RESUMO
The association between schizophrenia and nicotine addiction becomes evident during adolescence. Here, to investigate interactive events that might underlie the early establishment of this comorbidity, we used phencyclidine-evoked locomotor sensitization, a proxy model of psychotic behavior, and nicotine minipump infusions in adolescent mice. Considering the involvement of dopamine D2 receptors in both schizophrenia and addiction, we further tested their role by exposing mice to raclopride. Adolescent mice that were either exposed to nicotine (24 mg/Kg/day) or not, received single daily raclopride (0.5 mg/kg, s.c.) or saline followed by phencyclidine injections (10 mg/Kg, s.c.) during open field testing for 6 consecutive days (Acquisition phase, ACQ). Phencyclidine and nicotine challenges (Sensitization Test, ST) were carried out after a 5-day withdrawal. Ambulation escalated in response to repeated phencyclidine exposure during ACQ and was increased after phencyclidine challenge, evidencing development and expression of locomotor sensitization. Raclopride prevented phencyclidine-evoked development of sensitization. However, raclopride pre-exposure during ACQ only shortened its expression in phencyclidine-challenged mice. Nicotine failed to interfere with phencyclidine stimulatory effects during ACQ but potentiated raclopride inhibition during the first ACQ days. During ST, nicotine history shortened the expression of phencyclidine-evoked sensitization. Nicotine challenge had no impact on locomotion, which is consistent with a lack of nicotine/phencyclidine cross-sensitization. In conclusion, our results show that nicotine does not worsen, and may even ameliorate phencyclidine-sensitized psychotic-like behavior in adolescent mice. The potentiation of raclopride-mediated inhibition further suggests that nicotine transiently improves the therapeutic efficacy of medication on psychotic symptoms through mechanisms that converge on D2 receptors.
Assuntos
Nicotina , Fenciclidina , Camundongos , Animais , Fenciclidina/toxicidade , Nicotina/toxicidade , Racloprida/farmacologia , Locomoção , Atividade Motora , Receptores DopaminérgicosRESUMO
Ketamine has addictive potential, a troublesome fact due to its promising use as a therapeutic drug. An important phenomenon associated with drug addiction is behavioral sensitization, usually characterized as augmented locomotion. However, other behaviors may also be susceptible to sensitization, and/or interfere with locomotor activity. Thus, this study drew a comprehensive behavioral 'profiling' in an animal model of repeated administration of ketamine. Adult Swiss mice received single daily ketamine injections (30 or 50â¯mg/Kg, i.p.), which were followed by open field testing for 7â¯days (acquisition period, ACQ). A ketamine challenge (sensitization test, ST) was carried out after a 5-day withdrawal. Locomotion, rearing, grooming, rotation and falling were assessed during ACQ and ST. All behaviors were affected from the first ACQ day onwards, with no indication of competition between locomotion and the other behaviors. Only locomotion in response to 30â¯mg/Kg of ketamine both escalated during ACQ and expressed increased levels at ST, evidencing development and expression of locomotor sensitization. Considering the involvement of serotonin 5HT(2) and dopamine D(2) receptors on addiction mechanisms, we further tested the involvement of these receptors in ketamine-induced sensitization. Ketanserin (5HT2 antagonist, 3â¯mg/Kg, s.c.) prevented ketamine-evoked development of locomotor sensitization. However, ketanserin pretreatment during ACQ failed to inhibit its expression during ST. Raclopride (D2 antagonist, 0.5â¯mg/Kg, s.c.) evoked less robust reductions in locomotion but prevented the development of ketamine-evoked sensitization. Pretreatment during ACQ further inhibited the expression of sensitization during ST. These results indicate that a partial overlap in serotonergic and dopaminergic mechanisms underlies ketamine-induced locomotor sensitization.
Assuntos
Sensibilização do Sistema Nervoso Central/efeitos dos fármacos , Ketamina/farmacologia , Locomoção/efeitos dos fármacos , Receptores de Dopamina D2/fisiologia , Receptores 5-HT2 de Serotonina/fisiologia , Animais , Relação Dose-Resposta a Droga , Feminino , Ketamina/antagonistas & inibidores , Ketanserina/farmacologia , Masculino , Camundongos , Racloprida/farmacologia , Comportamento Estereotipado/efeitos dos fármacosRESUMO
The sensory nervous system controls cardiovascular homeostasis via capsaicin-sensitive neurons that release calcitonin gene-related peptide (CGRP), which subsequently activates CGRP receptors. How this perivascular CGRPergic discharge is modulated, nevertheless, remains unclear. In pithed rats, systemic vasodilation induced by CGRPergic discharge stimulation results in diastolic blood pressure (BP) decrements that are inhibited by the dopamine D2-like receptor agonist quinpirole. Since this inhibition is mediated by raclopride- or haloperidol-sensitive D2-like receptors (comprising the D2, D3, and D4 subtypes), the present study pharmacologically investigated the specific contribution of these subtypes to the modulation of the systemic CGRPergic vasodilation, using highly specific antagonists. To that end, 55 male Wistar rats were pithed for thoracic (T9-T12) spinal stimulation of the perivascular CGRPergic discharge. The resulting frequency-dependent decrements in diastolic BP were inhibited by quinpirole, and this sensory-inhibition was (a) unchanged after i.v. injections of the antagonists L-741,626 (D2) or L-745,870 (D4) and (b) completely blocked by SB-277011-A (D3). Accordingly, we suggest the main role of the D3 receptor subtypes in the inhibition by quinpirole of the neurogenic CGRPergic systemic vasodilation. These findings contribute to a better understanding of the dopaminergic modulation of the rat perivascular CGRPergic discharge producing systemic vasodilation.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Agonistas de Dopamina/farmacologia , Frequência Cardíaca/fisiologia , Receptores de Dopamina D3/antagonistas & inibidores , Vasodilatação/efeitos dos fármacos , Animais , Estimulação Elétrica , Frequência Cardíaca/efeitos dos fármacos , Masculino , Quimpirol/farmacologia , Racloprida/farmacologia , Ratos , Ratos WistarRESUMO
Toluene is an organic solvent commonly misused by inhalation among adolescents to experience psychoactive effects. Repeated toluene exposure produces several cognitive deficits, including working memory impairment in which the medial prefrontal cortex (mPFC) plays a central role. Among other effects, toluene antagonizes NMDA receptors, enhance GABAA receptor-mediated responses and increases dopamine release. We have recently reported that animals repeatedly exposed to toluene show increased mPFC excitability; however, alterations in synaptic transmission, including long-term synaptic plasticity of glutamatergic responses have not been studied thus far. Here we used extracellular recordings to determine the effects of repeated toluene exposure (8000â¯ppm for 30â¯min, twice a day, for ten days) on the synaptic transmission converging on prelimbic layer 5 pyramidal neurons of the mPFC in adolescent male Wistar rats. Repeated toluene exposure increased mPFC's synaptic strength and reduced the inhibitory transmission assessed by input-output curves and paired-pulse inhibition protocols, respectively. Both toluene and a selective D1 receptor antagonist blocked the ability of exogenous dopamine to induce synaptic potentiation. Repeated toluene exposure also altered the ability of NMDA to induce synaptic depression of excitatory transmission. Taken together, the changes in synaptic strength and impairment of the NMDA-mediated plasticity of the mPFC demonstrate a series of synaptic modifications of the glutamatergic transmission that may underlie the cognitive impairment resulting from repeated toluene exposure.
Assuntos
Córtex Pré-Frontal/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Tolueno/toxicidade , Animais , Dopamina/metabolismo , Ácido Glutâmico/metabolismo , Ácido Cinurênico/farmacologia , Masculino , N-Metilaspartato/metabolismo , Plasticidade Neuronal/efeitos dos fármacos , Picrotoxina/farmacologia , Racloprida/farmacologia , Ratos , Ratos WistarRESUMO
METH use causes neuroadaptations that negatively impact the prefrontal cortex (PFC) leading to addiction and associated cognitive decline in animals and humans. In contrast, modafinil enhances cognition by increasing PFC function. Accumulated evidence indicates that psychostimulant drugs, including modafinil and METH, regulate gene expression via epigenetic modifications. In this study, we measured the effects of single-dose injections of modafinil and METH on the protein levels of acetylated histone H3 (H3ac) and H4ac, deacetylases HDAC1 and HDAC2, and of the NMDA subunit GluN1 in the medial PFC (mPFC) of mice euthanized 1â¯h after drug administration. To test if dopamine (DA) receptors (DRs) participate in the biochemical effects of the two drugs, we injected the D1Rs antagonist, SCH23390, or the D2Rs antagonist, raclopride, 30â¯min before administration of METH and modafinil. We evaluated each drug effect on glutamate synaptic transmission in D1R-expressing layer V pyramidal neurons. We also measured the enrichment of H3ac and H4ac at the promoters of several genes including DA, NE, orexin, histamine, and glutamate receptors, and their mRNA expression, since they are responsive to chronic modafinil and METH treatment. Acute modafinil and METH injections caused similar effects on total histone acetylation, increasing H3ac and decreasing H4ac, and they also increased HDAC1, HDAC2 and GluN1 protein levels in the mouse mPFC. In addition, the effects of the drugs were prevented by pre-treatment with D1Rs and D2Rs antagonists. Specifically, the changes in H4ac, HDAC2, and GluN1 were responsive to SCH23390, whereas those of H3ac and GluN1 were responsive to raclopride. Whole-cell patch clamp in transgenic BAC-Drd1a-tdTomato mice showed that METH, but not modafinil, induced paired-pulse facilitation of EPSCs, suggesting reduced presynaptic probability of glutamate release onto layer V pyramidal neurons. Analysis of histone 3/4 enrichment at specific promoters revealed: i) distinct effects of the drugs on histone 3 acetylation, with modafinil increasing H3ac at Drd1 and Adra1b promoters, but METH increasing H3ac at Adra1a; ii) distinct effects on histone 4 acetylation enrichment, with modafinil increasing H4ac at the Drd2 promoter and decreasing it at Hrh1, but METH increasing H4ac at Drd1; iii) comparable effects of both psychostimulants, increasing H3ac at Drd2, Hcrtr1, and Hrh1 promoters, decreasing H3ac at Hrh3, increasing H4ac at Hcrtr1, and decreasing H4ac at Hcrtr2, Hrh3, and Grin1 promoters. Interestingly, only METH altered mRNA levels of genes with altered histone acetylation status, inducing increased expression of Drd1a, Adra1a, Hcrtr1, and Hrh1, and decreasing Grin1. Our study suggests that although acute METH and modafinil can both increase DA neurotransmission in the mPFC, there are similar and contrasting epigenetic and transcriptional consequences that may account for their divergent clinical effects.
Assuntos
Estimulantes do Sistema Nervoso Central/farmacologia , Epigênese Genética/efeitos dos fármacos , Metanfetamina/farmacologia , Modafinila/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Receptores Dopaminérgicos/metabolismo , Animais , Benzazepinas/farmacologia , Imunoprecipitação da Cromatina , Dopaminérgicos/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Histona Desacetilase 1/genética , Histona Desacetilase 1/metabolismo , Histonas/genética , Histonas/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Técnicas de Patch-Clamp , Córtex Pré-Frontal/citologia , Racloprida/farmacologia , Receptores de Amina Biogênica/genética , Receptores de Amina Biogênica/metabolismo , Receptores Dopaminérgicos/genéticaRESUMO
It has been suggested that N,N-di-n-propyl-dopamine (dopamine analogue) decreased heart rate in rats through stimulation of dopamine receptors. Nevertheless, the role of prejunctional dopamine D1/2-like receptors or even α2-adrenoceptors to mediate cardiac sympatho-inhibition induced by dopamine remains unclear. Hence, this study identified the pharmacological profile of the cardiac sympatho-inhibition to dopamine in pithed rats. Male Wistar rats were pithed and prepared to stimulate the cardiac sympathetic outflow or to receive i.v. bolus of exogenous noradrenaline. I.v. continuous infusions of dopamine (endogenous ligand) or quinpirole (D2-like agonist) dose-dependently inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline. In contrast, SKF-38393 (100 µg/kgâmin, D1-like agonist) failed to modify both of these responses. The sympatho-inhibition to dopamine (1.8 µg/kgâmin) or quinpirole (100 µg/kgâmin): i) remained unaltered after saline or the antagonists SCH-23390 (D1-like, 300 µg/kg) and rauwolscine (α2-adrenoceptors, 300 µg/kg); and ii) was significantly antagonized by raclopride (D2-like, 300 µg/kg). These antagonists, at the above doses, failed to modify the sympathetically-induced tachycardic responses. The above results suggest that the inhibition of the cardiac sympathetic outflow to dopamine and quinpirole is primarily mediated by prejunctional D2-like receptors but not D1-like receptors or α2-adrenoceptors.
Assuntos
Sistema Cardiovascular/efeitos dos fármacos , Sistema Cardiovascular/fisiopatologia , Estado de Descerebração/fisiopatologia , Dopamina/farmacologia , Receptores de Dopamina D2/efeitos dos fármacos , Receptores de Dopamina D2/fisiologia , Sistema Nervoso Simpático/fisiopatologia , 2,3,4,5-Tetra-Hidro-7,8-Di-Hidroxi-1-Fenil-1H-3-Benzazepina/farmacologia , Animais , Benzazepinas/antagonistas & inibidores , Benzazepinas/farmacologia , Relação Dose-Resposta a Droga , Frequência Cardíaca/efeitos dos fármacos , Masculino , Quimpirol/farmacologia , Racloprida/farmacologia , Ratos , Ratos Wistar , Sistema Nervoso Simpático/efeitos dos fármacos , Taquicardia/fisiopatologia , Ioimbina/antagonistas & inibidores , Ioimbina/farmacologiaRESUMO
Amygdaloid dopamine D(2) receptors play an important role in the modulation of fear/anxiety. Their topographical distribution within the amygdala is however unclear, and their role in unconditioned fear/anxiety remains largely unknown. The aim of this paper was to study the intra-amygdaloid distribution of D(2) receptors and to ascertain their role in unconditioned anxiety. Chemical anatomical studies in the rat, using D(2) and D(3)in situ hybridization, quantitative receptor autoradiography with either [(3)H]raclopride or [(125)I]sulpiride, and D(2)-like immunocytochemistry showed that the highest density of dopamine D(2) receptors is present in the central amygdaloid nucleus, particularly within its latero-capsular division, in which a D(2) but not a D(3) mRNA signal was observed. However, although at considerably reduced densities dopamine D(2) receptors were also found in other locations within the amygdala, including the basolateral nucleus. Behaviorally, the infusion of raclopride (0.75-4 µg/side) in the area of the central amygdaloid nucleus resulted at low doses in the appearance of anxiogenic-like effects in the Shock-Probe Burying test, whereas no effects of raclopride treatment were found at any dose in the Elevated Plus-Maze and the Open-Field test. Our results indicate that amygdaloid dopamine D(2)-like receptors have a topographically differentiated distribution within the rat amygdala, the major location being in the central amygdaloid nucleus. D(2)-like receptors play a role in the modulation of anxiety responses involving a potential differential function of D(2)-like receptors in the central amygdaloid nucleus versus the basolateral amygdaloid nucleus.
Assuntos
Tonsila do Cerebelo/metabolismo , Ansiedade/patologia , Condicionamento Psicológico/fisiologia , Medo , Regulação da Expressão Gênica/fisiologia , Receptores de Dopamina D2/metabolismo , Tonsila do Cerebelo/efeitos dos fármacos , Análise de Variância , Animais , Ansiedade/metabolismo , Autorradiografia , Antagonistas de Dopamina/farmacologia , Relação Dose-Resposta a Droga , Eletrochoque/efeitos adversos , Comportamento Exploratório/efeitos dos fármacos , Regulação da Expressão Gênica/efeitos dos fármacos , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , RNA Mensageiro/metabolismo , Racloprida/farmacologia , Ratos , Ratos Wistar , Receptores de Dopamina D2/genética , Receptores de Dopamina D3/genética , Receptores de Dopamina D3/metabolismoRESUMO
The role of dopamine receptors in regulating the formation of recognition memory remains poorly understood. Here we show the effects of systemic administration of dopamine receptor agonists and antagonists on the formation of memory for novel object recognition in rats. In Experiment I, rats received an intraperitoneal (i.p.) injection of vehicle, the selective D1 receptor agonist SKF38393 (1.0 and 5.0mg/kg), or the D2 receptor agonist quinpirole (1.0 and 5.0mg/kg) immediately after training. In Experiment II, rats received an injection of vehicle, the dopamine receptor antagonist SCH23390 (0.1 and 0.05 mg/kg), or the D2 receptor antagonist raclopride (0.5 and 0.1mg/kg) before training, followed by an injection of vehicle or the nonselective dopamine receptor agonist apomorphine (0.05 mg/kg) immediately after training. SKF38393 at 5mg/kg produced an enhancement of novel object recognition memory measured at both 24 and 72 h after training, whereas the dose of 10mg/kg impaired 24-h retention. Posttraining administration of quinpirole did not affect 24-h retention. Apomorphine enhanced memory in rats given pretraining raclopride, suggesting that the effect was mediated by selective activation of D1 receptors. The results indicate that activation of D1 receptors can enhance recognition memory consolidation. Importantly, pharmacological activation of D1 receptors enhanced novel object recognition memory even under conditions in which control rats showed significant retention.
Assuntos
Receptores de Dopamina D1/metabolismo , Receptores de Dopamina D2/metabolismo , Reconhecimento Psicológico/fisiologia , Retenção Psicológica/fisiologia , 2,3,4,5-Tetra-Hidro-7,8-Di-Hidroxi-1-Fenil-1H-3-Benzazepina/farmacologia , Análise de Variância , Animais , Apomorfina/farmacologia , Benzazepinas/farmacologia , Dopaminérgicos/farmacologia , Antagonistas dos Receptores de Dopamina D2 , Relação Dose-Resposta a Droga , Comportamento Exploratório/efeitos dos fármacos , Comportamento Exploratório/fisiologia , Masculino , Quimpirol/farmacologia , Racloprida/farmacologia , Ratos , Ratos Wistar , Receptores de Dopamina D1/agonistas , Receptores de Dopamina D1/antagonistas & inibidores , Receptores de Dopamina D2/agonistas , Reconhecimento Psicológico/efeitos dos fármacos , Retenção Psicológica/efeitos dos fármacos , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Estatísticas não Paramétricas , Fatores de TempoRESUMO
BACKGROUND: Fear extinction is dependent on plasticity in the infralimbic prefrontal cortex, an area heavily innervated by midbrain dopaminergic inputs. Dopamine D2 receptors are concentrated in infralimbic output neurons that are involved in the suppression of conditioned fear after extinction. Here, we examined the specific role of infralimbic D2 receptors in mediating associative learning underlying fear extinction using the selective D2 antagonist raclopride. METHODS: Raclopride was administered systemically or infused into the infralimbic prefrontal cortex before fear extinction, and extinction retention was tested the following day. Rats were also prepared for single-unit recording in the infralimbic prefrontal cortex to assess the effect of raclopride on firing properties. RESULTS: We found that systemic injection of raclopride given before extinction impaired retrieval of extinction when rats were tested drug-free the next day but also induced catalepsy during extinction training. To determine whether impaired extinction was due to impaired motor function or disruption of extinction consolidation, we infused raclopride directly into the infralimbic prefrontal cortex. Raclopride infused immediately before extinction training did not produce motor deficits but impaired recall of extinction when tested drug-free. Furthermore, in animals that underwent extinction training, systemic raclopride reduced the tone responsiveness of infralimbic prefrontal cortex neurons in layers 5/6, with no changes in average firing rate. CONCLUSIONS: We suggest that D2 receptors facilitate extinction by increasing the signal-to-noise of infralimbic prefrontal cortex neurons that consolidate extinction.
Assuntos
Condicionamento Psicológico/fisiologia , Extinção Psicológica/fisiologia , Medo/fisiologia , Sistema Límbico/metabolismo , Córtex Pré-Frontal/metabolismo , Receptores de Dopamina D2/metabolismo , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Condicionamento Psicológico/efeitos dos fármacos , Antagonistas de Dopamina/farmacologia , Extinção Psicológica/efeitos dos fármacos , Medo/efeitos dos fármacos , Sistema Límbico/efeitos dos fármacos , Masculino , Atividade Motora/efeitos dos fármacos , Atividade Motora/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Córtex Pré-Frontal/efeitos dos fármacos , Racloprida/farmacologia , Ratos , Ratos Sprague-DawleyRESUMO
Accumulating evidence points to the mesolimbic and the nigrostriatal dopamine systems as critical to behavioral sensitization induced by several drugs of abuse. In the present study, we analyzed D1 and D2 binding to brain regions related to these dopaminergic systems during the expression of ethanol-induced behavioral sensitization. The first experiment was performed to demonstrate the effectiveness of the ethanol treatment schedule and challenge used to induce the expression of the behavioral sensitization phenomenon. The second experiment was conducted to study D1 and D2 alterations in several brain regions during the expression of this phenomenon. Mice were ip treated with ethanol or saline for 21 consecutive days and 24 h after the last injection they received an ethanol or a saline challenge injection. Five minutes later, the animals were observed in an open-field for locomotion quantification or were sacrificed and their brains were submitted to autoradiographic binding analyses. No differences among the groups were found for D1 binding levels in all the brain regions analyzed. However, ethanol-sensitized mice showed reduced levels of D2 binding in the olfactory tubercle when compared to the other groups. Our data suggest that D2 receptor changes in the olfactory tubercle seem to play an important role in the expression of ethanol-induced behavioral sensitization.