EFFECTS OF DELTA-9-TETRAHYDROCANNABINOL AND (R)-METHANANDAMIDE ON OPEN-FIELD BEHAVIOR IN RATS

This study compared the effects of (R)-methanandamide, an analog of th e mammalian brain constituent anandamide, and delta-9-tetrahydrocannab inol on the open-field behavior of male Sprague Dawley rats. Rats were individually housed with free access to food and water. Animals were treated with 0, 1, 3, and 5.6 mg/kg delta-9-tetrahydrocannabinol given i.p. 30 min pre-session; and 0, 3, 10, and 18 mg/kg (R)-methanandamid e, 15 min pre-session. The behavioral categories recorded were ambulat ion (the number of squares crossed), rearing (the number of times the rat stood erect on its hind-legs), latency (the time in seconds to lea ve the starting area, the circle in the center of the field), circling (the number of times the animal turned around its vertical axis, 0.5 point given for each 180 degrees turn), grooming (the number of cleani ng bouts), urination and defecation (the number of urination spots and fecal boli deposited during the 5 min observation period). Delta-9-te trahydrocannabinol was more potent than (R)-methanandamide, but otherw ise the effects of delta-9-tetrahydrocannabinol and (R)-methanandamide were similar, with one exception; whereas delta-9-tetrahydrocannabino l produced dose-related increases in circling, (R)-methanandamide did not increase circling over the doses examined. The delta-9-tetrahydroc annabinol-induced increase in circling was blocked by the central cann abinoid receptor CB1 antagonist SR 141716. The differential effects wi th regard to circling may indicate that there are qualitative behavior al differences in the effects of delta-9-tetrahydrocannabinol and (R)- methanandamide. (C) 1998 Rapid Science Ltd.