Purpose: To develop a new rat model of postthoracotomy pain for investigati
ng its mechanisms and clarifying neurochemical changes.
Methods: Male Wistar rats were randomly assigned to three groups that under
went either fourth and fifth intercostal nerve ligation, cutting of the fou
rth and fifth ribs, or a sham operation in which only pleura was cut. For b
ehavioural response assessment during the following month, pinch and touch
were used as mechanical stimuli, and acetone was used as a cold thermal sti
mulus. in addition, I-125-substance P autoradiography was used to determine
neurokinin (NK) receptor density in spinal cord laminae I and II at one to
six weeks after surgery.
Results: In rats with nerve ligation, hypersensitivity to noxious and non-n
oxious stimuli continued throughout the month. The "mirror phenomenon" was
observed. The lowest threshold was obtained in the dorsomedial portion of t
he T4 dermatome on the side of surgery. In rats with rib cutting, a lowered
threshold to noxious and non-noxious stimuli was observed for two weeks. I
n rats with sham operations, hypersensitivity was seen only at postoperativ
e day one. NK-I receptor density on the side of operation increased signifi
cantly in rats with nerve ligation from day seven to 28. Receptor density w
as highest on day 14 (22.97 +/- 1.04 fmol(.)mg(-1) tissue vs control, 16.22
+/- 0.43), representing a 50% receptor excess on the side of ligation comp
ared to the contralateral side.
Conclusion: Intercostal nerve damage induces long-term postthoracotomy pain
and an increase of spinal NK-I receptors in rats. This model may be useful
for investigation of postthoracotomy pain.