[Relationship between NR1 subunit of N-methyl-D-aspartate receptor and visceral hypersensitivity caused by acute restraint stress: experiment with rats].

OBJECTIVE

To investigate the response of NR1 subunit of N-methyl-D-aspartate (NMDA) receptor to restraint stress in intestinal tract.

METHODS

Thirty Sprague-Dawley rats were randomly divided into 3 equal groups: acute stress group undergoing intraperitoneal injection of normal saline (NS), acute stress + MK-801 group, undergoing intraperitoneal injection of MK-801, a NMDA receptor inhibitor, and then acute restraint for 1 h, 30 min after the injection. Control group underwent intraperitoneal injection of NS without acute restraint to be used as. Then all rats underwent colorectal distension (CRD) at the pressure levels of 20, 40, 60, and 80 mm Hg respectively for 10 s 3 times with an interval of 40 s so as to establish visceral hypersensitivity models. Electromyography was performed at the external oblique muscle of abdomen to record the frequency of discharge to evaluate the visceral sensitivity. Then the rats were killed and specimens of ileocecum and the proximal and distal ends of colon were obtained. RT-PCR and Western blotting were used to detect the mRNA and protein expression of NMDA receptor NR1 subunit in intestinal tract.

RESULTS

(1) The frequencies of discharge of external oblique muscle of abdomen responding to CRD of the acute stress group at the pressure levels of 40, 60, and 80 mm Hg were 925 +/- 217, 1480 +/- 347, and 1732 +/- 344 respectively, all significantly higher than those of the control group (188 +/- 31, 510 +/- 68, and 765 +/- 103, all P < 0.01) and the acute stress + MK-801 group (210 +/- 47, 525 +/- 97, 841 +/- 156, all P < 0.05). But no significantly different from the acute stress + MK-801 group and the control group (all P > 0.05). (2) The A values of the mRNA expression of NR1 in the ileocecal junction, proximal colon end, and distal colon end of the acute stress group were 1.57 +/- 0.20, 2.00 +/- 0.20, and 1.36 +/- 0.17 respectively, all significantly higher than those of the control group (0.68 +/- 0.10, 0.87 +/- 0.19, and 0.74 +/- 0.15, all P < 0.01) and the acute stress + MK-801 group (0.84 +/- 0.13, 0.91 +/- 0.16, 0.79 +/- 0.13, all P < 0.05). But no significantly different from the acute stress + MK-801 group and the control group (all P > 0.05). (3) The A values of the protein expression of NR1 in the ileocecal junction, proximal colon end, and distal colon end of the acute stress group were 1.69 +/- 0.20, 1.41 +/- 0.12, and 1.63 +/- 0.15 respectively, all significantly higher than those of the control group (0.54 +/- 0.11, 0.71 +/- 0.06, 0.71 +/- 0.07, all P = 0.000) and the acute + MK-801 group (0.75 +/- 0.09, 0.70 +/- 0.11, 0.63 +/- 0.11, all P = 0.000). But no significantly different from the acute stress + MK-801 group and the control group (all P > 0.05).

CONCLUSION

NMDA receptor plays an important role in the visceral sensitivity induced by acute restraint stress.