Expression and Kinetics of Endogenous Cannabinoids in the Brain and Spinal Cord of a Spare Nerve Injury (SNI) Model of Neuropathic Pain

The role of endogenous cannabinoids in neuropathic pain has been actively studied, among which 2-arachidonoyl glycerol (2-AG) has received the most attention. However, owing to its chemical properties, direct detection of 2-AG distribution in tissues is difficult. Moreover, although desorption electrospray ionization mass spectrometry imaging (DESI-MSI) has enabled the detection of 2-AG, its distribution in the brain and spinal cord of neuropathic pain models has not been reported. In this study, the expression and distribution of 2-AG in the brain and spinal cord of a spare nerve injury (SNI) mice model of neuropathic pain was examined using DESI-MSI. The brain and lumbar spinal cord were collected and analyzed on days 3, 7, and 21 after treatment. On days 3 and 7 after treatment, 2-AG expression in the SNI model was decreased in the hypothalamus, midbrain, and especially in the periaqueductal gray (PAG) region but increased in the lumbar spinal cord. On day 21, the SNI model showed decreased 2-AG expression in the hypothalamus, but the difference from the control was not significant. Furthermore, there were no differences in 2-AG expression between the lumbar spinal cord, midbrain, or PAG. These data suggest that 2-AG might be involved in pain control.