Mouse brain astrocytes from primary cultures were found to contain both a l and 012 adrenergic receptors. 3H WB 4101 labeled one category of binding site (KD = 1.5 f 0.39 nM, Bmax = 64 f 7.9 fmoles/mg protein) with typical 01, adrenergic specificity (WB 4101 > prazosin > yohimbine). The density of a I adrenergic receptors was 2-3 times higher in mouse cerebral cortex than in glial cells.
Like rat brain [U' Pritchard et al, 1979; Rouot et al, 19801, mouse glial cells were found to contain two categories of 3H clonidine binding sites: high affinity sites, which were identical to the high but not to the low affinity sites found in rat brain, since 1) they displayed the same affinity for 3H clonidine (KD = 1.2 f 0.13 nM, n = 4) and the same typical a2 adrenergic specificity (yohimbine > WB 4101 > prazosin); 2) the dissociation rate constant for clonidine binding was equal to 0.06 min-I, a value close to that found previously for the high affinity 3H clonidine binding sites in rat brain (0.05 min"); and 3) divalent cations augmented and guanyl nucleotides reduced 3H clonidine binding as in rat brain. Na' decreased 3H clonidine binding in a complex manner.
The number of high affinity sites in glial cells (52 f 9.4 fmoles/mg protein, n = 4) was half the number found in mouse cerebral cortex (98 fmoles/mg protein). Low affinity 3H clonidine binding sites (KD = 81 f 18 nM, Bmax = 96 f 5.8 fmoles/mg protein, n = 3) were not fully characterized. described in brain, but their physiological function is not yet known.
In conclusion, glial cells contained the same a adrenergic receptors as those