Hi, need to submit a 2750 words essay on the topic Effects of steroids on calcium activated potassium channels and secretion of LH and FSH in Atlantic cod (Gadus morhua).
The secretion of these hormones by the gonadotropes is in turn mediated by the activity of gonadotropin releasing hormone (GnRH) produced by the BPG axis (Borg, 1994). Apart from regulating gametogenesis, these hormones also control steroidogenesis, a process that produces sex steroids involved in moderating gametogenesis (Schulz and Goos, 1999). Another important regulating hormone for the gonadotropins is dopamine, which has been reported as a down regulator in several teleost fish (Borg, 1994). The releasing hormone, GnRH, once produced binds and activates its receptors found on the membrane of the hormone producing cells of the pituitary gland (Bliss, Navratil, Xie, & Roberson, 2010). Contrastingly in teleost, there is a direct innervation of the pituitary gland by GnHR neurons, whereas, in humans and other mammals, the action of GnHR is via neurochemostasis (Mousa & Mousa, 2003).
The binding of GnHR to its receptors on the gonadotropes triggers an increase in intracellular calcium ion concentration an action that stimulates the secretion of the hormones by the activated cells. The initial and immediate secretion of the hormones is by exocytosis of hormone vesicles, which is later followed by long term gene transcription to sustain prolonged secretions. The increase in calcium ion concentration is mediated by various mechanisms, such as an influx via voltage-gated channels, and release from intracellular stores. For example, action potentials tend to promote the influx of extracellular calcium ions in voltage-gated calcium ion channels expressing cells. The elevated calcium ions concentration, in the cells activates, calcium activated Potassium channels (CAPC), a pathway that plays a significant role in modulating membrane potentials and thus the electrophysiological effect on hypothalamic releasing hormones (Fettiplace & Fuchs, 1999).