Dorsal periaqueductal gray stimulation facilitates anxiety-, but not panic-related, defensive responses in rats tested in the elevated T-maze

The escape response to electrical or chemical stimulation of the dorsal periaqueductal gray matter (DPAG) has been associated with panic attacks. In order to explore the validity of the DPAG stimulation model for the study of panic disorder, we determined if the aversive consequences of the electrical or chemical stimulation of this midbrain area can be detected subsequently in the elevated T-maze. This animal model, derived from the elevated plus-maze, permits the measurement in the same rat of a generalized anxiety- and a panic-related defensive response, i.e., inhibitory avoidance and escape, respectively. Facilitation of inhibitory avoidance, suggesting an anxiogenic effect, was detected in male Wistar rats (200-220 g) tested in the elevated T-maze 30 min after DPAG electrical stimulation (current generated by a sine-wave stimulator, frequency at 60 Hz) or after local microinjection of the GABA_A receptor antagonist bicuculline (5 pmol). Previous electrical (5, 15, 30 min, or 24 h before testing) or chemical stimulation of this midbrain area did not affect escape performance in the elevated T-maze or locomotion in an open-field. No change in the two behavioral tasks measured by the elevated T-maze was observed after repetitive (3 trials) electrical stimulation of the DPAG. The results indicate that activation of the DPAG caused a short-lived, but selective, increase in defensive behaviors associated with generalized anxiety.

SIMULAÇÃO DE RESERVATÓRIO DE PETRÓLEO UTILIZANDO O MODELO BLACK-OIL BASEADO EM FRAÇÕES MÁSSICAS EM CONJUNTO COM MALHAS NÃO-ESTRUTURADAS

Dentre as várias metodologias disponíveis para solução numérica de escoamentos, o método EbFVM em conjunto com malhas não-estruturadas tem recebido grande atenção por parte da comunidade de simulação de reservatórios de petróleo. Nesta metodologia o domínio de cálculo é divido em elementos e cada elemento é dividido em sub-elementos de acordo com o número de vértices. Os volumes de controle são construídos em torno dos vértices dos elementos, originando uma metodologia centrada nos vértices da malha (cell vertex). Este trabalho apresenta uma investigação da metodologia EbFVM usando o modelo black-oil com base na pressão e frações mássicas globais. Nesta abordagem, mesmo quando toda a fase gás encontra-se dissolvida na fase óleo à fração mássica global de gás será diferente de zero. Nesse trabalho, a abordagem previamente mencionada é aplicada a fluxos multifásicos envolvendo óleo, gás e água. As equações de balanço de massa em termos de fração mássica global de óleo, gás e água e pressão são aproximadas através da metodologia EbFVM, utilizando um procedimento totalmente implícito. Com o intuito de validar a formulação adotada neste trabalho serão também apresentados os resultados obtidos com o simulador IMEX da CMG em conjunto com malhas cartesianos para alguns dos casos testes selecionados.

Chronic imipramine treatment sensitizes 5-HT1A and 5-HT2A receptors in the dorsal periaqueductal gray matter: evidence from the elevated T-maze test of anxiety

The dorsal periaqueductal gray matter (DPAG) has been implicated in the mediation of escape, a defensive behavior associated with panic disorder (PD). Chronic treatment with the anti-panic agent imipramine enhances the inhibitory effect on escape evoked by DPAG electrical stimulation of intra-DPAG administration of the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and the preferential 5-HT 2 A receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI). In the present study we further explore the hypothesis that sensitization of 5-HT1A and 5-HT 2 A receptors in the DPAG is involved in the anti-panic effect of imipramine. To this end, Wistar rats, subchronically or chronically treated with imipramine, were intra-DPAG injected with 8-OH-DPAT (0.4 or 3.2 nmoles) or DOI (16 nmoles), and tested in the elevated T-maze. In addition to its possible relevance to panic disorder, this test also measures inhibitory avoidance, a behavior that has been associated with generalized anxiety disorder (GAD). The effects of these 5-HT agonists in the DPAG were also investigated in animals chronically injected with buspirone, a drug clinically effective in treating GAD, but not PD. The results showed that intra-DPAG administration of the highest dose of 8-OH-DPAT and of DOI inhibited escape, and this panicolytic-like effect was significantly higher in animals previously treated chronically, but not subchronically, with imipramine. 8-OH-DPAT (0.4 nmole), although not affecting escape in animals systemically treated with saline, had a panicolytic-like effect in those receiving long-term treatment with imipramine. Microinjection of 8-OH-DPAT (3.2 nmoles), but not of DOI, impaired inhibitory avoidance, and this anxiolytic effect did not differ between animals treated with saline or imipramine. Chronic buspirone did not change the effect of 8-OH-DPAT and DOI on inhibitory avoidance and escape. Therefore, chronic imipramine seems to sensitize both 5-HT1A and 5-HT 2 A receptors in the DPAG, strengthening the view that these receptors are involved in the mode of action of anti-panic drugs.

Effect of acute treatment with a water-alcohol extract of Erythrina mulungu on anxiety-related responses in rats

We investigated the effect of acute oral treatment with a water-alcohol extract of the inflorescence of Erythrina mulungu (EM, Leguminosae-Papilionaceae) (100, 200 and 400 mg/kg) on rats submitted to different anxiety models: the elevated T-maze (for inhibitory avoidance and escape measurements), the light/dark transition, and the cat odor test. These models were selected for their presumed capacity to demonstrate specific subtypes of anxiety disorders as recognized in clinical practice. Treatment with 200 mg/kg EM impaired avoidance latencies (avoidance 1 - 200 mg/kg EM: 18 +/- 7 s, control group: 40 +/- 9 s; avoidance 2 - 200 mg/kg EM: 15 +/- 4 s, control group: 110.33 +/- 38 s) in a way similar to the reference drug diazepam (avoidance 1: 3 +/- 0.79 s; avoidance 2: 3 +/- 0.76 s), without altering escape. Additionally, the same treatments increased the number of transitions (200 mg/kg EM: 6.33 +/- 0.90, diazepam: 10 +/- 1.54, control group: 2.78 +/- 0.60) between the two compartments and the time spent in the lighted compartment in the light/dark transition model (200 mg/kg EM: 39 +/- 7 s; diazepam: 61 +/- 9 s; control group: 14 +/- 4 s). The dose of 400 mg/kg EM also increased this last measurement (38 +/- 8 s). These results were not due to motor alterations since no significant effects were detected in the number of crossings or rearings in the arena. Furthermore, neither EM nor diazepam altered the behavioral responses of rats to a cloth impregnated with cat odor. These observations suggest that EM exerts anxiolytic-like effects on a specific subset of defensive behaviors, particularly those that have been shown to be sensitive to low doses of benzodiazepines.

Serotonergic regulation of inhibitory avoidance and one-way escape in the rat elevated T-maze

It has been proposed that distinct 5-HT pathways modulate different types of anxiety. Activation of the ascending dorsal raphe (DR)-5-HT pathway, innervating the amygdala and frontal cortex, would facilitate learned defensive behaviors. On the other hand, activation of the DR-periventricular 5-HT pathway, which innervates the dorsal periaqueductal gray matter (DPAG), would inhibit innate flight or fight reactions. Dysfunction of these pathways has been suggested to relate to generalized anxiety disorder (GAD) and panic disorder (PD) in humans, respectively. The elevated T-maze has been developed to separate conditioned (inhibitory avoidance) from unconditioned (escape) defensive responses in the same rat. Pharmacological validation of this model has shown that the GAD-effective serotonergic anxiolytic buspirone or the putative anxiolytic ritanserin selectively impaired inhibitory avoidance while leaving one-way escape unchanged. Chronic injection of the 5-HT/noradrenaline reuptake inhibitor imipramine impaired inhibitory avoidance and prolonged escape, an effect that may be related to the therapeutic action of this drug on both GAD and PD. Like imipramine, intra-DPAG injection of the 5-HT(1A) agonist 8-OH-DPAT impaired both inhibitory avoidance and one-way escape. Intra-DPAG administration of the 5-HT(2A/2C) agonist DOI prolonged escape, without affecting inhibitory avoidance. The reversible inactivation of the DRN by muscimol impaired inhibitory avoidance, while facilitating escape from the open arm. Taken together, these results suggest that 5-HT exerts differential control on inhibitory avoidance and escape response in the elevated T-maze, mobilizing different types of 5-HT receptors in key structures implicated in fear/anxiety.

Evaluation of the elevated T-maze as an animal model of anxiety in the mouse

The elevated T-maze has been developed as an animal model of anxiety to generate both conditioned and unconditioned fears in the same rat. This study explores a version of the elevated T-maze fit for mice. Inhibitory (passive) avoidance- conditioned fear-is measured by recording the latency to leave the enclosed arm during three consecutive trials. One-way escape- unconditioned fear-is measured by recording the time to withdraw from open arms. The results showed that mice do not appear to acquire inhibitory avoidance in the standard T-maze, since their latencies to leave enclosed arm did not increase along trials. Nevertheless, the open arms seemed to be aversive for mice, because the latency to leave the enclosed arm after the first trial was lower in a T-maze with the three enclosed arms than in the standard elevated T-maze. In agreement, the exposure of mice to an elevated T-maze without shield, that reduces the perception of openness, increased significantly the latencies to leave the enclosed arm. However, the absence of the shield also increased the time taken to leave the open arms when compared to that recorded in standard T-maze. Systematic observation of behavioral items in the enclosed arm has shown that risk assessment behavior decreases along trials while freezing increases. In the open arms, freezing did not appear to influence the high latency to leave this compartment, since mice spend only about 8% of their time exhibiting this behavior. These results suggest that mice acquire inhibitory avoidance of the open arms by decreasing and increasing time in risk assessment and freezing, respectively, along three consecutive trials. However, one-way escape could not be characterized. Therefore, there are important differences between mice (present results) and rats (previously reported results) in the performance of behavioral tasks in the elevated T-maze.

Role of 5-HT receptor subtypes in the modulation of dorsal periaqueductal gray generated aversion

To explore the role of 5-HT receptor subtypes in controlling aversion, we measured the effect of 5-HT1A and 5-HT2A/2C receptor agonists microinjected into the dorsal periaqueductal gray (DPAG) of rats on aversive behavior induced by electrical stimulation of the same brain area. The 5-HT1A agonists 8-OH-DPAT (4-16 nmol) and BAY-R-1531 (4-16 nmol) raised the threshold of aversive electrical stimulation in a dose-dependent way. Similarly, microinjection of the 5-HT2A/2C agonist DOI (4-16 nmol) increased the aversive mCPP (16 and 32 nmol) was ineffective. Previous intra-DPAG administration of the 5-HT1A receptor blocker NAN-190 (40 nmol) antagonized the antiaversive effect of 8-OH-DPAT (8 nmol), whereas pretreatment with the 5-HT2A receptor blocker spiperone (10 nmol) antagonized the effect of DOI (16 nmol). Spiperone also counteracted the effect of 8-OH-DPAT and NAN-190 counteracted the effect of DOI. These results indicate that activation of 5-HT1A and 5-HT2A receptors inhibits aversion in the DPAG and that both receptors have to be functional for the expression of each one's activation to occur.

Anxiolytic effect of glycine antagonists microinjected into the dorsal periaqueductal grey

To investigate if blockade of the modulatory glycine site of NMDA receptors in the dorsal periaqueductal grey (DPAG) would produce anxiolytic effects, groups of 9-14 rats received microinjections into this structure of 7-chloro-kynurenic acid (7-Cl-KY, 4 and 8 nmol) or 3-amino-1-hydroxypyrrolid-2-one (HA-966, 30 or 100 nmol), two selective antagonists at the strychnine-insensitive glycine modulatory site, and were submitted to the elevated plus-maze, an ethologically based animal model of anxiety. Both drugs increased the percentage of entries and of time spent in open arms as compared to rats receiving isotonic saline. Injections of the active compounds outside the DPAG were not effective. In another experiment microinjections of 7-Cl-KY (8 nmol) and HA-966 (100 nmol) into the DPAG raised the threshold of aversive electrical stimulation of the rat DPAG. These results indicate that microinjections of 7-Cl-KY and HA-966 into the DPAG cause anxiolytic effects in two different models of anxiety and support the proposal that NMDA-mediated neurotransmission in the DPAG may be related to anxiety and panic.

Role of the amygdala and periaqueductal gray in anxiety and panic

The amygdala (AM) and the periaqueductal gray (PAG) represent the rostral and the caudal pole, respectively, of a longitudinally organized neural system, that is responsible for the integration of behavioral and physiological manifestations of defensive reactions against innate and learned threats. Microinjection of benzodiazepine (BZD) anxiolytics, GABAA receptor agonists or 5-HT receptor antagonists into the AM has anxiolytic effects in conflict tests and other models of conditioned fear, while similar administration of 5-HT or of a 5-HT1A receptor agonist has anxiogenic effects. On the other hand, in the test of electrical stimulation of the PAG, microinjection of 5-HT, 5-HT mimetics, or of drugs that enhance the action of endogenous 5-HT into the same brain area has an antiaversive effect, like BZD and GABAA agonists. Furthermore, microinjection of midazolam, of the NMDA receptor antagonist AP-7, or of the 5-HT1A/1B receptor blocker propranolol increased the exploration of the open arms of the elevated plus-maze, having therefore an anxiolytic effect. These results point to an inhibitory role of the GABA-BZD system in both the AM and the PAG. In contrast, 5-HT seemingly enhances conditioned fear in the AM, while inhibiting unconditioned fear in the PAG. Thus, 5-HT2/1C antagonists reportedly release punished behavior when injected into the AM, whereas they antagonized the antiaversive effect of 5-HT, zimelidine and 5-HT1A/1B receptor blockers in the PAG. Since reported clinical studies revealed that one of such compounds, ritanserin, relieves generalized anxiety but tends to aggravate panic disorder, a relationship may be established between the AM and anxiety and the PAG and panic.