RESUMEN
BACKGROUND: Domoic acid (DOM) is a neurotoxin produced by some harmful algae blooms in coastal waters. California sea lions (Zalophus californianus) exposed to DOM often strand on beaches where they exhibit a variety of symptoms, including seizures. These animals typically show hippocampal atrophy on MRI scans. NEW METHOD: We describe an MRI protocol for comprehensive evaluation of DOM toxicosis in the sea lion brain. We intend to study brain development in pups exposed in utero. The protocol depicts the hippocampal formation as the primary region of interest. We include scans for quantitative morphometry, functional and structural connectivity, and a cerebral blood flow map. RESULTS: High-resolution 3D anatomical scans facilitate post hoc slicing in arbitrary planes and accurate morphometry. We demonstrate the first cerebral blood flow map using MRI, and the first structural tractography from a live sea lion brain. COMPARISON WITH EXISTING METHODS: Scans were compared to prior anatomical and functional studies in live sea lions, and structural connectivity in post mortem specimens. Hippocampal volumes were broadly in line with prior studies, with differences likely attributable to the 3D approach used here. Functional connectivity of the dorsal left hippocampus matched that found in a prior study conducted at a lower magnetic field, while structural connectivity in the live brain agreed with findings observed in post mortem studies. CONCLUSIONS: Our protocol provides a comprehensive, longitudinal view of the functional and anatomical changes expected to result from DOM toxicosis. It can also screen for other common neurological pathologies and is suitable for any pinniped that can fit inside an MRI scanner.
Asunto(s)
Leones Marinos , Animales , Encéfalo/diagnóstico por imagen , Hipocampo , Imagen por Resonancia MagnéticaRESUMEN
PURPOSE: We investigate the potential of a common dietary supplement, methylsulfonylmethane (MSM), to act as a chemical shift reference for in vivo 1 H MR spectroscopy (MRS). The scope of the investigation is 2-fold: (1) We use high-resolution nuclear MR (NMR) measurements of the chemical shift values of MSM to establish the stability of MSM resonance across the ranges of pH and temperature, and (2) we demonstrate MR properties of MSM in the healthy human brain. METHODS: The relationship of chemical shift with temperature and pH is examined using high-resolution 1 H NMR (14.1T) spectra of MSM in aqueous solution. MSM concentration in human brain tissue was measured as a function of time, together with the relaxation properties in the brain using 1 H MRS at 3T. RESULTS: The chemical shift of MSM remains stable in the range of the biologically relevant temperatures and pH values. The chemical shift at pH = 7.2 and 37°C was measured to be 3.142 ppm (relative to DSS, a common water-soluble NMR reference compound). Time course in the brain tissue in vivo confirmed an observable MSM signal 10 minutes after oral intake and a stable signal intensity within a ~3-hour window. CONCLUSION: The chemical and biological properties of MSM-rapid crossing of the blood-brain barrier, water solubility, a singlet resonance resolved from metabolite resonances, chemical shift stability with respect to pH/temperature, and stable temporal presence in the brain-lead us to propose its use as a frequency reference for MRS.