Organizaçäo neural de diferentes tipos de medo e suas implicaçöes na ansiedade / Neural organization of different types of fear: implications for the understanding of anxiety

A natureza das respostas de medo em animais expostos a situaçöes ameaçadoras depende da intensidade e da distância do estímulo aversivo. Esses estímulos podem ser potencialmente perigosos, distais ou proximais ao animal. Esforços têm sido feitos no sentido de identificar os circuitos neurais recrutados na organizaçäo das reaçöes defensivas a estas condiçöes aversivas. Neste artigo, sumarizamos evidências que associam os sistemas cerebrais de defesa ao conceito de medo-stress-ansiedade. Respostas de orientaçäo ao estímulo de perigo, à esquiva e à preparaçäo 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 manifestaçöes elementares de medo. A substância cinzenta periaquedutal dorsal constitui o principal substrato neural para a integraçäo desses estados aversivos no cérebro. Comportamentos defensivos desse tipo säo produzidos pela estimulaçäo elétrica e química desta estrutura. A medida que os estímulos ameaçadores, potenciais e distais däo lugar a estímulos de perigo muito intensos ou säo substituídos por estímulos proximais de medo, ocorre uma comutaçäo (switch) dos circuitos neurais usualmente responsáveis pela produçäo de respostas condicionadas de medo para reaçöes defensivas com baixo nível de regulaçäo e organizaçäo que se assemelham aos ataques de pânico. Portanto, dependendo da natureza do evento estressor ou do estímulo incondicionado, o padräo 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 elaboraçäo das respostas defensivas condicionadas ou incondicionadas

Interaction between NO and oxytocin: influence on LHRH release

Nitric oxide synthase (NOS)-containing neurons have been localized in various parts of the CNS. These neurons occur in the hypothalamus, mostly in the paraventricular and supraoptic nuclei and their axons project to the neural lobe of the pituitary gland. We have found that nitric oxide (NO) controls luteinizing hormone-releasing hormone (LHRH) release from the hypothalamus acting as a signal transducer in norepinephrine (NE)-induced LHRH release. LHRH not only releases LH from the pituitary but also induces sexual behavior.On the other hand, it is known that oxytocin also stimulates mating behavior and there is some evidence that oxytocin can increase NE release. Therefore, it occurred to us that oxytocin may also stimulate LHRH releave via NE and NO. To test this hypothesis, we incubated medial basal hypothalamic (MBH) explants from adult male rats in vitro. Following a preincubation period of 30 min, MBH fragments were incubated in Krebs-Ringer bicarbonate buffer in the presence of various concentrations of oxytocin. Oxytocin relesed LHRH at concentrations ranging from 0.1 nM to 1muM with a maximal stimulatory effect (P<0.001) at 0.1 muM, but with no stimulatory effect at 10 muM. That these effects were mediated by NO was shown by the fact that incubation of the tissues with NG-monomethyl-L-arginine (NMMA), a competitive inhibitor of NOS, blocked the stimulatory effects. Furthermore, the release of LHRH by oxytocin was also blocked by prazocin, an alpha1-adrenergic receptor antagonist, indicating that NE mediated this effect. Oxytocin at the same concentrations also increased the activity of NOS (P<0.01) as measured by the conversion of [14C]arginine to citrulline, which is produced in equimolar amounts with NO by the action of NOS. The release of LHRH induced by oxytocin was also accompanied by a significant (P<0.02) increase in the release of prostaglandin E2 (PGE2), a mediator of LHRH release that is released by NO. On the other hand, incubation of neural lobes with vaious concentrations of sodium nitroprusside (NP) (300 or 600 muM), a releaser of NO, revealed that NO acts to suppres (P<0.01) the release of oxytoxin. Therefore, our results indicate that oxytocin releases LHRH by stimulating NOS via NE, resulting in an increased release of NO, which increases PGE2 release that in turn induces LHRH release. Furthermore, the released NO can act back on oxytocinergic terminals to suppress the release of oxytocin in an ultrashort-loop negative feedback.

Correlation between ANP concentrations in atria, plasma and cerebral structures and sodium chloride preference in Wistar rats

We determined whether ANP (atrial natriuretic peptide) concentrations, measured by radioimmunoassay, in the ANPergic cerebral regions involved in regulation of sodium intake and excretion and pituitary gland correlated with differences in sodium preference among 40 Wistar male rats (l80-220 g). Sodium preference was measured as mean spontaneous ingestion of 1.5 per cent NaCl solution during a test period of 12 days. The relevant tissues included the olfactory bulb (OB), the posterior and anterior lobes of the pituitary gland (PP and AP, respectively), the median eminence (ME), the medial basal hypothalamus (MBH), and the region anteroventral to the third ventricle (AV3V). We also measured ANP contens in the right (RA) and left atrium (LA) and plasma. The concentrations of ANP in the OB and the AP were correlated with sodium ingestion during the preceding 24 h, since an increase of ANP in these structures was associated with a reduced ingestion and vice-versa (OB: r = -0.3649, P<0.05; AP: r = -0.3291, P<0.05). Moreover, the AP exhibited correlation between ANP concentration and mean NaCl intake (r = -0.4165, P<0.05), but this was not the case for the OB (r = 0.2422. This suggests that differences in sodium preference among individu male rats can be related to variations of AP ANP level. Earlier studies indicated that the OB is involved in the control of NaCl ingestion. Our data suggest that the OB ANP level may play a role mainly in day-today variations of sodium ingestion in the individual rat.

Regional distribution of Fos-like immunoreactivity in the rat brain after exposure to fear-inducing stimuli

Fos protein immunohistochemistry was used to identify the neural substrate of fear/anxiety. The structures activated by exposure of Long Evans male rats (280-300 g) to the elevated plus-maze, a widely used animal model of anxiety, were compared with those activated by chemical stimulation of two aversive areas of the brain, the dorsal periaqueductal gray matter and the medial hypothalamus. Three different patterns of activation were obtained: Pattern 1 resulted from microinjection of the excitatory amino acid kainate (60 pmol; N = 5) or of the GABA(A) receptor antagonist SR-95531 (16 pmol; N = 3) into the dorsal periaqueductal gray matter and consisted mainly of caudal structures; Pattern 2 was observed after kainate injection (60 pmol; N = 4) into the medial hypothalamus and had a predominantly prosencephalic distribution; Pattern 3 extended from rostral to caudal brain regions and was induced by microinjection of either SR-95531 (16 pmol; N = 1) or kainate (120 pmol; N = 3) into the medial hypothalamus, as well as by 15-min exposure to the plus-maze (N = 3). Control animals were either injected with saline into the MH (N = 3) or the PAG (N = 3) or were exposed for 15 s to the elevated plus maze (N = 3) and exhibited no significant labeling. These results further support the participation of periventricular structures in the regulation of fear and aversion.

Sustratos morfológicos de la vía ventricular de secreción y transporte de sustancias en la región tuberoinfundibular del hipotálamo: estudio ultraestructural / Morphologic substrates of the ventricular route of secretion and transport of substances in the tubero-infundibular region of the hypothalamus: ultrastructural study

Ultrastructural studies of the ependyma of the tuberoinfundibular region of the rat hypothalamus have revealed the existence of intraventricular axonal endings and of cytoplasmic blebs and bulbs that project from the apical surface of the ependymal cells to the ventricular lumen. All these structures account for the processes of ependymal apocrine secretion and the neuroventriculocrinia, and hence the release of biologically active substances into the cerebrospinal fluid (CSF). These substances contained in the CSF must act on the nervous nuclei of the tuberoinfundibular region, such as the arcuate nucleus, which is very important in the neuroendocrine regulation of the anterior pituitary gland. Dilated intercellular spaces among neighbouring ependymocytes of this region, small intraependymal cisternae and, in particular, a lateral prolongation of the infundibular recess, which courses through the nervous tissue between the arcuate nucleus and the median eminence from the vertex of the lateral angle of the infundibular recess, may be the route followed by the CSF from the third ventricle to the tissue compartment of the tuberoinfundibular region. Also studied are the cisternae of the region and the relationships of these with the lateral prolongation of the infundibular recess. Some of these cisternae may be filled by the CSF through the prolongation. In this way, the tissue compartment of CSF would be enlarged, and hence the ventricular route for the secretion and transport of biologically active substances would be potentiated

Influência dos adrenoceptores alfa1 e alfa2 do hipotálamo médio sobre a pressao arterial sistêmica em ratos / Role of the alfa1 and alfa2 adrenoceptores in the medial hypothalamus on the arterial pressure in rats

Foram estudados os efeitos sobre a pressäo arterial sistêmica após a administraçäo de noradrenalina e de dois antagonistas de alfa-adrenoceptores no hipotálamo médio de ratos normotensos. Tanto o prazosin quanto a ioimbina antagonizaram a açäo do agonista misto de alfa1/alfa2-adrenoceptores, a noradrenalina ; entretanto a administraçäo prévia de prazosin mostrou uma maior interaçäo da noradrenalina pelos adrenoceptores alfa1. Estes resultados sugerem que os adrenoceptores alfa1 do hipotálamo médio exerceriam uma maior influência que os adrenoceptores alfa2 no controle de pressäo arterial sistêmica

Behavioral effects of neurotensin applied to periventricular structures of rats

Neurotensin (NT), n active neuropeptide, and bicuculline, a GABA-A receptor antagonist, were microinjected into the rat hypothalaamus (MH) or the dorsal periaqueductal gray matter (DPAG). Bicuculline (80 pmol) produced behavioral activation which included jumping and NT (1-20 nmol) caused a dose-dependent behavioral activation accompanied by catalepsy rather than jumping. These results suggest that the behavioral activation produced by NT may be due to an interaction of the neuropeptide with specific receptors while its cataleptic effect may be attributed to the blockade of dopamine receptors

Contribuiçäo ao estudo das glândulas submandibulares, após lesäo da eminência média do hipotálamo, em ratos / Study of the submandibular glands following lesion of the hypothalamus middle eminence in rats

Os autores utilizam 65 ratos divididos em 3 grupos: grupo I - controle; grupo II - operaçäo simulante; e grupo III - submetidos a lesäo da eminência média do hipotálamo. Nesses animais procedeu-se à remoçäo cirúrgica das glândulas submandibulares, tendo-se nelas estudado o peso ponderal, assim como as alteraçöes histológicas. A análise dos resultados permitiu concluir que a lesäo da eminência média do hipotálamo ocasionou alteraçöes nas glândulas submandibulares, representadas por diminuiçäo da massa dessas glândulas, acompanhada de alteraçöes morfológicas caracterizadas por hipertrofia dos ácinos, picnose nuclear das células acinosas e aumento da quantidade de ductos granulosos

Defense reaction elicited by microinjection of Kainic acid in the medial hypothalamus of the rat

In order to localize groups of neurons commanding the defense reaction, a subtoxic dose (66 pmol) of kainic acid was microinjected into the medial hypothalamus of the rat. After drug treatment, the animals were placed inside a shuttle-box for 15 min and the number of midline crossings, rearings and forward leaps was recorded. Autonomic changes such as occurrence of micturition and defectation were also measured. Injection of kainic acid significantly increased locomotion, rearing and micturition, indicating that the medial hypothalamus of the rat contains perikarya/dendrites of neurons integrating the defense reaction

Modifications in alfa-MSH concentrations in different hypothalamic areas during the estrous cycle in the rat

Este trabajo fue realizado con el fin de 1) examinar las variaciones en la concentración de alfa-MSH en áreas hipolámicas a lo largo del ciclo estrual y 2) analizar si durante el ciclo el alfa-MSH que deriva de la proopiomelanocortina (POMC) tiene las mismas variaciones de concentración que el alfa-MSH que deriva del hipotálamo dorso lateral (HDL). La concentración de alfa-MSH en el hipotálamo mediobasal (HMB), área preóptica (APO) y HDL fue medida utilizando un radioinmunoensayo específico. Las ratas fueron sacrificadas cada cuatro horas mediante perfusión intracardíaca de solución fisiológica. Se observa un ritmo circadiano en todas las áreas estudiadas, excepto en HMB durante el estro. La concentración de alfa-MSH en HMB se mantuvo alta durante el período de luz a la inversa de lo que se observaba en el APO. En general cuando los niveles de alfa-MSH se encuentran elevados en HMB, se mantienen bajos en APO y viceversa. El perfil hallado en HDL es muy semejante al de APO. La acumulación de alfa-MSH en los cuerpos neuronales del sistema de la POMC, y su disminución en las fibras que provienen de dicho sistema durante la tarde del proestro, podrían relacionarse con la caracteristica liberación de LH y PRL que ocurre en ese momento

Papel dos adrenoceptores alfa1 e alfa2 do hipotálamo médio sobre a excreçäo de sódio e potássio / Role of alpha1 e alpha2 adrenoceptors of the medial hypothalamus on sodium and potassium excretion

Injeçäo de noradrenalina dentro do hipotálamo médio de ratos produziu uma estimulaçäo da excreçäo urinária de sódio e potássio. Ioimbina (10**-9 e 4.10**-9 M), um bloqueador dos adrenoceptores alfa 2, potencializou a excreçäo dos dois cátions quando injetado antes do agonista enquanto que o prazosin, um antagonista dos adrenoceptores alfa 1, inibiu estas respostas quando injetado nas mesmas doses. Por outro lado, injeçöes de clonidina, um agonista dos adrenoceptores alfa 2, dentro da mesma área produziu uma inibiçäo dose-dependente da excreçäo de Na+ e K+. O prazosin potencializou os efeitos da clonidina enquanto que a ioimbina inibiu estas repostas. Estes resultados sugerem a presença de dois tipos de adrenoceptores alfa para a modulaçäo das vias centrais que interferem com a regulaçäo dos dois cátions: a estimulaçäo dos adrenoceptores alfa 1 facilita enquanto a estimulaçäo dos adrenoceptores alfa 2 inibem a excreçäo dos ions

Histological survey of the healing process on tooth extraction wounds in rats after hypothalamic median eminence lesion

Foi estudado histologicamente em ratos lesados na eminência média do hipotálamo, o processo de reparo em feridas de extraçäo dental, seguido de um grupo-controle. A extraçäo dental foi realizada imediatamente após a verificaçäo da eficiência da lesäo e o sacrifício dos animais efetuado aos 3, 6, 9, 12, 18 e 21 dias pós-extraçäo. Nossos resultados mostraram que até o 6§ dia näo houve alteraçäo no processo de reparo alveolar. No período intermediário, do 9§ ao 12§ dia, foi verificado um atraso discreto na reparaçäo alveolar dos animais do grupo lesado. O resultado mais significativo ocorreu nos períodos de 18 e 21 dias, com um atraso no processo de reparo do alvéolo, principalmente em sua área central e nos terços cervical, médio e apical. Essas detecçöes levam-nos a concluir que, embora a lesäo tenha afetado o funcionamento hipofisário, em termos de neoformaçäo óssea, a manifestaçäo dessa disfunçäo aparece após um período aproximado de 11 dias