Long-term effects of maternal immune activation on depression-like behavior in the mouse

Abstract

Depression is a debilitating mental disease affecting a large population worldwide, the pathophysiological mechanisms of which remain incompletely understood. Prenatal infection and associated activation of the maternal immune system (MIA) are prominently related to an increased risk for the development of several psychiatric disorders including schizophrenia and autism in the offsprings. However, the role of MIA in the etiology of depression and its neurobiological basis are insufficiently investigated. Here we induced MIA in mice by challenge with polyinosinic:polycytidylic phosphate salt-a synthetic analog of double-stranded RNA, which enhances maternal levels of the cytokine interleukin-6 (IL-6)-and demonstrate a depression-like behavioral phenotype in adult offsprings. Adult offsprings additionally show deficits in cognition and hippocampal long-term potentiation (LTP) accompanied by disturbed proliferation of newborn cells in the dentate gyrus and compromised neuronal maturation and survival. The behavioral, neurogenic and functional deficiencies observed are associated with reduced hippocampal expression of vascular endothelial growth factor (VEGF)A-VEGFR2. IL-6-STAT3-dependent aberrant VEGFA-VEGFR2 signaling is proposed as neurobiological mechanism mediating the effects of MIA on the developing fetal brain and ensuing consequences in adulthood.

Figure 1

Maternal immune activation (MIA) at embryonic day 12.5 (PIC) increases depression-like behavior in adulthood. (a) Sucrose preference test to measure anhedonic behavior. (b) Behavioral despair analysis by the forced swim test. Controls (n=34) and PIC (n=20) mice. Data represent mean±s.e.m. of PIC relative to control mice. ***P<0.001.

Figure 2

Maternal immune activation (MIA) induces cognitive deficits but does not alter general behavioral function. Cognitive evaluation of adult PIC mice using the Morris water maze (MWM) task. (a) Latencies in the acquisition phase of MWM of PIC (red) relative to controls (blue). (b) Sample tracking pathways during the last training day (TD3). Target platform in top left quadrant. (c) Percentage of time spent in the target quadrant during the first 15 s of the probe trial. (d) Locomotor activity evaluated by the total distance traveled in the open field. (e) Motor coordination evaluation using the rota rod. n=10–34 per group. Data represent mean±s.e.m. *P<0.05, **P<0.01, n.s. not significant.

Figure 3

Maternal immune activation (MIA) impairs long-term potentiation (LTP) and paired pulse facilitation (ppF) in hippocampal slices. (a) Temporal course of percent slope change of field excitatory postsynaptic potentials (fEPSP) in hippocampal slices differed significantly between PIC (red) and controls (blue) as evaluated by mixed-model repeated-measures analysis of variance (ANOVA). (b) ppF as fold change from first response. n=16 per group. Data represent mean±s.e.m. **P<0.01.

Figure 4

Maternal immune activation (MIA) decreases proliferation of newborn cells in the dentate gyrus (DG) of the hippocampus. (a) Schematic representation of 5-bromodeoxyuridine (BrdU) injection protocols for proliferation and survival paradigms. (b) Approximated number of BrdU-labeled cells per hippocampus in the proliferation paradigm. Sample fluorescence microscope images (20 × ) of BrdU-labeled cells (red) show differences in proliferation between (c) control and (d) PIC mice. n=5–6 animals per group. Scale bars denote 100 μm. Data represent mean±s.e.m. **P<0.01.

Figure 5

Maternal immune activation (MIA) reduces survival of new born cells and affects differentiation morphology of neuronal cells in the dentate gyrus (DG) of the hippocampus. Total number of 5-bromodeoxyuridine (BrdU)-labeled cells in the DG. (a) Quantification of surviving BrdU-positive (BrdU+) cells show significantly lower number of surviving cells in PIC mice. Sample images (20 × ) depict a significant difference in the number of surviving BrdU-labeled cells between (b) control and (c) PIC animals. (d) Schematic and sample pictures (63 × ) illustrating differentiation analysis by morphological criteria using doublecortin (DCX) staining. (e) Percentages of BrdU+ cells in different stages of developmental morphology during the DCX period. (f) PIC animals show significantly lower number of BrdU+/NeuN+ cells. (g) No differences observed in BrdU+/glial fibrillary acidic protein (GFAP)+ cells. n=5-6 animals per group. Gray scale bars denote 50 μm, yellow scale bars denote 5 μm. Data represent mean±s.e.m. *P<0.05, **P<0.01, ***P<0.001, n.s. not significant.