Altered pallido‐pallidal synaptic transmission leads to aberrant firing of globus pallidus neurons in a rat model of Parkinson's disease

• Published in: The Journal of physiology Vol. 590; no. 22; pp. 5861 - 5875
• Main Authors: Miguelez, Cristina, Morin, Stéphanie, Martinez, Audrey, Goillandeau, Michel, Bezard, Erwan, Bioulac, Bernard, Baufreton, Jérôme
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 15.11.2012; Wiley Subscription Services, Inc; Wiley; Blackwell Science Inc
• Subjects: Animals; Calcium; Calcium - metabolism; Disease Models, Animal; Dopamine; Dopamine - deficiency; Dopamine Agonists; Dopamine Agonists - pharmacology; Ecstasy; GABAergic Neurons; GABAergic Neurons - physiology; Globus Pallidus; Globus Pallidus - physiopathology; Inhibitory Postsynaptic Potentials; Life Sciences; Miniature Postsynaptic Potentials; Neurobiology; Neurons; Neurons and Cognition; Neuroscience: Neurobiology of Disease; Optogenetics; Parkinson's disease; Parkinsonian Disorders; Parkinsonian Disorders - physiopathology; Quinpirole; Quinpirole - pharmacology; Rats; Rats, Sprague-Dawley; Strontium; Strontium - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2012.241331

Key points •  We used optogenetics approach to characterize the short‐term plasticity of striato‐pallidal (STR–GP) and pallido‐pallidal (GP–GP) GABAergic synapses in rat brain slices. •  We show that only GP–GP (and not STR–GP) transmission is augmented by chronic dopamine depletion. •  Finally, we report that altered GP–GP synaptic transmission promotes neuronal synchronization and rebound bursting in globus pallidus neurons. •  Our results support the conclusion that maladaptive GP–GP GABAergic transmission is likely to be a key underlying factor of the pathological activity in the globus pallidus observed in Parkinson's disease.   The pattern of activity of globus pallidus (GP) neurons is tightly regulated by GABAergic inhibition. In addition to extrinsic inputs from the striatum (STR–GP) the other source of GABA to GP neurons arises from intrinsic intranuclear axon collaterals (GP–GP). While the contribution of striatal inputs has been studied, notably its hyperactivity in Parkinson's disease (PD), the properties and function of intranuclear inhibition remain poorly understood. Our objective was therefore to test the impact of chronic dopamine depletion on pallido‐pallidal transmission. Using patch‐clamp whole‐cell recordings in rat brain slices, we combined electrical and optogenetic stimulations with pharmacology to differentiate basic synaptic properties of STR–GP and GP–GP GABAergic synapses. GP–GP synapses were characterized by activity‐dependent depression and insensitivity to the D2 receptor specific agonist quinpirole and STR–GP synapses by frequency‐dependent facilitation and quinpirole modulation. Chronic dopamine deprivation obtained in 6‐OHDA lesioned animals boosted the amplitude of GP–GP IPSCs but did not modify STR–GP transmission and increased the amplitude of miniature IPSCs. Replacement of calcium by strontium confirmed that the quantal amplitude was increased at GP–GP synapses. Finally, we demonstrated that boosted GP–GP transmission promotes resetting of autonomous activity and rebound‐burst firing after dopamine depletion. These results suggest that GP–GP synaptic transmission (but not STR–GP) is augmented by chronic dopamine depletion which could contribute to the aberrant GP neuronal activity observed in PD.