Cortisol decreases prefrontal glutamine concentrations

Abstract

In rodents, stress and corticosteroids rapidly increase excitatory neurotransmission. During excitatory neurotransmission, glutamate concentrations are maintained by conversion of glutamine to glutamate. The hypothesis was that cortisol would alter human prefrontal glutamine or glutamate concentrations. Glutamine and glutamate were measured in prefrontal cortex (n = 12) using 3.0 Tesla proton magnetic resonance spectroscopy (1H-MRS) before and after intravenous cortisol (hydrocortisone 35mg), in a randomized, double blind, placebo-controlled, within-subjects design. Glutamine decreased following cortisol compared with placebo (session by time, F(2,22) = 5.51; p = 0.012), whereas glutamate did not change (F(4,44) = 0.71; p = 0.59). Glutamine may be utilized to maintain glutamate concentrations during increased excitatory neurotransmission following cortisol. A limitation is that 1H-MRS does not measure metabolic flux rates directly. The effects of cortisol on glutamine could be a useful measure of altered central glucocorticoid responses in psychiatric disorders.