S. Roder et J. Ciriello, INNERVATION OF THE AMYGDALOID COMPLEX BY CATECHOLAMINERGIC CELL GROUPS OF THE VENTROLATERAL MEDULLA, Journal of comparative neurology, 332(1), 1993, pp. 105-122
The projections to the amygdaloid complex (AMG), originating in the ca
techolaminergic cell groups of the ventrolateral medulla (VLM), were s
tudied in the rat by using either the retrograde tracer fluorogold (FG
) or the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L)
in combination with tyrosine hydroxylase (TH) and/or phenylethanolami
ne-N-methyltransferase (PNMT) immunohistochemistry. In the first serie
s of experiments, injections of FG were made into regions of the centr
al nucleus of the amygdala (ACe) where dense TH and PNMT immunoreactiv
ity was previously observed, and then sections of the brainstem were p
rocessed for TH and PNMT immunoreactivity. FG retrogradely labelled ne
uronal cell bodies were observed throughout the rostrocaudal extent of
VLM, bilaterally, with a contralateral predominance. Approximately 44
% of the FG labelled cell bodies in VLM were also immunoreactive to th
e catecholamine biosynthetic enzymes TH and/or PNMT. Most of these cat
echolaminergic neurons were part of the Al noradrenergic cell group in
the caudal VLM and to a lesser extent part of the Cl adrenergic cell
group in the rostral VLM. In the second series of experiments, PHA-L w
as iontophoresed into VLM at different rostrocaudal levels where in th
e previous series of experiments FG retrogradely labelled cell bodies
were observed. Transverse sections of the forebrain and brainstem were
then processed for the demonstration of PHA-L and either TH or PNMT i
mmunoreactivity in cell bodies, axons, and presumptive axon terminals.
PHA-L injection sites within either the caudal or rostral VLM resulte
d in labelled axons and terminal bouton-like swellings primarily in th
e contralateral AMG and to a lesser extent in the ipsilateral AMG. The
ACe was observed to receive the greatest innervation from either VLM
site. Additionally, PHA-L labelled fibers and presumptive terminal bou
tons were observed within the intercalated, medial, basomedial, and ba
solateral nuclei of the AMG. Most of the PHA-L labelled fibers and pre
sumptive terminal boutons in the AMG after a caudal VLM (A1 region) in
jection also displayed TH immunoreactivity, whereas after a PHA-L inje
ction into the rostral VLM (Cl region) all of the labelled axons and a
xon terminals in the AMG also were immunoreactive to PNMT. These data
demonstrate that catecholaminergic neurons in A1 and C1 regions of VLM
innervate the AMG and suggest that these VLM neurons may be involved
in relaying afferent information directly to the AMG which influences
the activity of AMG neurons controlling autonomic, endocrine, and beha
vioural functions.