Many nerve messengers such as acetylcholine can attach to more than one type of protein, or receptor, on the outside of nerve cells. Through these different receptors, a single messenger can produce opposite effects in different cell types for example, turning one cell type on while turning another off. It is just this sort of complexity that makes it difficult to predict the likely effects of different chemical messengers, Prince said. He and his colleagues found that acetylcholine's ability to do two things at once increase horizontal communication and decrease vertical communication can be explained by a two-receptor model. After confirming the orientation of the cells by filling them with dye and studying their anatomy, the researchers found that the two cell types have two different receptors.
Acetylcholine attaches to both receptors but has different effects on the different cell types.
Acetylcholine increases horizontal communication by reducing nerve cell inhibition. Less GABA means more horizontal communication. But in the bipolar cells, they found that acetylcholine attaches to the nAChR and causes the cells to release more GABA, which turns off vertical communication. The new study is distinctive in that it considers the behavior of a large number of interacting nerve cells, rather than the response of a single cell type in a dish, Prince said. Effort has to be made to put molecular information together with that gathered from studies of anatomy and cell responses to neurotransmitters.