CHARACTERISATION OF CORTICOTROPH CELL ACTIVITY IN INTACT ZEBRAFISH LARVAE

Corticotroph cells of the anterior pituitary are key components of the hypothalamic-pituitary-adrenal (HPA) axis, integrating hypothalamic input to release adrenocorticotropin (ACTH). However, their population-level activity and functional organisation in an intact animal remain poorly understood. Here, we generated a novel transgenic zebrafish line expressing GCaMP8m in corticotroph cells using a pro-opiomelanocortin (pomc) promoter. In pomc:GCaMP8m transgenic line, all corticotrophs and the melanotroph cells express GCaMP8m, allowing single cell resolution population activity imaging of entire corticotroph cells in intact zebrafish larvae.
Calcium time-series were analysed to quantify single-cell response dynamics, assess variability across the corticotroph population, and examine patterns of coordinated activity, including functional connectivity between cells.
Our results reveal heterogeneity in activity patterns present already at basal condition. Further functional connectivity analysis uncovered the emergence of spatially segregated local ensembles of corticotroph cells. Acute stressors induced changes in individual corticotroph cell response dynamics and network properties were analysed to determine how stressor intensity and stressor types may be encoded in the corticotroph cell activities.
To assess the role of hypothalamic inputs in determining corticotroph cell activity, we characterised the expression of corticotropin-releasing hormone (CRH) receptor 1 and arginine vasopressin (AVP) receptor 1 and 2 in the corticotroph cell population. The receptor knockouts were generated and analysed to determine their contribution to both basal and stressor-induced corticotroph cell activity and functional network.
This work establishes an in vivo imaging paradigm to dissect corticotroph population dynamics and functional organisation during stress in an intact animal.