Muscarinic receptors in the cochlear nucleus and auditory nerve of the guinea pig.
The specific-binding properties of l-[3H]quinuclidinyl benzilate, a muscarinic acetylcholine-receptor antagonist, were investigated in synaptic and other membrane preparations of the guinea pig cochlear nucleus and auditory nerve. Binding parameters for all experiments were consistent with a single binding site with a Hill coefficient of 1.0. The binding of the ligand was specific and of high affinity, with values of KD in the range of 30-80 pM. Bmax was 0.352 +/- 0.023 pmol/mg protein for the dorsal cochlear nucleus and 0.215 +/- 0.011 pmol/mg protein for the ventral cochlear nucleus. The dorsal cochlear nucleus/ventral cochlear nucleus ratio for density of muscarinic receptors (1.6/1.0) was maintained across two different buffer systems, which varied with respect to the inclusion of proteolysis inhibitors. The results for auditory nerve indicated a level of binding much below that of the cochlear nucleus, with Bmax = 0.052 +/- 0.011 pmol/mg protein. The results of specific-binding experiments for l-[3H]quinuclidinyl benzilate support a role for acetylcholine as a neurotransmitter in the cochlear nucleus. The greater density of muscarinic receptors in the dorsal cochlear nucleus may indicate greater cholinergic activity in the dorsal relative to the ventral cochlear nucleus.
D000818:Animals; D003056:Cochlear Nerve / Q000378:metabolism*; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D014018:Tissue Distribution; D000159:Vestibulocochlear Nerve / Q000378:metabolism*
D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate