The hippocampus plays a role in new learning, memory and emotion and is
a component of the neuroanatomical stress circuit. The structure is involved in
terminating hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress
and attenuates stress responses by shutting off this axis.
The immunoreactivity (-ir) of c-Fos, NGF and its receptor TrkA following acute and
chronic open-field stress were studied in CA1-CA3 and the DG of the hippocampus.
The material consisted of 21 male adult rats divided into three groups: nonstressed
(control) animals and rats exposed to acute (15 min once) and chronic
(15 min daily for 21 days) aversive stimulation (open-field exposure). The brains
were stained with use of immunohistochemical methods for c-Fos, NGF or TrkA.
In the animals exposed to acute open-field stress the number of c-Fos-, TrkAand
NGF-ir cells was higher in all the structures studied than in the control animals.
However they were differentiated only in c-Fos immunoreactivity.
In the rats exposed to chronic open-field stress the number of c-Fos-ir cells in the
structures of the hippocampal formation studied was smaller than in rats exposed
to acute stress and was comparable to that in the control group. No differences
were observed between the groups exposed to acute and chronic stress in the
number of TrkA-ir cells in the structures under investigation. The number of NGF-ir
neurons in CA1 and CA2 was lower after exposure to chronic than after exposure
to acute stress but was still higher than that in the control group.
Our findings indicate that neurons of CA1-CA3 and the DG are engaged in the
stress response after acute as well as chronic open-field exposure. This is probably
related to the important role of the hippocampus in processing new spatial
information as well as in the habituation processes, although these appear to
have different mechanisms