Minocycline and risperidone prevent microglia activation and rescue behavioral deficits induced by neonatal intrahippocampal injection of lipopolysaccharide in rats

Abstract

Background: Various signs of activation of microglia have been reported in schizophrenia, and it is hypothesized that microglia activation is closely associated with the neuropathology of schizophrenia.

Methods: Neonatal intrahippocampal injection of lipopolysaccharide (LPS), an activator of microglia, was performed in rats at postnatal day 7 (P7), and they were separately given saline, risperidone (0.5 mg/kg), minocycline (40 mg/kg) or a combination of both of them at P42 for consecutive 14 days. Behavioral changes (locomotion activity, social interaction, novel object recognition and prepulse inhibition) were examined and the number of microglia was assessed by using immunohistochemistry in adulthood.

Results: The adult rats in LPS-injected group showed obvious behavioral alteration (e. g. deficits in social interaction, novel object recognition and prepulse inhibition) and a dramatic increase of number of activated microglial cells in the hippocampus and other brain regions such as cerebral cortex and thalamus compared to those in saline-injected group. Interestingly, application of either minocycline, risperidone or both of them significantly rescued behavioral deficits and attenuated microglia activation.

Conclusion: Our results suggest that inhibition of microglia activation may be one of mechanisms underlying the antipsychotic effect of minocycline and risperidone.

Figure 1. The timeline of treatment, behavioral testing and IHC.

Figure 2. Effects of minocycline, risperidone and combination of these two supplementation and LPS treatment on open-field task.

NS represents no significance. The data is shown as means ± SEM. n = 8 for each group.

Figure 3. Effects of minocycline, risperidone and combination of these two on LPS-induced social interaction behaviors shown by number of contact (Figure 3A) and time spent in contact (Figure 3B).

The data are shown as means ± SEM. n  =  8 for each group. ** P<0.01, compared with saline-injected group; # P<0.01, compared with LPS-injected group.

Figure 4. Effects of minocycline, risperidone and combination of these two on LPS-induced non-spatial memory deficits in rats (the training session as shown in Figure 4A and the retention session as shown in Figure 4B).

The data is shown as means ± SEM. n = 8 for each group. ** P<0.01, compared with saline-injected group; # P<0.01, compared with LPS-injected group.

Figure 5. Effects of minocycline,risperidone, minocycline combination with risperidone on LPS-induced PPI deficits in rats.

The data is shown as means ± SEM. n = 8 for each group. ** P<0.01. compared with saline-injected group; # P<0.01,compared with LPS-injected group.

Figure 6. Iba1-immunopositive cells in VH, Cx and Th of saline- and LPS-injected rats.

A small number of Iba1-immunopositive cells are present in VH, Cx and Th of rats received neonatal intrahippocampal injection of saline (A) and the saline-injected rats treated with minocycline (B), risperidone (C) or both of them (D). On the other hand, a large of number of Iba1-immunopositive cells are observed in VH, Cx and Th of the rats received neonatal intrahippocampal injection of LPS (E), but it is dramatically reduced after intragastric administration of minocycline (F), risperidone (G) or both of them (H). A'–H' are high magnification of the ventral hippocampus in A–H, respectively. Cx, cerebral cortex; Th, thalamus; VH, ventral hippocampus. Scale bars  = 200 μm in H (applied from A–G) and 20 μm in H' (applied for A'–G').

Figure 7. Comparison of number of Iba1-immunopositive cells in VH (A), Cx (B) and Th (C) among different groups.

The data is shown as means ± SEM. n = 4 for each group. ** P<0.01, compared with saline-injected group; # P<0.01, compared with LPS-injected group.