RESUMO
Serotonin (5-hydroxytryptamine, 5-HT) neurons are implicated in the etiology and therapeutics of anxiety and depression. Critical periods of vulnerability during brain development enable maladaptive mechanisms to produce detrimental consequences on adult mood and emotional responses. 5-HT plays a crucial role in these mechanisms; however, little is known about how synaptic inputs and modulatory systems that shape the activity of early 5-HT networks mature during postnatal development. We investigated in mice the postnatal trajectory of glutamate and GABA synaptic inputs to dorsal raphe nucleus (DRN) 5-HT neurons, the main source of forebrain 5-HT. High-resolution quantitative analyses with array tomography and ex vivo electrophysiology indicate that cortical glutamate and subcortical GABA synapses undergo a profound refinement process after the third postnatal week, whereas subcortical glutamate inputs do not. This refinement of DRN inputs is not accompanied by changes in 5-HT1A receptor-mediated inhibition over 5-HT neurons. Our study reveals a precise developmental pattern of synaptic refinement of DRN excitatory and inhibitory afferents, when 5-HT-related inhibitory mechanisms are in place. These findings contribute to the understanding of neurodevelopmental vulnerability to psychiatric disorders. This article has an associated 'The people behind the papers' interview.
Assuntos
Núcleo Dorsal da Rafe , Serotonina , Ratos , Camundongos , Animais , Ácido Glutâmico , Ratos Sprague-Dawley , Neurônios , Sinapses/fisiologia , Ácido gama-AminobutíricoRESUMO
RATIONALE: The abuse of psychostimulants has adverse consequences on the physiology of the central nervous system. In Argentina, and other South American countries, coca paste or "PACO" (cocaine and caffeine are its major components) is massively consumed with deleterious clinical consequences for the health and well-being of the general population. A scant number of studies have addressed the consequences of stimulant combination of cocaine and caffeine on the physiology of the somatosensory thalamocortical (ThCo) system. OBJECTIVES: Our aim was to study ion conductances that have important implications regulating sleep-wake states 24-h after an acute or chronic binge-like administration of a cocaine and caffeine mixture following previously analyzed pasta base samples ("PACO"-like binge") using mice. METHODS: We randomly injected (i.p.) male C57BL/6JFcen mice with a binge-like psychostimulants regimen during either 1 day (acute) or 1 day on/1 day off during 13 days for a total of 7 binges (chronic). Single-cell patch-clamp recordings of VB neurons were performed in thalamocortical slices 24 h after the last psychostimulant injection. We also recorded EEG/EMG from mice 24 h after being systemically treated with chronic administration of cocaine + caffeine versus saline, vehicle. RESULTS: Our results showed notorious changes in the intrinsic properties of the VB nucleus neurons that persist after 24-h of either acute or chronic binge administrations of combined cocaine and caffeine ("PACO"-like binge). Functional dysregulation of HCN (hyperpolarization-activated cyclic nucleotide-gated) and T-type VGC (voltage-gated calcium) channels was described 24-h after acute/chronic "PACO"-like administrations. Furthermore, intracellular basal [Ca2+] disturbances resulted a key factor that modulated the availability and the activation of T-type channels, altering T-type "window currents." As a result, all these changes ultimately shaped the low-threshold spikes (LTS)-associated Ca2+ transients, regulated the membrane excitability, and altered sleep-wake transitions. CONCLUSION: Our results suggest that deleterious consequences of stimulants cocaine and caffeine combination on the thalamocortical physiology as a whole might be related to potential neurotoxic effects of soaring intracellular [Ca2+].
Assuntos
Cafeína/efeitos adversos , Canais de Cálcio Tipo T/metabolismo , Estimulantes do Sistema Nervoso Central/efeitos adversos , Cocaína/efeitos adversos , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/metabolismo , Neurônios/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Animais , Cafeína/administração & dosagem , Estimulantes do Sistema Nervoso Central/administração & dosagem , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/metabolismo , Cocaína/administração & dosagem , Sinergismo Farmacológico , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Técnicas de Patch-Clamp , Distribuição Aleatória , Transtornos da Transição Sono-Vigília/induzido quimicamente , América do Sul , Tálamo/efeitos dos fármacos , Tálamo/metabolismoRESUMO
Leptin is an adipose-derived hormone that controls appetite and energy expenditure. Leptin receptors are expressed on extra-hypothalamic ventrobasal (VB) and reticular thalamic (RTN) nuclei from embryonic stages. Here, we studied the effects of pressure-puff, local application of leptin on both synaptic transmission and action potential properties of thalamic neurons in thalamocortical slices. We used whole-cell patch-clamp recordings of thalamocortical VB neurons from wild-type (WT) and leptin-deficient obese (ob/ob) mice. We observed differences in VB neurons action potentials and synaptic currents kinetics when comparing WT vs. ob/ob. Leptin reduced GABA release onto VB neurons throughout the activation of a JAK2-dependent pathway, without affecting excitatory glutamate transmission. We observed a rapid and reversible reduction by leptin of the number of action potentials of VB neurons via the activation of large conductance Ca2+-dependent potassium channels. These leptin effects were observed in thalamocortical slices from up to 5-week-old WT but not in leptin-deficient obese mice. Results described here suggest the existence of a leptin-mediated trophic modulation of thalamocortical excitability during postnatal development. These findings could contribute to a better understanding of leptin within the thalamocortical system and sleep deficits in obesity.
Assuntos
Potenciais de Ação/efeitos dos fármacos , Leptina/farmacologia , Neurônios/efeitos dos fármacos , Núcleos Talâmicos/citologia , Núcleos Talâmicos/metabolismo , Ácido gama-Aminobutírico/metabolismo , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Animais , Temperatura Corporal/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Janus Quinase 2/metabolismo , Leptina/deficiência , Leptina/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neurônios/fisiologia , Transdução de Sinais/efeitos dos fármacos , Bloqueadores dos Canais de Sódio/farmacologia , Potenciais Sinápticos/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Tetrodotoxina/farmacologia , Tirfostinas/farmacologiaRESUMO
The effects of adenosine on neurotransmission have been widely studied by monitoring transmitter release. However, the effects of adenosine on vesicle recycling are still unknown. We used fluorescence microscopy of FM2-10-labeled synaptic vesicles in combination with intracellular recordings to examine whether adenosine regulates vesicle recycling during high-frequency stimulation at mouse neuromuscular junctions. The A(1) adenosine receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine) increased the quantal content released during the first endplate potential, suggesting that vesicle exocytosis can be restricted by endogenous adenosine, which accordingly decreases the size of the recycling vesicle pool. Staining protocols designed to label specific vesicle pools that differ in their kinetics of release showed that all vesicles retrieved in the presence of 8-cyclopentyl-1,3-dipropylxanthine were recycled towards the fast-release pool, favoring its loading with FM2-10 and suggesting that endogenous adenosine promotes vesicle recycling towards the slow-release pool. In accordance with this effect, exogenous applied adenosine prevented the replenishment of the fast-release vesicle pool and, thus, hindered its loading with the dye. We had found that, during high-frequency stimulation, Ca(2+) influx through L-type channels directs newly formed vesicles to a fast-release pool (Perissinotti et al., 2008). We demonstrated that adenosine did not prevent the effect of the L-type blocker on transmitter release. Therefore, activation of the A(1) receptor promotes vesicle recycling towards the slow-release pool without a direct effect on the L-type channel. Further studies are necessary to elucidate the molecular mechanisms involved in the regulation of vesicle recycling by adenosine.
Assuntos
Adenosina/fisiologia , Junção Neuromuscular/metabolismo , Vesículas Sinápticas/metabolismo , Adenosina/antagonistas & inibidores , Animais , Masculino , Camundongos , Placa Motora/efeitos dos fármacos , Placa Motora/metabolismo , Junção Neuromuscular/efeitos dos fármacos , Terminações Pré-Sinápticas/efeitos dos fármacos , Terminações Pré-Sinápticas/metabolismo , Receptores Purinérgicos P1/metabolismo , Receptores Purinérgicos P1/fisiologia , Fatores de Tempo , Xantinas/farmacologiaRESUMO
The present work is aimed to establish, in Ctenomys talarum, the physiological and behavioral adjustments undergone by individuals when they are allowed to dig burrows in soils with different hardness and fed with diets of different quality. For each soil-diet combination, we estimated: resting metabolic rate (RMR), body temperature (T(b)), body mass, digestibility, food consumption rate, transit time, reingestion rate, feces production and time devoted to feeding, resting, locomotor activity and coprophagy. Soil type and diet quality affected RMR, but response to soil hardness was verified later. Animals fed with high quality (HQ) diet showed similar body temperature irrespective of soil condition, while animals fed with low quality (LQ) diet showed lower T(b) under soft soil (SS). Individuals fed with LQ diet showed lower RMR and both, lower digestibility and high transit time of food than those fed with HQ diet. Moreover, increments in feeding and defecation rates were observed in the former group. Number of reingested feces did not differ between animals fed with diets of different quality. However, when incidence of reingestion was considered, animals fed with HQ diet showed higher values of feces ingestion. Either feeding, resting and activity patterns were arrhythmic. However, for animals fed with LQ diet a tendency to rhythmic coprophagy was observed and it could be considered as a way to optimize feeding. This study shows that RMR is limited by digestive efficiency which is influenced by diet quality, but also thermal stress may limit the conversion of assimilated energy into work and heat.
Assuntos
Dieta , Meio Ambiente , Roedores/metabolismo , Solo , Animais , Metabolismo Basal , Comportamento Animal , Temperatura Corporal , Coprofagia , Digestão , Ingestão de Alimentos , Metabolismo Energético , Feminino , MasculinoRESUMO
We used fluorescence microscopy of FM dyes-labeled synaptic vesicles and electrophysiological recordings to examine the functional characteristics of vesicle recycling and study how different types of voltage-dependent Ca(2+) channels (VDCCs) regulate the coupling of exocytosis and endocytosis at mouse neuromuscular junction. Our results demonstrate the presence of at least two different pools of recycling vesicles: a high-probability release pool (i.e. a fast destaining vesicle pool), which is preferentially loaded during the first 5 s (250 action potentials) at 50 Hz; and a low-probability release pool (i.e. a slow destaining vesicle pool), which is loaded during prolonged stimulation and keeps on refilling after end of stimulation. Our results suggest that a fast recycling pool mediates neurotransmitter release when vesicle use is minimal (i.e. during brief high-frequency stimulation), while vesicle mobilization from a reserve pool is the prevailing mechanism when the level of synaptic activity increases. We observed that specific N- and L-type VDCC blockers had no effect on evoked transmitter release upon low-frequency stimulation (5 Hz). However, at high-frequency stimulation (50 Hz), L-type Ca(2+) channel blocker increased FM2-10 destaining and at the same time diminished quantal release. Furthermore, when L-type channels were blocked, FM2-10 loading during stimulation was diminished, while the amount of endocytosis after stimulation was increased. Our experiments suggest that L-type VDCCs promote endocytosis of synaptic vesicles, directing the newly formed vesicles to a high-probability release pool where they compete against unused vesicles.