Article Figures & Data
Figures
- Figure 1.
A, Two-compartment model used for characterizing transport of Gd-DTPA contrast into and out of the brain. The compartment model use the defined TSCs from the CM and whole brain (excluding CSF spaces) to calculate retention and loss. Compartments C1 and C2 are assumed to occupy the same space. The main input (K1) is represented by TSC from the CM. Tracer “retention” can be described as k3/k4 and “loss” (or clearance) as the parameter k2/(1 + k3/k4). Examples of raw data (blue) and fitted data derived from the two-compartment model (red) from representative rats in supine (B), prone (C), and RLD (D) positions. As can be seen, the calculated parameter for “retention” is highest for the rat in prone position and “loss” is most pronounced in the rat positioned in RLD.
- Figure 2.
TSCs from the CM of rats in different body positions. A, T1-weighted MRI of rat brain at the level of the CM ∼30 min after infusion of Gd-DTPA. Note that the CM catheter can be appreciated as a straight, high-signal-intensity line (white arrow). B, Average TSCs associated with infusion of Gd-DTPA into the CM for rats positioned in prone (blue, n = 7), supine (red, n = 9), and RLD (n = 8) body posture. Data are presented as mean ± SD. As can be observed, the TSCs from the three groups are identical and statistical analysis confirmed this statement (Table 1).
- Figure 3.
Effect of posture on brain transport of Gd-DTPA. Gd-DTPA transport/uptake for the cerebellum (A), hippocampus (B), midbrain (C), and orbital frontal cortex (D) represented by VT derived from executing the Logan plot. The data are presented as box-and-whisker plots (median, first quartile, third quartile, minimum, and maximum values); red: prone; blue: lateral, and black: supine. For each box-and-whisker plot, the corresponding 3D volume rendered brain region is shown: cerebellum (dark blue), hippocampus (light blue), midbrain (pink), and orbitofrontal cortices (turquoise). The VTs were compared between the three groups [prone (n = 7*), lateral (n = 8), supine (n = 9)] via the K–W test, which demonstrated positional dependence (p < 0.05) for all brain regions. The Wilcoxon rank-sum test was performed as a post hoc test to compare VTs between each of two groups with correction for multiple comparisons via FDR. This analysis showed that rats in prone position had significantly lower uptake of Gd-DTPA in the cerebellum (p < 0.05), hippocampus (p < 0.05), and midbrain (p < 0.03) compared with rats in the RLD position. *For the orbital frontal cortex, one rat's time activity curve in the prone group failed in the Logan-plot-fitting routine for estimation of VT and was excluded from the group analysis.
- Figure 4.
Anatomical key points of interest for Gd-DTPA efflux. Horizontal sections from T1-weighted MRIs at the level of the cochlea from rat brain before (A) and after (B) infusion of Gd-DTPA. The cochlea (Co) can be easily identified on the T1-weighted anatomical MRIs because it is shaped like a snail shell (A). The vagus nerve exits together with the glossopharyngeal (IX) nerve from the medulla oblongata below the vestibulocochlear nerve (VIII); the large nerve believed to be the vagus nerve is marked “X.” Note that part of the anatomy is obscured by susceptibility artifacts (dark spots marked by * in A and B). When contrast is infused into the CM, Gd-DTPA transport can be detected as an increase in signal intensity on the T1-weighted MRIs (brightness in B), which can be seen surrounding the cochlea 60 min after infusion start. (At later time points contrast is also seen inside the cochlea.) The exit points of the vagal nerve are also associated with Gd-DTPA contrast (B). C, D, 3D surface-rendered whole brains from a rat illustrating the spatial positions of the CM, cochlea (Co, blue), vagus nerve (X, black), and ICA (red). Only part of the ICA can be identified because its passage is partly obscured on the MRIs due to susceptibility artifacts and bony structures. E, 3D surface-rendered images of the cranium of a rat head acquired by CT to delineate all cranial components. The cranium is clearly visualized, including the squamosal (SQA), occipital (OCC), basis-phenoid (BAS), tympanic (TYM), pterygoid (PPI), paramastoid processes (PMP), and the foramen ovale (FOV). The temporal-mandibular joint (data not shown) and part of the PPI are causing the susceptibility artifacts on the MRIs obscuring the ICA as it enters the skull. Furthermore, part of the ICA runs through the bony carotid canal (CCA) shown as a dashed red line (E). F, G, Sagittal T1-weighted MRIs of a rat head at the level of the ICA shown before (F) and 80 min after (G) infusion of Gd-DTPA. The Gd-DTPA-induced signal changes appear as a bright signal that follow a well defined path along the ICA (sometimes along the ECA as well). H, I, Horizontal sections of T1-weighted MRIs from a rat head at the level of the SS sinus before (H) and 80 min after (I) infusion of Gd-DTPA into the CM. The SS sinus appears as a dark line in the middle of the two hemispheres (arrow, H) and, after infusion of contrast, areas adjacent to the SS sinus appear bright (arrows, I). J, Sagittal section from T1-weighted MRI before infusion of contrast at the level of the ICA and ECA showing more detail with regard to branching vessels including the occipital artery (aOCC) arising from the ECA and the pterygopalatine artery (aPTP) arising from the ICA.
- Figure 5.
Analysis of the effect of posture on efflux of Gd-DTPA. Average TSCs obtained from anatomical areas associated with efflux of Gd-DTPA from the three different groups (prone, n = 7; supine, n = 9; lateral, n = 8). The kinetics of the TSCs are different and dependent on anatomical point of interest. A, TSCs extracted from with areas along the SS sagittal sinus are characterized by a steady increase over time. B, C, Anatomical landmarks and illustration of the ROI measured along the SS sinus. Note that the SS sinus itself appears dark on the T1-weighted MRIs. Scale bars in B and C, 2 mm. D, TSCs extracted from the ROI-associated acoustic–cochlea complex (anatomical position illustrated in E and F; scale bar, 3 mm) are also characterized by a steady increase over time. G, TSCs associated with the vagus (Xth) nerve are characterized by a peak. H, I, Position of the vagus nerve (X) on a T1-weighted MRI in the sagittal plane at the level of the ICA and external carotid artery (ECA) before (H) and after (I) Gd-DTPA administration. Note that the path of the X nerve appears to be toward the ICA; the ROI associated with the vagal nerve is also indicated. Scale bar, 3 mm. J, TSCs derived from the areas along the ICA are characterized by a steady but variable signal change rising over time. An example of a ROI associated with this signal is shown in I. In general, CSF efflux associated with the vagus nerve was more pronounced compared with the other efflux pathways (G). Rats in prone position appear to have the largest amount of Gd-DTPA exiting along the ICA compared with the two other body positions (J).
- Figure 6.
Effect of posture on glymphatic transport using fluorescent and radiolabeled tracers. A, Small MW (Texas Red-conjugated dextran, 3 kDa) and large MW tracer (FITC-conjugated dextran, 2000 kDa) were injected intracisternally in mice placed in the prone, lateral, and supine position. B, Thirty minutes after injection, animals were perfusion fixed and whole-slice fluorescence was evaluated. Representative coronal sections are shown. CSF tracer influx in brain was significantly reduced in prone brain compared with lateral and supine brain (*p < 0.05, one-way ANOVA; for prone, n = 8, for lateral and supine, n = 6). C, Radiolabeled 125I-amyloid β1-40 was injected into cortex in mice in the same positions. Thirty minutes after injection, radiolabeled clearance was evaluated by gamma counting. 125I-Aβ1-40 clearance was significantly more efficient in the supine than in the lateral and prone positions (*p < 0.05; one-way ANOVA; for prone, n = 6; for lateral and supine, n = 7). D, Fluorescent tracer intensity was significantly higher in prone spinal cord compared with lateral and supine spinal cord. (*p < 0.05, one-way ANOVA; for prone, n = 6; for lateral, n = 5; and for supine, n = 6).
Tables
Parameter Prone (n = 7) Supine (n = 9) RLD (n = 8) p-value Mean SD Mean SD Mean SD AUC0–60 (% signal change * 60 min) 13534 2780 14217 3714 15103 2604 0.63 AUC0–120 (% signal change * 120 min) 23417 6493 25399 6757 26764 4995 0.41 Peak (% signal change from baseline) 437 78 429 95 454 49 0.79 Time-to-peak (min)* 33 (33, 36) 41 (37, 45) 37 (32, 38) 0.15 ↵*The median (1st quartile, 3rd quartile) rather than the mean (SD) was used for “time-to-peak.”
p < 0.05 was considered statistically significant. No significant group differences were found.
- Table 2.
Comparison of kinetic parameters derived from the whole-brain two-compartment analysis
Kinetic parameter Supine (n = 9) Prone (n = 6*) RLD (n = 8) p-value Retention = (k3/k4) 10.70 (9.88, 12.50) 14.98 (12.23, 16.53) 6.86 (6.28, 9.47) 0.008 Loss = k2/(1 + k3/k4) 0.23 (0.13, 0.26) 0.14 (0.09, 0.21) 0.31 (0.23, 0.40) 0.021 Data are presented as median (1st quartile, 3rd quartile) for each group.
↵*One rat in the prone group was excluded from analysis due to two-compartmental fitting failure of the whole-brain TSCs for unknown reasons.
Exits Parameter Prone (n = 7) Supine (n = 9) RLD (n = 8) p-value Mean SD Mean SD Mean SD Along superior sagittal sinus AUC0–120 (% signal change from baseline * 120 min) 3406 2594 2259 1661 3251 1368 0.423 Peak (% signal change from baseline) 57 41 38 22 55 24 0.368 Acoustic (VIII) cranial nerve and cochlea AUC0–120 (% signal change from baseline * 120 min) 3483 868 3344 1010 4072 1126 0.323 Peak (% signal change from baseline) 52 12 53 11 59 12 0.429 Vagus (X) cranial nerve AUC0–120 (% signal change from baseline * 120 min) 15170 5398 12891 4307 14989 6638 0.645 Peak (% signal change from baseline) 263 108 177 66 214 93 0.181 Along internal carotid artery AUC0–120 (% signal change from baseline * 120 min) 6132 3924 2194 958 2934 1765 0.069 Peak (% signal change from baseline) 148 86 54 26 77 47 0.049 One-way ANOVA was used to investigate whether the AUC0–120, a parameter representing “efflux” via anatomical key exits points, and “peak” magnitudes were different between the three positional groups. Welch's ANOVA was used if the variance homogeneity condition did not hold. p < 0.05 was considered statistically significant.
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