Functional Autoradiography Shows Unaltered Cannabinoid CB1 Receptor Signalling in Hippocampus and Cortex of APP/PS1 Transgenic Mice

Abstract

The cannabinoid CB1-receptor is among the most abundant G-protein-coupled receptors in the mammalian brain. Whereas post-mortem studies in Alzheimer's disease (AD) brains compared to age-matched controls have reported decreased CB1-receptor binding but no change in their protein levels (immunoreactivity), decreased or increased CB1- receptor protein levels have been reported in APP/PS1 transgenic mice modelling AD. To complete the picture, the present study used functional autoradiography to assess CB1-receptor-dependent G(i) protein activation in the hippocampus, entorhinal cortex and medial frontal cortex of 13- to 14-month-old female APPswe/PS1dE9 transgenic and wild-type littermate control mice. The mouse brains were processed for [³⁵S]GTPλS autoradiography so that brain sections were analysed in pairs of one transgenic and one control mouse brain. The autoradiography protocol was completed for each pair both in the absence and presence of dithiotreitol (DTT) to reveal possible redox-dependent alterations in CB1 receptor function. Five treatments were used: baseline, incubation with 10 μM GTPλS to assess nonspecific binding, and CB1 receptor agonist CP55,940 in three concentrations. By and large we found no statistically significant differences between the APP/PS1 transgenic and control mice in CB1 receptor signalling. The only exception was a modest redox-dependent alteration in entorhinal cortical CB1 receptors between the genotypes. Thus, in accordance with the majority of earlier human AD findings, we did not find evidence for notable changes in the number of functional CB1 receptors in the common APPswe/PS1dE9 mouse model of AD.