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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, B, Representative traces of spontaneous IPSCs in LCIs from R6/2 and WT mice at 65 d using Cs-Meth (A) or CsCl (B) internal solutions. In both cases, spontaneous IPSCs occurred more frequently in LCIs from R6/2 mice. C, D, Amplitude−frequency histograms of sIPSCs using Cs-Meth (C) and CsCl (D) internal solutions. In most amplitude bins, there was an increase in frequency in LCIs from R6/2 mice. The insets show the mean sIPSC frequency. Regardless of the internal solution used, there was a significant increase in LCIs frequency in R6/2s. E, F, Cumulative probability histograms of interevent intervals in WT and R6/2 mice at 65 d using Cs-Meth (E) and CsCl (F) internal solutions. A significant increase in short interevent intervals was observed in LCIs from R6/2 mice. G, H, Average frequency of mIPSCs in LCIs from WT and R6/2 mice was similar using Cs-Meth (G) or CsCl (H) internal solutions. The percent reduction in IPSC frequency after TTX was greater in LCIs from R6/2 mice and this difference was statistically significant for the CsCl internal solution (H, right). *p < 0.05, ***p < 0.001.
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Figure 3: A, B, Representative traces of spontaneous IPSCs in LCIs from R6/2 and WT mice at 65 d using Cs-Meth (A) or CsCl (B) internal solutions. In both cases, spontaneous IPSCs occurred more frequently in LCIs from R6/2 mice. C, D, Amplitude−frequency histograms of sIPSCs using Cs-Meth (C) and CsCl (D) internal solutions. In most amplitude bins, there was an increase in frequency in LCIs from R6/2 mice. The insets show the mean sIPSC frequency. Regardless of the internal solution used, there was a significant increase in LCIs frequency in R6/2s. E, F, Cumulative probability histograms of interevent intervals in WT and R6/2 mice at 65 d using Cs-Meth (E) and CsCl (F) internal solutions. A significant increase in short interevent intervals was observed in LCIs from R6/2 mice. G, H, Average frequency of mIPSCs in LCIs from WT and R6/2 mice was similar using Cs-Meth (G) or CsCl (H) internal solutions. The percent reduction in IPSC frequency after TTX was greater in LCIs from R6/2 mice and this difference was statistically significant for the CsCl internal solution (H, right). *p < 0.05, ***p < 0.001.

Mentions: MSNs from symptomatic R6/2 mice receive increased GABAergic inputs and feedforward inhibitory circuits play a major role in this effect (Cepeda et al., 2013). To determine if LCIs also are subject to increased GABAergic inhibition, sIPSCs were recorded (in the presence of ionotropic glutamate receptor antagonists) using the Cs-Meth internal solution and cells were held at +20 mV to increase the driving force of Cl− ions. The frequency of sIPSCs (1.7 ± 0.3 Hz in WT vs 1.1 ± 0.6 Hz in R6/2, p = 0.42) was not significantly different in LCIs from presymptomatic R6/2 compared to WT mice (n = 4 in each group, age 23 ± 1 d). In contrast, in symptomatic R6/2 mice (n = 10, age 64 ± 1 d), the average frequency of sIPSCs was significantly increased compared with WTs (n = 12, age 65 ± 1 d; Fig. 3A and C, inset). This increase was observed across amplitude bins and was statistically significant for the 10-20 pA bin (Fig. 3C). Further, the cumulative interevent interval probability distribution was shifted to the left, indicating more short interevent intervals in cells from R6/2 mice (p < 0.001; Fig. 3E). Application of TTX (1 μM) eliminated the increase in sIPSC frequency (Fig. 3D), indicating its dependence on presynaptic action potentials. In addition, the percent reduction in IPSC frequency after TTX application was greater in cells from R6/2 compared with WT mice, suggesting that more sIPSCs from R6/2 cells were action potential-dependent (Fig. 3G, right bar graph).


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, B, Representative traces of spontaneous IPSCs in LCIs from R6/2 and WT mice at 65 d using Cs-Meth (A) or CsCl (B) internal solutions. In both cases, spontaneous IPSCs occurred more frequently in LCIs from R6/2 mice. C, D, Amplitude−frequency histograms of sIPSCs using Cs-Meth (C) and CsCl (D) internal solutions. In most amplitude bins, there was an increase in frequency in LCIs from R6/2 mice. The insets show the mean sIPSC frequency. Regardless of the internal solution used, there was a significant increase in LCIs frequency in R6/2s. E, F, Cumulative probability histograms of interevent intervals in WT and R6/2 mice at 65 d using Cs-Meth (E) and CsCl (F) internal solutions. A significant increase in short interevent intervals was observed in LCIs from R6/2 mice. G, H, Average frequency of mIPSCs in LCIs from WT and R6/2 mice was similar using Cs-Meth (G) or CsCl (H) internal solutions. The percent reduction in IPSC frequency after TTX was greater in LCIs from R6/2 mice and this difference was statistically significant for the CsCl internal solution (H, right). *p < 0.05, ***p < 0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4507822&req=5

Figure 3: A, B, Representative traces of spontaneous IPSCs in LCIs from R6/2 and WT mice at 65 d using Cs-Meth (A) or CsCl (B) internal solutions. In both cases, spontaneous IPSCs occurred more frequently in LCIs from R6/2 mice. C, D, Amplitude−frequency histograms of sIPSCs using Cs-Meth (C) and CsCl (D) internal solutions. In most amplitude bins, there was an increase in frequency in LCIs from R6/2 mice. The insets show the mean sIPSC frequency. Regardless of the internal solution used, there was a significant increase in LCIs frequency in R6/2s. E, F, Cumulative probability histograms of interevent intervals in WT and R6/2 mice at 65 d using Cs-Meth (E) and CsCl (F) internal solutions. A significant increase in short interevent intervals was observed in LCIs from R6/2 mice. G, H, Average frequency of mIPSCs in LCIs from WT and R6/2 mice was similar using Cs-Meth (G) or CsCl (H) internal solutions. The percent reduction in IPSC frequency after TTX was greater in LCIs from R6/2 mice and this difference was statistically significant for the CsCl internal solution (H, right). *p < 0.05, ***p < 0.001.
Mentions: MSNs from symptomatic R6/2 mice receive increased GABAergic inputs and feedforward inhibitory circuits play a major role in this effect (Cepeda et al., 2013). To determine if LCIs also are subject to increased GABAergic inhibition, sIPSCs were recorded (in the presence of ionotropic glutamate receptor antagonists) using the Cs-Meth internal solution and cells were held at +20 mV to increase the driving force of Cl− ions. The frequency of sIPSCs (1.7 ± 0.3 Hz in WT vs 1.1 ± 0.6 Hz in R6/2, p = 0.42) was not significantly different in LCIs from presymptomatic R6/2 compared to WT mice (n = 4 in each group, age 23 ± 1 d). In contrast, in symptomatic R6/2 mice (n = 10, age 64 ± 1 d), the average frequency of sIPSCs was significantly increased compared with WTs (n = 12, age 65 ± 1 d; Fig. 3A and C, inset). This increase was observed across amplitude bins and was statistically significant for the 10-20 pA bin (Fig. 3C). Further, the cumulative interevent interval probability distribution was shifted to the left, indicating more short interevent intervals in cells from R6/2 mice (p < 0.001; Fig. 3E). Application of TTX (1 μM) eliminated the increase in sIPSC frequency (Fig. 3D), indicating its dependence on presynaptic action potentials. In addition, the percent reduction in IPSC frequency after TTX application was greater in cells from R6/2 compared with WT mice, suggesting that more sIPSCs from R6/2 cells were action potential-dependent (Fig. 3G, right bar graph).

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