Agouti-Related Protein 2 Is a New Player in the Teleost Stress Response System.

Agouti-related protein (AgRP) is a hypothalamic regulator of food consumption in mammals. However, AgRP has also been detected in circulation, but a possible endocrine role has not been examined. Zebrafish possess two agrp genes: hypothalamically expressed agrp1, considered functionally equivalent to the single mammalian agrp, and agrp2, which is expressed in pre-optic neurons and uncharacterized pineal gland cells and whose function is not well understood. By ablation of AgRP1-expressing neurons and knockout of the agrp1 gene, we show that AgRP1 stimulates food consumption in the zebrafish larvae. Single-cell sequencing of pineal agrp2-expressing cells revealed molecular resemblance to retinal-pigment epithelium cells, and anatomic analysis shows that these cells secrete peptides, possibly into the cerebrospinal fluid. Additionally, based on AgRP2 peptide localization and gene knockout analysis, we demonstrate that pre-optic AgRP2 is a neuroendocrine regulator of the stress axis that reduces cortisol secretion. We therefore suggest that the ancestral role of AgRP was functionally partitioned in zebrafish by the two AgRPs, with AgRP1 centrally regulating food consumption and AgRP2 acting as a neuroendocrine factor regulating the stress axis.

The sounds of silence: Barn owl noise in landing and taking off.

A barn owl swooping down generated a quieter, almost silent, noise (acoustic impulses) compared to a louder noise generated by the owl when taking off. These acoustic impulses are at low frequencies which are below the auditory threshold to most rodents. Therefore, rodents are less likely to hear these noises of owl flight. A previous study revealed that rodents exhibit frantic response to an owl taking off (as opposed to their typical freezing response during owl attack). The frantic response could be the result of tactile reception of the air-puffs generated by the owl's wingbeats and may reduce the success in subsequent attacks.