Forsøksdyr: Investigation of plasticity of gonadotrope cells in the fish pituitary in castrated animals

Godkjenningsdato 07.07.2020

Godkjenningsperiode 01.08.2020-30.10.2020

1 Purpose
Reproductive function in vertebrates is regulated by the brain-pituitary-gonad axis where the two pituitary gonadotropins, follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), play a major role. The gonadotropes, which produced gonadotropins, are regulated by the brain and by positive and negative feedback mechanisms via sex steroid hormones produced in the gonads.
Our first careful description of these two cell types indicate that the activity (mRNA synthesis) and the total number of specific cell types can change due to both mitotic division and phenotypic plasticity, allowing flexibility according to the physiological needs of the animal at different life stages or environments however the role of the different subpopulations in these processes is still unknown.
This project will take advantage of the castration technique allowing removal of the gonads and thus the main source of steroids to investigate the role of sex steroids in gonadotrope cell plasticity.
In brief, male and female fish will be gonadectomized under anaesthesia, Then, gonadotrope cells activity and number will be investigated.
Therefore, this study will allow us to investigate:
1- the effect of gonadectomy on the circulating levels of sex steroids
2- the role of sex steroids on gonadotrope cell proliferation and activity (hormone synthesis and release)

2 Distress
Moderate. The surgery will be practiced under anaesthesia and it is a common technique used in research model animals including fish and medaka. The person in charge of the surgery has been trained by experts in Japan that regularly use this technique in the same animal model with really high success rate.

3 Expected benefit
If successful, this experiment will provide a lot information on the role gonads play in circulating sex steroid levels and the role of sex steroids on pituitary cell plasticity

4 Number of animals, and what kind
We plan to use up to a total of 144 adult medaka fish (half males, half females) in our experiments.

5 How to adhere to 3R
We need to use animal models in our research, as ex vivo models do not reflect the physiological
conditions. Indeed, while we observed in vivo cell proliferation in the pituitary we could not observe this phenomenon occurring ex vivo. Therefore, to study cell plasticity in the pituitary, we argue that ex vivo experiments are not suitable to obtain our aim, which is to bring new information on pituitary plasticity. In addition, we have reduced the number of used animals to the minimum in order to get still relevant information.