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Deletion of Rapgef6, a candidate schizophrenia susceptibility gene, disrupts amygdala function in mice.

Levy RJ, Kvajo M, Li Y, Tsvetkov E, Dong W, Yoshikawa Y, Kataoka T, Bolshakov VY, Karayiorgou M, Gogos JA - Transl Psychiatry (2015)

Bottom Line: Rapgef6 deletion resulted in impaired amygdala function measured as reduced fear conditioning and anxiolysis.Hippocampal-dependent spatial memory and prefrontal cortex-dependent working memory tasks were intact.Electrophysiological analysis showed enhanced long-term potentiation at cortico-amygdala synapses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Columbia University, New York, NY, USA.

ABSTRACT
In human genetic studies of schizophrenia, we uncovered copy-number variants in RAPGEF6 and RAPGEF2 genes. To discern the effects of RAPGEF6 deletion in humans, we investigated the behavior and neural functions of a mouse lacking Rapgef6. Rapgef6 deletion resulted in impaired amygdala function measured as reduced fear conditioning and anxiolysis. Hippocampal-dependent spatial memory and prefrontal cortex-dependent working memory tasks were intact. Neural activation measured by cFOS phosphorylation demonstrated a reduction in hippocampal and amygdala activation after fear conditioning, while neural morphology assessment uncovered reduced spine density and primary dendrite number in pyramidal neurons of the CA3 hippocampal region of knockout mice. Electrophysiological analysis showed enhanced long-term potentiation at cortico-amygdala synapses. Rapgef6 deletion mice were most impaired in hippocampal and amygdalar function, brain regions implicated in schizophrenia pathophysiology. The results provide a deeper understanding of the role of the amygdala in schizophrenia and suggest that RAPGEF6 may be a novel therapeutic target in schizophrenia.

No MeSH data available.


Related in: MedlinePlus

Spike timing-dependent LTP in cortical input to the LA is enhanced in Rapgef6 knockout mice. (a) Spike timing-dependent LTP at the cortico-LA synapses in slices from WT and HOM mice. Insets show the average of 15 EPSPs recorded in current-clamp mode before and 40 min after induction. (b) Summary of LTP experiments in cortical input to the LA. (c) Evoked cortico-LA EPSCs (average of 15 traces) were recorded sequentially in same neurons at holding potentials −70 mV (bottom) and +40 mV (top) in slices from WT and HOM mice. The NMDA receptor-mediated component of the EPSC was measured at +40 mV at the dashed lines. (d) Summary of the NMDA/AMPA ratio values in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSP, excitatory postsynaptic potential; HOM, homozygous; LA, lateral nucleus of the amygdala; LTP, long-term potentiation; WT, wild type.
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fig5: Spike timing-dependent LTP in cortical input to the LA is enhanced in Rapgef6 knockout mice. (a) Spike timing-dependent LTP at the cortico-LA synapses in slices from WT and HOM mice. Insets show the average of 15 EPSPs recorded in current-clamp mode before and 40 min after induction. (b) Summary of LTP experiments in cortical input to the LA. (c) Evoked cortico-LA EPSCs (average of 15 traces) were recorded sequentially in same neurons at holding potentials −70 mV (bottom) and +40 mV (top) in slices from WT and HOM mice. The NMDA receptor-mediated component of the EPSC was measured at +40 mV at the dashed lines. (d) Summary of the NMDA/AMPA ratio values in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSP, excitatory postsynaptic potential; HOM, homozygous; LA, lateral nucleus of the amygdala; LTP, long-term potentiation; WT, wild type.

Mentions: Previous studies provide evidence that the mechanisms of LTP in the auditory CS pathways may contribute to the encoding and retention of conditioned fear memory.31, 55, 56, 57 Therefore, fear-conditioning deficits observed in Rapgef6−/− mice could result from LTP impairments in inputs to the LA delivering CS information. To test this possibility, we examined LTP of the EPSPs in cortical input to the LA in slices from control and mutant mice. LTP was induced in current-clamp mode by pairing presynaptic stimuli delivered at 2 Hz with action potentials evoked in a recorded postsynaptic neuron with 4–8 ms delay from the onset of each EPSP in the presence of the GABAA receptor antagonist picrotoxin (50 μM; Figure 5a).32, 58 Unexpectedly, we found that the magnitude of spike timing-dependent LTP at the cortico-LA synapses was enhanced in slices from Rapgef6−/− mice compared with slices from control animals (Figure 5b; n=5 neurons from three control mice, n=6 neurons from five Rapgef6−/− mice; unpaired t-test, P=0.013). The facilitating effect of the Rapgef6 ablation on LTP was not due to enhancements in the NMDA receptor-mediated synaptic responses, as we did not observe differences in the NMDA/AMPA amplitude ratio in the evoked EPSCs between control and Rapgef6−/−mice (Figures 5c and d; n=12 neurons from four control mice, n=15 neurons from six Rapgef6−/− mice; unpaired t-test, P=0.71). Given that the amplitude of mEPSCs (reflecting sensitivity of postsynaptic AMPA receptors to glutamate) was unaffected by the mutation, the lack of changes in the NMDA/AMPA amplitude ratio indicates that NMDA receptor-mediated synaptic responses remained unchanged in Rapgef6−/− mice.


Deletion of Rapgef6, a candidate schizophrenia susceptibility gene, disrupts amygdala function in mice.

Levy RJ, Kvajo M, Li Y, Tsvetkov E, Dong W, Yoshikawa Y, Kataoka T, Bolshakov VY, Karayiorgou M, Gogos JA - Transl Psychiatry (2015)

Spike timing-dependent LTP in cortical input to the LA is enhanced in Rapgef6 knockout mice. (a) Spike timing-dependent LTP at the cortico-LA synapses in slices from WT and HOM mice. Insets show the average of 15 EPSPs recorded in current-clamp mode before and 40 min after induction. (b) Summary of LTP experiments in cortical input to the LA. (c) Evoked cortico-LA EPSCs (average of 15 traces) were recorded sequentially in same neurons at holding potentials −70 mV (bottom) and +40 mV (top) in slices from WT and HOM mice. The NMDA receptor-mediated component of the EPSC was measured at +40 mV at the dashed lines. (d) Summary of the NMDA/AMPA ratio values in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSP, excitatory postsynaptic potential; HOM, homozygous; LA, lateral nucleus of the amygdala; LTP, long-term potentiation; WT, wild type.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4490285&req=5

fig5: Spike timing-dependent LTP in cortical input to the LA is enhanced in Rapgef6 knockout mice. (a) Spike timing-dependent LTP at the cortico-LA synapses in slices from WT and HOM mice. Insets show the average of 15 EPSPs recorded in current-clamp mode before and 40 min after induction. (b) Summary of LTP experiments in cortical input to the LA. (c) Evoked cortico-LA EPSCs (average of 15 traces) were recorded sequentially in same neurons at holding potentials −70 mV (bottom) and +40 mV (top) in slices from WT and HOM mice. The NMDA receptor-mediated component of the EPSC was measured at +40 mV at the dashed lines. (d) Summary of the NMDA/AMPA ratio values in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSP, excitatory postsynaptic potential; HOM, homozygous; LA, lateral nucleus of the amygdala; LTP, long-term potentiation; WT, wild type.
Mentions: Previous studies provide evidence that the mechanisms of LTP in the auditory CS pathways may contribute to the encoding and retention of conditioned fear memory.31, 55, 56, 57 Therefore, fear-conditioning deficits observed in Rapgef6−/− mice could result from LTP impairments in inputs to the LA delivering CS information. To test this possibility, we examined LTP of the EPSPs in cortical input to the LA in slices from control and mutant mice. LTP was induced in current-clamp mode by pairing presynaptic stimuli delivered at 2 Hz with action potentials evoked in a recorded postsynaptic neuron with 4–8 ms delay from the onset of each EPSP in the presence of the GABAA receptor antagonist picrotoxin (50 μM; Figure 5a).32, 58 Unexpectedly, we found that the magnitude of spike timing-dependent LTP at the cortico-LA synapses was enhanced in slices from Rapgef6−/− mice compared with slices from control animals (Figure 5b; n=5 neurons from three control mice, n=6 neurons from five Rapgef6−/− mice; unpaired t-test, P=0.013). The facilitating effect of the Rapgef6 ablation on LTP was not due to enhancements in the NMDA receptor-mediated synaptic responses, as we did not observe differences in the NMDA/AMPA amplitude ratio in the evoked EPSCs between control and Rapgef6−/−mice (Figures 5c and d; n=12 neurons from four control mice, n=15 neurons from six Rapgef6−/− mice; unpaired t-test, P=0.71). Given that the amplitude of mEPSCs (reflecting sensitivity of postsynaptic AMPA receptors to glutamate) was unaffected by the mutation, the lack of changes in the NMDA/AMPA amplitude ratio indicates that NMDA receptor-mediated synaptic responses remained unchanged in Rapgef6−/− mice.

Bottom Line: Rapgef6 deletion resulted in impaired amygdala function measured as reduced fear conditioning and anxiolysis.Hippocampal-dependent spatial memory and prefrontal cortex-dependent working memory tasks were intact.Electrophysiological analysis showed enhanced long-term potentiation at cortico-amygdala synapses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Columbia University, New York, NY, USA.

ABSTRACT
In human genetic studies of schizophrenia, we uncovered copy-number variants in RAPGEF6 and RAPGEF2 genes. To discern the effects of RAPGEF6 deletion in humans, we investigated the behavior and neural functions of a mouse lacking Rapgef6. Rapgef6 deletion resulted in impaired amygdala function measured as reduced fear conditioning and anxiolysis. Hippocampal-dependent spatial memory and prefrontal cortex-dependent working memory tasks were intact. Neural activation measured by cFOS phosphorylation demonstrated a reduction in hippocampal and amygdala activation after fear conditioning, while neural morphology assessment uncovered reduced spine density and primary dendrite number in pyramidal neurons of the CA3 hippocampal region of knockout mice. Electrophysiological analysis showed enhanced long-term potentiation at cortico-amygdala synapses. Rapgef6 deletion mice were most impaired in hippocampal and amygdalar function, brain regions implicated in schizophrenia pathophysiology. The results provide a deeper understanding of the role of the amygdala in schizophrenia and suggest that RAPGEF6 may be a novel therapeutic target in schizophrenia.

No MeSH data available.


Related in: MedlinePlus