Robust reproducible resting state networks in the awake rodent brain

Opto-fMRI analysis for exploring the neuronal connectivity of the hippocampal formation in rats

In recent years, optical stimulation of neurons that bear a light-gated cation channel, "Optogenetics", has opened a new avenue for exploring neuronal connectivity of the nervous system. In this study, we applied a technique, "Opto-fMRI", which combined optogenetics with blood oxygenation level-dependent (BOLD) functional MRI (fMRI), for examining the neuronal connectivity of the hippocampal formation in rats. Although the hippocampal formation is very important for memory formation and retrieval, there is little information on its neuronal connectivity, especially on its longitudinal axis of connection. For this purpose, we utilized a transgenic rat strain, expressing the light-gated cation channel channelrhodopsin-2 (ChR2) under the regulation of the Thy1.2 promoter which permits the expression of the integrated gene in neurons. After optical stimulation targeting the dentate gyrus of the transgenic rat, we detected BOLD response of not only the dentate gyrus (DG) but also at the CA3 area. In addition, we detected the longitudinal-axis activation of the hippocampus after optical stimulation. Our study suggests that Opto-fMRI could be a tool for exploring the neuronal connectivity of the hippocampal formation, to understand the neural basis of memory formation and retrieval.

In vivo high-resolution localized (1) H MR spectroscopy in the awake rat brain at 7 T

In vivo localized high-resolution (1) H MR spectroscopy was performed in multiple brain regions without the use of anesthetic or paralytic agents in awake head-restrained rats that were previously trained in a simulated MRI environment using a 7T MR system. Spectra were obtained using a short echo time single-voxel point-resolved spectroscopy technique with voxel size ranging from 27 to 32.4 mm(3) in the regions of anterior cingulate cortex, somatosensory cortex, hippocampus, and thalamus. Quantifiable spectra, without the need for any additional postprocessing to correct for possible motion, were reliably detected including the metabolites of interest such as γ-aminobutyric acid, glutamine, glutamate, myo-inositol, N-acetylaspartate, taurine, glycerophosphorylcholine/phosphorylcholine, creatine/phosphocreatine, and N-acetylaspartate/N-acetylaspartylglutamate. The spectral quality was comparable to spectra from anesthetized animals with sufficient spectral dispersion to separate metabolites such as glutamine and glutamate. Results from this study suggest that reliable information on major metabolites can be obtained without the confounding effects of anesthesia or paralytic agents in rodents.