Effects of intra-hippocampal injection of interleukin-2 on pain threshold and formaldehyde-induced substance P-like immunoreactivity in periaqueductal gray and spinal cord.
OBJECTIVE
To study the effects of intra-hippocampal injection of interleukin-2 (IL-2) on the substance P-like immunoreactivity (SP-LI) in both periaqueductal gray (PAG) and spinal cord, and on pain threshold in rats.


METHODS
Immunohistochemistry technique was used and the paw withdrawal threshold to radiant heat was measured.


RESULTS
Microinjection of hIL-2 480 U in hippocampus (Hip) increased the pain threshold (93% +/- 57%, P < 0.01). Injection of formaldehyde (For) in one hindpaw decreased SP-LI neuron number on both sides of PAG (2.9 +/- 2.8 vs 22.1 +/- 0.7, 12.3 +/- 2.0 vs 22.4 +/- 1.0, P < 0.01) and increased SP-LI in ipsilateral spinal cord (0.836 +/- 0.015 vs 0.59 +/- 0.09, P < 0.01). Microinjection of hIL-2 480 U in Hip inhibited the effects of For on the SP-LI on both sides of the PAG (11.3 +/- 2.3 vs 2.9 +/- 2.8, 16.9 +/- 3.4 vs 12.3 +/- 2.0, P < 0.05) and spinal cord (0.71 +/- 0.03 vs 0.836 +/- 0.015, P < 0.01). The combination of intraperitoneal injection of corticotropin and intra-hippocampal injection of IL-2 increased the number of SP-LI neurons in PAG furtherly as compared with IL-2 240 U alone (13.6 +/- 3.6 vs 7.6 +/- 4.3, P < 0.05).


CONCLUSIONS
The analgesic effects of intra-hippocampal injection of IL-2 are mediated, possibly, via the increased of SP in PAG and the decrease of SP in the spinal cord. There is a synergetic relation between IL-2 and corticotropin.
Wu
X
X
Department of Physiology, Third Military Medical University, Chongqing 400038, China.
Li
H D
HD
Li
X C
XC
Ruan
H Z
HZ
Wang
J
J
D000818:Animals; D006624:Hippocampus / Q000502:physiology; D007276:Injections, Intraventricular; D007376:Interleukin-2 / Q000494:pharmacology*; D009474:Neurons / Q000378:metabolism; D017288:Pain Threshold / Q000187:drug effects*; D010487:Periaqueductal Gray / Q000378:metabolism*; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*
D007376:Interleukin-2; D013373:Substance P