Metabolic alterations in the visual pathway of retinitis pigmentosa rats: A longitudinal multimodal magnetic resonance imaging study with histopathological validation.

Because retinitis pigmentosa (RP) has been shown to cause degenerative changes in the entire visual pathway, there is an urgent need to perform longitudinal assessments of RP-induced degeneration and identify imaging protocols to detect this degeneration as early as possible. In this study, we assessed a transgenic rat model of RP by using complementary noninvasive magnetic resonance imaging techniques, namely, proton magnetic resonance spectroscopy (1 H-MRS), to investigate the metabolic changes in RP. Our study demonstrated decreased concentrations and ratios to creatine (Cr) of N-acetylaspartate (NAA), glutamate (Glu), γ-aminobutyric acid (GABA), and taurine (Tau), whereas myo-inositol (Ins) and choline (Cho) were increased in the visual cortex of Royal College of Surgeons (RCS) rats compared with control rats (p < 0.05). Furthermore, with the progression of RP, the concentrations of NAA, Glu, GABA, and Tau, and the ratios of GABA/Cr and Tau/Cr significantly decreased over time, whereas the concentrations of Ins and Cho and the ratio of Ins/Cr significantly increased over time (p < 0.05). In addition, in RCS rats, NAA/Cr decreased significantly from 3 to 4 months postnatal (p < 0.001), and Cho/Cr increased significantly from 4 to 5 months postnatal (p = 0.005). Meanwhile, the 1 H-MRS indicators in 5-month postnatal RCS rats could be confirmed by immunohistochemical staining. In conclusion, with the progression of RP, the metabolic alterations in the visual cortex indicated progressive reprogramming with the decrease of neurons and axons, accompanied by the proliferation of gliocytes.

Diffusion tensor imaging in the evaluation of the long-term efficacy of HBO2 therapy in rats after traumatic spinal cord injury.

Objective: This study explored the feasibility of diffusion tensor imaging (DTI) in the evaluation of the long-term efficacy of hyperbaric oxygen (HBO2) therapy in rats after traumatic spinal cord injury (TSCI) with different degrees of injury. Method: Adult Sprague-Dawley rats (total n = 60) were randomly separated into three groups of mild, moderate and severe TSCI (20 rats per group). Each group was then randomly divided into TSCI and TSCI+HBO2 subgroups (10 rats per subgroup). Basso Beattie and Bresnahan (BBB) scores and DTI parameters including fractional anisotropy (FA), mean apparent diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) were collected at pre-TSCI and at 0, six and 24 hours, and three, seven, 14, 21, 28 and 56 days post-TSCI. Two-way repeated measures analysis of variance was used for comparison between the TSCI and TSCI+HBO2 subgroups over time in the mild, moderate and severe TSCI groups. Pearson correlation analysis was applied to analyze the correlations between BBB scores and DTI parameters. Results: BBB scores, FA, MD and RD values showed significant differences between the TSCI and TSCI+HBO2 subgroups over time in the mild, moderate and severe TSCI groups (all p<0.01). FA, MD and RD values were positively correlated with BBB scores in all TSCI and TSCI+HBO2 subgroups (all p<0.05). Conclusions: DTI parameters, especially MD, could quantifiably assess the long-term efficacy of HBO2 therapy and reflect the functional recovery in rats after TSCI with different degrees of injury.

Evaluation of hyperbaric oxygen therapy for spinal cord injury in rats with different treatment course using diffusion tensor imaging.

STUDY DESIGN: Animal study. OBJECTIVES: To evaluate the efficacy of hyperbaric oxygen (HBO) therapy for spinal cord injury (SCI) in rats with different treatment course using diffusion tensor imaging (DTI). SETTING: Hospital in Fuzhou, China. METHODS: Fifty adult Sprague-Dawley rats were grouped as: (A) sham-operated group (n = 10); (B) SCI without HBO therapy group (n = 10); (C) SCI with HBO therapy for 2 weeks (SCI+HBO2W) group (n = 10); (D) SCI with HBO therapy for 4 weeks (SCI+HBO4W) group (n = 10); (E) SCI with HBO therapy for 6 weeks (SCI+HBO6W) group (n = 10). Basso Beattie Bresnahan (BBB) scores and diffusion tensor imaging parameters including fractional anisotropy (FA), mean diffusivity (MD), radial diffusion (RD), and axial diffusion (AD) values in the injury epicenter, as well as 2 mm rostral and caudal to the injury epicenter were collected and analyzed 6 weeks post-injury. RESULTS: Higher BBB score and FA values were found in the SCI+HBO4W group than in the SCI and SCI+HBO2W groups (all P < 0.05), whereas no significant differences of these metrics were observed between the SCI+HBO4W and SCI+HBO6W groups. MD and RD values of the SCI+HBO4W group were significantly lower than those of the SCI group (all P < 0.01). FA values were positively correlated with BBB scores. MD and RD values were negatively correlated with BBB scores. CONCLUSION: DTI parameters, especially FA, could non-invasively and quantifiably evaluate the efficacy of HBO treatment for rats with SCI and 4 weeks may be the more appropriate treatment course.

Visual cortex and auditory cortex activation in early binocularly blind macaques: A BOLD-fMRI study using auditory stimuli.

Cross-modal plasticity within the visual and auditory cortices of early binocularly blind macaques is not well studied. In this study, four healthy neonatal macaques were assigned to group A (control group) or group B (binocularly blind group). Sixteen months later, blood oxygenation level-dependent functional imaging (BOLD-fMRI) was conducted to examine the activation in the visual and auditory cortices of each macaque while being tested using pure tones as auditory stimuli. The changes in the BOLD response in the visual and auditory cortices of all macaques were compared with immunofluorescence staining findings. Compared with group A, greater BOLD activity was observed in the bilateral visual cortices of group B, and this effect was particularly obvious in the right visual cortex. In addition, more activated volumes were found in the bilateral auditory cortices of group B than of group A, especially in the right auditory cortex. These findings were consistent with the fact that there were more c-Fos-positive cells in the bilateral visual and auditory cortices of group B compared with group A (p < 0.05). In conclusion, the bilateral visual cortices of binocularly blind macaques can be reorganized to process auditory stimuli after visual deprivation, and this effect is more obvious in the right than the left visual cortex. These results indicate the establishment of cross-modal plasticity within the visual and auditory cortices.