抄録
Peripheral nerve injury often leads to pathological pain processes including hyperalgesia and allodynia in animals and humans. Although peripheral neuronal mechanisms contribute to these pathological pain state, recent investigation shows that changes in central neuronal function, such as glutamatergic nerve activation and disinhibition of inhibitory neurons in the spinal cord, may play a pivotal role. Therefore, it is reasonable to determine whether apoptosis develops resulting from glutamatergic activation via acceleration of intracellular and nuclear signalling processes. The aim of the present study was to investigate the histopathological changes in relation to response to thermal stimulation with time in rats with chronic constriction injury (CCI). Male Sprague-Dawley rats were anesthetized with pentobarbital (50mg/kg, I.P.) and left sciatic nerve were ligated. Sham rats were performed skin incision only. Paw withdrawal latency times (PWL) of response to thermal stimulation were measured in these rats by using the plantar test equipment at the 6 th to 10 th postoperative days (POD). Immunohistochemical analysis for apoptosis (TUNEL stain) and neuronal degeneration (NAUTA stain) in the laminae I-II, III-VI and VII-IX in spinal cord (L3-5) in rats was performed with light microscope (40 and 400 times) at the 6 th, 7 th and 10 th POD, respectively. TUNEL stain score was obtained as 0 : no positive neuron to 3 : more than 10% neurons show positive, and NAUTA stain score was also obtained as 0 : normal neuron to 3 : more than 50% somato-dendritic argyrophyllic neurons. In the sham group, any remarkable change in the pain behaviour throughout period measured. While in the CCI rat, PWL decreased at the ipsilateral side after operation. In TUNEL stain, positive neurons developed in the ipsilateral laminae I-II at the 6th and 7th day and then became to less at the 10th day after CCI. In contrast, positive neurons of NAUTA stain were developed in the ipsilateral laminae III-VI after CCI (7th<10th day). The present results demonstrate that apoptosis development was firstly found in the superficial layer of spinal cord in rats with early state of hyperalgesia evoked by sciatic nerve ligation. This may suggest that sciatic nerve injury leads to increased ascending inputs or glutamatergic nerve activation followed by derangement of intracellular signalling-intranuclear process (c-fos expression) in the spinal cord which causes apoptosis leading to pain behaviour. It is also suggested that the delayed appearance of neuronal degeneration in the laminae III-VI causes dysfunction of inhibitory interneurons located in this region and this neuronal damage is sufficient to develop the sustained pain behaviour.
