A subpopulation of neurons in the rat rostral nucleus of the solitary tract that project to the parabrachial nucleus express glutamate-like immunoreactivity
Cf. Gill et al., A subpopulation of neurons in the rat rostral nucleus of the solitary tract that project to the parabrachial nucleus express glutamate-like immunoreactivity, BRAIN RES, 821(2), 1999, pp. 251-262
In rodents, gustatory information is transmitted from second order neurons
in the rostral nucleus of the solitary tract (rNST) to the parabrachial nuc
leus (PBN) in the pens. The chemical nature of this projection is unknown.
Therefore, the goal of the current study was to determine if rNST neurons t
hat project to the PEN express glutamate-like immunoreactivity. Projection
neurons were retrogradely labeled following stereotaxic injection of rhodam
ine-filled latex microspheres into the right PEN of seven rats while glutam
ate-immunoreactive (GLU-IR) structures were visualized in the same tissue u
sing an immunoperoxidase procedure. The number of single- and double-labele
d neurons located in the right (ipsilateral) and left rNST, in each of the
nuclear subdivisions as well as their position along the rostral-caudal axi
s of the rNST was determined. GLU-IR cell bodies were located throughout th
e rNST. Although the rostral central subdivision contained the highest perc
entage (33.8%) of GLU-IR perikarya, immunolabeled neurons were most concent
rated (number/area of subdivision) within the medial subnucleus. The rostra
l third of the rNST contained the fewest (20.5%) and lowest density of GLU-
IR cell bodies. The highest percentage of rNST neurons retrogradely labeled
from the PEN were located ipsilateral (85.4%) to the pontine injection sit
e, in the middle third of the nucleus (44.2%) and within the rostral centra
l subdivision (52.4%). Overall, 18% of the labeled rNST projection neurons
were GLU-IR. The distribution of double-labeled neurons mirrored that of th
e projection neurons with the largest number located in the ipsilateral rNS
T (84.5%), middle third of the nucleus (40.5%) and rostral central subdivis
ion (64.7%). These results indicate that glutamate may be a main component
of the ascending pathway from the rNST to the PEN. In addition, since GLU-I
R neurons were located throughout the rNST and most were not retrogradely-l
abeled, the current results suggest that glutamate may be an important neur
otrans-mitter within the medulla. (C) 1999 Elsevier Science B.V. All rights
reserved.