Early Changes in Glutamate Metabolism and Perfusion in Basal Ganglia following Hypoxia-Ischemia in Neonatal Piglets: A Multi-Sequence 3.0T MR Study

Abstract

The excitotoxicity of glutamate metabolism as well as hemodynamic disorders of the brain are both risk factors for neonatal hypoxic-ischemic brain damage (HIBD). In the present study, changes in glutamate metabolism in the basal ganglia were detected by proton magnetic resonance spectroscopy (¹H-MRS) at 0-6, 8-12, 24-30, and 48-60 h after the induction of hypoxia-ischemia (HI) in newborn piglets. Meanwhile, correlation analysis was performed by combining the microcirculatory perfusion informations acquired by intravoxel incoherent motion (IVIM) scan to explore their possible interaction mechanism. The results suggested that Glu level in the basal ganglia underwent a "two-phase" change after HI; perfusion fraction f, an IVIM-derived perfusion parameter, was clearly decreased in the early stage after HI, then demonstrated a transient and slight recovery process, and thereafter continued to decrease. The changes in f and Glu level were in a significant negative correlation (r = -0.643, P = 0.001). Our study results revealed that Glu level is closely associated with the microcirculatory perfusion changes in the acute stage of HIBD.

Keywords: 1H-MRS; IVIM; glutamate; hypoxic–ischemic brain damage; perfusion.

Figure 1

Representative T₂-weighted image and corresponding ¹H-MRS of a normal piglet. A MRS voxel was placed in the left basal ganglia (black square). LCModel fitting results (red), fit from 0.2 to 4.0 ppm, are presented. Glu, glutamate; Gln, glutamine; NAA, N-acetylaspartate; Lac, lactate; Cho, choline; Cr, creatine.

Figure 2

Representative IVIM images of newborn piglets before and after HI. (a–d) showed the axial diffusion-weighted imaging (DWI) image (b = 0 s/mm²) of a normal newborn piglet (a) (where the blue ellipse highlights the region of interest (ROI) marked in the left basal ganglia region), and the corresponding D, D^*, and f images obtained by IVIM post-processing software (b–d; D = 0.642 × 10⁻³ mm²/s, D^* = 13.207 × 10⁻³ mm²/s, f = 12.753%). (e–h) showed the axial DWI image (b = 0 s/mm²) of a newborn piglet at 6 h after HI (e), and the corresponding D, D^*, and f images (f–h; D = 0.269 × 10⁻³ mm²/s, D^* = 5.412 × 10⁻³ mm²/s, f = 7.197%). From the axial DWI images, we could see that at 6 h after HI, the signals of cerebral parenchyma were evidently enhanced, the cerebral cortex was obviously swollen and edematous, and the cortical sulci and gyrus became shallower; in the D and f images, weakened signals of cerebral parenchyma were observed after HI correspondingly, but the difference in the image of D^* was not significant.

Figure 3

¹H-MRS images of newborn piglets at different times points after HI injury. (A–C) and (D) represented four different time points after HI operation: 0–6, 8–12, 24–30, and 48–60 h. In the spectra, the Glu peak was elevated at 0–6 h (A), then slightly depressed at 8–12 h (B), and thereafter elevated again at 24–30 h (C), and 48–60 h (D). However, the Gln peak did not show significant changes in the above image. Glu, glutamate; Gln, glutamine; NAA, N-acetylaspartate; Lac, lactate; Cho, choline; Cr, creatine.

Figure 4

Quantification results measured by ¹H-MRS in control and model piglets at different time-points after HI insult, (A) Glu, (B) Gln, and (C) Glx. Errors bars indicate standard deviation values. ^*Compared with the control group, P < 0.05. Glu, glutamate; Gln, glutamine; Glx, glutamate + glutamine.

Figure 5

D (A), D^* (B), and f (C) parameters measured by IVIM scanning in control (black circles) and model piglets at different time-points, 0–6 h (black squares); 8–12 h (black regular triangles); 24–30 h (black inverted triangles); and 48–60 h (black diamonds). The horizontal lines in the scatter plots represent medians.

Figure 6

Scatter plots of IVIM-derived f (%) and D^* (×10⁻³mm²/s) parameters over concentrations (mmol/kg) of Glu, Gln, and Glx. A significant negative correlation between f values and the Glu concentration was observed (A), whereas an ordinary negative correlation between f values and the Glx concentration was observed (C). However, there was no correlation between f values and the Gln concentration (B). Unlike for f values, no correlation between D^* values and Glu (D), Gln (E), or Glx (F) concentrations was observed. Spearman's rank correlation coefficient r was calculated. Glu, glutamate; Gln, glutamine; Glx, glutamate + glutamine.