Shingo Kakeda MD, Abstract Co-Author: Nothing to Disclose

Johji Nishimura MD, Presenter: Nothing to Disclose

Shoudai Bun, Abstract Co-Author: Nothing to Disclose

Junji Moriya, Abstract Co-Author: Nothing to Disclose

Norihiro Ohnari, Abstract Co-Author: Nothing to Disclose

Yukunori Korogi MD, Abstract Co-Author: Nothing to Disclose

Although recent spectroscopic studies have found significant deficits of the occipital lobe GABA in depression and anxiety disorders, it has not been confirmed yet whether there is a regional difference and a circadian rhythm of brain GABA level in human. The aim of this study was to evaluate the fundamental characteristics of human brain GABA.

Study population consisted of 14 healthy adult volunteers. Each volunteer was examined with the GABA editing in the early morning and evening at 3T MR system (Signa EXCITE 3T; GE Medical Systems). Spectroscopy voxels (3 x 3 x 3 cm3) were placed in the frontal lobe and parieto-occipital lobe. GABA measurements were made using a MEGA-PRESS sequence for voxel localization, water suppression and editing of the 1.9ppm GABA resonance, to reveal the GABA+ peak at 3ppm while suppressing the overlapping Creatine (Cr) singlet (TR=3s, TE=68ms, 128 averages, 6min acquisition time). All spectra were analyzed with LC model using phantom-generated basis functions for the PRESS and MEGA-edited spectra.

The mean GABA/Cr ratios were significantly lower in the parieto-occipital lobe than in the frontal lobe (p<0.01) both in the morning and evening. For the intraindividual comparison in the parieto-occipital lobe, the mean GABA/Cr ratios was lower in the morning than in the evening (1.66 vs 2.57, p=0.05). In the frontal lobe, there was no difference in mean GABA/Cr ratios between the morning and evening.

There were significant differences of the mean GABA/Cr ratios between the frontal lobe and the parieto-occipital lobe as well as between the morning and evening.

It is necessary to consider a circadian rhythm of brain GABA when measuring GABA level. The measurements of brain GABA might also provide new insight into the mechanism of sleep disorders.

Kakeda, S, Nishimura, J, Bun, S, Moriya, J, Ohnari, N, Korogi, Y, Circadian Rhythm of Human Brain GABA at 3T 1H-MRS.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5010443.html