GnRH-Induced [Ca2+]i-Signalling Patterns in Mouse Gonadotrophs Recorded from Acute Pituitary Slices in vitro

In this study we used [Ca(2+)](i) imaging to monitor GnRH-induced intracellular Ca(2+) signalling from dozens of gonadotrophs in mouse male pituitary slices. Responses of individual cells vary in magnitude, latency, duration and frequency of oscillation. Approximately 20% of gonadotrophs in situ display Ca(2+) oscillations of increasing frequency at higher [GnRH] and biphasic (peak-plateau) responses at saturating [GnRH]. Nevertheless, this orderly progression, reported in cultured cells, is less well organized in 55% of cells. Furthermore, approximately 30% cells display non-oscillatory GnRH responses, reminiscent of immature gonadotrophs. Dose-response curves of slices from different animals suggest inter-individual differences in GnRH sensitivity. When the same dose of GnRH is applied repeatedly, individual cell responses are almost identical both in latency, oscillatory pattern and duration resembling the 'Ca(2+) fingerprint' phenomenon. In addition, gonadotrophs in situ are arranged in small clusters with similar GnRH-induced intracellular Ca(2+)-signalling patterns. Neighbouring gonadotrophs within clusters often display synchronized GnRH-induced responses with high correlation indices (>0.75). Nevertheless, synchronized responses between pairs of gonadotrophs are unaffected by incubation with blockers of gap-junction channels or P2X receptor channels, suggesting that they are not mediated by gap junctions or ATP. Alternative explanations are discussed, including pseudo-synchronization. In summary, while gonadotrophs in situ display GnRH-induced responses similar to those observed in cultured cells, different patterns and novel aspects of functional organization were found which deserve further investigation. This study on GnRH-induced Ca(2+) signalling in the acute mice pituitary gland might be of potential relevance for characterizing GnRH actions in gonadotrophs in transgenic and knockout animals.