Optogenetic elevation of endogenous glucocorticoid level in larval zebrafish

Abstract

The stress response is a suite of physiological and behavioral processes that help to maintain or reestablish homeostasis. Central to the stress response is the hypothalamic-pituitary-adrenal (HPA) axis, as it releases crucial hormones in response to stress. Glucocorticoids (GCs) are the final effector hormones of the HPA axis, and exert a variety of actions under both basal and stress conditions. Despite their far-reaching importance for health, specific GC effects have been difficult to pin-down due to a lack of methods for selectively manipulating endogenous GC levels. Hence, in order to study stress-induced GC effects, we developed a novel optogenetic approach to selectively manipulate the rise of GCs triggered by stress. Using this approach, we could induce both transient hypercortisolic states and persistent forms of hypercortisolaemia in freely behaving larval zebrafish. Our results also established that transient hypercortisolism leads to enhanced locomotion shortly after stressor exposure. Altogether, we present a highly specific method for manipulating the gain of the stress axis with high temporal accuracy, altering endocrine and behavioral responses to stress as well as basal GC levels. Our study offers a powerful tool for the analysis of rapid (non-genomic) and delayed (genomic) GC effects on brain function and behavior, feedbacks within the stress axis and developmental programming by GCs.

A Zebrafish Genetic Screen Identifies Neuromedin U as a Regulator of Sleep/Wake States

“…However, it was not determined which crh -expressing neurons were responsible for this effect. The hypothalamic-pituitary-interrenal (HPI) axis of zebrafish is homologous to the mammalian HPA axis, with cortisol/glucocorticoid receptor signaling conserved as the key effector of the HPA/HPI axis stress response (Alsop and Vijayan, 2008; De Marco et al, 2013; Wendelaar Bonga, 1997). To directly test the hypothesis that Nmu-induced hyperactivity is mediated by the HPA/HPI axis, we analyzed the effect of Nmu overexpression in zebrafish possessing a null mutation in the glucocorticoid receptor ( gr ) (Ziv et al, 2013), the classical target of the HPA/HPI cascade.…”

Engineering of a red-light–activated human cAMP/cGMP-specific phosphodiesterase

“…However, improved fluorescent BPhys no longer require exogenous biliverdin addition (39), indicating that not only the bioavailability of the chromophore but also the efficiency of its incorporation matters. Both cAMP and cGMP are involved in the regulation of manifold biological processes as diverse as the stress response in zebrafish (40), parasite infectivity (41), and Drosophila behavior (7), and LAPD augurs optogenetic control over these processes. Notably, red and far-red light penetrate tissue much more deeply than light of shorter wavelengths, thus making LAPD particularly well suited for optogenetic studies on whole animals (compare Fig.…”

Conspecific injury raises an alarm in medaka

“…200 μl of 1X Phosphate Buffered Saline (PBS; pH 7.2) at 4 °C was added to each tube and their content homogenized using an Ultra-Turrax Disperser (T10 basic; IKA). Cortisol was extracted in 1400 μl of Ethyl Acetate as recommended by56 by vortexing the tubes for 30 s, followed by centrifugation at 7000 G-force for 15-min at room temperature. The organic layer that contained cortisol was collected in fresh tubes and left in the fume hood overnight to allow ethyl acetate to evaporate.…”