Peripherally restricted cannabinoid type 1 receptor (CB1R) antagonist, AM6545, potentiates stress-induced hypothalamic-pituitary-adrenal axis activation via a non-CB1R mechanism

Sub-chronic administration of AM6545 enhances cognitive performance and induces hippocampal synaptic plasticity changes in naïve mice

BACKGROUND AND PURPOSE

There is evidence of crosstalk between the brain and peripheral tissues. However, how the periphery contributes to brain function is not well understood. The cannabinoid CB1 receptor is classically pictured to have a relevant role in cognitive function. We previously demonstrated a novel mechanism where acute administration of the CB1 receptor antagonist AM6545, largely restricted to the periphery, prolonged memory persistence in mice. Here, we have assessed the effects of repeated exposure to AM6545 on cognitive improvements.

EXPERIMENTAL APPROACH

We evaluated, in young adult male and female mice, the behavioural consequences of sub-chronic treatment with AM6545. An unbiased transcriptomic analysis, as well as electrophysiological and biochemical studies, was carried out to elucidate the central cellular and molecular consequences of such action at peripheral receptors.

KEY RESULTS

Sub-chronic AM6545 enhanced memory in low and high arousal conditions in male and female mice. Executive function was facilitated after repeated AM6545 administration in male mice. Transcriptional analysis of hippocampal synaptoneurosomes from treated mice revealed a preliminary, sex-dependent, modulation of synaptic transcripts by AM6545. Notably, AM6545 occluded long-term potentiation in CA3-CA1 synapses while enhancing input-output relation in male mice. This was accompanied by an increase in hippocampal expression of Bdnf and Ngf.

CONCLUSION AND IMPLICATIONS

Our results showed that repeated administration of AM6545 contributed to the modulation of memory persistence, executive function and hippocampal synaptic plasticity in mice, further indicating that peripheral CB1 receptors could act as a target for a novel class of nootropic compounds.

Peripheral CB1 receptor blockade acts as a memory enhancer through a noradrenergic mechanism

Peripheral inputs continuously shape brain function and can influence memory acquisition, but the underlying mechanisms have not been fully understood. Cannabinoid type-1 receptor (CB1R) is a well-recognized player in memory performance, and its systemic modulation significantly influences memory function. By assessing low arousal/non-emotional recognition memory in mice, we found a relevant role of peripheral CB1R in memory persistence. Indeed, the peripherally-restricted CB1R specific antagonist AM6545 showed significant mnemonic effects that were occluded in adrenalectomized mice, and after peripheral adrenergic blockade. AM6545 also transiently impaired contextual fear memory extinction. Vagus nerve chemogenetic inhibition reduced AM6545-induced mnemonic effect. Genetic CB1R deletion in dopamine β-hydroxylase-expressing cells enhanced recognition memory persistence. These observations support a role of peripheral CB1R modulating adrenergic tone relevant for cognition. Furthermore, AM6545 acutely improved brain connectivity and enhanced extracellular hippocampal norepinephrine. In agreement, intra-hippocampal β-adrenergic blockade prevented AM6545 mnemonic effects. Altogether, we disclose a novel CB1R-dependent peripheral mechanism with implications relevant for lengthening the duration of non-emotional memory.