Sex-dependent behavioral effects and morphological changes in the hippocampus after prenatal invasive interventions in rats: implications for animal models of schizophrenia

Abstract

Objectives: Although schizophrenia affects both human genders, there are gender-dependent differences with respect to age of onset, clinical characteristics, course and prognosis of the disease.

Methods: To investigate sex-dependent differences in motor coordination and activity as well as in cognitive and social behavior, we repeatedly tested female (n = 14) and male (n = 12) Fisher rats (postnatal days, PD 56-174) that had received intracerebroventricular injections of kainic acid as well as female (n = 15) and male (n = 16) control animals. The hippocampus was examined histologically.

Results: Compared to male controls, in the alcove test both female controls and female animals with prenatal intervention spent less time in a dark box before entering an unknown illuminated area. Again, animals that received prenatal injection (particularly females) made more perseveration errors in the T-maze alternation task compared to controls. Female rats exhibited a higher degree of activity than males, suggesting these effects to be sex-dependent. Finally, animals that received prenatal intervention maintained longer lasting social contacts. Histological analyses showed pyramidal cells in the hippocampal area CA3 (in both hemispheres) of control animals to be longer than those found in treated animals. Sex-dependent differences were found in the left hippocampi of control animals and animals after prenatal intervention.

Conclusion: These results demonstrate important differences between males and females in terms of weight gain, response to fear, working memory and social behavior. We also found sex-dependent differences in the lengths of hippocampal neurons. Further studies on larger sample sets with more detailed analyses of morphological changes are required to confirm our data.

Keywords: CA3 region; Neurodevelopment; Psychiatric disease; Social contact; Working memory.

Figure 1

Weight gains of male and female controls and prenatally interventioned Fisher rats. All animals were repeatedly weighed between PD 42 and PD 168. Depicted is the weight at weeks 6, 7, 8, 12, 16, 20 and 24. Female rats gained less weight over the course of 24 weeks than the males. The male control (n = 8) and prenatal intervention (n = 16) groups gained more weight over the course of 24 weeks than the females. In contrast to males, female controls (n = 10) did not differ from the female prenatal intervention group (n = 14) *p ≤ 0.007.

Figure 2

Alcove test. The time (in seconds) spent in a dark box before exploring a brightly lit open field was measured at weeks 8, 12, 16, 20 and 24 for the male (n = 6) and female (n = 6) controls and male (n = 16) and female (n = 14) prenatal intervention groups. The two latencies, A1 and A2, were summed. The male prenatal intervention group and the females exited the dark box more quickly than the male controls over the test period of 24 weeks. The values of males differed at weeks 12, 16 and 20; male and female controls displayed differences at weeks 16, 20 and 24; *p ≤ 0.01.

Figure 3

T-Maze perseveration errors. The number of perseveration errors of male (n = 13–16) and female (n = 12–14) animals that received prenatal intervention, and that of male (n = 5–8) and female (n = 9–13) controls was measured at weeks 8, 12, 16, 20 and 24. Male and female animals that received prenatal intervention demonstrated a higher number of perseveration errors than the controls. These differences were significant for females at weeks 12 and 16, and for males at weeks 16 and 20; *p ≤ 0.01

Figure 4

Social interaction test. Nose contact within 60 seconds for male (n = 5–9) and female (n = 8–13) control and male (n = 12–13) and female (n = 9–11) prenatal intervention groups with different partners** was measured at weeks 8, 12, 16, 20 and 24. In general, male and female prenatal intervention groups showed a greater extent of social contact than controls, depending on the degree of kinship. At week 12, there were differences between male and female controls and male and female animals which received prenatal intervention with MSC and FsiC/FSiPI as partners, and at week 16 for the male rats with FsiC/FsiPI as partners; *p ≤ 0.01. **MSC = male strange control; FSC = female strange control; MSiC or MSiPI = male sibling control or prenatal intervention; FSiC or FSiPI = female sibling control or prenatal intervention.

Figure 5

Length of the pyramidal cells of the hippocampus. Average (± SEM) length of the pyramidal cells in area CA3 of the right and left hippocampi of male (n = 12) and female (n = 14) controls and male (n = 16) and female (n = 14) animals with prenatal intervention was determined. Male and female prenatal intervention rats had significantly shorter cell lengths in both their right and left hippocampi compared to controls. Cells in right hemispheres of male and female prenatal intervention groups were significantly longer than those in left hemispheres. Male controls had significantly longer cells on the left side. Female controls had shorter cells in the left hippocampus, but this difference was not significant. With the exception of cell lengths on the right hippocampal side of male and female controls, cells in the hemispheres of males were longer than the respective cells in female animals. Compared to the left hemisphere, differences between right hemispheres of male and female controls and prenatal intervention groups were not significant. *p ≤ 0.05, **p ≤ 0.006 and ***p ≤ 0.0004.