial and astrocytic activation induced by sciatic nerve injury were attenuated in transgenic mice overexpressing CB 2 receptors. These results demonstrate the crucial role of CB 2 cannabinoid receptor in modulating glial activation in response to nerve injury. The enhanced manifestations of neuropathic pain were replicated in irradiated wild-type mice reconstituted with bone marrow cells from CB 2 knock-outs, thus demonstrating the implication of the CB 2 receptor expressed in hematopoietic cells in the development of neuropathic pain at the spinal cord.

We aimed to investigate the effect of atorvastatin (5 and 30 mg/kg/day for 2 weeks) on hepatic lipid metabolism in a well established model of dietary hypertriglyceridemia, the fructosefed rat. Fructose feeding (10% fructose in drinking water for 2 weeks) induced hepatic lipogenesis and reduced peroxisome proliferator-activated receptor ␣ (PPAR␣) expression and fatty acid oxidation. As a result, plasma and liver triglyceride and plasma apolipoprotein B (apoB) levels were increased. Atorvastatin, 5 and 30 mg/kg during 2 weeks, markedly reduced plasma triglyceride, but decreased apoB levels only at the highest dose tested (50%). Triglyceride biosynthetic enzymes and microsomal triglyceride transfer protein were unchanged, whereas liver PPAR␣, acyl-CoA oxidase, and carnitine palmitoyltransferase I mRNA levels (1.9-, 1.25-, and 3.4-fold, respectively) and hepatic fatty acid ␤-oxidation activity (1.25-fold) were increased by atorvastatin at 30 mg/kg. Furthermore, hepatic triglyceride content (45%) and plasma nonesterified fatty acids (NEFAs) (49%) were reduced. These results show for the first time that liver triglyceride increase in fructose-fed rats is linked to decreased expression of PPAR␣, which is prevented by atorvastatin treatment. The increase in PPAR␣ expression caused by atorvastatin was associated with reduced liver triglyceride and plasma NEFA levels.

Nerve injuries often lead to neuropathic pain syndrome. The mechanisms contributing to this syndrome involve local inflammatory responses, activation of glia cells, and changes in the plasticity of neuronal nociceptive pathways. Cannabinoid CB 2 receptors contribute to the local containment of neuropathic pain by modulating glial activation in response to nerve injury. Thus, neuropathic pain spreads in mice lacking CB 2 receptors beyond the site of nerve injury. To further investigate the mechanisms leading to the enhanced manifestation of neuropathic pain, we have established expression profiles of spinal cord tissues from wild-type and CB 2 -deficient mice after nerve injury. An enhanced interferon-␥ (IFN-␥) response was revealed in the absence of CB 2 signaling. Immunofluorescence stainings demonstrated an IFN-␥ production by astrocytes and neurons ispilateral to the nerve injury in wild-type animals. In contrast, CB 2 -deficient mice showed neuronal and astrocytic IFN-␥ immunoreactivity also in the contralateral region, thus matching the pattern of nociceptive hypersensitivity in these animals. Experiments in BV-2 microglia cells revealed that transcriptional changes induced by IFN-␥ in two key elements for neuropathic pain development, iNOS (inducible nitric oxide synthase) and CCR2, are modulated by CB 2 receptor signaling. The most direct support for a functional involvement of IFN-␥ as a mediator of CB 2 signaling was obtained with a double knock-out mouse strain deficient in CB 2 receptors and IFN-␥. These animals no longer show the enhanced manifestations of neuropathic pain observed in CB 2 knock-outs. These data clearly demonstrate that the CB 2 receptor-mediated control of neuropathic pain is IFN-␥ dependent.

The aim of this study was to examine the role of fatty acid amide hydrolase (FAAH) on ethanol sensitivity, preference, and dependence. The deletion of FAAH gene or the inhibition of FAAH by carbamoyl‐biphenyl‐3‐yl‐cyclohexylcarbamate (URB597) (0.1 mg/kg) markedly increased the preference for ethanol. The study further reveals that URB597 specifically acts through FAAH and that cannabinoid‐1 (CB1) receptor is critical for N‐arachidonoyl ethanolamide (AEA) mediated ethanol‐reinforced behavior as revealed by lack of URB597 effect in both FAAH and CB1−/− mice compared with vehicle‐treated −/− mice. The FAAH −/− mice displayed a lower sensitivity to hypothermic and sedative effects to acute ethanol challenge. The FAAH −/− mice also exhibited a reduction in the severity of handling‐induced convulsions following withdrawal from chronic ethanol exposure. The CB1 receptor and proenkephalin gene expressions, and CB1 receptor and μ‐opioid (MO) receptor‐mediated G‐protein activation were found to be significantly lower in the caudate‐putamen, nucleus accumbens core and shell of FAAH −/− than +/+ mice. Interestingly, the MO receptor‐stimulated G‐protein signaling was greater in the striatum of FAAH −/− than +/+ mice following voluntary ethanol consumption. These findings suggest that an elevation in the AEA content and its action on the limbic CB1 receptor and MO receptor might contribute to ethanol‐reinforced behavior. Treatment with drugs that decrease AEA tone might prove useful in reducing excessive ethanol consumption.

1 Old rats are resistant to fibrate-induced hypolipidemia owing to a reduction in hepatic peroxisome proliferator-activated receptor a (PPARa). We tested whether the age-related decrease in PPARa is prevented by atorvastatin (ATV), a hypolipidemic statin. 2 We determined the activity and expression of Liver X receptor a (LXRa) and PPARa in the liver of 18-month-old rats treated with 10 mg kg À1 of ATV for 21 days. We measured fatty acid oxidation (FAO), the expression of PPARa-target genes, liver triglyceride (TG) and cholesteryl ester (CE) contents and plasma concentrations of TG, cholesterol, glucose, nonesterified fatty acids (NEFA), insulin and leptin. While old female rats were practically unresponsive, ATV-treated old males showed lower liver TG (À41%) and CE (À48%), and plasma TG (À35%), glucose (À18%) and NEFA (À39%). Age-related alterations in LXRa expression and binding activity were reverted in ATVtreated old males. These changes were related to an increase in hepatic FAO (1.2-fold), and PPARa mRNA (2.2-fold), PPARa protein (1.6-fold), and PPARa-binding activity. 3 Hepatic nuclear factor-4 (HNF-4) and chicken ovalbumin upstream-transcription factor-II participate in the transcriptional regulation of the PPARa gene, while peroxisome proliferatoractivated receptor gamma coactivator 1 (PGC-1) behaves as a PPAR coactivator. Ageing reduced the hepatic content of HNF-4 (74%) and PGC-1 (77%) exclusively in male rats. ATV administration to old males enhanced the hepatic expression and binding activity (two-fold) of HNF-4. 4 ATV-induced changes in hepatic HNF-4 and PPARa may be responsible for the improvement of the lipid metabolic phenotype produced by ATV administration to senescent male rats.