Journal of Neuroscience, Vol 16, 1380-1388, Copyright © 1996 by Society for Neuroscience
PSD-95 is associated with the postsynaptic density and not with the presynaptic membrane at forebrain synapses
CA Hunt, LJ Schenker and MB Kennedy
Division of Biology, California Institute of Technology, Pasadena 91125, USA.
PSD-95, a prominent protein component of the postsynaptic density (PSD)
fraction from rat forebrain, has been localized by light microscopy to
dendrites of hippocampal neurons (Cho et al., 1992) and to the presynaptic
plexus of cerebellar basket cells (Kistner et al., 1993). Here we extend
these studies to show that an affinity-purified antibody to PSD-95 labels
the dendrites of most neurons in the forebrain and of a subset of neurons
in the cerebellum. To confirm that PSD-95 is associated with the PSD at
forebrain synapses and to clarify whether it is also associated with the
presynaptic membrane, we employed immunogold electron microscopy of
forebrain synaptosomes. Gold-labeled antibodies to PSD-95 labeled
postsynaptic densities in both intact and lysed forebrain synaptosomes but
did not label presynaptic terminals or the presynaptic membrane. The
asymmetric distribution of PSD-95 at synapses contrasts with that of its
homologs, disks-large and ZO-1, which are arranged symmetrically at septate
and tight junctions, respectively.