Brain activation during fear extinction recall in unmedicated patients with obsessive-compulsive disorder.

Specific brain activation patterns during fear conditioning and the recall of previously extinguished fear responses have been associated with obsessive-compulsive disorder (OCD). However, further replication studies are necessary. We measured skin-conductance response and blood oxygenation level-dependent responses in unmedicated adult patients with OCD (n = 27) and healthy participants (n = 22) submitted to a two-day fear-conditioning experiment comprising fear conditioning, extinction (day 1) and extinction recall (day 2). During conditioning, groups differed regarding the skin conductance reactivity to the aversive stimulus (shock) and regarding the activation of the right opercular cortex, insular cortex, putamen, and lingual gyrus in response to conditioned stimuli. During extinction recall, patients with OCD had higher responses to stimuli and smaller differences between responses to conditioned and neutral stimuli. For the entire sample, the higher the response delta between conditioned and neutral stimuli, the greater the dACC activation for the same contrast during early extinction recall. While activation of the dACC predicted the average difference between responses to stimuli for the entire sample, groups did not differ regarding the activation of the dACC during extinction recall. Larger unmedicated samples might be necessary to replicate the previous findings reported in patients with OCD.

Involvement of D2-like dopaminergic receptors in contextual fear conditioning in female rats: influence of estrous cycle.

Introduction: Dopamine has been increasingly recognized as a key neurotransmitter regulating fear/anxiety states. Nevertheless, the influence of sex and estrous cycle differences on the role of dopamine in fear responses needs further investigation. We aimed to evaluate the effects of sulpiride (a dopaminergic D2-like receptor antagonist) on contextual fear conditioning in females while exploring the influence of the estrous cycle. Methods: First, using a contextual fear conditioning paradigm, we assessed potential differences in acquisition, expression, and extinction of the conditioned freezing response in male and female (split in proestrus/estrus and metestrus/diestrus) Wistar rats. In a second cohort, we evaluated the effects of sulpiride (20 and 40 mg/kg) on contextual conditioned fear in females during proestrus/estrus and metestrus/diestrus. Potential nonspecific effects were assessed in motor activity assays (catalepsy and open-field tests). Results: No sex differences nor estrous cycle effects on freezing behavior were observed during the fear conditioning phases. Sulpiride reduced freezing expression in female rats. Moreover, females during the proestrus/estrus phases of the estrous cycle were more sensitive to the effects of sulpiride than females in metestrus/diestrus. Sulpiride did not cause motor impairments. Discussion: Although no sex or estrous cycle differences were observed in basal conditioned fear expression and extinction, the estrous cycle seems to influence the effects of D2-like antagonists on contextual fear conditioning.

Fear extinction in an obsessive-compulsive disorder animal model: Influence of sex and estrous cycle.

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition that affects men and women equally, but with a sexually dimorphic pattern of development. Reproductive cycle events can influence symptom severity of OCD in females, indicating that ovarian hormones or their interaction with distinct neurotransmitter systems may play a role in OCD pathophysiology. Clinical studies and animal models have confirmed the importance of the serotonergic (5-HT) system in the neurobiology and treatment of OCD. Accordingly, the non-selective 5-HT2c agonist, meta-chlorophenylpiperazine (mCPP), exacerbates symptoms in untreated OCD patients. In rodents, it evokes repetitive behaviors that engage brain areas that are homologous with those found to be dysfunctional in OCD patients. These regions, including the medial prefrontal and anterior cingulate cortices, are also involved in fear inhibition, which is impaired in OCD. Here, we treated rats with mCPP (0.5 and 3.0 mg/kg) to evaluate its influence on self-grooming behavior and assess potential fear extinction retention deficits, taking into account sex differences and females' estrous cycle. We found that mCPP exacerbated grooming in male and female rats, irrespective of the estrous cycle phase. Fear extinction retention, however, was impaired only in females. Moreover, females undergoing fear extinction training during the metestrus/diestrus phases of the estrous cycle were more sensitive to the impairments induced by mCPP. Our results indicate that mCPP can induce OCD-like symptoms, exacerbating self-grooming and impairing fear extinction. It suggests that changes in 5-HT signaling through 5-HT2c receptors may have an important role in the OCD pathophysiology and that the influence of gonadal hormones in OCD should be further investigated.

Rats with differential self-grooming expression in the elevated plus-maze do not differ in anxiety-related behaviors.

Individual differences are important biological predictors for reactivity to stressful stimulation. The extent to which trait differences underlie animal's reactions to conditioned and unconditioned fear stimuli, for example, is still to be clarified. Although grooming behavior has been associated with some aspects of the obsessive-compulsive disorder in humans, its relation with other anxiety disorders is still unknown. Given that grooming behavior could be a component of the whole spectrum of these disorders, in the present study we allocated male Wistar rats in low, intermediate and high self-grooming groups according to the duration of such behavior in the elevated plus-maze (EPM). These groups were then evaluated in unconditioned fear tests, such as the EPM and the open-field, and in conditioned fear tests, such as fear-potentiated startle and fear extinction retention. Additionally, we studied the expression of unconditioned behaviors in marble burying test and the sensorimotor gate function with prepulse inhibition test. Neurochemicals and neuroendocrine parameters were also evaluated, with the quantification of basal corticosterone in the plasma, and dopamine, serotonin and their metabolites in brain structures involved with fear processing. In general, rats classified according to grooming expression showed similar performance in all behavioral tests. Accordingly, corticosterone and monoamine concentrations were similar among groups. Thus, despite grooming expression elicited by different approaches--especially pharmacological ones--has been related with some aspects of anxiety disorders, rats with different expression of spontaneous self-grooming in the EPM do not differ in anxiety-like behaviors nor in neurochemical and neuroendocrine parameters generally associated with anxiety disorders.

Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact?

Haloperidol is a dopamine D2 receptor antagonist that induces catalepsy when systemically administered to rodents. The haloperidol-induced catalepsy is a state of akinesia and rigidity very similar to that seen in Parkinson's disease. There exists great interest in knowing whether or not some degree of emotionality underlies catalepsy. If so, what kind of emotional distress would permeate such motor disturbance? This study is an attempt to shed some light on this issue through an analysis of ultrasound vocalizations (USVs) of 22 kHz, open-field test, and contextual conditioned fear in rats with some degree of catalepsy induced by haloperidol. Systemic administration of haloperidol caused catalepsy and decreased exploratory activity in the open-field. There was no difference in the emission of USVs between groups during the catalepsy or the exploratory behavior in the open-field test. In the contextual conditioned fear, when administered before training session, haloperidol did not change the emission of USVs or the freezing response. When administered before testing session, haloperidol enhanced the freezing response and decreased the emission of USVs on the test day. These findings suggest that the involvement of dopaminergic mechanisms in threatening situations depends on the nature of the aversive stimulus. Activation of D2 receptors occurs in the setting up of adaptive responses to conditioned fear stimuli so that these mechanisms seem to be important for the emission of 22 kHz USVs during the testing phase of the contextual conditioned fear, but not during the training session or the open-field test (unconditioned fear stimuli). Catalepsy, on the other hand, is the result of the blockage of D2 receptors in neural circuits associated to motor behavior that appears to be dissociated from those directly linked to dopamine-mediated neural mechanisms associated to fear.

Envolvimento de mecanismos glutamatérgicos da substância cinzenta periaquedutal dorsal e do hipotálamo medial no medo condicionado à luz

A substância cinzenta periaquedutal dorsal (dPAG) e o hipotálamo medial (MH) são duas estruturas encefálicas que estão envolvidas na elaboração de estados aversivos e expressão de respostas defensivas. A estimulação elétrica da dPAG ou do MH produz uma série de respostas comportamentais que se assemelham às respostas defensivas induzidas pela presença de um predador. Esses mesmos comportamentos podem ser eliciados com a microinjeção local de agonistas glutamatérgicos nessas estruturas, indicando o envolvimento de aminoácidos excitatórios na expressão das respostas defensivas incondicionadas. Apesar disso, a participação destas estruturas no medo condicionado ainda é pouco conhecida. Assim, o objetivo deste estudo foi avaliar o envolvimento da mediação glutamatérgica da dPAG e de núcleos do MH núcleo anterior (AH) e núcleo pré-mamilar dorsal (PMd) na expressão do medo condicionado à luz. Para isso, foram avaliados os efeitos de agonistas e antagonistas glutamatérgicos (AMPA/Cainato e NMDA) administrados nessas estruturas no teste do sobressalto potencializado pelo medo (SPM) e na medida de congelamento condicionado. Ratos Wistar machos com cânulas-guias implantadas na dPAG, AH ou PMd foram submetidos ao condicionamento aversivo (pareamentos luz+choque). Vinte e quatro horas depois, esses animais receberam injeções intra-dPAG, AH ou PMd de NMDA ou ácido caínico (agonistas NMDA e AMPA/Cainato, respectivamente) ou AP7 ou NBQX (antagonistas NMDA e AMPA/Cainato, respectivamente)...(AU)

he dorsal periaqueductal gray matter (dPAG) and the medial hypothalamus (MH) are two brain structures that are involved in the elaboration of aversive states and expression of defensive responses. Electrical stimulation of the dPAG or MH produces a series of behavioral responses that resemble those defensive responses triggered in the presence of a predator. These same behaviors can be elicited with the local microinjection of glutamate agonists into these structures, indicating the involvement of excitatory amino acids in the expression of unconditioned fear responses. Nevertheless, the involvement of these structures in fear conditioning is still unknown. The objective of this study was to evaluate the involvement of glutamatergic mediation of the dPAG and MH nuclei anterior nucleus (AH) and dorsal pre-mammillary nucleus (PMd) in the expression of conditioned fear to the light. Thus, we evaluated the effects of glutamatergic agonists and antagonists (AMPA/Kainate and NMDA) administered into these structures in fear potentiated startle (FPS) and conditioned freezing responses to the light. Male Wistar rats with guide-cannulae implanted in the dPAG, AH or PMd were subjected to aversive conditioning (light+shock pairings). Twenty-four hours later, the animals were injected intra-dPAG, AH or PMd with NMDA or kainic acid (NMDA and AMPA/Kainate agonists, respectively)

Outlining new frontiers for the comprehension of obsessive-compulsive disorder: a review of its relationship with fear and anxiety.

UNLABELLED: Anxiety is an important component of the psychopathology of the obsessive-compulsive disorder (OCD). So far, most interventions that have proven to be effective for treating OCD are similar to those developed for other anxiety disorders. However, neurobiological studies of OCD came to conclusions that are not always compatible with those previously associated with other anxiety disorders. OBJECTIVES: The aim of this study is to review the degree of overlap between OCD and other anxiety disorders phenomenology and pathophysiology to support the rationale that guides research in this field. RESULTS: Clues about the neurocircuits involved in the manifestation of anxiety disorders have been obtained through the study of animal anxiety models, and structural and functional neuroimaging in humans. These investigations suggest that in OCD, in addition to dysfunction in cortico-striatal pathways, the functioning of an alternative neurocircuitry, which involves amygdalo-cortical interactions and participates in fear conditioning and extinction processes, may be impaired. CONCLUSION: It is likely that anxiety is a relevant dimension of OCD that impacts on other features of this disorder. Therefore, future studies may benefit from the investigation of the expression of fear and anxiety by OCD patients according to their type of obsessions and compulsions, age of OCD onset, comorbidities, and patterns of treatment response.

Outlining new frontiers for the comprehension of obsessive-compulsive disorder: a review of its relationship with fear and anxiety / Desenhando as novas fronteiras para a compreensão do transtorno obsessivo-compulsivo: uma revisão de sua relação com o medo e a ansiedade

Anxiety is an important component of the psychopathology of the obsessive-compulsive disorder (OCD). So far, most interventions that have proven to be effective for treating OCD are similar to those developed for other anxiety disorders. However, neurobiological studies of OCD came to conclusions that are not always compatible with those previously associated with other anxiety disorders. OBJECTIVES: The aim of this study is to review the degree of overlap between OCD and other anxiety disorders phenomenology and pathophysiology to support the rationale that guides research in this field. RESULTS: Clues about the neurocircuits involved in the manifestation of anxiety disorders have been obtained through the study of animal anxiety models, and structural and functional neuroimaging in humans. These investigations suggest that in OCD, in addition to dysfunction in cortico-striatal pathways, the functioning of an alternative neurocircuitry, which involves amygdalo-cortical interactions and participates in fear conditioning and extinction processes, may be impaired. CONCLUSION: It is likely that anxiety is a relevant dimension of OCD that impacts on other features of this disorder. Therefore, future studies may benefit from the investigation of the expression of fear and anxiety by OCD patients according to their type of obsessions and compulsions, age of OCD onset, comorbidities, and patterns of treatment response.

A ansiedade é um componente importante da psicopatologia do transtorno obsessivo-compulsivo (TOC). Até o momento, a maioria das intervenções que provaram ser eficazes para o tratamento de TOC é semelhante àquelas desenvolvidas para outros transtornos de ansiedade. No entanto, estudos que investigaram a neurobiologia do TOC chegaram a conclusões que nem sempre são compatíveis com aquelas anteriormente associadas aos demais transtornos de ansiedade. OBJETIVOS: Neste artigo, revisamos o grau de sobreposição entre as características do TOC e a fenomenologia e fisiopatologia dos demais transtornos de ansiedade com o intuito de dar suporte ao racional que orienta a pesquisa nesse campo. RESULTADOS: Alguns dados sobre os neurocircuitos envolvidos na manifestação dos transtornos de ansiedade foram obtidos a partir do estudo de modelos animais de ansiedade, e da neuroimagem estrutural e funcional em humanos. Esses trabalhos sugerem que no TOC, além da disfunção das vias corticoestriatais, o funcionamento do circuito amigdalocortical, essencial para a apresentação da resposta de medo e processos de extinção dessa resposta, também pode estar prejudicado. CONCLUSÃO: É provável que a ansiedade seja uma dimensão relevante do TOC, com impacto em outras características desse transtorno. Consequentemente, estudos futuros podem se beneficiar da investigação dos fenômenos de medo e ansiedade e de suas relações com os tipos de obsessões e compulsões, idade de início do TOC, comorbidades e padrões de resposta ao tratamento.

Conditioned fear is modulated by D2 receptor pathway connecting the ventral tegmental area and basolateral amygdala.

Excitation of the mesocorticolimbic pathway, originating from dopaminergic neurons in the ventral tegmental area (VTA), may be important for the development of exaggerated fear responding. Among the forebrain regions innervated by this pathway, the amygdala is an essential component of the neural circuitry of conditioned fear. The functional role of the dopaminergic pathway connecting the VTA to the basolateral amygdala (BLA) in fear and anxiety has received little attention. In vivo microdialysis was performed to measure dopamine levels in the BLA of Wistar rats that received the dopamine D(2) agonist quinpirole (1 µg/0.2 µl) into the VTA and were subjected to a fear conditioning test using a light as the conditioned stimulus (CS). The effects of intra-BLA injections of the D(1) antagonist SCH 23390 (1 and 2 µg/0.2 µl) and D(2) antagonist sulpiride (1 and 2 µg/0.2 µl) on fear-potentiated startle (FPS) to a light-CS were also assessed. Locomotor performance was evaluated by use of open-field and rotarod tests. Freezing and increased dopamine levels in the BLA in response to the CS were both inhibited by intra-VTA quinpirole. Whereas intra-BLA SCH 23390 did not affect FPS, intra-BLA sulpiride (2 µg) inhibited FPS. Sulpiride's ability to decrease FPS cannot be attributed to nonspecific effects because this drug did not affect motor performance. These findings indicate that the dopamine D(2) receptor pathway connecting the ventral tegmental area and the basolateral amygdala modulates fear and anxiety and may be a novel pharmacological target for the treatment of anxiety.

Involvement of GABAergic mechanisms of the dorsal periaqueductal gray and inferior colliculus on unconditioned fear

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.(AU)

Involvement of GABAergic mechanisms of the dorsal periaqueductal gray and inferior colliculus on unconditioned fear

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.

Role of dopamine receptors in the ventral tegmental area in conditioned fear.

The increased startle reflex in the presence of a stimulus that has been previously paired with footshock has been termed fear-potentiated startle (FPS) and is considered a reliable index of anxiety. Some studies have suggested an association between stressful situations and alterations in dopaminergic (DA) transmission. Many studies converge on the hypothesis that the mesocorticolimbic pathway, originating from DA neurons in the ventral tegmental area (VTA), is particularly sensitive to fear-arousing stimuli. The present study explored the involvement of VTA DA receptors in the acquisition and expression of conditioned fear to a light conditioned stimulus (CS). We evaluated the effects of intra-VTA administration of SKF 38393 (D(1) agonist), SCH 23390 (D(1) antagonist), quinpirole (D(2) agonist), and sulpiride (D(2) antagonist) on FPS. All drugs were administered bilaterally into the VTA (1.0 microg/0.2 microl/site). Locomotor activity/exploration and motor coordination were evaluated in the open-field and rotarod tests. None of the drugs produced significant effects on FPS when injected before conditioning, indicating that VTA DA receptors are not involved in the acquisition of conditioned fear to a light-CS. In contrast, when injected before the test session, quinpirole significantly reduced FPS, whereas the other drugs had no effect. Quinpirole's ability to decrease FPS may be the result of an action on VTA D(2) presynaptic autoreceptors that decrease dopamine levels in terminal fields of the mesocorticolimbic pathway. Altogether, the present results suggest the importance of VTA DA neurons in the fear-activating effects of Pavlovian conditioning. In addition to demonstrating the importance of dopaminergic mechanisms in the motivational consequences of footshock, the present findings also indicate that these neural circuits are mainly involved in the expression, rather than acquisition, of conditioned fear.

Envolvimento de mecanismos GaBaérgicos da substância cinzenta periaquedutal dorsal e do colículo inferiores no medo condicionado e incondicionado

A substância cinzenta periaquedutal dorsal (SCPd) e o colículo inferior (CI) são duas estruturas do teto mesencefálico que, juntamente com a amígdala, o hipotálamo dorsomedial e o colículo superior, estão envolvidas na modulação da expressão comportamental dos estados de medo. A estimulação química ou elétrica destas estruturas produz uma série de respostas comportamentais defensivas. Além disso, dados comportamentais com modelos animais de ansiedade têm fornecido evidências da existência de uma regulação inibitória tônica GABAérgica na SCPd e CI. Neste estudo investigamos o envolvimento da neurotransmissão GABAérgica na expressão do medo condicionado e do medo incondicionado. Para isso, os efeitos da administração de muscimol (agonista GABA-A) e semicarbazida (inibidor da descarboxilase do ácido glutâmico) na SCPd e CI foram analisados no teste do sobressalto potencializado pelo medo, na resposta de congelamento condicionada, nos limiares de congelamento e fuga determinados por estimulação elétrica dessas estruturas e no congelamento pós-estimulação. No modelo de medo incondicionado, microinjeções de muscimol intra-SCPd reduziram a aversividade da estimulação elétrica e o congelamento pós- estimulação, ao passo que a semicarbazida produziu efeitos opostos em ambas as condições. O muscimol também causou redução significativa no sobressalto potencializado pelo medo e congelamento condicionado, enquanto que a semicarbazida não alterou essas respostas. Já a microinjeção de ambas as drogas no CI não produziu efeitos no modelo condicionado, mas no teste incondicionado, o muscimol reduziu a aversividade da estimulação elétrica. Esses dados mostram uma participação diferencial de mecanismos GABAérgicos no medo condicionado e incondicionado. Estes mecanismos na SCPd parecem estar envolvidos tanto no medo condicionado quanto no incondicionado, enquanto que no CI eles parecem participar somente do medo incondicionado (AU)

Dopamine D2 receptor mechanisms in the expression of conditioned fear.

The increase in the startle reflex in the presence of a stimulus that has been previously paired to foot shock is taken as an index of anxiety and named fear potentiated startle (FPS). Freezing behavior, defined as a cessation of all observable movements except those associated with respiration, has also been used as an index of fear in rats. Recently, a growing body of evidence has suggested that dopaminergic mechanisms are significant for different aspects of affective memory, namely its formation, expression or retrieval. However, the results of studies that have directly examined the ability of the dopaminergic system to influence fear have been inconsistent. This work is aimed at examining the involvement of D1 and D2 receptors in the acquisition and expression of conditioned fear using the fear potentiated startle test and the freezing behavior. We evaluated the effects of systemic administration of the D1 antagonist SCH 23390, the D1 agonist SKF 38393, the D2 antagonist sulpiride and the D2 agonist quinpirole before and after conditioning on FPS and freezing as indices of fear memory. The motor activity of the animals was also evaluated in an open field test. Injections of SCH 23390, SKF 38393, sulpiride and quinpirole before conditioning sessions did not produce any significant effect on FPS, but SCH 23390 decreased freezing. Injections of SCH 23390, SKF 38393 and sulpiride before testing session did not produce any significant effect on FPS or freezing. Quinpirole caused significant reduction in FPS and freezing when injected before testing. Drugs' actions were not due to nonspecific impairments in the ability to respond to the CS because the identical drug treatments had no effect in an open field test. Our findings indicate that DA mechanisms mediated by D2 receptors are mainly involved in the expression rather than in the acquisition of fear.