Neuroendocrine regulation Flashcards
Why does latitude play a big role in the location of fish reproduction?
the seasons dictate food availability for fragile young that need fast growth
What steps are needed for successful reproduction?
Mate identification
Synchronisation of gonad maturity
Courtship
Synchronisation of gamete release
Fertilisation
When does reproduction start and what physiological events are involved in it?
It starts with gametogenesis
- endocrine regulation
- acquisition and mobilisation of energy reserves
- gamete development
What is gametogenesis driven by?
the endocrine system
Endocrine regulation of the reproductive system is complex and acts as a cascade from brain organs (hypothalamus and pituitary) down to the gonads (ovary and testis)
Primarily acts as an integrated feedback system that transduces environmental cues into physiological signals that regulate gametogenesis
basic. Brain (GnRH) -> Pituitary (FSH - associated with early stages of gametogenesis + LH - associated with egg maturation and sperm development) -> Liver (vitellogenini) -> ovary (E2) or testis (11KT) via T
Why is cell communication important?
Cells must communicate with one another for coordinated function of organs and the body
Three types of chemical cellular communication
- Autocrine
- Paracrine
- Endocrine
What are hormones?
Hormones act across distance and activate specific receptor proteins which are either membrane or nuclear bound
Different hormone types:
Amine hydrophilic membrane
Peptide hydrophilic membrane
Steroid Hydrophobic nuclear
What is the role of the brain in reproduction?
The brain plays an essential role in processing neural stimuli that are obtained from sensory neurons.
These stimuli will ultimately be transduced to an endocrine signalling pathway to the gonads
basic: Brain (GnRH) -> Pituitary (FSH + LH) -> Liver (vitellogenini) -> ovary (E2) or testis (11KT) via T
What does the hypothalamus do in regards of reproduction?
Hypothalamus produces and secretes releasing hormones
Gonadotropin releasing hormone (GnRH) is a peptide hormone that stimulates the release of the two gonadotropins:
Follicle stimulating hormone (FSH)
Luteinisinghormone (LH)
What is the gonadotropin (GtH) follicle stimulating hormone (FSH) associated with?
early stages of gametogenesis
What is the gonadotrophin (Gth) lusteinising hormone (LH) associated with?
egg maturation and sperm development
What is dopamine (DA) and what can it be synthesised from?
Dopamine is a small neurotransmitter synthesised from tyrosine
It acts on G coupled receptors D1 and D2 these either stimulate or inhibit adenyl cyclase, cAMP
D2 receptors common in freshwater teleosts(goldfish, carp, trout, tilapia) directly on GnRH terminals onto gonadotropes
How can the DA (Dopamine) inhibition of the GnRH system be overcome?
what are the effects?
Using DA inhibitors
e. g. pimozide or spiperiodone
- Tends to block LH release, therefore, gametes do not reach maturity
- Goldfish will not ovulate if environmental conditions are not suitable: e.g. water temperature is too cold or if vegetation for behaviour and spawning missing
- Males need female pheromone 17α, 20β P associated with decreased DA levels to be able to sperminate
- DA blocks FSH release in rainbow trout
- DA blocks sex change in T. bifasciatum
What is the HPG axis?
- Hypothalamus releases GnRH
- Pituitary produces & releases gonadotropins (LH, FSH)
- Gonad is stimulated to produce sex steroids (E2, T)
How are hormones quantified?
We can measure most hormones as long as we have antibodies that are specific for the target antigen
Hormones that are highly conserved across different species can be quantified using commercial kits
How are hormone assays made?
Sex steroids are conserved but peptide hormones such as FSH and LH are usually species specific.
To develop assays for these is time-consuming and extremely expensive
