The gonadotropin-releasing hormones (GnRH) are hypothalamic neuropeptides that play vital roles in vertebrate reproduction by controlling pituitary hormone production, and in turn sexual behavior, ovulation in females and sperm release in males.

The olfactory system plays an important role to control reproductive behavior in many animal species. The intimate connection between the olfactory system and reproductive development is illustrated by Kallmann syndrome, a severe condition in which GnRH neurons fail to migrate, resulting in anosmia (deficient sense of smell) and hypogonadotropic hypogonadism in adults. Although the significance of GnRH neurons for olfaction and courtship behavior is widely discussed, little is known about whether GnRH neurons can directly sense and transmit olfactory signals to modulate courtship behavior.

Recently, a research team led by Prof. HU Wei from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, in collaboration with the team of Prof. Vance L. Trudeau from the University of Ottawa, discovered that GnRH3 neurons in the olfactory epithelium of zebrafish are a type of crypt sensory neurons, which have a new function of directly sensing and transmitting sex pheromones, thereby inducing courtship behavior. This study was published in Science China Life Sciences.

By using laser confocal 3D imaging, the researchers reported new model for migration path and distribution pattern of GnRH3 neurons. Specifically, GnRH3 neurons undergo bidirectional migration along the olfactory nerve. The cell bodies of some GnRH3 neurons are distributed within the olfactory epithelium of adult zebrafish. These findings challenge the view over the last three decades that vertebrate GnRH neurons migrate from the olfactory placode to the hypothalamus in a unidirectional manner.

Anatomical, behavioral and physiological data support the researchers’ proposal that a new, previously unidentified population of GnRH3 neurons in the olfactory epithelium are a type of crypt olfactory sensory neuron which directly sense the post-ovulatory sex pheromone prostaglandin F2α.

The key findings are that males harboring gnrh3 mutations exhibit a diminished GnRH3 neuronal firing rate and an impaired ability to sense and transduce female sex pheromone-encoded information critical to courtship behavior and reproductive success. These males are less attractive to females and less competitive than normal male fish.

These findings uncover a new role for GnRH neurons in courtship behavior through direct sensing of female sex pheromones. The olfactory GnRH neurons the research team have uncovered act as a gating system transducing odor-encoded information critical to reproductive success. This study opens a new path towards understanding the relationship between anosmia and gonadal dysfunction.

(Online: May 8, 2025)

GnRH3 neurons initially distribute ventrally, beneath the olfactory placode. (Image by IHB)

(Editor: MA Yun)