Abstract
The biogenic monoamine octopamine is essential for ovulation and fertilization in insects. Release of this hormone from neurons in the thoracoabdominal ganglion triggers ovulation and sperm release from the spermathecae. Here we show that the effects of octopamine on ovulation are mediated by at least two different octopamine receptors. In addition to the Oamb receptor that is present in the epithelium of the oviduct, the octß2R receptor is essential for ovulation and fertilization. Octß2R is widely expressed in the female reproductive tract. Most prominent is expression in the oviduct muscle and the spermathecae. Animals deficient in expression of the receptor show a severe egg-laying defect. The corresponding females have a much larger ovary that is caused by egg retention in the ovary. Moreover, the very few laid eggs are not fertilized, indicating problems in the process of sperm delivery. We assume that octß2R acts in a similar way as ß2-adrenoreceptors in smooth muscles, were activation of this receptor induces an increase in cAMP levels that lead to relaxation of the muscle. Taken together, our findings show that octopaminergic control of ovulation and fertilization is more complex than anticipated and that various receptors located in different cells act together to enable a well-orchestrated activity of the female reproductive system in response to copulation.
