Effect of the anandamide transporter inhibitor,AM404, on anxiety response in rats

There are many and contradictory reports on the interaction between cannabinoids and anxiety. Both cannabinoid agonists and antagonists have been shown to have anxiolytic- and anxiogenic-like behavioural reactions in rodents depending on the dose and the context (Onaivi et al. 1990; Crawley et al. 1993; Onaivi et al. 1995; Rodriguez de Fonseca, 1996; Navarro et al., 1997; Akinshola et al. 1999; Haller et al., 2002; Berrendero and Maldonado 2002;Valjent et al.. 2002; Haller et al. 2004). The aim of the present work was to further elucidate the role of endocannabinoid system in anxiety response. For this purpose, the anandamide transport inhibitor, AM 404 (2.5-10 mg/kg), and D9–THC (0.015-1.5 mg/kg), previously evaluated in our laboratory for its reinforcing properties in a Conditioned Place Preference test (Braida et al., 2005), were studied in a plus-maze apparatus according to Pellow et al. (1985) The test length was 5 min and the total time spent in each arm and the number of arm entries were scored by trained observers in male Sprague-Dawley rats, 30 min after treatment. The role of the CB1 cannabinoid and opioid receptor was investigated pre-treating rats with SR 141716 (0.25-1 mg/kg) and naloxone (0.5-2 mg/kg), 10 min before D9–THC or AM 404. Both D9–THC (0.75 mg/kg) and AM 404 (10 mg/kg) significantly elevated the percentage of open arm entries and the time spent in the open arms, showing an anxiolytic activity. This effect was reversed by pre-treatment with SR 141716. An interaction with opioid system was also found. These findings further support a key role of endocannabinoid system in the regulation of emotional states.