Neurexin1α differentially regulates synaptic efficacy within striatal circuits

SUMMARY Mutations in genes essential for synaptic function, such as the presynaptic adhesion molecule Neurexin1α (Nrxn1α), are strongly implicated in neuropsychiatric pathophysiology. As the input nucleus of the basal ganglia, the striatum integrates diverse excitatory projections governing cognitive and motor control, and its impairment may represent a recurrent pathway to disease. Here, we test the functional relevance of Nrxn1α in striatal circuits by employing optogenetic-mediated afferent recruitment of dorsal prefrontal cortical (dPFC) and parafascicular thalamic connections onto dorsomedial striatal (DMS) spiny projection neurons (SPNs). For dPFC-DMS circuits, we find decreased synaptic strength specifically onto indirect pathway SPNs in both Nrxn1α+/− and Nrxn1α−/− mice, driven by reductions in neurotransmitter release. In contrast, thalamic excitatory inputs to DMS exhibit relatively normal excitatory synaptic strength despite changes in synaptic N-methyl-D-aspartate receptor (NMDAR) content. These findings suggest that dysregulation of Nrxn1α modulates striatal function in an input- and target-specific manner.

showing placement of cursors (typically from ~3.5ms -5ms after light stimulation) for analysis of fiber volley. (B) Field recording overlayed with recordings done at different LED intensities ranging from low LED (light gray) to higher LED intensities (black) and the change in fiber volley amplitude. (C) Measurement of field slope taken from 10-90% of the rising phase of the second negativity component of the field. Maximal optical EPSC amplitudes from dPFC projection (taken from input-output measurements in Figure 1) were similar across genotypes onto (A) dSPNs and was significantly reduced onto (B) iSPNs, regardless of normalization to the field fiber volley.
Data are means ± SEM; *significant difference between groups (ANOVA) Figure S5. Probability of release is unchanged at dPFC-dSPN synapses regardless of external calcium levels and spot illumination measurements (related to Fig.1).
(A) Plot of paired-pulse ratio across multiple ISIs for optical stimulation of dPFC-dSPN synapses using a 50μM spot (Mightex Optical Systems) and full field illumination. Further recordings were done using an ISI of 50ms (B).
(C) Graph of paired-pulse ratio, 50ms ISI, at external calcium levels of 1.3mM and 2.5mM employing 50uM spot illumination.
(D) Plot of paired-pulse ratio across multiple ISIs for 50μM optical stimulation of dPFC-dSPN at external calcium levels of 1.3mM in Nrxn1α WT and KO.
(E) Plot of frequency trains across multiple frequencies (right; 10Hz; 20Hz; 50Hz from left to right) recorded onto dSPNs in Nrxn1α WT and KO.
Summary data are mean ± SEM Figure S6. Altered NMDAR decay at thalamic projections onto iSPNs in Nrxn1α KO (related to Fig4).
(A, left) Representative traces across genotypes of NMDA currents measured at +40mV in the presence of 100μM picrotoxin at dPFC-dSPN and dPFC-iSPN synapses. Traces are rescaled to same amplitude for comparison of decay time constants. Summary graph of weighted NMDAR decay values calculated from a biexponential fit for (A) dSPNs (B) and iSPNs. (C, left) Representative NMDA currents for PFas-dSPN and PFas-iSPN synapses. Summary graph of weighted NMDAR decay values calculated from a biexponential fit for (C) dSPNs (D and iSPNs. Fast and slow decay components are used to calculate the weighted decay time constant using the equation τw= [A f/ Af + As)] x τf + [As / (Af + As) x τs. Af = fast component amplitude and As = slow component amplitude.
Summary data are mean ± SEM, *significant difference between groups (ANOVA) Figure S7. Initial EPSP amplitude and recording duration are similar in Nrxn1α WT and KO (related to Fig6 and Fig7).
(A) Frequencies represented in an in vivo modeled optical stimulus pattern represented as 500ms windows and their corresponding local frequencies.
(B, D) Plot of initial EPSP (averaged 10 traces) recorded at "down-state" membrane potential of -80mV on x-axis and overall spiking efficiency on y-axis for (B) dSPNs and (D) iSPNs across genotypes for dPFC projection.
(C, E) Plot of spiking efficiency across recording duration of 5 minutes consisting of 10 unique optical patterns, binned in 10-second intervals for (C) dSPNs and (E) iSPNs recorded in Nrxn1α WT, Het, and KO from dPFC projection.
(F, H) Plot of initial EPSP (averaged 10 traces) recorded at "down-state" membrane potential of -80mV on x-axis and overall spiking efficiency on y-axis for (F) dSPNs and (H) iSPNs across genotypes for PFas projection.
(G, I) Plot of spiking efficiency across recording duration of 5 minutes consisting of 10 unique optical patterns, binned in 10-second intervals for (G) dSPNs and (I) iSPNs recorded in Nrxn1α WT and KO from PFas projection.
Summary data are mean ± SEM.