Opposite changes in Imidazoline I2 receptors and α2-adrenoceptors density in rat frontal cortex after induced gliosis

Opposite age-dependent changes in α2-adrenoceptor and imidazoline I2 receptor (I2-IRs) density have been related to brain gliosis development with aging. To check this hypothesis we applied in rats a model of reactive gliosis induced by heat. The specific binding of [3H]idazoxan (0.5-20 nM) in the presence of (−)adrenaline (5 × 10− 6 M) to membranes from rat brain cortex showed that the density of I2-IRs was significantly higher in membranes of injured cortex (Bmax = 60 ± 6 fmol/mg protein; n = 9) than in control (Bmax = 38 ± 3 fmol/mg protein; n = 9; p = 0.0053). Conversely, the density of α2-adrenoceptors, measured by [3H]clonidine (0.25-16 nM), in the injured cortex (Bmax = 75 ± 4 fmol/mg protein; n = 9) was significantly lower than in sham membranes (Bmax = 103 ± 7 fmol/mg protein; n = 9; p = 0.0035). No significant differences in receptor's affinity were observed between both groups. These results support the hypothesis that gliosis induces opposite changes in α2-adrenoceptor and I2-IR density.