Brain-wide mapping and region-specific cellular characterization of Trhr1 reporter-labeled cells in mice using VISoR...

Thyrotropin-releasing hormone receptor 1 (TRHR1, encoded by Trhr, also referred to as Trhr1 in rodents) is a key component of the hypothalamic-pituitary-thyroid axis and has also been implicated in emotion, cognition, and stress-related regulation. However, the brain-wide distribution and cellular characteristics of Trhr1 reporter-labeled cells in the central nervous system remain incompletely understood. In this study, we generated Trhr-P2A-iCre; R26-tdTomato mice to genetically label Trhr1 reporter-labeled cells and combined this strategy with tissue clearing and volumetric imaging with synchronized on-the-fly scan and readout (VISoR) to construct a high-resolution brain-wide map. Quantitative analysis revealed that Trhr1 reporter-labeled cells were broadly distributed throughout the adult mouse brain, with marked regional heterogeneity. Higher densities were observed in the olfactory bulb, prefrontal cortex, striatum, hypothalamus, and amygdala, whereas lower densities were found in the hippocampus, thalamus, midbrain/brainstem, and cerebellum. Further immunofluorescence analysis indicated that Trhr1 reporter-labeled cells were predominantly neuronal in the examined regions, showing frequent co-localization with NeuN but not with Iba1 or GFAP. Many tdTomato-positive cells in selected cortical, amygdalar, and striatal regions co-localized with CaMKII, whereas overlap with PV or SST was limited; in the dentate gyrus, many co-localized with Prox1, indicating a granule-cell identity. Together, these findings provide a brain-wide anatomical map and region-specific cellular profile of Trhr1 reporter-labeled cells and establish a structural foundation for future studies of TRHR1-related neural circuits and functions.