Opposite age-dependent changes in alpha2-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 x 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 (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 alpha2-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 alpha2-adrenoceptor and I2-IR density.