Are the alpha 2-adrenoceptors in the noradrenaline cell body region of physiological significance?

Preganglionic stimulation of the cervical sympathetic increased the content of 3,4-dihydroxyphenylacetic acid (DOPAC) in the superior cervical ganglion of rats treated with the dopamine beta-hydroxylase inhibitor FLA-63. It also increased and decreased the concentrations of dopamine and noradrenaline, respectively, in the salivary gland. The effects were partially inhibited by the alpha 2-adrenoceptor agonist clonidine via a yohimbine-sensitive mechanism. The alpha 2-adrenoceptor antagonist yohimbine by itself did not enhance the stimulation-evoked increase in ganglionic DOPAC, but it markedly potentiated the stimulation-evoked changes in dopamine and noradrenaline in the salivary gland. The results indicate that there are inhibitory alpha 2-adrenoceptors both in the somatodendritic and in the axon terminal region of the noradrenaline neurons but that only the alpha 2-receptors of the axon terminals are physiologically stimulated.