Vm. Pickel et al., GABAERGIC NEURONS IN RAT NUCLEI OF SOLITARY TRACTS RECEIVE INHIBITORY-TYPE SYNAPSES FROM AMYGDALOID EFFERENTS LACKING DETECTABLE GABA-IMMUNOREACTIVITY, Journal of neuroscience research, 44(5), 1996, pp. 446-458
Gamma-aminobutyric acid (GABA) is a prominent inhibitory transmitter i
n both the central nucleus of the amygdala (Ce) and the medial nuclei
of the solitary tracts (mNTS). These regions are reciprocally connecte
d by anatomical pathways mediating the coordinated visceral responses
to emotional stress. To further determine whether GABA is present in t
he amygdaloid efferents or their targets in the mNTS, we combined pero
xidase labeling of Phaseolus vulgaris leucoagglutinin (PHA-L) or bioti
nylated dextran amine (BDA) anterogradely transported from the Ce with
immunogold-silver detection of antibodies against GABA in the rat mNT
S. By light microscopy, peroxidase labeling for either PHA-L or BDA wa
s seen in varicose processes, whereas immunogold-silver labeling for G
ABA was detected in perikarya and processes throughout the rostrocauda
l mNTS. The intermediate mNTS at the level of the area postrema, a reg
ion receiving mainly cardiorespiratory and gastric visceral afferents,
were examined by electron microscopy. In this region, anterograde lab
eling was observed exclusively in unmyelinated axons and axon terminal
s. These terminals lacked detectable GABA-immunoreactivity, but formed
symmetric synapses that are associated with inhibition. The targets o
f the anterogradely labeled terminals were medium-sized dendrites both
with and without GABA-labeling. These dendrites often also received c
onvergent input from terminals that were intensely GABA-immunoreactive
. We conclude that visceral activation accompanying emotional response
to stress is likely to involve inhibition of GABAergic neurons in the
mNTS by non-GABA-containing amygdaloid efferents. Furthermore, our re
sults indicate that the inhibition of these GABAergic neurons may be f
urther augmented by release of GABA from other converging terminals in
the mNTS. (C) 1996 Wiley-Liss, Inc.