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

Abstract Opposite age-dependent changes in α 2 -adrenoceptor and imidazoline I 2 receptor (I 2 -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 [ 3 H]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 I 2 -IRs was significantly higher in membranes of injured cortex ( B max  = 60 ± 6 fmol/mg protein; n  = 9) than in control ( B max  = 38 ± 3 fmol/mg protein; n  = 9; p  = 0.0053). Conversely, the density of α 2 -adrenoceptors, measured by [ 3 H]clonidine (0.25–16 nM), in the injured cortex ( B max  = 75 ± 4 fmol/mg protein; n  = 9) was significantly lower than in sham membranes ( B max  = 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 α 2 -adrenoceptor and I 2 -IR density.