Axonal mechanisms mediating GABA-A receptor inhibition of striatal dopamine release

Abstract

27Axons of midbrain dopaminergic neurons innervate the striatum where they 28 contribute to movement and reinforcement learning. Past work has shown that striatal 29 GABA tonically inhibits dopamine release, but whether GABA-A receptors directly 30 modulate transmission or act indirectly through circuit elements is unresolved. Here, we 31 use whole-cell and perforated-patch recordings to test for GABA-A receptors on the 32 main dopaminergic neuron axons and branching processes within striatum. Application 33 of GABA depolarized axons, but also decreased the amplitude of axonal spikes, limited 34 propagation and reduced striatal dopamine release. The mechanism of inhibition 35 involved sodium channel inactivation and shunting. Lastly, we show that the positive 36 allosteric modulator diazepam enhanced GABA-A currents on dopaminergic neuron 37 axons and directly inhibited release, but also likely acts by reducing excitatory drive 38 from cholinergic interneurons. Thus, we reveal the mechanisms of GABA-A receptor 39 modulation of dopamine release and provide new insight into the actions of 40 benzodiazepines within the striatum.41 42 43 101the study. Mice that underwent viral injections were injected at postnatal day 18 or older 102 and were used for ex vivo electrophysiology and imaging 3-12 weeks after injection. 103The following strains were used: DAT-Cre (SJL-Slc6a3(tm1.1(cre)Bkmn/J, The Jackson 104 Laboratory Cat#006660); Ai95-RCL-GCaMP6f-D (Cg-Gt(ROSA)26Sor(tm95.1(CAG-105 GCaMP6f)Hze)/MwarJ, The Jackson Laboratory Cat#028865); Ai9 106 (Gt(ROSA)26Sor(tm9(CAG-tdTomato)Hze), The Jackson Laboratory Cat#007909); TH-107 GFP (Tg(TH-EGFP)1Gsat) NIH MMRRC; C57/Bl6J Wild Type, The Jackson Laboratory 108 Cat#000664; Ai32 (B6.Cg -Gt(ROSA)26Sor(tm32(CAG-COP4*H143R/EYFP)Hze), The 109 Jackson Laboratory, Cat#024109). 110 Method Details 111 Viral Injections 112 All stereotaxic injections were conducted on a Stoelting QSI (Cat#53311). Mice 113 were maintained under anesthesia for the duration of the injection and allowed to 114 recover from anesthesia on a warmed pad. The AAV9-CAG-FLEX-TdTomato (Penn 115 Vector Core), AAV-Syn-FLEX-jGCaMP7f (Dana et al., 2019), and AAV9-hSyn-dLight1.2 116 (Patriarchi et al., 2018) viruses (0.5-1 µl) were injected bilaterally into either the medial 117 dorsal striatum (X: ± 1.7 Y: +0.8 Z: -3.3) or the SNc (X: ± 1.9 Y: -0.5 Z: -3.9) via a 118 Hamilton syringe. At the end of the injection, the needle was raised at a rate of 0.1 to 119 0.2 mm per minute for 10 minutes before the needle was removed. 120 Slicing and electrophysiology 121 Brain slice experiments were performed on male and female adult mice of at 122 least 6 weeks in age. Mice were anesthetized with isoflurane, decapitated, and brains 123 rapidly extracted. Horizontal sections (electrophysiology, dLight, calcium imaging) or 124 coronal sections (voltammetry) were cut at 330-400 µm thickness on a vibratome while 125 immersed in warmed, modified, slicing ACSF containing (in mM) 198 glycerol, 2.5 KCl, 126 1.2 NaH2PO4, 20 HEPES, 25 NaHC...

Functional Dissection of Basal Ganglia Inhibitory Inputs onto Substantia Nigra Dopaminergic Neurons

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GPCR-Based Dopamine Sensors—A Detailed Guide to Inform Sensor Choice for In Vivo Imaging

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