Serotonin inhibits luteinizing hormone release via 5-HT1A receptors in thezona incerta of ovariectomised, anaesthetised rats primed with steroids

The zona incerta (ZI), an area in the dorsal hypothalamus, contains neurona l systems that appear to control gonadotropin release. Previous findings sh ow that there is an inverse relationship between serotonin (5-HT) activity in the ZI and plasma luteinizing hormone (LH) levels, indicating that the 5 -HT system in this area has an inhibitory effect on LH release. Employing a naesthetised, ovariectomised rats primed with 5 mug oestradiol benzoate fol lowed at 48 h by 0.5 mg progesterone, we have shown that 2 mug/side 5-HT in the ZI inhibits the LH surge that normally occurs 4h after the progesteron e treatment. This effect was mimicked by 2 mug/side 8-OH-DPAT, a 5-HT1A ago nist, but not by DOI, a 5-HT2 agonist, BMY7378, a presynaptic 5-HT1A agonis t or MCPP, a 2B & 2C agonist. The inhibitory effect of 5-HT and 8-OH-DPAT w as prevented by pretreatment, 1 h before, with either 2 mg/kg i.p. WAY10013 5, a 5-HT1A antagonist or 0.25 mg/ kg i.p. ritanserin, a 5-HT2 antagonist, These results indicate that 5-HT in the ZI exerts its inhibitory effect on LH release via 5-HT1A receptors but that another 5-HT subtype may also be i nvolved. Copyright (C) 2000 S. Karger AG, Basel.