Emile G. Bruneau

Identification of Nicotinic Acetylcholine Receptor Recycling and Its Role in Maintaining Receptor Density at the Neuromuscular Junction In Vivo

In the CNS, receptor recycling is critical for synaptic plasticity; however, the recycling of receptors has never been observed at peripheral synapses. Using a novel imaging technique, we show here that nicotinic acetylcholine receptors (AChRs) recycle into the postsynaptic membrane of the neuromuscular junction. By sequentially labeling AChRs with biotin-bungarotoxin and streptavidin-fluorophore conjugates, we were able to distinguish recycled, preexisting, and new receptor pools at synapses in living mice. Time-lapse imaging revealed that recycled AChRs were incorporated into the synapse within hours of initial labeling, and their numbers increased with time. At fully functional synapses, AChR recycling was robust and comparable in magnitude with the insertion of newly synthesized receptors, whereas chronic synaptic activity blockade nearly abolished receptor recycling. Finally, using the same sequential labeling method, we found that acetylcholinesterase, another synaptic component, does not recycle. These results identify an activity-dependent AChR-recycling mechanism that enables the regulation of receptor density, which could lead to rapid alterations in synaptic efficacy.

Increased expression of glutaminase and glutamine synthetase mRNA in the thalamus in schizophrenia

Numerous molecules enable the handling of glutamate that is destined for neurotransmitter release, including transporters, receptors and glutamatergic enzymes. Previous work in our lab has shown altered levels of transcript expression of excitatory amino acid transporters and a vesicular glutamate transporter in the thalamus in schizophrenia. These changes suggest that molecules that facilitate the release and reuptake of glutamate may be abnormal in schizophrenia. In this study we determined the levels of expression of phosphate activated glutaminase (PAG), which converts glutamine to glutamate, and glutamine synthetase (GS), which converts glutamate to glutamine, with the hypothesis that thalamic PAG and GS transcript expression is altered in schizophrenia. We investigated expression of PAG and GS mRNA using in situ hybridization in six different thalamic nuclei (anterior, dorsomedial, centromedial, ventral anterior, ventral and reticular) from 13 persons with schizophrenia and 8 comparison subjects and found that transcripts for PAG and GS were significantly increased in schizophrenia. Increased PAG and GS transcripts suggest enhanced glutamatergic neurotransmission in the thalamus and its efferent targets in schizophrenia.

Running to stand still: ionotropic receptor dynamics at central and peripheral synapses.

For synapses to form and function, neurotransmitter receptors must be recruited to a location on the postsynaptic cell in direct apposition to presynaptic neurotransmitter release. However, once receptors are inserted into the postsynaptic membrane, they are not fixed in place but are continually exchanged between synaptic and extrasynaptic regions, and they cycle between the surface and intracellular compartments. This article highlights and compares the current knowledge about the dynamics of acetylcholine receptors at the vertebrate peripheral neuromuscular junction and AMPA, N-methyl-d-aspartate, and γ-aminobutyric acid receptors in central synapses.

Receptor-associated proteins and synaptic plasticity.

Changes in synaptic strength are important for synaptic development and synaptic plasticity. Most directly responsible for these synaptic changes are alterations in synaptic receptor number and density. Although alterations in receptor density mediated by the insertion, lateral mobility, removal, and recycling of receptors have been extensively studied, the dynamics and regulators of intracellular scaffolding proteins have only recently begun to be illuminated. In particular, a closer look at the receptor‐associated proteins, which bind to receptors and are necessary for their synaptic localization and clustering, has revealed broader functions than previously thought and some rather unexpected thematic similarities. More than just “placeholders” or members of a passive protein “scaffold,” receptor‐associated proteins in every synapse studied have been shown to provide a number of signaling roles. In addition, the most recent state‐of‐the‐art imaging has revealed that receptor‐associated proteins are highly dynamic and are involved in regulating synaptic receptor density. Together, these results challenge the view that receptor‐associated proteins are members of a static and stable scaffold and argue that their dynamic mobility may be essential for regulating activity‐dependent changes in synaptic strength.— Bruneau, E. G., Esteban, J. A., Akaaboune, M. Receptor‐associated proteins and synaptic plasticity. FASEB J. 23, 679–688 (2009)

Backlash: The Politics and Real-World Consequences of Minority Group Dehumanization

Research suggests that members of advantaged groups who feel dehumanized by other groups respond aggressively. But little is known about how meta-dehumanization affects disadvantaged minority group members, historically the primary targets of dehumanization. We examine this important question in the context of the 2016 U.S. Republican Primaries, which have witnessed the widespread derogation and dehumanization of Mexican immigrants and Muslims. Two initial studies document that Americans blatantly dehumanize Mexican immigrants and Muslims; this dehumanization uniquely predicts support for aggressive policies proposed by Republican nominees, and dehumanization is highly associated with supporting Republican candidates (especially Donald Trump). Two further studies show that, in this climate, Latinos and Muslims in the United States feel heavily dehumanized, which predicts hostile responses including support for violent versus non-violent collective action and unwillingness to assist counterterrorism efforts. Our results extend theorizing on dehumanization, and suggest that it may have cyclical and self-fulfilling consequences.Research suggests that members of advantaged groups who feel dehumanized by other groups respond aggressively. But little is known about how meta-dehumanization affects disadvantaged minority group members, historically the primary targets of dehumanization. We examine this important question in the context of the 2016 U.S. Republican Primaries, which have witnessed the widespread derogation and dehumanization of Mexican immigrants and Muslims. Two initial studies document that Americans blatantly dehumanize Mexican immigrants and Muslims; this dehumanization uniquely predicts support for aggressive policies proposed by Republican nominees, and dehumanization is highly associated with supporting Republican candidates (especially Donald Trump). Two further studies show that, in this climate, Latinos and Muslims in the United States feel heavily dehumanized, which predicts hostile responses including support for violent versus non-violent collective action and unwillingness to assist counterterrorism efforts. Our results extend theorizing on dehumanization, and suggest that it may have cyclical and self-fulfilling consequences.

The Dynamics of the Rapsyn Scaffolding Protein at Individual Acetylcholine Receptor Clusters

Rapsyn, a cytoplasmic receptor-associated protein, is required for the clustering of acetylcholine receptors (AChRs). Although AChR dynamics have been extensively studied, little is known about the dynamics of rapsyn. Here, we used a rapsyn-green fluorescent protein (GFP) fusion protein and quantitative fluorescent imaging to study the dynamics of rapsyn in transfected C2C12 myotubes. First, we found that rapsyn-GFP expression at clusters did not alter AChR aggregation, function, or turnover. Quantification of rapsyn immunofluorescence indicated that the expression of rapsyn-GFP proteins at clusters does not increase the overall rapsyn density compared with untransfected myotube clusters. Using time lapse imaging and fluorescence recovery after photobleaching, we demonstrated that the recovery of rapsyn-GFP fluorescence at clusters was very fast, with a halftime of about ∼1.5 h (∼3 times faster than AChRs). Inhibition of protein kinase C significantly altered receptor insertion, but it had no effect on rapsyn insertion. When cells were treated with the broad spectrum kinase inhibitor staurosporine, receptor insertion was decreased even further. However, inhibition of protein kinase A had no effect on insertion of either rapsyn or receptors. Finally, when cells were treated with neural agrin, rapsyn and AChRs were both directed away from preexisting clusters and accumulated together in new small clusters. These results demonstrate the remarkable dynamism of rapsyn, which may underlie the stability and maintenance of the postsynaptic scaffold and suggest that the insertion of different postsynaptic proteins may be operating independently.

Dynamics of the Rapsyn Scaffolding Protein at the Neuromuscular Junction of Live Mice

The efficacy of synaptic transmission depends on the maintenance of a high density of neurotransmitter receptors and their associated scaffold proteins in the postsynaptic membrane. While the dynamics of receptors has been extensively studied, the dynamics of the intracellular scaffold proteins that make up the postsynaptic density are largely unknown in vivo. Here, we focused on the dynamics of rapsyn, a protein required for the clustering and maintenance of acetylcholine receptor (AChR) density at postsynaptic sites. Using time-lapse imaging, we demonstrated that rapsyn is remarkably dynamic compared to AChRs at functional synapses, turning over 4–6 times more rapidly than AChRs. In addition we found that the rapid turnover of rapsyn is insensitive to alterations in synaptic activity, whereas AChR turnover is profoundly affected, illustrating that rapsyn and receptor dynamics are controlled by distinct mechanisms. These data indicate that individual postsynaptic components are in permanent exchange despite the overall stability of synaptic structure, which may play a role in synaptic plasticity.

Acetylcholine receptor clustering is required for the accumulation and maintenance of scaffolding proteins.

The maintenance of a high density of postsynaptic receptors is essential for proper synaptic function. At the neuromuscular junction, acetylcholine receptor (AChR) aggregation is induced by nerve-clustering factors and mediated by scaffolding proteins. Although the mechanisms underlying AChR clustering have been extensively studied, the role that the receptors themselves play in the clustering process and how they are organized with scaffolding proteins is not well understood. Here, we report that the exposure of AChRs labeled with Alexa 594 conjugates to relatively low-powered laser light caused an effect similar to chromaphore-assisted light inactivation (CALI) , which resulted in the unexpected dissipation of the illuminated AChRs from clusters on cultured myotubes. This technique enabled us to demonstrate that AChR removal from illuminated regions induced the removal of scaffolding proteins and prevented the accumulation of new AChRs and associated scaffolding proteins. Further, the dissipation of clustered AChRs and scaffold was spatially restricted to the illuminated region and had no effect on neighboring nonilluminated AChRs. These results provide direct evidence that AChRs are essential for the local maintenance and accumulation of intracellular scaffolding proteins and suggest that the scaffold is organized into distinct modular units at AChR clusters.

Minding the Gap: Narrative Descriptions about Mental States Attenuate Parochial Empathy

In three experiments, we examine parochial empathy (feeling more empathy for in-group than out-group members) across novel group boundaries, and test whether we can mitigate parochial empathy with brief narrative descriptions. In the absence of individuating information, participants consistently report more empathy for members of their own assigned group than a competitive out-group. However, individualized descriptions of in-group and out-group targets significantly reduce parochial empathy by interfering with encoding of targets’ group membership. Finally, the descriptions that most effectively decrease parochial empathy are those that describe targets’ mental states. These results support the role of individuating information in ameliorating parochial empathy, suggest a mechanism for their action, and show that descriptions emphasizing targets’ mental states are particularly effective.

Parochial Empathy Predicts Reduced Altruism and the Endorsement of Passive Harm

Empathic failures are common in hostile intergroup contexts; repairing empathy is therefore a major focus of peacebuilding efforts. However, it is unclear which aspect of empathy is most relevant to intergroup conflict. Although trait empathic concern predicts prosociality in interpersonal settings, we hypothesized that the best predictor of meaningful intergroup attitudes and behaviors might not be the general capacity for empathy (i.e., trait empathy), but the difference in empathy felt for the in-group versus the out-group, or “parochial empathy.” Specifically, we predicted that out-group empathy would inhibit intergroup harm and promote intergroup helping, whereas in-group empathy would have the opposite effect. In three intergroup contexts—Americans regarding Arabs, Hungarians regarding refugees, Greeks regarding Germans—we found support for this hypothesis. In all samples, in-group and out-group empathy had independent, significant, and opposite effects on intergroup outcomes, controlling for trait empathic concern.