Calcitonin gene-related peptide (CGRP) has recently been shown to induce a profound suppression of the hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator, resulting in an inhibition of pulsatile luteinising hormone (LH) secretion in the rat (Li et al., 2004). The aims of the present study were, (i) to determine the presence of the CGRP receptor subunits, receptor activity modifying protein-1 (RAMP-1) and calcitonin receptor like receptor (CL), both of which are required for functional activity, in the GT1-7 cell line, an established in vitro model for hypothalamic GnRH neurones (Mellon et al. 1990), and (ii) to test the hypothesis that CGRP acts directly on the GnRH neurone to suppress GnRH mRNA expression. GT1-7 cells were grown in DulbeccoÆs Modified Eagle Medium supplemented with 10% fetal calf serum, 4.5 mg/ml glucose and antibiotics and maintained at 37°C in an atmosphere of 5% CO₂. Cells were harvested on ice and total RNA was extracted. The mRNAs for both CL and RAMP-1 receptor subunits were detected by reverse transcription PCR (RT-PCR) in the GT1-7 cell. GT1-7 cells were cultured with different concentrations of CGRP ranging from 10^-6 to 10^-12 M, and for a series of time points at 6, 12, 24 and 36hrs. In addition, CGRP (10^-8 M) was also co-administered with a CGRP receptor specific antagonist CGRP_8-37 (10^-6 M). GnRH mRNA levels were investigated by quantitative real time RT-PCR. All treatments were run in triplicate and experiment were repeated three times. The levels of GnRH mRNA expression were significantly reduced after treatment with CGRP at 6, 12 and 24 hrs, with maximum inhibition at 24 hrs. CGRP resulted in a dose dependent suppression of GnRH mRNA expression, with the most effective dose at 10^-8M CGRP, resulting in 70.5±6.8% (mean±SEM, P<0.05 tested with one way ANOVA) suppression. Co-culture with CGRP and the selective receptor antagonist CGRP_8-37 was able to completely reverse the inhibitory effect of CGRP on GnRH mRNA expression. These results demonstrate for the first time the presence of the CGRP receptor in GT1-7 cells, and suggest that CGRP directly regulates GnRH gene expression via CGRP receptors, which might play a physiological role in the regulation of the GnRH pulse generator.