Possible role of "prenervous" neurotransmitters in cellular interactions of early embryogenesis: a hypothesis.

Evidence is presented in support of the working hypothesis that "prenervous" neurotransmitters directly participate in cell-cell interactions occurring during the first several cleavage divisions of sea urchin embryos, a function which may occur during the early development of higher animals as well. This intercellular signaling could be a link in the evolutionary progression from the use of these substances as intracellular regulators to their participation in cell-cell interactions occurring during synaptic transmission.