RIM1alpha and interacting proteins involved in presynaptic plasticity mediate prepulse inhibition and additional behaviors linked to schizophrenia

Abstract

Several presynaptic proteins involved in neurotransmitter release in the CNS have been implicated in schizophrenia in human clinical genetic studies, in postmortem studies, and in studies of putative animal models of schizophrenia. The presynaptic protein RIM1alpha mediates presynaptic plasticity and cognitive function. We now demonstrate that mice deficient in RIM1alpha exhibit abnormalities in multiple schizophrenia-relevant behavioral tasks including prepulse inhibition, response to psychotomimetic drugs, and social interaction. These schizophrenia-relevant behavioral findings are relatively selective to RIM1alpha-deficient mice, as mice bearing mutations in the RIM1alpha binding partners Rab3A or synaptotagmin 1 only show decreased prepulse inhibition. In addition to RIM1alpha's involvement in multiple behavioral abnormalities, these data suggest that alterations in presynaptic forms of short-term plasticity are linked to alterations in prepulse inhibition, a measure of sensorimotor gating.

Figure 1.

PPI deficits in presynaptic mutant mice with abnormal short-term, presynaptic facilitation (RIM1α^−/−, Rab3A^−/−, Syt1R233Q KI, but not RIM1αS413A KI). a, Significant decrease in prepulse inhibition of acoustic startle in RIM1α^−/− mice versus wild-type (WT) littermate controls at all levels of prepulse (4, 8, and 16 dB above background of 70 dB; N = 14 in a–c; two-way mixed ANOVA, main effect of genotype, F_(1,26) = 14.35, p < 0.001; main effect of prepulse level, F_(2,52) = 35.81, p < 0.001; no significant interaction; p values for post hoc planned comparisons at each prepulse level shown above bars in all panels). b, PPI deficit in Rim1α^−/− mice persists even after 4 preceding days of habituation to PPI chambers and background noise before repeat testing (two-way mixed ANOVA; main effect of genotype, F_(1,26) = 12.45, p < 0.01; main effect of prepulse level, F_(2,52) = 49.56, p < 0.001. c, Significant PPI deficits at all prepulse levels in Rab3A^−/− mice versus WT littermate controls (N = 15; two-way mixed ANOVA; main effect of genotype, F_(1,26) = 13.08, p < 0.01; main effect of prepulse level, F_(2,52) = 43.55, p < 0.001; no significant interaction). d, Significant PPI deficit at prepulse of 8 dB above background noise in Syt1R233Q KI mice versus WT littermate controls (N = 14; two-way mixed ANOVA revealed no significant main effect of genotype, F_(1,52) = 3.45, p = 0.07; main effect of prepulse level, F_(1,52) = 28.38, p < 0.0001; no significant interaction). Planned comparisons revealed a significant difference only at the 8 dB above background prepulse level (p < 0.05). e, No change in PPI at any prepulse level or in baseline startle in RIM1αS413A KI mice versus WT littermate controls (N = 11; two-way mixed ANOVA, no main effect of genotype, F_(1,21) = 0.01, p = 0.94; main effect of prepulse level, F_(2,42) = 73.0, p < 0.001; no significant interaction). Error bars indicate mean ± SEM.

Figure 2.

Selective deficit in social interaction in RIM1α^−/− mice. Time spent in social interaction with a juvenile target mouse, plotted normalized to respective WT littermate control, is significantly decreased in RIM1α^−/− mice versus WT littermate controls (N = 11; p < 0.05). Normal time spent in social interaction was observed in Rab3A^−/− (N = 13), Syt1R233Q KI (N = 13), and RIM1αS413A KI (N = 10) mice (p > 0.05). Error bars indicate mean ± SEM, *p < 0.05.

Figure 3.

Exaggerated response to the psychotomimetic drug MK-801 selectively in RIM1α^−/− mice. a, Locomotor activity is initially increased in RIM1α^−/− mice and habituates over 4 d even with hourly normal saline injections. b, After 4 d of locomotor habituation, RIM1α^−/− mice exhibit increased locomotor responses to escalating doses of MK-801 administered intraperitoneally at times indicated by arrows compared to WT littermate controls (N = 12). c–e, No difference in locomotor response to escalating doses of MK-801 in Rab3A^−/− (N = 12), SytIR233Q KI (N = 12), or RIM1αS413A KI (N = 11) mutant mice. Higher doses of MK-801 (0.4 and 0.6 mg/kg) also had no significantly different effect on SytIR233Q KI mice (data not shown). Error bars indicate mean ± SEM.

Figure 4.

Suggested mechanisms responsible for behavioral abnormalities. Alterations in short-term plasticity [PPF or paired-pulse depression (PPD)] are proposed to be responsible for altered sensorimotor gating or prepulse inhibition of startle (PPI) in the three presynaptic mutants (RIM1α^−/−, Rab3A^−/−, and SytIR233Q KI). Additional RIM1α^−/− associated synaptic abnormalities are proposed to play a role in the broader schizophrenia-relevant phenotypes in these mice.