Novelty, but Not Operant Aversive Learning, Enhances Fos and Egr-1 Expression in the Medial Prefrontal Cortex and Hippocampal Areas of Rats

Immediate early genes (IEG) are presumed to be activated in response to stress, novelty, and learning. Evidence supports the involvement of prefrontal and hippocampal areas in stress and learning, but also in the detection of novel events. This study examined whether a previous experience with shocks changes the pattern of Fos and Egr-1 expression in the medial prefrontal cortex (mPFC), the hippocampal cornus ammonis 1 (CA1), and dentate gyrus (DG) of adult male Wistar rats that learned to escape in an operant aversive test. Subjects previously exposed to inescapable footshocks that learned to escape from Shocks were assigned to the treated group (EXP). Subjects from Group Novelty (NOV) rested undisturbed during treatment and also learned to escape in the test. The nonshock group (NSH) rested undisturbed in both sessions. Standard immunohistochemistry procedures were used to detect the proteins in brain sections. The results show that a previous experience with shocks changed the pattern of IEG expression, then demonstrating c-fos and egr-1 induction as experience-dependent events. Compared with NSH and EXP an enhanced Fos expression was detected in the mPFC and CA1 subfield of Group NOV, which also exhibited increased Egr-1 expression in the mPFC and DG in comparison to NSH. No differences were found in the DG for Fos, or in the CA1 for Egr-1. Novelty, and not the operant aversive escape learning, seems to have generated IEG induction. The results suggest novel stimuli as a possible confounding factor in studies on Fos and/or Egr-1 expression in aversive conditions.

Medial prefrontal cortex endocannabinoid system modulates baroreflex activity through CB1 receptors

Ferreira-Junior NC, Fedoce AG, Alves FHF, Correa FMA, Resstel LBM. Medial prefrontal cortex endocannabinoid system modulates baroreflex activity through CB1 receptors. Am J Physiol Regul Integr Comp Physiol 302: R876-R885, 2012. First published December 28, 2011; doi: 10.1152/ajpregu.00330.2011.-Neural reflex mechanisms, such as the baroreflex, are involved in the regulation of cardiovascular system activity. Previous results from our group (Resstel LB, Correa FM. Medial prefrontal cortex NMDA receptors and nitric oxide modulate the parasympathetic component of the baroreflex. Eur J Neurosci 23: 481-488, 2006) have shown that glutamatergic synapses in the ventral portion of the medial prefrontal cortex (vMPFC) modulate baroreflex activity. Moreover, glutamatergic neurotransmission in the vMPFC can be modulated by the endocannabinoids system (eCBs), particularly the endocannabinoid anandamide, through presynaptic CB1 receptor activation. Therefore, in the present study, we investigated eCBs receptors that are present in the vMPFC, and more specifically whether CB1 receptors modulate baroreflex activity. We found that bilateral microinjection of the CB1 receptor antagonist AM251 (100 or 300 pmol/200 nl) into the vMPFC increased baroreflex activity in unanesthetized rats. Moreover, bilateral microinjection of either the anandamide transporter inhibitor AM404 (100 pmol/200 nl) or the inhibitor of the enzyme fatty acid amide hydrolase that degrades anandamide, URB597 (100 pmol/200 nl), into the MPFC decreased baroreflex activity. Finally, pretreatment of the vMPFC with an ineffective dose of AM251 (10 pmol/200 nl) was able to block baroreflex effects of both AM404 and URB597. Taken together, our results support the view that the eCBs in the vMPFC is involved in the modulation of baroreflex activity through the activation of CB1 receptors, which modulate local glutamate release.

The endocannabinoid and endovanilloid systems interact in the rat prelimbic medial prefrontal cortex to control anxiety-like behavior

Cannabinoid receptor 1 (CB1) agonists usually induce dose-dependent biphasic effects on anxiety-related responses. Low doses induce anxiolytic-like effects, whereas high doses are ineffective or anxiogenic, probably due to activation of Transient Receptor Potential Vanilloid Type 1 (TRPV1) channels. In this study we have investigated this hypothesis by verifying the effects of the CB1/TRPV1 agonist ACEA injected into the prelimbic medial prefrontal cortex (PL) and the participation of endocannabinoids in the anxiolytic-like responses induced by TRPV1 antagonism, using the elevated plus-maze (EPM) and the Vogel conflict test (VCT). Moreover, we verified the expression of these receptors in the PL by double labeling immunofluorescence. ACEA induced anxiolytic-like effect in the intermediate dose, which was attenuated by previous injection of AM251, a CB1 receptor antagonist. The higher and ineffective ACEA dose caused anxiogenic- and anxiolytic-like effects, when injected after AM251 or the TRPV1 antagonist 6-iodonordihydrocapsaicin (6-I-CPS), respectively. Higher dose of 6-I-CPS induced anxiolytic-like effects both in the EPM and the VCT, which were prevented by previous administration of AM251. In addition, immunofluorescence showed that CB1 and TRPV1 receptors are closely located in the PL These results indicate that the endocannabinoid and endovanilloid systems interact in the PL to control anxiety-like behavior. (C) 2012 Elsevier Ltd. All rights reserved.

Muscarinic and Nicotinic Modulation of Thalamo-Prefrontal Cortex Synaptic Pasticity In Vivo

The mediodorsal nucleus of the thalamus (MD) is a rich source of afferents to the medial prefrontal cortex (mPFC). Dysfunctions in the thalamo-prefrontal connections can impair networks implicated in working memory, some of which are affected in Alzheimer disease and schizophrenia. Considering the importance of the cholinergic system to cortical functioning, our study aimed to investigate the effects of global cholinergic activation of the brain on MD-mPFC synaptic plasticity by measuring the dynamics of long-term potentiation (LTP) and depression (LTD) in vivo. Therefore, rats received intraventricular injections either of the muscarinic agonist pilocarpine (PILO; 40 nmol/mu L), the nicotinic agonist nicotine (NIC; 320 nmol/mu L), or vehicle. The injections were administered prior to either thalamic high-frequency (HFS) or low-frequency stimulation (LFS). Test pulses were applied to MD for 30 min during baseline and 240 min after HFS or LFS, while field postsynaptic potentials were recorded in the mPFC. The transient oscillatory effects of PILO and NIC were monitored through recording of thalamic and cortical local field potentials. Our results show that HFS did not affect mPFC responses in vehicle-injected rats, but induced a delayed-onset LTP with distinct effects when applied following PILO or NIC. Conversely, LFS induced a stable LTD in control subjects, but was unable to induce LTD when applied after PILO or NIC. Taken together, our findings show distinct modulatory effects of each cholinergic brain activation on MD-mPFC plasticity following HFS and LFS. The LTP-inducing action and long-lasting suppression of cortical LTD induced by PILO and NIC might implicate differential modulation of thalamo-prefrontal functions under low and high input drive.

Prefrontal cortex modulation using transcranial DC stimulation reduces alcohol craving: A double-blind, sham-controlled study

Background: Functional neuroimaging studies have shown that specific brain areas are associated with alcohol craving including the dorsolateral prefrontal cortex (DLPFC). We tested whether modulation of DLPFC using transcranial direct current stimulation (tDCS) could alter alcohol craving in patients with alcohol dependence while being exposed to alcohol cues. Methods: We performed a randomized sham-controlled study in which 13 subjects received sham and active bilateral tDCS delivered to DLPFC (anodal left/cathodal right and anodal right/cathodal left). For sham stimulation, the electrodes were placed at the same positions as in active stimulation; however, the stimulator was turned off after 30 s of stimulation. Subjects were presented videos depicting alcohol consumption to increase alcohol craving. Results: Our results showed that both anodal left/cathodal right and anodal right/cathodal left significantly decreased alcohol craving compared to sham stimulation (p < 0.0001). In addition, we found that following treatment, craving could not be further increased by alcohol cues. Conclusions: Our findings showed that tDCS treatment to DLPFC can reduce alcohol craving. These findings extend the results of previous studies using noninvasive brain stimulation to reduce craving in humans. Given the relatively rapid suppressive effect of tDCS and the highly fluctuating nature of alcohol craving, this technique may prove to be a valuable treatment strategy within the clinical setting. (C) 2007 Elsevier Ireland Ltd. All rights reserved.

Decreased Reelin Expression in the Left Prefrontal Cortex (BA9) in Chronic Schizophrenia Patients

Background: Reelin is under epigenetic control and has been reported to be decreased in cortical regions in schizophrenia. Methods: To establish if expression of reelin is altered in specific cortical, hippocampal or thalamic regions of schizophrenia patients, we measured gene expression of reelin in a postmortem study of elderly patients with schizophrenia and non-affected controls in both hemispheres differentiating between gray and white matter. We compared cerebral postmortem samples (dorsolateral prefrontal cortex BA9 and BA46, superior temporal cortex BA22, entorhinal cortex BA28, sensoric cortex BA1-3, hippocampus, CA4, mediodorsal nucleus of the thalamus) from 12 schizophrenia patients with 13 normal subjects investigating gene expression of reelin in the gray and white matter of both hemispheres by in situ-hybridization. Results: The left prefrontal area (BA9) of schizophrenia patients revealed a decreased expression of reelin-mRNA of 29.1% in the white (p = 0.022) and 13.6% in the gray matter (p = 0.007) compared to the control group. None of the other regions examined showed any statistically significant differences. Conclusion: Since reelin is responsible for migration and synapse formation, the decreased gene expression of reelin in the left prefrontal area of schizophrenia patients points to neurodevelopmental deficits in neuronal migration and synaptic plasticity. However, our study group was small, and results should be verified using larger samples. Copyright (C) 2012 S. Karger AG, Basel

Risk assessment behaviors associated with corticosterone trigger the defense reaction to social isolation in rats: Role of the anterior cingulate cortex

The extent to which the hypothalamic-pituitary-adrenal axis is activated by short-term and long-term consequences of stress is still open to investigation. This study aimed to determine (i) the correlation between plasma corticosterone and exploratory behavior exhibited by rats subjected to the elevated plus maze (EPM) following different periods of social isolation, (ii) the effects of the corticosterone synthesis blocker, metyrapone, on the behavioral consequences of isolation, and (iii) whether corticosterone produces its effects through an action on the anterior cingulate cortex, area 1 (Cg1). Rats were subjected to 30-min, 2-h, 24-h, or 7-day isolation periods before EPM exposure and plasma corticosterone assessments. Isolation for longer periods of time produced greater anxiogenic-like effects on the EPM. However, stretched attend posture (SAP) and plasma corticosterone concentrations were increased significantly after 30 min of isolation. Among all of the behavioral categories measured in the EPM, only SAP positively correlated with plasma corticosterone. Metyrapone injected prior to the 24 h isolation period reversed the anxiogenic effects of isolation. Moreover, corticosterone injected into the Cg1 produced a selective increase in SAP. These findings indicate that risk assessment behavior induced by the action of corticosterone on Cg1 neurons initiates a cascade of defensive responses during exposure to stressors.

Environmental enrichment blocks ethanol-induced locomotor sensitization and decreases BDNF levels in the prefrontal cortex in mice

The use of addictive drugs can lead to long-term neuroplastic changes in the brain, including behavioral sensitization, a phenomenon related to addiction. Environmental enrichment (EE) is a strategy used to study the effect of environment on the response to several manipulations, including treatment with addictive drugs. Brain-derived neurotrophic factor (BDNF) has been associated with behaviors related to ethanol addiction. The aim of the present study was to evaluate the effects of EE on ethanol-induced behavioral sensitization and BDNF expression. Mice were exposed to EE and then repeatedly treated with a low dose (1.8 g/kg) of ethanol. Another group of mice was first subjected to repeated ethanol treatment according to the behavioral sensitization protocol and then exposed to EE. Environmental enrichment prevented the development of ethanol-induced behavioral sensitization and blocked behavioral sensitization in sensitized mice. Both repeated ethanol and EE decreased BDNF levels in the prefrontal cortex but not in the hippocampus. However, BDNF levels were lower in ethanol-treated mice exposed to EE. These findings suggest that EE can act on the mechanisms implicated in behavioral sensitization, a model for drug-induced neuroplasticity and relapse. Additionally, EE alters BDNF levels, which regulate addiction-related behaviors.

Changes in CREB activation in the prefrontal cortex and hippocampus blunt ethanol-induced behavioral sensitization in adolescent mice

Drug dependence is a major health problem in adults and has been recognized as a significant problem in adolescents. We previously demonstrated that repeated treatment with a behaviorally sensitizing dose of ethanol in adult mice induced tolerance or no sensitization in adolescents and that repeated ethanol-treated adolescents expressed lower Fos and Egr-1 expression than adult mice in the prefrontal cortex (PFC). In the present work, we investigated the effects of acute and repeated ethanol administration on cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) DNA-binding activity using the electrophoretic mobility shift assay (EMSA) and the phosphorylated CREB (pCREB)/CREB ratio using immunoblotting in both the PFC and hippocampus in adolescent and adult mice. Adult mice exhibited typical locomotor sensitization after 15 days of daily treatment with 2.0 g/kg ethanol, whereas adolescent mice did not exhibit sensitization. Overall, adolescent mice displayed lower CREB binding activity in the PFC compared with adult mice, whereas opposite effects were observed in the hippocampus. The present results indicate that ethanol exposure induces significant and differential neuroadaptive changes in CREB DNA-binding activity in the PFC and hippocampus in adolescent mice compared with adult mice. These differential molecular changes may contribute to the blunted ethanol-induced behavioral sensitization observed in adolescent mice.

Non-invasive brain stimulation for the management of arterial hypertension

The neural control of the cardiovascular system is a complex process that involves many structures at different levels of nervous system. Several cortical areas are involved in the control of systemic blood pressure, such as the sensorimotor cortex, the medial prefrontal cortex and the insular cortex. Non-invasive brain stimulation techniques - repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) - induce sustained and prolonged functional changes of the human cerebral cortex. rTMS and tDCS has led to positive results in the treatment of some neurological and psychiatric disorders. Because experiments in animals show that cortical modulation can be an effective method to regulate the cardiovascular system, non-invasive brain stimulation might be a novel tool in the therapeutics of human arterial hypertension. We here review the experimental evidence that non-invasive brain stimulation can influence the autonomic nervous system and discuss the hypothesis that focal modulation of cortical excitability by rTMS or tDCS can influence sympathetic outflow and, eventually, blood pressure, thus providing a novel therapeutic tool for human arterial hypertension. (C) 2009 Published by Elsevier Ltd.

Cardiovascular responses to glutamate microinjection in the dorsomedial periaqueductal gray of unanesthetized rats

The periaqueductal gray area (PAG) is a mesencephalic area involved in cardiovascular modulation. Glutamate (L-Glu) is an abundant excitatory amino acid in the central nervous system (CNS) and is present in the rat PAG. Moreover, data in the literature indicate its involvement in central blood pressure control. Here we report on the cardiovascular effects caused by microinjection of L-Glu into the dorsomedial PAG (dmPAG) of rats and the glutamatergic receptors as well as the peripheral mechanism involved in their mediation. The microinjection of L-Glu into the dmPAG of unanesthetized rats evoked dose-related pressor and bradycardiac responses. The cardiovascular response was significantly reduced by pretreatment of the dmPAG with a glutamatergic M-methyl-D-aspartate (NMDA) receptor antagonist (LY235959) and was not affected by pretreatment with a non-NMDA receptor antagonist (NBQX), suggesting a mediation of that response by the activation of NMDA receptors. Furthermore, the pressor response was blocked by pretreatment with the ganglion blocker pentolinium (5 mg/kg, intravenously), suggesting an involvement of the sympathetic nervous system in this response. Our results indicate that the microinjection of L-Glu into the dmPAG causes sympathetic-mediated pressor responses in unanesthetized rats, which are mediated by glutamatergic NMDA receptors in the dmPAG. (c) 2012 Wiley Periodicals, Inc.

Segregated anatomical input to sub-regions of the rodent superior colliculus associated with approach and defense

The superior colliculus (SC) is responsible for sensorimotor transformations required to direct gaze toward or a way from unexpected, biologically salient events. Significant changes in the external world are signaled to SC through primary multisensory afferents, spatially organized according to a retinotopic topography. For animals, where anunexpected event could indicate the presence of either predator or prey, early decisions to approach or avoid are particularly important. Rodents' ecology dictates predators are most often detected initially as movements in upper visual field (mapped in medial SC), while appetitive stimuli are normally found in lower visual field (mapped in lateral SC). Our purpose was to exploit this functional segregation to reveal neural sites that can bias or modulate initial approach or avoidance responses. Small injections of Fluoro-Gold were made into medial or lateral sub-regions of intermediate and deep layers of SC (SCm/SCl). A remarkable segregation of input to these two functionally defined areas was found. (i) There were structures that projected only to SCm (e.g., specific cortical areas, lateral geniculate and suprageniculate thalamic nuclei, ventromedial and premammillary hypothalamic nuclei, and several brain-stem areas) or SCl (e.g., primary somatosensory cortex representing upper body parts and vibrissae and parvicellular reticular nucleus in the brainstem). (ii) Other structures projected to both SCm and SCl but from topographically segregated populations of neurons (e.g., zona incerta and substantia nigra pars reticulata). (iii) There were a few brainstem areas in which retrogradely labeled neurons were spatially overlapping (e.g., pedunculopontine nucleus and locus coeruleus). These results indicate significantly more structures across the rat neuraxis are in a position to modulate defense responses evoked from SCm, and that neural mechanisms modulating SC-mediated defense or appetitive behavior are almost entirely segregated.

Effects of diazepam on BOLD activation during the processing of aversive faces

This study aimed to measure, using fMRI, the effect of diazepam on the haemodynamic response to emotional faces. Twelve healthy male volunteers (mean age = 24.83 +/- 3.16 years), were evaluated in a randomized, balanced-order, double-blind, placebo-controlled crossover design. Diazepam (10 mg) or placebo was given 1 h before the neuroimaging acquisition. In a blocked design covert face emotional task, subjects were presented with neutral (A) and aversive (B) (angry or fearful) faces. Participants were also submitted to an explicit emotional face recognition task, and subjective anxiety was evaluated throughout the procedures. Diazepam attenuated the activation of right amygdala and right orbitofrontal cortex and enhanced the activation of right anterior cingulate cortex (ACC) to fearful faces. In contrast, diazepam enhanced the activation of posterior left insula and attenuated the activation of bilateral ACC to angry faces. In the behavioural task, diazepam impaired the recognition of fear in female faces. Under the action of diazepam, volunteers were less anxious at the end of the experimental session. These results suggest that benzodiazepines can differentially modulate brain activation to aversive stimuli, depending on the stimulus features and indicate a role of amygdala and insula in the anxiolytic action of benzodiazepines.

Cannabidiol injected into the bed nucleus of the stria terminalis reduces the expression of contextual fear conditioning via 5-HT1A receptors

Systemic administration of cannabidiol (CBD) attenuates cardiovascular and behavioral changes induced by re-exposure to a context that had been previously paired with footshocks. Previous results from our group using cFos immunohistochemistry suggested that the bed nucleus of the stria terminalis (BNST) is involved in this effect. The mechanisms of CBD effects are still poorly understood, but could involve 5-HT1A receptor activation. Thus, the present work investigated if CBD administration into the BNST would attenuate the expression of contextual fear conditioning and if this effect would involve the activation of 5-HT1A receptors. Male Wistar rats with cannulae bilaterally implanted into the BNST were submitted to a 10 min conditioning session (six footshocks, 1.5 mA/3 s). Twenty-four hours later freezing and cardiovascular responses (mean arterial pressure and heart rate) to the conditioning box were measured for 10 min. CBD (15, 30 or 60 nmol) or vehicle was administered 10 min before the re-exposure to the aversive context. The second experiment was similar to the first one except that animals received microinjections of the 5-HT1A receptor antagonist WAY100635 (0.37 nmol) 5 min before CBD (30 nmol) treatment. The results showed that CBD (30 and 60 nmol) treatment significantly reduced the freezing and attenuated the cardiovascular responses induced by re-exposure to the aversive context. Moreover, WAY100635 by itself did not change the cardiovascular and behavioral response to context, but blocked the CBD effects. These results suggest that CBD can act in the BNST to attenuate aversive conditioning responses and this effect seems to involve 5-HT1A receptor-mediated neurotransmission.

Psychiatric comorbidities in temporal lobe epilepsy: Possible relationships between psychotic disorders and involvement of limbic circuits

Objective: Mounting evidence suggests that the limbic system is pathologically involved in cases of psychiatric comorbidities in temporal lobe epilepsy (TLE) patients. Our objective was to develop a conceptual framework describing how neuropathological and connectivity changes might contribute to the development of psychosis and to the potential neurobiological mechanisms that cause schizophrenia-like psychosis in TLE patients. Methods: In this review, clinical and neuropathological findings, especially brain circuitry of the limbic system, were examined together to enhance our understanding of the association between TLE and psychosis. Finally, the importance of animal models in epilepsy and psychiatric disorders was discussed. Conclusions: TLE and psychiatric symptoms coexist more frequently than chance would predict. Damage and deregulation among critical anatomical regions, such as the hippocampus, amygdala, thalamus, and the temporal, frontal and cingulate cortices, might predispose TLE brains to psychosis. Studies of the effects of kindling and injection of neuroactive substances on behavior and electrophysiological patterns may offer a model of how limbic seizures in humans increase the vulnerability of TLE patients to psychiatric symptoms.