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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.

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

A, LCIs were stained with ChAT antibody in WT and symptomatic R6/2 mice. Less intense staining and reduced cell size were evident. B, Bar graphs show that the mean somatic cross-sectional area was significantly smaller in R6/2 LCIs. In addition, mean striatal area was significantly reduced in hemi-slices from R6/2 mice. Striatal volume assessed stereologically was also significantly reduced. The number of striatal ChAT+ neurons was similar but, because of reduced striatal volume, the mean density of ChAT+ neurons was significantly increased in R6/2 mice. *p < 0.05, **p < 0.01.
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Figure 1: A, LCIs were stained with ChAT antibody in WT and symptomatic R6/2 mice. Less intense staining and reduced cell size were evident. B, Bar graphs show that the mean somatic cross-sectional area was significantly smaller in R6/2 LCIs. In addition, mean striatal area was significantly reduced in hemi-slices from R6/2 mice. Striatal volume assessed stereologically was also significantly reduced. The number of striatal ChAT+ neurons was similar but, because of reduced striatal volume, the mean density of ChAT+ neurons was significantly increased in R6/2 mice. *p < 0.05, **p < 0.01.

Mentions: Reduced MSN somatic area and dendritic elaboration have been previously shown in symptomatic R6/2 mice (Levine et al., 1999; Klapstein et al., 2001). However, morphological changes in LCIs have not been examined. We used ChAT immunohistochemistry to estimate cell numbers and changes in somatic area of LCIs in symptomatic R6/2 mice (n = 4, age 64 ± 2 d) and WT littermates (n = 4, age 60 ± 2 d). LCIs (n = 202 cells) from R6/2 mice showed a statistically significant decrease in somatic area compared to LCIs (n = 202 cells) from WT mice (p < 0.01; Fig. 1). To estimate changes in ChAT+ neuronal density, the area of individual slices was calculated first. Compared with WT littermates, mean striatal area of 30-μm-thick hemi-slices was significantly smaller in R6/2 compared to WT mice (p = 0.011). Stereological methods were used to calculate striatal volume and LCI total number and density. Striatal volume was significantly reduced in R6/2 compared to WT mice (p = 0.029), but the total numbers of ChAT+ neurons were not significantly different (p = 0.33). However, the stereological analysis revealed a statistically significant increase in striatal ChAT+ neuronal density (p = 0.013; Fig. 1B).


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, LCIs were stained with ChAT antibody in WT and symptomatic R6/2 mice. Less intense staining and reduced cell size were evident. B, Bar graphs show that the mean somatic cross-sectional area was significantly smaller in R6/2 LCIs. In addition, mean striatal area was significantly reduced in hemi-slices from R6/2 mice. Striatal volume assessed stereologically was also significantly reduced. The number of striatal ChAT+ neurons was similar but, because of reduced striatal volume, the mean density of ChAT+ neurons was significantly increased in 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 1: A, LCIs were stained with ChAT antibody in WT and symptomatic R6/2 mice. Less intense staining and reduced cell size were evident. B, Bar graphs show that the mean somatic cross-sectional area was significantly smaller in R6/2 LCIs. In addition, mean striatal area was significantly reduced in hemi-slices from R6/2 mice. Striatal volume assessed stereologically was also significantly reduced. The number of striatal ChAT+ neurons was similar but, because of reduced striatal volume, the mean density of ChAT+ neurons was significantly increased in R6/2 mice. *p < 0.05, **p < 0.01.
Mentions: Reduced MSN somatic area and dendritic elaboration have been previously shown in symptomatic R6/2 mice (Levine et al., 1999; Klapstein et al., 2001). However, morphological changes in LCIs have not been examined. We used ChAT immunohistochemistry to estimate cell numbers and changes in somatic area of LCIs in symptomatic R6/2 mice (n = 4, age 64 ± 2 d) and WT littermates (n = 4, age 60 ± 2 d). LCIs (n = 202 cells) from R6/2 mice showed a statistically significant decrease in somatic area compared to LCIs (n = 202 cells) from WT mice (p < 0.01; Fig. 1). To estimate changes in ChAT+ neuronal density, the area of individual slices was calculated first. Compared with WT littermates, mean striatal area of 30-μm-thick hemi-slices was significantly smaller in R6/2 compared to WT mice (p = 0.011). Stereological methods were used to calculate striatal volume and LCI total number and density. Striatal volume was significantly reduced in R6/2 compared to WT mice (p = 0.029), but the total numbers of ChAT+ neurons were not significantly different (p = 0.33). However, the stereological analysis revealed a statistically significant increase in striatal ChAT+ neuronal density (p = 0.013; Fig. 1B).

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