MYOSITIS-INDUCED FUNCTIONAL REORGANIZATION 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 neurotransmit ters/neuromodulators that are involved in the myositis-induced neuropl astic changes in spinal neurones. In anaesthetised rats, an experiment al myositis was induced in the gastrocnemius-soleus muscle and the act ivity of single dorsal horn neurones recorded in the segment L3, just rostral to the main input region from that muscle. During the developm ent of the myositis, the segment L3 was continuously superfused with a ntagonists to neurokinin receptors (GR 82.334, Spantide II), NMDA rece ptors (MK-801, AP 5) or AMPA/kainate receptors (CNQX). Each of the ant agonists reduced the myositis-induced increase in excitability, but ac ted on different aspects of the hyperexcitability. GR 82.334 was most effective in preventing the expansion of the neurone population that r esponded to A-fibre input from the inflamed muscle, which was the main myositis effect in the present study. None of the antagonists influen ced 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 differ ent mechanisms.