Behavioral alterations in rat offspring following maternal immune activation and ELR-CXC chemokine receptor antagonism during pregnancy: implications for neurodevelopmental psychiatric disorders

Abstract

Research suggests that maternal immune activation (MIA) during pregnancy increases the risk of neurodevelopmental disorders including schizophrenia and autism in the offspring. Current theories suggest that inflammatory mediators including cytokines and chemokines may underlie the increased risk of these disorders in humans. For example, elevated maternal interleukin-8 (IL-8) during pregnancy is associated with increased risk of schizophrenia in the offspring. Given this association, the present experiments examined ELR-CXC chemokines CXCL1 and CXCL2, rodent homologues of human IL-8, and activation of their receptors (CXCR1 and CXCR2) in an established rodent model of MIA. Pregnant Long Evans rats were treated with the viral mimetic polyinosinic-polycytidylic acid (polyI:C; 4 mg/kg, i.v.) on gestational day 15. Protein analysis using multiplex assays and ELISA showed that polyI:C significantly increased maternal serum concentrations of interleukin-1β, tumor necrosis factor, and CXCL1 3h after administration. Subsequent experiments tested the role of elevated maternal CXCL1 on behavior of the offspring by administering a CXCR1/CXCR2 antagonist (G31P; 500 μg/kg, i.p.; 1h before, 48 and 96 h after polyI:C treatment). The male offspring of dams treated with polyI:C demonstrated subtle impairments in prepulse inhibition (PPI), impaired associative and crossmodal recognition memory, and altered behavioral flexibility in an operant test battery. While G31P did not completely reverse the behavioral impairments caused by polyI:C, it enhanced PPI during adolescence and strategy set-shifting and reversal learning during young adulthood. These results suggest that while polyI:C treatment significantly increases maternal CXCL1, elevations of this chemokine are not solely responsible for the effects of polyI:C on the behavior of the offspring.

Keywords: Crossmodal memory; Interleukin-8; Polyi:C; Schizophrenia; Set-shifting.

Fig. 1

Effects of polyI:C and G31P treatment on cytokine concentrations in maternal serum. A. PolyI:C treatment significantly increased serum concentrations of CXCL1, IL-1β, TNF. G31P treatment significantly increased serum levels of INFγ, IL-1α, and IL-2. Group sizes were: sal–sal (n = 7), sal–polyI:C (n = 9), G31P–sal (n = 4), and G31P–polyI:C (n = 4). B. Serum concentration of CXCL1, but not CXCL2, was significantly increased by polyI:C treatment. Samples were the same as those in panel A except for that two were not available for testing from the sal–polyI:C group. Serum was collected 3 h after polyI:C treatment on gestational day 15. Multiplex data are presented as fold-change relative to the group mean of the sal–sal treated group as the concentrations of the cytokines in the saline-treated group varied. * indicates a significant main effect of either polyI:C or G31P. # indicates a significant difference between the sal–sal and sal–polyI:C groups.

Fig. 2

Effects of polyI:C and G31P treatment on maternal weight change (A), number of pups per litter (B), and average pup weight at birth (C). PolyI:C treatment caused a significant weight loss in the 48 h following treatment (A) and decreased the number of pups per litter (B), without affecting pup weight (C). Maternal weight change (A) was normalized to the weight of the dams immediately before the initial saline or G31P treatment on gestational day (GD) 15. G31P or saline (500 μg/kg, i.p.) treatments occurred on gestational days 15, 17, and 19. PolyI:C or saline (4 mg/kg, i.v.) treatments were administered on GD15, 60 min after G31P or saline. Group sizes were sal–sal (n = 15 dams), sal–polyI:C (n = 11 dams), G31P–sal (n = 11 dams), G31P–polyI:C (n = 12 dams). B, C. Number of litters assessed for pups per litter and average pup weight was: sal–sal (n = 15 litters), sal–polyI:C (n = 11 litters), G31P–sal (n = 11 litters), and G31P–polyI:C (n = 12 litters). * in panels A and B denote a significant main effect of polyI:C treatment. No significant effects of G31P were observed.

Fig. 3

Acoustic startle responses and prepulse inhibition (PPI) of the offspring following maternal polyI:C and G31P treatment. A, B. Acoustic startle responses (startle amplitude, arbitrary units) for 120 dB pulse trials before, during, and after the PPI trials at postnatal days (PNDs) 35 (A) and 56 (B) (sal–sal, n = 27; sal–polyI:C, n = 21; G31P–sal, n = 21; and G31P–polyI:C, n = 23). C, D. % PPI for trials with a 30 ms prepulse–pulse interval at PNDs 35 (C) and 56 (D). Data are averaged for the 3, 6, and 12 dB prepulse intensities. Negative % PPI values reflect an increase in startle to trials with a prepulse. G31P-exposed rats showed less prepulse facilitation than other rats (main effect of G31P). E, F. Percent PPI averaged by prepulse intensity for the 50, 80, and 140 ms prepulse–pulse intervals at PNDs 35 (E) and 56 (F). G, H. Percent PPI averaged by prepulse–pulse interval for 3, 6 and 12 dB prepulse intensities at PNDs 35 (G) and 56 (H). Group sizes for C, E, G: sal–sal (n = 24), sal–polyI:C (n = 20), G31P–sal (n = 21), and G31P–polyI:C (n = 22). Group sizes for D, F, H: sal–sal (n = 26), sal–polyI:C (n = 21), G31P–sal (n = 19), and G31P–polyI:C (n = 22). Number of litters included in testing: sal–sal (n = 15), sal–polyI:C (n = 11), G31P–sal (n = 11), and G31P–polyI:C (n = 12). # in panels F and H show the significant decreases in PPI for sal–polyI:C rats compared with sal–sal rats for trials with a 140 ms interval (F) and for trials with a 3 dB prepulse (H).

Fig. 4

Associative (A, B), visual (C, D), tactile (E, F), and crossmodal (G, H) recognition memory of the offspring following maternal polyI:C and G31P treatment. Schematics using an overhead view of each test are shown in panels A, C, E and G. A 1 h delay was used between the sample and test phases of all tests. Note that the black wall of the open field chamber in panel A is indicated with a thicker black line for the north wall. In panels C and G, thin lines in the maze arms depict transparent Plexiglas walls that prevent the rats from touching the objects. Discrimination ratios (DR) by group are depicted in panels B, D, F, H; note: the y-axis varies among these panels. B. Rats from the polyI:C groups had significantly decreased associative memory, as assayed by the object-in-place test (sal–sal, n = 19; sal–polyI:C, n = 17; G31P–sal, n = 15; G31P–polyI:C, n = 17). Rats in the sal–polyI:C group also had significantly lower crossmodal memory (H). Group sizes for D: sal–sal, n = 18; sal–polyI:C, n = 14; G31P–sal, n = 19; and G31P–polyI:C, n = 13. Group sizes for F: sal–sal, n = 22; sal–polyI:C, n = 20; G31P–sal, n = 19; and G31P–polyI:C, n = 21. Group sizes for H: sal–sal, n = 23; sal–polyI:C, n = 20; G31P–sal, n = 17; and G31P–polyI:C, n = 19. Number of litters included in B: sal–sal (n = 12), sal–polyI:C (n = 11), G31P–sal (n = 11), and G31P–polyI:C (n = 12). Number of litters included in D,F,H: sal–sal (n = –polyI:C ( 15), sal n = 11), G31P–sal (n = 11), and G31P–polyI:C (n = 10). * represents main effects, # represents simple main effects comparing sal–sal and sal–polyI:C rats.

Fig. 5

Visual cue discrimination of the offspring following maternal treatment with either polyI:C or G31P. (A) Trials to criterion, (B) total errors, and (C) average response latency. sal–sal, n = 23; sal–polyI:C, n = 20; G31P–sal, n = 17; and G31P–polyI:C, n = 20. Number of litters included in testing: sal–sal = 15, sal–poly = 11, G31P–sal = 10, and G31P–poly = 11. * indicates main effects of polyI:C treatment for the visual cue total errors.

Fig. 6

The effects of maternal polyI:C and G31P treatment on strategy set shifting from visual cue to response. (A) Trials to criterion, (B) total errors, and (C) analysis of error subtypes. The inset on panel C depicts the main effect of polyI:C on regressive errors. sal–sal, n = 23; sal–polyI:C, n = 21; G31P–sal, n = 17; and G31P–polyI:C, n = 20. Number of litters included in testing: sal–sal = 15, sal–poly = 11, G31P–sal = 10, and G31P–poly = 11. * indicates main effects of G31P treatment on trials to criterion, total errors, and regressive errors.

Fig. 7

Performance of the reversal learning task following maternal polyI:C and G31P treatment. (A) Trials to criterion, (B) total errors, and (C) analysis of error subtypes. sal–sal, n = 24; sal–polyI:C, n = 20; G31P–sal, n = 18; and G31P–polyI:C, n = 21. Number of litters included in testing: sal–sal = 15, sal–poly = 11, G31P–sal = 10, and G31P–poly = 11. * indicates a main effect of G31P treatment on regressive errors.