Influence of age, postmortem delay and freezing storage period on cannabinoid receptor density and functionality in human brain

It has been suggested that cannabimimetic drugs could be of interest in the treatment of several nervous disorders. Thus, it is important to analyse the distribution and properties of cannabinoid (CB) receptors directly in human brain. As postmortem human tissue is subjected to the effects of several biological variables, we have analyzed by autoradiography the influence of age, postmortem delay and freezing storage period (at -25 degrees C) on two parameters corresponding to cannabinoid CB1 receptors in human frontal cortex: receptor density and degree of activation of G-proteins ([35S]GTPgammaS assays). A significant decrease in the amount of both receptor density and agonist-stimulated G-protein activity was observed with age, revealing a mean reduction of about 10% per decade. In contrast, no significant correlations were found with postmortem delay either for CB1 receptors density or functionality. Finally, both parameters (receptor density and [35S]GTPgammaS response) were significantly reduced with freezing storage period at -25 degrees C in frontal cortical layers. Non-linear analysis of these data yielded values between 12 and 24 months of storage for a 50% reduction. In conclusion, when studying CB1 receptor properties in human brain samples, a careful analysis (and matching) for variables such as age and freezing storage period has to be carried out.