RESUMO
Cholinergic neurons project throughout the nervous system and activate nicotinic receptors to modulate synaptic function in ways that shape higher order brain function. The acute effects of nicotinic signaling on long-term synaptic plasticity have been well-characterized. Less well understood is how chronic exposure to low levels of nicotine, such as those encountered by habitual smokers, can alter neural connections to promote addiction and other lasting behavioral effects. We show here that chronic exposure of hippocampal neurons in culture to low levels of nicotine recruits AMPA and NMDA receptors to the cell surface and sequesters them at postsynaptic sites. The receptors include GluA2-containing AMPA receptors, which are responsible for most of the excitatory postsynaptic current mediated by AMPA receptors on the neurons, and include NMDA receptors containing GluN1 and GluN2B subunits. Moreover, we find that the nicotine treatment also increases expression of the presynaptic component synapsin 1 and arranges it in puncta juxtaposed to the additional AMPA and NMDA receptor puncta, suggestive of increases in synaptic contacts. Consistent with increased synaptic input, we find that the nicotine treatment leads to an increase in the excitatory postsynaptic currents mediated by AMPA and NMDA receptors. Further, the increases skew the ratio of excitatory-to-inhibitory input that the cell receives, and this holds both for pyramidal neurons and inhibitory neurons in the hippocampal CA1 region. The GluN2B-containing NMDA receptor redistribution at synapses is associated with a significant increase in GluN2B phosphorylation at Tyr1472, a site known to prevent GluN2B endocytosis. These results suggest that chronic exposure to low levels of nicotine not only alters functional connections but also is likely to change excitability levels across networks. Further, it may increase the propensity for synaptic plasticity, given the increase in synaptic NMDA receptors.
Assuntos
Potenciais Pós-Sinápticos Excitadores/fisiologia , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Células Piramidais/efeitos dos fármacos , Receptores de Glutamato/metabolismo , Análise de Variância , Animais , Animais Recém-Nascidos , Biotinilação , Células Cultivadas , Estimulação Elétrica , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Hipocampo/citologia , Técnicas In Vitro , Técnicas de Cultura de Órgãos , Técnicas de Patch-Clamp , Transporte Proteico/efeitos dos fármacos , Células Piramidais/fisiologia , Ratos , Ratos Sprague-Dawley , Receptores de GABA-A/metabolismoRESUMO
Glutamate is the primary excitatory transmitter in adult brain, acting through synapses on dendritic spines and shafts. Early in development, however, when glutamatergic synapses are only beginning to form, nicotinic cholinergic excitation is already widespread; it is mediated by acetylcholine activating nicotinic acetylcholine receptors (nAChRs) that generate waves of activity across brain regions. A major class of nAChRs contributing at this time is a species containing α7 subunits (α7-nAChRs). These receptors are highly permeable to calcium, influence a variety of calcium-dependent events, and are diversely distributed throughout the developing CNS. Here we show that α7-nAChRs unexpectedly promote formation of glutamatergic synapses during development. The dependence on α7-nAChRs becomes clear when comparing wild-type (WT) mice with mice constitutively lacking the α7-nAChR gene. Ultrastructural analysis, immunostaining, and patch-clamp recording all reveal synaptic deficits when α7-nAChR input is absent. Similarly, nicotinic activation of α7-nAChRs in WT organotypic culture, as well as cell culture, increases the number of glutamatergic synapses. RNA interference demonstrates that the α7-nAChRs must be expressed in the neuron being innervated for normal innervation to occur. Moreover, the deficits persist throughout the developmental period of major de novo synapse formation and are still fully apparent in the adult. GABAergic synapses, in contrast, are undiminished in number under such conditions. As a result, mice lacking α7-nAChRs have an altered balance in the excitatory/inhibitory input they receive. This ratio represents a fundamental feature of neural networks and shows for the first time that endogenous nicotinic cholinergic signaling plays a key role in network construction.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Ácido Glutâmico/metabolismo , Neurônios/fisiologia , Receptores Nicotínicos/fisiologia , Sinapses/fisiologia , Fatores Etários , Análise de Variância , Animais , Animais Recém-Nascidos , Células Cultivadas , Proteína 4 Homóloga a Disks-Large , Estimulação Elétrica , Embrião de Mamíferos , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , Feminino , Antagonistas GABAérgicos/farmacologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Regulação da Expressão Gênica no Desenvolvimento/genética , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Guanilato Quinases/metabolismo , Hipocampo/citologia , Masculino , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia Eletrônica de Transmissão , Neuritos/metabolismo , Neuritos/ultraestrutura , Neurônios/efeitos dos fármacos , Neurônios/ultraestrutura , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Técnicas de Cultura de Órgãos , Técnicas de Patch-Clamp , Piridazinas/farmacologia , Compostos de Piridínio , Compostos de Amônio Quaternário , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Ratos , Receptores de AMPA/metabolismo , Receptores Nicotínicos/deficiência , Receptores Nicotínicos/genética , Bloqueadores dos Canais de Sódio/farmacologia , Sinapses/ultraestrutura , Tetrodotoxina/farmacologia , Fatores de Tempo , Transdução Genética/métodos , Proteína Vesicular 1 de Transporte de Glutamato/metabolismo , Córtex Visual/citologia , Córtex Visual/metabolismo , Receptor Nicotínico de Acetilcolina alfa7RESUMO
Glutamatergic synapses are located mostly on dendritic spines in the adult nervous system. The spines serve as postsynaptic compartments, containing components that mediate and control the synaptic signal. Early in development, when glutamatergic synapses are initially forming, waves of excitatory activity pass through many parts of the nervous system and are driven in part by a class of heteropentameric ß2-containing nicotinic acetylcholine receptors (ß2*-nAChRs). These ß2*-nAChRs are widely distributed and, when activated, can depolarize the membrane and elevate intracellular calcium levels in neurons. We show here that ß2*-nAChRs are essential for acquisition of normal numbers of dendritic spines during development. Mice constitutively lacking the ß2-nAChR gene have fewer dendritic spines than do age-matched wild-type mice at all times examined. Activation of ß2*-nAChRs by nicotine either in vivo or in organotypic slice culture quickly elevates the number of spines. RNA interference studies both in vivo and in organotypic culture demonstrate that the ß2*-nAChRs act in a cell-autonomous manner to increase the number of spines. The increase depends on intracellular calcium and activation of calcium, calmodulin-dependent protein kinase II. Absence of ß2*-nAChRs in vivo causes a disproportionate number of glutamatergic synapses to be localized on dendritic shafts, rather than on spines as occurs in wild type. This shift in synapse location is found both in the hippocampus and cortex, indicating the breadth of the effect. Because spine synapses differ from shaft synapses in their signaling capabilities, the shift observed is likely to have significant consequences for network function.
Assuntos
Espinhas Dendríticas/metabolismo , Receptores Nicotínicos/fisiologia , Animais , Cálcio/metabolismo , Sinalização do Cálcio/fisiologia , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Células Cultivadas , Córtex Cerebral/citologia , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/metabolismo , Espinhas Dendríticas/efeitos dos fármacos , Ácido Glutâmico/metabolismo , Hipocampo/citologia , Hipocampo/efeitos dos fármacos , Hipocampo/crescimento & desenvolvimento , Hipocampo/metabolismo , Camundongos , Camundongos Knockout , Neurônios/citologia , Neurônios/efeitos dos fármacos , Nicotina/farmacologia , Subunidades Proteicas/fisiologia , RNA Interferente Pequeno/genética , Receptores Nicotínicos/genética , Sinapses/efeitos dos fármacos , Sinapses/metabolismo , Sinapses/fisiologia , Sinapses/ultraestruturaRESUMO
BACKGROUND: Nicotine intake induces addiction through neuroplasticity of the reward circuitry, altering the activity of dopaminergic neurons of the ventral tegmental area. Prior work demonstrated that altered circuit activity can change neurotransmitter expression in the developing and adult brain. Here we investigated the effects of neonatal nicotine exposure on the dopaminergic system and nicotine consumption in adulthood. METHODS: Male and female mice were used for two-bottle-choice test, progressive ratio breakpoint test, immunohistochemistry, RNAscope, quantitative polymerase chain reaction, calcium imaging, and DREADD (designer receptor exclusively activated by designer drugs)-mediated chemogenic activation/inhibition experiments. RESULTS: Neonatal nicotine exposure potentiates drug preference in adult mice, induces alterations in calcium spike activity of midbrain neurons, and increases the number of dopamine-expressing neurons in the ventral tegmental area. Specifically, glutamatergic neurons are first primed to express transcription factor Nurr1, then acquire the dopaminergic phenotype following nicotine re-exposure in adulthood. Enhanced neuronal activity combined with Nurr1 expression is both necessary and sufficient for the nicotine-mediated neurotransmitter plasticity to occur. CONCLUSIONS: Our findings illuminate a new mechanism of neuroplasticity by which early nicotine exposure primes the reward system to display increased susceptibility to drug consumption in adulthood.
Assuntos
Dopamina/fisiologia , Plasticidade Neuronal/efeitos dos fármacos , Nicotina/administração & dosagem , Área Tegmentar Ventral/fisiologia , Animais , Neurônios Dopaminérgicos/efeitos dos fármacos , Neurônios Dopaminérgicos/fisiologia , Feminino , Masculino , Mesencéfalo/efeitos dos fármacos , Mesencéfalo/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Fenótipo , Recompensa , Área Tegmentar Ventral/efeitos dos fármacosRESUMO
How do neurons in orofacial motor cortex (MCtx) orchestrate behaviors? We show that focal activation of MCtx corticobulbar neurons evokes behaviorally relevant concurrent movements of the forelimb, jaw, nose, and vibrissae. The projections from different locations in MCtx form gradients of boutons across premotor nuclei spinal trigeminal pars oralis (SpVO) and interpolaris rostralis (SpVIr). Furthermore, retrograde viral tracing from muscles that control orofacial actions shows that these premotor nuclei segregate their outputs. In the most dramatic case, both SpVO and SpVIr are premotor to forelimb and vibrissa muscles, while only SpVO is premotor to jaw muscles. Functional confirmation of the superimposed control by MCtx was obtained through selective optogenetic activation of corticobulbar neurons on the basis of their preferential projections to SpVO versus SpVIr. We conclude that neighboring projection neurons in orofacial MCtx form parallel pathways to distinct pools of trigeminal premotor neurons that coordinate motor actions into a behavior.
Assuntos
Vias Eferentes/fisiologia , Córtex Motor/fisiologia , Movimento/fisiologia , Neurônios/fisiologia , Núcleos do Trigêmeo/fisiologia , Animais , Comportamento Animal/fisiologia , Face/inervação , Feminino , Camundongos , Atividade Motora/fisiologiaRESUMO
BACKGROUND: In rat, deafferentation of one labyrinth (unilateral labyrinthectomy) results in a characteristic syndrome of ocular and motor postural disorders (e.g., barrel rotation, circling behavior, and spontaneous nystagmus). Behavioral recovery (e.g., diminished symptoms), encompassing 1 week after unilateral labyrinthectomy, has been termed vestibular compensation. Evidence suggesting that the histamine H3 receptor plays a key role in vestibular compensation comes from studies indicating that betahistine, a histamine-like drug that acts as both a partial histamine H1 receptor agonist and an H3 receptor antagonist, can accelerate the process of vestibular compensation. RESULTS: Expression levels for histamine H3 receptor (total) as well as three isoforms which display variable lengths of the third intracellular loop of the receptor were analyzed using in situ hybridization on brain sections containing the rat medial vestibular nucleus after unilateral labyrinthectomy. We compared these expression levels to H3 receptor binding densities. Total H3 receptor mRNA levels (detected by oligo probe H3X) as well as mRNA levels of the three receptor isoforms studied (detected by oligo probes H3A, H3B, and H3C) showed a pattern of increase, which was bilaterally significant at 24 h post-lesion for both H3X and H3C, followed by significant bilateral decreases in medial vestibular nuclei occurring 48 h (H3X and H3B) and 1 week post-lesion (H3A, H3B, and H3C). Expression levels of H3B was an exception to the forementioned pattern with significant decreases already detected at 24 h post-lesion. Coinciding with the decreasing trends in H3 receptor mRNA levels was an observed increase in H3 receptor binding densities occurring in the ipsilateral medial vestibular nuclei 48 h post-lesion. CONCLUSION: Progressive recovery of the resting discharge of the deafferentated medial vestibular nuclei neurons results in functional restoration of the static postural and occulomotor deficits, usually occurring within a time frame of 48 hours in rats. Our data suggests that the H3 receptor may be an essential part of pre-synaptic mechanisms required for reestablishing resting activities 48 h after unilateral labyrinthectomy.
Assuntos
Orelha Interna/cirurgia , Plasticidade Neuronal/fisiologia , Receptores Histamínicos H3/fisiologia , Núcleos Vestibulares/química , Núcleos Vestibulares/metabolismo , Animais , Autorradiografia/métodos , Sítios de Ligação/fisiologia , Imidazóis/metabolismo , Radioisótopos do Iodo/metabolismo , Masculino , Isoformas de Proteínas/fisiologia , Ratos , Ratos Sprague-Dawley , Núcleos Vestibulares/cirurgiaRESUMO
BACKGROUND: Hibernation is a state of extremely reduced physiological functions and a deep depression of CNS activity. We have previously shown that the histamine levels increase in the brain during hibernation, as does the ratio between histamine and its first metabolite, suggesting increased histamine turnover during this state. The inhibitory histamine H3 receptor has both auto- and heteroreceptor function, rendering it the most likely histamine receptor to be involved in regulating the activity of histamine as well as other neurotransmitters during hibernation. In view of accumulating evidence that there is a global depression of transcription and translation during hibernation, of all but a few proteins that are important for this physiological condition, we reasoned that an increase in histamine H3 receptor expression would clearly indicate an important hibernation-related function for the receptor. RESULTS: In this study we show, using in situ hybridization, that histamine H3 receptor mRNA increases in the cortex, caudate nucleus and putamen during hibernation, an increase that is accompanied by elevated receptor binding in the cerebral cortex, globus pallidus and substantia nigra. These results indicate that there is a hibernation-related increase in H3 receptor expression in cortical neurons and in striatopallidal and striatonigral GABAergic neurons. GTP-gamma-S binding autoradiography shows that the H3 receptors in the globus pallidus and substantia nigra can be stimulated by histamine throughout the hibernation cycle, suggesting that they are functionally active during hibernation. CONCLUSIONS: These results show that the histamine H3 receptor gene is one of the few with a transcript that increases during hibernation, indicating an important role for the receptor in regulating this state. Moreover, the receptor is functionally active in the basal ganglia, suggesting a function for it in regulating e.g. dopaminergic transmission during hibernation.
Assuntos
Encéfalo/metabolismo , Hibernação/fisiologia , Receptores Histamínicos H3/genética , Receptores Histamínicos H3/metabolismo , Sciuridae/metabolismo , Animais , Autorradiografia , Ligação Competitiva , Núcleo Caudado/metabolismo , Córtex Cerebral/metabolismo , Feminino , Globo Pálido/metabolismo , Guanosina 5'-O-(3-Tiotrifosfato)/farmacocinética , Hibridização In Situ , Neurônios/metabolismo , Putamen/metabolismo , RNA Mensageiro/metabolismo , Substância Negra/metabolismo , Regulação para CimaRESUMO
Hibernation is a state of extremely reduced physiological functions and a deep depression of CNS activity, which is thought to be under hippocampal control. Our previous findings indicate increased histamine turnover during hibernation in several brain regions, including the hippocampus. In this study we showed that histamine infused into the hippocampus significantly delayed arousal from hibernation. These findings indicate that histamine may contribute to maintaining the hibernating state, suggesting a novel role for histamine in controlling arousal state.
Assuntos
Nível de Alerta/efeitos dos fármacos , Hibernação/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Histamina/farmacologia , Animais , Nível de Alerta/fisiologia , Feminino , Hibernação/fisiologia , Hipocampo/fisiologia , Sciuridae/fisiologia , Fatores de TempoRESUMO
The hippocampus is one of only two regions in the adult brain where neurons are generated in significant numbers throughout the lifetime of the animal. Numerous studies have demonstrated that these adult-born neurons are essential for optimal cognitive function with unimpaired memory formation and retrieval. The extent to which adult-born neurons survive through an early "critical period" and become integrated into functional networks has been shown to depend on the richness of stimulation they receive during these formative stages. The dentate gyrus in the hippocampus - home of the adult-born neurons - receives extensive cholinergic innervation, and newly generated neurons in the adult hippocampus express substantial numbers of both major types of neuronal nicotinic acetylcholine receptors. Early studies indicated that nicotinic signaling may be important for the development of adult-born neurons: repeated exposure to nicotine impaired their long-term survival. Recent studies with mutant mice lacking either one of the two major nicotinic receptor subtypes demonstrate that receptor loss results in fewer adult-born neurons surviving the critical period and becoming integrated into neural networks. The key nicotinic receptor mediating the largest effects is one that has a high relative permeability to calcium. In view of this feature, it may not be surprising that excessive exposure to nicotine can have detrimental effects on survival and maturation of adult-born neurons in the dentate; these same receptors appear to be key. The results pose serious challenges for therapeutic strategies targeting an individual class of nicotinic receptors for global treatment in the recipient.
Assuntos
Hipocampo/fisiologia , Neurogênese/fisiologia , Neurônios/fisiologia , Nicotina/metabolismo , Receptores Nicotínicos/fisiologia , Adulto , Animais , Sobrevivência Celular/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Humanos , Neurogênese/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Nicotina/farmacologia , Subunidades Proteicas , Receptores Nicotínicos/metabolismoRESUMO
The median fins of fishes are key features of locomotor morphology which function as complex control surfaces during a variety of behaviors. However, very few studies have experimentally assessed median fin function, as most workers focus on axial structures. In particular, the dorsal fin of many teleost fishes possesses both spiny anterior and soft posterior portions which may function separately during locomotion. We analyzed the function of the soft region of the dorsal fin and of the dorsal inclinator (Di) muscles which are the primary muscles responsible for lateral flexion. We used electromyography to measure in vivo Di activity, as well as activity of the red myomeric muscles located at a similar longitudinal position. We quantified motor patterns during four locomotor behaviors: braking and three propulsive behaviors (steady swimming, kick and glide swimming, and C-starts). During the three propulsive swimming behaviors, the timing of Di activity was more similar to that of ipsilateral red myomeric muscle rather than to contralateral myomeric activity, whereas during braking the timing of activity of the Di muscles was similar to that of the contralateral myomeric musculature. During the three propulsive behaviors, when the Di muscles had activity, it was consistent with the function of stiffening the soft dorsal fin to oppose its tendency to bend as a result of the body being swept laterally through the water. In contrast, activity of the Di muscles during braking was consistent with the function of actively flexing the soft dorsal fin towards the side of the fish that had Di activity. Activity of the Di muscles during steady speed swimming was generally sufficient to resist lateral bending of the soft dorsal fin, whereas during high speed kick and glide swimming and C-starts, Di activity was not sufficient to resist the bending caused by resistive forces imposed by the water. Cumulative data from all four behaviors suggest that the Di muscles can be activated independently relative to the myomeric musculature rather than having a single phase relationship with the myomeric muscle common to all of the observed behaviors. © 1996 Wiley-Liss, Inc.
RESUMO
Hibernation is a physiological state characterized by a dramatic reduction in various functions, such as body temperature, heart rate, and metabolism. The hippocampus is thought to be important for regulation of the hibernation bout because it remains electrophysiologically active throughout this extremely depressed state. The question arises as to what neuronal influences act within the hippocampus during hibernation to sustain its activity. We hypothesized that histaminergic input might be an important contributor. Brain histamine is involved in functions relevant to hibernation, such as the regulation of diurnal rhythms, body temperature, and energy metabolism. Furthermore, we have previously shown that the histaminergic system appears to be activated during the hibernating state. In this study, we used receptor binding autoradiography, in situ hybridization, and GTP-gamma-S binding autoradiography to study changes in histamine receptors across the hibernation bout. We were able to demonstrate an increase in histamine H1 and H2 receptors in the hippocampus during hibernation, whereas the mRNA expression and receptor density of the inhibitory H3 receptor decreased. Histamine H3 receptors were shown to exhibit both histamine-activated and constitutive GTP-gamma-S-binding activity in the ground squirrel hippocampus, both of which decreased during hibernation, indicating a decrease in H3 receptor G-protein activation. Taken together, our results indicate that histamine may be involved in maintaining hibernation by sustaining hippocampal activity, possibly through H1 and H2 receptor activity and decreased inhibition by H3 receptors. The involvement of brain histamine, which is generally thought of as an arousal molecule, in maintaining a depressed state of the brain suggests a more general role for the amine in controlling arousal state.