How does apelin affect LH levels? An investigation at the level of GnRH and KNDy neurons

Hypothalamic control of reproduction relies on GnRH and kisspeptin (KP) secretions. KP neurons are sensitive to sex steroids and metabolic status and their distribution overlaps with neurons producing apelin, a metabolic hormone known to decrease LH secretion in rats. Here, we observed neuroanatomical contacts between apelin fibers and both KP and GnRH neurons in the hypothalamus of male rodents. Intracerebroventricular apelin infusion for 2 weeks in male mice did not decrease LH levels nor did it affect gene expression for KP, neurokinin B and dynorphin. Finally, increasing apelin concentrations did not modulate Ca2+ levels of cultured GnRH neurons, while 10 mu M apelin infusion on forskolin pretreated GnRH neurons revoked a rhythmic activity in 18% of GnRH neurons. These results suggest that acute apelin effect on LH secretion does not involve modulation of gene expression in KP neurons but may affect the secretory activity of GnRH neurons.

Automated summary

Hypothalamic control of reproduction relies on secretions of GnRH and kisspeptin (KP). This study found neuroanatomical contacts between apelin fibers and both KP and GnRH neurons in the hypothalamus of male rodents. Intracerebroventricular apelin infusion did not decrease LH levels nor affect gene expression for KP, neurokinin B, and dynorphin. However, apelin did affect the secretory activity of GnRH neurons.