Convergent cortical innervation of striatal projection neurons

Abstract

Anatomical studies have led to the assertion that intratelencephalic and pyramidal tract cortical neurons innervate different striatal projection neurons. To test this hypothesis, we measured the responses of mouse striatal neurons to optogenetic activation of intratelencephalic and pyramidal tract axons. Contrary to expectation, direct and indirect pathway striatal spiny projection neurons responded to both intratelencephalic and pyramidal tract activation, arguing that these cortical networks innervate both striatal projection neurons.

Figure 1

IT neurons equally innervated dSPNs and iSPNs. (a) Schematic of rabies virus containing ChR2-Vn (green) injected into the dorsolateral striatum (DLS), IT axons (green) within contralateral DLS (violet). (b) Top, ChR2-Vn expression within the DLS injection site (brightest area). Bottom, contralateral to the injection, cortex layer 5A/B labeled IT neurons and their axons within the DLS (violet). Scale bars: 1.5 mm (top), 500 µm (left and right). (c) Simultaneous dual whole-cell recordings of SPN EPSCs with IT ChR2 activation. dSPN positive for D₁-tdTomato (yellow) and unlabeled iSPN. Right, activation area (blue) encompassing SPNs dendritic arbors. Scale bars: 20 µm (right) and 250 µm (left). (d) IT ChR2 activation produced dSPN EPSC and iSPN EPSC (thick line represents the mean from several trials, shading represents the standard deviation). Scale bars represent 50 pA and 10 ms. (e) SPNs EPSC peak amplitude. Boxplots represent the median and interquartile range while whiskers represent the minimum/maximum values. Gray lines show simultaneous data pairings. Inset shows how the peak amplitude was measured. (f) SPNs EPSC charge. Inset shows the area under the EPSC trace as the calculated value for the EPSC charge. (g) EPSC responses at iSPN normalized to paired dSPN at the maximum activation light intensity.

Figure 2

PT neurons innervated both dSPNs and iSPNs, with stronger connections to dSPNs. (a) Schematics of rRabies-ChR2-Vn injection into the pons (black circle), labeling PT axons (green) within ipsilateral DLS (violet). (b) Top and left, ChR2-Vn injection site within pons (sagittal slice). Right, labeled PT axons in L5B (coronal slice). Scale bars: 1.5 mm (top), 500 µm (left), and 250 µm (right). (c) Dual recording of dSPN expressing D₁-tdTomato (yellow) and unlabeled iSPN. Scale bars 20 µm (left) and 250 µm (right). (d) SPNs EPSC after PT ChR2 activation in DLS. Scale bars represent 50 pA and 10 ms. (e) SPNs EPSC peak amplitude (* P< 0.05). (f) SPNs EPSC charge. (g) EPSC responses of iSPN normalized to paired dSPN at the maximum activation light intensity.