Chewing during prenatal stress prevents prenatal stress-induced suppression of neurogenesis, anxiety-like behavior and learning deficits in mouse offspring

Abstract

Prenatal stress (PS) induces learning deficits and anxiety-like behavior in mouse pups by increasing corticosterone levels in the dam. We examined the effects of maternal chewing during PS on arginine vasopressin (AVP) mRNA expression in the dams and on neurogenesis, brain-derived neurotrophic factor (BDNF) mRNA expression, learning deficits and anxiety-like behavior in the offspring. Mice were divided into control, stress and stress/chewing groups. Pregnant mice were exposed to restraint stress beginning on day 12 of pregnancy and continuing until delivery. Mice in the stress/chewing group were given a wooden stick to chew during restraint stress. PS significantly increased AVP mRNA expression in the paraventricular nucleus (PVN) of the hypothalamus in the dams. PS also impaired learning ability, suppressed neurogenesis and BDNF mRNA expression in the hippocampus, and induced anxiety-like behavior in the offspring. Chewing during PS prevented the PS-induced increase in AVP mRNA expression of the PVN in the dams. Chewing during PS significantly attenuated the PS-induced learning deficits, anxiety-like behavior, and suppression of neurogenesis and BDNF mRNA expression in the hippocampus of the offspring. Chewing during PS prevented the increase in plasma corticosterone in the dam by inhibiting the hypothalamic-pituitary-adrenal axis activity, and attenuated the attenuated the PS-induced suppression of neurogenesis and BDNF expression in the hippocampus of the pups, thereby ameliorating the PS-induced learning deficits and anxiety-like behavior. Chewing during PS is an effective stress-coping method for the dam to prevent PS-induced deficits in learning ability and anxiety-like behavior in the offspring.

Keywords: Anxiety-like behavior; BDNF; Chewing; Learning ability; Neurogenesis; Prenatal stress.

Figure 1

Photomicrographs showing vasopressin mRNA signals in the PVN (1A), the effect of chewing during PS on AVP mRNA expression in the PVN (1B). Mean [±SE] AVP expression in C, S, S/C groups [n=6/group]. The graph shows the change relative to the C group, with the C group used as a base of 100% (1B). Bars: 100 μm, **: P<0.01. Note the increase in AVP mRNA expression in the S group compared to the C and S/C groups.

Figure 2

Effects of chewing during PS on the hole-board test performance, i.e., Rearing (2A), Distance travelled (2B), Head-dip counts (2C), and Head-dip latency (2D). The results are expressed the mean count or time [mean±SE, n=5 for each group]. **: P<0.01, *: P<0.05. Note the greater reduction in the rearing, moving distance, head-dip counts, head-dip latency in the S group.

Figure 3

Spatial learning in the Morris water maze test. The results are expressed as the mean score [mean±SE, n=5/group] of four trials per day. Note that the S group required a longer time to reach the platform.

Figure 4

Representative dual immunofluorescence micrographs of BrdU and NeuN (a-c) or GFAP (d-f) in the hippocampal DG (4A). Colocation of BrdU (red, b and e) and NeuN (green, c) or GFAP (green, f) and the merged image (a and d). Bars: 100 μm. The percentage of newly generated cells [mean±SE, n=6 for each group] (4B). The percentage of BrdU+/NeuN+ cells was significantly decreased in the SC group. The percentage of BrdU+/GFAP+ cells did not differ significantly among the three groups.

Figure 5

Effects of chewing during PS on cell proliferation (5A) and survival (5B) of newborn cells in the DG of hippocampus. The results are expressed the mean number of BrdU-positive cells [mean±SE, n=6 for each group]. **: P<0.01. Note the greater reduction in cell proliferation and survival of newborn cells in the DG in the SC group.

Figure 6

Effects of chewing during PS on quantitative PCR BDNF expression levels. Mean [±SE] BDNF mRNA expression in the C, S, S/C groups [n=6/group]. The graph shows the change relative to the C group, with the C group used as a base of 100%. **: P<0.01. Note the decrease in BDNF mRNA expression in the S group compared with the C and S/C groups.