alpha 1- and alpha 2-adrenoceptors in rat cerebral cortex: effect of frontal lobotomy.

Surgical noradrenergic denervation of the cortex via frontal lobotomy was used to destroy the noradrenergic nerve endings and thus give some insight into the distribution of alpha-adrenoceptors. Frontal lobotomy caused a reduction in noradrenaline content in rat cerebral cortex (2.1 +/- 0.4 ng/mg protein for lesioned side, 6.0 +/- 0.3 mg/mg protein for non-lesioned side), indicating an effective noradrenergic denervation. The differences in 3H-clonidine and 3H-prazosin binding observed following surgery were a significant decrease in the number of alpha 2-adrenoreceptors (115.0 +/- 4.5 to 91.7 +/- 3.2 fmol/mg protein, n = 7, P less than 0.001) and a smaller but significant increase in the number of alpha 1-adrenoceptors (119.7 +/- 2.5 to 131.6 +/- 5.4 fmol/mg protein, n = 7, P less than 0.05) in the lesioned cortex. Results of this study indicate that alpha 2-adrenoceptors located on presynaptic noradrenergic terminals represent only a small proportion of the total alpha 2-adrenoceptors in rat cerebral cortex.