Autonomic neuromuscular junctions: current developments and future directions.

(1) The autonomic neuromuscular junction has been defined, with emphasis on the role of muscle effector bundles and en passage release of transmitter from extensive terminal nerve varicosities to diffuse to muscle across variable and often wide junctional clefts. (2) A multiplicity of neurotransmitters is described in the autonomic nervous system, including purines, peptides, amino acids and monoamines. The ultrastructural identification, projections, roles and interactions of the different nerve types have been discussed. (3) It has been suggested that the part played by peripheral neuroeffector control mechanisms has been underestimated and includes cotransmission, pre- and post-junctional neuromodulation, and the participation of locally released agents. (4) A time-lapse film was shown of the formation of autonomic neuromuscular junctions in culture, introducing questions relating to long-term 'trophic' influences in the autonomic nervous system.