Acute effects of delta 9-tetrahydrocannabinol on tuberoinfundibular dopamine activity, anterior pituitary sensitivity to dopamine and prolactin release vary as a function of estrous cycle.

The effects of delta 9-tetrahydrocannabinol (THC) on the activity of brain dopaminergic neurons might be subject to gonadal influence. In this work, we tested this hypothesis in relation to the effects of THC on tuberoinfundibular dopaminergic (TIDA) activity, the anterior pituitary sensitivity to dopamine (DA) and prolactin (PRL) secretion. To this end, we examined the effects of an acute dose of this cannabinoid administered during different phases of the estrous cycle in the morning or afternoon. The results were as follows. THC, administered during the morning of estrus, stimulated TIDA activity as reflected by increases in DA and L-3,4-dihydroxyphenylacetic acid (DOPAC) contents and tyrosine hydroxylase (TH) activity in the medial basal hypothalamus. This was accompanied by an increase in the responsiveness of the anterior pituitary to DA, as reflected by the increase in the density of D2 receptors and the corresponding decrease in PRL release. By contrast, plasma PRL levels increased when THC was administered on the afternoon of estrus, in parallel with a significant reduction in the number of D2 receptors in the anterior pituitary gland and no effects on TIDA activity. A similar decrease in the anterior pituitary density of D2 receptors, but with no changes in plasma PRL levels, was observed when THC was administered during the morning of diestrus. This effect was not accompanied by changes in TIDA activity either.(ABSTRACT TRUNCATED AT 250 WORDS)