Midbrain GABAergic Neurons Research Articles

P38 initiates degeneration of midbrain GABAergic and glutamatergic neurons in diabetes models.

Diabetes mellitus may cause tau protein hyperphosphorylation and neurodegeneration, but the exact mechanism by which diabetic conditions induce tau pathology remains unclear. Tau protein hyperphosphorylation is considered a major pathological hallmark of neurodegeneration and can be triggered by diabetes. Various tau-directed kinases, including P38, can be activated upon diabetic stress and induce tau hyperphosphorylation. Despite extensive research efforts, the exact tau specie(s) and kinases driving neurodegeneration in diabetes mellitus have not been clearly elucidated. We herein employed different techniques to determine the exact molecular mechanism of tau pathology triggered by diabetes in in vivo and in vitro models. We showed that diabetes-related stresses and glucose metabolism deficiency could induce cis P-tau (an early driver of the tau pathology) accumulation in the midbrain and corpus callosum of the diabetic mice models and cells treated with 2-deoxy-D-glucose, respectively. We found that the active phosphorylated level of P38 was increased in the treated cells and diabetic mice models. We observed that oxidative stress activated P38, which directly and indirectly drove tau pathology in the GABAergic and glutamatergic neurons of the midbrain of the diabetic mice after 96 h, which accumulated in the other neighboring brain areas after 2 months. Notably, P38 inhibition suppressed tau pathogenicity and risk-taking behaviors in the animal models after 96 h. The data establish P38 as a central mediator of diabetes mellitus-induced tau pathology. Our findings provide mechanistic insight into the consequences of this metabolic disorder on the nervous system.

Sequential Role of SOXB2 Factors in GABAergic Neuron Specification of the Dorsal Midbrain.

Studies proposed a model for embryonic neurogenesis where the expression levels of the SOXB2 and SOXB1 factors regulate the differentiation status of the neural stem cells. However, the precise role of the SOXB2 genes remains controversial. Therefore, this study aims to investigate the effects of individual deletions of the SOX21 and SOX14 genes during the development of the dorsal midbrain. We show that SOX21 and SOX14 function distinctly during the commitment of the GABAergic lineage. More explicitly, deletion of SOX21 reduced the expression of the GABAergic precursor marker GATA3 and BHLHB5 while the expression of GAD6, which marks GABAergic terminal differentiation, was not affected. In contrast deletion of SOX14 alone was sufficient to inhibit terminal differentiation of the dorsal midbrain GABAergic neurons. Furthermore, we demonstrate through gain-of-function experiments, that despite the homology of SOX21 and SOX14, they have unique gene targets and cannot compensate for the loss of each other. Taken together, these data do not support a pan-neurogenic function for SOXB2 genes in the dorsal midbrain, but instead they influence, sequentially, the specification of GABAergic neurons.

Inactivation of GATA cofactors Fog1 and Fog2 impairs the development of midbrain GABAergic neurons

Inactivation of GATA cofactors Fog1 and Fog2 impairs the development of midbrain GABAergic neurons

Menthol Alone Upregulates Midbrain nAChRs, Alters nAChR Subtype Stoichiometry, Alters Dopamine Neuron Firing Frequency, and Prevents Nicotine Reward.

Upregulation of β2 subunit-containing (β2*) nicotinic acetylcholine receptors (nAChRs) is implicated in several aspects of nicotine addiction, and menthol cigarette smokers tend to upregulate β2* nAChRs more than nonmenthol cigarette smokers. We investigated the effect of long-term menthol alone on midbrain neurons containing nAChRs. In midbrain dopaminergic (DA) neurons from mice containing fluorescent nAChR subunits, menthol alone increased the number of α4 and α6 nAChR subunits, but this upregulation did not occur in midbrain GABAergic neurons. Thus, chronic menthol produces a cell-type-selective upregulation of α4* nAChRs, complementing that of chronic nicotine alone, which upregulates α4 subunit-containing (α4*) nAChRs in GABAergic but not DA neurons. In mouse brain slices and cultured midbrain neurons, menthol reduced DA neuron firing frequency and altered DA neuron excitability following nAChR activation. Furthermore, menthol exposure before nicotine abolished nicotine reward-related behavior in mice. In neuroblastoma cells transfected with fluorescent nAChR subunits, exposure to 500 nm menthol alone also increased nAChR number and favored the formation of (α4)3(β2)2 nAChRs; this contrasts with the action of nicotine itself, which favors (α4)2(β2)3 nAChRs. Menthol alone also increases the number of α6β2 receptors that exclude the β3 subunit. Thus, menthol stabilizes lower-sensitivity α4* and α6 subunit-containing nAChRs, possibly by acting as a chemical chaperone. The abolition of nicotine reward-related behavior may be mediated through menthol's ability to stabilize lower-sensitivity nAChRs and alter DA neuron excitability. We conclude that menthol is more than a tobacco flavorant: administered alone chronically, it alters midbrain DA neurons of the nicotine reward-related pathway.

Hairy/Enhancer-of-Split MEGANE and Proneural MASH1 Factors Cooperate Synergistically in Midbrain GABAergic Neurogenesis.

GABAergic neurons are the primary inhibitory cell type in the mature brain and their dysfunction is associated with important neurological conditions like schizophrenia and anxiety. We aimed to discover the underlying mechanisms for dorsal/ventral midbrain GABAergic neurogenesis. Previous work by us and others has provided crucial insights into the key function of Mgn and Mash1 genes in determining GABAergic neurotransmitter fate. Induction of dorsal midbrain GABAergic neurons does not take place at any time during development in either of the single mutant mice. However, GABAergic neurons in the ventral midbrain remained unchanged. Thus, the similarities in MB-GABAergic phenotype observed in the Mgn and Mash1 single mutants suggest the existence of other factors that take over the function of MGN and MASH1 in the ventral midbrain or the existence of different molecular mechanisms. We show that this process essentially depends on heterodimers and homodimers formed by MGN and MASH1 and deciphered the in vivo relevance of the interaction by phenotypic analysis of Mgn/Mash1 double knockout and compound mice. Furthermore, the combination of gain- and loss-of-function experiments in the developing midbrain showed co-operative roles for Mgn and Mash1 genes in determining GABAergic identity. Transcription factors belonging to the Enhancer-of-split-related and proneural families have long been believed to counterpart each other’s function. This work uncovers a synergistic cooperation between these two families, and provides a novel paradigm for how these two families cooperate for the acquisition of MB-GABAergic neuronal identity. Understanding their molecular mechanisms is essential for cell therapy strategies to amend GABAergic deficits.

The role ofTal2andTal1in the differentiation of midbrain GABAergic neuron precursors

SummaryMidbrain- and hindbrain-derived GABAergic interneurons are critical for regulation of sleep, respiratory, sensory-motor and motivational processes, and they are implicated in human neurological disorders. However, the precise mechanisms that underlie generation of GABAergic neuron diversity in the midbrain–hindbrain region are poorly understood. Here, we show unique and overlapping requirements for the related bHLH proteins Tal1 and Tal2 in GABAergic neurogenesis in the midbrain. We show that Tal2 and Tal1 are specifically and sequentially activated during midbrain GABAergic neurogenesis. Similar to Gata2, a post-mitotic selector of the midbrain GABAergic neuron identity, Tal2 expression is activated very early during GABAergic neuron differentiation. Although the expression of Tal2 and Gata2 genes are independent of each other, Tal2 is important for normal midbrain GABAergic neurogenesis, possibly as a partner of Gata2. In the absence of Tal2, the majority of midbrain GABAergic neurons switch to a glutamatergic-like phenotype. In contrast, Tal1 expression is activated in a Gata2 and Tal2 dependent fashion in the more mature midbrain GABAergic neuron precursors, but Tal1 alone is not required for GABAergic neuron differentiation from the midbrain neuroepithelium. However, inactivation of both Tal2 and Tal1 in the developing midbrain suggests that the two factors co-operate to guide GABAergic neuron differentiation in a specific ventro-lateral midbrain domain. The observed similarities and differences between Tal1/Tal2 and Gata2 mutants suggest both co-operative and unique roles for these factors in determination of midbrain GABAergic neuron identities.

Distinct developmental origins and regulatory mechanisms for GABAergic neurons associated with dopaminergic nuclei in the ventral mesodiencephalic region

GABAergic neurons in the ventral mesodiencephalic region are highly important for the function of dopaminergic pathways that regulate multiple aspects of behavior. However, development of these neurons is poorly understood. We recently showed that molecular regulation of differentiation of the GABAergic neurons associated with the dopaminergic nuclei in the ventral midbrain (VTA and SNpr) is distinct from the rest of midbrain, but the reason for this difference remained elusive. Here, we have analyzed the developmental origin of the VTA and SNpr GABAergic neurons by genetic fate mapping. We demonstrate that the majority of these GABAergic neurons originate outside the midbrain, from rhombomere 1, and move into the ventral midbrain only as postmitotic neuronal precursors. We further show that Gata2, Gata3 and Tal1 define a subpopulation of GABAergic precursors in ventral rhombomere 1. A failure in GABAergic neuron differentiation in this region correlates with loss of VTA and SNpr GABAergic neurons in Tal1 mutant mice. In contrast to midbrain, GABAergic neurons of the anterior SNpr in the diencephalon are not derived from the rhombomere 1. These results suggest unique migratory pathways for the precursors of important GABAergic neuron subpopulations, and provide the basis for understanding diversity within midbrain GABAergic neurons.

Midbrain and forebrain patterning delivers immunocytochemically and functionally similar populations of neuropeptide Y containing GABAergic neurons

Neurons differentiated in vitro from embryonic stem cells (ESCs) have the potential to serve both as models of disease states and in drug discovery programs. In this study, we use sonic hedgehog (SHH) and fibroblast growth factor 8 (FGF-8) to enrich for forebrain and midbrain phenotypes from mouse ESCs. We then investigate, using Ca 2+ imaging and [ 3H]-GABA release studies, whether the GABAergic neurons produced exhibit distinct functional phenotypes. At day 24 of differentiation, reverse transcriptase-PCR showed the presence of both forebrain (Bf-1, Hesx1, Pgc-1α, Six3) and midbrain (GATA2, GATA3) selective mRNA markers in developing forebrain-enriched cultures. All markers were present in midbrain cultures except for Bf-1 and Pgc-1α. Irrespective of culture conditions all GABA immunoreactive neurons were also immunoreactive to neuropeptide Y (NPY) antibodies. Forebrain and midbrain GABAergic neurons responded to ATP (1 mM), l-glutamate (30 μM), noradrenaline (30 μM), acetylcholine (30 μM) and dopamine (30 μM), with similar elevations of intracellular Ca 2+([Ca 2+] i ). The presence of GABA A and GABA B antagonists, bicuculline (30 μM) and CGP55845 (1 μM), increased the elevation of [Ca 2+] i in response to dopamine (30 μM) in midbrain, but not forebrain GABAergic neurons. All agonists, except dopamine, elicited similar [ 3H]-GABA release from forebrain and midbrain cultures. Dopamine (30 μM) did not stimulate significant [ 3H]-GABA release in midbrain cultures, although it was effective in forebrain cultures. This study shows that differentiating neurons toward a midbrain fate restricts the expression of forebrain markers. Forebrain differentiation results in the expression of forebrain and midbrain markers. All GABA + neurons contain NPY, and show similar agonist-induced elevations of [Ca 2+] i and [ 3H]-GABA release. This study indicates that the pharmacological phenotype of these particular neurons may be independent of the addition of the patterning factors that direct neurons toward forebrain and midbrain fates.

Distinct requirements for Ascl1 in subpopulations of midbrain GABAergic neurons

Distinct requirements for Ascl1 in subpopulations of midbrain GABAergic neurons

Distinct requirements for Ascl1 in subpopulations of midbrain GABAergic neurons

Midbrain GABAergic neurons regulate multiple aspects of behavior and play important roles in psychiatric and neurological disease. These neurons constitute several anatomical and functional subpopulations, but their molecular heterogeneity and developmental regulatory mechanisms are poorly understood.Here we have studied the involvement of the proneural gene Ascl1 in the development of the midbrain GABAergic neurons. Analysis of Ascl1 mutant mice demonstrated highly region-specific requirements for Ascl1 for development of different GABAergic neuron subpopulations. Ascl1 is dispensable for the development of the ventral-most midbrain GABAergic neurons associated with dopaminergic nuclei substantia nigra pars reticulata (SNpr) and ventral tegmental area (VTA) GABAergic neurons. In the ventrolateral midbrain, loss of Ascl1 results in markedly delayed neurogenesis in the midbrain domains m3–m5. Within this region, Ascl1 has a unique role in m4, where it also regulates glutamatergic neurogenesis. Our results suggest that the m3–m5 midbrain neuroepithelium gives rise to the GABAergic neuron groups located in the midbrain reticular formation and ventrolateral periaqueductal gray. In contrast to m3–m5, Ascl1 is absolutely required in the dorsal midbrain domains m1–m2, for generation of the GABAergic neurons populating the superior and inferior colliculi as well as dorsal periaqueductal gray.These studies demonstrate different molecular regulatory mechanisms for the distinct midbrain GABAergic neuron subpopulations. Also, our results have implications on understanding the origins of the various midbrain GABAergic neuron groups in the embryonic neuroepithelium.

Gata2is a tissue-specific post-mitotic selector gene for midbrain GABAergic neurons

Midbrain GABAergic neurons control several aspects of behavior, but regulation of their development and diversity is poorly understood. Here, we further refine the midbrain regions active in GABAergic neurogenesis and show their correlation with the expression of the transcription factor Gata2. Using tissue-specific inactivation and ectopic expression, we show that Gata2 regulates GABAergic neuron development in the mouse midbrain, but not in rhombomere 1, where it is needed in the serotonergic lineage. Without Gata2, all the precursors in the embryonic midbrain fail to activate GABAergic neuron-specific gene expression and instead switch to a glutamatergic phenotype. Surprisingly, this fate switch is also observed throughout the neonatal midbrain, except for the GABAergic neurons located in the ventral dopaminergic nuclei, suggesting a distinct developmental pathway for these neurons. These studies identify Gata2 as an essential post-mitotic selector gene of the GABAergic neurotransmitter identity and demonstrate developmental heterogeneity of GABAergic neurons in the midbrain.