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• W4385668891 abstract "Full text Figures and data Side by side Abstract Editor's evaluation eLife digest Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract Midbrain dopamine (DA) neurons are key regulators of basal ganglia functions. The axonal domain of these neurons is highly complex, with a large subset of non-synaptic release sites and a smaller subset of synaptic terminals from which in addition to DA, glutamate or GABA are also released. The molecular mechanisms regulating the connectivity of DA neurons and their neurochemical identity are unknown. An emerging literature suggests that neuroligins, trans-synaptic cell adhesion molecules, regulate both DA neuron connectivity and neurotransmission. However, the contribution of their major interaction partners, neurexins (Nrxns), is unexplored. Here, we tested the hypothesis that Nrxns regulate DA neuron neurotransmission. Mice with conditional deletion of all Nrxns in DA neurons (DAT::NrxnsKO) exhibited normal basic motor functions. However, they showed an impaired locomotor response to the psychostimulant amphetamine. In line with an alteration in DA neurotransmission, decreased levels of the membrane DA transporter (DAT) and increased levels of the vesicular monoamine transporter (VMAT2) were detected in the striatum of DAT::NrxnsKO mice, along with reduced activity-dependent DA release. Strikingly, electrophysiological recordings revealed an increase of GABA co-release from DA neuron axons in the striatum of these mice. Together, these findings suggest that Nrxns act as regulators of the functional connectivity of DA neurons. Editor's evaluation In this study, the authors selectively delete the three main genes encoding neurexins from dopamine neurons in mice. The authors find that while dopamine axonal architecture and synaptic ultrastructure are generally unaffected by loss of neurexins, there are changes in dopamine reuptake, amphetamine-induced locomotion, and GABA co-release, and notably, these changes are region specific, with most of the effects observed in the ventral striatum. The results are solid, and these findings are valuable and useful, providing new information regarding the potential roles of neurexins in regulating dopamine neuron output. https://doi.org/10.7554/eLife.87902.sa0 Decision letter eLife's review process eLife digest The human brain contains billions of nerve cells, known as neurons, which receive input from the outside world and process this information in the brain. Neurons communicate with each other by releasing chemical messengers from specialized structures, called axon terminals, some of which form junctions known as synapses. These messengers then generate signals in the target neurons. Based on the type of chemical they release, neurons can be classified into different types. For example, neurons releasing dopamine are considered to act as key regulators of learning, movements and motivation. Such neurons establish very large numbers of axon terminals, but very few of them form synapses. Specific sets of proteins, including neurexins and neuroligins, are thought to help regulate the activity of the connexions between these neurons. Previous research has shown that when neuroligins were removed from the neurons of worms or mice, it affected the ability of the animals to move. So far, the role of neurexins in managing the connectivity of regulatory neurons, such as those releasing dopamine, has received much less attention. To bridge this knowledge gap, Ducrot et al. explored how removing neurexins from dopamine neurons in mice affected their behaviour. The experiments revealed that eliminating neurexins did not affect their motor skills on a rotating rod, but it did reduce their movements in response to the psychostimulant amphetamine, a molecule known to enhance dopamine-associated behaviours. The cellular structure of dopamine neurons lacking neurexins was the same as in neurons containing this protein. But dopamine neurons without neurexins were slower to recycle dopamine, and they released a higher amount of the inhibitory messenger GABA. This suggests that neurexin acts as an important suppressor of GABA secretion to help regulate the signals released by dopamine neurons. These findings set the stage for further research into the role of neurexins in regulating dopamine and other populations of neurons in conditions such as Parkinson’s disease, where movement and coordination are affected. Introduction Dopamine (DA) neurons from the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) project densely to the ventral striatum (vSTR) and to the dorsal striatum (dSTR), respectively (Descarries et al., 1980; Matsuda et al., 2009) and are critical regulators of basal ganglia functions, motivation, and cognition (Schultz, 2007; Surmeier et al., 2014). The connectivity of the DA system is predominantly non-synaptic (Descarries et al., 2008; Ducrot et al., 2021; Wildenberg et al., 2021), with a majority of DA-releasing terminals not located in close apposition to a postsynaptic domain (Caillé et al., 1996; Descarries et al., 2008; Descarries et al., 1996; Descarries and Mechawar, 2000; Ducrot et al., 2021). A smaller synaptic subset of DA neuron terminals has the ability to co-release glutamate or GABA (Dal Bo et al., 2004; Mendez et al., 2008; Stuber et al., 2010; Sulzer et al., 1998; Tritsch et al., 2016; Tritsch et al., 2012). Despite the functional importance of DA in the brain, little is presently known about the molecular mechanisms underlying the formation and regulation of the complex axonal arbor and release sites established by DA neurons. Only a limited number of studies have until now explored the molecular mechanisms underlying DA release (Banerjee et al., 2022; Banerjee et al., 2020; Delignat-Lavaud et al., 2021; Ducrot et al., 2021; Liu et al., 2018; Mendez et al., 2011; Robinson et al., 2019, Delignat-Lavaud et al., 2023). Interestingly, a growing body of work suggests that the trans-synaptic cell adhesion neuroligins (NLs) directly or indirectly regulate the connectivity of DA neurons. Impaired DA-mediated motor behaviors were reported in Caenorhabditis elegans lacking NL-1 (Izquierdo et al., 2013; Rodríguez-Ramos et al., 2017). Downregulation of NL-2 in striatal neurons was also suggested to reduce the frequency of contacts between DA neuron axons and the dendrites of striatal neurons (Uchigashima et al., 2016). Mutations in NL-3 in mice lead to impaired synaptic inhibition onto striatal D1 DA receptor expressing neurons (Rothwell et al., 2014). Finally, both NL-1 and NL-2 are permissive for the formation of synapse-like contacts by DA neuron axons (Ducrot et al., 2021; Uchigashima et al., 2016). Although NLs mediate some of their cellular and synaptic effects by interacting with neurexins (Nrxns) (Chen et al., 2017; Zhang et al., 2015), the role of this family of presynaptic cell adhesion molecules in DA neurons is presently unexplored. Nrxns were initially identified as α-latrotoxin receptors (Ushkaryov et al., 1992). In mammals, Nrxns are expressed in two principal forms: longer α-Nrxns isoforms and shorter β-Nrxns isoforms (Tabuchi and Südhof, 2002). The Nrxn proteins on axon terminals interact with postsynaptic NL proteins and have been shown to regulate synapse formation and function (Graf et al., 2004; Ichtchenko et al., 1995; Ko et al., 2009). NLs only bind to Nrxns, whereas Nrxns have large numbers of splice variants with differential binding affinities with multiple postsynaptic partners. Several key studies using a strategy of conditional Nrxns deletion in mice demonstrated that Nrxns regulate neurotransmission through different mechanisms in a cell type-specific manner (Chen et al., 2017; Luo et al., 2021; Luo et al., 2020). Here, we tested the hypothesis that Nrxns play a key role in regulating the connectivity and functions of DA neurons by deleting all Nrxns in these cells. We crossed DAT-IRES-Cre mice with Nrxn123α/β floxed mice (Nrxn123 triple conditional KO mice [cKO] [Chen et al., 2017; Figure 1—figure supplement 1]). We found that these mice show impaired amphetamine-induced locomotion but unaltered synapse ultrastructure. DA signaling was impacted after the loss of Nrxns, as revealed by slower DA reuptake, decreased density of DA transporter (DAT), increased density of vesicular monoamine transporter (VMAT2) and reduced activity-dependent DA release. Finally, electrophysiological recordings showed an increase in GABA release from DA terminals in the vSTR but not dSTR in KO mice, suggesting a region-specific regulatory role of Nrxns on GABA co-transmission in DA neurons. Results Deletion of Nrxns reduces amphetamine-induced locomotion without affecting basal motor activity or coordination Previous work provided evidence for the presence of Nrxn mRNA in mesencephalic DA neurons (Uchigashima et al., 2019; Uchigashima et al., 2016). However, no study has previously compared the levels of expression of each Nrxn in this neuronal population. Here, we examined this by measuring mRNA purified from postnatal VTA or SNc DA neurons obtained from transgenic mice expressing the green fluorescent protein (GFP) gene under control of the tyrosine hydroxylase (TH) promoter (TH-GFP mice) by using fluorescence activated cell sorting (FACS) and RNASeq. We found that while mRNA for all three forms of Nrxn are found at high levels in both VTA and SNc DA neurons, Nrxn1 is found at higher levels in VTA neurons, Nrxn2 is similarly expressed in both populations and Nrxn3 is found at higher levels in SNc neurons (Table 1). Validating the precision of VTA and SNc dissections, we found that mRNA of the transcription factor Sox6 was found at higher levels in SNc neurons, while that of the vesicular glutamate transporter VGLUT2 and of the calcium binding protein calbindin-1 were found at higher levels in VTA neurons, in line with previous work (Table 1; Dal Bo et al., 2004; Panman et al., 2014; Pereira Luppi et al., 2021; Poulin et al., 2014). Next, with the objective of understanding the canonical function of all Nrxns in DA neurons, we selectively deleted Nrxn 1, 2, and 3 from DA neurons by crossing Nrxn123flox/flox mice with DAT-IRES-Cre mice (DAT::NrxnsKO; Figure 1—figure supplement 1) and examined in male mice the global functional impact of this gene deletion by quantifying motor behaviors. DA neurons are key regulators of movement, motivation, and reward-dependent learning and several studies using mouse lines with impaired DA transmission reported deficits in basal or psychostimulant-evoked locomotion and learning on the accelerating rotarod (Birgner et al., 2010; Ogura et al., 2005; Zhou and Palmiter, 1995). Table 1 All three neurexins (Nrxns) are expressed in dopamine (DA) neurons. Table showing Nrxn, Sox6, Slc17a6, and Calbn1 mRNA levels determined by RNASeq in fluorescence activated cell sorting (FACS)-purified ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) DA neurons. Results are presented as FKPM (fragments per kilobase of transcript per million fragments) values. Each value is the average of three independent samples. The statistics refer to the difference between SNc and VTA, determined using a t-test. mRNA levelsVTA DA neuronsSNc DA neuronsStatisticsNrxn112,280±36910,698±-359p<0.005Nrxn213,505±104214,038±82p>0.05Nrxn37854±29512,857±239p<0.001Sox6195±172862±63p<0.001Slc17a61953±144587±34p<0.001Calb18373±-5191791±49p<0.001 In the first series of experiments, we evaluated motor coordination and learning using the accelerating rotarod task with two different protocols (Figure 1A and Figure 1—figure supplement 2A). The first protocol evaluated the rate of learning to perform this task over a total of nine sessions in 3 days, with two sessions performed on the first day, three sessions on the second day, and four sessions on the third day, with a speed of rotation accelerating from 4 to 40 rpm over 10 min. The measure of latency to fall did not reveal a significant difference between the genotypes, with all groups showing a comparable increase in performance (Figure 1B, two-way repeated measures ANOVA, F(1, 14)=1.43, p=0.25). An analysis of the slope of the change in performance across the nine sessions similarly did not reveal any difference between the genotypes in the latency to fall (simple linear regression, F(1, 140)=0.56, p=0.45, results not shown). Similar results were obtained when evaluating the progression of the performance of the mice by comparing the first and last sessions, with mice of both genotypes showing equivalent learning (Figure 1C; two-way ANOVA, main effect of training session, F(1, 28)=21.72, p<0.0001; Sidak’s multiple comparisons test, S1 vs S9: WT, p=0.022 and KO, p=0.001). The speed of rotation at the end of each trial across all nine trials was also unchanged (Figure 1D; two-way repeated measures ANOVA, F(1, 14)=1.44, p=0.25). A separate cohort of mice were tested using a more challenging version of the rotarod (Figure 1—figure supplement 2A), with speed of rotation accelerating from 4 to 40 rpm over 2 min. In this cohort, the latency to fall was not significantly different in DAT::NrxnsKO compared to DAT::NrxnsWT, although a tendency for impaired performance was observed (Figure 1—figure supplement 2B, two-way ANOVA, repeated measures, F(1, 16)=4.00, p=0.06). In this task, performance failed to improve over the trials, revealing a limited capacity to improve performance, as shown by comparing performance in the first and last sessions (Figure 1—figure supplement 2C; two-way ANOVA, F(1, 32)=0.037, p=0.84). The speed of rotation at the end of each trial across all nine trials (Figure 1—figure supplement 2D) was similar in DAT::NrxnsKO mice compared to the control mice (two-way repeated measures ANOVA, F(1, 16)=3.50, p=0.08). These results suggest that deletion of Nrxn123 from DA neurons does not lead to major motor coordination and motor learning deficits. Figure 1 with 2 supplements see all Download asset Open asset DAT::NrxnsKO mice exhibit impaired amphetamine-induced motor activity. (A) Schematic representation of a mouse on a rotarod and the diagram of the rotarod testing protocol for the speed 1. (B) Performance on the accelerating rotarod during nine sessions over 3 consecutive days. Latency to fall was quantified at rotation speeds from 4 to 40 rpm over 10 min. (C) Performance of DAT::NrxnsKO and WT littermate mice on the rotarod was evaluated comparing the last session and the first session for each mouse. The results show a significant improvement in performance irrespective of genotype. (D) Quantification of the terminal speed over all the sessions shows no difference between the DAT::NrxnsKO and WT littermate mice. (E) Basal horizontal activity in a novel environment before and after a saline injection (10 mL/kg) over a total of 60 min. (F) Horizontal activity before and after a cocaine injection (20 mg/kg; 10 mL/kg) over a total of 60 min. (G) Horizontal activity before and after an amphetamine injection (5 mg/kg; 10 mL/kg) over 60 min shows reduced locomotion in the DAT::NrxnsKO compared to the control mice. For rotarod and locomotor activity experiments, 7–10 animals per group were used. For all analyses, the plots represent the mean ± SEM. Statistical analyses were carried out by two-way ANOVAs followed by Tukey’s multiple comparison tests or Sidak’s multiple comparisons test. The stars in panel D represent the level of significance of the post hoc tests (*p<0.05; **p<0.01). Figure 1—source data 1 Contains the primary data for Figure 1 and Figure 1—figure supplement 2. https://cdn.elifesciences.org/articles/87902/elife-87902-fig1-data1-v2.xlsx Download elife-87902-fig1-data1-v2.xlsx General motor abilities were next evaluated using the pole test and the open field test. In the pole test, no difference was observed between genotypes for the time required for the mice to orient downward (Figure 1—figure supplement 2E; unpaired t-test, p=0.15) but interestingly the time required to climb down the pole was significantly higher for the DAT::NrxnsKO mice (Figure 1—figure supplement 2F; unpaired t-test, p=0.034). Basal locomotion in the open field over a 60 min period was also not different between genotypes (Figure 1E; two-way ANOVA, repeated measures, F(1; 18)=3.77, p=0.068). We next challenged the dopaminergic system of these mice using the psychostimulants cocaine and amphetamine (Di Chiara and Imperato, 1988). Although locomotion induced by cocaine (20 mg/kg) was comparable between genotypes (Figure 1F, two-way ANOVA, repeated measures, F(1; 16)=0.64, p=0.43), locomotion induced in response to amphetamine (5 mg/kg) was strongly reduced in DAT::NrxnsKO mice compared to DAT::NrxnsWT mice (Figure 1G, two-way ANOVA, repeated measures, F(1; 13)=6.66, main effect of genotype, p=0.023). The finding of reduced behavioral response to amphetamine suggests that loss of Nrxns in DA neurons leads to some alteration of the functionality of the DA system and some DA-dependent behaviors. Because altered DA neurotransmission is often associated with changes in states of hedonia, we next examined the performance of the mice in a well-established sucrose preference task (Figure 1—figure supplement 2G). On the initial two conditioning days (CD1 and CD2), mice of all genotypes equally licked at both bottles (Figure 1—figure supplement 2H). Similarly, during the next three testing days (TD1, -2, and -3), when mice were given a choice between water and sucrose, DAT::NrxnsKO and WT mice both showed a similar marked preference for the sucrose bottle (Figure 1—figure supplement 2H; two-way ANOVA, main effect of choice F(3; 20)=487.0; Tukey’s multiple comparisons test, TD1, -2, -3, water versus sucrose, all genotypes, p<0.0001). These findings suggest that the response of DAT::NrxnsKO mice to natural rewards was unaltered. Altered DAT and VMAT2 levels in the vSTR confirm a perturbation of the DA system in Nrxns KO mice The reduced locomotor response to amphetamine in DAT::NrxnsKO mice suggests the possibility that the structure or the function of DA neurons or their terminals in the striatum are altered in the absence of Nrxns. First, we performed immunohistochemistry to examine the levels of the DA biosynthetic enzyme TH, the VMAT2, and the membrane DAT. The immunopositive surface area of these markers was quantified in a series of three striatal brain sections ranging from bregma +0.74 to bregma –0.82 mm, with a total of seven different regions in each hemisphere distributed to cover the ventral and dorsal sectors of the striatum. We found that TH surface area was unchanged in both the vSTR and dSTR (Figure 2A–B , and E). However, the surface of VMAT2 immunoreactivity was significantly increased in the vSTR, but not in the dSTR, of the KO mice (Figure 2A–B , and G; vSTR, unpaired t-test, Welch’s corrected, p=0.045). In contrast, DAT surface area was significantly decreased in the vSTR, but not in the dSTR, of the KO mice (Figure 2C and F; vSTR, unpaired t-test, p=0.034). Figure 2 Download asset Open asset Increased vesicular monoamine transporter (VMAT2) but decreased dopamine transporter (DAT) expression in dopamine (DA) axon terminals lacking neurexins (Nrxns). (A and B) Immunohistochemistry characterization of ventral (A) and dorsal (B) striatal slices from 8-week-old DAT::NrxnsKO and DAT::NrxnsWT mice (60× confocal) using tyrosine hydroxylase (TH, red) and VMAT2 (green) antibodies. (C and D) Immunohistochemistry of ventral (C) and dorsal (D) striatal slices from DAT::NrxnsKO and DAT::NrxnsWT mice using TH (red) and DAT (green) antibodies. (E–J) Quantification of signal intensity and signal surface (% of WT) for TH, VMAT2, and DAT in the different striatal regions examined: ventral striatum (vSTR) and dorsal striatum (dSTR) (DAT::NrxnsKO = 14 hemispheres/7 mice; DAT::NrxnsWT = 12 hemispheres/6 mice). TH surface area: vSTR = 123.6 ± 18.99% and dSTR = 99.49 ± 7.73% of control. TH signal intensity: vSTR = 109.6 ± 7.36% and dSTR = 97.96 ± 5.98% of control. VMAT2 surface area: vSTR = 168.3 ± 28.27% and dSTR = 136.7 ± 13.85% of control. VMAT2 signal intensity: vSTR = 122.1 ± 10.48% and dSTR = 114.4 ± 6.25% of control. DAT surface area: vSTR = 59.00 ± 10.71% and dSTR1=83.70 ± 2.70% of control DAT signal intensity: vSTR = 74.37 ± 5.56% and dSTR = 84.42 ± 4.40% of control. Statistical analysis was carried out by unpaired t-test for each substructure. Surface and intensity for each signal were measured in striatal slice from bregma + 0.74 mm, with a total of seven different spots for each hemisphere from six DAT::NrxnsWT mice and seven DAT::NrxnsKO mice. Error bars represent ± SEM (*p<0.05). Figure 2—source data 1 Contains the primary data for Figure 2. https://cdn.elifesciences.org/articles/87902/elife-87902-fig2-data1-v2.xlsx Download elife-87902-fig2-data1-v2.xlsx In addition to the surface of immunopositive signal, the average intensity was also quantified. TH, VMAT2, and DAT signal intensity of DAT::NrxnsKO mice were unchanged in both vSTR and dSTR (Figure 2A–D, F, H and J). Nrxn123 ablation does not impair synapse ultrastructure in DA neurons The changes in DAT and VMAT2 immunoreactivity could represent changes in protein expression or axon terminal density or structure. To gain insight into this, we next examined the integrity of axon terminals and synapses established by DA neurons in the intact brain by transmission electron microscopy (TEM). We focused on terminals in the vSTR, where we observed significant changes in VMAT2 and DAT, which is the most characterized brain region showing DA neuron-mediated glutamate and GABA co-transmission (Bérubé-Carrière et al., 2012; Stuber et al., 2010). Our results show that, irrespective of the genotype, most axonal varicosities contained synaptic vesicles and mitochondria (Figure 3A–B). Furthermore, TH-positive dopaminergic terminals in the vSTR of DAT::NrxnsKO mice were not different compared to DAT::NrxnsWT mice in terms of their overall perimeters (P) (Figure 3C–D; unpaired t-test, p=0.94), length (L) (Figure 3E, unpaired t-test, p=0.94), width (w) (Figure 3F, unpaired t-test, p=0.43), or surface area (Figure 3G, unpaired t-test, p=0.92). Figure 3 Download asset Open asset Synaptic and non-synaptic ultrastructure of dopamine (DA) terminals is unchanged after the deletion of neurexins (Nrxns) in DA neurons. (A–B) Electron micrographs showing DA neuron terminals without any postsynaptic density (PSD) domain (top images) or in apposition to a PSD domain in ventral striatal tissue from DAT::NrxnsWT and KO mice. The lower micrograph represents a magnified view of the regions identified by the doted lines in the middle images. The asterisk identifies a synapse and the black arrowheads delimitate the postsynaptic domain. (C) Schematic representation of a dopaminergic varicosity. (D) Bar graph representing the perimeter of the DA axonal varicosity from WT and KO mice (2353±81.83 nm and 2366±174.8 nm, respectively). (E and F) Bar graphs representing the size of the axonal varicosities, quantified as length (E) (897.3±38.06 nm and 902.7±38.06 nm, respectively) and width (F) (468.7±38.06 nm and 431.5±22.02 nm, respectively). (G) Bar graphs showing the surface area of DA neuron varicosities from WT and KO animals (323,537±45,861 nm2 and 317,887±40,227 nm2, respectively). (H) Bar graphs representing the PSD domain size from individual synapses (232.8±23.40 nm and 197.1±35.71 nm, respectively, for WT and KO mice). For all analyses, WT = 101 and KO = 189 axonal varicosities from four different mice for each genotype. For all analyses, plots represent the mean ± SEM. Statistical analyses were carried out by unpaired t-tests. Figure 3—source data 1 Contains the primary data for Figure 3. https://cdn.elifesciences.org/articles/87902/elife-87902-fig3-data1-v2.xlsx Download elife-87902-fig3-data1-v2.xlsx In addition, the propensity of these terminals to make contact with a postsynaptic density (PSD) domain was unchanged in DAT::NrxnsKO mice. The synaptic incidence of TH-positive terminals was 6.34% (12 terminals with a PSD domain/189 TH-positive varicosities) for DAT::NrxnsKO mice and 4.95% (5 terminals with a PSD domain/101 TH-positive varicosities) for control mice (data not shown), a low proportion in line with previous work (Bérubé-Carrière et al., 2012; Stuber et al., 2010). Among these synaptic TH-positive varicosities, the size of the PSD was similar (Figure 3H, unpaired t-test, p=0.54). Together, these results show that loss of Nrxns123 does not impair the basic ultrastructure of DA release sites in the vSTR. FSCV reveals altered DA release parameters after conditional deletion of all Nrxns in DA neurons The impaired response to amphetamine suggests a perturbation of extracellular DA dynamics or DA action on target cells. To examine this possibility, we first employed fast-scan cyclic voltammetry (FSCV) in acute brain slices of the vSTR and dSTR to measure electrically evoked DA overflow (DAo), the identify of which was confirmed by the shape of cyclic voltamograms (Figure 4—figure supplement 1A–D). In the first series of experiments performed in normal extracellular saline, we found no difference in peak DAo between the DAT::NrxnsWT and DAT::NrxnsKO mice (Figure 4A–B and E–F). Figure 4 with 2 supplements see all Download asset Open asset Impaired dopamine (DA) overflow in DAT::NrxnsKO mice. (A) Representative traces of electrically evoked DA overflow detected by fast-scan cyclic voltammetry in the ventral striatum, measured in slices prepared from DAT::NrxnsWT and DAT::NrxnsKO mice. (B) Bar graphs showing the average peak DA levels (µM) detected in the ventral striatum (WT = 0.98 ± 0.04 µM and KO = 0.98 ± 0.06 µM). (C) Evaluation of DA overflow kinetics in the ventral striatum estimated by quantifying tau (WT = 0.35 ± 0.02 and KO = 0.42 ± 0.02). (D) Short-term paired-pulse induced plasticity of DA overflow in ventral striatal slices, estimated by calculating (P2-P1/P1) with an inter-pulse interval of 100 ms. The low ratio values reflect the strong paired-pulse depression seen at such release sites in acute brain slices. (E) Representative traces of electrically evoked DA overflows detected by fast-scan cyclic voltammetry in the dorsal striatum. (F) Bar graphs showing the average peak DA levels (µM) detected in the dorsal striatum (WT = 1.33 ± 0.05 µM and KO = 1.35 ± 0.07 µM). (G) Evaluation of DA overflow kinetics in the dorsal striatum, estimated by quantifying tau (WT = 0.36 ± 0.02 s and KO = 0.45 ± 0.03 s). (H) Short-term paired-pulse induced plasticity of DA overflow in dorsal striatal slices, estimated by calculating (P2-P1/P1) with an inter-pulse interval at 100 ms. The low ratio values reflect the strong paired-pulse depression seen at such release sites in acute brain slices. (I) Representative traces of electrically evoked DA overflow detected by fast-scan cyclic voltammetry in the ventral striatum, measured in slices prepared from DAT::NrxnsWT and DAT::NrxnsKO mice in the presence of the nicotinic receptor antagonist DHßE. (J) Bar graphs showing the average peak DA levels (µM) detected in the ventral striatum (WT = 0.47 ± 0.09 µM and KO = 0.24 ± 0.06 µM). (K) Evaluation of DA overflow kinetics in the ventral striatum estimated by quantifying tau (WT = 1.35 ± 0.17 s and KO = 1.63 ± 0.16 s). (L) Short-term paired-pulse induced plasticity of DA overflow in ventral striatal slices, estimated by calculating (P2-P1/P1) with an inter-pulse interval of 100 ms. The low ratio values reflect the strong paired-pulse depression seen at such release sites in acute brain slices. (M) Representative traces of electrically evoked DA overflow detected by fast-scan cyclic voltammetry in the dorsal striatum in the presence of the nicotinic receptor antagonist DHßE. (N) Bar graphs showing the average peak DA levels (µM) detected in the dorsal striatum (WT = 0.43 ± 0.05 µM and KO = 0.24 ± 0.03 µM). (O) Evaluation of DA overflow kinetics in the dorsal striatum, estimated by quantifying tau (WT = 1.37 ± 0.22 s and KO = 1.21 ± 0.24 s). (P) Short-term paired-pulse induced plasticity of DA overflow in dorsal striatal slices, estimated by calculating (P2-P1/P1) with an inter-pulse interval at 100 ms. The low ratio values reflect the strong paired-pulse depression seen at such release sites in acute brain slices. Data are presented as mean ± SEM. Statistical analyses were performed with Student’s t-tests (*p<0.05; **p<0.01). Figure 4—source data 1 Contains the primary data for Figure 4 and Figure 4—figure supplements 1 and 2. https://cdn.elifesciences.org/articles/87902/elife-87902-fig4-data1-v2.xlsx Download elife-87902-fig4-data1-v2.xlsx However, an examination of the kinetics of DAo, often used to identify changes in DA release efficiency and reuptake (Yorgason et al., 2011), revealed that the tau value of DA recovery in the vSTR was significantly higher in DAT::NrxnsKO compared to DAT::NrxnsWT mice (Figure 4A and C, unpaired t-test, p=0.008). We also observed a similar increase in tau for the rate of DA recovery in the dSTR (Figure 4E and G; unpaired t-test, p=0.019). Quantification of the rise time of evoked DAo in the vSTR and dSTR revealed no significant genotype difference (Figure 4—figure supplement 2A–B). Short-term plasticity of electrically evoked DA release in the striatum was examined using a paired-pulse stimulation paradigm. DAo in acute brain slices typically shows a large paired-pulse depression, more extensively so in the dSTR compared to the vSTR (Condon et al., 2019; Sanchez et al.," @default.
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• W4385668891 date "2023-04-19" @default.
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• W4385668891 title "Editor's evaluation: Conditional deletion of neurexins dysregulates neurotransmission from dopamine neurons" @default.
• W4385668891 doi "https://doi.org/10.7554/elife.87902.sa0" @default.
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