Polysynaptic inhibition between striatal cholinergic interneurons shapes their network activity patterns in a dopamine-dependent manner

Striatal activity is dynamically modulated by acetylcholine and dopamine, both of which are essential for basal ganglia function. Synchronized pauses in the activity of striatal cholinergic interneurons (ChINs) are correlated with elevated activity of midbrain dopaminergic neurons, whereas synchronous firing of ChINs induces local release of dopamine. The mechanisms underlying ChIN synchronization and its interplay with dopamine release are not fully understood. Here we show that polysynaptic inhibition between ChINs is a robust network motif and instrumental in shaping the network activity of ChINs. Action potentials in ChINs evoke large inhibitory responses in multiple neighboring ChINs, strong enough to suppress their tonic activity. Using a combination of optogenetics and chemogenetics we show the involvement of striatal tyrosine hydroxylase-expressing interneurons in mediating this inhibition. Inhibition between ChINs is attenuated by dopaminergic midbrain afferents acting presynaptically on D2 receptors. Our results present a novel form of interaction between striatal dopamine and acetylcholine dynamics.

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Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A list of figures that have associated raw data -A description of any restrictions on data availability Gilad Silberberg Feb 7, 2020 Ex vivo electrophysiology data was collected using Igor Pro 6.34A (Wavemetrics, USA). In vivo electrophysiology data was collected and analysed using custom scripts in Matlab (MathWorks, USA). Ex vivo images were acquired using MicroManager 1.4.22 (UCSF, USA). Fixed tissue images were collected using Zen 2 black edition (Zeiss, Germany). Fast-Scan Cyclic voltammetry data was acquired with TH 1.0 CV program (ESA, USA).
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No a priori sample size calculation was performed. For electrophysiology and FSCV data, at least 4 mice were used for each condition for at least 8 data-points in each comparison to enable statistical analysis. For the remaining experiments, notably retrograde tracing and dopaminelesion data, at least three mice were used to confirm the existence of labeled somata in midbrain areas in all trials; as these experiments confirmed our larger anterograde data-sets, no further experiments were deemed necessary.
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All main results were reproduced in multiple animals and multiple neurons with exact n numbers for each experiment provided in the manuscript. Key findings were replicated successfully through alternative methods where applicable: the dopamine-afferent independence of polysynaptic inhibition was replicated through dopamine neuron ablation with 6-OHDA, chemogenetic silencing, viral silencing (Tetanus Toxin Light Chain) and viral ablation (Dipthera Toxin A). TH-neuron reciprocal connectivity was confirmed through optogenetic activation, direct patch-clamp electrophysiology, and its involvement in polysynaptic inhibitoin was confirmed through optogenetic synapse depletion, chemogenetic silencing and pharmacological manipulation. Dopamine neuron input on striatal ChINs was confirmed through anteriograde excitation of DAT-cre animals, retrograde activation in DAT-cre animals, and anterograde activation in TH-cre animals, with further controls in dopamine-neuron-depleted animals and tests for monosynaptic input performed through pharmacological manipulation.
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