Connections of some auditory-responsive posterior thalamic nuclei putatively involved in activation of the hypothalamo-pituitary-adrenocortical axis in response to audiogenic stress in rats: An anterograde and retrograde tract tracing study combined with fos expression
S. Campeau et Sj. Watson, Connections of some auditory-responsive posterior thalamic nuclei putatively involved in activation of the hypothalamo-pituitary-adrenocortical axis in response to audiogenic stress in rats: An anterograde and retrograde tract tracing study combined with fos expression, J COMP NEUR, 423(3), 2000, pp. 474-491
Prior studies in our laboratory demonstrated that part of the thalamus is n
ecessary for activating the hypothalamo-pituitary-adrenocortical (HPA) axis
in response to audiogenic stress in rats. The present studies were designe
d to determine how the auditory-responsive thalamic nuclei might activate t
he HPA axis. Both retrograde Fluoro-Gold (FG)I and anterograde [Pha-soleus
vulgaris-leucoagglutinin (PHA-L) and biotinylated dextran amines (BDA)] tra
cers were employed to study the putative connectivity between the thalamus
and the medial parvocellular region of the hypothalamic paraventricular nuc
leus (PAmp). In addition, rats receiving FG in the PAmp were subjected to a
udiogenic stress, and the distribution of both FG and the protein product o
f the immediate-early gene c-fos, Fos, were determined by double immunochis
tochemistry, to help assess putative functional links between the auditory-
responsive thalamic nuclei and PAmp. The results of PAmp FG placement indic
ated retrogradely labeled cells in several areas, including the bed nucleus
of the stria terminalis, hypothalamic regions, the supramammillary nucleus
, some thalamic regions, and importantly, a few multisensory nuclei of the
thalamus, including the parvicellular division of the subparafascicular and
posterior intralaminar nuclei. Injections of the tracers PHA-L or BDA into
these auditory-responsive posterior thalamic nuclei provided further evide
nce of projections to the PAmp. In addition, several forebrain areas were o
bserved to receive moderate to heavy innervation. These areas included most
of the regions described above, which, in turn, project to the PAmp. Becau
se cells in the multisensory thalamic nuclei, hypothalamic, and forebrain a
reas were double labeled with FG and Fos, the results suggest that either d
irect projections from the thalamus to PAmp neurons, or indirect projection
s from the thalamus to stress-responsive forebrain areas projecting to the
PAmp, might mediate activation of the HPA axis by audiogenic stress. (C) 20
00 Wiley-Liss, Inc.