The G-protein coupled receptor 3 (GPR3), a member of the class A rhodopsin-type GPR family, constitutively activates Gαs proteins without any ligands. Although there have been several reports concerning the functions of GPR3 in neurons, the physiological roles of GPR3 have not been fully elucidated. To address this issue, we analyzed GPR3 distribution in detail using fluorescence-based X-gal staining in heterozygous GPR3 knockout/LacZ knock-in mice, and further investigated the types of GPR3-expressing neurons using fluorescent double labeling with various EF-hand Ca²⁺-binding proteins. In addition to the previously reported GPR3-expressing areas, we identified GPR3 expression in the basal ganglia and in many nuclei of the cranial nerves, in regions related to olfactory, auditory, emotional, and motor functions. In addition, GPR3 was not only observed in excitatory neurons in layer V of the cerebral cortex, the CA2 region of the hippocampus, and the lateral nucleus of the thalamus, but also in γ-aminobutyric acid (GABA)-ergic interneurons in the cortex, hippocampus, thalamus, striatum, and cerebellum. GPR3 was frequently co-expressed with neuronal Ca²⁺-binding protein 2 (NECAB2) in neurons in various regions of the central nervous system, especially in the hippocampal CA2, medial habenular nucleus, lateral thalamic nucleus, dorsolateral striatum, brainstem, and spinal cord anterior horn. Furthermore, GPR3 also co-localized with NECAB2 at the tips of neurites in differentiated PC12 cells. These results suggest that GPR3 and NECAB2 are highly co-expressed in specific neurons, and that GPR3 may modulate Ca²⁺ signaling by interacting with NECAB2 in specific areas of the central nervous system.

G 蛋白偶联受体 3 (GPR3) 是 A 类视紫质型 GPR 家族的成员，在没有任何配体的情况下组成性激活 Gαs 蛋白。尽管已经有一些关于 GPR3 在神经元中的功能的报道，但 GPR3 的生理作用尚未完全阐明。为了解决这个问题，我们使用基于荧光的 X-gal 染色在杂合GPR3敲除/ LacZ敲入小鼠中详细分析了 GPR3 分布，并使用各种 EF-hand Ca 的荧光双标记进一步研究了 GPR3 表达神经元的类型²⁺-结合蛋白。除了先前报道的 GPR3 表达区域外，我们还在与嗅觉、听觉、情绪和运动功能相关的区域中，在基底神经节和许多颅神经核中发现了 GPR3 表达。此外，GPR3不仅在大脑皮层V层、海马CA2区和丘脑外侧核的兴奋性神经元中观察到，而且在皮质中的γ-氨基丁酸（GABA）-能神经元中也观察到。 、海马、丘脑、纹状体和小脑。GPR3 经常与神经元 Ca ²⁺共表达中枢神经系统各个区域的神经元中的结合蛋白 2 (NECAB2)，尤其是海马 CA2、内侧缰核、外侧丘脑核、背外侧纹状体、脑干和脊髓前角。此外，GPR3 还与 NECAB2 共定位在分化的 PC12 细胞中的神经突尖端。这些结果表明 GPR3 和 NECAB2 在特定神经元中高度共表达，并且 GPR3 可能通过与中枢神经系统特定区域中的 NECAB2 相互作用来调节 Ca ²⁺信号传导。