A Subset of Folliculo-Stellate Cells Expresses Gpr37l1 in The Adult Rat Anterior Pituitary

G protein-coupled receptor 37 (GPR37) and GPR37-like 1 (GPR37L1) are orphan G protein-coupled receptors enriched in the central nervous system. However, their cellular distribution in pituitary tissue remains unclear. Here, we mapped Gpr37l1 expression in the adult rat anterior pituitary and identified the expressing cell type(s). Quantitative real-time PCR demonstrated that Gpr37l1 mRNA is significantly more abundant than Gpr37 in the anterior lobe. In situ hybridization (ISH) revealed sparsely distributed Gpr37l1-positive cells throughout the anterior lobe, and the signals did not colocalize with major hormone-producing cell types. Combined ISH and immunohistochemistry further showed that Gpr37l1 mRNA is localized to S100B protein-immunoreactive cells, commonly referred to as folliculo-stellate (FS) cells, and that only a subset of S100B-positive FS cells expresses Gpr37l1. Single-cell RNA-seq analysis corroborated these findings, as Gpr37l1-expressing cells were distributed within the broader S100b-expressing cluster, without forming a distinct subcluster, while showing no detectable Gpr37l1 expression in endocrine lineages or vascular-associated cell populations. Together, these data provide a cell-type-resolved map of Gpr37l1 expression in the adult rat anterior pituitary and identify Gpr37l1 as a marker of heterogeneity within FS cells, establishing a foundation for future studies on GPR37L1 signaling in pituitary microenvironmental regulation.