Purpose Hypothalamic GABA signaling has been shown to regulate the hormonal response to hypoglycemia in animals. The hypothalamus is a challenging brain region for magnetic resonance spectroscopy (MRS) due to its small size and central location. To investigate the feasibility of measuring GABA in the hypothalamus in humans, ultra-high field MRS was used. Methods GABA levels in the hypothalamus and occipital cortex (control region) were measured in healthy volunteers during euglycemia and hypoglycemia at 7 tesla using short-echo STEAM (TE = 8 ms, TR = 5 s). Results Hypothalamic GABA levels were quantified with a mean within-session test-retest coefficient of variance of 9%. Relatively high GABA levels were observed in the hypothalamus compared with other brain regions. Hypothalamic GABA levels were 3.5 ± 0.3 μmol/g during euglycemia (glucose 89 ± 6 mg/dL) vs. 3.0 ± 0.4 μmol/g during hypoglycemia (glucose 61 ± 3 mg/dL) (P = 0.06, N = 7). In the occipital cortex, GABA levels remained constant at 1.4 ± 0.4 vs.1.4 ± 0.3 μmol/g (P = 0.3, N = 5) as glucose fell from 91 ± 4 to 61 ± 4 mg/dL. Conclusion GABA concentration can be quantified in the human hypothalamus and shows a trend toward decrease in response to an acute fall in blood glucose. These methods can be used to further investigate role of GABA signaling in the counterregulatory response to hypoglycemia in humans.
- 7 tesla
- magnetic resonance spectroscopy