Journal of Neuroscience, Vol 1, 1003-1007, Copyright © 1981 by Society for Neuroscience
Postsynaptic localization of alpha 2-adrenergic receptors in rat submandibular gland
DB Bylund and JR Martinez
Norepinephrine is known to inhibit its own release from presynaptic nerve
terminals through alpha 2-adrenergic receptors, which presumably have a
presynaptic localization. alpha 2-Adrenergic receptors (as determined by
[3H]clonidine binding) appear in rat submandibular gland membranes
following reserpine treatment. These alpha 2 receptors seem to be localized
postsynaptically, based on the following evidence. (1) Partial destruction
of the presynaptic nerve terminals with 6- hydroxydopamine did not decrease
the density of alpha 2-adrenergic receptors following subsequent reserpine
administration. (2) Duct ligation, which results in atrophy of the gland,
markedly decreased the density of the receptors following subsequent
reserpine administration. (3) Surgical denervation resulted in the
appearance of high levels of alpha 2-adrenergic receptors. (4) The changes
in alpha 2 receptors paralleled the changes in postsynaptic beta-adrenergic
receptor binding (as determined by [3H]dihydroalprenolol). While these
results establish the existence of postsynaptic alpha 2-adrenergic
receptors in an innervated tissue, the concomitant presence of a low
density of presynaptic alpha 2 receptors has not been eliminated.