BDNF regulates neuronal sensitivity to endocannabinoids

Cannabidiol Modulates Emotional Function and Brain-Derived Neurotrophic Factor Expression in Middle-Aged Female Rats Exposed to Social Isolation

Aging is associated with changes in cognitive and emotional function. Cannabidiol (CBD) has been reported to attenuate stress and anxiety in human and animal studies. In this study, we aimed to assess the therapeutic potential of CBD among middle-aged female rats exposed to social isolation (SI) and the potential involvement of brain-derived neurotrophic factor (BDNF) in these effects. Thirteen-month-old female rats were group-housed (GH) or exposed to social isolation (SI) and treated with vehicle or CBD (10 mg/kg). CBD restored the SI-induced immobility in the forced swim test and the SI-induced decrease in the expression of BDNF protein levels in the nucleus accumbens (NAc). CBD also increased the time that rats spent in the center in an open field, improved spatial training, and increased BDNF expression in the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA). BDNF expression was found to be correlated with an antidepressant (in the NAc) and an anxiolytic (in the mPFC, BLA, NAc) phenotype, and with learning improvement in the PFC. Together, our results suggest that CBD may serve as a beneficial agent for wellbeing in old age and may help with age-related cognitive decline.

Neuromodulation in Parkinson's disease targeting opioid and cannabinoid receptors, understanding the role of NLRP3 pathway: a novel therapeutic approach

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, resulting in motor and non-motor symptoms. Although levodopa is the primary medication for PD, its long-term use is associated with complications such as dyskinesia and drug resistance, necessitating novel therapeutic approaches. Recent research has highlighted the potential of targeting opioid and cannabinoid receptors as innovative strategies for PD treatment. Modulating opioid transmission, particularly through activating µ (MOR) and δ (DOR) receptors while inhibiting κ (KOR) receptors, shows promise in preventing motor complications and reducing L-DOPA-induced dyskinesia. Opioids also possess neuroprotective properties and play a role in neuroprotection and seizure control. Similar to this, endocannabinoid signalling via CB1 and CB2 receptors influences the basal ganglia and may contribute to PD pathophysiology, making it a potential therapeutic target. In addition to opioid and cannabinoid receptor targeting, the NLRP3 pathway, implicated in neuroinflammation and neurodegeneration, emerges as another potential therapeutic avenue for PD. Recent studies suggest that targeting this pathway holds promise as a therapeutic strategy for PD management. This comprehensive review focuses on neuromodulation and novel therapeutic approaches for PD, specifically highlighting the targeting of opioid and cannabinoid receptors and the NLRP3 pathway. A better understanding of these mechanisms has the potential to enhance the quality of life for PD patients.

Cell-autonomous and differential endocannabinoid signaling impacts the development of presynaptic retinal ganglion cell axon connectivity in vivo

Cannabis exposure during gestation evokes significant molecular modifications to neurodevelopmental programs leading to neurophysiological and behavioral abnormalities in humans. The main neuronal receptor for Δ⁹-tetrahydrocannabinol (THC) is the type-1 cannabinoid receptor CB₁R, one of the most abundant G-protein-coupled receptors in the nervous system. While THC is the major psychoactive phytocannabinoid, endocannabinoids (eCBs) are the endogenous ligands of CB₁R and are known to act as retrograde messengers to modulate synaptic plasticity at different time scales in the adult brain. Accumulating evidence indicates that eCB signaling through activation of CB₁R plays a central role in neural development. During development, most CB₁R localized to axons of projection neurons, and in mice eCB signaling impacts axon fasciculation. Understanding of eCB-mediated structural plasticity during development, however, requires the identification of the precise spatial and temporal dynamics of CB₁R-mediated modifications at the level of individual neurons in the intact brain. Here, the cell-autonomous role of CB₁R and the effects of CB₁R-mediated eCB signaling were investigated using targeted single-cell knockdown and pharmacologic treatments in Xenopus. We imaged axonal arbors of retinal ganglion cells (RGCs) in real time following downregulation of CB₁R via morpholino (MO) knockdown. We also analyzed RGC axons with altered eCB signaling following treatment with URB597, a selective inhibitor of the enzyme that degrades Anandamide (AEA), or JZL184, an inhibitor of the enzyme that blocks 2-Arachidonoylglycerol (2-AG) hydrolysis, at two distinct stages of retinotectal development. Our results demonstrate that CB₁R knockdown impacts RGC axon branching at their target and that differential 2-AG and AEA-mediated eCB signaling contributes to presynaptic structural connectivity at the time that axons terminate and when retinotectal synaptic connections are made. Altering CB₁R levels through CB₁R MO knockdown similarly impacted dendritic morphology of tectal neurons, thus supporting both pre- and postsynaptic cell-autonomous roles for CB₁R-mediated eCB signaling.

Negative relationship between brain-derived neurotrophic factor (BDNF) and attention: A possible elevation in BDNF level among high-altitude migrants

Objective

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophic family that plays a vital role in regulating neuronal activity and synaptic plasticity in the brain, affects attention. However, studies investigating the association between BDNF and attention in long-term high-altitude (HA) migrants are limited in the literature. As HA affects both BDNF and attention, the relationship between these factors becomes more complex. Therefore, this study aimed to evaluate the relationship between peripheral blood concentrations of BDNF and the three attentional networks in both behavioral and electrical aspects of the brain in long-term HA migrants.

Materials and methods

Ninety-eight Han adults (mean age: 34.74 ± 3.48 years, 51 females and 47 males, all have lived at Lhasa for 11.30 ± 3.82 years) were recruited in this study. For all participants, the serum BDNF levels were assessed using enzyme-linked immunosorbent assay; event-related potentials (N1, P1, and P3) were recorded during the Attentional Networks Test, which was used as the measure of three attentional networks.

Results

Executive control scores were negatively correlated with P3 amplitude (r = -0.20, p = 0.044), and serum BDNF levels were positively correlated with executive control scores (r = 0.24, p = 0.019) and negatively correlated with P3 amplitude (r = -0.22, p = 0.027). Through grouping of BDNF levels and three attentional networks, executive control was found to be significantly higher in the high BDNF group than in the low BDNF group (p = 0.010). Different BDNF levels were associated with both orienting scores (χ² = 6.99, p = 0.030) and executive control scores (χ² = 9.03, p = 0.011). The higher the BDNF level, the worse was the executive function and the lower was the average P3 amplitude and vice versa. Females were found to have higher alerting scores than males (p = 0.023).

Conclusion

This study presented the relationship between BDNF and attention under HA. The higher the BDNF level, the worse was the executive control, suggesting that after long-term exposure to HA, hypoxia injury of the brain may occur in individuals with relatively higher BDNF levels, and this higher BDNF level may be the result of self-rehabilitation tackling the adverse effects brought by the HA environment.

Rapid treatments for depression: Endocannabinoid system as a therapeutic target

Current first-line treatments for major depressive disorder (MDD), i.e., antidepressant drugs and psychotherapy, show delayed onset of therapeutic effect as late as 2-3 weeks or more. In the clinic, the speed of beginning of the actions of antidepressant drugs or other interventions is vital for many reasons. Late-onset means that depression, its related disability, and the potential danger of suicide remain a threat for some patients. There are some rapid-acting antidepressant interventions, such as sleep deprivation, ketamine, acute exercise, which induce a significant response, ranging from a few hours to maximally one week, and most of them share a common characteristic that is the activation of the endocannabinoid (eCB) system. Activation of this system, i.e., augmentation of eCB signaling, appears to have anti-depressant-like actions. This article puts the idea forward that the activation of eCB signaling represents a critical mechanism of rapid-acting therapeutic interventions in MDD, and this system might contribute to the development of novel rapid-acting treatments for MDD.

Roles of the Cannabinoid System in the Basal Ganglia in Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease usually caused by neuroinflammation, oxidative stress and other etiologies. Recent studies have found that the cannabinoid system present in the basal ganglia has a strong influence on the progression of PD. Altering the cannabinoid receptor activation status by modulating endogenous cannabinoid (eCB) levels can exert an anti-movement disorder effect. Therefore, the development of drugs that modulate the endocannabinoid system may be a novel strategy for the treatment of PD. However, eCB regulation is complex, with diverse cannabinoid receptor functions and the presence of dopaminergic, glutamatergic, and γ-aminobutyric signals interacting with cannabinoid signaling in the basal ganglia region. Therefore, the study of eCB is challenging. Here, we have described the function of the cannabinoid system in the basal ganglia and its association with PD in three parts (eCBs, cannabinoid receptors, and factors regulating the cannabinoid metabolism) and summarized the mechanisms of action related to the cannabinoid analogs currently aimed at treating PD. The shortcomings identified from previous studies and the directions that should be explored in the future will provide insights into new approaches and ideas for the future development of cannabinoid-based drugs and the treatment of PD.

Exercise Training Improves Memory Performance in Older Adults: A Narrative Review of Evidence and Possible Mechanisms

As human life expectancy increases, cognitive decline and memory impairment threaten independence and quality of life. Therefore, finding prevention and treatment strategies for memory impairment is an important health concern. Moreover, a better understanding of the mechanisms involved underlying memory preservation will enable the development of appropriate pharmaceuticals drugs for those who are activity limited. Exercise training as a non-pharmacological tool, has been known to increase the mean lifespan by maintaining general body health and improving the cardiovascular and nervous systems function. Among different exercise training protocols, aerobic exercise has been reported to prevent the progression of memory decline, provided adequate exertion level, duration, and frequency. Mechanisms underlying exercise training effects on memory performance have not been understood yet. Convergent evidence suggest several direct and indirect mechanisms at molecular and supramolecular levels. The supramolecular level includes improvement in blood circulation, synaptic plasticity and neurogenesis which are under controls of complex molecular signaling of neurotransmitters, neurotrophic factors, exerkines, and epigenetics factors. Among these various factors, irisin/BDNF signaling seems to be one of the important mediators of crosstalk between contracted skeletal muscles and the brain during exercise training. This review provides an affordable and effective method to improve cognitive function in old ages, particularly those who are most vulnerable to neurodegenerative disorders.

Mechanisms of endocannabinoid control of synaptic plasticity

The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB₁Rs).

Neurobiological Processes Induced by Aerobic Exercise through the Endocannabinoidome

Evidence suggesting the triangulation of the endocannabinoid system, exercise, and neurological health is emerging. In addition to the endocannabinoids N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), the expanded endocannabinoid system, known as the endocannabinoidome (eCBome), appears to be an important player in this relationship. The eCBome includes several endocannabinoid-like mediators such as N-acylethanolamines and 2-monoacylglycerols, the enzymes involved in their biosynthesis and degradation, and the receptors they affect. This review aims to relate the functional interactions between aerobic exercise, and the molecular and cellular pathways related to endocannabinoids, in the hypothalamus, hippocampus, and the periphery, with special attention given to associations with emotional state, cognition, and mental health. Given the well-documented roles of many eCBome members in regulating stress and neurological processes, we posit that the eCBome is an important effector of exercise-induced central and peripheral adaptive mechanisms that benefit mental health. Gut microbiota imbalance, affecting the gut-brain axis and metabolism, also influences certain eCBome-modulated inflammation pathways. The integrity of the gut microbiota could thus be crucial in the onset of neuroinflammation and mental conditions. Further studies on how the modulation by exercise of the peripheral eCBome affects brain functions could reveal to be key elements in the prevention and treatment of neuropsychological disorders.

Resilience to fear: The role of individual factors in amygdala response to stressors

Resilience to stress is an adaptive process that varies individually. Resilience refers to the adaptation, or the ability to maintain or regain mental health, despite being subject to adverse situation. Resilience is a dynamic concept that reflects a combination of internal individual factors, including age and gender interacting with external factors such as social, cultural and environmental factors. In the last decade, we have witnessed an increase in the prevalence of anxiety disorders, including post-traumatic stress disorder. Given that stress in unavoidable, it is of great interest to understand the neurophysiological mechanisms of resilience, the individual factors that may contribute to susceptibility and promote efficacious approaches to improve resilience. Here, we address this complex question, attempting at defining clear and operational definitions that may allow us to improve our analysis of behavior incorporating individuality. We examine how individual perception of the stressor can alter the outcome of an adverse situation using as an example, the fear-conditioning paradigm and discuss how individual differences in the reward system can contribute to resilience. Given the central role of the endocannabinoid system in regulating fear responses and anxiety, we discuss the evidence that polymorphisms in several molecules of this signaling system contribute to different anxiety phenotypes. The endocannabinoid system is highly interconnected with the serotoninergic and dopaminergic modulatory systems, contributing to individual differences in stress perception and coping mechanisms. We review how the individual variability in these modulatory systems can be used towards a multivariable assessment of stress risk. Incorporating individuality in our research will allow us to define biomarkers of anxiety disorders as well as assess prognosis, towards a personalized clinical approach to mental health.

Recovery of BDNF and CB1R in the Prefrontal Cortex Underlying Improvement of Working Memory in Prenatal DEHP-Exposed Male Rats after Aerobic Exercise

Early-life exposure to di-(2-ethylhexyl)-phthalate (DEHP) has been suggested to relate to hyperactivity, lack of attention, and working memory deficits in school-age children. Brain-derived neurotrophic factor (BDNF) and endocannabinoids are induced by aerobic exercises to provide beneficial effects on brain functions. This study investigated the mechanisms underlying working memory impairment and the protective role of exercise in prenatal DEHP-exposed male rats. Sprague Dawley dams were fed with vehicle or DEHP during gestation. The male offspring were trained to exercise on a treadmill for 5 weeks, which was followed by an assessment of their working memory with a T-maze delayed non-match-to-sample task. The expressions of BDNF, dopamine D1 receptor (D1R), cannabinoid receptor 1 (CB1R), and fatty acid amide hydrolase (FAAH) in the prefrontal cortex were detected by Western blot. The results showed that DEHP-exposed rats exhibited working memory impairments without significant alterations in locomotor activities. The reduced expressions of prefrontal BDNF and CB1R were obtained in the DEHP-exposed rats, while D1R and FAAH were barely affected. Importantly, aerobic exercise during childhood-adolescence prevented the impairment of working memory in the DEHP-exposed rats by recovering the BDNF and CB1R expressions in the prefrontal cortex. These findings suggest that exercise may provide beneficial effects in ameliorating the impairment of working memory in the prenatal DEHP-exposed male rats at late adolescence.

The therapeutic role of cannabinoid receptors and its agonists or antagonists in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease and its characteristic is the progressive degeneration of dopaminergic neurons within the substantia nigra (SN) of the midbrain. There is hardly any clinically proven efficient therapeutics for its cure in several recent preclinical advances proposed to treat PD. Recent studies have found that the endocannabinoid signaling system in particular the comprised two receptors, CB1 and CB2 receptors, has a significant regulatory function in basal ganglia and is involved in the pathogenesis of PD. Therefore, adding new insights into the biochemical interactions between cannabinoids and other signaling pathways may help develop new pharmacological strategies. Factors of the endocannabinoid system (ECS) are abundantly expressed in the neural circuits of basal ganglia, where they interact interactively with glutamatergic, γ-aminobutyric acid-ergic (GABAergic), and dopaminergic signaling systems. Although preclinical studies on PD are promising, the use of cannabinoids at the clinical level has not been thoroughly studied. In this review, we evaluated the available evidence and reviewed the involvement of ECS in etiologies, symptoms and treatments related to PD. Since CB1 and CB2 receptors are the two main receptors of endocannabinoids, we primarily put the focus on the therapeutic role of CB1 and CB2 receptors in PD. We will try to determine future research clues that will help understand the potential therapeutic benefits of the ECS in the treatment of PD, aiming to open up new strategies and ideas for the treatment of PD.

Interaction of Cannabis Use and Aging: From Molecule to Mind

Given the aging Baby Boomer generation, changes in cannabis legislation, and the growing acknowledgment of cannabis for its therapeutic potential, it is predicted that cannabis use in the older population will escalate. It is, therefore, important to determine the interaction between the effects of cannabis and aging. The aim of this report is to describe the link between cannabis use and the aging brain. Our review of the literature found few and inconsistent empirical studies that directly address the impact of cannabis use on the aging brain. However, research focused on long-term cannabis use points toward cumulative effects on multimodal systems in the brain that are similarly affected during aging. Specifically, the effects of cannabis and aging converge on overlapping networks in the endocannabinoid, opioid, and dopamine systems that may affect functional decline particularly in the hippocampus and prefrontal cortex, which are critical areas for memory and executive functioning. To conclude, despite the limited current knowledge on the potential interactive effects between cannabis and aging, evidence from the literature suggests that cannabis and aging effects are concurrently present across several neurotransmitter systems. There is a great need for future research to directly test the interactions between cannabis and aging.

Endocannabinoid-Dependent Long-Term Potentiation of Synaptic Transmission at Rat Barrel Cortex

Brain-derived neurotrophic factor (BDNF) plays a critical role in modulating plasticity in sensory cortices. Indeed, a BDNF-dependent long-term potentiation (LTP) at distal basal excitatory synapses of Layer 5 pyramidal neurons (L5PNs) has been demonstrated in disinhibited rat barrel cortex slices. Although it is well established that this LTP requires the pairing of excitatory postsynaptic potentials (PSPs) with Ca2+ spikes, its induction when synaptic inhibition is working remains unexplored. Here we show that low-frequency stimulation at basal dendrites of L5PNs is able to trigger a PSP followed by an action potential (AP) and a slow depolarization (termed PSP-Ca2+ response) in thalamocortical slices without blocking synaptic inhibition. We demonstrate that AP barrage-mediated release of endocannabinoids (eCBs) from the recorded L5PNs induces PSP-Ca2+ response facilitation and BDNF-dependent LTP. Indeed, this LTP requires the type 1 cannabinoid receptors activation, is prevented by postsynaptic intracellular 1,2-bis(2-aminophenoxy) ethane-N,N,N,N'-tetraacetic acid (BAPTA) or the anandamide membrane transporter inhibitor AM404, and only occurs in L5PNs neurons showing depolarization-induced suppression of inhibition. Additionally, electrical stimulation at the posteromedial thalamic nucleus induced similar response and LTP. These results reveal a novel form of eCB-dependent LTP at L5PNs that could be relevant in the processing of sensory information in the barrel cortex.

BDNF Controls Bidirectional Endocannabinoid Plasticity at Corticostriatal Synapses

The dorsal striatum exhibits bidirectional corticostriatal synaptic plasticity, NMDAR and endocannabinoids (eCB) mediated, necessary for the encoding of procedural learning. Therefore, characterizing factors controlling corticostriatal plasticity is of crucial importance. Brain-derived neurotrophic factor (BDNF) and its receptor, the tropomyosine receptor kinase-B (TrkB), shape striatal functions, and their dysfunction deeply affects basal ganglia. BDNF/TrkB signaling controls NMDAR plasticity in various brain structures including the striatum. However, despite cross-talk between BDNF and eCBs, the role of BDNF in eCB plasticity remains unknown. Here, we show that BDNF/TrkB signaling promotes eCB-plasticity (LTD and LTP) induced by rate-based (low-frequency stimulation) or spike-timing–based (spike-timing–dependent plasticity, STDP) paradigm in striatum. We show that TrkB activation is required for the expression and the scaling of both eCB-LTD and eCB-LTP. Using 2-photon imaging of dendritic spines combined with patch-clamp recordings, we show that TrkB activation prolongs intracellular calcium transients, thus increasing eCB synthesis and release. We provide a mathematical model for the dynamics of the signaling pathways involved in corticostriatal plasticity. Finally, we show that TrkB activation enlarges the domain of expression of eCB-STDP. Our results reveal a novel role for BDNF/TrkB signaling in governing eCB-plasticity expression in striatum and thus the engram of procedural learning.

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.

Cannabinoid signalling in embryonic and adult neurogenesis: possible implications for psychiatric and neurological disorders

Cannabinoid signalling modulates several aspects of brain function, including the generation and survival of neurons during embryonic and adult periods. The present review intended to summarise evidence supporting a role for the endocannabinoid system on the control of neurogenesis and neurogenesis-dependent functions. Studies reporting participation of cannabinoids on the regulation of any step of neurogenesis and the effects of cannabinoid compounds on animal models possessing neurogenesis-dependent features were selected from Medline. Qualitative evaluation of the selected studies indicated that activation of cannabinoid receptors may change neurogenesis in embryonic or adult nervous systems alongside rescue of phenotypes in animal models of different psychiatric and neurological disorders. The text offers an overview on the effects of cannabinoids on central nervous system development and the possible links with psychiatric and neurological disorders such as anxiety, depression, schizophrenia, brain ischaemia/stroke and Alzheimer's disease. An understanding of the mechanisms by which cannabinoid signalling influences developmental and adult neurogenesis will help foster the development of new therapeutic strategies for neurodevelopmental, psychiatric and neurological disorders.

Levetiracetam combined with ACEA, highly selective cannabinoid CB1 receptor agonist changes neurogenesis in mouse brain

The aim of the study was to evaluate the impact of second generation antiepileptic drug levetiracetam (LEV) with arachidonyl-2'-chloroethylamide (ACEA) on proliferating neural precursor cells in mouse brain. Additionally, we established the relationship between treatment with ACEA in combination with LEV and hippocampal neurogenesis in mouse brain. All experiments were performed on male CB57/BL mice injected i.p. with LEV (10 mg/kg), ACEA (10 mg/kg) and PMSF (30 mg/kg) for 10 days. Experiments were provided in two stages: stage 1- an acute response of proliferating neural precursor cells to ACEA and LEV administration (Ki-67 staining), stage 2 - a long term response to ACEA and LEV administration (BrDU, NeuN, GFAP staining). Results indicate that ACEA + PMSF and ACEA + PMSF + LEV significantly increased the total number of Ki-67 positive cells comparing to the control group. PMSF and LEV administered alone and in combination had no significant impact on cell proliferation compared to the control group. Results from neurogenesis study indicated that ACEA + PMSF administered alone and in combination with LEV increased the total number of BrDU cells compared to the control group, although LEV on its own decreased the number of BrDU cells. Moreover, the combination of ACEA + PMSF + LEV significantly increased the total number of newborn neurons compared to the control group. In turn, LEV significantly decreased the process of neurogenesis. Astrocytes were considerably reduced in all treated groups as compare to the control mice. These data provide substantial evidence that LEV administered chronically decreases the proliferation and differentiation of newly born cells while combination of LEV + ACEA significantly increases the level of newborn neurons in the dentate subgranular zone.

Brain-Derived Neurotrophic Factor (BDNF) Role in Cannabinoid-Mediated Neurogenesis

The adult mammalian brain can produce new neurons in a process called adult neurogenesis, which occurs mainly in the subventricular zone (SVZ) and in the hippocampal dentate gyrus (DG). Brain-derived neurotrophic factor (BDNF) signaling and cannabinoid type 1 and 2 receptors (CB1R and CB2R) have been shown to independently modulate neurogenesis, but how they may interact is unknown. We now used SVZ and DG neurosphere cultures from early (P1-3) postnatal rats to study the CB1R and CB2R crosstalk with BDNF in modulating neurogenesis. BDNF promoted an increase in SVZ and DG stemness and cell proliferation, an effect blocked by a CB2R selective antagonist. CB2R selective activation promoted an increase in DG multipotency, which was inhibited by the presence of a BDNF scavenger. CB1R activation induced an increase in SVZ and DG cell proliferation, being both effects dependent on BDNF. Furthermore, SVZ and DG neuronal differentiation was facilitated by CB1R and/or CB2R activation and this effect was blocked by sequestering endogenous BDNF. Conversely, BDNF promoted neuronal differentiation, an effect abrogated in SVZ cells by CB1R or CB2R blockade while in DG cells was inhibited by CB2R blockade. We conclude that endogenous BDNF is crucial for the cannabinoid-mediated effects on SVZ and DG neurogenesis. On the other hand, cannabinoid receptor signaling is also determinant for BDNF actions upon neurogenesis. These findings provide support for an interaction between BDNF and endocannabinoid signaling to control neurogenesis at distinct levels, further contributing to highlight novel mechanisms in the emerging field of brain repair.

Molecular Imaging in Huntington's Disease

Huntington's disease (HD) is a rare monogenic neurodegenerative disorder caused by a trinucleotide CAG repeat expansion in the huntingtin gene resulting in the formation of intranuclear inclusions of mutated huntingtin. The accumulation of mutated huntingtin leads to loss of GABAergic medium spiny neurons (MSNs); subsequently resulting in the development of chorea, cognitive dysfunction and psychiatric symptoms. Premanifest HD gene expansion carriers, provide a unique cohort to examine very early molecular changes, occurring before the development of overt symptoms, to elucidate disease pathophysiology and identify reliable biomarkers of HD progression. Positron emission tomography (PET) is a non-invasive molecular imaging technique allowing the evaluation of specific molecular targets in vivo. Selective PET radioligands provide invaluable tools to investigate the role of the dopaminergic system, brain metabolism, microglial activation, phosphodiesterase 10A, and cannabinoid, GABA, adenosine and opioid receptors in HD. PET has been employed to monitor disease progression aiming to identify a reliable biomarker to predict phenoconversion from premanifest to manifest HD.

Cannabinoids prevent depressive-like symptoms and alterations in BDNF expression in a rat model of PTSD

Posttraumatic stress disorder (PTSD) is a debilitating condition highly comorbid with depression. The endocannabinoid (eCB) system and brain-derived neurotrophic factor (BDNF) are suggestively involved in both disorders. We examined whether cannabinoids can prevent the long-term depressive-like symptoms induced by exposure to the shock and situational reminders (SRs) model of PTSD. The CB1/2 receptor agonist WIN55,212-2 (0.5 mg/kg; i.p.), the fatty acid hydrolase (FAAH) inhibitor URB597 (0.3 mg/kg, i.p.) or vehicle were administered 2 h after severe shock. Cannabinoids prevented the shock/SRs-induced alterations in social recognition memory, locomotion, passive coping, anxiety-like behavior, anhedonia, fear retrieval, fear extinction and startle response as well as the decrease in BDNF levels in the hippocampus and prefrontal cortex (PFC). Furthermore, significant correlations were found between depressive-like behaviors and BDNF levels in the brain. The findings suggest that cannabinoids may prevent both depressive- and PTSD-like symptoms following exposure to severe stress and that alterations in BDNF levels in the brains' fear circuit are involved in these effects.

Cerebellar BDNF Promotes Exploration and Seeking for Novelty

Background

Approach system considered a motivational system that activates reward-seeking behavior is associated with exploration/impulsivity, whereas avoidance system considered an attentional system that promotes inhibition of appetitive responses is associated with active overt withdrawal. Approach and avoidance dispositions are modulated by distinct neurochemical profiles and synaptic patterns. However, the precise working of neurons and trafficking of molecules in the brain activity predisposing to approach and avoidance are yet unclear.

Methods

In 3 phenotypes of inbred mice, avoiding, balancing, and approaching mice, selected by using the Approach/Avoidance Y-maze, we analyzed endogenous brain levels of brain derived neurotrophic factor, one of the main secretory proteins with pleiotropic action. To verify the effects of the acute increase of brain derived neurotrophic factor, balancing and avoiding mice were bilaterally brain derived neurotrophic factor-infused in the cortical cerebellar regions.

Results

Approaching animals showed high levels of explorative behavior and response to novelty and exhibited higher brain derived neurotrophic factor levels in the cerebellar structures in comparison to the other 2 phenotypes of mice. Interestingly, brain derived neurotrophic factor-infused balancing and avoiding mice significantly increased their explorative behavior and response to novelty.

Conclusions

Cerebellar brain derived neurotrophic factor may play a role in explorative and novelty-seeking responses that sustain the approach predisposition.

Molecular mechanisms of experience-dependent maturation in cortical GABAergic inhibition

Critical periods (CP) in early post-natal life are periods of plasticity during which the neuronal circuitry is most receptive to environmental stimuli. These early experiences translate to a more permanent and sophisticated neuronal connection in the adult brain systems. Multiple studies have pointed to the development of inhibitory circuitry as one of the central factors for the onset of critical periods. We discuss several molecular mechanisms regulating inhibitory circuit maturation and CP, from gene transcription level to protein signaling level. Also, beyond the level of gene sequences, we briefly consider recent information on dynamic epigenetic regulation of gene expression through histone methylation and acetylation and their implication on timed development of the inhibitory circuitry for the onset of CP.

Evaluation of monoacylglycerol lipase as a therapeutic target in a transgenic mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of the motor neuron system with limited therapeutic options. While an increasing number of ALS patients can be linked to a small number of autosomal-dominantly inherited cases, most cases are termed sporadic. Both forms are clinically and histopathologically indistinguishable, raising the prospect that they share key pathogenic steps, including potential therapeutic intervention points. The endocannabinoid system is emerging as a versatile, druggable therapeutic target in the CNS and its dysregulation is an early hallmark of neurodegeneration. Whether this is a defense mechanism or part of the pathogenesis remains to be determined. The neuroprotective and anti-inflammatory endocannabinoid 2-arachidonoylglycerol (2-AG), which is degraded by monoacylglycerol lipase (MAGL), accumulates in the spinal cords of transgenic models of ALS. We tested the hypothesis that this 2-AG increase is a protective response in the low-copy SOD1^G93A mouse model of ALS. We show that oral application of the MAGL inhibitor KML29 delays disease onset, progression and survival. Furthermore, we could demonstrate that KML29 reduced proinflammatory cytokines and increased brain-derived neurotrophic factor (BDNF) expression levels in the spinal cord, the major site of neurodegeneration in ALS. Moreover, treatment of primary mouse neurons and primary mousecroglia with 2-AG confirmed the neuroprotective and anti-inflammatory action by increasing BDNF and arginase-1 and decreasing proinflammatory cytokines in vitro. In summary, we show that elevating 2-AG levels by MAGL inhibition is a therapeutic target in ALS and demonstrate that the endocannabinoid defense mechanisms can be exploited therapeutically in neurodegenerative diseases. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

BDNF-induced endocannabinoid release modulates neocortical glutamatergic neurotransmission

Endocannabinoids (eCBs) and neurotrophins, particularly brain-derived neurotrophic factor (BDNF), are potent neuromodulators found throughout the mammalian neocortex. Both eCBs and BDNF play critical roles in many behavioral and neurophysiological processes and are targets for the development of novel therapeutics. The effects of eCBs and BDNF are primarily mediated by the type 1 cannabinoid (CB1) receptor and the trkB tyrosine kinase receptor, respectively. Our laboratory and others have previously established that BDNF potentiates excitatory transmission by enhancing presynaptic glutamate release and modulating NMDA receptors. In contrast, we have shown that BDNF attenuates inhibitory transmission by inducing postsynaptic release of eCBs that act retrogradely to suppress GABA release in layer 2/3 of somatosensory cortex. Here, we hypothesized that BDNF also induces release of eCBs at excitatory synapses, which could have a mitigating or opposing effect on the direct presynaptic effects of BDNF. We found the highest levels of expression of CB1 and trkB and receptors in layers 2/3 and 5. Surprisingly, BDNF did not increase the frequency of spontaneous miniature excitatory postsynaptic currents (mEPSCs) onto layer 5 pyramidal neurons in somatosensory cortex, in contrast to its effects in the hippocampus and visual cortex. However, the effect of BDNF on mEPSC frequency in somatosensory cortex was unmasked by blocking CB1 receptors or disrupting eCB release. Thus, BDNF-trKB signaling regulates glutamate release in the somatosensory cortex via opposing effects, a direct presynaptic enhancement of release probability, and simultaneous postsynaptically-induced eCB release that decreases release probability via presynaptic CB1 receptors.

Regulation of fear extinction by long-term depression: The roles of endocannabinoids and brain derived neurotrophic factor

The extinction of a conditioned fear response is of great interest in the search for a means of ameliorating adverse neurobiological changes resulting from stress. The discovery that endocannibinoid (EC) levels are inversely related to the extent of such stress, and that the amygdala is a primary site mediating stress, suggests that ECs in this brain region might play a major role in extinction. Supporting this are the observations that the basolateral complex of the amygdala shows an increase in ECs only during extinction and that early clinical trials indicate that cannabinoid-like agents, when taken orally by patients suffering from post traumatic stress disorder (PTSD), reduce insomnia and nightmares. In order to optimize the potential of these agents to ameliorate symptoms of PTSD four important questions need to be answered: first, what is the identity of the cells that release ECs in the amygdala during extinction; second, what are their sites of action; third, what roles do the ECs play in the alleviation of long- depression (LTD), a process central to extinction; and finally, to what extent does brain derived neurotrophic factor (BDNF) facilitate the release of ECs? A review of the relevant literature is presented in an attempt to answer these questions. It is suggested that the principal cell involved in EC synthesis and release during extinction is the so-called excitatory extinction neuron in the basal nucleus of the amygdala. Furthermore that the main site of action of the ECs is the adjacent calcitonin gene-related peptide inhibitory interneurons, whose normal role of blocking the excitatory neurons is greatly diminished. The molecular pathways leading (during extinction trials) to the synthesis and release of ECs from synaptic spines of extinction neurons, that is potentiated by BDNF, are also delineated in this review. Finally, consideration is given to how the autocrine action of BDNF, linked to the release of ECs, can lead to the sustained release of these, so maintaining extinction over long times.

The role of cannabinoids in adult neurogenesis

The processes underpinning post-developmental neurogenesis in the mammalian brain continue to be defined. Such processes involve the proliferation of neural stem cells and neural progenitor cells (NPCs), neuronal migration, differentiation and integration into a network of functional synapses within the brain. Both intrinsic (cell signalling cascades) and extrinsic (neurotrophins, neurotransmitters, cytokines, hormones) signalling molecules are intimately associated with adult neurogenesis and largely dictate the proliferative activity and differentiation capacity of neural cells. Cannabinoids are a unique class of chemical compounds incorporating plant-derived cannabinoids (the active components of Cannabis sativa), the endogenous cannabinoids and synthetic cannabinoid ligands, and these compounds are becoming increasingly recognized for their roles in neural developmental processes. Indeed, cannabinoids have clear modulatory roles in adult neurogenesis, probably through activation of both CB1 and CB2 receptors. In recent years, a large body of literature has deciphered the signalling networks involved in cannabinoid-mediated regulation of neurogenesis. This timely review summarizes the evidence that the cannabinoid system is intricately associated with neuronal differentiation and maturation of NPCs and highlights intrinsic/extrinsic signalling mechanisms that are cannabinoid targets. Overall, these findings identify the central role of the cannabinoid system in adult neurogenesis in the hippocampus and the lateral ventricles and hence provide insight into the processes underlying post-developmental neurogenesis in the mammalian brain.

BDNF interacts with endocannabinoids to regulate cocaine-induced synaptic plasticity in mouse midbrain dopamine neurons

Brain-derived neurotrophic factor (BDNF) and endocannabinoids (eCBs) have been individually implicated in behavioral effects of cocaine. The present study examined how BDNF-eCB interaction regulates cocaine-induced synaptic plasticity in the ventral tegmental area and behavioral effects. We report that BDNF and selective tyrosine kinase receptor B (TrkB) agonist 7,8-dihydroxyflavone (DHF) activated the TrkB receptor to facilitate two forms of eCB-mediated synaptic depression, depolarization-induced suppression of inhibition (DSI), and long-term depression (I-LTD) of IPSCs in ventral tegmental area dopamine neurons in mouse midbrain slices. The facilitation appears to be mediated by an increase in eCB production via phospholipase Cγ pathway, but not by an increase in CB1 receptor responsiveness or a decrease in eCB hydrolysis. Using Cre-loxP technology to specifically delete BDNF in dopamine neurons, we showed that eCB-mediated I-LTD, cocaine-induced reduction of GABAergic inhibition, and potentiation of glutamatergic excitation remained intact in wild-type control mice, but were impaired in BDNF conditional knock-out mice. We also showed that cocaine-induced conditioned place preference was attenuated in BDNF conditional knock-out mice, in vivo pretreatments with DHF before place conditioning restored cocaine conditioned place preference in these mice, and the behavioral effect of DHF was blocked by a CB₁ receptor antagonist. Together, these results suggest that BDNF in dopamine neurons regulates eCB responses, cocaine-induced synaptic plasticity, and associative learning.

Promising cannabinoid-based therapies for Parkinson's disease: motor symptoms to neuroprotection

Parkinson’s disease (PD) is a slow insidious neurological disorder characterized by a loss of dopaminergic neurons in the midbrain. Although several recent preclinical advances have proposed to treat PD, there is hardly any clinically proved new therapeutic for its cure. Increasing evidence suggests a prominent modulatory function of the cannabinoid signaling system in the basal ganglia. Hence, use of cannabinoids as a new therapeutic target has been recommended as a promising therapy for PD. The elements of the endocannabinoid system are highly expressed in the neural circuit of basal ganglia wherein they bidirectionally interact with dopaminergic, glutamatergic, and GABAergic signaling systems. As the cannabinoid signaling system undergoes a biphasic pattern of change during progression of PD, it explains the motor inhibition typically observed in patients with PD. Cannabinoid agonists such as WIN-55,212-2 have been demonstrated experimentally as neuroprotective agents in PD, with respect to their ability to suppress excitotoxicity, glial activation, and oxidative injury that causes degeneration of dopaminergic neurons. Additional benefits provided by cannabinoid related compounds including CE-178253, oleoylethanolamide, nabilone and HU-210 have been reported to possess efficacy against bradykinesia and levodopa-induced dyskinesia in PD. Despite promising preclinical studies for PD, use of cannabinoids has not been studied extensively at the clinical level. In this review, we reassess the existing evidence suggesting involvement of the endocannabinoid system in the cause, symptomatology, and treatment of PD. We will try to identify future threads of research that will help in the understanding of the potential therapeutic benefits of the cannabinoid system for treating PD.

Role for Endogenous BDNF in Endocannabinoid-Mediated Long-Term Depression at Neocortical Inhibitory Synapses

The endogenous cannabinoid (endocannabinoid) system is an important regulator of synaptic function. Endocannabinoids acutely modulate inhibitory and excitatory transmission, and also mediate long-term depression at GABAergic and glutamatergic synapses. Typically, endocannabinoid synthesis and release is stimulated by depolarization-induced calcium influx and/or activation of phospholipase-C (PLC) signaling triggered by mGluR activation. Recently it has been shown that brain-derived neurotrophic factor (BDNF) can also induce endocannabinoid release. Although there is growing evidence for cross-talk between BDNF and endocannabinoid signaling, little is known about the functional relevance of these interactions. In the present studies, we examined BDNF - endocannabinoid interactions in regulating activity-dependent long-term depression at inhibitory synapses (iLTD). We found that theta burst stimulation (TBS) in layer 2/3 of mouse somatosensory cortical slices can induce a form of endocannabinoid-mediated iLTD that is independent of metabotropic glutamate receptor (mGluR) activation. This endocannabinoid-dependent iLTD, however, requires endogenous BDNF-trkB signaling, as it is blocked by a trk tyrosine kinase inhibitor and by a trkB receptor antagonist, and also requires activation of diacylglycerol lipase (DAG-lipase, DGL). In addition, endocannabinoid-mediated iLTD can be induced by combining a subthreshold concentration of exogenous BDNF with weak TBS stimulation that by itself is insufficient to induce iLTD. Taken together, our results suggest that TBS can induce the release of endogenous BDNF, which triggers DGL-dependent endocannabinoid mobilization and cannabinoid receptor-dependent iLTD at layer 2/3 cortical synapses.

Pharmacology of cognitive enhancers for exposure-based therapy of fear, anxiety and trauma-related disorders

Pathological fear and anxiety are highly debilitating and, despite considerable advances in psychotherapy and pharmacotherapy they remain insufficiently treated in many patients with PTSD, phobias, panic and other anxiety disorders. Increasing preclinical and clinical evidence indicates that pharmacological treatments including cognitive enhancers, when given as adjuncts to psychotherapeutic approaches [cognitive behavioral therapy including extinction-based exposure therapy] enhance treatment efficacy, while using anxiolytics such as benzodiazepines as adjuncts can undermine long-term treatment success. The purpose of this review is to outline the literature showing how pharmacological interventions targeting neurotransmitter systems including serotonin, dopamine, noradrenaline, histamine, glutamate, GABA, cannabinoids, neuropeptides (oxytocin, neuropeptides Y and S, opioids) and other targets (neurotrophins BDNF and FGF2, glucocorticoids, L-type-calcium channels, epigenetic modifications) as well as their downstream signaling pathways, can augment fear extinction and strengthen extinction memory persistently in preclinical models. Particularly promising approaches are discussed in regard to their effects on specific aspects of fear extinction namely, acquisition, consolidation and retrieval, including long-term protection from return of fear (relapse) phenomena like spontaneous recovery, reinstatement and renewal of fear. We also highlight the promising translational value of the preclinial research and the clinical potential of targeting certain neurochemical systems with, for example d-cycloserine, yohimbine, cortisol, and L-DOPA. The current body of research reveals important new insights into the neurobiology and neurochemistry of fear extinction and holds significant promise for pharmacologically-augmented psychotherapy as an improved approach to treat trauma and anxiety-related disorders in a more efficient and persistent way promoting enhanced symptom remission and recovery.

Regional effects of endocannabinoid, BDNF and FGF receptor signalling on neuroblast motility and guidance along the rostral migratory stream

During development and after birth neural stem cells in the subventricular zone (SVZ) generate neuroblasts that migrate along the rostral migratory stream (RMS) to populate the olfactory bulb (OB) with neurons. Multiple factors promote neuroblast migration, but the contribution that many of these make to guidance within the intact RMS is not known. In the present study we have characterised in detail how endocannabinoid (eCB), BDNF and FGF receptor (FGFR) signalling regulates motility and guidance, and also determined whether any of these receptors operate in a regionally restricted manner. We used in vivo electroporation in postnatal mice to fluorescently label neuroblasts, and live cell imaging to detail their migratory properties. Cannabinoid receptor antagonists rendered neuroblasts less mobile, and when they did move guidance was lost. Similar results were obtained when eCB synthesis was blocked with diacylglycerol lipase (DAGL) inhibitors, and importantly eCB function is required for directed migration at both ends of the RMS. Likewise, inhibition of BDNF signalling disrupted motility and guidance in a similar manner along the entire RMS. In contrast, altering FGFR signalling inhibits motility and perturbs guidance, but only at the beginning of the stream. Inhibition of FGFR signalling in vivo also reduces the length of the leading process on migratory neuroblasts in a graded manner along the RMS. These results provide evidence for a guidance function for all three of the above receptor systems in the intact RMS, but show that FGFR signalling is unique as it is required in a regionally specific manner.

Programming of neural cells by (endo)cannabinoids: from physiological rules to emerging therapies

Among the many signalling lipids, endocannabinoids are increasingly recognized for their important roles in neuronal and glial development. Recent experimental evidence suggests that, during neuronal differentiation, endocannabinoid signalling undergoes a fundamental switch from the prenatal determination of cell fate to the homeostatic regulation of synaptic neurotransmission and bioenergetics in the mature nervous system. These studies also offer novel insights into neuropsychiatric disease mechanisms and contribute to the public debate about the benefits and the risks of cannabis use during pregnancy and in adolescence.

Endocannabinoid signals in the developmental programming of delayed-onset neuropsychiatric and metabolic illnesses

It is increasingly recognized that maternal exposure to metabolic (nutritional) stimuli, infections, illicit or prescription drugs and environmental stressors during pregnancy can predispose affected offspring to developing devastating postnatal illnesses. If detrimental maternal stimuli coincide with critical periods of tissue production and organogenesis then they can permanently derail key cellular differentiation programs. Maternal programming can thus either provoke developmental failure directly ('direct hit') or introduce latent developmental errors that enable otherwise sub-threshold secondary stressors to manifest as disease ('double hit') postnatally. Accumulating evidence suggests that nervous system development is tightly controlled by maternal metabolic stimuli, and whose synaptic wiring and integrative capacity are adversely affected by dietary and hormonal challenges, infections or episodes of illicit drug use. Endocannabinoids, a family of signal lipids derived from polyunsaturated fatty acids, have been implicated in neuronal fate determination, the control of axonal growth, synaptogenesis and synaptic neurotransmission. Therefore the continuum and interdependence of endocannabinoid actions during the formation and function of synapses together with dynamic changes in focal and circulating endocannabinoid levels upon maternal nutritional imbalance suggest that endocannabinoids can execute the 'reprogramming' of specific neuronal networks. In the present paper, we review molecular evidence suggesting that maternal nutrition and metabolism during pregnancy can affect the formation and function of the hippocampus and hypothalamus by altering endocannabinoid signalling such that neuropsychiatric diseases and obesity respectively ensue in affected offspring. Moreover, we propose that the placenta, fetal adipose and nervous tissues interact via endocannabinoid signals. Thus endocannabinoids are hypothesized to act as a molecular substrate of maternal programming.

The influence of cannabinoids on generic traits of neurodegeneration

In an increasingly ageing population, the incidence of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Huntington's disease are rising. While the aetiologies of these disorders are different, a number of common mechanisms that underlie their neurodegenerative components have been elucidated; namely neuroinflammation, excitotoxicity, mitochondrial dysfunction and reduced trophic support. Current therapies focus on treatment of the symptoms and attempt to delay the progression of these diseases but there is currently no cure. Modulation of the endogenous cannabinoid system is emerging as a potentially viable option in the treatment of neurodegeneration. Endocannabinoid signalling has been found to be altered in many neurodegenerative disorders. To this end, pharmacological manipulation of the endogenous cannabinoid system, as well as application of phytocannabinoids and synthetic cannabinoids have been investigated. Signalling from the CB1 and CB2 receptors are known to be involved in the regulation of Ca(2+) homeostasis, mitochondrial function, trophic support and inflammatory status, respectively, while other receptors gated by cannabinoids such as PPARγ, are gaining interest in their anti-inflammatory properties. Through multiple lines of evidence, this evolutionarily conserved neurosignalling system has shown neuroprotective capabilities and is therefore a potential target for neurodegenerative disorders. This review details the mechanisms of neurodegeneration and highlights the beneficial effects of cannabinoid treatment.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

BDNF-endocannabinoid interactions at neocortical inhibitory synapses require phospholipase C signaling

Endogenous cannabinoids (endocannabinoids) and neurotrophins, particularly brain-derived neurotrophic factor (BDNF), are potent synaptic modulators that are expressed throughout the forebrain and play critical roles in many behavioral processes. Although the effects of BDNF at excitatory synapses have been well characterized, the mechanisms of action of BDNF at inhibitory synapses are not well understood. Previously we have found that BDNF suppresses presynaptic GABA release in layer 2/3 of the neocortex via postsynaptic tropomyosin-related kinase receptor B (trkB) receptor-induced release of endocannabinoids. To examine the intracellular signaling pathways that underlie this effect, we used pharmacological approaches and whole cell patch-clamp techniques in layer 2/3 pyramidal neurons of somatosensory cortex in brain slices from juvenile Swiss CD1 mice. Our results indicated that phospholipase Cγ (PLCγ) is involved in the CB1 receptor-mediated synaptic effect of BDNF, because the BDNF effect was blocked in the presence of the broad-spectrum PLC inhibitors U-73122 and edelfosine, whereas the inactive analog U-73343 did not alter the suppressive effect of BDNF at inhibitory synapses. Endocannabinoid release can also be triggered by metabotropic glutamate receptor (mGluR)-mediated activation of PLCβ, and BDNF has been shown to enhance spontaneous glutamate release. An mGluR antagonist, E4CPG, however, did not block the BDNF effect. In addition, the effect of BDNF was independent of other signaling pathways downstream of trkB receptor activation, namely, mitogen-activated protein kinase and phosphoinositide 3-kinase pathways, as well as protein kinase C signaling.

Cannabinoid receptor signaling in progenitor/stem cell proliferation and differentiation

Cannabinoids, the active components of cannabis (Cannabis sativa) extracts, have attracted the attention of human civilizations for centuries, much earlier than the discovery and characterization of their substrate of action, the endocannabinoid system (ECS). The latter is an ensemble of endogenous lipids, their receptors [in particular type-1 (CB1) and type-2 (CB2) cannabinoid receptors] and metabolic enzymes. Cannabinoid signaling regulates cell proliferation, differentiation and survival, with different outcomes depending on the molecular targets and cellular context involved. Cannabinoid receptors are expressed and functional from the very early developmental stages, when they regulate embryonic and trophoblast stem cell survival and differentiation, and thus may affect the formation of manifold adult specialized tissues derived from the three different germ layers (ectoderm, mesoderm and endoderm). In the ectoderm-derived nervous system, both CB1 and CB2 receptors are present in neural progenitor/stem cells and control their self-renewal, proliferation and differentiation. CB1 and CB2 show opposite patterns of expression, the former increasing and the latter decreasing along neuronal differentiation. Recently, endocannabinoid (eCB) signaling has also been shown to regulate proliferation and differentiation of mesoderm-derived hematopoietic and mesenchymal stem cells, with a key role in determining the formation of several cell types in peripheral tissues, including blood cells, adipocytes, osteoblasts/osteoclasts and epithelial cells. Here, we will review these new findings, which unveil the involvement of eCB signaling in the regulation of progenitor/stem cell fate in the nervous system and in the periphery. The developmental regulation of cannabinoid receptor expression and cellular/subcellular localization, together with their role in progenitor/stem cell biology, may have important implications in human health and disease.

GPCRs in stem cell function

Many tissues of the body cannot only repair themselves, but also self-renew, a property mainly due to stem cells and the various mechanisms that regulate their behavior. Stem cell biology is a relatively new field. While advances are slowly being realized, stem cells possess huge potential to ameliorate disease and counteract the aging process, causing its speculation as the next panacea. Amidst public pressure to advance rapidly to clinical trials, there is a need to understand the biology of stem cells and to support basic research programs. Without a proper comprehension of how cells and tissues are maintained during the adult life span, clinical trials are bound to fail. This review will cover the basic biology of stem cells, the various types of stem cells, their potential function, and the advantages and disadvantages to their use in medicine. We will next cover the role of G protein-coupled receptors in the regulation of stem cells and their potential in future clinical applications.

The molecular basis of the cooperation between EGF, FGF and eCB receptors in the regulation of neural stem cell function

Adult neurogenesis relies on EGF and FGF receptor (EGFR/FGFR) function and endocannabinoid (eCB) signalling. Here we have used a neural stem cell (NSC) line to determine how these systems cooperate to regulate neurogenesis. The results show the EGFR to be solely responsible for maintaining PI3K activation explaining its dominant role in promoting NSC survival. The EGFR and FGFR synergistically regulate the ERK/MAPK pathway, and this explains the requirement for both for optimal cell proliferation. The eCB receptors did not contribute to activation of the PI3K or ERK/MAPK pathways, highlighting the importance of another major proliferation pathway. The EGFR plays the dominant role in maintaining the transcriptome, with significant changes in the expression of over 3500 transcripts seen within hours of inhibition or activation of this receptor. The FGFR has a more modest effect on transcription with evidence for nodal integration with EGFR signalling at the level of the ERK/MAPK pathway. A common set of transcripts are regulated by the CB1 and CB2 receptors, with cooperation between these receptors and the EGFR apparent in the regulation of a pool of transcripts, most likely representing signal integration downstream from an as yet to be identified node. Finally, a first level molecular analysis of the transcriptional response shows regulation of a number of key growth factors, growth factor receptors and GPCRs to be under the control of the EGFR.

G-protein-coupled receptors in adult neurogenesis

The importance of adult neurogenesis has only recently been accepted, resulting in a completely new field of investigation within stem cell biology. The regulation and functional significance of adult neurogenesis is currently an area of highly active research. G-protein-coupled receptors (GPCRs) have emerged as potential modulators of adult neurogenesis. GPCRs represent a class of proteins with significant clinical importance, because approximately 30% of all modern therapeutic treatments target these receptors. GPCRs bind to a large class of neurotransmitters and neuromodulators such as norepinephrine, dopamine, and serotonin. Besides their typical role in cellular communication, GPCRs are expressed on adult neural stem cells and their progenitors that relay specific signals to regulate the neurogenic process. This review summarizes the field of adult neurogenesis and its methods and specifies the roles of various GPCRs and their signal transduction pathways that are involved in the regulation of adult neural stem cells and their progenitors. Current evidence supporting adult neurogenesis as a model for self-repair in neuropathologic conditions, adult neural stem cell therapeutic strategies, and potential avenues for GPCR-based therapeutics are also discussed.

Fear extinction and BDNF: translating animal models of PTSD to the clinic

Brain-derived neurotrophic factor (BDNF) is the most studied neurotrophin involved in synaptic plasticity processes that are required for long-term learning and memory. Specifically, BDNF gene expression and activation of its high-affinity tropomyosin-related kinase B (TrkB) receptor are necessary in the amygdala, hippocampus and prefrontal cortex for the formation of emotional memories, including fear memories. Among the psychiatric disorders with altered fear processing, there is post-traumatic stress disorder (PTSD) which is characterized by an inability to extinguish fear memories. Since BDNF appears to enhance extinction of fear, targeting impaired extinction in anxiety disorders such as PTSD via BDNF signalling may be an important and novel way to enhance treatment efficacy. The aim of this review is to provide a translational point of view that stems from findings in the BDNF regulation of synaptic plasticity and fear extinction. In addition, there are different systems that seem to alter fear extinction through BDNF modulation like the endocannabinoid system and the hypothalamic-pituitary adrenal axis. Recent work also finds that the pituitary adenylate cyclase-activating polypeptide and PAC1 receptor, which are upstream of BDNF activation, may be implicated in PTSD. Especially interesting are data that exogenous fear extinction enhancers such as antidepressants, histone deacetylases inhibitors and D-cycloserine, a partial N-methyl d-aspartate agonist, may act through or in concert with the BDNF-TrkB system. Finally, we review studies where recombinant BDNF and a putative TrkB agonist, 7,8-dihydroxyflavone, may enhance extinction of fear. These approaches may lead to novel agents that improve extinction in animal models and eventually humans.

The multiplicity of action of cannabinoids: implications for treating neurodegeneration

The cannabinoid (CB) system is widespread in the central nervous system and is crucial for controlling a range of neurophysiological processes such as pain, appetite, and cognition. The endogenous CB molecules, anandamide, and 2-arachidonoyl glycerol, interact with the G-protein coupled CB receptors, CB(1) and CB(2). These receptors are also targets for the phytocannabinoids isolated from the cannabis plant and synthetic CB receptor ligands. The CB system is emerging as a key regulator of neuronal cell fate and is capable of conferring neuroprotection by the direct engagement of prosurvival pathways and the control of neurogenesis. Many neurological conditions feature a neurodegenerative component that is associated with excitotoxicity, oxidative stress, and neuroinflammation, and certain CB molecules have been demonstrated to inhibit these events to halt the progression of neurodegeneration. Such properties are attractive in the development of new strategies to treat neurodegenerative conditions of diverse etiology, such as Alzheimer's disease, multiple sclerosis, and cerebral ischemia. This article will discuss the experimental and clinical evidence supporting a potential role for CB-based therapies in the treatment of certain neurological diseases that feature a neurodegenerative component.

Molecular model of cannabis sensitivity in developing neuronal circuits

Prenatal cannabis exposure can complicate in utero development of the nervous system. Cannabis impacts the formation and functions of neuronal circuitries by targeting cannabinoid receptors. Endocannabinoid signaling emerges as a signaling cassette that orchestrates neuronal differentiation programs through the precisely timed interaction of endocannabinoid ligands with their cognate cannabinoid receptors. By indiscriminately prolonging the 'switched-on' period of cannabinoid receptors, cannabis can hijack endocannabinoid signals to evoke molecular rearrangements, leading to the erroneous wiring of neuronal networks. Here, we formulate a hierarchical network design necessary and sufficient to describe the molecular underpinnings of cannabis-induced neural growth defects. We integrate signalosome components, deduced from genome- and proteome-wide arrays and candidate analyses, to propose a mechanistic hypothesis of how cannabis-induced ectopic cannabinoid receptor activity overrides physiological neurodevelopmental endocannabinoid signals, affecting the timely formation of synapses.

Endocannabinoids regulate the migration of subventricular zone-derived neuroblasts in the postnatal brain

In the adult brain, neural stem cells proliferate within the subventricular zone before differentiating into migratory neuroblasts that travel along the rostral migratory stream (RMS) to populate the olfactory bulb with new neurons. Because neuroblasts have been shown to migrate to areas of brain injury, understanding the cues regulating this migration could be important for brain repair. Recent studies have highlighted an important role for endocannabinoid (eCB) signaling in the proliferation of the stem cell population, but it remained to be determined whether this pathway also played a role in cell migration. We now show that mouse migratory neuroblasts express cannabinoid receptors, diacylglycerol lipase α (DAGLα), the enzyme that synthesizes the endocannabinoid 2-arachidonoylglycerol (2-AG), and monoacylglycerol lipase, the enzyme responsible for its degradation. Using a scratch wound assay for a neural stem cell line and RMS explant cultures, we show that inhibition of DAGL activity or CB(1)/CB(2) receptors substantially decreases migration. In contrast, direct activation of cannabinoid receptors or preventing the breakdown of 2-AG increases migration. Detailed analysis of primary neuroblast migration by time-lapse imaging reveals that nucleokinesis, as well as the length and branching of the migratory processes are under dynamic control of the eCB system. Finally, similar effects are observed in vivo by analyzing the morphology of green fluorescent protein-labeled neuroblasts in brain slices from mice treated with CB(1) or CB(2) antagonists. These results describe a novel role for the endocannabinoid system in neuroblast migration in vivo, highlighting its importance in regulating an additional essential step in adult neurogenesis.