Changes in vasotocin levels in relation to ovarian development in the catfish Heteropneustes fossilis exposed to altered photoperiod and temperature

Abstract

Photoperiod and temperature are the major proximate factors that activate the brain-pituitary-gonadal-endocrine axis stimulating gonadal recrudescence. Vasotocin (VT), the basic nonapeptide hormone, is secreted by the nucleus preopticus in the hypothalamus and released from the pituitary into circulation as a neurohormone for physiological actions. Additionally, VT is secreted de novo in the ovary of the catfish and has been implicated in ovarian functions. In the present study, we evaluated the changes in VT secretion during altered photoperiod and temperature exposure. The ovarian changes were monitored over gonadosomatic index (GSI) and plasma steroid hormone levels. Exposure of the catfish to long photoperiod (LP, 16L:08D) daily, alone or in combination with high temperature (HT, 28 ± 2 °C), for 14 or 28 days resulted in a decrease in brain-pituitary VT level with a concomitant increase in plasma and ovarian VT levels. The changes were greater in the LP + HT group on day 28. Concurrently, the treatments stimulated the GSI and plasma estradiol-17β (E2), testosterone (T) and progesterone (P4) levels with higher more responses in the LP + HT group. Exposure of the catfish to short photoperiod (SP, 08L:16D) daily or total darkness (TD, 24L:00D) daily, with or without changing the ambient temperature, for 14 or 28 days produced a depressing effect on VT, GSI and steroid hormone levels, the range of the response varied with the temperature. The brain VT level was low except in the TD + NT group. Plasma and ovarian VT levels decreased more in the SP and TD groups under ambient temperature than in the groups at the raised temperature. The GSI and plasma steroid hormones (E2, T and P4) responded in a similar manner. Plasma cortisol level registered a significant increase in all the groups compared to the initial control groups, and the increase was significantly higher on day 28. The simultaneous activation of VT secretion and ovarian recrudescence by photoperiod and temperature suggests the peptide's involvement in the hormonal control of gametogenesis.

Advances in Reproductive Endocrinology and Neuroendocrine Research Using Catfish Models

“…Variety of hormones/metabolites/neurotransmitters showed oocytes maturation effects in addition to maturation-inducing hormone (MIH) in catfish species. This included cortisol, vasotocin (VT), CEs and CAs [ 61 , 170 , 171 , 172 , 173 , 174 , 175 , 176 , 177 , 178 ]. Both GTH and ovarian steroids modulate VT levels in catfish to influence follicular growth, ovulation, and spawning [ 174 , 175 , 179 ].…”

High hydrostatic pressure effects on arginine vasotocin levels in fish

“…Arginine vasotocin (AVT), the non-mammalian homolog of vasopressin, is a nonapeptide synthesized in the preoptic area of the hypothalamus of fish, amphibians, birds and reptiles (Acher 1996). AVT works as a neurotransmitter in brain regions that are in contact with vasotocinergic projections (Absil et al 2002, Maruska et al 2007 and, as a hormone, it is released into the blood from specific vasotocinergic axonal projections of the pituitary neurohypophyseal lobe (Duarte et al 2001, Uchiyama et al 2014, Chaube et al 2015.…”