Naltrexone attenuates stress-induced suppression of LH secretion in the pituitary gland in the Cichlid fish Oreochromis mossambicus: evidence for the opioidergic mediation of reproductive stress response

Abstract

Opioid peptide β-endorphin (β-EP) plays a modulatory role in vertebrate reproduction. However, the role of opioid peptides in reproductive stress response is least understood in fishes. The aim of the present study was to determine the effect of different doses of β-EP on luteinizing hormone (LH) secretion in normal and the opioid receptor antagonist naltrexone (NALT) in stressed female tilapia Oreochromis mossambicus. Administration of 4 μg β-EP, but not 0.5 or 1.5 μg β-EP, daily for 22 days caused suppression of LH-secreting cells at the proximal pars distalis of the pituitary gland, concomitant with a significant reduction in the mean GSI and HSI in 4 μg β-EP-treated fish compared to controls. On the other hand, exposure of the fish to mild acute stressors for 22 days caused changes in the LH-secreting cells similar to that of high dose of β-EP, whereas administration of NALT attenuated these effects. Taken together, the results indicate that increased concentration of β-EP as may occur during stressful conditions can cause suppression of LH secretion, leading to the inhibition of spawning, and that treatment of NALT attenuates the stress-induced inhibition of LH secretion in fish.

Glucocorticoid synthesis inhibitor metyrapone blocks stress-induced suppression along luteinizing hormone secreting cells-ovary axis in the fishOreochromis mossambicus

“…Complete blockade of the immunoreactions following these control procedures confirmed the specificity of the antisera. The specificity of LHβ antiserum used in the present study has also been reported previously for O. mossambicus (Chabbi and Ganesh, ; Ganesh and Chabbi, ), C. mrigala (Sakharkar et al, ), and Clarius batrachus (Mazumdar et al, ; Barsagade et al, ; Singh et al, ).…”

“…For instance, opioid peptide β‐endorphin is released in response to stress in the fish gilthead sea bream Sparus aurata (Mosconi et al, ; Arends et al, ). Our previous studies also have suggested a role for the involvement of β‐endorphin in mediation of reproductive stress response as shown by the suppression of LH secretion in the pituitary gland (Ganesh and Chabbi, ) and inhibition of vitellogenic follicular growth (Chabbi and Ganesh, ) in O. mossambicus . Therefore, the possibility of involvement of other inhibitory factors, which might act at the multiple sites of endocrine axis during reproductive stress response, cannot be ruled out for this species.…”

“…Similarly, treatment of naloxone prior to CRH injection blocked the inhibitory effect of CRH on pulse generator frequency of GnRH in rhesus monkey (Williams et al, ). Indeed, the possibility of opioidergic mediation in suppression of LH content in the pituitary gland (Ganesh and Chabbi, ) and vitellogenic follicular growth in the ovary (Chabbi and Ganesh, ) during reproductive stress response is shown in tilapia. Since the possibility of crossing of adequate CRH through the blood–brain barrier is not clear in the present study, we cannot comment about its centrally mediated effects.…”

Intermittent Moderate Energy Restriction Improves Weight Loss Efficiency in Diet-Induced Obese Mice

“…β-endorphin increases energy intake and body weight [ 59 ], at least partially via antagonism of the anorexigenic and weight-reducing effect of α-MSH [ 60 ]. β-endorphin is also known to inhibit the hypothalamo-pituitary-gonadal axis in several species, via actions in the hypothalamus and peripheral tissues [ 61 , 62 ], consistent with the significantly reduced seminal vesicle weight seen in mice on the continuous but not the intermittent diet. These suppositions are speculative, however, and further work would be required to show whether or not reduced hypothalamic POMC expression—as well as other pathways, such as reduced gut nutrient absorption, increased thyroid function and increased energy expenditure—might be related to the effects of intermittent versus continuous energy restriction.…”

The opioid peptide dynorphin suppresses pituitary‐ovary axis in the tilapia Oreochromis mossambicus

“…Endogenous opioid peptides have been shown to be involved in the regulation of several physiological functions, including reproduction, in different vertebrates (Ciarcia et al ., ; Facchinetti et al ., ; Faletti et al ., ; Ganesh & Yajurvedi, ; Leadem & Kalra, ; Olson et al ., ; Polzonetti‐Magni et al ., ; Zerani & Gobbetti, ). Among fishes, treatment with an opioid peptide, β‐endorphin (β‐EP), inhibits the function of the pituitary–ovary axis (Chabbi & Ganesh, ; Ganesh & Chabbi, ), whereas a dose‐dependent stimulatory as well as an inhibitory effect of leucine enkephalin on reproductive axis is demonstrated in the cichlid fish Oreochromis mossambicus (Peters 1852) (Vijayalaxmi & Ganesh, ). Dynorphin is another class of opioid peptide, which is produced from the prodynorphin gene and exists in different forms such as dynorphin‐A (DYN), dynorphin‐B and β‐neoendorphin, among which dynorphin‐A (1–17) is highly conserved and most potent (Civelli et al ., ; James et al ., ).…”