Integrated anatomical and physiological mapping of striatal afferent projections

Abstract

The dorsomedial striatum, a key site of reward-sensitive motor output, receives extensive afferent input from cortex, thalamus and midbrain. These projections are integrated by striatal microcircuits containing both spiny projection neurons and local circuit interneurons. To explore target cell specificity of these projections, we compared inputs onto D1-dopamine receptor-positive spiny neurons, parvalbumin-positive fast-spiking interneurons and somatostatin-positive low-threshold-spiking interneurons, using cell type-specific rabies virus tracing and optogenetic-mediated projection neuron recruitment in mice. While the relative proportion of retrogradely labelled projection neurons was similar between target cell types, the convergence of inputs was systematically higher for projections onto fast-spiking interneurons. Rabies virus is frequently used to assess cell-specific anatomical connectivity but it is unclear how this correlates to synaptic connectivity and efficacy. To test this, we compared tracing data with target cell-specific measures of synaptic efficacy for anterior cingulate cortex and parafascicular thalamic projections using novel quantitative optogenetic measures. We found that target-specific patterns of convergence were extensively modified according to region of projection neuron origin and postsynaptic cell type. Furthermore, we observed significant divergence between cell type-specific anatomical connectivity and measures of excitatory synaptic strength, particularly for low-threshold-spiking interneurons. Taken together, this suggests a basic uniform connectivity map for striatal afferent inputs upon which presynaptic-postsynaptic interactions impose substantial diversity of physiological connectivity.

M2 Cortex-Dorsolateral striatum stimulation reverses motor symptoms and synaptic deficits in Huntington’s Disease

“…Mouse brain sagittal sections were obtained on a vibratome (Microm HM 650 V, Thermo Scientific, Waltham, MA, USA) at 350 μm thickness in oxygenated (95% O2, 5% CO2) icecold artificial cerebrospinal fluid (aCSF) containing (in mM) 124 NaCl, 24 NaHCO3, 13 glucose, 5 HEPES, 2.5 KCl, 2.5 CaCl2, 1.2 NaH2PO4. 1.3 MgSO4, Slices were then transferred to oxygenated 32ºC recovery solution of the following composition (in mM): 92 NMDG, 30 NaHCO3, 25 glucose, 20 HEPES, 10 MgSO4, 5 sodium ascorbate, 2.5 KCl, 1.2 NaH2PO4, 3 sodium pyruvate, 2 thiourea, and 0.5 CaCl2; for 15 min (Choi et al, 2019). Then, slices were transferred to oxygenated aCSF at room temperature and left for at least 1 h before recording.…”

Neurexin1α differentially regulates synaptic efficacy within striatal circuits

“…To assess whether Neurexin1⍺ deletion impacts excitatory synaptic function onto dorsal striatal SPNs, we performed whole-cell voltage-clamp recordings in the dorsomedial striatum (DMS) of acute slices taken from Neurexin1⍺ heterozygote and homozygous knock-out (KO) animals. Mice were crossed onto the Drd1a-tdTomato BAC transgenic line, permitting identification of dSPNs and putative iSPNs (Ade et al, 2011;Choi et al, 2019 1C). To broadly assess spontaneous inhibitory transmission, we also recorded miniature inhibitory postsynaptic currents (mIPSCs).…”

“…In light of this as well as evidence for distinct pools for spontaneous and evoked synaptic release (Sara et al, 2005), we employed optogenetic-mediated recruitment of specific striatal circuits to explore action-potential evoked excitatory transmission in Nrxn1⍺ mutant mice. Prior cell type-specific monosynaptic tracing from spiny neuron and local interneuron subtypes within DMS revealed extensive connectivity from dorso-prefrontal cortical (dPFC) and parafascicular thalamic regions (Choi et al, 2019).…”

Nucleus Accumbens Fast-Spiking Interneurons Constrain Impulsive Action

“…We also measured synaptic interactions between FSIs and MSNs using whole-cell patch-clamp electrophysiology. To stimulate FSIs and their synaptic outputs, we injected PV-2A-Cre mice with a Credependent AAV expressing ChIEF, an engineered hybrid of channelrhodopsin-1 and channelrhodopsin-2 with optimized biophysical properties (55,56). We then prepared acute brain slices and performed voltage-clamp recordings from uninfected MSNs, evoking optical inhibitory post-synaptic currents (oIPSCs) with blue light pulses (Figure 4F).…”