RESUMO
There is substantial evidence that GABAB agonist, baclofen, prevents somatic and motivational responses induced by nicotine withdrawal and may target drug cue vulnerabilities in humans. In this context, we explored different aspects associated with the possible mechanisms whereby the GABAB receptors might influence nicotine withdrawal. Male mice received nicotine (2.5 mg/kg, s.c.) 4 times daily, for 7 consecutive days. Nicotine-treated mice received the nicotinic acetylcholine receptor antagonist, mecamylamine (MEC, 2 or 3.5 mg/kg, s.c.), to precipitate the withdrawal state. A second group of dependent mice received 2-hydroxysaclofen (GABAB receptor antagonist, 1 mg/kg, s.c.) before MEC-precipitated abstinence. Somatic signs of nicotine withdrawal were measured for 30 min. Anxiogenic-like response associated to nicotine withdrawal was assessed by the elevated plus maze test. The dysphoric/aversive effect induced by nicotine withdrawal was evaluated using conditioned place aversion paradigm. Dopamine, serotonin and its metabolites concentrations were determined by HPLC in the striatum, cortex and hippocampus. Finally, α4ß2 nicotinic acetylcholine receptor density was determined in several brain regions using autoradiography assays. The results showed that MEC-precipitated nicotine withdrawal induced somatic manifestations, anxiogenic-like response and dysphoric/aversive effect, and 2-hydroxysaclofen potentiated these behavioral responses. Additionally, 2-hydroxysaclofen was able to change striatal dopamine levels and α4ß2 nicotinic acetylcholine receptor density, both altered by MEC-precipitated nicotine withdrawal. These findings provide important contributions to elucidate neurobiological mechanisms implicated in nicotine withdrawal. We suggest that GABAB receptor activity is necessary to control alterations induced by nicotine withdrawal, which supports the idea of targeting GABAB receptors to treat tobacco addiction in humans.
Assuntos
Receptores de GABA-B/metabolismo , Síndrome de Abstinência a Substâncias/metabolismo , Animais , Baclofeno/análogos & derivados , Baclofeno/farmacologia , Comportamento Animal/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Dopamina/metabolismo , Antagonistas de Receptores de GABA-B/farmacologia , Masculino , Mecamilamina/farmacologia , Camundongos , Nicotina/farmacologia , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/metabolismoRESUMO
Previous studies showed that mecamylamine a noncompetitive and nonspecific blocker of nicotinic acetylcholine receptors (nAChRs), stimulates the activity of the dorsal raphe nucleus (DRN) serotonergic neurons and DRN serotonin (5-HT) release. In the present study, the mechanisms involved in these mecamylamine-induced effects were examined using electrophysiology and calcium-imaging studies, both performed in Wistar rat midbrain slices. Mecamylamine (0.5-9 µM), bath administered, increased the firing frequency of identified 5-HT DRN neurons by a maximum of 5% at 3 µM. This effect was accompanied by a 112 % increase in the frequency of spontaneous excitatory postsynaptic currents of 5-HT DRN neurons. It was blocked by the AMPA/kainate receptor blocker CNQX (10 µM) and by the specific α4ß2 nAChRs blocker dihydro-ß-erythroidine (100 nM) but was not affected by tetrodotoxin (TTX, 500 nM). Simultaneously, mecamylamine produced a 58 % decrease in the frequency of GABAergic spontaneous inhibitory postsynaptic currents, an effect that was not influenced by TTX. Calcium-imaging studies support the results obtained with the electrophysiological studies by showing that mecamylamine (3 µM) increases the activity of a cell population located in the midline of the DRN, which was sensitive to the inhibitory effects of 8-OH-DPAT, an agonist at 5-HT1A receptors. It is assumed that mecamylamine, in low concentrations, acts as an agonist of α4ß2 nAChRs present on the glutamatergic DRN terminals, thus increasing intra-raphe glutamate release. This stimulatory effect is reinforced by the decrease in DRN GABA release, which is dependent on the mecamylamine-induced blockade of α7 nAChRs located on DRN GABAergic terminals. We hypothesize that at least a part of mecamylamine antidepressant effects described in animal models of depression are mediated by an increase in DRN 5-HT release.
Assuntos
Potenciais de Ação/efeitos dos fármacos , Núcleo Dorsal da Rafe/efeitos dos fármacos , Bloqueadores Ganglionares/farmacologia , Mecamilamina/farmacologia , Neurônios Serotoninérgicos/efeitos dos fármacos , Animais , Cálcio/metabolismo , Núcleo Dorsal da Rafe/metabolismo , Masculino , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Neurônios Serotoninérgicos/metabolismoRESUMO
The nucleus of the solitary tract (NTS) is an important area of the brainstem that receives and integrates afferent cardiorespiratory sensorial information, including those from arterial chemoreceptors and baroreceptors. It was described that acetylcholine (ACh) in the commissural subnucleus of the NTS (cNTS) promotes an increase in the phrenic nerve activity (PNA) and antagonism of nicotinic receptors in the same region reduces the magnitude of tachypneic response to peripheral chemoreceptor stimulation, suggesting a functional role of cholinergic transmission within the cNTS in the chemosensory control of respiratory activity. In the present study, we investigated whether cholinergic receptor antagonism in the cNTS modifies the sympathetic and respiratory reflex responses to hypercapnia. Using an arterially perfused in situ preparation of juvenile male Holtzman rats, we found that the nicotinic antagonist (mecamylamine, 5 mM), but not the muscarinic antagonist (atropine, 5 mM), into the cNTS attenuated the hypercapnia-induced increase of hypoglossal activity. Furthermore, mecamylamine in the cNTS potentiated the generation of late-expiratory (late-E) activity in abdominal nerve induced by hypercapnia. None of the cholinergic antagonists microinjected in the cNTS changed either the sympathetic or the phrenic nerve responses to hypercapnia. Our data provide evidence for the role of cholinergic transmission in the cNTS, acting on nicotinic receptors, modulating the hypoglossal and abdominal responses to hypercapnia.
Assuntos
Neurônios Colinérgicos/fisiologia , Hipercapnia/metabolismo , Respiração , Transmissão Sináptica , Comissuras Telencefálicas/fisiologia , Animais , Atropina/farmacologia , Neurônios Colinérgicos/efeitos dos fármacos , Hipercapnia/fisiopatologia , Nervo Hipoglosso/fisiologia , Masculino , Mecamilamina/farmacologia , Agonistas Muscarínicos/farmacologia , Antagonistas Nicotínicos/farmacologia , Nervo Frênico/fisiologia , Ratos , Receptores Colinérgicos/metabolismo , Reflexo , Núcleo Solitário/fisiologia , Núcleo Solitário/fisiopatologia , Comissuras Telencefálicas/fisiopatologiaRESUMO
Repeated nicotine administration has been associated with increased paradoxical sleep in rats and antinociceptive properties, whereas paradoxical sleep deprivation (PSD) elicits pronociceptive and inflammatory responses. Thus, we aimed to evaluate the effect of repeated nicotine administration and its withdrawal combined with PSD on pain sensitivity and inflammatory markers. Sixty adult male Wistar rats were subjected to repeated injections of saline (SAL) or nicotine (NIC) for 12 days or 7 days of nicotine followed by acute mecamylamine administration on day 8 to precipitate nicotine abstinence (ABST). On day 9, the animals were submitted to PSD for 72 h or remained in control condition (CTRL); on day 12, thermal pain threshold was assessed by the hot plate test. PSD significantly decreased the latency to paw withdrawal in all groups compared to their respective controls. ABST-PSD animals presented higher levels of interleukin (IL)-6 compared to all groups, except ABST-CTRL. After adjustment for weight loss, IL-6, IL-4 and tumor necrosis factor alpha, ABST-PSD was associated with the lowest pain threshold. Nicotine and IL-4 levels were predictors of higher pain threshold. Hyperalgesia induced by PSD prevailed over the antinociceptive action of nicotine, while the association between PSD and ABST synergistically increased IL-6 concentrations and decreased pain threshold.
Assuntos
Nicotina/efeitos adversos , Limiar da Dor/efeitos dos fármacos , Privação do Sono/fisiopatologia , Animais , Hiperalgesia/complicações , Imunidade/efeitos dos fármacos , Interleucina-4/metabolismo , Interleucina-6/metabolismo , Masculino , Mecamilamina/farmacologia , Nicotina/farmacologia , Dor/complicações , Medição da Dor , Ratos , Ratos Wistar , Privação do Sono/complicações , Privação do Sono/metabolismo , Sono REM/fisiologia , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Previously we have demonstrated that microinjection of acetylcholine (ACh) into the intermediate nucleus of the solitary tract (iNTS) induced sympatho-inhibition combined with a decrease in the phrenic nerve activity (PNA), whereas in the commissural NTS (cNTS), ACh did not change sympathetic nerve activity (SNA), but increased the PNA. In view of these demonstrated distinctive effects of ACh in different subnuclei of the NTS the current studies were undertaken to examine, using patch clamp techniques, the specific effects of ACh on the excitability of individual neurons in the NTS, as well as the neuropharmacology of these actions. Coronal slices of the brainstem containing either cNTS or iNTS subnuclei were used, and whole cell patch clamp recordings obtained from individual neurons in these two subnuclei. In cNTS, 58% of recorded neurons (n=12) demonstrated rapid reversible depolarizations in response to ACh (10mM), effects which were inhibited by the nicotinic antagonist mecamylamine (10µM), but unaffected by the muscarinic antagonist atropine (10µM). Similarly, bath application of ACh depolarized 76% of iNTS neurons (n=17), although in this case both atropine and mecamylamine reduced the ACh-induced depolarization. These data demonstrate that ACh depolarizes cNTS neurons through actions on nicotinic receptors, while depolarizing effects in iNTS are apparently mediated by both receptors.
Assuntos
Antagonistas Colinérgicos/farmacologia , Antagonistas Muscarínicos/farmacologia , Neurônios/efeitos dos fármacos , Antagonistas Nicotínicos/farmacologia , Núcleo Solitário/efeitos dos fármacos , Acetilcolina/farmacologia , Animais , Atropina/farmacologia , Agonistas Colinérgicos/farmacologia , Masculino , Mecamilamina/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Neurônios/metabolismo , Técnicas de Patch-Clamp , Ratos Sprague-Dawley , Núcleo Solitário/metabolismo , Técnicas de Cultura de TecidosRESUMO
The hippocampus is a brain region that is rich in nicotinic acetylcholine receptors (nAChRs), especially the α7 subtype. The hippocampus is severely affected in disorders that have a neuroinflammatory component, such as Alzheimer's disease, Parkinson's disease, and schizophrenia. Previous studies demonstrated both in vivo and in vitro that nicotine inhibits immunological responses, including those that are triggered by the inflammatory agent lipopolysaccharide (LPS), the endotoxin of Gram-negative bacteria. The present study investigated whether chronically administered nicotine interferes with the nuclear binding of nuclear factor-κB (NF-κB) and the expression of LPS-induced inflammatory response genes. The results indicated that chronic nicotine administration (0.1mg/kg, s.c., 14days) inhibited the LPS-induced nuclear binding of NF-κB and mRNA expression levels of Tnf, Il1b, Nos2, and Tlr4. The presence of both the selective α7 nAChR antagonist methyllycaconitine (MLA; 5.0mg/kg i.p., 14days) and the nonselective nAChR antagonist mecamylamine (Meca; 1.0mg/kg, s.c., 14days) reversed the inhibitory effects of nicotine. These results suggest that the chronic activation of α7- and αxßy-containing nAChRs reduces acute inflammatory responses in the brain.
Assuntos
Hipocampo/efeitos dos fármacos , Lipopolissacarídeos/farmacologia , NF-kappa B/metabolismo , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Transdução de Sinais/efeitos dos fármacos , Receptor 4 Toll-Like/metabolismo , Aconitina/análogos & derivados , Aconitina/farmacologia , Animais , Hipocampo/metabolismo , Inflamação/metabolismo , Masculino , Mecamilamina/farmacologia , Ratos Wistar , Receptores Nicotínicos/metabolismoRESUMO
Post-ictal antinociception is characterised by an increase in the nociceptive threshold that accompanies tonic and tonic-clonic seizures (TCS). The locus coeruleus (LC) receives profuse cholinergic inputs from the pedunculopontine tegmental nucleus. Different concentrations (1µg, 3µg and 5µg/0.2µL) of the muscarinic cholinergic receptor antagonist atropine and the nicotinic cholinergic receptor antagonist mecamylamine were microinjected into the LC of Wistar rats to investigate the role of cholinergic mechanisms in the severity of TCS and the post-ictal antinociceptive response. Five minutes later, TCS were induced by systemic administration of pentylenetetrazole (PTZ) (64mg/kg). Seizures were recorded inside the open field apparatus for an average of 10min. Immediately after seizures, the nociceptive threshold was recorded for 130min using the tail-flick test. Pre-treatment of the LC with 1µg, 3µg and 5µg/0.2µL concentrations of both atropine and mecamylamine did not cause a significant effect on seizure severity. However, the same treatments decreased the post-ictal antinociceptive phenomenon. In addition, mecamylamine caused an earlier decrease in the post-ictal antinociception compared to atropine. These results suggest that muscarinic and mainly nicotinic cholinergic receptors of the LC are recruited to organise tonic-clonic seizure-induced antinociception.
Assuntos
Locus Cerúleo/metabolismo , Dor Nociceptiva/metabolismo , Receptores Muscarínicos/metabolismo , Receptores Nicotínicos/metabolismo , Convulsões/metabolismo , Transmissão Sináptica/fisiologia , Acetilcolina/metabolismo , Animais , Atropina/farmacologia , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Locus Cerúleo/efeitos dos fármacos , Masculino , Mecamilamina/farmacologia , Antagonistas Muscarínicos/farmacologia , Antagonistas Nicotínicos/farmacologia , Pentilenotetrazol , Ratos Wistar , Transmissão Sináptica/efeitos dos fármacosRESUMO
The aim of this study was to identify the effect of beta-adrenergic receptor activation on neutrophil migration in experimental peritonitis elucidating the neuroimmune components involved such as nicotinic receptors and the spleen. Mice pre-treated with mecamylamine (nicotinic antagonist) and propranolol (beta-adrenergic antagonist) or splenectomized animals were treated with isoproterenol (beta-adrenergic agonist) prior to intraperitoneal injection of carrageenan. After 4 h, the infiltrating neutrophils and the local cytokine/chemokine levels were evaluated in the peritoneal lavage. The effect of isoproterenol on neutrophil chemotaxis was investigated in a Boyden chamber. Isoproterenol inhibited neutrophil trafficking, reducing the cytokine/chemokine release and neutrophil chemotaxis. Surprisingly, the isoproterenol effect on neutrophil migration was totally reverted by splenectomy and mecamylamine pre-treatment. In contrast, the inhibitory effect of nicotine on neutrophil migration was abrogated only by splenectomy but not by propranolol pre-treatment. Collectively, our data show that beta-adrenergic receptor activation regulates the acute neutrophil recruitment via splenic nicotinic receptor.
Assuntos
Infiltração de Neutrófilos/efeitos dos fármacos , Receptores Adrenérgicos beta/metabolismo , Receptores Nicotínicos/metabolismo , Baço , Agonistas Adrenérgicos beta/farmacologia , Animais , Quimiotaxia de Leucócito/efeitos dos fármacos , Citocinas/análise , Isoproterenol/farmacologia , Mecamilamina/farmacologia , Camundongos , Antagonistas Nicotínicos/farmacologia , Peritonite , Baço/química , Baço/metabolismo , EsplenectomiaRESUMO
AIMS: There has been growing interest in the synthesis of new derivatives from isatin, found in Isatis genus. Our objectives were to characterize the antinociceptive mechanism of action of isatin, N-methyl-isatin (MI) and N-methyl-3-(2-oxopropyl)-3-hydroxy-2-oxindole (MOI). MATERIALS AND METHODS: Substances (0.1-10mg/kg, p.o.) were studied in chemical (paw licking induced by formalin, capsaicin or glutamate) or thermal (hot plate) models of nociception. The involvement of several systems was evaluated using different receptor antagonists. KEY FINDINGS: All three substances inhibit both phases of formalin-induced licking, increase the area under the curve and MI and MOI have a higher effect than that of morphine (in hot plate). Capsaicin and glutamate-induced licking were also reduced by all three substances. In the hot plate model, the antinociceptive effect of isatin was reduced by naloxone and atropine; naloxone, atropine and L-NAME reduced MI effect while naloxone, atropine, L-NAME, mecamylamine and ondansetron reduced MOI effect. SIGNIFICANCE: Our results suggest that isatin, MI and MOI: 1) present activity in models of nociception; 2) capsaicin and glutamate receptors seems to participate in the mechanism of action; 3) opioid, cholinergic, serotoninergic, nitrergic and adrenergic systems may be involved, at least in part, in the mechanism of action of some of these substances.
Assuntos
Analgésicos/farmacologia , Isatina/análogos & derivados , Isatina/farmacologia , Dor/tratamento farmacológico , Animais , Atropina/farmacologia , Relação Dose-Resposta a Droga , Isatina/uso terapêutico , Mecamilamina/farmacologia , Camundongos , Morfina/farmacologia , NG-Nitroarginina Metil Éster/farmacologia , Naloxona/farmacologia , Ondansetron/farmacologia , Medição da Dor/efeitos dos fármacosRESUMO
The dorsal raphe nucleus (DRN) is a key structure of the endogenous pain inhibitory system. Although the DRN is rich in serotoninergic neurons, cholinergic neurons are also found in that nucleus. Both ictal and inter-ictal states are followed by post-ictal analgesia. The present study investigated the role of cholinergic mechanisms in postictal antinociceptive processes using microinjections of atropine and mecamylamine, muscarinic and nicotinic cholinergic receptor antagonists, respectively, in the DRN of rats. Intraperitoneal injection of pentylenetetrazole (PTZ) (at 64mg/kg) caused tonic and tonic-clonic seizures. The convulsive motor reactions were followed by an increase in pain thresholds, a phenomenon known as post-ictal analgesia. Pre-treatment of the DRN with atropine or mecamylamine at 1µg, 3µg and 5µg/0.2µL decreased the post-ictal antinociceptive phenomenon. The present results showed that the post-ictal analgesia was mediated by muscarinic and nicotinic cholinergic receptors in the DRN, a structure crucially involved in the neural network that organises post-ictal hypoalgesia.