Modification of GABAB1 and GABAB2 receptor subunits in the somatosensory cerebral cortex and thalamus of rats with absence seizures (GAERS)

In the present study, we have investigated GABAB receptor expression in somatosensory cortex (S1) and the ventrobasal (VB) and reticular (Rt) thalamic nuclei of Genetic Absence Epilepsy Rats from Strasbourg (GAERS), which represent an animal model for the human absence epilepsy. We focused our attention on the thalamocortical network because it has been demonstrated that absence seizures are generated in this specific circuit, which is under the control of several inhibitory, e.g. GABA, and excitatory systems. Autoradiography data obtained with the GABAB receptor antagonist [3H]CGP62349 did not show any differences in Kd or Bmax values between control rats and GAERS. In situ hybridisation (ISH) results showed a significant increase in messenger RNA for GABAB1 in the S1 and a decrease in the VB thalamic nucleus but not in the Rt thalamic nucleus. By contrast the immunocytochemical data revealed an increased expression of both GABAB1 and GABAB2 receptor subunits in all the regions examined, somatosensory cerebral cortex, VB thalamus and Rt nucleus in GAERS compared to controls. The main finding was an up-regulation of GABAB receptor protein in the corticothalamic circuit in GAERS compared to controls.