Neurochemical Changes in Brain Induced by Chronic Morphine Treatment: NMR Studies in Thalamus and Somatosensory Cortex of Rats

To investigate the effects of chronic morphine treatment and its cessation on thalamus and the somatosensory cortex, an ex vivo high resolution (500 MHz) ¹H nuclear magnetic resonance spectroscopy (NMRS), in the present study, was applied to detect multiple alterations of neurochemicals and/or neurometabolites in the rats. Ten days of chronic morphine administration was observed to markedly increase the total amount of lactate (Lac), myo-inositol (my-Ins) (each P < 0.01) and aspartate (Asp) (P < 0.05), and significantly decrease that of glutamate (Glu) and glutamine (Gln) in the rats thalamus (each P < 0.05). In the somatosensory cortex, chronic morphine was shown to increase the level of Lac and my-Ins, and decrease that of Glu (each P < 0.05). Interestingly, the ratio of Glu/GABA was found to decrease in these two brain areas after chronic morphine treatment, and among the detectable neurochemicals in those two cerebral areas, only taurine (Tau) showed to result in a significant increment in thalamus during the process of morphine discontinuation (P < 0.05). Moreover, the alterations of multiple neurochemicals due to chronic morphine exhibited a tendency of recovery to the normal level over the course of morphine withdrawal. The results suggested that, in thalamus and the somatosensory cortex, chronic morphine administration and its cessation could induce multiple neurochemical changes, which may involve in the brain energy metabolism, activity and transition of neurotransmitters.