Abstracts

We previously reported that Long Evans Hooded rats, treated early in life with AY9944, a cholesterol synthesis inhibitor (CSI model rats), had increased occurrence of spike-waves in EEG recordings, and that neurons acutely dissociated from reticular nuclei (nRt) of CSI model rat thalamus demonstrated decreased GABA[sub]A[/sub]-receptor sensitivity to benzodiazepines (Wu at al., 2004). The present experiments were designed to investigate changes in the gamma-2 and alpha-1 subunits of the GABA[sub]A[/sub] receptor in CSI model rats, as possible mechanisms of these changes. EEG recordings were made to analyze the occurrences of spike-waves in control and CSI model rats; Western blot, immunohistochemistry and real-time PCR techniques were performed to measure the levels of and signals for gamma-2 and alpha-1 subunits of the GABA[sub]A[/sub] receptor in the reticular (nRt) and ventrobasal (VB) relay nuclei of thalamus, and in somatosensory cortex. CSI model rats had significantly higher spike-wave scores, compared to control rats (control, n=6: 0.54 [plusmn] 0.14 vs. CSI model rats, n=5: 1.0 [plusmn] 0, p [lt] 0.05), suggesting higher seizure susceptibility in the CSI model rats. Western blot results demonstrated GABA[sub]A[/sub] receptor subunit specific alterations in thalamus and cortex. GABA[sub]A[/sub] receptor gamma-2 subunit protein expression significantly decreased in CSI model thalamic nRt and VB nuclei (control, n=6: 0.17 [plusmn] 0.02 vs. CSI model, n=6: 0.11 [plusmn] 0.01, p [lt] 0.05). This difference was not observed in somatosensory cortex (control, n=6: 0.96 [plusmn] 0.15 vs. CSI model, n=6: 0.92 [plusmn] 0.07, p= 0.8). Conversely, GABA[sub]A[/sub] receptor subunit alpha-1 protein expression decreased in CSI model somatosensory cortex (control, n=6: 1.32 [plusmn] 0.11 vs. CSI model cortex, n=6: 0.83 [plusmn] 0.12, p [lt] 0.05), but not in thalamic nRt and VB nuclei (control, n=6: 0.5 [plusmn] 0.09 vs. CSI model, n=6: 0.38 [plusmn] 0.06, p =0.3). Immunohistochemistry results confirmed Western blot results and demonstrated that the decrease in GABA[sub]A[/sub] subunits was not due to neuron loss in CSI model thalamus and cortex. The present results demonstrate that early life block of cholesterol synthesis produces region- and subunit-specific decreases in GABA[sub]A[/sub] receptor gamma-2 and alpha-1 subunits in rat nRt and VB nuclei of thalamus and cortex, respectively. The physiological significance of the selective reductions in GABA[sub]A[/sub] receptor subunits in thalamic nRt and VB nuclei and cortex remains to be determined. (Supported by Maslah Saul MD Chair, James and Carrie Anderson Research Fund, the Susan Horngren Fund for Epilepsy Research and NIH RO1 NS34774.)