Regeneration, Repair, and Developmental NeuroscienceResearch PaperNerve growth factor (NGF) immunoreactive neurons in the juvenile rat hippocampus: response to acute and long-term high-light open-field (HL-OF) or forced swim (FS) stress stimulation
Highlights
▶NGF is expressed in hippocampal cells of juvenile rats. ▶We studied the effects of acute and long-term HL-OF and FS stress on NGF-ir cells. ▶Both types of stimulations led to an increase in the density of NGF-ir cells. ▶After long-term HL-OF or FS stress habituation did not occur in juvenile rats.
Section snippets
Animals
Twenty-five Wistar Han rats were housed with their mothers (one mother with five pups per cage) from birth until the end of the experiment, when they reached 28 days of age (P28; P-postnatal day). The animals were kept in impoverished polycarbonate cages (T. IV, 56 cm×36 cm ×20 cm+7 cm cage lid) containing only sawdust on the floor, but they had free access to water and food pellets. Temperature (21±1 °C) and lighting (light on from 7:00 am–7:00 pm) regimens were maintained at constant levels
NGF-immunoreactive cells in hippocampal structures (CA1, CA3, and DG) in P28 control rats
In juvenile (P28) control rats, NGF-ir cells were observed in the pyramidal layer of the CA1 and CA3 areas, as well as in the granular layer of the DG subregion of the hippocampus (Fig. 1, Fig. 2, Fig. 3A, Fig. 1, Fig. 2, Fig. 3B–B′). The density of NGF-ir cells in CA1 and CA3 was comparable (CA1: 1403.62±95.54, CA3: 1348.13±87.27), but in DG the number was slightly higher (1738.19±82.06) (Fig. 1, Fig. 2, Fig. 3A). Varying intensity of NGF immunostaining was observed in the somata (cytoplasm)
Discussion
Our experiment demonstrated that both acute and long-term HL-OF or FS stress resulted in a statistically significant increase in the density of NGF-ir neurons in juvenile (P28) rats in all investigated hippocampal regions.
An immunohistochemical study showed that NGF-ir neurons occurred in the pyramidal cell layers of CA1 and CA3 and in the DG granular cell layer of the unstressed juvenile rats. The presence of NGF-immunoreactive cells in these areas during early postnatal life has been reported
Conclusions
Applied stress stimuli (HL-OF or FS) led to an increase in the density of NGF-ir neurons in the hippocampus of juvenile rats, which might have affected HPA axis activity. In hippocampal structures acute vs. chronic stress stimulation was not reflected in the changes of the density of NGF containing neurons after HL-OF or FS. Long-term HL-OF or FS stressors were probably so aggravating that the phenomenon of habituation did not occur. The type of stress stimulus (HL-OF vs. FS) was generally not
Acknowledgments
This study was supported by funds from the Polish Committee of Scientific Research (research project No N401 011 31/0168). We would like to thank, Dr. Jerzy Diewiątkowski for statistic analysis.
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