In this study, we investigated the effects of enhancement of endocannabinoid and cholinergic neurotransmitter system separately and simultaneously using donepezil (cholinesterase inhibitor) and URB-597 (endocannabinoid degrading enzyme inhibitor) on anxiety-like behavior. Key findings of this study included: (1) Injection of three doses of URB-597(cannabinoid-degrading enzyme inhibitor) reduced anxiety. (2) Administering doses of 0.5, 1 or 2 of donepezil (cholinesterase inhibitor) decreased anxiety (3) Coadministation of donepezil and URB597 at low, medium and high doses did not affect the number of open arms entries, but reduced the number of entries to the closed arms.
The results of URB-597 injection showed that different doses of URB-597 increased the number and time spent of open arms, decreased the number and time spent of closed arms and increased the percentage the number and time spent of open arms to closed arms. Taken together, these results indicate the anxiolytic effect of this drug. However, there was no significant difference between the doses used but doses of 0.3 mg/kg and 0.1 mg/kg had more significant effect on some parameters than dose group 1mg/kg.
These results are consistent with the other results regarding a role in the modulation of anxiolytic effects of cannabinoids by type 1 receptor (CB1) [19]. Another study showed contradictory result for example cannabinoid receptor agonists (CP55940, WIN55212-2) produced anxiolytic effects in mice only at low doses [20] whereas at higher doses had anxiogenic effect [21]. Other contradictions are the natural compound in the cannabis plant (Delta 9-tetrahydrocannabinol) that produced an anxiolytic effect in mice in the light-dark test [27] while in the same test had anxiolytic effect [28].
It has also been reported that WIN 55,212-2 drug in mice reduces anxiety by intervention in GABAergic transmission, whereas it increases anxiety through intervention in glutamatergic synaptic transmission [29]. The anxiolytic effects created by URB-597 are also similar to the anxiolytic effect of diazepam. According to the pervious report, administration of URB-597 may interfere with GABAergic transmission [30].
The results regarding donepezil at doses of 0.5, 1, or 2 showed that it increased the number and the time spent of open arms and decreased the number and time spent of closed arms. The high dose of donepezil had no significant effect on the total number of mice entering the open and closed arms of the maze compared to the control group. The administration of different doses of donepezil also increased the percentage of open arms to closed arms and increased the percentage of time spent in open arms to closed arms.
Overall, donepezil as a cholinergic system, has anxiolytic effect. These results are consistent with previous studies in which administration of scopolamine (a muscarinic receptor antagonist) in mice produced anxiogenic effect [31, 32]. In contrast, administration of type 1 muscarinic (Xanomeline) [33] or nicotine receptors agonists has anxiolytic effect [34]. Further studies are needed to clarify the contribution of each of these receptors more precisely.
The results of coadministration URB-597 with donepezil at low, medium and high doses, did not affect the number of open arms entries, while reducing the number or spending time of closed arms entry. The anxiolytic effect observed in the simultaneous administration of the above drugs is lower than the anxiolytic effect of each drug alone. There is no study about interaction these systems in anxiety-like behavior. In memory studies showed the interaction between cannabinoid (WIN-2; a synthetic cannabinoid) and cholinergic systems (acetylcholinesterase inhibitor) on memory, showed that WIN-2 significantly decreased rates of hippocampal principal cells performance and that rivastigmine reversed these short memory deficits and normalized hippocampal discharge rates [35].