Electrophysiological and anatomical characterization of synaptic remodeling in the mouse whisker thalamus.
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ABSTRACT:
SUBMITTER: Ueta Y
PROVIDER: S-EPMC8369072 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The thalamic reticular nucleus (TRN) neurons, projecting across the external medullary lamina, have long been considered to be the only significant source of inhibition of the somatosensory ventral posterior (VP) nuclei of the thalamus. Here we report for the first time effective local inhibition and disinhibition in the VP. Inhibitory interneurons were found in GAD67-GFP-expressing mice and studied using in vitro multiple patch clamp. Inhibitory interneurons have expansive bipolar or tripolar morphologies, reach across most of the VP nucleus and display low threshold bursting behaviour. They form triadic and non-triadic synaptic connections onto thalamocortical relay neurons and other interneurons, mediating feedforward inhibition and disinhibition. Synaptic inputs arrive before those expected from the TRN neurons, suggesting that local inhibition plays an early and significant role in the functioning of the somatosensory thalamus. KEY POINTS: The physiology and structure of local interneurons in the mouse somatosensory thalamus is described for the first time. Inhibitory interneurons have extensive dendritic arborization providing significant local dendro-dendritic inhibition in the somatosensory thalamus. Triadic and non-triadic synaptic connectivity onto thalamic relay neurons and other interneurons provides both local feedforward inhibition and disinhibition. Interneurons of the somatosensory thalamus provide inhibition before the thalamic reticular nucleus, suggesting they play an important role in sensory perception.
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Project description:Stimulus specific adaptation has been studied extensively in different modalities. High specificity implies that deviant stimulus induces a stronger response compared to a common stimulus. The thalamus gates sensory information to the cortex, therefore, the specificity of adaptation in the thalamus must have a great impact on cortical processing of sensory inputs. We studied the specificity of adaptation to whisker identity in the ventral posteromedial nucleus of the thalamus (VPM) in rats using extracellular and intracellular recordings. We found that subsequent to repetitive stimulation that induced strong adaptation, the response to stimulation of the same, or any other responsive whisker was equally adapted, indicating that thalamic adaptation is non-specific. In contrast, adaptation of single units in the upstream brainstem principal trigeminal nucleus (PrV) was significantly more specific. Depolarization of intracellularly recorded VPM cells demonstrated that adaptation is not due to buildup of inhibition. In addition, adaptation increased the probability of observing complete synaptic failures to tactile stimulation. In accordance with short-term synaptic depression models, the evoked synaptic potentials in response to whisker stimulation, subsequent to a response failure, were facilitated. In summary, we show that local short-term synaptic plasticity is involved in the transformation of adaptation in the trigemino-thalamic synapse and that the low specificity of adaptation in the VPM emerges locally rather than cascades from earlier stages. Taken together we suggest that during sustained stimulation, local thalamic mechanisms equally suppress inputs arriving from different whiskers before being gated to the cortex.
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Project description:Conventional anti-Parkinsonian dopamine replacement therapy is often complicated by side effects that limit the use of these medications. There is a continuing need to develop nondopaminergic approaches to treat Parkinsonism. One such approach is to use medications that normalize dopamine depletion-related firing abnormalities in the basal ganglia-thalamocortical circuitry. In this study, we assessed the potential of a specific T-type calcium channel blocker (ML218) to eliminate pathologic burst patterns of firing in the basal ganglia-receiving territory of the motor thalamus in Parkinsonian monkeys. We also carried out an anatomical study, demonstrating that the immunoreactivity for T-type calcium channels is strongly expressed in the motor thalamus in normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. At the electron microscopic level, dendrites accounted for >90% of all tissue elements that were immunoreactive for voltage-gated calcium channel, type 3.2-containing T-type calcium channels in normal and Parkinsonian monkeys. Subsequent in vivo electrophysiologic studies in awake MPTP-treated Parkinsonian monkeys demonstrated that intrathalamic microinjections of ML218 (0.5 μl of a 2.5-mM solution, injected at 0.1-0.2 μl/min) partially normalized the thalamic activity by reducing the proportion of rebound bursts and increasing the proportion of spikes in non-rebound bursts. The drug also attenuated oscillatory activity in the 3-13-Hz frequency range and increased gamma frequency oscillations. However, ML218 did not normalize Parkinsonism-related changes in firing rates and oscillatory activity in the beta frequency range. Whereas the described changes are promising, a more complete assessment of the cellular and behavioral effects of ML218 (or similar drugs) is needed for a full appraisal of their anti-Parkinsonian potential.
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Project description:Whisker deprivation weakens excitatory layer 4 (L4) inputs to L2/3 pyramidal cells in rat primary somatosensory (S1) cortex, which is likely to contribute to whisker map plasticity. This weakening has been proposed to represent long-term depression (LTD) induced by sensory deprivation in vivo. Here, we studied the synaptic expression mechanisms for deprivation-induced weakening of L4-L2/3 inputs and assessed its similarity to LTD, which is known to be expressed presynaptically at L4-L2/3 synapses. Whisker deprivation increased the paired pulse ratio at L4-L2/3 synapses and slowed the use-dependent block of NMDA receptor currents by MK-801 [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate], indicating that deprivation reduced transmitter release probability at these synapses. In contrast, deprivation did not alter either miniature EPSC amplitude in L2/3 neurons or the amplitude of quantal L4-L2/3 synaptic responses measured in strontium, indicating that postsynaptic responsiveness was unchanged. In young postnatal day 12 (P12) rats, at least 4 d of deprivation were required to significantly weaken L4-L2/3 synapses. Similar weakening occurred when deprivation began at older ages (P20), when synapses are mostly mature, indicating that weakening is unlikely to represent a failure of synaptic maturation but instead represents a reduction in the strength of existing synapses. Thus, whisker deprivation weakens L4-L2/3 synapses by decreasing presynaptic function, similar to known LTD mechanisms at this synapse.
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Project description:Alterations of synaptic function in individuals with schizophrenia have been found in transcriptomics, proteomics, and genome wide association studies. Impaired synaptic glutamatergic (excitatory) and GABAergic (inhibitory) neurotransmission in affected brain regions (e.g. dorsolateral prefrontal cortex; DLPFC) is thought to be involved in the core symptoms of schizophrenia. However, there are no quantitative measurements of synaptic function in the human DLPFC, therefore concrete and specific functional alterations of voltage gated ion channels of glutamate and GABA receptors are lacking. We have begun to address this problem by directly measuring AMPA- and GABA receptor-mediated synaptic currents in postmortem brains from subjects with schizophrenia and contrasting to controls. We demonstrate in our preliminary work that the function of synaptic receptors is maintained in postmortem brains and is significantly decreased in schizophrenia compared to controls. Our overarching hypothesis is that reductions in both inhibitory and excitatory currents underlie synaptic deficits in schizophrenia. We will test rigor and reproducibility of this hypothesis in independent case-control cohorts. These deficits in synaptic currents can be statistically modeled with transcriptomic data which will be useful in downstream studies that pharmacologically challenge activation of these currents.
2023-03-20 | GSE224683 | GEO
Project description:Purpose: We aimed to resolve if there is a matched expression of neuropeptide receptor(s) and their ligand(s) between the sensory trunk of the trigeminal nerve (Pr5) and the ventrobasal hypothalamus on postnatal day 7 (P7) in mice. We hypothesized that a coincidence of neuropeptide expression and release from the ventrobasal thalamus and the cognate receptor(s) for the specific neuropeptide(s) in trigeminal neurons could allow for novel hypotheses be built on intercellular communication between peripheral axons and their postsynaptic targets in the thalamus. Thereby, this work can be informative of the developmental integration of the whisker pathway, one of the major sensory modalities in laboratory rodents. To this end, we used single-cell RNA-seq on cells dissociated from the ventrobasal thalamus and Pr5 on P7. Results: We tested this hypothesis by single-nucleus RNA-seq performed in parallel on the ventrobasal thalamus and Pr5 at P7. At this developmental stage, the ventrobasal thalamus contained two subtypes of Slc17a6+(glutamatergic) neurons, one subtype of Gad1/Gad2+ (GABA) neurons, astroglia, oligodendrocytes, and vascular components (n = 923 nuclei isolated from n = 3 pups of mixed sex). Slc17a6+ neurons, which we recognize as cortically projecting glutamate neurons, co-expressed molecular components underpinning barrel map formation (e.g., Grin1, Adcy1, Prkaca,99 Ache, Slc6a4) and a significant amount of the thalamocortical neuronal marker Cck, while other neuropeptides/hormones were absent or barely present (e.g., Npy, Sst). At the same time, we harvested n = 731 nuclei from the Pr5 by micro-excision at P7, of which ∼98% expressed Slc17a6, thus qualifying, in total or in part, as centrally-projecting sensory neurons. This neuronal cohort harbored axon guidance molecules, and neuropeptide receptors. Conclusions: We suggest that neuropeptides, particularly galanin, could participate in guidance decisions of Pr5 axons given the complementarity of ligand-receptor expression patterns, and that Galr1 expression could be a time locked feature for those neurons that actively undergo neuritogenesis at a given time.
2024-04-01 | GSE230180 | GEO
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