Background: Kisspeptin and its cognate receptor GPR54 are the central driving forces in the hypothalamus-pituitary-gonadal axis essential for sexual maturation and reproduction. Kisspeptin/GPR54 signalling stimulates gonadotropin-releasing hormone (GnRH) neurones and induces pulsatile GnRH release. The molecular signalling pathway by which kisspeptin stimulates GnRH neurones is currently under investigation. Methods: Primary GnRH neurones were isolated from young adult rats and loaded with the calcium indicator Fura Red. Cytosolic calcium was measured while the cells were stimulated with kisspeptin. Results: GnRH neurones show a maintained increase of cytosolic calcium upon stimulation with 100 nM kisspeptin-10. The calcium elevation was inhibited 30% by 1 µM tetrodotoxin, a voltage-gated sodium channel blocker, and 76% by 30 µM SKF96365, an inhibitor of receptor-mediated calcium entry. Furthermore, removal of extracellular calcium completely abolished the kisspeptin-induced calcium elevation. Conclusion: Our results suggest that the major part of the kisspeptin-evoked calcium signal is generated by an action potential-independent calcium influx, possibly through channels of the classical transient receptor potential type, with an additional influx through voltage-gated calcium channels activated by sodium action potentials.

The effects of lead acetate on respiration in cerebral and cerebellar mitochondria from immature and adult rats were studied polarographically. With all substrates low lead concentrations produced an increase in respiration. Higher concentrations produced an inhibition of both this lead-induced respiration and ADP-dependent (State 3) respiration. Lead-induced respiration required inorganic phosphate and was inhibited by oligomycin, suggesting a coupling to oxidative phosphorylation. Inhibition of respiration was produced by much lower lead concentrations with NAD-linked citric acid cycle substrates than with succinate or alpha-glycerophosphate. In partially disrupted mitochondria, NAD-linked substrate oxidation was inhibited at lead concentrations which did not affect NADH oxidation. Thus, in brain mitochondria the NAD-linked dehydrogenases, located in the matrix space, were more sensitive to inhibition by lead than were inner membrane enzymes. All in vitro lead effects on mitochondrial respiration were comparable in cerebral and cerebellar mitochondria isolated from both immature and adult rats.

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