Neuromediators and neuromodulators. Evolution of compounds and evolution of hypotheses.

The probable features of the evolution of neuromediators (NM) and neuromodulators (NR) of different types are discussed. The assumption concerning the high rate of evolution of peptide NM and NR and the greater potentialities of the formation of new NM and NR of this type is substantiated. Monomolecular NM and NR are presumably more conservative, but have an advantage as regards the strict individualism of the systems of synthesis and degradation. Peptides, individual amino acids, and ATP are probably among the oldest NM and NR.