Biology subjects

Nakamoto, C.

Publications and source records attributed to Nakamoto, C..

4 recordsLinked to original sources

bioRxiv2026

Hippocampal CA2 modulates trace fear conditioning through circuit-specific control of CA1

Forming associations between temporally separated events depends on pathways linking the CA1, the subiculum (SUB), and the entorhinal cortex. The degree to which this process requires the CA2, which shares extensive connectivity with these regions, remains unknown. Using trace fear conditioning (TFC), where mice learn to associate a tone and shock separated by a temporal gap, we showed that the dCA2 contributes to TFC. Interestingly, whereas chronic dCA2 inhibition decreased cue-associated freezing, acute dCA2[->]dCA1 projection inhibition increased freezing. Combined with differential effects on cFos expression, this suggests that global and projection-specific perturbations of the dCA2 have distinct effects on TFC and hippocampal activity states. Fiber photometry revealed that dCA2[->]dCA1 activity shifted from tone responsiveness during conditioning to expected shock activation during recall, consistent with learning-associated activity remodeling. Together, these findings identify the dCA2 as a contributor to TFC and implicate dCA2[->]dCA1 signaling in shaping fear expression across learning and recall.

neuroscience↗

bioRxiv2020

A genetically encoded red fluorescence dopamine biosensor enables dual imaging of dopamine and norepinephrine

Dopamine (DA) and norepinephrine (NE) are pivotal neuromodulators that regulate a broad range of brain functions, often in concert. Despite their physiological importance, untangling the relationship between DA and NE in finely controlling output functions is currently challenging, primarily due to a lack of techniques to visualize spatiotemporal dynamics with sufficiently high selectivity. Although genetically encoded fluorescent biosensors have been developed to detect DA, their poor selectivity prevents distinguishing DA from NE. Here, we report the development of a red fluorescent genetically encoded GPCR (G protein-coupled receptor)-activation reporter for DA termed R-GenGAR-DA. More specifically, a circular permutated red fluorescent protein (cpmApple) was inserted into the third intracellular loop of human DA receptor D1 (DRD1) followed by the screening of mutants within the linkers between DRD1 and cpmApple. We developed two variants: R-GenGAR-DA1.1, which brightened following DA stimulation, and R-GenGAR-DA1.2, which dimmed. R-GenGAR-DA1.2 demonstrated reasonable dynamic range ({Delta}F/F0 = -50%) and DA affinity (EC50 = 0.7 {micro}M) as well as the highest selectivity for DA over NE (143-fold) amongst available DA biosensors. Due to its high selectivity, R-GenGAR-DA1.2 allowed dual-color fluorescence live imaging for monitoring DA and NE, combined with the existing green-NE biosensor GRABNE1m, which has high selectivity for NE over DA (>350-fold) in HeLa cells and hippocampal neurons grown from primary culture. By enabling precise measurement of DA, as well as simultaneous visualization of DA and NE, the red-DA biosensor R-GenGAR-DA1.2 is promising in advancing our understanding of the interplay between DA and NE in organizing key brain functions. Significance StatementThe neuromodulators dopamine and norepinephrine modulate a broad range of brain functions, often in concert. One current challenge is to measure dopamine and norepinephrine dynamics simultaneously with high spatial and temporal resolution. We therefore developed a red-dopamine biosensor that has 143-fold higher selectivity for dopamine over norepinephrine. Taking advantage of its high selectivity for dopamine over norepinephrine, this red-dopamine biosensor allowed dual-color fluorescence live imaging for monitoring dopamine and norepinephrine in both HeLa cells and hippocampal neurons in vitro combined with the existing green-norepinephrine biosensor that has 350-fold selectivity for norepinephrine over dopamine. Thus, this approach can provide new opportunities to advance our understanding of high spatial and temporal dynamics of dopamine and norepinephrine in normal and abnormal brain functions.

cell biology↗

bioRxiv2019

GluD1 knockout mice with a pure C57BL/6N background show impaired fear memory, social interaction, and enhanced depressive-like behavior

The GluD1 gene is associated with susceptibility for schizophrenia, autism, depression, and bipolar disorder. However, the function of GluD1 and how it is involved in these conditions remain elusive. In this study, we generated a GluD1-knockout (GluD1-KO) mouse line with a pure C57BL/6N genetic background and performed several behavioral analyses. Compared to a control group, GluD1-KO mice showed no significant anxiety-related behavioral differences, evaluated using behavior in an open field, elevated plus maze, a light-dark transition test, the resident-intruder test of aggression and sensorimotor gating evaluated by the prepulse inhibition test. However, GluD1-KO mice showed (1) hyper locomotor activity in the open field, (2) decreased sociability and social novelty preference in the three-chambered social interaction test, (3) impaired memory in contextual, but not cued fear conditioning tests, and (4) enhanced depressive-like behavior in a forced swim test. Pharmacological studies revealed that enhanced depressive-like behavior in GluD1-KO mice was restored by the serotonin reuptake inhibitors imipramine and fluoxetine, but not the norepinephrine transporter inhibitor desipramine. In addition, biochemical analysis revealed no significant difference in protein expression levels, such as other glutamate receptors in the synaptosome and postsynaptic densities prepared from the frontal cortex and the hippocampus. These results suggest that GluD1 plays critical roles in fear memory, sociability, and depressive-like behavior.

neuroscience↗

bioRxiv2018

Nell2 regulates the contralateral-versus-ipsilateral visual projection as a layer-specific positional cue

SUMMARY STATEMENTNell2 is an ipsilateral layer-specific axon guidance cue in the visual thalamus and contributes to establishment of the eye-specific retinogeniculate projection by specifically inhibiting contralateral retinal axons.\n\nABSTRACTIn mammals with binocular vision, retinal ganglion cell (RGC) axons from each eye project to eye-specific layers in the contralateral and ipsilateral dorsal lateral geniculate nucleus (dLGN). Although layer-specific axon guidance cues that discriminate contralateral and ipsilateral RGC axons have long been postulated as a key mechanism for development of the eye-specificretinogeniculate projection, the molecular nature of such cues has remained elusive. Here we show that the extracellular glycoprotein Nell2 (also known as Nel) is expressed in the dorsomedial region of the dLGN, which corresponds to the layer receiving ipsilateral RGC axons. In Nell2 mutant mice, contralateral RGC axons invaded the ipsilateral layer of the dLGN, and ipsilateral axons terminated in partially fragmented patches, forming a mosaic pattern of contralateral and ipsilateral axon termination zones. In vitro, Nell2 exerted inhibitory effects on contralateral, but not ipsilateral, RGC axons. These results provide evidence that Nell2 acts as a layer-specific positional label in the dLGN that discriminates contralateral and ipsilateral RGC axons, and that it plays essential roles in establishment of the eye-specific projection patterns in the retinogeniculate system.

developmental biology↗