Acute administration of Manning compound during the spawning period reduces reproductive success in female zebrafish

The vertebrate nonapeptide vasotocin (Avp) is evolutionarily conserved and homologous to mammalian vasopressin. Previous work using avp ^-/- zebrafish demonstrated a role for Avp in female, but not male, zebrafish reproduction. The phenotype manifested as reductions in pair-breeding success, viable egg release, ovarian Prostaglandin F_2a (PGF_2a) concentration, and reduction in ovarian transcripts coding for PGF_2a. synthesis enzymes. However, mutants exhibited life-long hypercortisolism, confounding the investigation of the mechanistic basis of Avp in female zebrafish reproductive success.

Here, we used acute pharmacological manipulation via the Avpr1 receptor antagonist Manning compound alone (dose-response experiment) or in conjunction with PGF_2a (rescue experiment) to investigate the role of Avp1-type receptor (Avpr1) signalling in female zebrafish reproductive success.

In the dose-response experiment, acute female intraperitoneal injection of MC at the lowest dose tested (5 ng/g bodyweight) reduced breeding pair success, quivering behaviour, and the number of released viable eggs compared to saline-injected controls. Whole-body cortisol and reproductive hormone concentrations, clutch size, hatchability and larval survival were unaffected at this concentration. Additional effects on courtship behaviours and increases in estradiol and progesterone concentrations were observed exclusively in females injected with higher doses of MC, suggesting no contribution to the reproductive phenotype observed at the lowest MC dose. The rescue experiment revealed that the phenotype elicited by 5 ng/g bw MC was rescued by co-injection with 5 mg/g bw PGF_2a.

Together, these data suggest that Avp acutely promotes female zebrafish spawning through action on Avpr1 receptors and likely involve downstream activation of PGF_2a. Because Avp may regulate female reproductive success at the ovarian level, future studies should explore the location, regulation, and function of the ovarian Avp receptors in detail.