Limits...
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

Basal synaptic transmission in the LA is normal in Rapgef6 knockout mice. (a) Synaptic input–output curves for the EPSCs recorded at the cortico-LA synapses in slices from WT and HOM mice. The EPSCs were recorded under voltage-clamp conditions at a holding potential of −70 mV. (b) Same as in a, but the EPSCs were recorded in thalamic input to the LA. (c) Top, examples of paired-pulse facilitation of the cortico–amygdala EPSCs recorded at different interstimulus intervals (50 ms, 70 ms, 100 ms and 200 ms) at a holding potential of −70 mV in slices from WT and HOM mice. Superimposed traces are averages of 10 EPSCs at each interstimulus interval. Bottom, summary plot of paired-pulse facilitation experiments in cortico-LA projections. (d) The experiments were identical to c but the EPSCs were recorded in thalamic input to the LA. (e) Rapgef6 ablation had no effect on the parameters of glutamatergic mEPSCs. mEPScs were recorded in LA neurons at −70 mV in slices from WT (upper) and HOM mice (lower) in the presence of 1 μM TTX. (f) Summary plot showing mean peak amplitude (upper) and frequency (lower) of mEPSCs recorded in LA neurons in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSC, excitatory postsynaptic current; HET, heterozygous; HOM, homozygous; LA, lateral nucleus of the amygdala; TTX, tetrodotoxin; WT, wild type.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4490285&req=5

fig4: Basal synaptic transmission in the LA is normal in Rapgef6 knockout mice. (a) Synaptic input–output curves for the EPSCs recorded at the cortico-LA synapses in slices from WT and HOM mice. The EPSCs were recorded under voltage-clamp conditions at a holding potential of −70 mV. (b) Same as in a, but the EPSCs were recorded in thalamic input to the LA. (c) Top, examples of paired-pulse facilitation of the cortico–amygdala EPSCs recorded at different interstimulus intervals (50 ms, 70 ms, 100 ms and 200 ms) at a holding potential of −70 mV in slices from WT and HOM mice. Superimposed traces are averages of 10 EPSCs at each interstimulus interval. Bottom, summary plot of paired-pulse facilitation experiments in cortico-LA projections. (d) The experiments were identical to c but the EPSCs were recorded in thalamic input to the LA. (e) Rapgef6 ablation had no effect on the parameters of glutamatergic mEPSCs. mEPScs were recorded in LA neurons at −70 mV in slices from WT (upper) and HOM mice (lower) in the presence of 1 μM TTX. (f) Summary plot showing mean peak amplitude (upper) and frequency (lower) of mEPSCs recorded in LA neurons in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSC, excitatory postsynaptic current; HET, heterozygous; HOM, homozygous; LA, lateral nucleus of the amygdala; TTX, tetrodotoxin; WT, wild type.

Mentions: As auditory fear conditioning was impaired in Rapgef6−/− mice, we explored the effects of Rapgef6 ablation on excitatory synaptic transmission in projections to the lateral nucleus of the amygdala (LA) from the auditory thalamus and auditory cortex, which deliver the conditioned stimulus (CS) information to the amygdala during both the acquisition and retrieval of conditioned fear memory.51 To assay synaptic function in auditory inputs to the LA, we recorded EPSCs in LA principal neurons, stimulating fibers either in the external capsule (cortical input) or the internal capsule (thalamic input).31, 32, 52, 53 Notably, synapses in these two converging pathways could be activated independently with our stimulation techniques.54 We found that synaptic strength, assayed with synaptic input–output curves for the AMPA receptor-mediated EPSCs, was unaffected in Rapgef6−/− mice in both studied inputs to the LA (Figures 4a and b; cortical input: n=10 neurons from four control mice, n=13 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,189)=0.03, P=0.86; thalamic input: n=11 neurons from four control mice, n=11 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,180)=0.08, P=0.77). The magnitude of paired-pulse facilitation, which, if changed, is indicative of changes in the probability of neurotransmitter release,31 was also not different between control and Rapgef6−/− mice at both cortico-LA and thalamo-LA synapses (Figures 4c and d; cortical input: n=13 neurons from six control mice, n=8 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,76)=0.7, P=0.41; thalamic input: n=13 neurons from four control mice, n=9 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,80)=0.13, P=0.72). This finding indicates that Rapgef6 ablation had no effect on presynaptic function in the CS pathways. Moreover, we found no differences between control and mutant mice in the frequency or amplitude of spontaneous miniature excitatory postsynaptic currents (mEPSCs), recorded in principal neurons in the LA in the presence of a sodium channel blocker tetrodotoxin (1 μM; Figures 4e and f; n=15 neurons from four control mice, n=9 neurons from three Rapgef6−/− mice; frequency: unpaired t-test, P=0.82; amplitude: unpaired t-test, P=0.49). Taken together, these results show that genetic ablation of the Rapgef6 gene had no effect on basal excitatory synaptic transmission or synaptic facilitation in the LA.


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)

Basal synaptic transmission in the LA is normal in Rapgef6 knockout mice. (a) Synaptic input–output curves for the EPSCs recorded at the cortico-LA synapses in slices from WT and HOM mice. The EPSCs were recorded under voltage-clamp conditions at a holding potential of −70 mV. (b) Same as in a, but the EPSCs were recorded in thalamic input to the LA. (c) Top, examples of paired-pulse facilitation of the cortico–amygdala EPSCs recorded at different interstimulus intervals (50 ms, 70 ms, 100 ms and 200 ms) at a holding potential of −70 mV in slices from WT and HOM mice. Superimposed traces are averages of 10 EPSCs at each interstimulus interval. Bottom, summary plot of paired-pulse facilitation experiments in cortico-LA projections. (d) The experiments were identical to c but the EPSCs were recorded in thalamic input to the LA. (e) Rapgef6 ablation had no effect on the parameters of glutamatergic mEPSCs. mEPScs were recorded in LA neurons at −70 mV in slices from WT (upper) and HOM mice (lower) in the presence of 1 μM TTX. (f) Summary plot showing mean peak amplitude (upper) and frequency (lower) of mEPSCs recorded in LA neurons in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSC, excitatory postsynaptic current; HET, heterozygous; HOM, homozygous; LA, lateral nucleus of the amygdala; TTX, tetrodotoxin; WT, wild type.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490285&req=5

fig4: Basal synaptic transmission in the LA is normal in Rapgef6 knockout mice. (a) Synaptic input–output curves for the EPSCs recorded at the cortico-LA synapses in slices from WT and HOM mice. The EPSCs were recorded under voltage-clamp conditions at a holding potential of −70 mV. (b) Same as in a, but the EPSCs were recorded in thalamic input to the LA. (c) Top, examples of paired-pulse facilitation of the cortico–amygdala EPSCs recorded at different interstimulus intervals (50 ms, 70 ms, 100 ms and 200 ms) at a holding potential of −70 mV in slices from WT and HOM mice. Superimposed traces are averages of 10 EPSCs at each interstimulus interval. Bottom, summary plot of paired-pulse facilitation experiments in cortico-LA projections. (d) The experiments were identical to c but the EPSCs were recorded in thalamic input to the LA. (e) Rapgef6 ablation had no effect on the parameters of glutamatergic mEPSCs. mEPScs were recorded in LA neurons at −70 mV in slices from WT (upper) and HOM mice (lower) in the presence of 1 μM TTX. (f) Summary plot showing mean peak amplitude (upper) and frequency (lower) of mEPSCs recorded in LA neurons in slices from WT and HOM mice. Results are shown as mean±s.e.m. EPSC, excitatory postsynaptic current; HET, heterozygous; HOM, homozygous; LA, lateral nucleus of the amygdala; TTX, tetrodotoxin; WT, wild type.
Mentions: As auditory fear conditioning was impaired in Rapgef6−/− mice, we explored the effects of Rapgef6 ablation on excitatory synaptic transmission in projections to the lateral nucleus of the amygdala (LA) from the auditory thalamus and auditory cortex, which deliver the conditioned stimulus (CS) information to the amygdala during both the acquisition and retrieval of conditioned fear memory.51 To assay synaptic function in auditory inputs to the LA, we recorded EPSCs in LA principal neurons, stimulating fibers either in the external capsule (cortical input) or the internal capsule (thalamic input).31, 32, 52, 53 Notably, synapses in these two converging pathways could be activated independently with our stimulation techniques.54 We found that synaptic strength, assayed with synaptic input–output curves for the AMPA receptor-mediated EPSCs, was unaffected in Rapgef6−/− mice in both studied inputs to the LA (Figures 4a and b; cortical input: n=10 neurons from four control mice, n=13 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,189)=0.03, P=0.86; thalamic input: n=11 neurons from four control mice, n=11 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,180)=0.08, P=0.77). The magnitude of paired-pulse facilitation, which, if changed, is indicative of changes in the probability of neurotransmitter release,31 was also not different between control and Rapgef6−/− mice at both cortico-LA and thalamo-LA synapses (Figures 4c and d; cortical input: n=13 neurons from six control mice, n=8 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,76)=0.7, P=0.41; thalamic input: n=13 neurons from four control mice, n=9 neurons from three Rapgef6−/− mice, two-way ANOVA, F(1,80)=0.13, P=0.72). This finding indicates that Rapgef6 ablation had no effect on presynaptic function in the CS pathways. Moreover, we found no differences between control and mutant mice in the frequency or amplitude of spontaneous miniature excitatory postsynaptic currents (mEPSCs), recorded in principal neurons in the LA in the presence of a sodium channel blocker tetrodotoxin (1 μM; Figures 4e and f; n=15 neurons from four control mice, n=9 neurons from three Rapgef6−/− mice; frequency: unpaired t-test, P=0.82; amplitude: unpaired t-test, P=0.49). Taken together, these results show that genetic ablation of the Rapgef6 gene had no effect on basal excitatory synaptic transmission or synaptic facilitation in the LA.

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