Subsynaptic Distribution,Lipid Raft Targeting and G Protein-Dependent Signalling of the Type 1 Cannabinoid Receptor in Synaptosomes from the Mouse Hippocampus and Frontal Cortex

Numerous studies have investigated the roles of the type 1 cannabinoid receptor (CB1) in glutamatergic and GABAergic neurons. Here, we used the cell-type-specific CB1 rescue model in mice to gain insight into the organizational principles of plasma membrane targeting and Gαi/o protein signalling of the CB1 receptor at excitatory and inhibitory terminals of the frontal cortex and hippocampus. By applying biochemical fractionation techniques and Western blot analyses to synaptosomal membranes, we explored the subsynaptic distribution (pre-, post-, and extra-synaptic) and CB1 receptor compartmentalization into lipid and non-lipid raft plasma membrane microdomains and the signalling properties. These data infer that the plasma membrane partitioning of the CB1 receptor and its functional coupling to Gαi/o proteins are not biased towards the cell type of CB1 receptor rescue. The extent of the canonical Gαi/o protein-dependent CB1 receptor signalling correlated with the abundance of CB1 receptor in the respective cell type (glutamatergic versus GABAergic neurons) both in frontal cortical and hippocampal synaptosomes. In summary, our results provide an updated view of the functional coupling of the CB1 receptor to Gαi/o proteins at excitatory and inhibitory terminals and substantiate the utility of the CB1 rescue model in studying endocannabinoid physiology at the subcellular level.     

A new tetracyclic saponin from Astragalus glycyphyllos L. and its neuroprotective and hMAO-B inhibiting activity

Abstract

A new tetracyclic saponin, 17(R),20(R)-3β,6α,16β-trihydroxycycloartanyl-23-carboxylic acid 16-lactone 3-O-β-D-glucopyranoside (1) together with one known flavonoid, camelliaside A (2) were isolated from the aerial parts of Astragalus glycyphyllos L. Their structures were determined by chemical, HRESIMS and NMR methods. On 6-hydroxydopamine in vitro model on isolated rat brain synaptosomes, compounds 1–2 had statistically significant neuroprotective activity similar to that of Silibinin, tested at 100?μM. Saponin 1 possessed the most prominent neuroprotective and antioxidant effects in this in vitro model. On human recombinant monoamine oxidase type B enzyme compound 1 displayed strong inhibiting activity, compared to Selegiline (1?μM). It could be concluded that the new epoxycycloartane saponin 1 could be a promising leading structure in respect of neurodegenerative diseases.