Pathological gamma oscillations, impaired dopamine release, synapse loss and reduced dynamic range of unitary glutamatergic synaptic transmission in the striatum of hypokinetic Q175 Huntington mice.

Abstract

Huntington's disease (HD) is a severe genetically inherited neurodegenerative disorder. Patients present with three principal phenotypes of motor symptoms: choreatic, hypokinetic-rigid and mixed. The Q175 mouse model of disease offers an opportunity to investigate the cellular basis of the hypokinetic-rigid form of HD. At the age of 1 year homozygote Q175 mice exhibited the following signs of hypokinesia: Reduced frequency of spontaneous movements on a precision balance at daytime (-55%), increased total time spent without movement in an open field (+42%), failures in the execution of unconditioned avoidance reactions (+32%), reduced ability for conditioned avoidance (-96%) and increased reaction times (+65%) in a shuttle box. Local field potential recordings revealed low-frequency gamma oscillations in the striatum as a characteristic feature of HD mice at rest. There was no significant loss of DARPP-32 immunolabeled striatal projection neurons (SPNs) although the level of DARPP-32 immunoreactivity was lower in HD. As a potential cause of hypokinesia, HD mice revealed a strong reduction in striatal KCl-induced dopamine release, accompanied by a decrease in the number of tyrosine hydroxylase-(TH)- and VMAT2-positive synaptic varicosities. The presynaptic TH fluorescence level was also reduced. Patch-clamp experiments were performed in slices from 1-year-old mice to record unitary EPSCs (uEPSCs) of presumed cortical origin in the absence of G-protein-mediated modulation. In HD mice, the maximal amplitudes of uEPSCs amounted to 69% of the WT level which matches the loss of VGluT1+/SYP+ synaptic terminals in immunostained sections. These results identify impairment of cortico-striatal synaptic transmission and dopamine release as a potential basis of hypokinesia in HD.

• Authors: T Rothe, M Deliano, A M Wójtowicz, A Dvorzhak, D Harnack, S Paul, T Vagner, I Melnick, H Stark, R Grantyn
• Journal: Neuroscience (Neuroscience) Vol. 311 Pg. 519-38 (Dec 17 2015) ISSN: 1873-7544 [Electronic] United States
• PMID: 26546830 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

Chemical References

• Dopamine and cAMP-Regulated Phosphoprotein 32
• Ppp1r1b protein, mouse
• Slc18a2 protein, mouse
• Vesicular Monoamine Transport Proteins
• Tyrosine 3-Monooxygenase
• Dopamine

Topics

• Animals
• Corpus Striatum (pathology, physiopathology)
• Disease Models, Animal
• Dopamine (metabolism)
• Dopamine and cAMP-Regulated Phosphoprotein 32 (metabolism)
• Excitatory Postsynaptic Potentials (physiology)
• Gamma Rhythm (physiology)
• Humans
• Huntington Disease (pathology, physiopathology)
• Male
• Mice, Transgenic
• Motor Activity (physiology)
• Synapses (pathology, physiology)
• Synaptic Transmission (physiology)
• Tissue Culture Techniques
• Tyrosine 3-Monooxygenase (metabolism)
• Vesicular Monoamine Transport Proteins (metabolism)