Effects of Ethanol Exposure on the Neurochemical Profile of a Transgenic Mouse Model with Enhanced Glutamate Release Using In Vivo 1H MRS

Abstract

Ethanol (EtOH) intake leads to modulation of glutamatergic transmission, which may contribute to ethanol intoxication, tolerance and dependence. To study metabolic responses to the hyper glutamatergic status at synapses during ethanol exposure, we used Glud1 transgenic (tg) mice that over-express the enzyme glutamate dehydrogenase in brain neurons and release excess glutamate (Glu) in synapses. We measured neurochemical changes in the hippocampus and striatum of tg and wild-type (wt) mice using proton magnetic resonance spectroscopy before and after the animals were fed with diets within which EtOH constituting up to 6.4% of total calories for 24 weeks. In the hippocampus, the EtOH diet led to significant increases in concentrations of EtOH, glutamine (Gln), Glu, phosphocholine (PCho), taurine, and Gln + Glu, when compared with their baseline concentrations. In the striatum, the EtOH diet led to significant increases in concentrations of GABA, Gln, Gln + Glu, and PCho. In general, neurochemical changes were more pronounced in the striatum than the hippocampus in both tg and wt mice. Overall neurochemical changes due to EtOH exposure were very similar in tg and wt mice. This study describes time courses of neurochemical profiles before and during chronic EtOH exposure, which can serve as a reference for future studies investigating ethanol-induced neurochemical changes.

Keywords: Enhanced glutamate release; Ethanol exposure; Glud1 transgenic mice; Magnetic resonance spectroscopy.

Figure 1.

In vivo ¹H MR spectra at 9.4 T in the hippocampus (A, B) and the striatum (D, E) of wt mice before (B, E) and after (A, D) introduction of the EtOH diet. Spectra were acquired from volumes of 3.9 – 6.1 μL localized in the hippocampus and striatum using SPECIAL with TE = 3 ms, TR = 4 s, and 320 – 480 and 480 – 640 transients, respectively. Difference between spectra before and after initiation of the EtOH diet are shown in C and F, respectively. The spectra were scaled based on the weighted average of NAA concentrations on E0 and E2 to visually show differences of the corresponding spectra. The difference spectra are not quantitatively accurate because of the linewidth differences between the spectra, and residual spectral distortion due to phase and frequency differences.

Figure 2.

In vivo ¹H MR spectra at 9.4 T in the hippocampus (A, B) and the striatum (D, E) of Glud1 tg mice before (B, E) and after (A, D) introduction of the EtOH diet. Other details of the figure are the same as Figure 1.

Figure 3.

Effects of EtOH on the concentration of neurochemicals in the hippocampus of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).

Figure 3.

Effects of EtOH on the concentration of neurochemicals in the hippocampus of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).

Figure 3.

Effects of EtOH on the concentration of neurochemicals in the hippocampus of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).

Figure 4.

Effects of EtOH on the concentration of neurochemicals in the striatum of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).

Figure 4.

Effects of EtOH on the concentration of neurochemicals in the striatum of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).

Figure 4.

Effects of EtOH on the concentration of neurochemicals in the striatum of wt and Glud1 tg mice, shown in the left and right columns, respectively, measured at the indicated intervals of EtOH diet. An asterisk (*) denotes significant differences, p < 0.05, between the concentration of a neurochemical at E0 (n = 28 for tg; n = 15 for wt) and other time points of EtOH diet (n = 14, 8, and 7 at E2, E12, and E24 respectively for both tg and wt groups).