Cannabinoid receptor 1 regulates the spatial learning and memory function and the expression of NR1 subunit of N-methyl-D-aspartic acid receptor in medial prefrontal cortex of neuropathic pain model rat

Abstract

Objective To investigate the effect of cannabinoid receptor 1 (CBR1) on spatial learning and memory function of neuropathic pain (NP) model rats and the expression of N-methyl-D-aspartic acid receptor 1(NR1) subunit in medial prefrontal cortex (mPFC). Methods Thirty-six healthy male Wistar rats were randomly divided into 4 groups, with 9 rats in each group: the sham operated group (SO group), the neuropathic pain model group (NP group), the NP model group with an mPFC injection of saline (NS group), and the NP model group with an mPFC injection of the CBR1 antagonist AM251 (AM251 group). The NP model was prepared using the operation of chronic constriction injury (CCI) of the right sciatic nerve. The mechanical withdrawal threshold (MWT) and the thermal withdrawal latency (TWL) of the rats in each group were detected at 3, 7, 14, 21 and 28 days after the operation. At 29 days after the operation, 18 rats of NP model were randomly selected and given an mPFC injection of saline or AM251 using a three-dimensional brain puncture. At days 30-37 after operation, the eight-arm maze test was performed to detect the spatial learning and memory function of the rats, and the rats were sacrificed immediately after this test. The expression levels of CBR1, NR1 and phosphorylated-N-methyl-D-aspartic acid receptor 1 (p-NR1 ) (Ser896) in the mPFC brain region were detected by Western blotting, RT-PCR and immunofluorescence. Results Compared with the SO group, the pain thresholds and the spatial learning and memory function of the rats in the NP group were significantly lower (both P<0.05). Compared with the NS group, the rats in the AM251 group showed improvement about spatial learning and memory function (P<0.05). Compared with the SO group (the mRNA and protein level of CBR1: 0.23±0.06, 0.42±0.03), the mRNA(0.43±0.12) and protein (0.53±0.05) level of CBR1 in NP group increased (both P<0.05). Compared with the NS group (the mRNA and protein level of CBR1: 0.42±0.11, 0.52±0.10), the mRNA (0.53±0.05) and protein (0.98±0.17) level of CBR1 in AM251 group increased (both P<0.05). Compared with the SO group (the mRNA and protein level of NR1 and the protein level of p-NR1: 1.50±0.15, 0.65±0.05, 0.79±0.15), the mRNA (0.94±0.07) and protein (0.24±0.05) level of NR1 in NP group decreased (both P<0.05), the protein level of p-NR1 (0.33±0.04) decreased (P<0.05). Compared with the NS group (the mRNA and protein level of NR1 and the protein level of p-NR1: 1.09±0.14, 0.26±0.06, 0.31±0.08), the mRNA(1.58±0.10) and protein (1.42±0.10) level of NR1 in AM251 group increased (both P<0.05), the protein (0.95±0.15) level of p-NR1 increased (P<0.05). Conclusion CBR1 can decrease the expression level of NR1 and p-NR1 in the mPFC brain region of NP model rats and induce the spatial learning and memory impairment. Key words: Neuropathic pain; Cannabinoid receptor 1; N-methyl-D-aspartic acid receptor