The amygdala is a critical component of the neuroanatomical stress circuit. It
plays a role in the generation of responses to emotional stimuli. The central
(CeA) and medial (MeA) amygdaloid nuclei are implicated in activation of the
hypothalamic-pituitary-adrenocortical (HPA) axis.
The immunoreactivity (-ir) of c-Fos, NGF and its receptor, TrkA, following acute
and chronic open-field stress were studied in the CeA and MeA nuclei of the
amygdala. The material consisted of 21 male adult rats divided into three groups:
non-stressed (control) animals, rats exposed to acute (once only lasting 15 min)
and chronic (15 min daily over 21 days) aversive stimulation (open-field exposure).
The brains were stained with the use of immunohistochemical methods
for c-Fos, NGF or TrkA.
In the control rats c-Fos-, TrkA- and NGF-ir cells were observed in the nuclei
studied, but the quantity varied, being moderate or high (immunoreactive to
TrkA and NGF) or low (immunoreactive to c-Fos).
In the animals exposed to acute open-field stress the number of c-Fos-ir, NGF-ir
and TrkA-ir cells in the nuclei under examination was differentiated but higher
than that in the control animals.
In the animals exposed to chronic open-field stress the number of c-Fos-ir cells
in the nuclei studied was similar and was smaller than those in animals exposed
to acute stress. The number of TrkA-ir neurons was also lower in comparison to
that in animals exposed to acute stress. However, no significant differences in
the number of NGF-ir cells were observed between the groups exposed to acute
and chronic stress.
Diverse expression of c-Fos protein following both acute and chronic stress stimulation
may prove the functional heterogeneity of the amygdaloid nuclei investigated.
The decrease observed in both c-Fos- and TrkA-ir in MeA (only TrkA in
CeA) of animals exposed to chronic stress may indicate the phenomenon of
habituation
