Cannabinoid receptors and the proconvulsant effect of toxoplasmosis in mice

The effects of leptin and cannabinoid CB1 receptor agonist/antagonist in cerebral tissues of epileptic rats

OBJECTIVE

In this study, the effects of leptin, cannabinoid-1 (CB1) receptor agonist ACEA and antagonist AM251, and the interactions between leptin and CB1 receptor agonist/antagonist on oxidant and antioxidant enzymes in the cerebrum, cerebellum, and pedunculus cerebri tissue samples were investigated in the penicillin-induced epileptic model.

METHODS

Male Wistar albino rats (n=56) were included in this study. In anesthetized animals, 500 IU penicillin-G potassium was injected into the cortex to induce epileptiform activity. Leptin (1 μg), ACEA (7.5 μg), AM251 (0.25 μg), and the combinations of the leptin+ACEA and leptin+AM251 were administered intracerebroventricularly (i.c.v.) after penicillin injections. Malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPx) levels were measured in the cerebral tissue samples and plasma with the ELISA method.

RESULTS

MDA levels increased, while SOD and GPx levels decreased after penicillin injection in the cerebrum and cerebellum. The efficacy of penicillin on SOD, MDA and GPx levels was further enhanced after leptin or AM251 injections. Whereas, ACEA decreased the MDA levels and increased GPx levels compared with the penicillin group. Administration of AM251+leptin did not change any oxidation parameter compared with the AM251. Furthermore, co-administration of ACEA and leptin significantly increased oxidative stress compared with the ACEA-treated group by increasing MDA and decreasing GPx levels.

CONCLUSION

It was concluded that leptin reversed the effect of ACEA on oxidative stress. Co-administration of AM251 and leptin did not change oxidative stress compared with the AM251-treated group suggesting AM251 and leptin affect oxidative stress using the same pathways.

CB2 receptor in the CNS: from immune and neuronal modulation to behavior

Despite low levels of cannabinoid receptor type 2 (CB2R) expression in the central nervous system in human and rodents, a growing body of evidence shows CB2R involvement in many processes at the behavioral level, through both immune and neuronal modulations. Recent in vitro and in vivo evidence have highlighted the complex role of CB2R under physiological and inflammatory conditions. Under neuroinflammatory states, its activation seems to protect the brain and its functions, making it a promising target in a wide range of neurological disorders. Here, we provide a complete and updated overview of CB2R function in the central nervous system of rodents, spanning from modulation of immune function in microglia but also in other cell types, to behavior and neuronal activity, in both physiological and neuroinflammatory contexts.

Prolonged Activation of Brain CB2 Signaling Modulates Hypothalamic Microgliosis and Astrogliosis in High Fat Diet-Fed Mice

Low-grade inflammation of the hypothalamus is associated with the disturbance of energy balance. The endocannabinoid system has been implicated in the development and maintenance of obesity as well as in the control of immune responses. The type 2 cannabinoid receptor (CB2) signaling has been associated with anti-inflammatory effects. Therefore, in high fat diet (HFD)-induced obese mice, we modulated CB2 signaling and investigated its effects on energy homeostasis and hypothalamic microgliosis/astrogliosis. We observed no effect on caloric intake and body weight gain in control diet-fed animals that received prolonged icv infusion of the CB2 receptor agonist HU308. Interestingly, we observed a decrease in glucose tolerance in HFD-fed animals treated with HU308. Prolonged icv infusion of HU308 increases astrogliosis in the ventromedial nucleus (VMH) of obese animals and reduced HFD-induced microgliosis in the hypothalamic arcuate (ARC) but not in the paraventricular (PVN) or VMH nuclei. These data indicate that central CB2 signaling modulates glucose homeostasis and glial reactivity in obesogenic conditions, irrespective of changes in body weight.

Modulation of mRNA Expression of Monoacylglycerol Lipase, Diacylglycerol Lipase and Cannabinoid Receptor-1 in Mice Experimentally Infected with T. gondii

Toxoplasma gondii, an obligate intracellular parasite, infects more than 30% of world's population. This parasite is considered to be neurotropic, and has high tropism for the central nervous system, and potentially induces cryptogenic epilepsy by no clear mechanism. The current study aimed to investigate the alteration of the main components of the endocannabinoid signaling systems in T. gondii-infected mice. For this purpose, the levels of mRNA expression of monoacylglycerol lipase (MAGL), diacylglycerol lipase (DAGL) and cannabinoid receptor-1 (CB1), were measured by quantitative real time PCR.The mRNA expression level of MAGL was increased by ~ 8-fold in the brains of the Toxoplasma-infected group in comparison with non-infected mice (P<0.0001). The mRNA expression of CB1 gene in the brain of the infected mice was ~ 2 times higher than that measured in control group (P<0.01). The mRNA expression level of DAGL remained unchanged in the infected mice. Overall a substantial increase in MAGL and CB1 expression without any changes in DAGL, in the brain of infected mice suggests that T. gondii disturbs the endocannabinoid signaling pathways, which are known as neurotransmitter modulators involved in epilepsy.

The ω-3 endocannabinoid docosahexaenoyl ethanolamide reduces seizure susceptibility in mice by activating cannabinoid type 1 receptors

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are the most recognized omega-3 unsaturated fatty acids showing neuroprotective activity in animal and clinical studies. Docosahexaenoyl ethanolamide (DHEA) and eicosapentaenoyl ethanolamide (EPEA) are non-oxygenated endogenous metabolites of DHA and EPA, which might be in charge of the anti-seizure activity of the parent molecules. We examined the effect of these metabolites on the threshold of clonic seizures induced by pentylenetetrazole (PTZ). DHEA and EPEA possess similar chemical structure to the endogenous cannabinoids. Therefore, involvement of cannabinoid (CB) receptors in the anti-seizure effect of these metabolites was also investigated. DHA, DHEA, EPEA, AM251 (CB1 receptor antagonist), and AM630 (CB2 receptor antagonist) were administered to mice by intracerebroventricular (i.c.v.) route. Threshold of clonic seizures was determined 10 and/or 15 min thereafter by intravenous infusion of PTZ. The effect of DHA and DHEA on seizure threshold was then determined in mice, which were pretreated with AM251 and/or AM630. DHA (300μM), and DHEA (100 and 300 μM) significantly increased seizure threshold, 15 (p < 0.05) and 10 min (p < 0.01) after administration, respectively. DHEA was more potent than its parent lipid, DHA in decreasing seizure susceptibility. EPEA (300 and 1000 μM) did not change seizure threshold. AM251 fully prevented the increasing effect of DHA and DHEA on seizure threshold (p < 0.05). AM630 did not inhibit the effect of DHA and DHEA on seizure threshold. This is the first report indicating that DHEA but not EPEA, possesses anti-seizure action via activating CB1 receptors. DHEA is more potent than its parent ω-3 fatty acid DHA in diminishing seizure susceptibility.