Plasticity of GABAB receptor in rat spinal cord detected by autoradiography

Prolonged administration of (+/-)-baclofen induces tolerance to its antinociceptive effect in mice. In the present study we compare the effects of 21 days administration of (-)-baclofen or GABAB (gamma-aminobutyric acidB) receptor antagonists, with saline on the density of GABAB receptor binding sites in rat spinal cord using receptor autoradiography. Treatment with (-)-baclofen significantly reduced the number of silver grains (71%) whilst GABAB receptor antagonists, CGP 36742 (3-aminopropyl-n-butyl-phosphinic acid) and CGP 46381 (3-aminopropyl-cyclohexylmethylphosphinic acid), increased the grain count by 114% and 89%, respectively. These data indicate that GABAB receptors in the spinal cord can be influenced by prolonged administration of receptor ligands.