Transmitter sensitivities among various types of cultured brain stem neurons

We prepared cultures of dissociated cells from the lower brain stem of 14- to 15- day-old rat fetuses, and studied how neuronal activities of various types of neurons were influenced by application of various transmitters or transmitter-like substances. Unit discharges of the cultured neurons were recorded extracellularly, using suction micropipette, while the test substances were applied iontophoretically to the surface membrane of the cell body. We selected for testing 4 types of neurons with the typical appearance, i.e. multipolar, pyramidal, polygonal and fusiform one. Each type of neuron had specific sensitivities to acetylcholine and leucine-enkephalin. Amino acids and substance P acted to 4 types of neurons as either unanimous excitant or inhibitor. Monoamines and leucine-enkephalin had both inhibitory and facilitatory effect on unit discharges, although the inhibitory effect was dominant. These findings suggest that there is a specific relation between morphological properties of the brain stem neurons and their sensitivities to transmitters.