[Neurotransmitter-mediated regulatory mechanisms of axoplasmic transport--acetylcholine and adrenaline].

It has not been known whether or not the axoplasmic transport depends on regulatory influences mediated by neurotransmitters. The video-enhanced microscope technique has made it possible to visualize the real-time movement of micro-particles along axons and thus to observe its quick response to external signals. Using this technique, the effects of acetylcholine (ACh) and adrenaline on the axoplasmic transport in cultured cervical ganglion (SCG) cells were examined. Application of ACh inhibited the transport in both anterograde and retrograde directions. This effect was mimicked by the muscarinic receptor agonist arecoline, but not by the nicotinic receptor agonist nicotine. The response to ACh was inhibited by QNX (3-quinuclidinyl-xanthine-9-carboxylate), a muscarinic receptor antagonist. Immunocytochemistry and in situ hybridization with anti-muscarinic receptor subtypes compounds demonstrated the expression of m2 receptors on the SCG cell. Islet-activation protein (IAP), a G-protein inhibitor, completely blocked the suppressive effect of ACh. The protein kinase A (PKA) inhibitor KT-5720 induced a similar effect to that of ACh. In contrast to the effect of ACh, adrenaline increased both anterograde and retrograde transport. The beta 2-receptor agonist (albuterol), but not alpha-receptor agonists (phenylphrine and clonidine) or beta 1-receptor agonist (dobutamine), mimicked the effect of adrenaline. The beta 2-receptor antagonist butoxamine abolished the facilitatory response to adrenaline. Dibutyryl cyclic AMP, a membrane permeable cAMP, and forskolin, an activator of adenylyl cyclase, induced a similiar effect to that of adrenaline. These results suggest that 1) ACh, acting through m2-receptors, activates Gi-protein and thus inhibits cAMP synthesis, 2) adrenaline, acting through beta 2-receptors, increases intracellular cAMP concentration, and 3) these changes in cyclic AMP levels inhibit or enhance the activity of PKA to phosphorylate proteins related to the axoplasmic transport.