Alterações da default mode network provocadas pela ingestão de Ayahuasca investigadas por Ressonância Magnética Funcional

Ayahuasca is psychotropic beverage that has been used for ages by indigenous populations in South America, notably in the Amazon region, for religious and medicinal purposes. The tea is obtained by the decoction of leaves from the Psychotria viridis with the bark and stalk of a shrub, the Banisteriopsis caapi. The first is rich in N-N-dimethyltryptamine (DMT), which has an important and well-known hallucinogenic effect due to its agonistic action in serotonin receptors, specifically 5-HT2A. On the other hand, β-carbolines present in B. caapi, particularly harmine and harmaline, are potent monoamine oxidase inhibitors (MAOi). In addition, the tetrahydroharmine (THH), also present in B. caapi, acts as mild selective serotonin reuptake inhibitor and a weak MAOi. This unique composition induces a number of affective, sensitive, perceptual and cognitive changes in individuals under the effect of Ayahuasca. On the other hand, there is growing interest in the Default Mode Network (DMN), which has been consistently observed in functional neuroimaging studies. The key components of this network include structures in the brain midline, as the anterior medial frontal cortex, ventral medial frontal cortex, posterior cingulate cortex, precuneus, and some regions within the inferior parietal lobe and middle temporal gyrus. It has been argued that DMN participate in tasks involving self-judgments, autobiographical memory retrieval, mental simulations, thinking in perspective, meditative states, and others. In general, these tasks require an internal focus of attention, hence the conclusion that the DMN is associated with introspective mental activity. Therefore, this study aimed to evaluate by functional magnetic resonance imaging (fMRI) changes in DMN caused via the ingestion of Ayahuasca by 10 healthy subjects while submitted to two fMRI protocols: a verbal fluency task and a resting state acquisition. In general, it was observed that Ayahuasca causes a reduction in the fMRI signal in central nodes of DMN, such as the anterior cingulate cortex, the medial prefrontal cortex, the posterior cingulate cortex, precuneus and inferior parietal lobe. Furthermore, changes in connectivity patterns of the DMN were observed, especially a decrease in the functional connectivity of the precuneus. Together, these findings indicate an association between the altered state of consciousness experienced by individuals under the effect of Ayahuasca, and changes in the stream of spontaneous thoughts leading to an increased introspective mental activity

Caracterização comportamental e distribuição de neurônios inibitórios em um modelo animal de autismo induzido por ácido valpróico

Autism comprises a heterogeneous group of neurodevelopmental disorders that affects the brain maturation and produces sensorial, motor, language and social interaction deficits in early childhood. Several studies have shown a major involvement of genetic factors leading to a predisposition to autism, which are possibly affected by environmental modulators during embryonic and post-natal life. Recent studies in animal models indicate that alterations in epigenetic control during development can generate neuronal maturation disturbances and produce a hyper-excitable circuit, resulting in typical symptoms of autism. In the animal model of autism induced by valproic acid (VPA) during rat pregnancy, behavioral, electrophysiological and cellular alterations have been reported which can also be observed in patients with autism. However, only a few studies have correlated behavioral alterations with the supposed neuronal hyper-excitability in this model. The aim of this project was to generate an animal model of autism by pre-natal exposure to VPA and evaluate the early post-natal development and pre-puberal (PND30) behavior in the offspring. Furthermore, we quantified the parvalbumin-positive neuronal distribution in the medial prefrontal cortex and Purkinje cells in the cerebellum of VPA animals. Our results show that VPA treatment induced developmental alterations, which were observed in behavioral changes as compared to vehicle-treated controls. VPA animals showed clear behavioral abnormalities such as hyperlocomotion, prolonged stereotipies and reduced social interaction with an unfamiliar mate. Cellular quantification revealed a decrease in the number of parvalbumin-positive interneurons in the anterior cingulate cortex and in the prelimbic cortex of the mPFC, suggesting an excitatory/inhibitory unbalance in this animal model of autism. Moreover, we also observed that the neuronal reduction occurred mainly in the cortical layers II/III and V/VI. We did not detect any change in the density of Purkinje neurons in the Crus I region of the cerebellar cortex. Together, our results strengthens the face validity of the VPA model in rats and shed light on specific changes in the inhibitory circuitry of the prefrontal cortex in this autism model. Further studies should address the challenges to clarify particular electrophysiological correlates of the cellular alterations in order to better understand the behavioral dysfunctions

Caracterização de subpopulações de interneurônios imunorreativos para proteínas ligantes de cálcio no córtex pré-frontal do Sagui (Callithrix jacchus): distribuição e morfologia

Cortical interneurons are characterized by their distinct morphological, physiological and biochemical properties, acting as modulators of the excitatory activity by pyramidal neurons, for example. Various studies have revealed differences in both distribution and density of this cell group throughout distinct cortical areas in several species. A particular class of interneuron closely related to cortical modulation is revealed by the immunohistochemistry for calcium binding proteins calbindin (CB), calretinina (CR) and parvalbumin (PV). Despite the growing amount of studies focusing on calcium binding proteins, the prefrontal cortex of primates remains relatively little explored, particularly in what concerns a better understanding of the organization of the inhibitory circuitry across its subdivisions. In the present study we characterized the morphology and distribution of neurons rich in calcium-binding proteins in the medial, orbital and dorsolateral areas of the prefrontal cortex of the marmoset (Callithrix jacchus). Using both morphometric and stereological techniques, we found that CR-reactive neurons (mainly double bouquet and bipolar cells) have a more complex dendritic arborization than CB-reactive (bitufted and basket cells) and PV-reactive neurons (chandelier cells). The neuronal densities of CR- and CB-reactive cells are higher in the supragranular layers (II/III) whilst PV-reactive neurons, conversely, are more concentrated in the infragranular layers (V/VI). CR-reactive neurons were the predominant group in the three regions evaluated, being most prevalent in dorsomedial region. Our findings point out to fundamental differences in the inhibitory circuitry of the different areas of the prefrontal cortex in marmoset

Expressão de genes imediatos induzidos por vocalizações em sagüis-comuns (Callithrix jacchus)

Immediate-early genes (IEGs) expression has been widely used as a valuable tool to investigate brain areas activated by specific stimuli. Studies of natural vocalizations, specially in songbirds, have largely benefited from this tool. Here we used IEGs expression to investigate brain areas activated by the hearing of conspecific common marmoset (Callithrix jacchus) vocalizations and/or utterance of antiphonal vocalizations. Nine adult male common marmosets were housed in sound-attenuating cages. Six animals were stimulated with playbacks of freely recorded natural long distance vocalizations (phee calls and twitters; 45 min. total duration). Three of them vocalized in response (O/V group) and three did not (O/n group). The control group (C) was composed by the remaining animals, which neither heard the playbacks nor spontaneously vocalized. After one hour of the stimulation onset (or no stimulation, in the case of the C group), animals were perfused with 0,9% phosphate-saline buffer and 4% paraformaldehyde. The tissue was coronally sectioned at 20 micro meter in a cryostat and submitted to immunohistochemistry for the IEGs egr-1 and c-fos. Marked immunoreactivity was observed in the auditory cortex of O/V and O/n subjects and in the anterior cingulate cortex, the dorsomedial prefrontal cortex and the ventrolateral prefrontal cortex of O/V subjects. In this study, brain areas activated by vocalizations of common marmosets were investigated using IEGs expression for the first time. Our results with the egr-1 gene indicate that potential plastic phenomena occur in areas related to hearing and uttering conspecific vocalizations.

Caracterização dos acoplamentos fase-amplitude na região CA1 do hopocampo

Brain oscillation are not completely independent, but able to interact with each other through cross-frequency coupling (CFC) in at least four different ways: power-to-power, phase-to-phase, phase-to-frequency and phase-to-power. Recent evidence suggests that not only the rhythms per se, but also their interactions are involved in the execution of cognitive tasks, mainly those requiring selective attention, information flow and memory consolidation. It was recently proposed that fast gamma oscillations (60 150 Hz) convey spatial information from the medial entorhinal cortex to the CA1 region of the hippocampus by means of theta (4-12 Hz) phase coupling. Despite these findings, however, little is known about general characteristics of CFCs in several brain regions. In this work we recorded local field potentials using multielectrode arrays aimed at the CA1 region of the dorsal hippocampus for chronic recording. Cross-frequency coupling was evaluated by using comodulogram analysis, a CFC tool recently developted (Tort et al. 2008, Tort et al. 2010). All data analyses were performed using MATLAB (MathWorks Inc). Here we describe two functionally distinct oscillations within the fast gamma frequency range, both coupled to the theta rhythm during active exploration and REM sleep: an oscillation with peak activity at ~80 Hz, and a faster oscillation centered at ~140 Hz. The two oscillations are differentially modulated by the phase of theta depending on the CA1 layer; theta-80 Hz coupling is strongest at stratum lacunosum-moleculare, while theta-140 Hz coupling is strongest at stratum oriens-alveus. This laminar profile suggests that the ~80 Hz oscillation originates from entorhinal cortex inputs to deeper CA1 layers, while the ~140 Hz oscillation reflects CA1 activity in superficial layers. We further show that the ~140 Hz oscillation differs from sharp-wave associated ripple oscillations in several key characteristics. Our results demonstrate the existence of novel theta-associated high-frequency oscillations, and suggest a redefinition of fast gamma oscillations

A neuromodulação do córtex pré-frontal dorsolateral na percepção de tempo em contexto neutro ou emocionalmente ativo

The time perception is critical for environmental adaptation in humans and other species. The temporal processing, has evolved through different neural systems, each responsible for processing different time scales. Among the most studied scales is that spans the arrangement of seconds to minutes. Evidence suggests that the dorsolateral prefrontal (DLPFC) cortex has relationship with the time perception scale of seconds. However, it is unclear whether the deficit of time perception in patients with brain injuries or even "reversible lesions" caused by transcranial magnetic stimulation (TMS) in this region, whether by disruption of other cognitive processes (such as attention and working memory) or the time perception itself. Studies also link the region of DLPFC in emotional regulation and specifically the judgment and emotional anticipation. Given this, our objective was to study the role of the dorsolateral prefrontal cortex in the time perception intervals of active and emotionally neutral stimuli, from the effects of cortical modulation by transcranial direct current stimulation (tDCS), through the cortical excitation (anodic current), inhibition (cathode current) and control (sham) using the ranges of 4 and 8 seconds. Our results showed that there is an underestimation when the picture was presented by 8 seconds, with the anodic current in the right DLPFC, there is an underestimation and with cathodic current in the left DLPFC, there is an overestimation of the time reproduction with neutral ones. The cathodic current over the left DLPFC leads to an inverse effect of neutral ones, an underestimation of time with negative pictures. Positive or negative pictures improved estimates for 8 second and positive pictures inhibited the effect of tDCS in DLPFC in estimating time to 4 seconds. With this work, we conclude that the DLPFC plays a key role in the o time perception and largely corresponds to the stages of memory and decision on the internal clock model. The left hemisphere participates in the perception of time in both active and emotionally neutral contexts, and we can conclude that the ETCC and an effective method to study the cortical functions in the time perception in terms of cause and effect.