RESUMEN
OBJECTIVES: The purpose of this study was to assess the reproducibility of substantia nigra pars compacta (SNpc) and locus coeruleus (LC) delineation and measurement with neuromelanin-sensitive MRI. MATERIALS AND METHODS: Eleven subjects underwent two neuromelanin-sensitive MRI scans. SNpc and LC volumes were extracted for each scan. Reproducibility of volume and magnetization transfer contrast measurements in SNpc and LC was assessed using intraclass correlation coefficients (ICC) and dice similarity coefficients (DSC). RESULTS: SNpc and LC volume measurements showed excellent reproducibility (SNpc-ICC: 0.94, p < 0.001; LC-ICC: 0.96, p < 0.001). SNpc and LC were accurately delineated between scans (SNpc-DSC: 0.80 ± 0.03; LC-DSC: 0.63 ± 0.07). CONCLUSION: Neuromelanin-sensitive MRI can consistently delineate SNpc and LC.
Asunto(s)
Locus Coeruleus/diagnóstico por imagen , Melaninas/química , Sustancia Negra/diagnóstico por imagen , Adulto , Biomarcadores/metabolismo , Encéfalo/diagnóstico por imagen , Estudios de Cohortes , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Imagen por Resonancia Magnética , Masculino , Reproducibilidad de los ResultadosRESUMEN
The ability to optically stimulate and inhibit neurons has revolutionized neuroscience research. Here, we present a direct, potent, user-friendly chemical approach for optically silencing neurons. We have rendered saxitoxin (STX), a naturally occurring paralytic agent, transiently inert through chemical protection with a previously undisclosed nitrobenzyl-derived photocleavable group. Exposing the caged toxin, STX-bpc, to a brief (5 ms) pulse of light effects rapid release of a potent STX derivative and transient, spatially precise blockade of voltage-gated sodium channels (NaVs). We demonstrate the efficacy of STX-bpc for parametrically manipulating action potentials in mammalian neurons and brain slice. Additionally, we show the effectiveness of this reagent for silencing neural activity by dissecting sensory-evoked swimming in larval zebrafish. Photo-uncaging of STX-bpc is a straightforward method for non-invasive, reversible, spatiotemporally precise neural silencing without the need for genetic access, thus removing barriers for comparative research.