CHANGES IN CHOLINERGIC AND OPIOID RECEPTORS IN THE RAT SPINAL-CORD, DORSAL-ROOT AND SCIATIC-NERVE AFTER VENTRAL AND DORSAL-ROOT LESION

Changes in the distribution of H-3-quinuclidinylbenzilate (H-3-QNB), H-3-acetylcholine (H-3-ACh) and H-3-alpha-bungarotoxin (alpha-BTx) binding sites were studied with the use of quantitative in vitro autoradiography in the L4-L6 segments of rats 7 days after ventral L4-L6-rhizotomies and 24 hours after ligation of the dorsal roots L4-L6. The changes in the binding sites of these ligands and of H-3-etorphine binding sites were also studied in the dorsal roots of the rats operated with dorsal root ligation and in the sciatic nerves (around a ligature) in the rats operated with ventral rhizotomy. After ventral rhizotomy H-3-QNB binding sites in the ipsilateral motor neuron area were decreased by about 25% from 100 +/- 5 to 73 +/- 5 fmol/mg wet weight. After dorsal root ligation H-3-QNB binding sites in the ipsilateral posterior horn were reduced by about 30% from 91 +/- 5 to 64 +/- 7 fmol/mg wet weight. No significant changes in the binding of the other cholinergic ligands in the spinal cords were observed after the operations. In the dorsal root H-3-alpha-Btx and H-3-etorphine binding sites were higher on the distal side of the ligation (3.5 +/- 0.8 and 14 +/- 4 fmol/mg wet weight, respectively) than on the proximal side (0.7 +/- 0.5 and 2.4 +/- 1.2 fmol/mg wet weight, respectively). The same level of H-3-ACh (total, muscarinic and nicotinic) binding was observed on both sides of the ligation. In the sciatic nerve H-3-QNB and total, muscarinic and nicotinic ACh binding sites were higher on the proximal side of the ligation than on the distal side. Except for a small emergence of muscarinic-ACh binding distally to the ligation there were no changes in the number of binding sites in the sciatic nerve after the ventral rhizotomy. Muscarinic antagonist binding sites are probably located on the perikarya of the motor neurons and presynaptically on the primary afferents in the posterior horn and in the dorsal root. Cholinergic agonist binding sites in the spinal cord seem less sensitive to axonal damage than antagonist binding sites. Cholinergic and opioid receptors in peripheral nerves are transported in both anterograde and retrograde directions and their origin seems to be the dorsal root ganglion.