Defining Dysbiosis in Disorders of Movement and Motivation

The gut microbiota has emerged as a critical player in shaping and modulating brain function and has been shown to influence numerous behaviors, including anxiety and depression-like behaviors, sociability, and cognition. However, the effects of the gut microbiota on specific disorders associated with thalamo-cortico-basal ganglia circuits, ranging from compulsive behavior and addiction to altered sensation and motor output, are only recently being explored. Wholesale depletion and alteration of gut microbial communities in rodent models of disorders, such as Parkinson's disease, autism, and addiction, robustly affect movement and motivated behavior. A new frontier therefore lies in identifying specific microbial alterations that affect these behaviors and understanding the underlying mechanisms of action. Comparing alterations in gut microbiota across multiple basal-ganglia associated disease states allows for identification of common mechanistic pathways that may interact with distinct environmental and genetic risk factors to produce disease-specific outcomes

Defining Dysbiosis in Disorders of Movement and Motivation

The gut microbiota has emerged as a critical player in shaping and modulating brain function and has been shown to influence numerous behaviors, including anxiety and depression-like behaviors, sociability, and cognition. However, the effects of the gut microbiota on specific disorders associated with thalamo-cortico-basal ganglia circuits, ranging from compulsive behavior and addiction to altered sensation and motor output, are only recently being explored. Wholesale depletion and alteration of gut microbial communities in rodent models of disorders, such as Parkinson's disease, autism, and addiction, robustly affect movement and motivated behavior. A new frontier therefore lies in identifying specific microbial alterations that affect these behaviors and understanding the underlying mechanisms of action. Comparing alterations in gut microbiota across multiple basal-ganglia associated disease states allows for identification of common mechanistic pathways that may interact with distinct environmental and genetic risk factors to produce disease-specific outcomes

Characterization of the Rho-GEF Kalirin-7 in the Mouse Brain: Evidence for a Role in Learning and Addictive-Like Behaviors, as Well as Neuronal Morphology and NMDA Receptor Signaling.

Kalirin-7 (Kal7) is a Rho-guanine nucleotide exchange factor localized to the post-synaptic density (PSD) of neurons in the forebrain. For several years, Kal7 has been known to be an important regulator of dendritic spine formation and stabilization in cultured neurons. However, the functional consequences of these morphological changes remained largely unexplored. A transgenic mouse with a constitutive genetic deletion of Kal7 (Kal7KO) was developed and characterized. Initial studies on this mouse showed that Kal7 was essential for normal dendritic spine formation in the hippocampus and hippocampal long-term potentiation. Additionally, Kal7KO mice displayed decreased anxiety-like behavior and fear conditioning, while exhibiting normal behavior in other hippocampal-dependent learning tasks. Biochemical characterization of these mice showed that Kal7KO caused a compensatory increase in other splice variants of Kalirin, and decreased PSD levels of the NR2B subunit of the NMDA receptor. Following this initial characterization, Kal7KO mice were examined in models of cocaine addiction. Kal7KO mice exhibited increased locomotor sensitivity to cocaine, but showed decreased preference for cocaine in a conditioned place preference assay. While wild-type mice exhibited an increase in dendritic spine density in the nucleus accumbens following cocaine treatments, Kal7KO mice did not. Hence, we looked more closely at the decrease in NR2B levels in Kal7KO mice. We saw specific decreases in NR2B currents and cell surface localization in the Kal7KO. Biochemical studies revealed a direct interaction between Kal7 and NR2B. Inhibition of NR2B currents prior to fear or cocaine conditioning caused wild-type mice to phenocopy Kal7KO mice, while leaving the Kal7KO unaffected. This suggests that decreases in NR2B mediated currents account for behavioral abnormalities seen in Kal7KO mice. Finally, we used mass spectrometry to identify \u3e30 sites of phosphorylation in Kal7 isolated from mouse brain and transfected cells. Phosphorylation sites for a number of kinases known to be crucial for normal synaptic plasticity were identified. These studies identify Kal7 as a critical component of morphological response and NMDA receptor function in dendritic spines, consistent with its essential role in normal behavioral adaptations

Kalrn Promoter Usage And Isoform Expression Respond To Chronic Cocaine Exposure

Background The long-term effects of cocaine on behavior are accompanied by structural changes in excitatory glutamatergic synapses onto the medium spiny neurons of the striatum. The Kalrn gene encodes several functionally distinct isoforms; these multidomain guanine nucleotide exchange factors (GEFs) contain additional domains known to interact with phosphatidylinositides as well as with a number of different proteins. Through their activation of Rho proteins and their interactions with other proteins, the different Kalirin isoforms affect cytoskeletal organization. Chronic exposure of adult male rodents to cocaine increases levels of Kalirin 7 in the striatum. When exposed chronically to cocaine, mice lacking Kalirin 7, the major adult isoform, fail to show an increase in dendritic spine density in the nucleus accumbens, show diminished place preference for cocaine, and exhibit increased locomotor activity in response to cocaine. Results The use of alternate promoters and 3\u27-terminal exons of the mouse Kalrn gene were investigated using real-time quantitative polymerase chain reaction. While the two most distal full-length Kalrn promoters are used equally in the prefrontal cortex, the more proximal of these promoters accounts for most of the transcripts expressed in the nucleus accumbens. The 3\u27-terminal exon unique to the Kalirin 7 isoform accounts for a greater percentage of the Kalrn transcripts in prefrontal cortex than in nucleus accumbens. Western blot analyses confirmed these differences. Chronic cocaine treatment increases usage of the promoter encoding the Δ-Kalirin isoforms but does not alter full-length Kalirin promoter usage. Usage of the 3\u27-terminal exon unique to Kalirin 7 increases following chronic cocaine exposure. Conclusions Kalrn promoter and 3\u27-terminal exon utilization are region-specific. In the nucleus accumbens, cocaine-mediated alterations in promoter usage and 3\u27-terminal exon usage favor expression of Kalirin 7 and Δ-Kalirin 7. The Δ-isoform, which lacks a Sec14p domain and four of the nine spectrin-like repeats found in full-length Kalirin isoforms, increases spine headsize without increasing dendritic spine numbers. Thus cocaine-mediated changes in alternative splicing of the Kalrn gene may contribute importantly to the behavioral, morphological and biochemical responses observed

Kalirin-7 is necessary for normal NMDA receptor-dependent synaptic plasticity

<p>Abstract</p> <p>Background</p> <p>Dendritic spines represent the postsynaptic component of the vast majority of excitatory synapses present in the mammalian forebrain. The ability of spines to rapidly alter their shape, size, number and receptor content in response to stimulation is considered to be of paramount importance during the development of synaptic plasticity. Indeed, long-term potentiation (LTP), widely believed to be a cellular correlate of learning and memory, has been repeatedly shown to induce both spine enlargement and the formation of new dendritic spines. In our studies, we focus on Kalirin-7 (Kal7), a Rho GDP/GTP exchange factor (Rho-GEF) localized to the postsynaptic density that plays a crucial role in the development and maintenance of dendritic spines both <it>in vitro </it>and <it>in vivo</it>. Previous studies have shown that mice lacking Kal7 (Kal7^KO) have decreased dendritic spine density in the hippocampus as well as focal hippocampal-dependent learning impairments.</p> <p>Results</p> <p>We have performed a detailed electrophysiological characterization of the role of Kal7 in hippocampal synaptic plasticity. We show that loss of Kal7 results in impaired NMDA receptor-dependent LTP and long-term depression, whereas a <b>NMDA receptor-independent </b>form of LTP is shown to be normal in the absence of Kal7.</p> <p>Conclusions</p> <p>These results indicate that Kal7 is an essential and selective modulator of NMDA receptor-dependent synaptic plasticity in the hippocampus.</p

Granulocyte-Colony-Stimulating Factor Alters the Proteomic Landscape of the Ventral Tegmental Area

Cocaine addiction is characterized by aberrant plasticity of the mesolimbic dopamine circuit, leading to dysregulation of motivation to seek and take drug. Despite the significant toll that cocaine use disorder exacts on society, there are currently no available pharmacotherapies. We have recently identified granulocyte-colony stimulating factor (G-CSF) as a soluble cytokine that alters the behavioral response to cocaine and which increases dopamine release from the ventral tegmental area (VTA). Despite these known effects on behavior and neurophysiology, the molecular mechanisms by which G-CSF affects brain function are unclear. In this study mice were treated with repeated injections of G-CSF, cocaine or a combination and changes in protein expression in the VTA were examined using an unbiased proteomics approach. Repeated G-CSF treatment resulted in alterations in multiple signaling pathways related to synaptic plasticity and neuronal morphology. While the treatment groups had marked overlap in their effect, injections of cocaine and the combination of cocaine and G-CSF lead to distinct patterns of significantly regulated proteins. These experiments provide valuable information as to the molecular pathways that G-CSF activates in an important limbic brain region and will help to guide further characterization of G-CSF function and evaluation as a possible translational target