Autoradiographic studies of central α2A- and α2C-adrenoceptors in the rat using [H]MK912 and subtype-selective drugs

In the present study we examined the distribution of α_2A- and α_2C-adrenoceptors in tissue slices from the rat cervical spinal cord and from brain slices collected at the level of the striatum. To differentiate between α_2A- and α_2C-adrenoceptors, the slices were incubated with [³H]MK912 in the presence of graded concentrations of the α_2A-selective drug, BRL44408, or the α_2C-selective drug, spiroxatrine. Computer analysis of the autoradiograms indicated that 0.4 nM [³H]MK912 plus 185 nM BRL44408 selectively labeled α_2C-adrenoceptors, while 0.4 nM [³H]MK912 plus 220 nM spiroxatrine selectively labeled α_2A-adrenoceptors. Using this approach, α_2C-adrenoceptors were detected in the striatum, while α_2A-adrenoceptors predominated in the cortical layers 1–4, the spinal cord distal dorsal horn, the septum and the endopiriform nucleus.