Medial prefrontal cortex Transient Receptor Potential Vanilloid Type 1 (TRPV1) in the expression of contextual fear conditioning in Wistar rats

The expression of contextual fear conditioning involves the dorsal hippocampus TRPV1 receptor interacting with the NMDA/NO/cGMP signalling pathway

BACKGROUND AND PURPOSE

The dorsal hippocampus (dHIP) is pivotal for learning, memory, and defensive responses. Transient receptor potential vanilloid type 1 (TRPV1) receptors in the dHIP modulate contextual fear conditioning by triggering a cascade involving glutamate release, nitric oxide (NO) formation and cyclic guanosine monophosphate (cGMP) production. The present study investigated the involvement of dHIP TRPV1 receptors and their interaction with the glutamate/NO/cGMP signalling pathway in modulating the expression of contextual fear conditioning (CFC).

EXPERIMENTAL APPROACH

Male Wistar rats were submitted to an aversive contextual conditioning session and, 48 h later, were re-introduced to the same aversive environment where the freezing response and autonomic activity (evidenced by increased arterial pressure and heart rate and a decrease in tail temperature) were measured.

KEY RESULTS

The results demonstrated that the TRPV1 antagonist 6-I-CPS in dHIP reduced the expression of CFC, whereas the agonist capsaicin had the opposite effect. Furthermore, dHIP pre-treatment with an NMDA receptor antagonist (AP7), neuronal NO synthase inhibitor (N-propyl-L-arginine), NO scavenger (c-PTIO) or guanylate cyclase inhibitor (ODQ) attenuated capsaicin-induced increases in CFC. Finally, we observed that re-exposure to the aversive chamber increased dHIP NO levels in conditioned animals compared with a non-conditioned group, which was prevented by the administration of the TRPV1 antagonist, 6-I-CPS.

CONCLUSION AND IMPLICATIONS

Our study revealed that TRPV1 receptors in the dHIP play a crucial role in modulating contextual fear expression by acting through the NMDA receptor/NO/cGMP signalling pathway, providing important insights into the underlying mechanisms and potential therapeutic avenues associated with these pathways.

Interplay between endocannabinoid and endovanilloid mechanisms in fear conditioning

OBJECTIVE

The transient receptor potential cation channel, subfamily V (vanilloid), member 1 (TRPV1) mediates pain perception to thermal and chemical stimuli in peripheral neurons. The cannabinoid receptor type 1 (CB1), on the other hand, promotes analgesia in both the periphery and the brain. TRPV1 and CB1 have also been implicated in learned fear, which involves the association of a previously neutral stimulus with an aversive event. In this review, we elaborate on the interplay between CB1 receptors and TRPV1 channels in learned fear processing.

METHODS

We conducted a PubMed search for a narrative review on endocannabinoid and endovanilloid mechanisms on fear conditioning.

RESULTS

TRPV1 and CB1 receptors are activated by a common endogenous agonist, arachidonoyl ethanolamide (anandamide), Moreover, they are expressed in common neuroanatomical structures and recruit converging cellular pathways, acting in concert to modulate fear learning. However, evidence suggests that TRPV1 exerts a facilitatory role, whereas CB1 restrains fear responses.

CONCLUSION

TRPV1 and CB1 seem to mediate protective and aversive roles of anandamide, respectively. However, more research is needed to achieve a better understanding of how these receptors interact to modulate fear learning.

TRPV1 channel in the pathophysiology of epilepsy and its potential as a molecular target for the development of new antiseizure drug candidates

Identification of transient receptor potential cation channel, subfamily V member 1 (TRPV1), also known as capsaicin receptor, in 1997 was a milestone achievement in the research on temperature sensation and pain signalling. Very soon after it became evident that TRPV1 is implicated in a wide array of physiological processes in different peripheral tissues, as well as in the central nervous system, and thereby could be involved in the pathophysiology of numerous diseases. Increasing evidence suggests that modulation of TRPV1 may also affect seizure susceptibility and epilepsy. This channel is localized in brain regions associated with seizures and epilepsy, and its overexpression was found both in animal models of seizures and in brain samples from epileptic patients. Moreover, modulation of TRPV1 on non-neuronal cells (microglia, astrocytes, and/or peripheral immune cells) may have an impact on the neuroinflammatory processes that play a role in epilepsy and epileptogenesis. In this paper, we provide a comprehensive and critical overview of currently available data on TRPV1 as a possible molecular target for epilepsy management, trying to identify research gaps and future directions. Overall, several converging lines of evidence implicate TRPV1 channel as a potentially attractive target in epilepsy research but more studies are needed to exploit the possible role of TRPV1 in seizures/epilepsy and to evaluate the value of TRPV1 ligands as candidates for new antiseizure drugs.

Functional lateralization in the medial prefrontal cortex control of contextual conditioned emotional responses in rats

A functional lateralization has been reported in control of emotional responses by the medial prefrontal cortex (mPFC). However, a hemisphere asymmetry in involvement of the mPFC in expression of fear conditioning responses has never been reported. Therefore, we investigated whether control by mPFC of freezing and cardiovascular responses during re-exposure to an aversively conditioned context is lateralized. For this, rats had guide cannulas directed to the mPFC implanted bilaterally or unilaterally in the right or left hemispheres. Vehicle or the non-selective synaptic inhibitor CoCl2 was microinjected into the mPFC 10 min before re-exposure to a chamber where the animals had previously received footshocks. A catheter was implanted into the femoral artery before the fear retrieval test for cardiovascular recordings. We observed that bilateral microinjection of CoCl2 into the mPFC reduced both the freezing behavior (enhancing locomotion and rearing) and arterial pressure and heart rate increases during re-exposure to the aversively conditioned context. Unilateral microinjection of CoCl2 into the right hemisphere of the mPFC also decreased the freezing behavior (enhancing locomotion and rearing), but without affecting the cardiovascular changes. Conversely, unilateral synaptic inhibition in the left mPFC did not affect either behavioral or cardiovascular responses during fear retrieval test. Taken together, these results suggest that the right hemisphere of the mPFC is necessary and sufficient for expression of freezing behavior to contextual fear conditioning. However, the control of cardiovascular responses and freezing behavior during fear retrieval test is somehow dissociated in the mPFC, being the former bilaterally processed.

Decoding the language of fear: Unveiling objective and subjective indicators in rodent models through a systematic review and meta-analysis

While rodent models are vital for studying mental disorders, the underestimation of construct validity of fear indicators has led to limitations in translating to effective clinical treatments. Addressing this gap, we systematically reviewed 5054 articles from the 1960 s, understanding underlying theoretical advancement, and selected 68 articles with at least two fear indicators for a three-level meta-analysis. We hypothesized correlations between different indicators would elucidate similar functions, while magnitude differences could reveal distinct neural or behavioral mechanisms. Our findings reveal a shift towards using freezing behavior as the primary fear indicator in rodent models, and strong, moderate, and weak correlations between freezing and conditioned suppression ratios, 22-kHz ultrasonic vocalizations, and autonomic nervous system responses, respectively. Using freezing as a reference, moderator analysis shows treatment types and fear stages significantly influenced differences in magnitudes between two indicators. Our analysis supports a two-system model of fear in rodents, where objective and subjective fears could operate on a threshold-based mechanism.

Exposure time as an influencing factor among rheumatoid arthritis patients subjected to traditional Siwan therapy

Rheumatoid arthritis (RA) is a long-term autoimmune disease characterized by intra- and extra-articular manifestations. Sand therapy is traditionally indicated for RA, chronic pain, skin diseases, and musculoskeletal disorders. Many places in the world use sand therapy, including Siwa, which is a famous place in Egypt. This study investigated the exposure time to Siwan traditional therapy as a factor influencing central sensitization, pain severity, pain threshold, and kinesiophobia in RA by measuring the central sensory inventory (CSI), visual analogue scale, pressure algometer, and TAMPA kinesiophobia scale, respectively. Twenty-four patients with RA were recruited from 6 traditional healing centers, 24 RA patients were recruited and randomly assigned to 2 equal groups (GI and GII). The first received Siwan traditional therapy for 3 days, while the second received the same program for 5 days. The results revealed a significant difference in CSI between pre- and posttreatment within the GII (P = .038). The Tampa Scale score improved significantly in both groups (P = .004 and P = .014, respectively). Pain severity and pain threshold at all sites showed significant posttreatment improvements in the GII. Significant posttreatment changes were only found for GI in terms of pain severity and the most painful joint (P = .010 and P = .035, respectively). Significant changes were observed in kinesiophobia, pain severity, and pain threshold in the most painful joint 3 and 5 days after Siwan traditional therapy. Despite the nonsignificant differences in all parameters between the 2 groups, all the measured parameters produced favorable results after 5 days of treatment, suggesting the need for a long-term effect investigation.

Endocannabinoid signaling and epigenetics modifications in the neurobiology of stress-related disorders

Stress exposure is associated with psychiatric conditions, such as depression, anxiety, and post-traumatic stress disorder (PTSD). It is also a vulnerability factor to developing or reinstating substance use disorder. Stress causes several changes in the neuro-immune-endocrine axis, potentially resulting in prolonged dysfunction and diseases. Changes in several transmitters, including serotonin, dopamine, glutamate, gamma-aminobutyric acid (GABA), glucocorticoids, and cytokines, are associated with psychiatric disorders or behavioral alterations in preclinical studies. Complex and interacting mechanisms make it very difficult to understand the physiopathology of psychiatry conditions; therefore, studying regulatory mechanisms that impact these alterations is a good approach. In the last decades, the impact of stress on biology through epigenetic markers, which directly impact gene expression, is under intense investigation; these mechanisms are associated with behavioral alterations in animal models after stress or drug exposure, for example. The endocannabinoid (eCB) system modulates stress response, reward circuits, and other physiological functions, including hypothalamus-pituitary-adrenal axis activation and immune response. eCBs, for example, act retrogradely at presynaptic neurons, limiting the release of neurotransmitters, a mechanism implicated in the antidepressant and anxiolytic effects after stress. Epigenetic mechanisms can impact the expression of eCB system molecules, which in turn can regulate epigenetic mechanisms. This review will present evidence of how the eCB system and epigenetic mechanisms interact and the consequences of this interaction in modulating behavioral changes after stress exposure in preclinical studies or psychiatric conditions. Moreover, evidence that correlates the involvement of the eCB system and epigenetic mechanisms in drug abuse contexts will be discussed.

Contextual fear expression engages a complex set of interactions between ventromedial prefrontal cortex cholinergic, glutamatergic, nitrergic and cannabinergic signaling

Rats re-exposed to an environment previously associated with the onset of shocks evoke a set of conditioned defensive responses in preparation to an eventual flight or fight reaction. Ventromedial prefrontal cortex (vmPFC) is mutually important for controlling the behavioral/physiological consequences of stress exposure and the one's ability to satisfactorily undergo spatial navigation. While cholinergic, cannabinergic and glutamatergic/nitrergic neurotransmissions within the vmPFC are shown as important for modulating both behavioral and autonomic defensive responses, there is a gap on how these systems would interact to ultimately coordinate such conditioned reactions. Then, males Wistar rats had guide cannulas bilaterally implanted to allow drugs to be administered in vmPFC 10 min before their re-exposure to the conditioning chamber where three shocks were delivered at the intensity of 0.85 mA for 2 s two days ago. A femoral catheter was implanted for cardiovascular recordings the day before fear retrieval test. It was found that the increment of freezing behavior and autonomic responses induced by vmPFC infusion of neostigmine (acetylcholinesterase inhibitor) were prevented by prior infusion of a transient receptor potential vanilloid type 1 (TRPV1) antagonist, N-methyl-d-aspartate receptor antagonist, neuronal nitric oxide synthase inhibitor, nitric oxide scavenger and soluble guanylate cyclase inhibitor. A type 3 muscarinic receptor antagonist was unable to prevent the boosting in conditioned responses triggered by a TRPV1 agonist and a cannabinoid receptors type 1 antagonist. Altogether, our results suggest that expression of contextual conditioned responses involves a complex set of signaling steps comprising different but complementary neurotransmitter pathways.

Bed nucleus of the stria terminalis CB1 receptors and the FAAH enzyme modulate anxiety behavior depending on previous stress exposure

The endocannabinoid (eCB) anandamide (AEA) is synthesized on-demand in the post-synaptic terminal and can act on presynaptic cannabinoid type 1 (CB1) receptors, decreasing the release of neurotransmitters, including glutamate. AEA action is ended through enzymatic hydrolysis via FAAH (fatty acid amid hydrolase) in the post-synaptic neuron. eCB system molecules are widely expressed in brain areas involved in the modulation of fear and anxiety responses, including the Bed Nucleus of the Stria Terminalis (BNST), which is involved in the integration of autonomic, neuroendocrine, and behavioral regulation. The presence of the CB1 and FAAH was described in the BNST; however, their role in the modulation of defensive reactions is not fully comprehended. In the present work we aimed at investigating the role of AEA and CB1 receptors in the BNST in modulating anxiety-related behaviors. Adult male Wistar rats received local BNST injections of the CB1 receptor antagonist AM251 (0.1-0.6 nmol) and/or the FAAH inhibitor (URB597; 0.001-0.1 nmol) and were evaluated in the elevated plus maze (EPM) test, with or without previous acute restraint stress (2 h) exposure, or in the contextual fear conditioning. We observed that although AM251 and URB597 had no effects on the EPM, they increased and decreased, respectively, the conditioned fear response. Supporting a possible influence of stress in these differences, URB597 was able to prevent the restraint stress-induced anxiogenic effect in the EPM. The present data, therefore, suggest that eCB signaling in the BNST is recruited during more aversive situations to counteract the stress effect.

The medial prefrontal cortex and the cardiac baroreflex activity: physiological and pathological implications

The cardiac baroreflex is an autonomic neural mechanism involved in the modulation of the cardiovascular system. It influences the heart rate and peripheral vascular resistance to preserve arterial blood pressure within a narrow variation range. This mechanism is mainly controlled by medullary nuclei located in the brain stem. However, supramedullary areas, such as the ventral portion of medial prefrontal cortex (vMPFC), are also involved. Particularly, the glutamatergic NMDA/NO pathway in the vMPFC can facilitate baroreflex bradycardic and tachycardic responses. In addition, cannabinoid receptors in this same area can reduce or increase those cardiac responses, possibly through alteration in glutamate release. This vMPFC network has been associated to cardiovascular responses during stressful situations. Recent results showed an involvement of glutamatergic, nitrergic, and endocannabinoid systems in the blood pressure and heart rate increases in animals after aversive conditioning. Consequently, baroreflex could be modified by the vMPFC neurotransmission during stressful situations, allowing necessary cardiovascular adjustments. Remarkably, some mental, neurological and neurodegenerative disorders can involve damage in the vMPFC, such as posttraumatic stress disorder, major depressive disorder, Alzheimer's disease, and neuropathic pain. These pathologies are also associated with alterations in glutamate/NO release and endocannabinoid functions along with baroreflex impairment. Thus, the vMPFC seems to play a crucial role on the baroreflex control, either during pathological or physiological stress-related responses. The study of baroreflex mechanism under such pathological view may be helpful to establish causality mechanisms for the autonomic and cardiovascular imbalance found in those conditions. It can explain in the future the reasons of the high cardiovascular risk some neurological and neurodegenerative disease patients undergo. Additionally, the present work offers insights on the possible contributions of vMPFC dysfunction on baroreflex alterations, which, in turn, may raise questions in what extent other brain areas may play a role in autonomic deregulation under such pathological situations.

TRPV1 modulation of contextual fear memory depends on stimulus intensity and endocannabinoid signalling in the dorsal hippocampus

The transient receptor potential vanilloid type-1 (TRPV1) channels have been implicated in the modulation of aversive responses. The endocannabinoid anandamide acts as an endogenous TRPV1 agonist, exerting opposite functions at TRPV1 and type-1 cannabinoid receptors (CB₁R). Here we tested the hypothesis that hippocampal TRPV1 modulates contextual fear memory retrieval and investigated the influence of the aversive stimulus intensity as well as the role of endocannabinoid signaling. Male C57BL/6J mice were tested for contextual fear memory after low-, moderate-, or high-intensity shock protocols. The selective TRPV1 blockers SB366791 (1-10 nmol) and 6-I-NC (2 nmol) were infused via intra-dorsal hippocampus before the retrieval test session. The local levels of endocannabinoids and Arc and Zif268 mRNAs, involved in synaptic plasticity and memory, were quantified. First, both TRPV1 blockers reduced memory retrieval in animals exposed to moderate or high (but not low) intensity training protocols. In the second series of results, the magnitude of the freezing responses positively correlated with the hippocampal anandamide levels; TRPV1 and CB₁R were found co-localized in this brain region; and the CB₁R antagonist, AM251, prevented the effects of SB366791. Thus, endocannabinoid signaling possibly mediates the effects of TRPV1 blockers. Finally, inhibition of memory retrieval by TRPV1 blockers increased Arc and Zif268 mRNAs and impaired fear memory reinstatement. In conclusion, the modulation of fear memories by dorsal hippocampal TRPV1 channels may depend on the aversive stimulus intensity and occur via anandamide/CB₁ signaling. Moreover, TRPV1 blockers promote Arc and Zif268 transcription, with subsequent attenuation of aversive memory reinstatement.

Magnetic nanomaterials for wireless thermal and mechanical neuromodulation

Magnetic fields are very attractive for non-invasive neuromodulation because they easily penetrate trough the skull and tissue. Cell specific neuromodulation requires the magnetic field energy to be converted by an actuator to a biologically relevant signal. Miniaturized actuators available today range from small, isotropic magnetic nanoparticles to larger, submicron anisotropic magnetic nanomaterials. Depending on the parameters of external magnetic fields and the properties of the nanoactuators, they create either a thermal or a mechanical stimulus. Ferromagnetic nanomaterials generate heat in response to high frequency alternating magnetic fields associated with dissipative losses. Anisotropic nanomaterials with large magnetic moments are capable of exerting forces at stationary or slowly varying magnetic fields. These tools allow exploiting thermosensitive or mechanosensitive neurons in circuit or cell specific tetherless neuromodulation schemes. This review will address assortment of available magnetic nanomaterial-based neuromodulation techniques that rely on application of external magnetic fields.

Structure-Based Virtual Screening Identifies Novobiocin, Montelukast, and Cinnarizine as TRPV1 Modulators with Anticonvulsant Activity In Vivo

The transient receptor potential vanilloid 1 (TRPV1) receptor is a nonselective cation channel, known to be involved in the regulation of many important physiological and pathological processes. In the last few years, it has been proposed as a promising target to develop novel anticonvulsant compounds. However, thermoregulatory effects associated with the channel inhibition have hampered the path for TRPV1 antagonists to become marketed drugs. In this regard, we conducted a structure-based virtual screening campaign to find potential TRPV1 modulators among approved drugs, which are known to be safe and thermally neutral. To this end, different docking models were developed and validated by assessing their pose and score prediction powers. Novobiocin, montelukast, and cinnarizine were selected from the screening as promising candidates for experimental testing and all of them exhibited nanomolar inhibitory activity. Moreover, the in vivo profiles showed promising results in at least one of the three models of seizures tested.

Transient Receptor Potential Vanilloid 1 Function at Central Synapses in Health and Disease

The transient receptor potential vanilloid 1 (TRPV1), a ligand-gated nonselective cation channel, is well known for mediating heat and pain sensation in the periphery. Increasing evidence suggests that TRPV1 is also expressed at various central synapses, where it plays a role in different types of activity-dependent synaptic changes. Although its precise localizations remain a matter of debate, TRPV1 has been shown to modulate both neurotransmitter release at presynaptic terminals and synaptic efficacy in postsynaptic compartments. In addition to being required in these forms of synaptic plasticity, TRPV1 can also modify the inducibility of other types of plasticity. Here, we highlight current evidence of the potential roles for TRPV1 in regulating synaptic function in various brain regions, with an emphasis on principal mechanisms underlying TRPV1-mediated synaptic plasticity and metaplasticity. Finally, we discuss the putative contributions of TRPV1 in diverse brain disorders in order to expedite the development of next-generation therapeutic treatments.

TRPV1 blockers as potential new treatments for psychiatric disorders

The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.

Review of Noninvasive or Minimally Invasive Deep Brain Stimulation

Brain stimulation is a critical technique in neuroscience research and clinical application. Traditional transcranial brain stimulation techniques, such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and deep brain stimulation (DBS) have been widely investigated in neuroscience for decades. However, TMS and tDCS have poor spatial resolution and penetration depth, and DBS requires electrode implantation in deep brain structures. These disadvantages have limited the clinical applications of these techniques. Owing to developments in science and technology, substantial advances in noninvasive and precise deep stimulation have been achieved by neuromodulation studies. Second-generation brain stimulation techniques that mainly rely on acoustic, electronic, optical, and magnetic signals, such as focused ultrasound, temporal interference, near-infrared optogenetic, and nanomaterial-enabled magnetic stimulation, offer great prospects for neuromodulation. This review summarized the mechanisms, development, applications, and strengths of these techniques and the prospects and challenges in their development. We believe that these second-generation brain stimulation techniques pave the way for brain disorder therapy.

The role of endocannabinoids in consolidation, retrieval, reconsolidation, and extinction of fear memory

Endocannabinoids are involved in various physiological functions, including synaptic plasticity and memory, and some psychiatric disorders, such as posttraumatic stress disorder (PTSD), through the activation of cannabinoid (CB) receptors. Patients with PTSD often show excessive fear memory and impairment of fear extinction (FE). It has been reported that the stability of acquired fear memory is altered through multiple memory stages, such as consolidation and reconsolidation. FE also affects the stability of fear memory. Each stage of fear memory formation and FE are regulated by different molecular mechanisms, including the CB system. However, to the best of our knowledge, no review summarizes the role of the CB system during each stage of fear memory formation and FE. In this review, we summarize the roles of endocannabinoids in fear memory formation and FE. Moreover, based on the summary, we propose a new hypothesis for the role of endocannabinoids in fear regulation, and discuss treatment for PTSD using CB system-related drugs.

Differential modulation of the contextual conditioned emotional response by CB1 and TRPV1 receptors in the ventromedial prefrontal cortex: Possible involvement of NMDA/nitric oxide-related mechanisms

BACKGROUND

Blockade of cannabinoid CB1 or vanilloid TRPV1 receptors in the ventromedial prefrontal cortex of rats respectively increases or decreases the conditioned emotional response during re-exposure to a context previously paired with footshocks. Although these mechanisms are unknown, they may involve local modulation of glutamatergic and nitrergic signaling.

AIM

We investigated whether these mechanisms are involved in the reported effects of CB1 and TRPV1 modulation in the ventromedial prefrontal cortex.

METHODS

Freezing behavior and autonomic parameters were recorded during the conditioned response expression.

RESULTS

The CB1 receptors antagonist NIDA, or the TRPV1 agonist capsaicin (CPS) in the ventromedial prefrontal cortex increased the conditioned emotional response expression, and these effects were prevented by TRPV1 and CB1 antagonism, respectively. The increased conditioned emotional response evoked by NIDA and CPS were prevented by an NMDA antagonist or a neuronal nitric oxide synthase inhibitor. A nitric oxide scavenger or a soluble guanylate cyclase inhibitor prevented only the NIDA effects and the CPS effect was prevented by a non-selective antioxidant drug, as nitric oxide can also induce reactive oxygen species production.

CONCLUSION

Our results suggest that CB1 and TRPV1 receptors in the ventromedial prefrontal cortex differently modulate the expression of conditioned emotional response through glutamatergic and nitrergic mechanisms, although different pathways may be involved.

The involvement of TRP channels in memory formation and task retrieval in a passive avoidance task in one-day old chicks

An increase in the intracellular Ca2+ level in neurons is one of the main steps in the memory formation cascade. The increase results from extracellular Ca2+ influx by activation of ionotropic glutamate receptors and release from intracellular stores by the stimulation of IP3 receptors (IP3Rs) via group I metabotropic glutamate receptors (mGluR1/5). Recent data indicate an additional mechanism resulting in Ca2+ influx into neurons, triggered by intracellular signals that are directly connected to the activation of group I mGluRs. This influx occurs through transient receptor potential (TRP) channels, which are permeable to Na+, K+ and, mainly, Ca2+. These channels are activated by increases in intracellular Ca2+, diacylglycerol (DAC) and inositol 1,4,5-triphosphate (IP3) level resulting from a group I mGluR activation. The aim of the present study was to investigate the participation of TRP channels, especially from TRPC and TRPV groups, in memory consolidation and reconsolidation and memory retrieval processes in a passive avoidance task in one-day old chicks. TRP channels were blocked by the injection of the unspecific channel modulators SKF 96365 (2.5 µl 30 µM/hemisphere) and 2-APB (2.5 µl 10 µM/hemisphere) directly into the intermediate medial mesopallium (IMM) region of the chick brain immediately after initial training or after a reminder. The inhibition of specific TRP channels (TRPV1, TRPV3 or TRPC3) was achieved by the application of selective antibodies. Our results demonstrate that the inhibition of TRP channels by the application of both modulators disrupted memory consolidation, resulting in permanent task amnesia. The inhibition of the TRPV1, TRPC3 and TRPV3 channels by specific antibodies resulted in similar amnesia. Moreover, the inhibition of TRP channels by SKF 96365 and 2-APB at different time points after initial training or after the reminder also resulted in amnesia, indicating the role of TRP channels in memory retrieval. The inhibition of calcium influx through these channels resulted in permanent memory disruption, which suggests that the calcium signal generated by TRP channels is crucial for memory formation and retrieval processes. For the first time, the important role of TRPV3 channels in memory formation was demonstrated.

Progress in neuromodulation of the brain: A role for magnetic nanoparticles?

The field of neuromodulation is developing rapidly. Current techniques, however, are still limited as they i) either depend on permanent implants, ii) require invasive procedures, iii) are not cell-type specific, iv) involve slow pharmacokinetics or v) have a restricted penetration depth making it difficult to stimulate regions deep within the brain. Refinements into the different fields of neuromodulation are thus needed. In this review, we will provide background information on the different techniques of neuromodulation discussing their latest refinements and future potentials including the implementation of nanoparticles (NPs). In particular we will highlight the usage of magnetic nanoparticles (MNPs) as transducers in advanced neuromodulation. When exposed to an alternating magnetic field (AMF), certain MNPs can generate heat through hysteresis. This MNP heating has been promising in the field of cancer therapy and has recently been introduced as a method for remote and wireless neuromodulation. This indicates that MNPs may aid in the exploration of brain functions via neuromodulation and may eventually be applied for treatment of neuropsychiatric disorders. We will address the materials chemistry of MNPs, their biomedical applications, their delivery into the brain, their mechanisms of stimulation with emphasis on MNP heating and their remote control in living tissue. The final section compares and discusses the parameters used for MNP heating in brain cancer treatment and neuromodulation. Concluding, using MNPs for nanomaterial-mediated neuromodulation seem promising in a variety of techniques and could be applied for different neuropsychiatric disorders when more extensively investigated.

Dual mechanism of TRKB activation by anandamide through CB1 and TRPV1 receptors

BACKGROUND

Administration of anandamide (AEA) or 2-arachidonoylglycerol (2AG) induces CB1 coupling and activation of TRKB receptors, regulating the neuronal migration and maturation in the developing cortex. However, at higher concentrations AEA also engages vanilloid receptor TRPV1, usually with opposed consequences on behavior.

METHODS AND RESULTS

Using primary cell cultures from the cortex of rat embryos (E18) we determined the effects of AEA on phosphorylated TRKB (pTRK). We observed that AEA (at 100 and 200 nM) induced a significant increase in pTRK levels. Such effect of AEA at 100 nM was blocked by pretreatment with the CB1 antagonist AM251 (200 nM) and, at the higher concentration of 200 nM by the TRPV1 antagonist capsazepine (200 nM), but mildly attenuated by AM251. Interestingly, the effect of AEA or capsaicin (a TRPV1 agonist, also at 200 nM) on pTRK was blocked by TRKB.Fc (a soluble form of TRKB able to bind BDNF) or capsazepine, suggesting a mechanism dependent on BDNF release. Using the marble-burying test (MBT) in mice, we observed that the local administration of ACEA (a CB1 agonist) into the prelimbic region of prefrontal cortex (PL-PFC) was sufficient to reduce the burying behavior, while capsaicin or BDNF exerted the opposite effect, increasing the number of buried marbles. In addition, both ACEA and capsaicin effects were blocked by previous administration of k252a (an antagonist of TRK receptors) into PL-PFC. The effect of systemically injected CB1 agonist WIN55,212-2 was blocked by previous administration of k252a. We also observed a partial colocalization of CB1/TRPV1/TRKB in the PL-PFC, and the localization of TRPV1 in CaMK2+ cells.

CONCLUSION

Taken together, our data indicate that anandamide engages a coordinated activation of TRKB, via CB1 and TRPV1. Thus, acting upon CB1 and TRPV1, AEA could regulate the TRKB-dependent plasticity in both pre- and postsynaptic compartments.

Tempering aversive/traumatic memories with cannabinoids: a review of evidence from animal and human studies

RATIONALE

Aversive learning and memory are essential to cope with dangerous and stressful stimuli present in an ever-changing environment. When this process is dysfunctional, however, it is associated with posttraumatic stress disorder (PTSD). The endocannabinoid (eCB) system has been implicated in synaptic plasticity associated with physiological and pathological aversive learning and memory.

OBJECTIVE AND METHODS

The objective of this study was to review and discuss evidence on how and where in the brain genetic or pharmacological interventions targeting the eCB system would attenuate aversive/traumatic memories through extinction facilitation in laboratory animals and humans. The effect size of the experimental intervention under investigation was also calculated.

RESULTS

Currently available data indicate that direct or indirect activation of cannabinoid type-1 (CB1) receptor facilitates the extinction of aversive/traumatic memories. Activating CB1 receptors around the formation of aversive/traumatic memories or their reminders can potentiate their subsequent extinction. In most cases, the effect size has been large (Cohen's d ≥ 1.0). The brain areas responsible for the abovementioned effects include the medial prefrontal cortex, amygdala, and/or hippocampus. The potential role of cannabinoid type-2 (CB2) receptors in extinction learning is now under investigation.

CONCLUSION

Drugs augmenting the brain eCB activity can temper the impact of aversive/traumatic experiences by diverse mechanisms depending on the moment of their administration. Considering the pivotal role the extinction process plays in PTSD, the therapeutic potential of these drugs is evident. The sparse number of clinical trials testing these compounds in stress-related disorders is a gap in the literature that needs to be addressed.

Medial prefrontal cortex TRPV1 and CB1 receptors modulate cardiac baroreflex activity by regulating the NMDA receptor/nitric oxide pathway

The ventral medial prefrontal cortex (vMPFC) facilitates the cardiac baroreflex response through N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) formation by neuronal NO synthase (nNOS) and soluble guanylate cyclase (sGC) triggering. Glutamatergic transmission is modulated by the cannabinoid receptor type 1 (CB₁) and transient receptor potential vanilloid type 1 (TRPV₁) receptors, which may inhibit or stimulate glutamate release in the brain, respectively. Interestingly, vMPFC CB₁ receptors decrease cardiac baroreflex responses, while TRPV₁ channels facilitate them. Therefore, the hypothesis of the present study is that the vMPFC NMDA/NO pathway is regulated by both CB₁ and TRPV₁ receptors in the modulation of cardiac baroreflex activity. In order to test this assumption, we used male Wistar rats that had stainless steel guide cannulae bilaterally implanted in the vMPFC. Subsequently, a catheter was inserted into the femoral artery, for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. The increase in tachycardic and bradycardic responses observed after the microinjection of a CB₁ receptors antagonist into the vMPFC was prevented by an NMDA antagonist as well as by the nNOS and sGC inhibition. NO extracellular scavenging also abolished these responses. These same pharmacological manipulations inhibited cardiac reflex enhancement induced by TRPV₁ agonist injection into the area. Based on these results, we conclude that vMPFC CB₁ and TRPV₁ receptors inhibit or facilitate the cardiac baroreflex activity by stimulating or blocking the NMDA activation and NO synthesis.

M3 muscarinic receptor in the ventral medial prefrontal cortex modulating the expression of contextual fear conditioning in rats

RATIONALE

Basal forebrain cholinergic neurons modulate the activation of cortical neurons by several stimuli such as fear and anxiety. However, the role of the muscarinic receptor in the medial prefrontal cortex (MPFC) in the modulation of the conditioned emotional response (CER) evoked in the model contextual conditioned fear remains unclear.

OBJECTIVES

The objective of this study is to test the hypothesis that inhibition of the muscarinic receptor in ventral MPFC modulates CER observed during animal's re-exposure to the aversive context.

METHODS

Rats implanted with cannulae aimed at the prelimbic (PL) or the infralimbic (IL) were submitted to a high-intensity contextual fear conditioning protocol. Before the test session, they received microinjections of the hemicholinium (choline reuptake blocker), atropine (muscarinic antagonist), J104129 fumarate (M1-M3 muscarinic antagonists), pirenzepine (M1 muscarinic antagonist), neostigmine (inhibitor acetylcholinesterase enzyme), or the systemic administration of the FG7142 (inverse benzodiazepine agonist). Additional independent groups received the neostigmine or FG7142 before the ineffective doses of J104129 fumarate in the low-intensity protocol of contextual fear conditioning.

RESULTS

In the high-intensity protocol, the administration of hemicholinium (1 nmol), atropine (0.06-6 nmol), J104129 fumarate (6 nmol), or pirenzepine (6 nmol) attenuated the expression of CER in rats. However, in the low-intensity protocol, only J10129 fumarate (0.06 nmol) reduced the expression of the CER. Finally, neostigmine (0.1-1 nmol) or FG7142 (8 mg/Kg) increased CER expression, an effect inhibited by the low dose of the J10129 fumarate.

CONCLUSIONS

These results indicated that the blockade of M3 muscarinic receptor in the vMPFC attenuates the CER expression.

Dorsolateral periaqueductal gray matter CB1 and TRPV1 receptors exert opposite modulation on expression of contextual fear conditioning

Cannabinoid type 1 (CB1) and Transient Potential Vanilloid type 1 (TRPV1) receptors in the dorsolateral periaqueductal gray (dlPAG) matter are involved in the modulation of conditioned response. Both CB1 and TRPV1 receptors are related to glutamate release and nitric oxide (NO) synthesis. It was previously demonstrated that both NMDA glutamate receptors and NO are involved in the conditioned emotional response. Therefore, one aim of this work was to verify whether dlPAG CB1 and TRPV1 receptors modulate the expression of contextual conditioned emotional response. Moreover, we also investigated the involvement of NMDA receptors and the NO pathway in this response. Male Wistar rats with local dlPAG guide cannula were submitted to contextual fear conditioning. Following 24 h, a polyethylene catheter was implanted in the femoral artery for cardiovascular recordings. After an additional 24 h, drugs were administered in the dlPAG and freezing behavior and autonomic responses were recorded during chamber re-exposure. Both a CB1 antagonist (AM251) and a TRPV1 agonist (Capsaicin; CPS) increased the expression of a conditioned emotional response. This response was prevented by an NMDA antagonist, a preferential neuronal NO synthase inhibitor, an NO scavenger and a soluble guanylate cyclase inhibitor (sGC). Furthermore, pretreatment with a TRPV1 antagonist also prevented the increased conditioned emotional response induced by AM251. Considering that GABA can counterbalance glutamate effects, we also investigated whether GABAA receptors were involved in the effect of a higher dose of AM251. Pretreatment with a GABAA receptor antagonist caused an increased conditioned emotional response by AM251. Our results support the possibility that dlPAG CB1 and TRPV1 receptors are involved in the expression of conditioned emotional response through the NMDA/NO/sGC pathway. Moreover, the opposite effects exerted by GABA and glutamate could produce different outcomes of drugs modulating eCBs.

Medial prefrontal cortex TRPV1 channels modulate the baroreflex cardiac activity in rats

BACKGROUND AND PURPOSE

The ventral portion of the medial prefrontal cortex (vMPFC) comprises the infralimbic (IL), prelimbic (PL) and dorsopenducular (DP) cortices. The IL and PL regions facilitate the baroreceptor reflex arc. This facilitatory effect on the baroreflex is thought to be mediated by vMPFC glutamatergic transmission, through NMDA receptors. The glutamatergic transmission can be modulated by other neurotransmitters, such as the endocannabinoids, which are agonists of the TRPV1 receptor. TRPV1 channels facilitate glutamatergic transmission in the brain. Thus, we hypothesized that TRPV1 receptors in the vMPFC enhance the cardiac baroreflex response.

EXPERIMENTAL APPROACH

Stainless steel guide cannulae were bilaterally implanted into the vMPFC of male Wistar rats. Afterwards, a catheter was inserted into the femoral artery, for recording MAP and HR, and into the femoral vein for assessing baroreflex activation.

KEY RESULTS

Microinjections of the TRPV1 receptor antagonists capsazepine and 6-iodo-nordihydrocapsaicin (6-IODO) into the vMPFC reduced the cardiac baroreflex activity in unanaesthetized rats. Capsaicin microinjected into the vMPFC increased the cardiac baroreflex activity in unanaesthetized rats. When an ineffective dose of the TRPV1 receptor antagonist 6-IODO was used, the capsaicin-induced increase in the cardiac baroreflex response was abolished. The higher doses of capsaicin administered into the vMPFC after the ineffective dose of 6-IODO displaced the dose-response curve of the baroreflex parameters to the right, with no alteration in the maximum effect of capsaicin.

CONCLUSIONS AND IMPLICATIONS

The results of the present study show that stimulation of the TRPV1 receptors in the vMPFC increases the cardiac baroreceptor reflex response.

Compartment-specific modulation of GABAergic synaptic transmission by TRPV1 channels in the dentate gyrus

The transient receptor potential TRPV1 or vanilloid receptor is a nonselective ligand-gated channel highly expressed in primary sensory neurons where it mediates nociception. TRPV1 is also expressed in the brain where its activation depresses excitatory synaptic transmission. Whether TRPV1 also regulates inhibitory synapses in the brain is unclear. Here, using a combination of pharmacology, electrophysiology, and an in vivo knockdown strategy, we report that TRPV1 activation by capsaicin or by the endocannabinoid anandamide depresses somatic, but not dendritic inhibitory transmission in both rat and mouse dentate gyrus. The effect on somatic inhibition was absent in TRPV1 knock-out mice and was also eliminated by two different TRPV1 shRNAs expressed in dentate granule cells, strongly supporting a functional role for TRPV1 in modulating GABAergic synaptic function. Moreover, TRPV1-mediated depression occurs independently of GABA release, requires postsynaptic Ca(2+) rise and activation of calcineurin, and is likely due to clathrin-dependent internalization of GABA receptors. Altogether, these findings reveal a novel form of compartment-specific regulation whereby TRPV1 channels can modify synaptic function in the brain.