RÉSUMÉ
High-threshold dorsal root ganglion (HT DRG) neurons fire at low frequencies during inflammatory injury, and low-frequency stimulation (LFS) of HT DRG neurons selectively potentiates excitatory synapses onto spinal neurons projecting to the periaqueductal gray (spino-PAG). Here, in male and female mice, we have identified an underlying peripheral sensory population driving this plasticity and its effects on the output of spino-PAG neurons. We provide the first evidence that Trpv1-lineage sensory neurons predominantly induce burst firing, a unique mode of neuronal activity, in lamina I spino-PAG projection neurons. We modeled inflammatory injury by optogenetically stimulating Trpv1+ primary afferents at 2â Hz for 2â min (LFS), as peripheral inflammation induces 1-2â Hz firing in high-threshold C fibers. LFS of Trpv1+ afferents enhanced the synaptically evoked and intrinsic excitability of spino-PAG projection neurons, eliciting a stable increase in the number of action potentials (APs) within a Trpv1+ fiber-induced burst, while decreasing the intrinsic AP threshold and increasing the membrane resistance. Further experiments revealed that this plasticity required Trpv1+ afferent input, postsynaptic G protein-coupled signaling, and NMDA receptor activation. Intriguingly, an inflammatory injury and heat exposure in vivo also increased APs per burst, in vitro These results suggest that inflammatory injury-mediated plasticity is driven though Trpv1+ DRG neurons and amplifies the spino-PAG pathway. Spinal inputs to the PAG could play an integral role in its modulation of heat sensation during peripheral inflammation, warranting further exploration of the organization and function of these neural pathways.
Sujet(s)
Interneurones , Substance grise centrale du mésencéphale , Rats , Animaux , Souris , Femelle , Mâle , Rat Sprague-Dawley , Cellules réceptrices sensorielles , Inflammation , Canaux cationiques TRPV/génétiqueRÉSUMÉ
BACKGROUND: Neuropeptides are contained in nearly every neuron in the central nervous system and can be released not only from nerve terminals but also from somatodendritic sites. Cholecystokinin (CCK), among the most abundant neuropeptides in the brain, is expressed in the majority of midbrain dopamine neurons. Despite this high expression, CCK function within the ventral tegmental area (VTA) is not well understood. METHODS: We confirmed CCK expression in VTA dopamine neurons through immunohistochemistry and in situ hybridization and detected optogenetically induced CCK release using an enzyme-linked immunosorbent assay. To investigate whether CCK modulates VTA circuit activity, we used whole-cell patch clamp recordings in mouse brain slices. We infused CCK locally in vivo and tested food intake and locomotion in fasted mice. We also used in vivo fiber photometry to measure Ca2+ transients in dopamine neurons during feeding. RESULTS: Here we report that VTA dopamine neurons release CCK from somatodendritic regions, where it triggers long-term potentiation of GABAergic (gamma-aminobutyric acidergic) synapses. The somatodendritic release occurs during trains of optogenetic stimuli or prolonged but modest depolarization and is dependent on synaptotagmin-7 and T-type Ca2+ channels. Depolarization-induced long-term potentiation is blocked by a CCK2 receptor antagonist and mimicked by exogenous CCK. Local infusion of CCK in vivo inhibits food consumption and decreases distance traveled in an open field test. Furthermore, intra-VTA-infused CCK reduced dopamine cell Ca2+ signals during food consumption after an overnight fast and was correlated with reduced food intake. CONCLUSIONS: Our experiments introduce somatodendritic neuropeptide release as a previously unknown feedback regulator of VTA dopamine cell excitability and dopamine-related behaviors.
Sujet(s)
Dopamine , Aire tegmentale ventrale , Souris , Animaux , Dopamine/métabolisme , Cholécystokinine/métabolisme , Cholécystokinine/pharmacologie , Synapses/métabolisme , Neurones dopaminergiquesRÉSUMÉ
Locus coeruleus (LC) is among the first brain areas to degenerate in Alzheimer's disease and Parkinson's disease; however, the underlying causes for the vulnerability of LC neurons are not well defined. Here we report a novel mechanism of degeneration of LC neurons caused by loss of the mitochondrial enzyme glutamate pyruvate transaminase 2 (GPT2). GPT2 Deficiency is a newly-recognized childhood neurometabolic disorder. The GPT2 enzyme regulates cell growth through replenishment of tricarboxylic acid (TCA) cycle intermediates and modulation of amino acid metabolism. In Gpt2-null mice, we observe an early loss of tyrosine hydroxylase (TH)-positive neurons in LC and reduced soma size at postnatal day 18. Gpt2-null LC shows selective positive Fluoro-Jade C staining. Neuron loss is accompanied by selective, prominent microgliosis and astrogliosis in LC. We observe reduced noradrenergic projections to and norepinephrine levels in hippocampus and spinal cord. Whole cell recordings in Gpt2-null LC slices show reduced soma size and abnormal action potentials with altered firing kinetics. Strikingly, we observe early decreases in phosphorylated S6 in Gpt2-null LC, preceding prominent p62 aggregation, increased LC3B-II to LC3B-I ratio, and neuronal loss. These data are consistent with a possible mechanism involving deficiency in protein synthesis and cell growth, associated subsequently with abnormal autophagy and neurodegeneration. As compared to the few genetic animal models with LC degeneration, loss of LC neurons in Gpt2-null mice is developmentally the earliest. Early neuron loss in LC in a model of human neurometabolic disease provides important clues regarding the metabolic vulnerability of LC and may lead to new therapeutic targets.
Sujet(s)
Locus ceruleus , Tyrosine 3-monooxygenase , Acides aminés/métabolisme , Animaux , Enfant , Glutamates/métabolisme , Humains , Locus ceruleus/métabolisme , Souris , Dégénérescence nerveuse/anatomopathologie , Norépinéphrine/métabolisme , Pyruvates/métabolisme , Transaminases/métabolisme , Triacides carboxyliques/métabolisme , Tyrosine 3-monooxygenase/métabolismeRÉSUMÉ
Sleep disturbances frequently occur in neurodevelopmental disorders such as autism, but the developmental role of sleep is largely unexplored, and a causal relationship between developmental sleep defects and behavioral consequences in adulthood remains elusive. Here, we show that in mice, sleep disruption (SD) in adolescence, but not in adulthood, causes long-lasting impairment in social novelty preference. Furthermore, adolescent SD alters the activation and release patterns of dopaminergic neurons in the ventral tegmental area (VTA) in response to social novelty. This developmental sleep function is mediated by balanced VTA activity during adolescence; chemogenetic excitation mimics, whereas silencing rescues, the social deficits of adolescent SD. Finally, we show that in Shank3-mutant mice, improving sleep or rectifying VTA activity during adolescence ameliorates adult social deficits. Together, our results identify a critical role of sleep and dopaminergic activity in the development of social interaction behavior.
Sujet(s)
Neurones dopaminergiques , Aire tegmentale ventrale , Animaux , Dopamine , Neurones dopaminergiques/physiologie , Souris , Protéines des microfilaments , Protéines de tissu nerveux , Sommeil/physiologie , Comportement social , Aire tegmentale ventrale/physiologieRÉSUMÉ
Sleep quality declines with age; however, the underlying mechanisms remain elusive. We found that hyperexcitable hypocretin/orexin (Hcrt/OX) neurons drive sleep fragmentation during aging. In aged mice, Hcrt neurons exhibited more frequent neuronal activity epochs driving wake bouts, and optogenetic activation of Hcrt neurons elicited more prolonged wakefulness. Aged Hcrt neurons showed hyperexcitability with lower KCNQ2 expression and impaired M-current, mediated by KCNQ2/3 channels. Single-nucleus RNA-sequencing revealed adaptive changes to Hcrt neuron loss in the aging brain. Disruption of Kcnq2/3 genes in Hcrt neurons of young mice destabilized sleep, mimicking aging-associated sleep fragmentation, whereas the KCNQ-selective activator flupirtine hyperpolarized Hcrt neurons and rejuvenated sleep architecture in aged mice. Our findings demonstrate a mechanism underlying sleep instability during aging and a strategy to improve sleep continuity.
Sujet(s)
Vieillissement , Neurones/physiologie , Orexines/physiologie , Privation de sommeil/physiopathologie , Sommeil , Vigilance , Aminopyridines/pharmacologie , Animaux , Systèmes CRISPR-Cas , Électroencéphalographie , Électromyographie , Femelle , Aire hypothalamique latérale/physiopathologie , Canal potassique KCNQ2/génétique , Canal potassique KCNQ2/métabolisme , Canal potassique KCNQ3/génétique , Canal potassique KCNQ3/métabolisme , Mâle , Souris , Narcolepsie/génétique , Narcolepsie/physiopathologie , Protéines de tissu nerveux/génétique , Protéines de tissu nerveux/métabolisme , Voies nerveuses , Optogénétique , Techniques de patch-clamp , RNA-Seq , Qualité du sommeilRÉSUMÉ
Understanding percepts, engrams and actions requires methods for selectively modulating synaptic communication between specific subsets of interconnected cells. Here, we develop an approach to control synaptically connected elements using bioluminescent light: Luciferase-generated light, originating from a presynaptic axon terminal, modulates an opsin in its postsynaptic target. Vesicular-localized luciferase is released into the synaptic cleft in response to presynaptic activity, creating a real-time Optical Synapse. Light production is under experimenter-control by introduction of the small molecule luciferin. Signal transmission across this optical synapse is temporally defined by the presence of both the luciferin and presynaptic activity. We validate synaptic Interluminescence by multi-electrode recording in cultured neurons and in mice in vivo. Interluminescence represents a powerful approach to achieve synapse-specific and activity-dependent circuit control in vivo.
Sujet(s)
Neurones/métabolisme , Optogénétique/méthodes , Synapses/métabolisme , Animaux , Encéphale/cytologie , Cellules cultivées , Luciferases/génétique , Luciferases/métabolisme , Luciférines/métabolisme , Mâle , Souris , Souris transgéniques , RatsRÉSUMÉ
The opsins have been studied extensively for their functions in visual phototransduction; however, the mechanisms underlying extraocular opsin signaling remain poorly understood. The first mammalian extraocular opsin to be discovered, opsin 3 (OPN3), was found in the brain more than two decades ago, yet its function remains unknown. A significant hindrance to studying OPN3 has been a lack of specific antibodies against mammalian OPN3, resulting in an incomplete understanding of its expression in the brain. Although Opn3 promoter-driven reporter mice have been generated to examine general OPN3 localization, they lack the regulated expression of the endogenous protein and the ability to study its subcellular localization. To circumvent these issues, we have created a knock-in OPN3-mCherry mouse model in which the fusion protein OPN3-mCherry is expressed under the endogenous Opn3 promoter. Viable and fertile homozygotes for the OPN3-mCherry allele were used to create an extensive map of OPN3-mCherry expression across the adult mouse brain. OPN3-mCherry was readily visualized in distinct layers of the cerebral cortex (CTX), the hippocampal formation (HCF), distinct nuclei of the thalamus, as well as many other regions in both neuronal and non-neuronal cells. Our mouse model offers a new platform to investigate the function of OPN3 in the brain.
Sujet(s)
Opsines , Opsines des bâtonnets , Animaux , Encéphale/métabolisme , Souris , Opsines/génétique , Opsines des bâtonnets/métabolisme , Transduction du signalRÉSUMÉ
The ventral tegmental area (VTA) is a major target of addictive drugs and receives multiple GABAergic projections originating outside the VTA. We describe differences in synaptic plasticity and behavior when optogenetically driving two opiate-sensitive GABAergic inputs to the VTA, the rostromedial tegmental nucleus (RMTg), and the periaqueductal gray (PAG). Activation of GABAergic RMTg terminals in the VTA in vivo is aversive, and low-frequency stimulation induces long-term depression in vitro. Low-frequency stimulation of PAG afferents in vitro unexpectedly causes long-term potentiation. Opioid receptor activation profoundly depresses PAG and RMTg inhibitory synapses but prevents synaptic plasticity only at PAG synapses. Activation of the GABAergic PAG terminals in the VTA promotes immobility, and optogenetically-driven immobility is blocked by morphine. Our data reveal the PAG as a source of highly opioid-sensitive GABAergic afferents and support the idea that different GABAergic pathways to the VTA control distinct behaviors.
Sujet(s)
Analgésiques morphiniques/pharmacologie , Plasticité neuronale/physiologie , Neurones afférents/physiologie , Substance grise centrale du mésencéphale/physiologie , Aire tegmentale ventrale/physiologie , Animaux , Femelle , Neurones GABAergiques/effets des médicaments et des substances chimiques , Neurones GABAergiques/physiologie , Mâle , Souris , Souris de lignée C57BL , Morphine/pharmacologie , Plasticité neuronale/effets des médicaments et des substances chimiques , Neurones afférents/effets des médicaments et des substances chimiques , Substance grise centrale du mésencéphale/effets des médicaments et des substances chimiques , Tegmentum du mésencéphale , Aire tegmentale ventrale/effets des médicaments et des substances chimiquesRÉSUMÉ
Of the fast ionotropic synapses, glycinergic synapses are the least well understood, but are vital for the maintenance of inhibitory signaling in the brain and spinal cord. Glycinergic signaling comprises half of the inhibitory signaling in the spinal cord, and glycinergic synapses are likely to regulate local nociceptive processing as well as the transmission to the brain of peripheral nociceptive information. Here we have investigated the rapid and prolonged potentiation of glycinergic synapses in the superficial dorsal horn of young male and female mice after brief activation of NMDA receptors (NMDARs). Glycinergic inhibitory postsynaptic currents (IPSCs) evoked with lamina II-III stimulation in identified GABAergic neurons in lamina II were potentiated by bath-applied Zn2+ and were depressed by the prostaglandin PGE2, consistent with the presence of both GlyRα1- and GlyRα3-containing receptors. NMDA application rapidly potentiated synaptic glycinergic currents. Whole-cell currents evoked by exogenous glycine were also readily potentiated by NMDA, indicating that the potentiation results from altered numbers or conductance of postsynaptic glycine receptors. Repetitive depolarization alone of the postsynaptic GABAergic neuron also potentiated glycinergic synapses, and intracellular EGTA prevented both NMDA-induced and depolarization-induced potentiation of glycinergic IPSCs. Optogenetic activation of trpv1 lineage afferents also triggered NMDAR-dependent potentiation of glycinergic synapses. Our results suggest that during peripheral injury or inflammation, nociceptor firing during injury is likely to potentiate glycinergic synapses on GABAergic neurons. This disinhibition mechanism may be engaged rapidly, altering dorsal horn circuitry to promote the transmission of nociceptive information to the brain.
Sujet(s)
Glycine/métabolisme , Potentialisation à long terme , Récepteurs du N-méthyl-D-aspartate/métabolisme , Synapses/physiologie , Animaux , Calcium/métabolisme , Femelle , Potentiels post-synaptiques inhibiteurs , Mâle , Souris , Nociception/physiologie , Récepteur de la glycine/métabolisme , Corne dorsale de la moelle spinale/cytologie , Corne dorsale de la moelle spinale/physiologie , Synapses/métabolismeRÉSUMÉ
The trigeminal nucleus caudalis (TNc) receives extensive afferent innervation from peripheral sensory neurons of the trigeminal ganglion (TG), and is the first central relay in the circuitry underpinning orofacial pain. Despite the initial characterization of the neurons in the superficial laminae, many questions remain. Here we report on electrophysiological properties of 535 superficial lamina I/II TNc neurons. Based on their firing pattern, we assigned these cells to five main groups, including (1) tonic, (2) phasic, (3) delayed, (4) H-current, and (5) tonic-phasic neurons, groups that exhibit distinct intrinsic properties and share some similarity with groups identified in the spinal dorsal horn. Driving predominantly nociceptive TG primary afferents using optogenetic stimulation in TRPV1/ChR2 animals, we found that tonic and H-current cells are most likely to receive pure monosynaptic input, whereas delayed neurons are more likely to exhibit inputs that appear polysynaptic. Finally, for the first time in TNc neurons, we used unsupervised clustering analysis methods and found that the kinetics of the action potentials and other intrinsic properties of these groups differ significantly from one another. Unsupervised spectral clustering based solely on a single voltage response to rheobase current was sufficient to group cells with shared properties independent of action potential discharge pattern, indicating that this approach can be effectively applied to identify functional neuronal subclasses. Together, our data illustrate that cells in the TNc with distinct patterns of TRPV1/ChR2 afferent innervation are physiologically diverse, but can be understood as a few major groups of cells having shared functional properties.
Sujet(s)
Neurones/physiologie , Noyaux du nerf trijumeau/cytologie , Potentiels d'action/physiologie , Voies afférentes/physiologie , Animaux , Analyse de regroupements , Phénomènes électrophysiologiques , Potentiels évoqués/physiologie , Femelle , Mâle , Potentiels de membrane/physiologie , Souris knockout , Neurones afférents/physiologie , Lamina nucléaire/physiologie , Optogénétique/méthodes , Techniques de patch-clamp , Stimulation lumineuse/méthodes , Synapses/physiologie , Canaux cationiques TRPV/physiologie , Noyaux du nerf trijumeau/physiologieRÉSUMÉ
In this issue of Neuron, Li et al. (2019) distinguish two separable GABAergic projections from the ventral tegmental area (VTA) to the dorsal raphe nucleus (DRN), with differential µ-opioid receptor regulation, each targeting different postsynaptic neurons and promoting opposing behavioral states.
Sujet(s)
Noyau dorsal du raphé , Troubles liés aux opiacés , Humains , Neurones , Aire tegmentale ventraleRÉSUMÉ
The peripheral trigeminovascular pathway mediates orofacial and craniofacial pain and projects centrally to the brainstem trigeminal nucleus caudalis (TNc). Sensitization of this pathway is involved in many pain conditions, but little is known about synaptic plasticity at its first central synapse. We have taken advantage of optogenetics to investigate plasticity selectively evoked at synapses of nociceptive primary afferents onto TNc neurons. Based on immunolabeling in the trigeminal ganglia, TRPV1-lineage neurons comprise primarily peptidergic and nonpeptidergic nociceptors. Optical stimulation of channelrhodopsin-expressing axons in the TRPV1/ChR2 mouse in TNc slices thus allowed us to activate a nociceptor-enriched subset of primary afferents. We recorded from lamina I/II neurons in acutely prepared transverse TNc slices, and alternately stimulated two independent afferent pathways, one with light-activated nociceptive afferents and the other with electrically-activated inputs. Low-frequency optical stimulation induced robust long-term depression (LTD) of optically-evoked EPSCs, but not of electrically-evoked EPSCs in the same neurons. Blocking NMDA receptors or nitric oxide synthase strongly attenuated LTD, whereas a cannabinoid receptor 1 antagonist had no effect. The neuropeptide PACAP-38 or the nitric oxide donors nitroglycerin or sodium nitroprusside are pharmacologic triggers of human headache. Bath application of any of these three compounds also persistently depressed optically-evoked EPSCs. Together, our data show that LTD of nociceptive afferent synapses on trigeminal nucleus neurons is elicited when the afferents are activated at frequencies consistent with the development of central sensitization of the trigeminovascular pathway.SIGNIFICANCE STATEMENT Animal models suggest that sensitization of trigeminovascular afferents plays a major role in craniofacial pain syndromes including primary headaches and trigeminal neuralgia, yet little is known about synaptic transmission and plasticity in the brainstem trigeminal nucleus caudalis (TNc). Here we used optogenetics to selectively drive a nociceptor-enriched population of trigeminal afferents while recording from superficial laminae neurons in the TNc. Low-frequency optical stimulation evoked robust long-term depression at TRPV1/ChR2 synapses. Moreover, application of three different headache trigger drugs also depressed TRPV1/ChR2 synapses. Synaptic depression at these primary afferent synapses may represent a newly identified mechanism contributing to central sensitization during headache.
Sujet(s)
Céphalée/physiopathologie , Plasticité neuronale/physiologie , Nocicepteurs/physiologie , Sous-noyau caudal du noyau spinal du nerf trijumeau/physiologie , Voies afférentes/effets des radiations , Animaux , Sensibilisation du système nerveux central , Potentiels post-synaptiques excitateurs/effets des médicaments et des substances chimiques , Potentiels post-synaptiques excitateurs/effets des radiations , Femelle , Gènes rapporteurs , Céphalée/induit chimiquement , Mâle , Souris , Plasticité neuronale/effets des médicaments et des substances chimiques , Plasticité neuronale/effets des radiations , Neurones/effets des médicaments et des substances chimiques , Neurones/physiologie , Nitroglycérine/pharmacologie , Nitroprussiate/pharmacologie , Nocicepteurs/effets des médicaments et des substances chimiques , Optogénétique , Techniques de patch-clamp , Polypeptide activateur de l'adénylcyclase hypophysaire/pharmacologie , Canaux cationiques TRPV/effets des médicaments et des substances chimiques , Sous-noyau caudal du noyau spinal du nerf trijumeau/cytologieRÉSUMÉ
Short-term synaptic plasticity contributes to many computations in the brain and allows synapses to keep a finite record of recent activity. Here we have investigated the mechanisms underlying an intriguing form of short-term plasticity termed labile LTP, at hippocampal and PFC synapses in male rats and male and female mice. In the hippocampus, labile LTP is triggered by high-frequency activation of presynaptic axons and is rapidly discharged with further activation of those axons. However, if the synapses are quiescent, they remain potentiated until further presynaptic activation. To distinguish labile LTP from NMDAR-dependent forms of potentiation, we blocked NMDARs in all experiments. Labile LTP was synapse-specific and was accompanied by a decreased paired pulse ratio, consistent with an increased release probability. Presynaptic Ca2+ and protein kinase activation during the tetanus appeared to be required for its initiation. Labile LTP was not reversed by a PKC inhibitor and did not require either RIM1α or synaptotagmin-7, proteins implicated in other forms of presynaptic short-term plasticity. Similar NMDAR-independent potentiation could be elicited at synapses in mPFC. Labile LTP allows for rapid information storage that is erased under controlled circumstances and could have a role in a variety of hippocampal and prefrontal cortical computations related to short-term memory.SIGNIFICANCE STATEMENT Changes in synaptic strength are thought to represent information storage relevant to particular nervous system tasks. A single synapse can exhibit multiple overlapping forms of plasticity that shape information transfer from presynaptic to postsynaptic neurons. Here we investigate the mechanisms underlying labile LTP, an NMDAR-independent form of plasticity induced at hippocampal synapses. The potentiation is maintained for long periods as long as the synapses are infrequently active, but with regular activation, the synapses are depotentiated. Similar NMDAR-independent potentiation can also be induced at L2/3-to-L5 synapses in mPFC. Labile LTP requires a rise in presynaptic Ca2+ and protein kinase activation but is unaffected in RIM1α or synaptotagmin-7 mutant mice. Labile LTP may contribute to short-term or working memory in hippocampus and mPFC.
Sujet(s)
Hippocampe/physiologie , Potentialisation à long terme/physiologie , Synapses/physiologie , Animaux , Femelle , Mâle , Souris , Souris de lignée C57BL , Plasticité neuronale/physiologie , Rats , Rat Sprague-DawleyRÉSUMÉ
Ventral tegmental area (VTA) dopaminergic neurons are key components of the reward pathway, and their activity is powerfully controlled by a diverse array of inhibitory GABAergic inputs. Two major sources of GABAergic nerve terminals within the VTA are local VTA interneurons and neurons in the rostromedial tegmental nucleus (RMTg). Here, using optogenetics, we compared synaptic properties of GABAergic synapses on VTA dopamine neurons using selective activation of afferents that originate from these two cell populations. We found little evidence of co-release of glutamate from either input, but RMTg-originating synaptic currents were reduced by strychnine, suggesting co-release of glycine and GABA. VTA-originating synapses displayed a lower initial release probability, and at higher frequency stimulation, short-term depression was more marked in VTA- but not RMTg-originating synapses. We previously reported that nitric oxide (NO)-induced potentiation of GABAergic synapses on VTA dopaminergic cells is lost after exposure to drugs of abuse or acute stress; in these experiments, multiple GABAergic afferents were simultaneously activated by electrical stimulation. Here we found that optogenetically-activated VTA-originating synapses on presumptive dopamine neurons also exhibited NO-induced potentiation, whereas RMTg-originating synapses did not. Despite providing a robust inhibitory input to the VTA, RMTg GABAergic synapses are most likely not those previously shown by our work to be persistently altered by addictive drugs and stress. Our work emphasises the idea that dopamine neuron excitability is controlled by diverse inhibitory inputs expected to exert varying degrees of inhibition and to participate differently in a range of behaviours.
Sujet(s)
Neurones dopaminergiques/physiologie , Neurones GABAergiques/physiologie , Glycine/métabolisme , Interneurones/physiologie , Potentialisation à long terme/physiologie , Inhibition nerveuse/physiologie , Plasticité neuronale/physiologie , Synapses/physiologie , Aire tegmentale ventrale/physiologie , Acide gamma-amino-butyrique/métabolisme , Animaux , Neurones dopaminergiques/métabolisme , Neurones GABAergiques/métabolisme , Interneurones/métabolisme , Souris , Optogénétique , Synapses/métabolisme , Aire tegmentale ventrale/métabolismeRÉSUMÉ
Stressful experiences potently activate kappa opioid receptors (κORs). κORs in the ventral tegmental area regulate multiple aspects of dopaminergic and non-dopaminergic cell function. Here we show that at GABAergic synapses on rat VTA dopamine neurons, a single exposure to a brief cold-water swim stress induces prolonged activation of κORs. This is mediated by activation of the receptor during the stressor followed by a persistent, ligand-independent constitutive activation of the κOR itself. This lasting change in function is not seen at κORs at neighboring excitatory synapses, suggesting distinct time courses and mechanisms of regulation of different subsets of κORs. We also provide evidence that constitutive activity of κORs governs the prolonged reinstatement to cocaine-seeking observed after cold water swim stress. Together, our studies indicate that stress-induced constitutive activation is a novel mechanism of κOR regulation that plays a critical role in reinstatement of drug seeking.
Sujet(s)
Neurones GABAergiques/physiologie , Récepteur kappa/métabolisme , Stress physiologique , Synapses/métabolisme , Aire tegmentale ventrale/physiologie , Animaux , Femelle , Rat Sprague-DawleyRÉSUMÉ
There is a high demand for in vitro models of the central nervous system (CNS) to study neurological disorders, injuries, toxicity, and drug efficacy. Three-dimensional (3D) in vitro models can bridge the gap between traditional two-dimensional culture and animal models because they present an in vivo-like microenvironment in a tailorable experimental platform. Within the expanding variety of sophisticated 3D cultures, scaffold-free, self-assembled spheroid culture avoids the introduction of foreign materials and preserves the native cell populations and extracellular matrix types. In this study, we generated 3D spheroids with primary postnatal rat cortical cells using an accessible, size-controlled, reproducible, and cost-effective method. Neurons and glia formed laminin-containing 3D networks within the spheroids. The neurons were electrically active and formed circuitry through both excitatory and inhibitory synapses. The mechanical properties of the spheroids were in the range of brain tissue. These in vivo-like features of 3D cortical spheroids provide the potential for relevant and translatable investigations of the CNS in vitro.
Sujet(s)
Techniques de culture cellulaire/méthodes , Microenvironnement cellulaire , Neurones/cytologie , Neurones/métabolisme , Sphéroïdes de cellules/cytologie , Sphéroïdes de cellules/métabolisme , Animaux , RatsRÉSUMÉ
In this issue of Neuron, Ma et al. (2014) show that long-term depression of two independent prefrontal cortical inputs to nucleus accumbens modifies behavioral responses controlling incubation of cocaine craving. Intriguingly, one input increases while the other attenuates behavioral responses, hinting that both "prorelapse" and "antirelapse" pathways are strengthened after cocaine self-administration.
Sujet(s)
Troubles liés à la cocaïne/physiopathologie , Besoin impérieux/physiologie , Noyau accumbens/physiopathologie , Cortex préfrontal/physiopathologie , Synapses/physiologie , Animaux , MâleRÉSUMÉ
BACKGROUND: Dopaminergic neurons in the ventral tegmental area of the brain are an important site of convergence of drugs and stress. We previously identified a form of long-term potentiation of gamma-aminobutyric acid (GABA)ergic synapses on these neurons (LTPGABA). Our studies have shown that exposure to acute stress blocks this LTP and that reversal of the block of LTPGABA is correlated with prevention of stress-induced reinstatement of cocaine-seeking behavior. METHODS: Sprague-Dawley rats were subjected to cold-water swim stress. Midbrain slices were prepared following stress, and whole-cell patch clamp recordings of inhibitory postsynaptic currents were performed from ventral tegmental area dopamine neurons. Antagonists of glucocorticoid receptors and kappa opioid receptors (κORs) were administered at varying time points after stress. Additionally, the ability of a kappa antagonist administered following stress to block forced swim stress-induced reinstatement of cocaine self-administration was tested. RESULTS: We found that an acute stressor blocks LTPGABA for 5 days after stress through a transient activation of glucocorticoid receptors and more lasting contribution of κORs. Even pharmacological block of κORs beginning 4 days after stress has occurred reversed the block of LTPGABA. Administration of a κORs antagonist following stress prevents reinstatement of cocaine-seeking behavior. CONCLUSIONS: A brief stressor produces changes in the reward circuitry lasting several days. Our findings reveal roles for glucocorticoid receptors and κORs as mediators of the lasting effects of stress on synaptic plasticity. κORs antagonists reverse the neuroadaptations underlying stress-induced drug-seeking behavior and may be useful in the treatment of cocaine addiction.
Sujet(s)
Cocaïne/pharmacologie , Comportement de recherche de substances/physiologie , Potentiels post-synaptiques inhibiteurs , Potentialisation à long terme , Récepteur kappa/physiologie , Stress psychologique/physiopathologie , Animaux , Corticostérone/sang , Dexaméthasone/pharmacologie , Neurones dopaminergiques/effets des médicaments et des substances chimiques , Neurones dopaminergiques/physiologie , Neurones GABAergiques/effets des médicaments et des substances chimiques , Neurones GABAergiques/physiologie , Glucocorticoïdes/pharmacologie , Mâle , Rats , Rat Sprague-Dawley , Récepteurs aux glucocorticoïdes/agonistes , Récepteurs aux glucocorticoïdes/métabolisme , Autoadministration , Natation , Tegmentum du mésencéphale/effets des médicaments et des substances chimiques , Tegmentum du mésencéphale/physiologieRÉSUMÉ
Long-term potentiation (LTP) is a persistent increase in synaptic strength required for many behavioral adaptations, including learning and memory, visual and somatosensory system functional development, and drug addiction. Recent work has suggested a role for LTP-like phenomena in the processing of nociceptive information in the dorsal horn and in the generation of central sensitization during chronic pain states. Whereas LTP of glutamatergic and GABAergic synapses has been characterized throughout the central nervous system, to our knowledge there have been no reports of LTP at mammalian glycinergic synapses. Glycine receptors (GlyRs) are structurally related to GABAA receptors and have a similar inhibitory role. Here we report that in the superficial dorsal horn of the spinal cord, glycinergic synapses on inhibitory GABAergic neurons exhibit LTP, occurring rapidly after exposure to the inflammatory cytokine interleukin-1 beta. This form of LTP (GlyR LTP) results from an increase in the number and/or change in biophysical properties of postsynaptic glycine receptors. Notably, formalin-induced peripheral inflammation in vivo potentiates glycinergic synapses on dorsal horn neurons, suggesting that GlyR LTP is triggered during inflammatory peripheral injury. Our results define a previously unidentified mechanism that could disinhibit neurons transmitting nociceptive information and may represent a useful therapeutic target for the treatment of pain.
Sujet(s)
Glycine/métabolisme , Interleukine-1 bêta/physiologie , Potentialisation à long terme/physiologie , Névralgie/physiopathologie , Cellules de la corne dorsale/physiologie , Synapses/physiologie , Animaux , Comportement animal/physiologie , Neurones GABAergiques/métabolisme , Neurones GABAergiques/physiologie , Hyperalgésie/métabolisme , Hyperalgésie/physiopathologie , Interleukine-1 bêta/métabolisme , Interleukine-1 bêta/pharmacologie , Interneurones/métabolisme , Interneurones/physiologie , Potentialisation à long terme/effets des médicaments et des substances chimiques , Souris , Souris de lignée C57BL , Souris knockout , Névralgie/métabolisme , Névrite/métabolisme , Névrite/physiopathologie , Techniques de culture d'organes , Cellules de la corne dorsale/effets des médicaments et des substances chimiques , Cellules de la corne dorsale/métabolisme , Transduction du signal/physiologie , Moelle spinale/cytologie , Moelle spinale/effets des médicaments et des substances chimiques , Moelle spinale/physiologieRÉSUMÉ
While stressful experiences are a part of everyone's life, they can also exact a major toll on health. Stressful life experiences are associated with increased substance abuse, and there exists significant co-morbidity between mental illness and substance use disorders [N.D. Volkow & T.K. Li (2004) Nat. Rev. Neurosci., 5, 963-970; G. Koob & M.J. Kreek (2007) Am. J. Psych., 164, 1149-1159; R. Sinha (2008) Annals N.Y. Acad. Sci., 1141, 105-130]. The risk for development of mood or anxiety disorders after stress is positively associated with the risk for substance use disorders [R. Sinha (2008) Annals N.Y. Acad. Sci., 1141, 105-130], suggesting that there are common substrates for vulnerability to addictive and affective disorders. Understanding the molecular and physiological substrates of stress may lead to improved therapeutic interventions for the treatment of substance use disorders and mental illnesses.