RESUMEN
Dorsal root ganglia (DRG) neurons transduce and convey somatosensory information from the periphery to the central nervous system. Adrenergic mediators are known to modulate nociceptive inputs in DRG neurons, acting as up- or down-regulators of neuronal excitability. They are also important in the development of sympathetic neuropathy. ATP-activated P2X channels and capsaicin-activated TRPV1 channels are directly involved in the transduction of nociceptive stimuli. In this work, we show that long-term (up to 3 days) in vitro stimulation of DRG neurons with selective α1-adrenergic agonist increased slow but not fast ATP-activated currents, with no effect on capsaicin currents. Selective agonists for α2, ß1 and ß3-adrenergic receptors decreased capsaicin activated currents and had no effect on ATP currents. Capsaicin currents were associated with increased neuronal excitability, while none of the adrenergic modulators produced change in rheobase. These results demonstrate that chronic adrenergic activation modulates two nociceptive transducer molecules, increasing or decreasing channel current depending on the adrenergic receptor subtype. These observations aid our understanding of nociceptive or antinociceptive effects of adrenergic agonists.
Asunto(s)
Agonistas Adrenérgicos , Capsaicina , Capsaicina/farmacología , Agonistas Adrenérgicos/farmacología , Nocicepción , Canales Iónicos/farmacología , Adenosina Trifosfato/farmacología , Ganglios Espinales , Canales Catiónicos TRPVRESUMEN
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease characterized by chorea, incoordination and psychiatric and behavioral symptoms. The leading cause of death in HD patients is aspiration pneumonia, associated with respiratory dysfunction, decreased respiratory muscle strength and dysphagia. Although most of the motor symptoms are derived from alterations in the central nervous system, some might be associated with changes in the components of motor units (MU). To explore this hypothesis, we evaluated morphofunctional aspects of the diaphragm muscle in a mouse model for HD (BACHD). We showed that the axons of the phrenic nerves were not affected in 12-months-old BACHD mice, but the axon terminals that form the neuromuscular junctions (NMJs) were more fragmented in these animals in comparison with the wild-type mice. In BACHD mice, the synaptic vesicles of the diaphragm NMJs presented a decreased exocytosis rate. Quantal content and quantal size were smaller and there was less synaptic depression whereas the estimated size of the readily releasable vesicle pool was not changed. At the ultrastructure level, the diaphragm NMJs of these mice presented fewer synaptic vesicles with flattened and oval shapes, which might be associated with the reduced expression of the vesicular acetylcholine transporter protein. Furthermore, mitochondria of the diaphragm muscle presented signs of degeneration in BACHD mice. Interestingly, despite all these cellular alterations, BACHD diaphragmatic function was not compromised, suggesting a higher resistance threshold of this muscle. A putative resistance mechanism may be protecting this vital muscle. Our data contribute to expanding the current understanding of the effects of mutated huntingtin in the neuromuscular synapse and the diaphragm muscle function.
Asunto(s)
Diafragma/metabolismo , Enfermedad de Huntington/metabolismo , Sinapsis/metabolismo , Vesículas Sinápticas/metabolismo , Animales , Diafragma/patología , Modelos Animales de Enfermedad , Humanos , Enfermedad de Huntington/patología , Unión Neuromuscular/metabolismo , Terminales Presinápticos/metabolismoRESUMEN
INTRODUCTION: Short-term plasticity of synaptic function is an important physiological control of transmitter release. Short-term plasticity can be regulated by intracellular calcium released by ryanodine and inositol triphosphate (IP3) receptors, but the role of these receptors at the neuromuscular junction is understood incompletely. METHODS: We measured short-term plasticity of evoked endplate potential (EPP) amplitudes from frog neuromuscular junctions treated with ryanodine, 2-aminoethoxydiphenylborane (2-APB), or 1-[6-[[(17ß)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U- 73122). RESULTS: Ryanodine decreases paired-pulse facilitation for intervals <20 ms and markedly decreases tetanic depression. Treatment with 2-APB reduces EPP amplitude, increases paired-pulse facilitation for intervals of <20 ms, and significantly reduces tetanic depression. U-73122 decreases EPP amplitude and decreases paired-pulse depression for intervals <20 ms. CONCLUSIONS: Ryanodine, IP3 receptors, and phospholipase C modulate short-term plasticity of transmitter release at the neuromuscular junction. These results suggest possible targets for improving the safety factor of neuromuscular transmission during repetitive activity of the neuromuscular junction.
Asunto(s)
Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Unión Neuromuscular/metabolismo , Plasticidad Neuronal/fisiología , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Animales , Anuros , Biofisica , Compuestos de Boro/farmacología , Calcio/metabolismo , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Electrofisiología , Estrenos/farmacología , Técnicas In Vitro , Unión Neuromuscular/efectos de los fármacos , Plasticidad Neuronal/efectos de los fármacos , Inhibidores de Fosfodiesterasa/farmacología , Pirrolidinonas/farmacología , Rianodina/farmacologíaRESUMEN
In vertebrates, nerve muscle communication is mediated by the release of the neurotransmitter acetylcholine packed inside synaptic vesicles by a specific vesicular acetylcholine transporter (VAChT). Here we used a mouse model (VAChT KD(HOM)) with 70% reduction in the expression of VAChT to investigate the morphological and functional consequences of a decreased acetylcholine uptake and release in neuromuscular synapses. Upon hypertonic stimulation, VAChT KD(HOM) mice presented a reduction in the amplitude and frequency of miniature endplate potentials, FM 1-43 staining intensity, total number of synaptic vesicles and altered distribution of vesicles within the synaptic terminal. In contrast, under electrical stimulation or no stimulation, VAChT KD(HOM) neuromuscular junctions did not differ from WT on total number of vesicles but showed altered distribution. Additionally, motor nerve terminals in VAChT KD(HOM) exhibited small and flattened synaptic vesicles similar to that observed in WT mice treated with vesamicol that blocks acetylcholine uptake. Based on these results, we propose that decreased VAChT levels affect synaptic vesicle biogenesis and distribution whereas a lower ACh content affects vesicles shape.
Asunto(s)
Acetilcolina/metabolismo , Placa Motora/metabolismo , Transmisión Sináptica/fisiología , Vesículas Sinápticas/metabolismo , Proteínas de Transporte Vesicular de Acetilcolina/metabolismo , Acetilcolina/genética , Animales , Estimulación Eléctrica , Ratones , Ratones Noqueados , Placa Motora/genética , Placa Motora/ultraestructura , Vesículas Sinápticas/genética , Vesículas Sinápticas/ultraestructura , Proteínas de Transporte Vesicular de Acetilcolina/genéticaRESUMEN
We investigated the effects of cholesterol removal on spontaneous and KCl-evoked synaptic vesicle recycling at the frog neuromuscular junction. Cholesterol removal by methyl-ß-cyclodextrin (MßCD) induced an increase in the frequency of miniature end-plate potentials (MEPPs) and spontaneous destaining of synaptic vesicles labeled with the styryl dye FM1-43. Treatment with MßCD also increased the size of MEPPs without causing significant changes in nicotinic receptor clustering. At the ultrastructural level, synaptic vesicles from nerve terminals treated with MßCD were larger than those from control. In addition, treatment with MßCD reduced the fusion of synaptic vesicles that are mobilized during KCl-evoked stimulation, but induced recycling of those vesicles that fuse spontaneously. We therefore suggest that MßCD might favor the release of vesicles that belong to a pool that is different from that involved in the KCl-evoked release. These results reveal fundamental differences in the synaptic vesicle cycle for spontaneous and evoked release, and suggest that deregulation of cholesterol affects synaptic vesicle biogenesis and increases transmitter packing.
Asunto(s)
Membrana Celular/fisiología , Colesterol/metabolismo , Unión Neuromuscular/fisiología , Vesículas Sinápticas/fisiología , Animales , Membrana Celular/efectos de los fármacos , Exocitosis/efectos de los fármacos , Exocitosis/fisiología , Microelectrodos , Microscopía Electrónica de Transmisión , Microscopía Fluorescente , Potenciales Postsinápticos Miniatura/efectos de los fármacos , Potenciales Postsinápticos Miniatura/fisiología , Fármacos Neuromusculares/farmacología , Unión Neuromuscular/efectos de los fármacos , Unión Neuromuscular/ultraestructura , Cloruro de Potasio/farmacología , Compuestos de Piridinio , Compuestos de Amonio Cuaternario , Rana catesbeiana , Receptores Nicotínicos/metabolismo , Vesículas Sinápticas/efectos de los fármacos , Vesículas Sinápticas/ultraestructura , Técnicas de Cultivo de Tejidos , beta-Ciclodextrinas/farmacologíaRESUMEN
We examined modification of sodium channel gating by Tityus bahiensis scorpion venom (TbScV), and compared effects on native tetrodotoxin-sensitive and tetrodotoxin-resistant sodium currents from rat dorsal root ganglion neurons and cardiac myocytes. In neurons, TbScV dramatically reduced the rate of sodium current inactivation, increased current amplitude, and caused a negative shift in the voltage-dependence of activation and inactivation of tetrodotoxin-sensitive channels. Enhanced activation of modified sodium channels was independent of a depolarizing prepulse. We identified two components of neuronal tetrodotoxin-resistant current with biophysical properties similar to those described for NaV1.8 and NaV1.9. In contrast to its effects on neuronal tetrodotoxin-sensitive current, TbScV caused a small decrease in neuronal tetrodotoxin-resistant sodium current amplitude and the gating modifications described above were absent. A third tetrodotoxin-resistant current, NaV1.5 recorded in rat cardiac ventricular myocytes, was inhibited approximately 50% by TbScV, and the remaining current exhibited markedly slowed activation and inactivation. In conclusion, TbScV has very different effects on different sodium channel isoforms. Among the neuronal types, currents resistant to tetrodotoxin are also resistant to gating modification by TbScV. The cardiac tetrodotoxin-resistant current has complex sensitivity that includes both inhibition of current amplitude and slowing of activation and inactivation.