DYNORPHIN-IMMUNOREACTIVE TERMINALS IN THE RAT NUCLEUS-ACCUMBENS - CELLULAR SITES FOR MODULATION OF TARGET NEURONS AND INTERACTIONS WITH CATECHOLAMINE AFFERENTS
Ej. Vanbockstaele et al., DYNORPHIN-IMMUNOREACTIVE TERMINALS IN THE RAT NUCLEUS-ACCUMBENS - CELLULAR SITES FOR MODULATION OF TARGET NEURONS AND INTERACTIONS WITH CATECHOLAMINE AFFERENTS, Journal of comparative neurology, 341(1), 1994, pp. 1-15
Dynorphin facilitates conditioned place aversion and reduces locomotor
activity through mechanisms potentially involving direct activation o
f target neurons or release of catecholamines from afferents in the nu
cleus accumbens. We examined the ultrastructural substrates underlying
these actions by combining immunoperoxidase labeling for dynorphin 1-
8 and immunogold silver labeling for the catecholamine synthesizing en
zyme, tyrosine hydroxylase (TH). The two markers were simultaneously v
isualized in single coronal sections through the rat nucleus accumbens
. By light microscopy, dynorphin immunoreactivity was seen as patches
of immunoreactive varicosities throughout all rostrocaudal levels of t
he nucleus accumbens. The dynorphin-immunoreactive terminals identifie
d by electron microscopy ranged from 0.2 to 1.5 mu m in cross-sectiona
l diameter, contained numerous small (30-40 nm) clear vesicles, as wel
l as one or more large (80-100 nm) dense core vesicles. From the dynor
phin-immunoreactive terminals quantitatively examined in single sectio
ns, 74% (173/370) showed symmetric synaptic junctions mainly with larg
e unlabeled dendrites. Of the dynorphin-immunoreactive terminals formi
ng identifiable Synapses, approximately 30% contacted more than one de
ndritic target. In addition, single dendrites frequently received conv
ergent input from more than one dynorphin-labeled terminal. Irrespecti
ve of their dendritic associations, dynorphin-immunoreactive terminals
also frequently showed close appositions with other axons and termina
ls; these included unlabeled (41%), TH-labeled (10%) or dynorphin-labe
led axons (14%). In contrast to dynorphin-immunoreactive terminals, TH
-labeled terminals formed primarily symmetric synapses with small dend
rites and spines or lacked recognizable specializations in the plane o
f section analyzed. In some cases, single dendrites were postsynaptic
to both dynorphin and TH-immunoreactive terminals. We conclude that dy
norphin-immunoreactive terminals potently modulate, and most likely in
hibit, target neurons in both subregions of the rat nucleus accumbens.
This modulatory action could attenuate or potentiate incoming catecho
lamine signals on more distal dendrites of the accumbens neurons. The
findings also suggest potential sites for presynaptic modulatory inter
actions involving dynorphin and catecholamine or other transmitters in
apposed terminals. (C) 1994 Wiley-Liss, Inc.