Maria-Paz Viveros

Endocannabinoid system and stress and anxiety responses

Cannabinoid agonists induce complex and often contradictory effects on anxiety in humans and experimental animals. The data from animal tests provide evidence of dose-dependent bidirectional modulation of anxiety by the cannabinoid system and the importance of environmental context. The mechanisms mediating the effects of cannabinoids on anxiety-related responses appear to involve CB1 and non-CB1 cannabinoid receptors. In addition, the CRH, GABA(A), cholecystokinin, opioid and serotonergic systems have also been implicated. Brain regions such as the amygdala, hippocampus and cortex, directly involved in the regulation of emotional behavior, contain high densities of CB1 receptors. Mutant mice lacking CB1 receptors show anxiogenic-like and depressive-like phenotypes in several tests, as well as profound alterations in their adrenocortical activity. Pharmacological blockade of CB1 receptors induces anxiety in rats, and inhibition of anandamide metabolism produces anxiolytic-like effects. Thus, the endocannabinoid system appears to play a pivotal role in the regulation of emotional states and may constitute a novel pharmacological target for anti-anxiety therapy.

The endocannabinoid system, eating behavior and energy homeostasis: the end or a new beginning?

The endocannabinoid system (ECS) consists of two receptors (CB(1) and CB(2)), several endogenous ligands (primarily anandamide and 2-AG), and over a dozen ligand-metabolizing enzymes. The ECS regulates many aspects of embryological development and homeostasis, including neuroprotection and neural plasticity, immunity and inflammation, apoptosis and carcinogenesis, pain and emotional memory, and the focus of this review: hunger, feeding, and metabolism. This mini-review summarizes the main findings that supported the clinical use of CB1 antagonists/inverse agonists, the clinical concerns that have emerged, and the possible future of cannabinoid-based therapy of obesity and related diseases. The ECS controls energy balance and lipid metabolism centrally (in the hypothalamus and mesolimbic pathways) and peripherally (in adipocytes, liver, skeletal muscle and pancreatic islet cells), acting through numerous anorexigenic and orexigenic pathways. Obese people seem to display an increased endocannabinoid tone, driving CB(1) receptor in a feed-forward dysfunction. Several CB(1) antagonists/inverse agonists have been developed for the treatment of obesity. Although these drugs were found to be efficacious at reducing food intake as well as abdominal adiposity and cardiometabolic risk factors, they resulted in adverse psychiatric effects that limited their use and finally led to the end of the clinical use of systemic CB(1) ligands with significant inverse agonist activity for complicated obesity. However, the existence of alternatives such as CB(1) partial agonists, neutral antagonists, antagonists restricted to the periphery, allosteric modulators and other potential targets within the ECS indicate that a cannabinoid-based therapy for the management of obesity and its associated cardiometabolic sequelae should remain open for consideration.

Involvement of 5-HT1A receptors in behavioural effects of the cannabinoid receptor agonist CP 55,940 in male rats

We have studied the possible interaction between the cannabinoid receptor agonist CP 55,940 (1 and 50 μg/kg) and the 5-HT1A receptor antagonist WAY 100635 (1 mg/kg) in the modulation of plus-maze and holeboard activity in Wistar adult male rats. In the plus-maze, the higher dose of CP 55,940 induced an anxiogenic-like effect, whereas the lower dose induced anxiolytic-like responses. The 5-HT1A antagonist, which was silent in this test, attenuated the anxiogenic, but not the anxiolytic, effect of CP 55,940. In the holeboard, the higher dose of CP 55,940 significantly decreased head-dipping duration, and WAY 100635, which did not affect exploratory head-dipping when administered alone, antagonized this effect. The administration of WAY 100635 significantly increased grooming behaviour, and this effect was inhibited by the two doses of CP 55,940, which did not exert any effect, per se, on this parameter. We provide the first evidence implicating 5-HT1A receptors in anxiety-related behavioural responses to a cannabinoid agonist.

Role of cannabis and endocannabinoids in the genesis of schizophrenia

RationaleCannabis abuse and endocannabinoids are associated to schizophrenia.ObjectivesIt is important to discern the association between schizophrenia and exogenous Cannabis sativa, on one hand, and the endogenous cannabinoid system, on the other hand.ResultsOn one hand, there is substantial evidence that cannabis abuse is a risk factor for psychosis in genetically predisposed people, may lead to a worse outcome of the disease, or it can affect normal brain development during adolescence, increasing the risk for schizophrenia in adulthood. Regarding genetic predisposition, alterations affecting the cannabinoid CNR1 gene could be related to schizophrenia. On the other hand, the endogenous cannabinoid system is altered in schizophrenia (i.e., increased density of cannabinoid CB1 receptor binding in corticolimbic regions, enhanced cerebrospinal fluid anandamide levels), and dysregulation of this system can interact with neurotransmitter systems in such a way that a “cannabinoid hypothesis” can be integrated in the neurobiological hypotheses of schizophrenia. Finally, there is also evidence that some genetic alterations of the CNR1 gene can act as a protectant factor against schizophrenia or can induce a better pharmacological response to atypical antipsychotics.ConclusionsCannabis abuse is a risk factor for psychosis in predisposed people, it can affect neurodevelopment during adolescence leading to schizophrenia, and a dysregulation of the endocannabinoid system can participate in schizophrenia. It is also worth noting that some specific cannabinoid alterations can act as neuroprotectant for schizophrenia or can be a psychopharmacogenetic rather than a vulnerability factor.

Species differences in cannabinoid receptor 2 (CNR2 gene): identification of novel human and rodent CB2 isoforms, differential tissue expression, and regulation by cannabinoid receptor ligands

Cannabinoids, endocannabinoids and marijuana activate two well‐characterized cannabinoid receptors (CB‐Rs), CB1‐Rs and CB2‐Rs. The expression of CB1‐Rs in the brain and periphery has been well studied, but neuronal CB2‐Rs have received much less attention than CB1‐Rs. Many studies have now identified and characterized functional glial and neuronal CB2‐Rs in the central nervous system. However, many features of CB2‐R gene structure, regulation and variation remain poorly characterized in comparison with the CB1‐R. In this study, we report on the discovery of a novel human CB2 gene promoter transcribing testis (CB2A) isoform with starting exon located ca 45 kb upstream from the previously identified promoter transcribing the spleen isoform (CB2B). The 5′ exons of both CB2 isoforms are untranslated 5′UTRs and alternatively spliced to the major protein coding exon of the CB2 gene. CB2A is expressed higher in testis and brain than CB2B that is expressed higher in other peripheral tissues than CB2A. Species comparison found that the CB2 gene of human, rat and mouse genomes deviated in their gene structures and isoform expression patterns. mCB2A expression was increased significantly in the cerebellum of mice treated with the CB‐R mixed agonist, WIN55212‐2. These results provide much improved information about CB2 gene structure and its human and rodent variants that should be considered in developing CB2‐R‐based therapeutic agents.

Endocannabinoid System and Synaptic Plasticity: Implications for Emotional Responses

The endocannabinoid system has been involved in the regulation of anxiety, and proposed as an inhibitory modulator of neuronal, behavioral and adrenocortical responses to stressful stimuli. Brain regions such as the amygdala, hippocampus and cortex, which are directly involved in the regulation of emotional behavior, contain high densities of cannabinoid CB1 receptors. Mutant mice lacking CB1 receptors show anxiogenic and depressive-like behaviors as well as an altered hypothalamus pituitary adrenal axis activity, whereas enhancement of endocannabinoid signaling produces anxiolytic and antidepressant-like effects. Genetic and pharmacological approaches also support an involvement of endocannabinoids in extinction of aversive memories. Thus, the endocannabinoid system appears to play a pivotal role in the regulation of emotional states. Endocannabinoids have emerged as mediators of short- and long-term synaptic plasticity in diverse brain structures. Despite the fact that most of the studies on this field have been performed using in vitro models, endocannabinoid-mediated plasticity might be considered as a plausible candidate underlying some of the diverse physiological functions of the endogenous cannabinoid system, including developmental, affective and cognitive processes. In this paper, we will focus on the functional relevance of endocannabinoid-mediated plasticity within the framework of emotional responses. Alterations of the endocannabinoid system may constitute an important factor in the aetiology of certain neuropsychiatric disorders, and, in turn, enhancers of endocannabinoid signaling could represent a potential therapeutical tool in the treatment of both anxiety and depressive symptoms.

Early maternal deprivation induces gender‐dependent changes on the expression of hippocampal CB1 and CB2 cannabinoid receptors of neonatal rats

Early maternal deprivation (MD) in rats (24 h, postnatal day 9–10) is a model for neurodevelopmental stress. There are some data proving that MD affects the endocannabinoid system (ECS) in a gender‐dependent manner, and that these changes may account for the proposed schizophrenia‐like phenotype of MD rats. The impact of MD on cannabinoid receptor distribution in the hippocampus is unknown. The aim of this study is to evaluate the expression of CB1 and CB2 receptors in diverse relevant subregions (DG, CA1, and CA3) of the hippocampus in 13‐day‐old rats by immunohistochemistry and densitometry. MD induced a significant decrease in CB1 immunoreactivity (more marked in males than in females), which was mainly associated with fibers in the strata pyramidale and radiatum of CA1 and in the strata oriens, pyramidale, and radiatum of CA3. In contrast, MD males and females showed a significant increase in CB2 immunoreactivity in the three hippocampal areas analyzed that was detected in neuropil and puncta in the stratum oriens of CA1 and CA3, and in the polymorphic cell layer of the dentate gyrus. A marked sex dimorphism was observed in CA3, with females exhibiting higher CB1 immunoreactivity than males, and in dentate gyrus, with females exhibiting lower CB2 immunoreactivity than males. These results point to a clear association between developmental stress and dysregulation of the ECS. The present MD procedure may provide an interesting experimental model to further address the role of the ECS in neurodevelopmental mental illnesses such as schizophrenia.

Behavioural and neuroendocrine effects of cannabinoids in critical developmental periods.

The present article focuses on psychoneuroendocrine effects of cannabinoids in developing animals, with special emphasis on the perinatal, periweanling and periadolescent periods. We describe and discuss published data dealing with acute and long-term effects of exposure to cannabinoid agonists in such critical periods. Human studies have demonstrated that the consumption of marijuana by women during pregnancy affects the neurobehavioural development of their children. Investigations using animal models provide useful information for a better understanding of the long-lasting deleterious consequences of cannabis exposure during pregnancy and lactation. The increasing use of cannabis among adolescents and its associated public health problems have led to a parallel increase in basic research on appropriate animal models. Chronic administration of cannabinoid agonists during the periadolescent period causes persistent behavioural alterations in adult animals. Some of these alterations may be related to a possible increased risk of psychosis and other neuropsychiatric disorders in early onset cannabis users.

Nicotine and cannabinoids: Parallels, contrasts and interactions

After a brief outline of the nicotinic and cannabinoid systems, we review the interactions between the pharmacological effects of nicotine and cannabis, two of the most widely used drugs of dependence. These drugs are increasingly taken in combination, particularly among the adolescents and young adults. The review focuses on addiction-related processes, gateway and reverse gateway theories of addiction and therapeutic implications. It then reviews studies on the important period of adolescence, an area that is in urgent need of further investigation and in which the importance of sex differences is emerging. Three other areas of research, which might be particularly relevant to the onset and/or maintenance of dependence, are then reviewed. Firstly, the effects of the two drugs on anxiety-related behaviours are discussed and then their effects on food intake and cognition, two areas in which they have contrasting effects. Certain animal studies suggest that reinforcing effects are likely to be enhanced by joint consumption of nicotine and cannabis, as also may be anxiolytic effects. If this was the case in humans, the latter might be viewed as an advantage particularly by adolescent girls, although the increased weight gain associated with cannabis would be a disadvantage. The two drugs also have opposite effects on cognition and the possibility of long-lasting cognitive impairments resulting from adolescent consumption of cannabis is of particular concern.

Involvement of the κ-opioid receptor in the anxiogenic-like effect of CP 55,940 in male rats

We have studied the possible interaction between three selective opioid-receptor antagonists, nor-binaltorphimine (NB: kappa) (5 mg/kg), cyprodime (CY: mu) (10 mg/kg) and naltrindole (NTI: delta) (1 mg/kg), and the cannabinoid receptor agonist CP 55,940, in the modulation of anxiety (plus-maze) and adrenocortical activity (serum corticosterone levels by radioimmunoassay) in male rats. The holeboard was used to evaluate motor activity and directed exploration. CP 55,940 (75 microg/kg, but not 10 microg/kg) induced an anxiogenic-like effect, which was antagonised by NB. The other effects of CP 55,940 (75 microg/kg), a decreased holeboard activity and stimulation of adrenocortical activity, were not antagonised by any of the three opioid receptor antagonists. CY and NTI, when administered alone, induced marked reductions in motor activity, anxiogenic-like effects and stimulation of adrenocortical activity. The selective kappa-opioid receptor antagonist NB, on its own, did not modify the level of anxiety but stimulated adrenocortical activity. We provide the first pharmacological evidence about the involvement of the kappa-opioid receptor in the anxiogenic-like effect of CP 55,940.