I. Colin et al., LOCALIZATION OF COMPONENTS OF GLYCINERGIC SYNAPSES DURING RAT SPINAL-CORD DEVELOPMENT, Journal of comparative neurology, 398(3), 1998, pp. 359-372
The sequence of events leading to the chemical matching of presynaptic
neurotransmitters and postsynaptic transmitter receptors is investiga
ted here in vivo for the spinal glycine receptor (GlyR) by using immun
ocytochemical methods. In the ventral horn of adult rat spinal cord, G
lyRs are only present at glycinergic postsynaptic differentiations whe
re they are stabilized by the associated protein gephyrin. With quanti
tative confocal microscopy, we found that gephyrin is detected before
GlyRs at embryonic day (E)13-E14 and at E15, respectively, inside the
cytoplasm and at plasmalemmal loci. Around the time of birth, the numb
er of cell surface gephyrin-immunoreactive (-IR) spots exceeds that of
GlyR. They first match 10 days after birth. The densities of postsyna
ptic gephyrin- and GlyR-IR were quantified between birth and the adult
stage with post-embedding immunogold staining. Immunostaining for gep
hyrin and GlyR was not detected in the extrasynaptic membrane. The den
sity of staining in postsynaptic membrane increased progressively with
development. The inhibitory aminoacid content of the presynaptic term
inal boutons opposed to gephyrin-IR sites was also analyzed. In the ne
wborn, postnatal day 10, and adult, more than 90% of these boutons wer
e immunostained for glycine. As seen with serial sections, 38% and 51.
2% of the terminals also contained gamma-aminobutyric acid (GABA) in n
eonate and adult, respectively. These data indicate that around the ti
me of birth, most glycine-containing boutons, some also containing GAB
A, are opposed to gephyrin-IR postsynaptic densities, whereas GlyRs ar
e not present. Our results suggest that gephyrin determines subsynapti
c loci an the plasma membrane where GlyR will subsequently accumulate.
J. Comp. Neurol. 398:359-372, 1998. (C) 1998 Wiley-Liss, Inc.