Nasal administration of gonadotropin releasing hormone (GnRH) elicits sperm production in Fowler’s toads (Anaxyrus fowleri)

Authors: JULIEN, ALISON - Mississippi State University; KOUBA, ANDREW - Mississippi State University; KABELIK, DAVID - Mississippi State University; FEUGANG, JEAN - Mississippi State University; WILLARD, SCOTT - Mississippi State University; VANCE, CARRIE - Mississippi State University

Submitted to: BMC Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2019
Publication Date: 5/22/2019
Citation: Julien, A., Kouba, A., Kabelik, D., Feugang, J., Willard, S., Vance, C. 2019. Nasal administration of gonadotropin releasing hormone (GnRH) elicits sperm production in Fowler’s toads (Anaxyrus fowleri). BMC Biology. 4(3):2-10.

Interpretive Summary: We are using amphibians as model species for studies in reproduction of fishes in aquaculture and birds in poultry sciences, and the effects of external stressors to reproductive output. Amphibians are more closely related to fishes and birds than mammals and have similar hormone responses in breeding. Amphibian reproduction is a complex sequence of events that couples environmental, social, and physical cues leading to hormonal cascades, eventually resulting in gamete development and release. To best trigger these breeding events in many species we are looking of r a more non-invasive means to administer the hormones. We are testing modes of delivery through the skin and mucus membranes and also testing the flow of hormone through the body using fluorescent quantum dots.

Technical Abstract: Like most vertebrates, the neuroendocrine hormone gonadotropin releasing hormone (GnRH) in amphibians mediates gamete production through the hypothalamic-pituitary-gonadal (HPG) axis. Upon onset of favorable environmental conditions, GnRH is released by the hypothalamus to stimulate the anterior pituitary, which then secretes the gonadotropins luteinizing hormone (LH) and follicle- stimulating hormone (FSH). These gonadotropins then travel through the bloodstream to the gonads, where they mediate steroid hormone synthesis and gametogenesis [1, 2, 3]. Exogenous GnRH treatment has become a powerful tool in stimulating gamete production from a variety of species. For example, GnRH receptor agonists have been successful in inducing spawning for commercial fish farming in species such as snook [4] and bream [5]. In amphibians, GnRH has been found to cause upregulation of GnRH receptors [6], increased production and release of sperm in males [3, 7, 8], and follicular development and ovulation in females [9]. Uteshev et al. [10] found that the effects of exogenous GnRH on amphibian spermiation was similar to that found using pituitary extract, leading to the theory that exogenous GnRH stimulates a natural gonadotropin-release cascade. The purpose of this study was to determine whether intranasal administration of a gonadotropin releasing hormone analog (GnRHs) elicits sperm production in anurans. Methods: Male Anaxyrus fowleri (n = 15/trt) were nasally administered GnRH (1, 5, 10, and 20 µg) in phosphate buffered saline (PBS) using a pipette. Spermic urine was collected from animals over an 8-hour period. Samples were assessed for sperm presence, motility, and concentration. Treatment of male toads with a PBS control and 1 µg of GnRH did not elicit sperm production. Nasal administration of GnRH resulted in sperm production from 60%, 93%, and 80% of males in the 5, 10, and 20 µg treatment groups, respectively. Sperm motilities averaged 70%, 63%, and 52% within the 5, 10, and 20 µg treatment groups, respectively, with the highest (p < 0.05) sperm motility observed using 5 µg of GnRH. Significantly higher sperm concentrations were observed in males treated with 10 µg of GnRH compared with 5 or 20 µg of GnRH. Conclusion: Nasal administration of GnRH was successful in eliciting spermiation from male Anaxyrus fowleri, which typically began less than three hours after treatment. Nasal administration of GnRH may provide a novel non-invasive method of hormone delivery for at-risk amphibian species that have low reproductive output.