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Scientific Reports Jun 2024Nicotinic acetylcholine receptors (nAChRs) in the medial habenula (MHb)-interpeduncular nucleus (IPN) pathway play critical roles in nicotine-related behaviors. This...
Nicotinic acetylcholine receptors (nAChRs) in the medial habenula (MHb)-interpeduncular nucleus (IPN) pathway play critical roles in nicotine-related behaviors. This pathway is particularly enriched in nAChR α3 and β4 subunits, both of which are genetically linked to nicotine dependence. However, the cellular and subcellular expression of endogenous α3β4-containing nAChRs remains largely unknown because specific antibodies and appropriate detection methods were unavailable. Here, we successfully uncovered the expression of endogenous nAChRs containing α3 and β4 subunits in the MHb-IPN pathway using novel specific antibodies and a fixative glyoxal that enables simultaneous detection of synaptic and extrasynaptic molecules. Immunofluorescence and immunoelectron microscopy revealed that both subunits were predominantly localized to the extrasynaptic cell surface of somatodendritic and axonal compartments of MHb neurons but not at their synaptic junctions. Immunolabeling for α3 and β4 subunits disappeared in α5β4-knockout brains, which we used as negative controls. The enriched and diffuse extrasynaptic expression along the MHb-IPN pathway suggests that α3β4-containing nAChRs may enhance the excitability of MHb neurons and neurotransmitter release from their presynaptic terminals in the IPN. The revealed distribution pattern provides a molecular and anatomical basis for understanding the functional role of α3β4-containing nAChRs in the crucial pathway of nicotine dependence.
Topics: Animals; Receptors, Nicotinic; Habenula; Interpeduncular Nucleus; Mice; Mice, Knockout; Neurons; Synapses; Mice, Inbred C57BL; Male
PubMed: 38902419
DOI: 10.1038/s41598-024-65076-3 -
Cells Jun 2024Presynaptic Ca influx through voltage-gated Ca channels (VGCCs) is a key signal for synaptic vesicle release. Synaptic neurexins can partially determine the strength of...
Presynaptic Ca influx through voltage-gated Ca channels (VGCCs) is a key signal for synaptic vesicle release. Synaptic neurexins can partially determine the strength of transmission by regulating VGCCs. However, it is unknown whether neurexins modulate Ca influx via all VGCC subtypes similarly. Here, we performed live cell imaging of synaptic boutons from primary hippocampal neurons with a Ca indicator. We used the expression of inactive and active Cre recombinase to compare control to conditional knockout neurons lacking either all or selected neurexin variants. We found that reduced total presynaptic Ca transients caused by the deletion of all neurexins were primarily due to the reduced contribution of P/Q-type VGCCs. The deletion of neurexin1α alone also reduced the total presynaptic Ca influx but increased Ca influx via N-type VGCCs. Moreover, we tested whether the decrease in Ca influx induced by activation of cannabinoid receptor 1 (CB1-receptor) is modulated by neurexins. Unlike earlier observations emphasizing a role for β-neurexins, we found that the decrease in presynaptic Ca transients induced by CB1-receptor activation depended more strongly on the presence of α-neurexins in hippocampal neurons. Together, our results suggest that neurexins have unique roles in the modulation of presynaptic Ca influx through VGCC subtypes and that different neurexin variants may affect specific VGCCs.
Topics: Animals; Calcium; Presynaptic Terminals; Hippocampus; Mice; Mice, Knockout; Calcium Channels; Neurons; Receptor, Cannabinoid, CB1; Calcium Signaling; Gene Knockout Techniques; Neurexins
PubMed: 38891114
DOI: 10.3390/cells13110981 -
ENeuro Jun 2024Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III...
Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III isoform is usually downregulated after development, but in hippocampal mossy fiber boutons it persists in adulthood. Mossy fiber boutons express presynaptic forms of short- and long-term plasticity, which are thought to underlie different forms of learning. Previous research on synapsins at this synapse focused on synapsin isoforms I and II. Thus, a complete picture regarding the role of synapsins in mossy fiber plasticity is still missing. Here, we investigated presynaptic plasticity at hippocampal mossy fiber boutons by combining electrophysiological field recordings and transmission electron microscopy in a mouse model lacking all synapsin isoforms. We found decreased short-term plasticity - i.e. decreased facilitation and post-tetanic potentiation - but increased long-term potentiation in male synapsin triple knockout mice. At the ultrastructural level, we observed more dispersed vesicles and a higher density of active zones in mossy fiber boutons from knockout animals. Our results indicate that all synapsin isoforms are required for fine regulation of short- and long-term presynaptic plasticity at the mossy fiber synapse. Synapsins cluster vesicles at presynaptic terminals and shape presynaptic plasticity at giant hippocampal mossy fiber boutons. Deletion of all synapsin isoforms results in decreased short- but increased long-term plasticity.
PubMed: 38866497
DOI: 10.1523/ENEURO.0330-23.2024 -
Learning & Memory (Cold Spring Harbor,... May 2024The intricate molecular and structural sequences guiding the formation and consolidation of memories within neuronal circuits remain largely elusive. In this study, we...
The intricate molecular and structural sequences guiding the formation and consolidation of memories within neuronal circuits remain largely elusive. In this study, we investigate the roles of two pivotal presynaptic regulators, the small GTPase Rab3, enriched at synaptic vesicles, and the cell adhesion protein Neurexin-1, in the formation of distinct memory phases within the mushroom body Kenyon cells. Our findings suggest that both proteins play crucial roles in memory-supporting processes within the presynaptic terminal, operating within distinct plasticity modules. These modules likely encompass remodeling and maturation of existing active zones (AZs), as well as the formation of new AZs.
Topics: Animals; Mushroom Bodies; Presynaptic Terminals; Drosophila Proteins; Memory; rab3 GTP-Binding Proteins; Nerve Tissue Proteins; Drosophila; Synaptic Vesicles
PubMed: 38862173
DOI: 10.1101/lm.054013.124 -
Acta Neuropathologica Jun 2024Widespread cortical accumulation of misfolded pathological tau proteins (ptau) in the form of paired helical filaments is a major hallmark of Alzheimer's disease....
Widespread cortical accumulation of misfolded pathological tau proteins (ptau) in the form of paired helical filaments is a major hallmark of Alzheimer's disease. Subcellular localization of ptau at various stages of disease progression is likely to be informative of the cellular mechanisms involving its spread. Here, we found that the density of ptau within several distinct rostral thalamic nuclei in post-mortem human tissue (n = 25 cases) increased with the disease stage, with the anterodorsal nucleus (ADn) consistently being the most affected. In the ADn, ptau-positive elements were present already in the pre-cortical (Braak 0) stage. Tau pathology preferentially affected the calretinin-expressing subpopulation of glutamatergic neurons in the ADn. At the subcellular level, we detected ptau immunoreactivity in ADn cell bodies, dendrites, and in a specialized type of presynaptic terminal that expresses vesicular glutamate transporter 2 (vGLUT2) and likely originates from the mammillary body. The ptau-containing terminals displayed signs of degeneration, including endosomal/lysosomal organelles. In contrast, corticothalamic axon terminals lacked ptau. The data demonstrate the involvement of a specific cell population in ADn at the onset of the disease. The presence of ptau in subcortical glutamatergic presynaptic terminals supports hypotheses about the transsynaptic spread of tau selectively affecting specialized axonal pathways.
Topics: Humans; tau Proteins; Female; Male; Aged; Aged, 80 and over; Alzheimer Disease; Middle Aged; Neurons; Vesicular Glutamate Transport Protein 2; Glutamic Acid; Anterior Thalamic Nuclei; Calbindin 2; Neurofibrillary Tangles; Presynaptic Terminals
PubMed: 38861157
DOI: 10.1007/s00401-024-02749-3 -
Philosophical Transactions of the Royal... Jul 2024Nitric oxide (NO) is a key diffusible messenger in the mammalian brain. It has been proposed that NO may diffuse retrogradely into presynaptic terminals, contributing to...
Nitric oxide (NO) is a key diffusible messenger in the mammalian brain. It has been proposed that NO may diffuse retrogradely into presynaptic terminals, contributing to the induction of hippocampal long-term potentiation (LTP). Here, we present novel evidence that NO is required for kainate receptor (KAR)-dependent presynaptic form of LTP (pre-LTP) in the adult insular cortex (IC). In the IC, we found that inhibition of NO synthase erased the maintenance of pre-LTP, while the induction of pre-LTP required the activation of KAR. Furthermore, NO is essential for pre-LTP induced between two pyramidal cells in the IC using the double patch-clamp recording. These results suggest that NO is required for homosynaptic pre-LTP in the IC. Our results present strong evidence for the critical roles of NO in pre-LTP in the IC. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.
Topics: Long-Term Potentiation; Nitric Oxide; Animals; Cerebral Cortex; Presynaptic Terminals; Receptors, Kainic Acid; Patch-Clamp Techniques; Rats; Pyramidal Cells; Nitric Oxide Synthase; Mice
PubMed: 38853563
DOI: 10.1098/rstb.2023.0475 -
Nature Communications Jun 2024Brain evolution has primarily been studied at the macroscopic level by comparing the relative size of homologous brain centers between species. How neuronal circuits...
Brain evolution has primarily been studied at the macroscopic level by comparing the relative size of homologous brain centers between species. How neuronal circuits change at the cellular level over evolutionary time remains largely unanswered. Here, using a phylogenetically informed framework, we compare the olfactory circuits of three closely related Drosophila species that differ in their chemical ecology: the generalists Drosophila melanogaster and Drosophila simulans and Drosophila sechellia that specializes on ripe noni fruit. We examine a central part of the olfactory circuit that, to our knowledge, has not been investigated in these species-the connections between projection neurons and the Kenyon cells of the mushroom body-and identify species-specific connectivity patterns. We found that neurons encoding food odors connect more frequently with Kenyon cells, giving rise to species-specific biases in connectivity. These species-specific connectivity differences reflect two distinct neuronal phenotypes: in the number of projection neurons or in the number of presynaptic boutons formed by individual projection neurons. Finally, behavioral analyses suggest that such increased connectivity enhances learning performance in an associative task. Our study shows how fine-grained aspects of connectivity architecture in an associative brain center can change during evolution to reflect the chemical ecology of a species.
Topics: Animals; Mushroom Bodies; Drosophila; Biological Evolution; Species Specificity; Neurons; Drosophila melanogaster; Phylogeny; Smell; Odorants; Olfactory Pathways; Male; Female; Presynaptic Terminals
PubMed: 38849331
DOI: 10.1038/s41467-024-48839-4 -
IScience Jun 2024N- and P/Q-type voltage-gated Ca channels are critical for synaptic transmission. While their expression is increased in the dorsal root ganglion (DRG) neuron cell...
N- and P/Q-type voltage-gated Ca channels are critical for synaptic transmission. While their expression is increased in the dorsal root ganglion (DRG) neuron cell bodies during neuropathic pain conditions, less is known about their synaptic remodeling. Here, we combined genetic tools with 2-photon Ca imaging to explore the functional remodeling that occurs in central presynaptic terminals of DRG neurons during neuropathic pain. We imaged GCaMP6s fluorescence responses in an spinal cord preparation from mice expressing GCaMP6s in Trpv1-Cre lineage nociceptors. We show that Ca transient amplitude is increased in central terminals of these neurons after spared nerve injury, and that this increase is mediated by both N- and P/Q-type channels. We found that GABA-B receptor-dependent inhibition of Ca transients was potentiated in the superficial layer of the dorsal horn. Our results provide direct evidence toward nerve injury-induced functional remodeling of presynaptic Ca channels in Trpv1-lineage nociceptor terminals.
PubMed: 38827405
DOI: 10.1016/j.isci.2024.109973 -
Neural Regeneration Research Feb 2025During the development of the nervous system, there is an overproduction of neurons and synapses. Hebbian competition between neighboring nerve endings and synapses...
During the development of the nervous system, there is an overproduction of neurons and synapses. Hebbian competition between neighboring nerve endings and synapses performing different activity levels leads to their elimination or strengthening. We have extensively studied the involvement of the brain-derived neurotrophic factor-Tropomyosin-related kinase B receptor neurotrophic retrograde pathway, at the neuromuscular junction, in the axonal development and synapse elimination process versus the synapse consolidation. The purpose of this review is to describe the neurotrophic influence on developmental synapse elimination, in relation to other molecular pathways that we and others have found to regulate this process. In particular, we summarize our published results based on transmitter release analysis and axonal counts to show the different involvement of the presynaptic acetylcholine muscarinic autoreceptors, coupled to downstream serine-threonine protein kinases A and C (PKA and PKC) and voltage-gated calcium channels, at different nerve endings in developmental competition. The dynamic changes that occur simultaneously in several nerve terminals and synapses converge across a postsynaptic site, influence each other, and require careful studies to individualize the mechanisms of specific endings. We describe an activity-dependent balance (related to the extent of transmitter release) between the presynaptic muscarinic subtypes and the neurotrophin-mediated TrkB/p75NTR pathways that can influence the timing and fate of the competitive interactions between the different axon terminals. The downstream displacement of the PKA/PKC activity ratio to lower values, both in competing nerve terminals and at postsynaptic sites, plays a relevant role in controlling the elimination of supernumerary synapses. Finally, calcium entry through L- and P/Q- subtypes of voltage-gated calcium channels (both channels are present, together with the N-type channel in developing nerve terminals) contributes to reduce transmitter release and promote withdrawal of the most unfavorable nerve terminals during elimination (the weakest in acetylcholine release and those that have already become silent). The main findings contribute to a better understanding of punishment-rewarding interactions between nerve endings during development. Identifying the molecular targets and signaling pathways that allow synapse consolidation or withdrawal of synapses in different situations is important for potential therapies in neurodegenerative diseases.
PubMed: 38819042
DOI: 10.4103/1673-5374.391314 -
Frontiers in Molecular Neuroscience 2024Dm9 neurons in have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit...
Dm9 neurons in have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit function, two-photon calcium imaging in Dm9 and inner photoreceptors, and immunohistochemical analysis to reveal novel insights into the functional role of Dm9 in early visual processing. Our experiments show that Dm9 receive input from all four types of inner photoreceptor R7p, R7y, R8p, and R8y. Histamine released from all types R7/R8 directly inhibits Dm9 via the histamine receptor Ort, and outweighs simultaneous histamine-independent excitation of Dm9 by UV-sensitive R7. Dm9 in turn provides inhibitory feedback to all R7/R8, which is sufficient for color-opponent processing in R7 but not R8. Color opponent processing in R8 requires additional synaptic inhibition by R7 of the same ommatidium via axo-axonal synapses and the second histamine receptor HisCl1. Notably, optogenetic inhibition of Dm9 prohibits color opponent processing in all types of R7/R8 and decreases intracellular calcium in photoreceptor terminals. The latter likely results from reduced release of excitatory glutamate from Dm9 and shifts overall photoreceptor sensitivity toward higher light intensities. In summary, our results underscore a key role of Dm9 in color opponent processing in and suggest a second role of Dm9 in regulating light adaptation in inner photoreceptors. These novel findings on Dm9 are indeed reminiscent of the versatile functions of horizontal cells in the vertebrate retina.
PubMed: 38813436
DOI: 10.3389/fnmol.2024.1347540