Effects of the synthetic cannabinoid 5F-AMB on anxiety and recognition memory in mice

N-[[1-(5-fluoropentyl)-1H-indazol-3-yl]carbonyl]-L-valine methyl ester (5F-AMB) is a synthetic cannabinoid that has been distributed recently. Although inhalation of 5F-AMB produces adverse effects, such as impaired memory and disturbed consciousness, in humans, the psychopharmacological effects of 5F-AMB in rodents have not been investigated.

We first examined the effects of intraperitoneal and intracerebroventricular injections of 5F-AMB on anxiety-like behavior and locomotor activity in the open field (OF) test and recognition memory in the novel object recognition test (NOR) in C57BL/6J mice. We also examined whether a cannabinoid 1 (CB1) receptor antagonist AM251 blocks the effects of 5F-AMB. We next examined the effects of 5F-AMB infusion into the medial prefrontal cortex (mPFC), a brain region associated with anxiety and memory, on these tests.

Intraperitoneal injection of 5F-AMB (0.3 mg/kg) dramatically decreased locomotor activity in the OF, and this effect was partially reversed by AM251 (3 mg/kg). Intracerebroventricular infusion of 5F-AMB (10 nmol) produced an anxiolytic effect in the OF and impaired acquisition, but not retrieval, of recognition memory in the NOR, and these effects were blocked by co-infusion of AM251 (1.8 nmol). Bilateral intra-mPFC infusion of 5F-AMB (10 pmol/side) similarly produced impaired recognition memory acquisition, but no anxiolytic effect.

The results demonstrate that centrally administered 5F-AMB produces anxiolytic effect and impaired recognition memory acquisition via activation of CB1 receptors, while systemic 5F-AMB severely impaired locomotor activity. The mPFC is involved in 5F-AMB-induced impairment of recognition memory acquisition. However, other brain region(s) may contribute to the 5F-AMB-induced anxiolytic effect.