RESUMO
Post-traumatic stress disorder (PTSD) is associated with decreased activity in the prefrontal cortex. PTSD-like pathophysiology and behaviors have been observed in rodents exposed to a single prolonged stress (SPS) procedure. When animals are left alone for 7 days after SPS treatment, they show increased anxiety-like behavior and impaired extinction of conditioned fear, and reduced activity in the prefrontal cortex. Here, we tested the hypothesis that daily optogenetic stimulation of the infralimbic region (IL) of the medial prefrontal cortex (mPFC) during the 7 days after SPS would reverse SPS effects on anxiety and fear extinction. Male Sprague-Dawley rats underwent SPS and then received daily optogenetic stimulation (20 Hz, 2 s trains, every 10 s for 15 min/day) of glutamatergic neurons of the left or right IL for seven days. After this incubation period, rats were tested in the elevated plus-maze (EPM). Twenty-four hours after the EPM test, rats underwent auditory fear conditioning (AFC), extinction training and a retention test. SPS increased anxiety-like behavior in the EPM task and produced a profound impairment in extinction of AFC. Optogenetic stimulation of the left IL, but not right, during the 7-day incubation period reversed the extinction impairment. Optogenetic stimulation did not reverse the increased anxiety-like behavior, suggesting that the extinction effects are not due to a treatment-induced reduction in anxiety. Results indicate that increased activity of the left IL after traumatic experiences can prevent development of extinction impairments. These findings suggest that non-invasive brain stimulation may be a useful tool for preventing maladaptive responses to trauma.
RESUMO
The dorsolateral region of the midbrain periaqueductal gray (dlPAG) modulates both innate and conditioned fear responses. However, the contribution of the rostrocaudal portions of the dlPAG to defense reactions and aversive memories remains unclear. Here, we sought to investigate the effects of N-methyl-d-aspartate (NMDA) receptor blockade within rostral or caudal dlPAG of rats exposed to innate and learned fear to cat odor. For this, adult male Wistar rats were microinjected with the NMDA antagonist D-2-amino-5-phosphono-pentanoate (AP5; 3 or 6nmol/0.2µl) into the rostral or caudal dlPAG before and after the exposure to the cat odor or to the context paired with the predator odor. The results demonstrated that cat odor exposure induced unconditioned defensive behaviors as well as contextual fear. AP5 microinjected in the rostral dlPAG reduced the defensive responses to cat odor and impaired the acquisition, but not consolidation of contextual fear. On the other hand, AP5 infused within the caudal dlPAG promoted long-lasting reduction of contextual fear expression. Altogether, our data suggest that NMDA receptors mediate a functional dichotomy in the rostrocaudal axis of dlPAG regulating unconditioned and conditioned defensive reactions to predatory cues.
Assuntos
Medo , Memória/fisiologia , Odorantes , Substância Cinzenta Periaquedutal/efeitos dos fármacos , Animais , Condicionamento Clássico/efeitos dos fármacos , Relação Dose-Resposta a Droga , Antagonistas de Aminoácidos Excitatórios/farmacologia , Masculino , Memória/efeitos dos fármacos , Microinjeções , Ratos , Ratos Wistar , Valina/análogos & derivados , Valina/farmacologiaRESUMO
There is general agreement that the substantial modification in memory and motivational states exerted by corticosteroids after a traumatic experience is mediated in complementary manner by the mineralocorticoid (MR) and glucocorticoid (GR) receptors. Here we tested the hypothesis that pharmacological manipulation of MR activity would affect behavioral strategy and information storage in an olfactory fear conditioning (OFC) task. Male Wistar rats were submitted to the OFC with different training intensities. We observed that following high intensity OFC acquisition, a set of defensive coping strategies, which includes avoidance and risk assessment behaviors, was elicited when subjects were exposed to the conditioned stimulus (CS) 48 h later. In addition, following either OFC acquisition or retrieval (CS-I test) a profound corticosterone secretion was also detected. Systemic administration of the MR antagonist spironolactone altered the behavioral coping style irrespective the antagonist was administered 60 min prior to the acquisition or before the retrieval session. Surprisingly, the MR agonist fludrocortisone given 60 min prior to acquisition or retrieval of OFC had similar effects as the antagonist. In addition, post-training administration of fludrocortisone, following a weak training procedure, facilitated the consolidation of OFC. Fludrocortisone rather than spironolactone reduced serum corticosterone levels, suggesting that, at least in part, the effects of the MR agonist may derive from additional GR-mediated HPA-axis suppression. In conclusion, the present study suggests the involvement of the MR in the fine-tuning of behavioral adaptation necessary for optimal information storage and expression, as revealed by the marked alterations in the risk assessment behavior.
Assuntos
Condicionamento Psicológico/efeitos dos fármacos , Medo/efeitos dos fármacos , Memória/efeitos dos fármacos , Antagonistas de Receptores de Mineralocorticoides/farmacologia , Percepção Olfatória/efeitos dos fármacos , Receptores de Mineralocorticoides/agonistas , Animais , Condicionamento Psicológico/fisiologia , Corticosterona/sangue , Medo/fisiologia , Fludrocortisona/farmacologia , Masculino , Memória/fisiologia , Atividade Motora/efeitos dos fármacos , Percepção Olfatória/fisiologia , Ratos , Ratos Wistar , Receptores de Mineralocorticoides/metabolismo , Espironolactona/farmacologiaRESUMO
Previous studies have implicated cannabinoids in extinction of conditioned fear. We have recently showed that intraventricular infusion of the phytocannabinoid cannabidiol (CBD) facilitates fear extinction, but the brain regions underlying this effect remained unknown. Here we demonstrate that repeated microinjections of CBD into the infralimbic cortex (IL) facilitated fear extinction, as indicated by reduced levels of freezing during extinction test. Systemic administration of the CB1 receptor antagonist rimonabant blocked the effects of intra-IL CBD, suggesting that CBD acts through CB1 receptors to facilitate fear extinction. Our findings suggest a potential therapeutic use of CBD for extinction-based therapies of aversive memories in humans.
Assuntos
Canabidiol/farmacologia , Córtex Cerebral/efeitos dos fármacos , Condicionamento Clássico/efeitos dos fármacos , Extinção Psicológica/efeitos dos fármacos , Medo/efeitos dos fármacos , Receptor CB1 de Canabinoide/metabolismo , Animais , Antagonistas de Receptores de Canabinoides/farmacologia , Córtex Cerebral/fisiologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Eletrochoque/efeitos adversos , Medo/psicologia , Reação de Congelamento Cataléptica/efeitos dos fármacos , Masculino , Microinjeções , Piperidinas/farmacologia , Pirazóis/farmacologia , Ratos , Ratos Long-Evans , Rimonabanto , Fatores de TempoRESUMO
The alpha-1 adrenergic antagonist prazosin has been used to alleviate the symptoms of PTSD, but the mechanism remains unclear. One possibility is that prazosin may disrupt fear memory reconsolidation, leading to attenuation of fear responses. To test this hypothesis, we administered a single systemic injection of prazosin during the reconsolidation of olfactory fear conditioning in rats. We found that a post-retrieval injection of prazosin disrupted subsequent retrieval of fear. Similarly, intra-prelimbic cortex infusion of prazosin during the reconsolidation period also disrupted subsequent retrieval of fear. These findings suggest that fear memory undergoes reconsolidation through activation of alpha-1 adrenergic receptors in the prelimbic cortex.