J. Ciriello et al., COLLATERAL AXONAL PROJECTIONS FROM VENTROLATERAL MEDULLARY NONCATECHOLAMINERGIC NEURONS TO CENTRAL NUCLEUS OF THE AMYGDALA, Brain research, 663(2), 1994, pp. 346-351
Retrograde tract-tracing techniques were used to investigate whether c
atecholaminergic neurons in the ventrolateral medulla (VLM) send colla
teral axonal projections to both central nuclei of the amygdala (ACe)
in the rat. Rhodamine-labelled latex microspheres or fluorogold (2%) w
ere microinjected into the region of either the right or left ACe. Aft
er a survival period of 10-12 days, the rats were sacrificed and trans
verse sections of the brainstem were processed immunohistochemically f
or the identification of cell bodies containing the catecholamine bios
ynthetic enzymes tyrosine hydroxylase (TH) or phenylethanolamine-N-met
hyltransferase (PNMT). Neuronal perikarya containing the retrogradely
transported tracers were observed throughout the rostrocaudal extent o
f VLM, bilaterally. Approximately 10% of the retrogradely labelled neu
rons were observed to contain both retrograde tracers. The majority (7
9 +/- 6.8%) of these double labelled neurons were located within the c
audal VLM and their number decreased rostrally. In addition, the propo
rtion of double labelled neurons to single labelled neurons in VLM dec
reased rostrally; approximately 11% in the caudal VLM and 6% in the ro
stral VLM. Furthermore, approximately 21% of all VLM neurons that proj
ected to ACe were found to be catecholaminergic: 75% of these were imm
unoreactive to TH and 25% to PNMT. However, no neurons were found in V
LM that contained both retrograde tracers and immunoreactivity to TH o
r PNMT. These data demonstrate that axons originating from non-catecho
laminergic neurons in VLM bifurcate to innervate ACe bilaterally. Alth
ough the function of these VLM neurons that project to both ACe is not
known, they may be the anatomical substrate by which VLM neurons rela
y simultaneously autonomic and/or visceral sensory information to infl
uence the activity of ACe.