Brain region-specific and time-dependent decreases of G alpha i2 in amygdala-kindled rats

Immunoreactivity levels of G protein alpha-subunits, Galphas (45 and 52 kDa), Galphai1, and Galphai2, were determined in plasma membranes prepared from ipsilateral amygdala-pyriform cortex (AM/PC), contralateral AM/PC, dorsal hippocampus (DH), and ventral hippocampus (VH) in amygdala-kindled rats 24 h, 1 month, and 3 months after the last seizure. Relative to sham controls, immunoreactivity levels of Galphai2 were significantly reduced in ipsilateral AM/PC and DH, with maximal decreases observed, respectively, at 24 h (26% form control levels) and 1 month (18% from control levels) postseizure. No significant alterations in the levels of Galphai1 or either of the Galphas isoforms were observed. The reduction in Galphai2 levels was, however, not accompanied by measurable changes in Galphai-mediated inhibition of adenylyl cyclase, as estimated by GppNHp modulation of forskolin-activated adenylyl cyclase activity. The present findings add support to the hypothesis that long-term changes in brain functioning following kindling may involve altered expression and/or function of components of the transmembrane signalling cascade, including G proteins.