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Search Results: 1 - 10 of 5399 matches for " Marcus Lira; "
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The First Forum on the Neurobiology of Stress
Marcus Lira Brand?o
Psychology & Neuroscience , 2010,
Abstract:
Gabaergic mechanisms of anterior and ventromedial hypothalamic nuclei in the expression of freezing in response to a light-conditioned stimulus
Santos, Julia Maria dos;Brand?o, Marcus Lira;
Psychology & Neuroscience , 2011, DOI: 10.3922/j.psns.2011.2.006
Abstract: the amygdala, dorsal periaqueductal gray (dpag), and medial hypothalamus have long been recognized to comprise a neural system responsible for the generation and elaboration of unconditioned fear in the brain. this neural substrate is well known to be under tonic inhibitory control exerted by γ-aminobutyric acid (gaba) mechanisms. some evidence also suggests that these structures integrate conditioned fear. a recent study using the fear-potentiated startle paradigm showed that gabaergic mechanisms in the anterior hypothalamic nucleus (ahn) and dorsomedial part of the ventromedial hypothalamic nucleus (vmhdm) regulate conditioned fear. the present study examined the extent to which gabaergic mechanisms in these brain regions are involved in conditioned fear by measuring freezing in response to a light used as a conditioned stimulus (cs). the gabaa receptor agonist muscimol and the gaba-synthesizing enzyme glutamic acid decarboxylase inhibitor semicarbazide were used as an enhancer and inhibitor of gaba mechanisms, respectively. muscimol and semicarbazide were injected into the ahn or vmhdm of rats before fear conditioning. muscimol injections into the ahn and vmhdm significantly reduced conditioned freezing, whereas inhibition of gaba transmission increased this conditioned response in the ahn. the present study further supports the hypothesis that gabaergic mechanisms in the ahn and vmhdm exert inhibitory control on the neural substrates of conditioned fear in the hypothalamus.
Hormonal and cognitive factors associated with the exploratory behavior of rats submitted to repeated sessions of the elevated plus-maze
Lucas Albrechet-Souza,Marcus Lira Brand?o
Psychology & Neuroscience , 2010,
Abstract: Naive rats submitted to the elevated plus-maze (EPM) display a characteristic increase in open arm exploration and reduced risk assessment behaviors (RABs) after the administration of anxiolytic drugs. Upon re-exposure to the maze, however, the traditional measures of the EPM become resistant to these drugs. This intriguing phenomenon was initially observed for the benzodiazepine chlordiazepoxide and referred as one-trial tolerance (OTT). In this review, we summarized hormonal, cognitive and neuroanatomical data obtained from rats submitted to the test/retest protocol in the EPM. The re-exposure to the EPM is characterized by more prominent RABs and a distinct Fos protein distribution in the brain, particularly in limbic structures involved with the cognitive aspects of fear, such as the ventral regions of the medial prefrontal cortex (mPFC) and amygdala. Interestingly, naive rats treated with midazolam had a significant decrease in the number of Fos-positive neurons in the anterior cingulate cortex, area 1 (Cg1), anterior and dorsal premammillary nuclei of hypothalamus. On the other hand, midazolam caused a significant decrease in the number of Fos-positive neurons in the mPFC, amygdala, dorsomedial nucleus of hypothalamus and raphe nuclei in maze-experienced rats. Cg1 was the only structure targeted by the benzodiazepine in both sessions. Systemically administered midazolam before test or retest sessions reduced the RABs and plasma corticosterone levels in rats submitted to both sessions. Similar behavioral results were obtained with intra-Cg1 infusions of midazolam. The results reviewed here support the view of the crucial role of the RABs in the development of the OTT and point to this mPFC area as an important locus for the anxiolytic-like action of benzodiazepines in rodents.
GABAergic mechanisms of anterior and ventromedial hypothalamic nuclei in the expression of freezing in response to a light-conditioned stimulus
Julia Maria dos Santos,Marcus Lira Brand?o
Psychology & Neuroscience , 2011,
Abstract: The amygdala, dorsal periaqueductal gray (dPAG), and medial hypothalamus have long been recognized to comprise a neural system responsible for the generation and elaboration of unconditioned fear in the brain. This neural substrate is well known to be under tonic inhibitory control exerted by γ-aminobutyric acid (GABA) mechanisms. Some evidence also suggests that these structures integrate conditioned fear. A recent study using the fear-potentiated startle paradigm showed that GABAergic mechanisms in the anterior hypothalamic nucleus (AHN) and dorsomedial part of the ventromedial hypothalamic nucleus (VMHDM) regulate conditioned fear. The present study examined the extent to which GABAergic mechanisms in these brain regions are involved in conditioned fear by measuring freezing in response to a light used as a conditioned stimulus (CS). The GABAA receptor agonist muscimol and the GABA-synthesizing enzyme glutamic acid decarboxylase inhibitor semicarbazide were used as an enhancer and inhibitor of GABA mechanisms, respectively. Muscimol and semicarbazide were injected into the AHN or VMHDM of rats before fear conditioning. Muscimol injections into the AHN and VMHDM signifcantly reduced conditioned freezing, whereas inhibition of GABA transmission increased this conditioned response in the AHN. The present study further supports the hypothesis that GABAergic mechanisms in the AHN and VMHDM exert inhibitory control on the neural substrates of conditioned fear in the hypothalamus.
Padr?es de respostas defensivas de congelamento associados a diferentes transtornos de ansiedade
Landeira-Fernandez, Jesus;Cruz, Antonio Pedro de Mello;Brand?o, Marcus Lira;
Psicologia USP , 2006, DOI: 10.1590/S0103-65642006000400010
Abstract: although anxiety disorders are exclusive to humans, it is possible to find correlation between these disorders and defensive responses that animals present when facing dangerous situations. the present article presents a series of evidence that indicate that different freezing defensive patterns might be associated with specific anxiety disorders. particularly, there is an excellent isomorphism between freeing response to contextual stimuli associated with electrical shocks and generalized anxiety disorder. much evidence also shows that freezing response triggered directly through the electrical stimulation of the dorsal periaqueductal gray matter (dpag) is an excellent animal model of panic attack. moreover, freezing response observed after the interruption of the electrical stimulation of the dpag which triggers an escape response seems to be associated with panic disorder. finally, it is hypothesized that freezing to contextual stimuli previously associated with intense electrical stimulation of the dpag might be related to panic disorder with agoraphobia.
Involvement of GABAergic mechanisms of the dorsal periaqueductal gray and inferior colliculus on unconditioned fear
Reimer, Adriano Edgar;Oliveira, Amanda Ribeiro de;Brand?o, Marcus Lira;
Psychology & Neuroscience , 2009, DOI: 10.3922/j.psns.2009.1.08
Abstract: the fact that the dorsal periaqueductal gray (dpag) and inferior colliculus (ic), together with superior colliculus, medial hypothalamus and amygdala, constitute the brain aversion system has been well-established. stepwise increases in the intensity of electrical stimulation of dpag or ic cause freezing and escape responses, which are followed by a freezing behavior that lasts after the interruption of the stimulation. freezing and escape are unconditioned defensive behaviors derived from the stimulation of the output centers for the defense reaction, whereas the post-stimulation freezing is the behavioral counterpart of the processing of aversive information. although gaba-a mechanisms of the midbrain tectum exert a tonic inhibitory influence on the neural substrates of unconditioned fear, their influence on the processing of aversive information is not completely understood. thus, the present study examines the effects of injections of the gaba-a receptor agonist muscimol (1 and 2 nmol/0.2 μl) or the glutamic acid decarboxylase blocker semicarbazide (5 and 7.5 μg/0.2 μl) into dpag or ic of wistar rats on freezing and escape thresholds determined by electrical stimulation of these same structures and on post-stimulation freezing. intra-dpag injections of muscimol increased and semicarbazide decreased the freezing and escape thresholds of electrical stimulation of the dpag. only semicarbazide enhanced the dpag post-stimulation freezing. intra-ic injections of muscimol significantly increased aversive thresholds, while having no effect on ic post-stimulation freezing. intra-ic injections of semicarbazide had no significant effects. these findings suggest that gabaergic mechanisms are important regulators of the expression of unconditioned fear in dpag and ic, whereas only in dpag gaba appears to play a role on the sensory gating towards aversive information during post-stimulation freezing.
Organiza??o neural de diferentes tipos de medo e suas implica??es na ansiedade
Brand?o, Marcus Lira;Vianna, Daniel Machado;Masson, Sueli;Santos, Júlia;
Revista Brasileira de Psiquiatria , 2003, DOI: 10.1590/S1516-44462003000600009
Abstract: the dangerous stimuli may be potentially dangerous, distal or proximal and the recognition by the animals of each one of these conditions is determinant for the nature of the fear responses. in the present article a parallel with this particular process is drawn taking into account that different fear responses are generated by light, tones and contexts used as conditioned stimuli and by unconditioned stimulation of the dorsal periaqueductal gray (dpag). in this review we summarize the efforts that have been made to characterize the neural circuits recruited in the organization of defensive reactions to the conditioned and unconditioned aversive stimulations, particularly evidence linking the brain's defense response systems to the concept of fear-stress-anxiety. the dpag constitute the main neural substrates for the integration of aversive states in response to proximal aversive stimuli. in fact, panic-like behaviors often result when this structure is electrically or chemically stimulated. on the other hand, successful preparatory processes of danger-orientation and preparedness to flee seem to be linked to anxiety. the pre-frontal and cingulate cortex, median raphe nucleus, septum and hippocampus seem to be implicated in the elaboration and organization of these responses. as a working hypothesis, it is advanced that increasing the intensity and proximity of the danger may lead to an emotional shift. when the animals are submitted to this gradual increase in aversiveness there is a switch from the neural circuits responsible for the production of the orientated and organized motor patterns of appropriate defensive response to a conditioned stimulus towards the incomplete and uncoordinated defense responses related to panic attacks. the circuits in the amygdala and the medial hypothalamus responsible for the organization of the defense reaction may well subserve to this switch process.
Estimativa da produ??o anual de serapilheira dos bosques de mangue no Furo Grande, Bragan?a-Pará
Fernandes, Marcus Emanuel Barroncas;Nascimento, Antonia Aparecida Monteiro do;Carvalho, Muzenilha Lira;
Revista árvore , 2007, DOI: 10.1590/S0100-67622007000500019
Abstract: it is well known that environmental conditions of a determined place can influence the productivity of mangroves. so, the present study estimated the total and components litter production in furo grande, bragan?a-pa. this study comprised four annual cycles (july/2000 to august/2004) at three sites. seven traps were placed at each site along a 140 m transect, with 20 m intervals. each trap had a useful area of 1 m2, with 1 mm2 mesh, suspended above the spring tide level. accumulated material in the traps was collected on a monthly basis, sorted manually into leaves, flowers, fruits, stipules, twigs, and miscellaneous and then oven-dried to constant weight at 70oc. the mean production of four years was 9.85 t.ha-1.year-1 at site 1, 6.41 t.ha-1. year -1 at site 2, and 5.99 t.ha-1. year -1 at site 3, with significant difference between sites 1 and 3 (h=7.53; df=2; p<0.05). overall, the results showed that leaf was the most productive component, and together with flower, had peak in the dry season, which seems to favor energy saving to invest in reproduction, whereas fruit peak in the wet season, providing propagule dispersion and hence the renewal and maintenance of these forests.
Organiza o neural de diferentes tipos de medo e suas implica es na ansiedade
Brand?o Marcus Lira,Vianna Daniel Machado,Masson Sueli,Santos Júlia
Revista Brasileira de Psiquiatria , 2003,
Abstract: A natureza das respostas de medo em animais expostos a situa es amea adoras depende da intensidade e da distancia do estímulo aversivo. Esses estímulos podem ser potencialmente perigosos, distais ou proximais ao animal. Esfor os têm sido feitos no sentido de identificar os circuitos neurais recrutados na organiza o das rea es defensivas a estas condi es aversivas. Neste artigo, sumarizamos evidências que associam os sistemas cerebrais de defesa ao conceito de medo-stress-ansiedade. Respostas de orienta o ao estímulo de perigo, à esquiva e à prepara o para o enfrentamento do perigo parecem estar associados à ansiedade. O giro do cíngulo e o córtex pré-frontal de um lado; o núcleo mediano da rafe, septo e o hipocampo de outro fazem parte dos circuitos cerebrais que integram essas respostas emocionais. No outro extremo, estímulos de medo que induzem formas ativas de defesa, mas pouco elaboradas, determinam estados emocionais de natureza diferente e parecem associadas a manifesta es elementares de medo. A substancia cinzenta periaquedutal dorsal constitui o principal substrato neural para a integra o desses estados aversivos no cérebro. Comportamentos defensivos desse tipo s o produzidos pela estimula o elétrica e química desta estrutura. à medida que os estímulos amea adores, potenciais e distais d o lugar a estímulos de perigo muito intensos ou s o substituídos por estímulos proximais de medo, ocorre uma comuta o (switch) dos circuitos neurais usualmente responsáveis pela produ o de respostas condicionadas de medo para rea es defensivas com baixo nível de regula o e organiza o que se assemelham aos ataques de panico. Portanto, dependendo da natureza do evento estressor ou do estímulo incondicionado, o padr o de respostas defensivas orientadas e organizadas cede lugar a respostas motoras incoordenadas e incompletas. A amígdala e o hipotálamo medial podem funcionar como uma espécie de interface comutando os estímulos para os substratos neurais apropriados para elabora o das respostas defensivas condicionadas ou incondicionadas.
Involvement of GABAergic mechanisms of the dorsal periaqueductal gray and inferior colliculus on unconditioned fear
Adriano Edgar Reimer, Amanda Ribeiro de Oliveira and Marcus Lira Branda?o
Psychology & Neuroscience , 2009,
Abstract: The fact that the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), together with superior colliculus, medial hypothalamus and amygdala, constitute the brain aversion system has been well-established. Stepwise increases in the intensity of electrical stimulation of dPAG or IC cause freezing and escape responses, which are followed by a freezing behavior that lasts after the interruption of the stimulation. Freezing and escape are unconditioned defensive behaviors derived from the stimulation of the output centers for the defense reaction, whereas the post-stimulation freezing is the behavioral counterpart of the processing of aversive information. Although GABA-A mechanisms of the midbrain tectum exert a tonic inhibitory influence on the neural substrates of unconditioned fear, their influence on the processing of aversive information is not completely understood. Thus, the present study examines the effects of injections of the GABA-A receptor agonist muscimol (1 and 2 nmol/0.2 μL) or the glutamic acid decarboxylase blocker semicarbazide (5 and 7.5 μg/0.2 μL) into dPAG or IC of Wistar rats on freezing and escape thresholds determined by electrical stimulation of these same structures and on post-stimulation freezing. Intra-dPAG injections of muscimol increased and semicarbazide decreased the freezing and escape thresholds of electrical stimulation of the dPAG. Only semicarbazide enhanced the dPAG post-stimulation freezing. Intra-IC injections of muscimol significantly increased aversive thresholds, while having no effect on IC post-stimulation freezing. Intra-IC injections of semicarbazide had no significant effects. These findings suggest that GABAergic mechanisms are important regulators of the expression of unconditioned fear in dPAG and IC, whereas only in dPAG GABA appears to play a role on the sensory gating towards aversive information during post-stimulation freezing.
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