Current research in neurobiology最新文献

Genetically encoded synthetic receptors, such as the chemogenetic and optogenetic proteins, are powerful tools for functional brain studies in animals. In the primate brain, with its comparatively large, intricate anatomical structures, it can be challenging to express transgenes, such as the hM4Di chemogenetic receptor, in a defined anatomical structure with high penetrance. Here, we compare parameters for lentivirus vector injections in the rhesus monkey amygdala. We find that four injections of 20 μl, infused at 0.5 μl/min, can achieve neuronal hM4Di expression in 50–100% of neurons within a 60 mm³ volume, without observable damage from overexpression. Increasing the number of hM4Di_CFP lentivirus injections to up to 12 sites per hemisphere, resulted in 30%–40% neuronal coverage of the overall amygdala volume, with coverage reaching 60% in some subnuclei. Manganese Chloride was mixed with lentivirus and used as an MRI marker to verify targeting accuracy and correct unsuccessful injections in these experiments. In a separate monkey we visualized, in vivo, viral expression of the hM4Di receptor protein in the amygdala, using Positron Emission Tomography. Together, these data show efficient and verifiable expression of a chemogenetic receptor in old-world monkey amygdala.

Impulsivity, the tendency to react quickly and without consideration of consequences, is correlated with asymmetry in the volume of the caudate nucleus in human patients. In this study, we sought to determine whether the induction of functional asymmetry in the caudate nucleus of monkeys would produce phenomenologically comparable behavior. We found that unilateral suppression of the ventral caudate nucleus increases impulsive behavior in rhesus monkeys. Impulsivity was modeled by the subjects’ inability to maintain hold of a touch-sensitive bar until presentation of an imperative signal. Two methods were used to suppress activity in the caudate region. First, muscimol was locally infused. Second, a viral construct expressing the hM₄Di DREADD (designer receptor exclusively activated by designer drug) was injected at the same site. Clozapine N-oxide and deschloroclozapine activate the DREADD to suppress neuronal activity. Both methods of suppression, pharmacological and chemogenetic, increased the rate of early bar releases, a behavior we interpret to indicate impulsivity. Thus, we demonstrate a causal relationship between caudate asymmetry and impulsivity.

Developing optogenetic methods for research in non-human primates (NHP) is important for translational neuroscience and for delineating brain function with unprecedented specificity. Here we assess, in macaque monkeys, the selectivity by which optogenetic stimulation of the primary visual cortex (V1) drives the local laminar and widespread cortical connectivity related to visual perception. Towards this end, we transfected neurons with light-sensitive channelrhodopsin in dorsal V1. fMRI revealed that optogenetic stimulation of V1 using blue light at 40 Hz increased functional activity in the visual association cortex, including areas V2/V3, V4, motion-sensitive area MT and frontal eye fields, although nonspecific heating and eye movement contributions to this effect could not be ruled out. Neurophysiology and immunohistochemistry analyses confirmed optogenetic modulation of spiking activity and opsin expression with the strongest expression in layer 4-B in V1. Stimulating this pathway during a perceptual decision task effectively elicited a phosphene percept in the receptive field of the stimulated neurons in one monkey. Taken together, our findings demonstrate the great potential of optogenetic methods to drive the large-scale cortical circuits of the primate brain with high functional and spatial specificity.

A growing body of evidence has implicated progranulin in neurodevelopment and indicated that aberrant progranulin expression may be involved in neurodevelopmental disease. Specifically, increased progranulin expression in the prefrontal cortex has been suggested to be pathologically relevant in male Fmr1 knockout (Fmr1 KO) mice, a mouse model of Fragile X Syndrome (FXS). Further investigation into the role of progranulin in FXS is warranted to determine if therapies that reduce progranulin expression represent a viable strategy for treating patients with FXS. Several key knowledge gaps remain. The mechanism of increased progranulin expression in Fmr1 KO mice is poorly understood and the extent of progranulin's involvement in FXS-like phenotypes in Fmr1 KO mice has been incompletely explored. To this end, we have performed a thorough characterization of progranulin expression in Fmr1 KO mice. We find that the phenomenon of increased progranulin expression is post-translational and tissue-specific. We also demonstrate for the first time an association between progranulin mRNA and FMRP, suggesting that progranulin mRNA is an FMRP target. Subsequently, we show that progranulin over-expression in Fmr1 wild-type mice causes reduced repetitive behaviour engagement in females and mild hyperactivity in males but is largely insufficient to recapitulate FXS-associated behavioural, morphological, and electrophysiological abnormalities. Lastly, we determine that genetic reduction of progranulin expression on an Fmr1 KO background reduces macroorchidism but does not alter other FXS-associated behaviours or biochemical phenotypes.

Background

In the last decades different preclinical animal models of Parkinson's disease (PD) have been generated, aiming to mimic the progressive neuronal loss of midbrain dopaminergic (DA) cells as well as motor and non-motor impairment. Among all the available models, AAV-based models of human alpha-synuclein (h-aSYN) overexpression are promising tools for investigation of disease progression and therapeutic interventions.

Objectives

The goal with this work was to characterise the impairment in motor and non-motor domains following nigrostriatal overexpression of h-aSYN and correlate the behavioural deficits with histological assessment of associated pathology.

Methods

Intranigral injection of an AAV9 expressing h-aSYN was compared with untreated animals, 6-OHDA and AAV9 expressing either no transgene or GFP. The animals were assessed on a series of simple and complex behavioural tasks probing motor and non-motor domains. Post-mortem neuropathology was analysed using immunohistochemical methods.

Results

Overexpression of h-aSYN led to progressive degeneration of DA neurons of the SN and axonal terminals in the striatum (STR). We observed extensive nigral and striatal pathology, resembling that of human PD brain, as well as the development of stable progressive deficit in simple motor tasks and in non-motor domains such as deficits in motivation and lateralised neglect.

Conclusions

In the present work we characterized a rat model of PD that closely resembles human PD pathology at the histological and behavioural level. The correlation of cell loss with behavioural performance enables the selection of rats which can be used in neuroprotective or neurorestorative therapies.

Type 2 diabetes mellitus has steadily increased in prevalence over the past five decades. Among the health risks associated with this disorder are cognitive decline and are increased risk of developing dementia. To further investigate the link between diabetes and cognition, here we test memory performance and hippocampal function in the Goto-Kakizaki (GK) rat, a robust model of diabetes. Relative to age-matched Wistar rats, GK rats show impairments in a conjunctive memory task that requires discriminating objects not only on the basis of their physical characteristics, but also on the basis of where and when they were last seen. Concomitant to these deficits are changes in the pattern of expression of Egr1 (an immediate-early gene critical for memory) in dentate gyrus granule cells, consistent with dentate hypoactivity leading to unstable hippocampal representations. These data support the hypothesis that diabetes confers a phenotype of accelerated senescence on the hippocampus, and help to link this disorder with changes in hippocampal circuits.

Earlier age of cannabis usage poses higher risk of Cannabis Use Disorder and adverse consequences, such as addiction, anxiety, dysphoria, psychosis, largely attributed to its principal psychoactive component, Δ9-tetrahydrocannabinol (THC) and altered dopaminergic function. As dopamine D1-D2 receptor heteromer activation causes anxiety and anhedonia, this signaling complex was postulated to contribute to THC-induced affective symptoms. To investigate this, we administered THC repeatedly to adolescent monkeys and adolescent or adult rats. Drug-naïve adolescent rat had lower striatal densities of D1-D2 heteromer compared to adult rat. Repeated administration of THC to adolescent rat or adolescent monkey did not alter D1-D2 heteromer expression in nucleus accumbens or dorsal striatum but upregulated it in adult rat. Behaviourally, THC-treated adult, but not adolescent rat manifested anxiety and anhedonia-like behaviour, with elevated composite negative emotionality scores that correlated with striatal D1-D2 density. THC modified downstream markers of D1-D2 activation in adult, but not adolescent striatum. THC administered with cannabidiol did not alter D1-D2 expression. In adult rat, co-administration of CB1 receptor (CB1R) inverse agonist with THC attenuated D1-D2 upregulation, implicating cannabinoids in the regulation of striatal D1-D2 heteromer expression. THC exposure revealed an adaptable age-specific, anxiogenic, anti-reward mechanism operant in adult striatum but deficient in adolescent rat and monkey striatum that may confer increased sensitivity to THC reward in adolescence while limiting its negative effects, thus promoting continued use and increasing vulnerability to long-term adverse cannabis effects.

The chromodomain helicase DNA-binding protein 8 (CHD8) is a chromatin remodeler whose mutation is associated, with high penetrance, with autism. Individuals with CHD8 mutations share common symptoms such as autistic behaviour, cognitive impairment, schizophrenia comorbidity, and phenotypic features such as macrocephaly and facial defects. Chd8-deficient mouse models recapitulate most of the phenotypes seen in the brain and other organs of humans. It is known that CHD8 regulates - directly and indirectly - neuronal, autism spectrum disorder (ASDs)-associated genes and long non-coding RNAs (lncRNAs) genes, which, in turn, regulate fundamental aspects of neuronal differentiation and brain development and function. A major characteristic of CHD8 regulation of gene expression is its non-linear and dosage-sensitive nature. CHD8 mutations appear to affect males predominantly, although the reasons for this observed sex bias remain- unknown. We have recently reported that CHD8 directly regulates X chromosome inactivation (XCI) through the transcriptional control of the Xist long non-coding RNA (lncRNA), the master regulator of mammalian XCI. We identified a role for CHD8 in regulating accessibility at the Xist promoter through competitive binding with transcription factors (TFs) at Xist regulatory regions. We speculate here that CHD8 might also regulate accessibility at neuronal/ASD targets through a similar competitive binding mechanism during neurogenesis and brain development. However, whilst such a model can reconcile the phenotypic differences observed in Chd8 knock-down (KD) vs knock-out (KO) mouse models, explaining the observed CHD8 non-linear dosage-dependent activity, it cannot on its own explain the observed disease sex bias.

Brain serotonin (5-hydroxytryptamine, 5-HT) is a key molecule for the mediation of depression-related brain states, but the neural mechanisms underlying 5-HT mediation need further investigation. A possible mechanism of the therapeutic antidepressant effects is neurogenic cell production, as stimulated by 5-HT signaling. Neurogenesis, the proliferation of neural stem cells (NSCs), and cell differentiation and maturation occur across brain regions, particularly the hippocampal dentate gyrus and the subventricular zone, throughout one's lifespan. 5-HT plays a major role in the mediation of neurogenic processes, which in turn leads to the therapeutic effect on depression-related states. In this review article, we aim to identify how the neuronal 5-HT system mediates the process of neurogenesis, including cell proliferation, cell-type differentiation and maturation. First, we will provide an overview of the neurogenic cell transformation that occurs in brain regions containing or lacking NSCs. Second, we will review brain region-specific mechanisms of 5-HT-mediated neurogenesis by comparing regions localized to NSCs, i.e., the hippocampus and subventricular zone, with those not containing NSCs. Highlighting these 5-HT mechanisms that mediate neurogenic cell production processes in a brain-region-specific manner would provide unique insights into the role of 5-HT in neurogenesis and its associated effects on depression.

The ability to process speech in noise (SPiN) declines with age, with a detrimental impact on life quality. Music-making activities such as singing and playing a musical instrument have raised interest as potential prevention strategies for SPiN perception decline because of their positive impact on several brain system, especially the auditory system, which is critical for SPiN. However, the literature on the effect of musicianship on SPiN performance has yielded mixed results. By critically assessing the existing literature with a systematic review and a meta-analysis, we aim to provide a comprehensive portrait of the relationship between music-making activities and SPiN in different experimental conditions. 38/49 articles, most focusing on young adults, were included in the quantitative analysis. The results show a positive relationship between music-making activities and SPiN, with the strongest effects found in the most challenging listening conditions, and little to no effect in less challenging situations. This pattern of results supports the notion of a relative advantage for musicians on SPiN performance and clarify the scope of this effect. However, further studies, especially with older adults, using adequate randomization methods, are needed to extend the present conclusions and assess the potential for musical activities to be used to mitigate SPiN decline in seniors.