Pup exposure elicits hippocampal cell proliferation in the prairie vole

Abstract

The onset of parental behavior has profound and enduring effects on behavior and neurobiology across a variety of species. In some cases, mere exposure to a foster neonate (and a subsequent parental response) can have similar effects. In the present experiment, we exposed adult male and female prairie voles (Microtus ochrogaster) to two foster pups for 20 min and quantified cell proliferation in the dentate gyrus of the hippocampus (DG), medial amygdala (MeA) and cortical amygdala (CorA). Prairie voles are highly social rodents that typically display biparental care and spontaneous parental care when exposed to foster pups. Comparisons were made between the animals that responded parentally or non-parentally towards the pups, as well as control conditions. Cell proliferation was assessed using injections of 5-bromo-2'-deoxyuridine (BrdU) and immunocytochemical localization of this marker. The phenotype of the cells was determined using double label immunofluoresence for BrdU and TuJ1 (a neuronal marker). An increase in cell proliferation in the DG was seen in animals exposed to pups. However, animals that responded non-parentally had a greater number of BrdU labeled cells in the DG compared to those that responded parentally. The majority of BrdU labeled cells co-expressed TuJ1 across all groups. These results demonstrate that exposure to a foster pup and the behavioral reaction to it (parental or non-parental) are associated with site-specific changes in cell proliferation.

Figure 1

Schedule of behavioral testing and BrdU injections.

Figure 2

BrdU-ir in the DG. The parental group had a significantly greater number of BrdU-immunoreactive cells in the DG than the no pup group, significantly fewer than the non-parental group, and showed no difference with the tootsie roll group. Bars represent means + SE. Different letters designate groups that are statistically different at p < 0.05. (Tootsie roll group is not significantly different from parental or non-parental groups.) N’s are within each bar.

Figure 3

BrdU-ir in the DG. Panels on the left hand side are taken at low magnification; scale bars = 100 microns. Panels on the right are taken at high magnification; scale bars = 25 microns. Photomicrographs were taken using differential interference contrast.

Figure 4

BrdU-ir in the MeA (left) and CorA (right). Bars represent means + SE. N= 8– 12 per group.

Figure 5

BrdU-TuJ1 Double Label Immunofluorescence in the DG. BrdU-ir cells, single label (top). TuJ1-ir cells, single label (middle). Merged image showing BrdU/TuJ1 double labeled cells (in yellow) in a parental prairie vole (bottom). Scale bar = 25 microns.