Myositis-induced functional reorganisation of the rat dorsal horn: effects of spinal superfusion with antagonists to neurokinin and glutamate receptors.

The study aimed at identifying some of the receptors for neurotransmitters/neuromodulators that are involved in the myositis-induced neuroplastic changes in spinal neurones. In anaesthetised rats, an experimental myositis was induced in the gastrocnemius-soleus muscle and the activity of single dorsal horn neurones recorded in the segment L3, just rostral to the main input region from that muscle. During the development of the myositis, the segment L3 was continuously superfused with antagonists to neurokinin receptors (GR 82.334, Spantide II), NMDA receptors (MK-801, AP 5) or AMPA/kainate receptors (CNQX). Each of the antagonists reduced the myositis-induced increase in excitability, but acted on different aspects of the hyperexcitability. GR 82.334 was most effective in preventing the expansion of the neurone population that responded to A-fibre input from the inflamed muscle, which was the main myositis effect in the present study. None of the antagonists influenced the background activity of the neurones. The results show that in the myositis-induced hyperexcitability of dorsal horn neurones all of the above receptors are involved. Excitability by peripheral input and background activity of the neurones are probably controlled by different mechanisms.