Introduction Approximately 50 million people worldwide are affected by epilepsy, one of the most common neurological conditions. A non invasive technique is necessary in order to study the pathology in humans and for targeting drug research. For this reason, MRI has been widely used in experimental epilepsy studies [1]. The present work shows a comparison between 1H-MRS and T2 maps on pilocarpine-induced status epilepticus (SE) in adult rats, in early stages of the acute phase. Rats were scanned from 5 minutes to 4 hours after SE-onset , in order to investigate differences in T2 relaxation as well as in the metabolites levels in three brain regions (Cortex, Medial Thalamus and Hippocampus). These regions were chosen because recent evidences pointed out a critical role of extra-hippocampal regions in the etiopathogenesis of pilocarpine-induced epilepsy [2-3]. Methods and Materials Wistar rats (n=19 in total) were divided as follows: (Group A) control (PBS-injected, n=5), (Groups B-D) pilocarpine-injected observed at different time points after SE-onset: (B) 5' after SE-onset (n=4, one died during experiment), (C) 60' after SE-onset (n=5), (D) 240' after SE-onset (n=5). Treated rats were injected with pilocarpine hydrochloride (Sigma-Aldrich; 360mg/kg in saline, i.p.) and 30 min before with methylscopolamine (1 mg/kg in saline intraperitoneally, i.p.; Sigma-Aldrich, St. Louis,MO) to prevent peripheral cholinergic side effects. Localized 1H spectra and MR images were acquired using a 4.7 T Bruker Biospec System and a cross coil configuration for rat brain. Water suppressed spectra were acquired using PRESS sequence with TR/TE=4000/11 ms, 1024 points; a VAPOR pulse sequence was used for water suppression. The water reference spectrum was also acquired in each selected voxel. Spectra were acquired from three voxels placed in the Motor Cortex, Hippocampus and Medial Thalamus (see Fig.1) having volumes of 2x2.5x5 mm 3, 7x1.75x3 mm 3 and 5x2.25x3 mm 3. Analysis was performed by using LCModel [4]: the NAA content relatively to Choline containing compounds and PhosphoCholine (GPC+PCho) was quantitatively determined. Quantification was also performed relatively to (Cr+PCr) as suggested in [5,6]. T2 maps were acquired using a RARE sequence with the following parameters: TR=3s, TE=15->120 ms, 8 echo images, NA=1. Results and Discussion T2 values show significant difference between control and pilocarpine-treated animals only 240’ after SE-onset in the Motor Cortex (see Fig.2). In the other regions of the brain, no significant change in T2 can be observed at any investigated time point. LCModel quantification on 1H-MRS spectra (see Fig.3) shows a statistically significant decrease of (NAA+NAAG)/(GPC+PCh) in the Motor Cortex in the treated rats, compared to controls, starting from the first investigated time point (5' after SE-onset). The decrease was more pronounced at the subsequent time points with a consequent increase in the statistical significance. No significant alteration of (NAA+NAAG)/(GPC+PCh) was observed in Medial Thalamus and Hippocampus. By quantifying (NAA+NAAG)/(Cr+PCr), a similar decreasing trend was observed, but the statistical significance was p>0.10 for 5' after SE-onset, p=0.0556 for 60' and p<0.01 for 240'. The present results suggest that NAA changes, detected by MRS, may precede morphological lesions, detected by T2, in the pilocarpine model. Conclusion 1H-MRS and T2 relaxation maps constitute two non invasive techniques, which can allow a deep investigation in the epilepsy stages, as proved in the present work. We are hereby proposing that 1H-MRS is able to identify differences in NAA in the cortex since early stages, before any alterations observed by T2 maps. These observations may be important for boosting 1H-MRS as a valuable tool in developing drug targeting experiments on this model of pilocarpine-induced epilepsy and for humans studies. Absolute quantification is currently in progress.

T2 relaxion and ¹H-MRS in early stage of pilocarpine-induced status epilepticus

PELLITTERI, Michele;
2010-01-01

Abstract

Introduction Approximately 50 million people worldwide are affected by epilepsy, one of the most common neurological conditions. A non invasive technique is necessary in order to study the pathology in humans and for targeting drug research. For this reason, MRI has been widely used in experimental epilepsy studies [1]. The present work shows a comparison between 1H-MRS and T2 maps on pilocarpine-induced status epilepticus (SE) in adult rats, in early stages of the acute phase. Rats were scanned from 5 minutes to 4 hours after SE-onset , in order to investigate differences in T2 relaxation as well as in the metabolites levels in three brain regions (Cortex, Medial Thalamus and Hippocampus). These regions were chosen because recent evidences pointed out a critical role of extra-hippocampal regions in the etiopathogenesis of pilocarpine-induced epilepsy [2-3]. Methods and Materials Wistar rats (n=19 in total) were divided as follows: (Group A) control (PBS-injected, n=5), (Groups B-D) pilocarpine-injected observed at different time points after SE-onset: (B) 5' after SE-onset (n=4, one died during experiment), (C) 60' after SE-onset (n=5), (D) 240' after SE-onset (n=5). Treated rats were injected with pilocarpine hydrochloride (Sigma-Aldrich; 360mg/kg in saline, i.p.) and 30 min before with methylscopolamine (1 mg/kg in saline intraperitoneally, i.p.; Sigma-Aldrich, St. Louis,MO) to prevent peripheral cholinergic side effects. Localized 1H spectra and MR images were acquired using a 4.7 T Bruker Biospec System and a cross coil configuration for rat brain. Water suppressed spectra were acquired using PRESS sequence with TR/TE=4000/11 ms, 1024 points; a VAPOR pulse sequence was used for water suppression. The water reference spectrum was also acquired in each selected voxel. Spectra were acquired from three voxels placed in the Motor Cortex, Hippocampus and Medial Thalamus (see Fig.1) having volumes of 2x2.5x5 mm 3, 7x1.75x3 mm 3 and 5x2.25x3 mm 3. Analysis was performed by using LCModel [4]: the NAA content relatively to Choline containing compounds and PhosphoCholine (GPC+PCho) was quantitatively determined. Quantification was also performed relatively to (Cr+PCr) as suggested in [5,6]. T2 maps were acquired using a RARE sequence with the following parameters: TR=3s, TE=15->120 ms, 8 echo images, NA=1. Results and Discussion T2 values show significant difference between control and pilocarpine-treated animals only 240’ after SE-onset in the Motor Cortex (see Fig.2). In the other regions of the brain, no significant change in T2 can be observed at any investigated time point. LCModel quantification on 1H-MRS spectra (see Fig.3) shows a statistically significant decrease of (NAA+NAAG)/(GPC+PCh) in the Motor Cortex in the treated rats, compared to controls, starting from the first investigated time point (5' after SE-onset). The decrease was more pronounced at the subsequent time points with a consequent increase in the statistical significance. No significant alteration of (NAA+NAAG)/(GPC+PCh) was observed in Medial Thalamus and Hippocampus. By quantifying (NAA+NAAG)/(Cr+PCr), a similar decreasing trend was observed, but the statistical significance was p>0.10 for 5' after SE-onset, p=0.0556 for 60' and p<0.01 for 240'. The present results suggest that NAA changes, detected by MRS, may precede morphological lesions, detected by T2, in the pilocarpine model. Conclusion 1H-MRS and T2 relaxation maps constitute two non invasive techniques, which can allow a deep investigation in the epilepsy stages, as proved in the present work. We are hereby proposing that 1H-MRS is able to identify differences in NAA in the cortex since early stages, before any alterations observed by T2 maps. These observations may be important for boosting 1H-MRS as a valuable tool in developing drug targeting experiments on this model of pilocarpine-induced epilepsy and for humans studies. Absolute quantification is currently in progress.
1H-MRS; T2; rat; epilepsy; pilocarpine
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11562/340688
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