Chapter 6 Regulation And Contribution Of The Corticotropic, Melanotropic And Thyrotropic Axes To The Stress Response In Fishes

Abstract

Publisher Summary This chapter discusses the regulatory pathways, the targets, the functions, and the interactions among the corticotropic, melanotropic, and thyrotropic axes, and the evidence that implicates each axis in the stress response. Multiple hypothalamic factors are involved in the regulation of the secretions from the corticotrope, melanotrope, and thyrotrope pituitary cells in fishes. Among these factors, corticotropin‐releasing factor (CRF) and thyrotropin‐releasing hormone (TRH) stimulate, and dopamine generally inhibits the secretions from all three hypothalamo–pituitary axes. The CRF system also plays a master role in the regulation of the endocrine response to stressors. In general, the contributions of the corticotropic, melanotropic, and thyrotropic axes to the stress response are species‐specific and depend on the challenge imposed on the system, its duration, and the homeostatic resilience of the fish. Multiple interactions and feedback effects have been identified among these endocrine axes. In the chapter it has been postulated that the extensive multidirectional communication as well as the cross‐talk among the corticotropic, melanotropic, and thyrotropic axes forms a “stress web” that exerts well‐concerted actions on energy metabolism as its prime task.