Jb. Cabot et al., POSTSYNAPTIC GEPHYRIN IMMUNOREACTIVITY EXHIBITS A NEARLY ONE-TO-ONE CORRESPONDENCE WITH GAMMA-AMINOBUTYRIC ACID-LIKE IMMUNOGOLD-LABELED SYNAPTIC INPUTS TO SYMPATHETIC PREGANGLIONIC NEURONS, Journal of comparative neurology, 356(3), 1995, pp. 418-432
Peripheral regulation of cardiovascular function is fundamentally infl
uenced by central excitation and inhibition of sympathetic preganglion
ic neurons in thoracic spinal cord. This electron microscopy study inv
estigated whether the gamma-aminobutyric acid (GABA)-ergic and glycine
rgic inhibitory innervation of sympathetic preganglionic neurons arise
s from mutually exclusive afferent populations. Sympathetic preganglio
nic neurons were retrogradely labeled with cholera beta subunit. GABAe
rgic terminals were identified using strict quantitative statistical a
nalyses as those boutons containing significantly elevated levels of G
ABA-like immunogold labeling (GABA(+)). Glycinergic terminals were cla
ssified as those boutons opposite postsynaptic gephyrin immunostaining
containing background levels of GABA-like immunogold labeling (gephyr
in(+)/GABA(-) association). Approximately 43% of the synaptic terminal
s that contacted sympathetic preganglionic somata and proximal dendrit
es and that were opposite gephyrin were GABA(-); the remaining 57% wer
e GABA(+). Only two GABA(+) boutons (4%) that synapsed on identified s
ympathetic preganglionic neuron (SPN) processes were not opposite geph
yrin immunostaining(GABA(+)/gephyrin(-) association). GABA(-)/gephyrin
(+) associations were anticipated given prior anatomical, physiologica
l, and pharmacological data. The observed nearly one-to-one correspond
ence between postsynaptic gephyrin immunoreactivity and GABA(+) bouton
s was unexpected. Prior physiological and pharmacological experiments
suggest that the postsynaptic effects of GABAergic inputs to sympathet
ic preganglionic neurons are mediated by activation of GABA(A) recepto
rs. Those data, the present results, and other molecular, biochemical,
and anatomical studies of gephyrin in the central nervous system (CNS
) are consistent with two hypotheses: 1) Postsynaptic gephyrin is asso
ciated with GABA(A) receptors in the membranes of sympathetic pregangl
ionic neurons, and 2) GABA(+)/gephyrin(+) associations do not necessar
ily predict colocalization of GABA and glycine within single boutons s
ynapsing on sympathetic preganglionic somata and dendrites. (C) 1995 W
iley-Liss, Inc.