Regional Distribution Of Neurotensin In Spinal Ventral Horn And Its Change Under Neuropathic Conditions In Rats

Neurotensin,a tridecapeptide, is widely distributed throughout the nervous system and gastrointestinal tract, and has been involved in several physiological functions, including modulation of nociception in the central nervous system. In the spinal cord, neurotensin is mainly derived from intrinsic neurons and evidently has analgesia effect most probably via its high-affinity receptor or low-affinity receptor.It has been confirmed that neurotensin is distributed both in the dorsal and ventral horn of the spinal cord, and we have got detailed information about its distribution in the dorsal horn. While little is known about how it is distributed in the ventral horn. Further more, the source of neurotensin implicated in the modulation of nociception is not understood. In this study, we first observed the characteristics of regional distribution of neurotensin in the ventral horn of the spinal cord with morphological method, and then established the Chronic Constrictive Injury model in SD rats to investigate the distributional change of neurotensin in the spinal cord under neuropathic conditions, aiming at approaching the probable mechanism of neurotensin in nociceptive modulation in the spinal cord.Part One The regional distribution of neurotensin in the ventral horn of spinal cordIn this study, Nissl-staining and acetylcholinesterase staining method were firstly applied to label the motor neurons in the ventral horn of the spinal cord, and then, immunohistochemistry technique with the multiclonal antibody of neurotensin was used to observe the neurotensin-like immunoreactive cells in the ventral horn of the spinal cord, by comparing with the different neurons with the different methods, we found:Neurotensin-like immunoreactive products (NT-LI) were both found in large neural cells and small neural cells. The former were multipolar or bipolar neurons, mainly in Laminaâ…¨, and were morphologically consistent with the motor neurons found both in Nissl-staining and acetylcholinesterase(AChE) staining; The latter were dispersedly distributed in VH. The small neurons, though we knew little about its characteristics, may probably the regulatory interneurons.Part Two The establishment of Chronic Constrictive Injury model in ratsAdult male SD rats were randomly divided into three groups: operated group, sham operated group, and normal group. And then, Chronic Constrictive Injury model was established with the operated group by ligating the right sciatic nerve four times consecutively with 5-0 silk thread. The treatment of the sham operated group was identical with operated group except for not ligating the sciatic nerve. When the model was established, the thermal pain threshold was monitored consecutively by recording the latency of lifting the hind paw. And the behaviors were also observed every day.It was found that:The spontaneous pain and paraesthesia on the operated group rats such as lifting the paw spontaneously, licking the paw, not walking on the right occurred after the first day of the operation, along with the decrease of the pain threshold. Further more, the abnormity such as flexuosity and inversion of the hind paw was also found. The symptoms above were at the peak on the 5-7 days after the operation and then gradually recovered on the 13-14 days after the operation except the flexuosity and inversion of the hind paw. No apparent symptoms above were found on the sham operated group and the normal group rats.Part Three The upregulation of neurotensin in the spinal ventral horn under neuropathic conditionsUnder normal conditions, intrathecal injection of exogenous neurotensin in the spinal level exerts a dramatical analgesia effect. To research the change of endogenous neurotensin level in the spinal cord under neuropathic conditions, we used immunohistochemistry technique, along with monitoring the pain threshold based on Chronic Constrictive Injury model, observed the change of neurotensin level both on the 7th day(when the pain threshold was at the lowest level ) and on the 14th day(when the pain threshold was back to the normal level) respectively among the operated group, sham operated group and the normal group.It was found that:1.On the laminaâ…¨,there was no dramatic difference of the area of the large neurotensin-live immunoreactive cells among the three groups whether on the 7th day or on the 14th day, which meant the large cells containing neurotensin did not change both in the lowest pain threshold period and in the recovery of the pain threshold; While the number of the small neurons in the operated group dramatically increased on the 7th day compared with sham operated group and normal group, and gradually decreased back to the normal level on the 14th day. The same phenomenon was also found with the small neurons on the laminaâ…§. No substantial difference of the number of the small neurons was found on any other parts of the spinal cord among the three groups.2. The neurotensin level was dramatically increased in the substantia gelatinosa(SG) of the spinal dorsal horn of the operated group on the 7th day, showing the apparent eyebrow-like structure, and on the 14th day, the neurotensin level was gradually decreased, along with the disappearance of the eyebrow-like structure.In summary, the existing evidence in our study suggests that neurotensin may be distributed in motor neurons and some regulatory interneurons in the ventral horn of the spinal cord and probably be involved in the modulation of nociception under neuropathic conditions.