Direct assessment of presynaptic modulation of cortico-striatal glutamate release in a Huntington’s disease mouse model

Abstract

Glutamate is the main excitatory neurotransmitter in the brain, and impairments in its signaling are associated with many neurological disorders, including Huntington’s disease (HD). Previous studies in HD mouse models demonstrate altered glutamate receptor distribution and signaling at cortico-striatal synapses, and some studies suggest that glutamate release is altered; however, traditional methods to study synaptic glutamate release are indirect or have poor temporal resolution. Here we utilize iGluSnFR, a modified green fluorescent protein reporter for real-time imaging of glutamate transmission, to study presynaptic modulation of cortical glutamate release in the striatum of the YAC128 HD mouse model. We determined that iGluSnFR can be used to accurately measure short- and long-term changes in glutamate release caused by modulation of extracellular Ca2+ levels, activation of presynaptic receptors, and high-frequency stimulation (HFS) protocols. We also confirmed a difference in the expression of HFS-induced long-term depression in YAC128. Together, this research demonstrates the utility of iGluSnFR in studying presynaptic modulation of glutamate release in healthy mice and disease models that display impairments in glutamate signaling. NEW & NOTEWORTHY We use iGluSnFR to directly assess presynaptic modulation of cortico-striatal glutamate release in brain slice and compare changes in glutamate release between wild type and a Huntington’s disease mouse model, YAC128. We observed reductions in glutamate release after low extracellular Ca2+ and activation of various presynaptic receptors. We also demonstrate a presynaptic mechanism of reduced glutamate release in high-frequency stimulation-induced long-term depression and show this to be altered in YAC128.

The Effect of GLT-1 Upregulation on Extracellular Glutamate Dynamics

“…A heatmap depicting representative iGluSnFR responses to 2, 20, and 50 pulses is shown in Figure 1B, and average iGluSnFR responses to 2, 20, and 50 pulses are shown in Figures 1C-E, respectively. Response peaks, indicative of the relative amount of glutamate released (Koch et al, 2018), were not significantly different in saline compared to ceftriaxone-treated mice, although a strong non-significant trend toward a reduction in iGluSnFR peaks was observed in the ceftriaxone group. As expected, there was a significant effect of the number of pulses, with longer 100 Hz stimulations generating larger iGluSnFR peaks (Figure 1F, saline n = 14, ceftriaxone n = 16, two-way RM ANOVA, treatment p = 0.084, # of pulses p < 0.001, interaction p = 0.330).…”

Dysfunctional striatal dopamine signaling in Huntington's disease

“…Further studies are needed to clarify the extent of changes in dopamine levels over disease progression, particularly at early stages. In studies of glutamate dynamics in HD, the creation of glutamate sensing fluorescent reporters has allowed researchers to directly compare glutamate transmission between WT and HD mice (Koch, Woodard, & Raymond, ; Parsons et al, ). Similarly, new optogenetic sensors for real‐time imaging of dopamine dynamics (Patriarchi et al, ; Sun et al, ) could be used to directly assess dopamine dynamics in HD striatum.…”

A Review of the Clinical Evidence for Complementary and Alternative Medicine in Huntington’s Disease

“…Compelling animal data have demonstrated that striatal degeneration in HD may be secondary to excessive activation of glutamate-gated ion channels. 38 In studies of a neuron-like cell line, antioxidants were found to be able to protect against glutamate-induced cytolysis. 39 Two lipophilic, centrally active antioxidants were studied in HD: d-alpha-tocopheral (vitamin E) and idebenone.…”