TRH-R1 (Thyrotropin-releasing hormone receptor type 1 ) is recognized for its abundant expression in the anterior pituitary, where it plays a role in the release of thyroid-stimulating hormone (TSH). In addition, TRH-R1 is widely distributed in the central nervous system, including the hippocampus. Previous studies have revealed that TRH plays a significant role as a neurotransmitter/neuromodulator, influencing synaptic function related to emotions, learning, and memory in the hippocampus. However, the precise localization and expression pattern of TRH-R1 remain elusive. We conducted in situ hybridization of TRH-R1, and our analysis confirmed the expression of TRH-R1 mRNA in the granule cell layer of the ventral hippocampal dentate gyrus. Interestingly, we observed that a cell layer near the subgranular zone where neurogenesis is taking place does not express TRH-R1. Notably, we observed a lack of TRH-R1 expression in Doublecortin-positive cells. Moreover, under the influence of aging, there was an increase in the expression levels of TRH-R1 within the hippocampal dentate gyrus. The data suggest that the expression of TRH-R1 in the dentate gyrus of the hippocampus increases during the development/aging of neurons.