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Enhanced GABAergic Inputs Contribute to Functional Alterations of Cholinergic Interneurons in the R6/2 Mouse Model of Huntington's Disease.

Holley SM, Joshi PR, Parievsky A, Galvan L, Chen JY, Fisher YE, Huynh MN, Cepeda C, Levine MS - eNeuro (2015 Jan-Feb)

Bottom Line: In Huntington's disease (HD), a hereditary neurodegenerative disorder, striatal medium-sized spiny neurons undergo degenerative changes.They also displayed a higher frequency of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) and larger amplitude of electrically evoked IPSCs.In contrast, glutamatergic spontaneous or evoked postsynaptic currents were not affected.

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Affiliation: Intellectual and Developmental Disabilities Research Center, Semel Institute for Neuroscience and Human Behavior, University of California at Los Angeles, Los Angeles, CA 90095.

ABSTRACT

In Huntington's disease (HD), a hereditary neurodegenerative disorder, striatal medium-sized spiny neurons undergo degenerative changes. In contrast, large cholinergic interneurons (LCIs) are relatively spared. However, their ability to release acetylcholine (ACh) is impaired. The present experiments examined morphological and electrophysiological properties of LCIs in the R6/2 mouse model of HD. R6/2 mice show a severe, rapidly progressing phenotype. Immunocytochemical analysis of choline acetyltransferase-positive striatal neurons showed that, although the total number of cells was not changed, somatic areas were significantly smaller in symptomatic R6/2 mice compared to wildtype (WT) littermates, For electrophysiology, brain slices were obtained from presymptomatic (3-4 weeks) and symptomatic (>8 weeks) R6/2 mice and their WT littermates. Striatal LCIs were identified by somatic size and spontaneous action potential firing in the cell-attached mode. Passive and active membrane properties of LCIs were similar in presymptomatic R6/2 and WT mice. In contrast, LCIs from symptomatic R6/2 animals displayed smaller membrane capacitance and higher input resistance, consistent with reduced somatic size. In addition, more LCIs from symptomatic mice displayed irregular firing patterns and bursts of action potentials. They also displayed a higher frequency of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) and larger amplitude of electrically evoked IPSCs. Selective optogenetic stimulation of somatostatin- but not parvalbumin-containing interneurons also evoked larger amplitude IPSCs in LCIs from R6/2 mice. In contrast, glutamatergic spontaneous or evoked postsynaptic currents were not affected. Morphological and electrophysiological alterations, in conjunction with the presence of mutant huntingtin in LCIs, could explain impaired ACh release in HD mouse models.

No MeSH data available.


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A, Representative traces of eIPSCs recorded with Cs-Meth internal solution and holding the membrane at +10 mV in LCIs from WT and symptomatic R6/2 mice. eIPSCs had multiple components and amplitude of the earliest peak was measured (arrows). B, Graph shows the input−output relationship. Current response amplitudes were significantly increased at intensities of 0.04 mA and higher. C, eIPSCs recorded in LCIs at −70 mV with high Cl− internal solution in WT and R6/2 mice at 65 d. D, Similar to recordings with Cs-Meth, there was a significant increase in IPSC amplitudes in cells from R6/2 mice. *p < 0.05, **p < 0.01.
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Figure 4: A, Representative traces of eIPSCs recorded with Cs-Meth internal solution and holding the membrane at +10 mV in LCIs from WT and symptomatic R6/2 mice. eIPSCs had multiple components and amplitude of the earliest peak was measured (arrows). B, Graph shows the input−output relationship. Current response amplitudes were significantly increased at intensities of 0.04 mA and higher. C, eIPSCs recorded in LCIs at −70 mV with high Cl− internal solution in WT and R6/2 mice at 65 d. D, Similar to recordings with Cs-Meth, there was a significant increase in IPSC amplitudes in cells from R6/2 mice. *p < 0.05, **p < 0.01.

Mentions: eIPSCs were recorded at +10 mV in the presence of glutamate receptor antagonists. Intrastriatal stimulation typically evoked polysynaptic GABAergic currents with two or more peaks (Fig. 4A,C). Application of BIC (10 μM) completely blocked all evoked currents. Amplitude of peak current with the shortest latency, presumably monosynaptic, was measured (arrows in Fig. 4A,C). eIPSC peak currents were similar over a range of stimulus intensities (0.01-0.06 mA) in LCIs from WT and presymptomatic R6/2 mice (data not shown). In LCIs from symptomatic animals (n = 3, age 61 ± 3 d), mean peak currents recorded at +10 mV holding potential using the Cs-Meth internal solution were significantly larger (p < 0.001) than in LCIs from WT mice (n = 3, age 66 ± 5 d; Fig. 4B). Evoked GABAergic currents also were examined using high Cl− internal solution, with cells voltage-clamped at −70 mV. Under these conditions, intrastriatal stimulation also typically evoked polysynaptic inward currents with characteristic multiple peaks (Fig. 4C). Amplitudes of peak currents with the shortest latency were significantly greater across a range of stimulus intensities in LCIs from R6/2 compared with mice (p < 0.001; Fig. 4D).


Enhanced GABAergic Inputs Contribute to Functional Alterations of Cholinergic Interneurons in the R6/2 Mouse Model of Huntington's Disease.

Holley SM, Joshi PR, Parievsky A, Galvan L, Chen JY, Fisher YE, Huynh MN, Cepeda C, Levine MS - eNeuro (2015 Jan-Feb)

A, Representative traces of eIPSCs recorded with Cs-Meth internal solution and holding the membrane at +10 mV in LCIs from WT and symptomatic R6/2 mice. eIPSCs had multiple components and amplitude of the earliest peak was measured (arrows). B, Graph shows the input−output relationship. Current response amplitudes were significantly increased at intensities of 0.04 mA and higher. C, eIPSCs recorded in LCIs at −70 mV with high Cl− internal solution in WT and R6/2 mice at 65 d. D, Similar to recordings with Cs-Meth, there was a significant increase in IPSC amplitudes in cells from R6/2 mice. *p < 0.05, **p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507822&req=5

Figure 4: A, Representative traces of eIPSCs recorded with Cs-Meth internal solution and holding the membrane at +10 mV in LCIs from WT and symptomatic R6/2 mice. eIPSCs had multiple components and amplitude of the earliest peak was measured (arrows). B, Graph shows the input−output relationship. Current response amplitudes were significantly increased at intensities of 0.04 mA and higher. C, eIPSCs recorded in LCIs at −70 mV with high Cl− internal solution in WT and R6/2 mice at 65 d. D, Similar to recordings with Cs-Meth, there was a significant increase in IPSC amplitudes in cells from R6/2 mice. *p < 0.05, **p < 0.01.
Mentions: eIPSCs were recorded at +10 mV in the presence of glutamate receptor antagonists. Intrastriatal stimulation typically evoked polysynaptic GABAergic currents with two or more peaks (Fig. 4A,C). Application of BIC (10 μM) completely blocked all evoked currents. Amplitude of peak current with the shortest latency, presumably monosynaptic, was measured (arrows in Fig. 4A,C). eIPSC peak currents were similar over a range of stimulus intensities (0.01-0.06 mA) in LCIs from WT and presymptomatic R6/2 mice (data not shown). In LCIs from symptomatic animals (n = 3, age 61 ± 3 d), mean peak currents recorded at +10 mV holding potential using the Cs-Meth internal solution were significantly larger (p < 0.001) than in LCIs from WT mice (n = 3, age 66 ± 5 d; Fig. 4B). Evoked GABAergic currents also were examined using high Cl− internal solution, with cells voltage-clamped at −70 mV. Under these conditions, intrastriatal stimulation also typically evoked polysynaptic inward currents with characteristic multiple peaks (Fig. 4C). Amplitudes of peak currents with the shortest latency were significantly greater across a range of stimulus intensities in LCIs from R6/2 compared with mice (p < 0.001; Fig. 4D).

Bottom Line: In Huntington's disease (HD), a hereditary neurodegenerative disorder, striatal medium-sized spiny neurons undergo degenerative changes.They also displayed a higher frequency of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) and larger amplitude of electrically evoked IPSCs.In contrast, glutamatergic spontaneous or evoked postsynaptic currents were not affected.

View Article: PubMed Central - HTML - PubMed

Affiliation: Intellectual and Developmental Disabilities Research Center, Semel Institute for Neuroscience and Human Behavior, University of California at Los Angeles, Los Angeles, CA 90095.

ABSTRACT

In Huntington's disease (HD), a hereditary neurodegenerative disorder, striatal medium-sized spiny neurons undergo degenerative changes. In contrast, large cholinergic interneurons (LCIs) are relatively spared. However, their ability to release acetylcholine (ACh) is impaired. The present experiments examined morphological and electrophysiological properties of LCIs in the R6/2 mouse model of HD. R6/2 mice show a severe, rapidly progressing phenotype. Immunocytochemical analysis of choline acetyltransferase-positive striatal neurons showed that, although the total number of cells was not changed, somatic areas were significantly smaller in symptomatic R6/2 mice compared to wildtype (WT) littermates, For electrophysiology, brain slices were obtained from presymptomatic (3-4 weeks) and symptomatic (>8 weeks) R6/2 mice and their WT littermates. Striatal LCIs were identified by somatic size and spontaneous action potential firing in the cell-attached mode. Passive and active membrane properties of LCIs were similar in presymptomatic R6/2 and WT mice. In contrast, LCIs from symptomatic R6/2 animals displayed smaller membrane capacitance and higher input resistance, consistent with reduced somatic size. In addition, more LCIs from symptomatic mice displayed irregular firing patterns and bursts of action potentials. They also displayed a higher frequency of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) and larger amplitude of electrically evoked IPSCs. Selective optogenetic stimulation of somatostatin- but not parvalbumin-containing interneurons also evoked larger amplitude IPSCs in LCIs from R6/2 mice. In contrast, glutamatergic spontaneous or evoked postsynaptic currents were not affected. Morphological and electrophysiological alterations, in conjunction with the presence of mutant huntingtin in LCIs, could explain impaired ACh release in HD mouse models.

No MeSH data available.


Related in: MedlinePlus