Milner, T. | Search bioRxiv

bioRxiv2026

Subcellular Localization of Dopamine D1 and D2 Receptors in the Mouse Hippocampus

Dopamine signaling through dopamine 1 receptors (D1R) and dopamine 2 receptors (D2R) regulates hippocampal synaptic plasticity underlying learning and memory, yet their subcellular localization within the hippocampus is unknown. Here we performed electron microscopic immunocytochemistry to elucidate the distribution of D1R and D2R in subregions of the mouse hippocampus. In CA1 and CA3 stratum radiatum (SR), D1R- and D2R-immunoreactivity was found primarily on pyramidal cell dendritic spines and unmyelinated axons, and to a lesser extent in axon terminals and glia. In both regions, D1R-labeled terminals formed predominantly asymmetric (excitatory-type) synapses on dendritic spines, whereas D2R-labeled terminals formed mainly symmetric (inhibitory-type) synapses on pyramidal cell dendritic shafts. In the dentate gyrus (DG) hilus, D1R-labeling was almost exclusively found in unmyelinated axons and glia. D2R immunoreactivity in the hilus similarly was present in unmyelinated axons and glia but was also detected in dendritic spines originating from mossy cells and in terminals forming symmetric synapses. These findings indicate that dopamine receptors are positioned to influence excitatory and inhibitory signaling in the murine hippocampus. As D1R and D2R exert opposing effects on neuronal signaling, their localization on pyramidal neuron compartments provides a structural substrate for bidirectional modulation of synaptic plasticity and pyramidal cell activity. In addition, the presence of D2Rs on inhibitory terminals contacting pyramidal neurons and hilar interneurons suggests a role in regulating inhibitory circuitry within the hippocampus.

neuroscience↗

bioRxiv2020

Distribution and localization of phosphatidylinositol 5-phosphate, 4-kinase alpha and beta in the brain

Phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) is critical for synaptic vesicle docking and fusion and generation of the second messengers, diacylglycerol and inositol-1,4,5-trisphosphate. PI-4,5-P2 can be generated by two families of kinases: type 1 phosphatidylinositol-4-phosphate 5-kinases, encoded by PIP5K1A, PIP5K1B and PIP5K1C, and type 2 phosphatidylinositol-5-phosphate 4-kinases, encoded by PIP4K2A, PIP4K2B, and PIP4K2C. While the roles of the type 1 enzymes in brain function have been extensively studied, the roles of the type 2 enzymes are poorly understood. Using selective antibodies validated by genetic deletion of pip4k2a or pip4k2b in mouse brain, we characterized the location of the enzymes, PI5P4K and PI5P4K{beta}, encoded by these genes. In mice, we demonstrate that PI5P4K is expressed in adulthood, whereas PI5P4K{beta} is expressed early in development. PI5P4K localizes to white matter tracts, especially the corpus callosum, and at a low level in neurons, while PI5P4K{beta} is expressed in neuronal populations, especially hippocampus and cortex. Dual labeling studies demonstrate that PI5P4K co-localizes with the oligodendrocyte marker, Olig2, whereas PI5P4K{beta} co-localizes with the neuronal marker, NeuN. Immunohistochemical subcellular distribution studies demonstrate that PI5P4K and PI5P4K{beta} are expressed in the early endosome system. Ultrastructural analysis demonstrates that both kinases are contained in axon terminals and dendritic spines adjacent to the synaptic membrane, which support a potential role in synaptic transmission. Immunohistochemical analysis of macaque and human brain tissue demonstrate a conserved pattern for PI5P4K and PI5P4K{beta}. These results highlight the diverse cell-autonomous expression of PI5P4K and PI5P4K{beta} and support further exploration into their role in synaptic function in the brain.

neuroscience↗