RESUMO
Amphetamines (AMPH) are psychostimulants widely used for therapy as well as for recreational purposes. Previous results of our group showed that AMPH exposure in pregnant rats induces physiological and behavioral changes in the offspring at prepubertal and postpubertal ages. In addition, several reports have shown that AMPH are capable of modifying the morphology of neurons in some regions of the limbic system. These modifications can cause some psychiatric conditions. However, it is still unclear if there are changes to behavioral and morphological levels when low doses of AMPH are administered at a juvenile age. The aim of this study was to assess the effect of AMPH administration (1mg/kg) in Sprague-Dawley rats (postnatal day, PD21-PD35) on locomotor activity in a novel environment and compare the neuronal morphology of limbic system areas at three different ages: prepubertal (PD 36), pubertal (PD50) and postpubertal (PD 62). We found that AMPH altered locomotor activity in the prepubertal group, but did not have an effect on the other two age groups. The Golgi-Cox staining method was used to describe the neural morphology of five limbic regions: (Layers 3 and 5) the medial prefrontal cortex (mPFC), the dorsal and ventral hippocampus, the nucleus accumbens and the amygdala, showing that AMPH induced changes at pubertal ages in arborization and spine density of these neurons, but interestingly these changes did not persist at postpubertal ages. Our findings suggest that even early-life AMPH exposure does not induce long-term behavioral and morphological changes, however it causes alterations at pubertal ages in the limbic system networks, a stage of life strongly associated with the development of substance abuse behaviors.
Assuntos
Anfetamina/farmacologia , Estimulantes do Sistema Nervoso Central/farmacologia , Sistema Límbico/citologia , Sistema Límbico/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/ultraestrutura , Envelhecimento , Animais , Espinhas Dendríticas/efeitos dos fármacos , Espinhas Dendríticas/ultraestrutura , Feminino , Sistema Límbico/crescimento & desenvolvimento , Masculino , Atividade Motora/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Maturidade SexualRESUMO
MK801 is a prototypical non-competitive NMDA receptor-antagonist that induces behavioural changes and reversible toxicity at low doses, while at higher doses triggers neuronal death that mainly affects the retrosplenial cortex (RSC) and to a lesser extent other structures such as the posterolateral cortical amygdaloid nucleus (PLCo). The mechanism of MK801-induced neurodegeneration remains poorly understood. In this study we analysed the participation of GABA-ergic and glutamatergic neurotransmission in MK801-induced neuronal death. We used a single i.p. injection of MK801 (2.5 mg/kg) that induced moderate neuronal death in the RSC and PLCo of female rats, and combined this treatment with the i.p., i.c.v., or intra-RSC infusion of drugs that are selective agonists or antagonists of the GABA-ergic or glutamatergic neurotransmission. We found that neuronal death in the RSC, but not the PLCo, was significantly reduced by the i.p. injection of thiopental, and the i.c.v. application of muscimol, both GABA-A agonists. MK801-toxicity in RSC was abrogated by intra-RSC infusion of muscimol, but the GABA antagonist picrotoxin had no effect. HPLC-analysis showed that levels of glutamate, but not GABA, in the RSC decreased after i.p. treatment with MK801. Intra-RSC infusion of MK801 did not enhance toxicity triggered by the i.p. injection of MK801, indicating that toxicity is not due to direct blockade of NMDA receptors in RSC neurons. MK801-toxicity in the RSC was abrogated by i.c.v. and intra-RSC infusions of the AMPA/kainate antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). Interestingly, i.c.v. application of neither muscimol or DNQX inhibited MK801-toxicity in the PLCo, suggesting that the mechanism of neuronal death in the RSC and the PLCo might be different. 1-naphthylacetyl spermine trihydrochloride (NASPM), which blocks Ca2+ permeable AMPA/kainate receptors, also reduced MK801-induced toxicity in the RSC. Intra-RSC infusion of AMPA or kainic acid alone promoted death of RSC neurons and was reminiscent of the degeneration induced by the i.p. treatment with MK801. Collectively, these experiments provide evidence for an AMPA/kainate-dependent mechanism of excitotoxicity in the death of RSC neurons after i.p. treatment with MK801.
Assuntos
Córtex Cerebral/efeitos dos fármacos , Maleato de Dizocilpina/farmacologia , Sistema Límbico/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Receptores de AMPA/fisiologia , Receptores de Ácido Caínico/fisiologia , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Tonsila do Cerebelo/citologia , Tonsila do Cerebelo/efeitos dos fármacos , Tonsila do Cerebelo/metabolismo , Animais , Morte Celular/efeitos dos fármacos , Córtex Cerebral/citologia , Córtex Cerebral/metabolismo , Feminino , Ácido Glutâmico/fisiologia , Ácido Caínico/farmacologia , Sistema Límbico/citologia , Sistema Límbico/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Ratos , Ratos Wistar , Receptores de AMPA/agonistas , Receptores de AMPA/antagonistas & inibidores , Receptores de Ácido Caínico/agonistas , Receptores de Ácido Caínico/antagonistas & inibidores , Transmissão Sináptica , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/farmacologia , Ácido gama-Aminobutírico/fisiologiaRESUMO
Intrahippocampal administration of kainic acid (KA) induces synaptic release of neurotrophins, mainly brain-derived neurotrophic factor, which contributes to the acute neuronal excitation produced by the toxin. Two protein tyrosine kinase inhibitors, herbimycin A and K252a, were administered intracerebroventricularly, in a single dose, to attenuate neurotrophin signaling during the acute effects of KA, and their role in epileptogenesis was evaluated in adult, male Wistar rats weighing 250-300 g. The latency for the first Racine stage V seizure was 90 +/- 8 min in saline controls (N = 4) which increased to 369 +/- 71 and 322 +/- 63 min in animals receiving herbimycin A (1.74 nmol, N = 4) and K252a (10 pmol, N = 4), respectively. Behavioral alterations were accompanied by diminished duration of EEG paroxysms in herbimycin A- and K252a-treated animals. Notwithstanding the reduction in seizure severity, cell death (60-90% of cell loss in KA-treated animals) in limbic regions was unchanged by herbimycin A and K252a. However, aberrant mossy fiber sprouting was significantly reduced in the ipsilateral dorsal hippocampus of K252a-treated animals. In this model of temporal lobe epilepsy, both protein kinase inhibitors diminished the acute epileptic activity triggered by KA and the ensuing morphological alterations in the dentate gyrus without diminishing cell loss. Our current data indicating that K252a, but not herbimycin, has an influence over KA-induced mossy fiber sprouting further suggest that protein tyrosine kinase receptors are not the only factors which control this plasticity. Further experiments are necessary to elucidate the exact signaling systems associated with this K252a effect.
Assuntos
Benzoquinonas/farmacologia , Carbazóis/farmacologia , Epilepsia do Lobo Temporal/fisiopatologia , Alcaloides Indólicos/farmacologia , Ácido Caínico/antagonistas & inibidores , Lactamas Macrocíclicas/farmacologia , Fibras Musgosas Hipocampais/efeitos dos fármacos , Proteínas Tirosina Quinases/antagonistas & inibidores , Análise de Variância , Animais , Morte Celular/efeitos dos fármacos , Morte Celular/fisiologia , Eletroencefalografia , Inibidores Enzimáticos/farmacologia , Epilepsia do Lobo Temporal/induzido quimicamente , Epilepsia do Lobo Temporal/patologia , Agonistas de Aminoácidos Excitatórios/farmacologia , Ácido Caínico/farmacologia , Sistema Límbico/citologia , Sistema Límbico/efeitos dos fármacos , Masculino , Fibras Musgosas Hipocampais/patologia , Fibras Musgosas Hipocampais/fisiopatologia , Fatores de Crescimento Neural/metabolismo , Ratos , Ratos Wistar , Rifabutina/análogos & derivados , Convulsões/fisiopatologia , Estatísticas não ParamétricasRESUMO
Intrahippocampal administration of kainic acid (KA) induces synaptic release of neurotrophins, mainly brain-derived neurotrophic factor, which contributes to the acute neuronal excitation produced by the toxin. Two protein tyrosine kinase inhibitors, herbimycin A and K252a, were administered intracerebroventricularly, in a single dose, to attenuate neurotrophin signaling during the acute effects of KA, and their role in epileptogenesis was evaluated in adult, male Wistar rats weighing 250-300 g. The latency for the first Racine stage V seizure was 90 ± 8 min in saline controls (N = 4) which increased to 369 ± 71 and 322 ± 63 min in animals receiving herbimycin A (1.74 nmol, N = 4) and K252a (10 pmol, N = 4), respectively. Behavioral alterations were accompanied by diminished duration of EEG paroxysms in herbimycin A- and K252a-treated animals. Notwithstanding the reduction in seizure severity, cell death (60-90 percent of cell loss in KA-treated animals) in limbic regions was unchanged by herbimycin A and K252a. However, aberrant mossy fiber sprouting was significantly reduced in the ipsilateral dorsal hippocampus of K252a-treated animals. In this model of temporal lobe epilepsy, both protein kinase inhibitors diminished the acute epileptic activity triggered by KA and the ensuing morphological alterations in the dentate gyrus without diminishing cell loss. Our current data indicating that K252a, but not herbimycin, has an influence over KA-induced mossy fiber sprouting further suggest that protein tyrosine kinase receptors are not the only factors which control this plasticity. Further experiments are necessary to elucidate the exact signaling systems associated with this K252a effect.
Assuntos
Animais , Masculino , Ratos , Benzoquinonas/farmacologia , Carbazóis/farmacologia , Epilepsia do Lobo Temporal/fisiopatologia , Alcaloides Indólicos/farmacologia , Ácido Caínico/antagonistas & inibidores , Lactamas Macrocíclicas/farmacologia , Fibras Musgosas Hipocampais/efeitos dos fármacos , Proteínas Tirosina Quinases/antagonistas & inibidores , Análise de Variância , Morte Celular/efeitos dos fármacos , Morte Celular/fisiologia , Eletroencefalografia , Inibidores Enzimáticos/farmacologia , Epilepsia do Lobo Temporal/induzido quimicamente , Epilepsia do Lobo Temporal/patologia , Agonistas de Aminoácidos Excitatórios/farmacologia , Ácido Caínico/farmacologia , Sistema Límbico/citologia , Sistema Límbico/efeitos dos fármacos , Fibras Musgosas Hipocampais/patologia , Fibras Musgosas Hipocampais/fisiopatologia , Fatores de Crescimento Neural , Ratos Wistar , Estatísticas não Paramétricas , Convulsões/fisiopatologiaRESUMO
Extinction of conditioned fear is an active learning process involving inhibition of fear expression. It has been proposed that fear extinction potentiates neurons in the infralimbic (IL) prefrontal cortex, but the cellular mechanisms underlying this potentiation remain unknown. It is also not known whether this potentiation occurs locally in IL neurons as opposed to IL afferents. To determine whether extinction enhances the intrinsic excitability of IL pyramidal neurons in layers II/III and V, we performed whole-cell patch-clamp recordings in slices from naive, conditioned, or conditioned-extinguished rats. We observed that conditioning depressed IL excitability compared with slices from naive animals, as evidenced by a decreased number of spikes evoked by injected current and an increase in the slow afterhyperpolarizing potential (sAHP). Extinction reversed these conditioning-induced effects. Furthermore, IL neurons from extinguished rats showed increased burst spiking compared with naive rats, which was correlated with extinction recall. These changes were specific to IL prefrontal cortex and were not observed in prelimbic prefrontal cortex. Together, these findings suggest that IL intrinsic excitability is reduced to allow for expression of conditioning memory and enhanced for expression of extinction memory through the modulation of Ca(2+)-gated K(+) channels underlying the sAHP. Inappropriate modulation of these intrinsic mechanisms may underlie anxiety disorders, characterized by exaggerated fear and deficient extinction.
Assuntos
Condicionamento Clássico/fisiologia , Extinção Psicológica/fisiologia , Medo , Sistema Límbico/fisiologia , Córtex Pré-Frontal/fisiologia , Células Piramidais/fisiologia , Estimulação Acústica , Potenciais de Ação , Animais , Aprendizagem por Associação/fisiologia , Eletrofisiologia , Eletrochoque , Técnicas In Vitro , Sistema Límbico/citologia , Masculino , Técnicas de Patch-Clamp , Córtex Pré-Frontal/citologia , Ratos , Ratos Sprague-DawleyRESUMO
Entrainment by daily restricted feeding schedules (RFS) produces food anticipatory activity (FAA) which involves motivational processes which may be regulated by corticolimbic structures and the nucleus accumbens. The present study aimed first to determine whether corticolimbic structures participate in the expression of FAA, therefore c-Fos immunoreactivity (Fos-IR) was employed as marker of neuronal activity. The second goal was to characterize diurnal rhythms of the clock protein protein Per1 (PER1) in corticolimbic structures and to determine the influence of RFS on the diurnal temporal pattern. Rats were maintained under RFS with food access for 2 h daily, a control group was fed ad libitum. Food entrainment produced a pattern of increased Fos-IR during FAA and after mealtime in the two sub-regions of the nucleus accumbens (ACC), in the basolateral and central amygdala, in the bed nucleus of the stria terminalis (BNST), in the lateral septum (LS), in the prefrontal cortex (PFC), and in the paraventricular thalamic nucleus (PVT). No increased Fos-IR was observed in the hippocampus. Under ad libitum conditions all structures studied showed daily oscillations of PER1, excluding both amygdalar nuclei and the PFC. RFS shifted and set the daily peaks at zeitgeber time (ZT) 12 for both sub-regions in the accumbens, the hippocampus, lateral septum and PFC. RFS enhanced the amplitude at ZT12 of the BNST and shifted the peak of the PVT to ZT6. No changes were observed in the amygdalar nuclei. Present data indicate that cellular activation of corticolimbic structures is associated with behavioral events related to food anticipatory activity and that mealtime is a relevant signal that shifts daily oscillations of PER1 in corticolimbic structures. Data suggest a relevant role of corticolimbic structures as oscillators for FAA.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Córtex Cerebral/metabolismo , Ritmo Circadiano/fisiologia , Comportamento Alimentar/fisiologia , Genes fos/fisiologia , Sistema Límbico/metabolismo , Animais , Contagem de Células , Proteínas de Ciclo Celular/biossíntese , Córtex Cerebral/citologia , Córtex Cerebral/efeitos dos fármacos , Interpretação Estatística de Dados , Imuno-Histoquímica , Sistema Límbico/citologia , Sistema Límbico/efeitos dos fármacos , Masculino , Motivação , Proteínas Circadianas Period , Ratos , Ratos WistarRESUMO
The effect of chronic ethanol consumption during pregnancy and lactation on thyrotropin releasing hormone (TRH) metabolism was investigated in the hypothalamus and limbic areas of female rats and their weaned pups. Pregnant female rats received ethanol or isocaloric glucose solution during pregnancy either alone, or also during the 3 weeks of lactation. Thyrotropin (TSH) and corticosterone levels were measured in serum; TRH and TRH-gly concentrations were determined in hypothalamus, hippocampus, n.accumbens, frontal cortex and amygdala of dams and pups at 21 days after parturition. Ethanol or glucose consumption during pregnancy and lactation produced a decrease in TSH levels compared with control animals fed at libitum; water replacement during lactation normalized TSH levels only in glucose-fed dams. Pups from ethanol or pair-fed dams showed low weight and increased TSH levels compared with normal rats. Variations in TRH metabolism were detected in limbic areas. Chronic ethanol caused a decrease in the levels of TRH in the hippocampus and frontal cortex of dams. In contrast, glucose chronic ingestion increased TRH content specifically in n.accumbens and amygdala of dams. Most of the variations in TRH content of limbic areas of pups were not specific for glucose or ethanol treatment and correlated with the deleterious effect of the mother's thyroid condition, although some differences were observed depending on pup's gender. These results support the involvement of TRHergic neurons in the limbic system of the female rat exposed to alcohol or glucose during pregnancy and lactation.
Assuntos
Etanol/farmacologia , Glucose/farmacologia , Hipotálamo/efeitos dos fármacos , Sistema Límbico/efeitos dos fármacos , Hormônio Liberador de Tireotropina/metabolismo , Animais , Peso Corporal , Etanol/administração & dosagem , Feminino , Glucose/administração & dosagem , Hipotálamo/citologia , Hipotálamo/metabolismo , Sistema Límbico/citologia , Sistema Límbico/metabolismo , Masculino , Neurônios/metabolismo , Gravidez , Ratos , Ratos WistarRESUMO
Biochemical and pharmacological evidence suggest that the dopaminergic mesolimbic system plays a key role in mediating the reinforcing properties of alcohol and other drugs of abuse. Alcohol reinforcement and high alcohol drinking behavior have been postulated to be partially mediated by a neurobiological mechanism involving the alcohol-induced activation of the endogenous opioid system. The aim of this work was to study the effect of the in vivo acute administration of ethanol on mu (mu) opioid receptors in the rat dopaminergic meso-accumbens and mesocortical pathways by quantitative receptor autoradiography. [(3)H]DAMGO binding was significantly decreased in the ventral tegmental area (VTA) 30 min after ethanol administration. A small ethanol-induced reduction was observed in the shell region of the nucleus accumbens 1 h after exposure. In contrast, 2 h after ethanol administration, [(3)H]DAMGO binding was significantly increased in the frontal and prefrontal cortices. The observed changes correlated well with high ethanol plasma levels. Our results suggest that the reinforcing properties of ethanol may be partially mediated by mechanisms involving the ethanol-induced down- and up-regulation of mu receptors in the dopaminergic mesolimbic system. Mu receptors in the VTA and the frontal and prefrontal cortices may be involved in the in vivo acute responses to ethanol and could play a key role in modulating the dopaminergic activity of the mesocortical pathway in response to the drug. In contrast, the contribution of both mu and delta receptors in the nucleus accumbens might be relevant in these processes.
Assuntos
Depressores do Sistema Nervoso Central/farmacologia , Córtex Cerebral/efeitos dos fármacos , Etanol/farmacologia , Núcleo Accumbens/efeitos dos fármacos , Receptores Opioides mu/metabolismo , Área Tegmentar Ventral/efeitos dos fármacos , Alcoolismo/fisiopatologia , Analgésicos Opioides/metabolismo , Analgésicos Opioides/farmacologia , Animais , Autorradiografia , Depressores do Sistema Nervoso Central/sangue , Córtex Cerebral/citologia , Córtex Cerebral/metabolismo , Dopamina/metabolismo , Ala(2)-MePhe(4)-Gly(5)-Encefalina/metabolismo , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , Etanol/sangue , Sistema Límbico/citologia , Sistema Límbico/efeitos dos fármacos , Sistema Límbico/metabolismo , Masculino , Vias Neurais , Núcleo Accumbens/citologia , Núcleo Accumbens/metabolismo , Peptídeos Opioides/metabolismo , Ensaio Radioligante , Ratos , Ratos Wistar , Trítio , Área Tegmentar Ventral/citologia , Área Tegmentar Ventral/metabolismoRESUMO
The dorsal premammillary nucleus (PMd) is thought to play a critical role for the expression of fear responses to environmental threats. We have reported previously that during an encounter with a predator the PMd presents an impressive increase in Fos levels and cell body-specific chemical lesions therein virtually eliminate the expression of escape and freezing responses. In the present study, we carried out a systematic analysis of PMd afferent connections combining anterograde and retrograde tracing methods in the rat. We show that the nucleus receives inputs from several widely distributed areas in the forebrain and, to a much lesser extent, from the brainstem as well. From this information, it seems that the major telencephalic source of input to the PMd is the interfascicular nucleus of the bed nuclei of the stria terminalis. In addition, substantial telencephalic inputs to the nucleus seem to arise from the infralimbic and prelimbic areas, and the lateral septal nucleus. In the diencephalon, massive inputs to the PMd arise from the anterior hypothalamic nucleus, specific parts of the perifornical region, the retinoceptive region of the lateral hypothalamic area, and the anterior and dorsomedial parts of the ventromedial hypothalamic nucleus. In contrast, the ventral tegmental nucleus seems to be the only brainstem site that provides substantial inputs to the PMd. Overall, the present analysis helps to delineate prosencephalic circuits seemingly critical for the organization of innate fear responses to environmental threats, where the PMd presents a major associative role. Furthermore, by means of massive inputs from the ventral tegmental nucleus, the PMd is in a position to integrate information from a neural system involved in spatial working memory, which may be of particular relevance for an effect of attentional mechanisms on the selection of appropriate escape strategies.
Assuntos
Vias Aferentes/citologia , Medo/fisiologia , Hipotálamo/citologia , Vias Aferentes/fisiologia , Animais , Mapeamento Encefálico , Tronco Encefálico/citologia , Tronco Encefálico/fisiologia , Hipotálamo/fisiologia , Sistema Límbico/citologia , Sistema Límbico/fisiologia , Masculino , Memória de Curto Prazo/fisiologia , Ratos , Ratos Wistar , Núcleos Septais/citologia , Núcleos Septais/fisiologia , Telencéfalo/citologia , Telencéfalo/fisiologia , Tálamo/citologia , Tálamo/fisiologiaRESUMO
The principal fast neurotransmitters in the CNS are glutamate and GABA. Our aim was to provide a baseline account on the ultrastructure of the axon terminals immunoreactive to glutamate or GABA present in the nucleus tractus solitarius (NTS) of the rat. In addition, we wanted to complete our study of cortico-solitary afferents at the electron microscopic level, by analyzing the inputs from the infralimbic cortex. Using post-embedding immunogold, we found that nearly 61% of the axon terminals were glutamatergic, and 36% were GABAergic in the rat visceral NTS. In general, axons making asymmetric synaptic contacts were enriched in glutamate, compared to axons involved in symmetric synapses. In contrast, the vast majority of the GABAergic axon terminals made symmetric synaptic contacts. We could discern five types of glutamatergic and two types of GABAergic axon terminals that differed in their fine structure. Afferents from the infralimbic cortex were small, with clear synaptic vesicles and no dense core vesicles; they made asymmetric contacts with fine dendrites, and were glutamatergic. We conclude that most axon terminals in the NTS use glutamate or GABA as fast transmitters, in addition to being a heterogeneous population of morphological types.