Differential effects of chronic treatment with either dopamine D1 or D2 receptor agonists on the acute neuroendocrine actions of the highly potent synthetic cannabinoid HU-210 in male rats.

Acute exposure to delta 9-tetrahydrocannabinol (THC), the main psychoactive constituent of marijuana, produces a well-characterized set of neuroendocrine effects. The recent description of both brain cannabinoid receptors (CB-1) and anandamide, their proposed endogenous ligand, has renewed the interest in cannabinoid actions in the brain. However, the neurobiological mechanisms underlying the neuroendocrine effects of natural cannabinoids are not yet fully understood because of several mechanisms involved in their actions. In this work we have studied the role of hypothalamic dopaminergic receptors in the mediation of the acute neuroendocrine effects of (-)-delta 8-tetrahydrocannabinol-dimethyl-heptyl (HU-210, 20 micrograms/kg), a highly potent agonist of CB-1. The use of this low dose of HU-210 precludes the multiple unspecific effects which appear with an equipotent dose of THC. Rats were exposed during 21 days to either the dopamine (DA) D2 receptor agonist quinpirole (1 mg/kg, daily), the DA D1 receptor agonist SKF 38393 (8 mg/kg, twice a day) or vehicle (twice a day). Twenty-four hours after the last injection, a single dose of HU-210 (20 micrograms/kg) was administered intraperitoneally, and the animals were sacrificed 90 min later. Acute exposure to HU-210 produced both a decrease in plasma prolactin and a rise of plasma corticosterone levels. HU-210 treatment also resulted in both an increase in the L-3,4-dihydroxyphenylacetic acid/DA ratio and a decrease in noradrenaline contents, measured in the medial basal hypothalamus. These neuroendocrine actions were prevented by chronic exposure to quinpirole, but not after chronic SKF 38393 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)