PGP 9.5--a new marker for vertebrate neurons and neuroendocrine cells.

PGP 9.5 is a new cytoplasmic neuron-specific protein structurally and immunologically distinct from neuron-specific enolase. A specific antiserum has now shown that this protein is widely distributed in vertebrate brains and is also present in cells of the human diffuse neuroendocrine system. PGP 9.5 appears to be older than neuron-specific enolase in evolutionary terms, as an immunologically-related protein can be found in species as remote as the trout.