Deletion of muscarinic acetylcholine receptor 3 in microglia impacts brain ischemic injury.

Microglia are the immune cells of the brain and become activated during any type of brain injury. In the middle cerebral artery occlusion (MCAo) model, a mouse model for ischemic stroke, we have previously shown that microglia and invaded monocytes upregulate the expression of the muscarinic acetylcholine receptor 3 (M3R) in the ischemic lesion. Here we tested whether this upregulation has an impact on the pathogenesis of MCAo. We depleted the m3R receptor in microglia, but not in circulating monocytes by giving tamoxifen to CX3CR1-CreERT+/+M3Rflox/flox (M3RKOmi) animals 3 weeks prior to MCAo. We found that M3RKOmi male mice had bigger lesions, more pronounced motor deficits after one week and cognitive deficits after about one month compared to control males. The density of Iba1+ cells was lower in the lesions of M3RKO male mice in the early, but not in the late disease phase. In females, these differences were not significant. By giving tamoxifen 1 week prior to MCAo, we depleted m3R in microglia and in circulating monocytes (M3RKOmi/mo). Male M3RKOmi/mo did not differ in lesion size, but had a lower survival rate, showed motor deficits and a reduced accumulation of Iba1+ positive cells into the lesion site. In conclusion, our data suggest that the upregulation of m3R in microglia and monocytes in stroke has a beneficial effect on the clinical outcome in male mice.

Neurotensin-specific corticothalamic circuit regulates innate response conflict.

Animals must simultaneously select and balance multiple action contingencies in ambiguous situations: for instance, evading danger during feeding. This has rarely been examined in the context of information selection; despite corticothalamic pathways that mediate sensory attention being relatively well characterized, neural mechanisms filtering conflicting actions remain unclear. Here, we develop a new loom/feed test to observe conflict between naturally induced fear and feeding and identify a novel anterior cingulate cortex (ACC) output to the ventral anterior and ventral lateral thalamus (VA/VL) that adjusts selectivity between these innate actions. Using micro-endoscopy and fiber photometry, we reveal that activity in corticofugal outputs was lowered during unbalanced/singularly occupied periods, as were the resulting decreased thalamic initiation-related signals for less-favored actions, suggesting that the integration of ACC-thalamic firing may directly regulate the output of behavior choices. Accordingly, the optoinhibition of ACC-VA/VL circuits induced high bias toward feeding at the expense of defense. To identify upstream "commander" cortical cells gating this output, we established dual-order tracing (DOT)-translating ribosome affinity purification (TRAP)-a scheme to label upstream neurons with transcriptome analysis-and found a novel population of neurotensin-positive interneurons (ACCNts). The photoexcitation of ACCNts cells indeed caused similarly hyper-selective behaviors. Collectively, this new "corticofugal action filter" scheme suggests that communication in multi-step cingulate circuits may critically influence the summation of motor signals in thalamic outputs, regulating bias between innate action types.

Central Role of Hypothalamic Circuits for Acupuncture's Anti-Parkinsonian Effects.

Despite clinical data stretching over millennia, the neurobiological basis of the effectiveness of acupuncture in treating diseases of the central nervous system has remained elusive. Here, using an established model of acupuncture treatment in Parkinson's disease (PD) model mice, we show that peripheral acupuncture stimulation activates hypothalamic melanin-concentrating hormone (MCH) neurons via nerve conduction. We further identify two separate neural pathways originating from anatomically and electrophysiologically distinct MCH neuronal subpopulations, projecting to the substantia nigra and hippocampus, respectively. Through chemogenetic manipulation specifically targeting these MCH projections, their respective roles in mediating the acupuncture-induced motor recovery and memory improvements following PD onset are demonstrated, as well as the underlying mechanisms mediating recovery from dopaminergic neurodegeneration, reactive gliosis, and impaired hippocampal synaptic plasticity. Collectively, these MCH neurons constitute not only a circuit-based explanation for the therapeutic effectiveness of traditional acupuncture, but also a potential cellular target for treating both motor and non-motor PD symptoms.

Adenovirus-induced Reactive Astrogliosis Exacerbates the Pathology of Parkinson's Disease.

Parkinson's disease (PD) is the most prevalent neurodegenerative motor disorder. While PD has been attributed to dopaminergic neuronal death in substantia nigra pars compacta (SNpc), accumulating lines of evidence have suggested that reactive astrogliosis is critically involved in PD pathology. These pathological changes are associated with α-synuclein aggregation, which is more prone to be induced by an A53T mutation. Therefore, the overexpression of A53T-mutated α-synuclein (A53T-α-syn) has been utilized as a popular animal model of PD. However, this animal model only shows marginal-to-moderate extents of reactive astrogliosis and astrocytic α-synuclein accumulation, while these phenomena are prominent in human PD brains. Here we show that Adeno-GFAP-GFP virus injection into SNpc causes severe reactive astrogliosis and exacerbates the A53T-α-syn-mediated PD pathology. In particular, we demonstrate that AAV-CMV-A53T-α-syn injection, when combined with Adeno-GFAP-GFP, causes more significant loss of dopaminergic neuronal tyrosine hydroxylase level and gain of astrocytic GFAP and GABA levels. Moreover, the combination of AAV-CMV-A53T-α-syn and Adeno-GFAP-GFP causes an extensive astrocytic α-syn expression, just as in human PD brains. These results are in marked contrast to previous reports that AAV-CMV-A53T-α-syn alone causes α-syn expression mostly in neurons but rarely in astrocytes. Furthermore, the combination causes a severe PD-like motor dysfunction as assessed by rotarod and cylinder tests within three weeks from the virus injection, whereas Adeno-GFAP-GFP alone or AAV-CMV-A53T-α-syn alone does not. Our findings implicate that inducing reactive astrogliosis exacerbates PD-like pathologies and propose the virus combination as an advanced strategy for developing a new animal model of PD.

Redefining differential roles of MAO-A in dopamine degradation and MAO-B in tonic GABA synthesis.

Monoamine oxidase (MAO) is believed to mediate the degradation of monoamine neurotransmitters, including dopamine, in the brain. Between the two types of MAO, MAO-B has been believed to be involved in dopamine degradation, which supports the idea that the therapeutic efficacy of MAO-B inhibitors in Parkinson's disease can be attributed to an increase in extracellular dopamine concentration. However, this belief has been controversial. Here, by utilizing in vivo phasic and basal electrochemical monitoring of extracellular dopamine with fast-scan cyclic voltammetry and multiple-cyclic square wave voltammetry and ex vivo fluorescence imaging of dopamine with GRABDA2m, we demonstrate that MAO-A, but not MAO-B, mainly contributes to striatal dopamine degradation. In contrast, our whole-cell patch-clamp results demonstrated that MAO-B, but not MAO-A, was responsible for astrocytic GABA-mediated tonic inhibitory currents in the rat striatum. We conclude that, in contrast to the traditional belief, MAO-A and MAO-B have profoundly different roles: MAO-A regulates dopamine levels, whereas MAO-B controls tonic GABA levels.

Bimodal neural probe for highly co-localized chemical and electrical monitoring of neural activities in vivo.

Investigation of the chemical and electrical signals of cells in vivo is critical for studying functional connectivity and brain diseases. Most previous studies have observed either the electrical signals or the chemical signals of cells because recording electrical signals and neurochemicals are done by fundamentally different methods. Herein, we present a bimodal MEMS neural probe that is monolithically integrated with an array of microelectrodes for recording electrical activity, microfluidic channels for sampling extracellular fluid, and a microfluidic interface chip for multiple drug delivery and sample isolation from the localized region at the cellular level. In this work, we successfully demonstrated the functionality of our probe by monitoring and modulating bimodal (electrical and chemical) neural activities through the delivery of chemicals in a co-localized brain region in vivo. We expect our bimodal probe to provide opportunities for a variety of in-depth studies of brain functions as well as for the investigation of neural circuits related to brain diseases.