Tomás Palomo

Impaired action of anxiolytic drugs in mice deficient in cannabinoid CB1 receptors.

The role of cannabinoid CB(1) receptors in the action of anxiolytics was examined. Deletion of CB(1) receptors resulted in increased anxiety-like behaviours in light/dark box, elevated plus maze and social interaction tests. Mutant mice presented basal low corticosterone concentrations and low proopiomelanocortin gene expression in the anterior lobe of the pituitary gland compared to wild-type mice. Ten minutes of restraint stress resulted in a twofold increase in corticosterone concentrations in the plasma of mutant mice, compared to wild-type mice. Bromazepam (50 or 100 microg/kg) markedly increased the time spent in light area in wild-type animals, though both doses were without effect in mutant mice. Administration of buspirone (1 or 2 mg/kg) produced anxiolytic effects in wild-type mice. In contrast, only the highest dose of buspirone had anxiolytic results in mutant mice. Our findings reveal that CB(1) receptors are involved in the regulation of emotional responses, and play a pivotal role in the action mechanism of anxiolytics. They suggest that alterations in the functional activity of the CB(1) receptor may be related to the emergence of anxiety disorders, and may affect treatment with anxiolytics.

Downregulation of rat brain cannabinoid binding sites after chronic Δ9-tetrahydrocannabinol treatment

Specific cannabinoid receptors have been recently described in extrapyramidal and limbic areas and presumably might mediate the effects of marijuana exposure on behavioral processes related to those areas. In this work, we examined whether cannabinoid receptors exhibit downregulation as a consequence of the chronic exposure to delta 9-tetrahydrocannabinol (THC), which might explain certain tolerance phenomena observed in relation to motor and limbic effects of marijuana. To this end, we first characterized the binding of cannabinoid receptors, by using [3H]CP-55,940 binding assays, in the striatum, limbic forebrain, and ventral mesencephalon of male rats, and, second, we measured the density and affinity of those receptors in these brain areas after 7 days of a daily treatment with THC. Development of a tolerance phenomenon was behaviorally tested by using an open-field technique. Results were as follows. The three areas studies presented specific and saturable binding for the cannabinoid ligand, as revealed by their corresponding association and dissociation curves, displacement by THC, saturation curves, and Scatchard plots. A chronic treatment with THC produced the expected tolerance phenomenon: The decrease caused by an acute dose in spontaneous locomotor (49.4%) and exploratory (59.7%) activities and, mainly, the increase in the time spent by the rat in inactivity (181.7%) were diminished after 7 days of daily treatment (39.4, 40.4, and 31.7%, respectively). This tolerance was accompanied by significant decreases in the density of cannabinoid receptors in the striatum and limbic forebrain, the areas where nerve terminals for nigrostriatal and mesolimbic dopaminergic systems, respectively, which play an important role in those processes, are located.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of behavioral impulsivity in the development of alcohol dependence: a 4-year follow-up study.

BACKGROUND Although many studies have established a close relation between impulsivity and alcohol use disorders, little is known about the role of behavioral impulsivity in the development of these disorders. OBJECTIVES To determine the role of 2 laboratory paradigms of impulsivity in the development of alcohol use disorders. METHODS Follow-up study carried out with 471 participants diagnosed as heavy drinkers (HD) and followed-up for 4 years. Initially, they were compared with a healthy control group. Assessment of behavioral impulsivity was carried out with the Continuous Performance Test (CPT), and the Stop-Signal Task (SST) assessed behavioral inhibitory control. Differential reinforcement for low-rate responding (DRLR) was used to evaluate the delay reward dimension. The Structured Clinical Interview (SCID-DSM-IV) was used to diagnose alcohol dependence. RESULTS The HD performed worse than the control group in all the behavioral tests of impulsivity. Performance in DRLR was the only behavioral impulsivity test that classified the HD correctly compared to controls. Logistic regression analysis indicated that performance on SST was a significant predictor [odds = 1.52(CI = 1.08-2.31)] of developing alcohol dependence. CONCLUSIONS Our results support the relation between behavioral impulsivity and alcohol use disorders. The paradigm related to delay of reward may be a factor associated with the use of alcohol and the incapacity to control inhibition as dependence develops.

Chronic (−)-Δ9-tetrahydrocannabinol treatment induces sensitization to the psychomotor effects of amphetamine in rats

Clinical and basic research studies have linked cannabinoid consumption to the onset of psychosis, specially schizophrenia. In the present study we have evaluated the effects of the natural psychoactive constituent of Cannabis (-)-delta9-tetrahydrocannabinol on the acute actions of the psychostimulant, D-amphetamine, on behaviour displayed by male rats on a hole-board, a proposed animal model of amphetamine-induced psychosis. Cannabinoid-amphetamine interactions were studied (1) 30 min after acute injection of (-)-delta9-tetrahydrocannabinol (0.1 or 6.4 mg/kg, i.p.); (2) 30 min after the last injection of 14-daily treatment with (-)-delta9-tetrahydrocannabinol (0.1 or 6.4 mg/kg) and 3) 24 h after the last injection of 14-daily treatment with (-)-delta9-tetrahydrocannabinol (6.4 mg/kg). Acute cannabinoid exposure antagonized the amphetamine-induced dose-dependent increase in locomotion, exploration and the decrease in inactivity. Chronic treatment with (-)-delta9-tetrahydrocannabinol resulted in tolerance to this antagonistic effect on locomotion and inactivity but not on exploration, and potentiated amphetamine-induced stereotypies. Lastly, 24 h of withdrawal after 14 days of cannabinoid treatment resulted in sensitization to the effects of D-amphetamine on locomotion, exploration and stereotypies. Since (-)-delta9-tetrahydrocannabinol is a cannabinoid CB1 receptor agonist, densely present in limbic and basal ganglia circuits, and since amphetamine enhances monoaminergic inputs (i.e., dopamine, serotonin) in these brain areas, the present data support the hypothesis of a role for the cannabinoid CB1 receptor as a regulatory mechanism of monoaminergic neuron-mediated psychomotor activation. These findings may be relevant for the understanding of both cannabinoid-monoamines interactions and Cannabis-associated psychosis.

Increase in gray matter and decrease in white matter volumes in the cortex during treatment with atypical neuroleptics in schizophrenia

The effects of atypical antipsychotic treatment on the brain volume deficits associated with schizophrenia are poorly understood. We assessed the brain volumes of eleven healthy controls and 29 patients with schizophrenia, using magnetic resonance imaging at baseline and at follow-up after two years of treatment with atypical neuroleptics. Two groups of patients were analyzed: treatment-naïve patients (n = 17) and chronic treatment-resistant patients (n = 12). Treatment-naïve patients received risperidone during the follow-up period, whereas chronic patients received clozapine. Gray matter (GM) and white matter (WM) volumes in the frontal, parietal, occipital, and temporal lobes were measured. Contrary to the controls, both groups of patients presented GM increases and WM decreases in the parietal and occipital lobes (p < .005). Frontal GM also increased in the chronic group with clozapine. There was a significant (p < .001) inverse relationship between the baseline volumes (GM deficit/WM excess) and the longitudinal change. These GM and WM changes were not related to changes in weight. Thus, treatment with risperidone and clozapine in schizophrenia may have an effect on gray and white matter volume and needs further exploration.

Attention-Deficit-Hyperactivity Disorder and Reward Deficiency Syndrome

Molecular genetic studies have identified several genes that may mediate susceptibility to attention deficit hyperactivity disorder (ADHD). A consensus of the literature suggests that when there is a dysfunction in the “brain reward cascade,” especially in the dopamine system, causing a low or hypo-dopaminergic trait, the brain may require dopamine for individuals to avoid unpleasant feelings. This high-risk genetic trait leads to multiple drug-seeking behaviors, because the drugs activate release of dopamine, which can diminish abnormal cravings. Moreover, this genetic trait is due in part to a form of a gene (DRD2 A1 allele) that prevents the expression of the normal laying down of dopamine receptors in brain reward sites. This gene, and others involved in neurophysiological processing of specific neurotransmitters, have been associated with deficient functions and predispose individuals to have a high risk for addictive, impulsive, and compulsive behavioral propensities. It has been proposed that genetic variants of dopaminergic genes and other “reward genes” are important common determinants of reward deficiency syndrome (RDS), which we hypothesize includes ADHD as a behavioral subtype. We further hypothesize that early diagnosis through genetic polymorphic identification in combination with DNA-based customized nutraceutical administration to young children may attenuate behavioral symptoms associated with ADHD. Moreover, it is concluded that dopamine and serotonin releasers might be useful therapeutic adjuncts for the treatment of other RDS behavioral subtypes, including addictions.

Anatomical and functional brain variables associated with clozapine response in treatment-resistant schizophrenia

Clozapine alleviates the symptoms of a significant proportion of treatment-resistant schizophrenic patients. Previous studies suggest that the response to clozapine may be associated with prefrontal and temporal anatomy as well as with prefrontal, basal ganglia and thalamic metabolism. A sample of 25 treatment-resistant (TR) schizophrenic patients underwent magnetic resonance imaging (MRI) and 18F-deoxyglucose positron emission tomography (PET) before and after treatment with clozapine. We investigated the association between changes in positive, disorganized, and negative schizophrenic syndromes with clozapine treatment and a set of cerebral variables that included total intracranial volume (ICV); hippocampal, dorsolateral prefrontal (DLPF) and temporal gray-matter volume and metabolism; and metabolic activity of the thalamus, pallidum/putamen, and caudate head. Improvement in positive symptoms with clozapine was directly related to temporal gray-matter volume, whereas improvement of disorganization symptoms was inversely related to ICV and hippocampal volume. Patients with high baseline DLPF cortical volume and metabolic activity were more likely to experience improvement in their negative symptoms. We conclude that clinical improvement with clozapine may be related with the anatomy and metabolic activity of specific brain areas, with the structural integrity of the DLPF and temporal regions showing the maximum predictive capacity.

Extinction of Cocaine Self-Administration Produces a Differential Time-Related Regulation of Proenkephalin Gene Expression in Rat Brain

The purpose of this study was to examine the time course effects of extinction of cocaine self-administration behavior on proenkephalin (PENK) gene expression in caudate-putamen nucleus (ST), nucleus accumbens (Acc), olfactory tubercle (Tu), piriform cortex (Pir), ventromedial hypothalamic nucleus (VMN), and central amygdala (Ce) as measured by in situ hybridization histochemistry. Seventy-two littermate male Lewis rats were randomly assigned in triads to one of three conditions: (1) contingent intravenous self-administration of 1 mg/kg/injection of cocaine (CONT); (2) noncontingent injections of either 1 mg/kg/injection of cocaine (NONCONT); or (3) saline yoked (SALINE) to the intake of the self-administering subject. The self-administering rats were trained to self-administer cocaine under a FR5 schedule of reinforcement for a minimum of 3 weeks. After stable baseline levels of drug intake had been reached, saline was substituted for drug. Following this first extinction period, cocaine self-administration was reinstated for an additional period of 2 weeks. Immediately after cessation of the last session of cocaine self-administration (day 0) and 1-, 5-, and 10-day after the second extinction period, animal brains in each triad were removed to be processed for in situ hybridization. PENK mRNA levels were significantly higher in the cocaine groups when compared with SALINE group in the ST, Acc, Pir, and Tu regions on days 0, 1, 5, and 10 of the extinction and lower in the Ce region of CONT group when compared to NONCONT and SALINE groups on days 1, 5, and 10 of the extinction period. In the VMN nucleus, PENK mRNA content in CONT group versus NONCONT and SALINE groups was also lower, but there were statistically significant differences only on day 5. These results suggest that changes in PENK gene expression after contingent cocaine administration might be involved in cocaine withdrawal states.

The ANKK1 Kinase Gene and Psychiatric Disorders

The TaqIA single nucleotide polymorphism (SNP, rs1800497), which is located in the gene that codes for the putative kinase ANKK1 (ANKK1) near the termination codon of the D2 dopamine receptor gene (DRD2; chromosome 11q22–q23), is the most studied genetic variation in a broad range of psychiatric disorders and personality traits. A large number of individual genetic association studies have found that the TaqIA SNP is linked to alcoholism and antisocial traits. In addition, it has also been related to other conditions such as schizophrenia, eating disorders, and some behavioral childhood disorders. The TaqIA A1 allele is mainly associated with addictions, antisocial disorders, eating disorders, and attention-deficit/hyperactivity disorders, while the A2 allele occurs more frequently in schizophrenic and obsessive-compulsive patients. Current data show that the TaqIA polymorphism may be a marker of both DRD2 and ANKK1 genetic variants. ANKK1 would belong to a family of kinases involved in signal transduction. This raises the question of whether signaling players intervene in the pathophysiology of psychiatric disorders. Basic research on the ANKK1 protein and its putative interaction with the D2 dopamine receptor could shed light on this issue.

The anti-inflammatory prostaglandin 15d-PGJ2 and its nuclear receptor PPARgamma are decreased in schizophrenia

A number of findings suggest that inflammation plays a role in the pathophysiology of schizophrenia. Taking into account a physiological balance between pro- and anti-inflammatory mediators, we measured the plasma levels of cyclooxygenase-derived mediators and other key pro- and anti-inflammatory transcription factors in peripheral blood mononuclear cells (PBMC). Forty healthy subjects and 46 treated chronic schizophrenic patients with an acutely exacerbated condition who met DSM-IV criteria were included. COX by-products prostaglandin E2 (PGE2) and 15d-prostaglandin J2 (15d-PGJ2) plasma levels were measured by EIA. Peroxisome proliferator-activated receptor gamma (PPARγ) as well as nuclear factor kappaB (NFκB) activity in nuclear extracts from PBMC and expression of its inhibitory subunit IκBα in cytosolic extracts were determined using ELISA-based kits. Schizophrenic patients showed higher plasma levels of pro-inflammatory PGE2 than age-matched controls (p=0.043). On the contrary, levels of anti-inflammatory 15-d-PGJ2 were lower (p=0.004), correlating with a lower expression of its nuclear target, PPARγ in nuclear extracts from PBMC (p=0.001). Although no changes in NFκB activity were observed between patients and healthy controls, the expression of its inhibitory protein IκBα was lower in the patients compared to the controls (p=0.027). These findings suggest that schizophrenia is associated with a systemic imbalance in the plasma levels of pro-inflammatory/anti-inflammatory prostaglandins in favor of the former. Furthermore, the expression and activity of anti-inflammatory PPARγ are diminished in PBMC, which indicates a state of inflammation and blunted anti-inflammatory counterbalancing mechanisms at systemic level in these patients.