PLASTICITY OF GABA(B) RECEPTOR IN RAT SPINAL-CORD DETECTED BY AUTORADIOGRAPHY

Prolonged administration of (+/-)-baclofen induces tolerance to its an tinociceptive effect in mice. In the present study we compare the effe cts of 21 days administration of (-)-baclofen or GABA(B) (gamma-aminob utyric acid(B)) receptor antagonists, with saline on the density of GA BA(B) receptor binding sites in rat spinal cord using receptor autorad iograpy. Treatment with (-)-baclofen significantly reduced the number of silver grains (71%) whilst GABA(B) receptor antagonists. CGP 36742 (3-aminopropyl-n-butyl-phosphinic acid) and CGP 46381 (3-aminopropyl-c yclohexylmethylphosphinic acid), increased the grain count by 114% and 89%, respectively. These data indicate that GABA(B) receptors in the spinal cord can be influenced by prolonged administration of receptor ligands.