Francisco Navarrete

Deletion of CB2 cannabinoid receptor induces schizophrenia-related behaviors in mice

The possible role of the CB2 receptor (CB2r) in psychiatric disorders has been considered. Several animal models use knockout (KO) mice that display schizophrenia-like behaviors and this study evaluated the role of CB2r in the regulation of such behaviors. Mice lacking the CB2r (CB2KO) were challenged in open field, light–dark box, elevated plus-maze, tail suspension, step down inhibitory avoidance, and pre-pulse inhibition tests (PPI). Furthermore, the effects of treatment with cocaine and risperidone were evaluated using the OF and the PPI test. Gene expression of dopamine D2 (D2r), adrenergic-α2C (α2Cr), serotonergic 5-HT2A and 5-HT2C receptors (5-HT2Ar and 5-HT2Cr) were studied by RT-PCR in brain regions related to schizophrenia. Deletion of CB2r decreased motor activity in the OF test, but enhanced response to acute cocaine and produced mood-related alterations, PPI deficit, and cognitive impairment. Chronic treatment with risperidone tended to impair PPI in WT mice, whereas it ‘normalized’ the PPI deficit in CB2KO mice. CB2KO mice presented increased D2r and α2Cr gene expressions in the prefrontal cortex (PFC) and locus coeruleus (LC), decreased 5-HT2Cr gene expression in the dorsal raphe (DR), and 5-HT2Ar gene expression in the PFC. Chronic risperidone treatment in WT mice left α2Cr gene expression unchanged, decreased D2r gene expression (15 μg/kg), and decreased 5-HT2Cr and 5-HT2Ar in PFC and DR. In CB2KO, the gene expression of D2r in the PFC, of α2Cr in the LC, and of 5-HT2Cr and 5-HT2Ar in PFC was reduced; 5-HT2Cr and 5-HT2Ar gene expressions in DR were increased after treatment with risperidone. These results suggest that deletion of CB2r has a relation with schizophrenia-like behaviors. Pharmacological manipulation of CB2r may merit further study as a potential therapeutic target for the treatment of schizophrenia-related disorders.

Role of CB2 cannabinoid receptors in the rewarding, reinforcing, and physical effects of nicotine.

This study was aimed to evaluate the involvement of CB2 cannabinoid receptors (CB2r) in the rewarding, reinforcing and motivational effects of nicotine. Conditioned place preference (CPP) and intravenous self-administration experiments were carried out in knockout mice lacking CB2r (CB2KO) and wild-type (WT) littermates treated with the CB2r antagonist AM630 (1 and 3 mg/kg). Gene expression analyses of tyrosine hydroxylase (TH) and α3- and α4-nicotinic acetylcholine receptor subunits (nAChRs) in the ventral tegmental area (VTA) and immunohistochemical studies to elucidate whether CB2r colocalized with α3- and α4-nAChRs in the nucleus accumbens and VTA were performed. Mecamylamine-precipitated withdrawal syndrome after chronic nicotine exposure was evaluated in CB2KO mice and WT mice treated with AM630 (1 and 3 mg/kg). CB2KO mice did not show nicotine-induced place conditioning and self-administered significantly less nicotine. In addition, AM630 was able to block (3 mg/kg) nicotine-induced CPP and reduce (1 and 3 mg/kg) nicotine self-administration. Under baseline conditions, TH, α3-nAChR, and α4-nAChR mRNA levels in the VTA of CB2KO mice were significantly lower compared with WT mice. Confocal microscopy images revealed that CB2r colocalized with α3- and α4-nAChRs. Somatic signs of nicotine withdrawal (rearings, groomings, scratches, teeth chattering, and body tremors) increased significantly in WT but were absent in CB2KO mice. Interestingly, the administration of AM630 blocked the nicotine withdrawal syndrome and failed to alter basal behavior in saline-treated WT mice. These results suggest that CB2r play a relevant role in the rewarding, reinforcing, and motivational effects of nicotine. Pharmacological manipulation of this receptor deserves further consideration as a potential new valuable target for the treatment of nicotine dependence.

Cannabinoid CB2 receptor-mediated regulation of impulsive-like behaviour in DBA/2 mice

BACKGROUND AND PURPOSE This study evaluated gene expression differences between two mouse strains, characterized by opposite impulsivity‐like traits and the involvement of the cannabinoid CB2 receptor in the modulation of impulsivity.

Gene and protein alterations of FKBP5 and glucocorticoid receptor in the amygdala of suicide victims

Recent reports suggest that FKBP5 gene and its corresponding FKBP5 protein play a relevant role in the regulation of anxiety and depression in animal models and human stress-related disorders. In the present study, FKBP5 and glucocorticoid receptor (GR) gene and protein expression were analyzed in the amygdala (AMY) of suicide victims (n=13 males, without clinical psychiatric history and non-treated with anxiolytic or antidepressant drugs) and its corresponding controls (n=13 males) by real-time PCR and Western blotting. The results revealed that FKBP5 and GR gene expression were significantly reduced in the AMY (-38% and -48%, respectively) of suicide victims compared with controls. Interestingly, FKBP5 and GR protein expression were also significantly decreased (-41% and -42%, respectively) in the AMY of suicide victims compared with controls. These results suggest that the FKBP5 plays a relevant role in human emotional responses and suggest this receptor as a new promising target in the treatment of suicide behavior.

Differences in maternal and paternal age between Schizophrenia and other psychiatric disorders

Advanced parental age has been shown to increase offspring risk for a number of neuropsychiatric disorders including schizophrenia and Downs syndrome. Other psychiatric disorders have been less studied with respect to the effect of parental age on offspring risk. In this study we examine if advanced parental age increased risk for ICD-10 diagnoses. We hypothesized that advanced parental age would increase risk for offspring psychotic disorders and mental retardation but not other ICD-10 diagnoses. We examined follow-up data for 30,965 subjects treated in outpatient psychiatric facilities between 1980 and 2007. Subjects were younger than 18 years of age at their first outpatient visit. A comparison group was obtained from data on registered births in Spain from 1975. We compared parental age (maternal, paternal, combined) across diagnostic categories using ANOVA and logistic regression was used to estimate the risk of psychopathology in the offspring with advanced parental age (maternal, paternal, combined). Maternal and paternal ages were higher for subjects diagnosed with mental retardation. Risk for psychotic disorders showed a significant linear increase only with advancing maternal age, and not paternal age as is more often reported.

Overexpression of CB2 cannabinoid receptors results in neuroprotection against behavioral and neurochemical alterations induced by intracaudate administration of 6-hydroxydopamine

The role of CB2 cannabinoid receptors in the behavioral and neurochemical changes induced by intracaudate administration of 6-hydroxydopamine (6-OHDA) was evaluated. 6-OHDA (12 μg/4 μL) or its vehicle was injected in the caudate-putamen (CPu) of mice overexpressing the CB2 cannabinoid receptor (CB2xP) and wild type (WT) mice. Motor impairment, emotional behavior, and cognitive alterations were evaluated. Tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were measured by immunocytochemistry in the CPu and/or substantia nigra (SN) of CB2xP mice and WT mice. Oxidative/nitrosative and neuroinflammatory parameters were also measured in the CPu and cortex of 6-OHDA-treated and sham-treated mice. 6-OHDA-treated CB2xP mice presented significantly less motor deterioration than 6-OHDA-treated WT mice. Immunocytochemical analysis of tyrosine hydroxylase in the SN and CPu revealed significantly fewer lesions in CB2xP mice than in WT mice. GFAP and Iba-1 immunostaining revealed less astrocyte and microglia recruitment to the treated area of the CPu in CB2xP mice. Malonyldialdehyde (MDA) concentrations were lower in the striatum and cerebral cortex of sham-treated CB2xP mice than in sham-treated WT mice. The administration of 6-OHDA increased MDA levels in both WT mice and CB2xP mice; it increased the oxidized (GSSG)/reduced (GSH) glutathione ratio in the striatum in WT mice alone compared with matched sham-treated controls. The results revealed that overexpression of CB2 cannabinoid receptors decreased the extent of motor impairment and dopaminergic neuronal loss, reduced the recruitment of astrocytes and microglia to the lesion, and decreased the level of various oxidative parameters. These results suggest that CB2 receptors offer neuroprotection against dopaminergic injury.

Role of cannabinoid CB2 receptor in the reinforcing actions of ethanol

This study examines the role of the cannabinoid CB2 receptor (CB2r) on the vulnerability to ethanol consumption. The time‐related and dose‐response effects of ethanol on rectal temperature, handling‐induced convulsions (HIC) and blood ethanol concentrations were evaluated in CB2KO and wild‐type (WT) mice. The reinforcing properties of ethanol were evaluated in conditioned place preference (CPP), preference and voluntary ethanol consumption and oral ethanol self‐administration. Water‐maintained behavior schedule was performed to evaluate the degree of motivation induced by a natural stimulus. Preference for non‐alcohol tastants assay was performed to evaluate the differences in taste sensitivity. Tyrosine hydroxylase (TH) and μ‐opioid receptor gene expressions were also measured in the ventral tegmental area and nucleus accumbens (NAcc), respectively. CB2KO mice presented increased HIC score, ethanol‐CPP, voluntary ethanol consumption and preference, acquisition of ethanol self‐administration, and increased motivation to drink ethanol compared with WT mice. No differences were found between genotypes in the water‐maintained behavior schedule or preference for non‐alcohol tastants. Naïve CB2KO mice presented increased μ‐opioid receptor gene expression in NAcc. Acute ethanol administration (1–2 g/kg) increased TH and μ‐opioid receptor gene expressions in CB2KO mice, whereas the lower dose of ethanol decreased TH gene expression in WT mice. These results suggest that deletion of the CB2r gene increased preference for and vulnerability to ethanol consumption, at least in part, by increased ethanol‐induced sensitivity of the TH and μ‐opioid receptor gene expressions in mesolimbic neurons. Future studies will determine the role of CB2r as a target for the treatment of problems related with alcohol consumption.

Social defeat in adolescent mice increases vulnerability to alcohol consumption.

This study employs an oral operant conditioning paradigm to evaluate the effects of repeated social defeat during adolescence on the reinforcing and motivational actions of ethanol in adult OF1 mice. Social interaction, emotional and cognitive behavioral aspects were also analyzed, and real‐time polymerase chain reaction (PCR) experiments were performed to study gene expression changes in the mesocorticolimbic and hypothalamus‐hypophysis‐adrenal (HHA) axis. Social defeat did not alter anxiety‐like behavior in the elevated plus maze or cognitive performance in the passive avoidance and Hebb–Williams tests. A social interaction test revealed depression‐like symptoms and social subordination behavior in defeated OF1 mice. Interestingly, social defeat in adolescence significantly increased the number of effective responses, ethanol consumption values and motivation to drink. Finally, real‐time PCR analyses revealed that social defeat significantly increased tyrosine hydroxylase and corticotropin‐releasing hormone in the ventral tegmental area and paraventricular nucleus, respectively. In contrast, mu‐opioid receptor gene expression was decreased in the nucleus accumbens of socially defeated mice. In summary, these findings suggest that exposure to social defeat during adolescence increases vulnerability to the rewarding effects of ethanol without affecting emotional or cognitive performance. The gene expression alterations we have observed in the mesocorticolimbic and HHA axis systems of defeated mice could be related with their increased ethanol consumption. These results endorse future research into pharmacological strategies that modulate these systems for the treatment of social stress‐related alcohol consumption problems.

Role of the endocannabinoid system in the emotional manifestations of osteoarthritis pain.

Abstract In this study, we investigated the role of the endocannabinoid system (ECS) in the emotional and cognitive alterations associated with osteoarthritis pain. The monosodium iodoacetate model was used to evaluate the affective and cognitive manifestations of osteoarthritis pain in type 1 (CB1R) and type 2 (CB2R) cannabinoid receptor knockout and wild-type mice and the ability of CB1R (ACEA) and CB2R (JWH133) selective agonists to improve these manifestations during a 3-week time period. The levels of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured in plasma and brain areas involved in the control of these manifestations. Patients with knee osteoarthritis and healthy controls were recruited to evaluate pain, affective, and cognitive symptoms, as well as plasma endocannabinoid levels and cannabinoid receptor gene expression in peripheral blood lymphocytes. The affective manifestations of osteoarthritis were enhanced in CB1R knockout mice and absent in CB2R knockouts. Interestingly, both ACEA and JWH133 ameliorated the nociceptive and affective alterations, whereas ACEA also improved the associated memory impairment. An increase of 2-AG levels in prefrontal cortex and plasma was observed in this mouse model of osteoarthritis. In agreement, an increase of 2-AG plasmatic levels and an upregulation of CB1R and CB2R gene expression in peripheral blood lymphocytes were observed in patients with osteoarthritis compared with healthy subjects. Changes found in these biomarkers of the ECS correlated with pain, affective, and cognitive symptoms in these patients. The ECS plays a crucial role in osteoarthritis and represents an interesting pharmacological target and biomarker of this disease.

Increased vulnerability to ethanol consumption in adolescent maternal separated mice.

The purpose of this study was to evaluate the effects of early life stress on the vulnerability to ethanol consumption in adolescence. To this aim, mice were separated from their mothers for 12 hours/day on postnatal days 8 and 12. Emotional behavior (light‐dark box, elevated plus maze and tail suspension tests) and pre‐attentional deficit (pre‐pulse inhibition) were evaluated in adolescent maternal separated (MS) mice. Alterations of the corticotropin‐releasing factor (CRF), glucocorticoid receptor (NR3C1), tyrosine hydroxylase (TH), mu‐opioid receptor (MOr), brain‐derived neurotrophic factor (BDNF), neuronal nuclei (NeuN), microtubule‐associated protein 2 (MAP2) and neurofilament heavy (NF200)‐immunoreactive fibers were studied in the paraventricular nucleus of the hypothalamus (PVN), ventral tegmental area (VTA), nucleus accumbens (NAc) or hippocampus (HIP). The effects of maternal separation (alone or in combination with additional stressful stimuli) on ethanol consumption during adolescence were evaluated using the oral ethanol self‐administration paradigm. MS mice presented mood‐related alterations and pre‐attentional deficit. Increased CRF, MOr and TH, and reduced BDNF, NR3C1, NeuN, MAP2 and NF200‐immunoreactive fibers were observed in the PVN, NAc and HIP of adolescent MS mice. In the oral ethanol self‐administration test, adolescent MS mice presented higher ethanol consumption and motivation. Exposure to additional new stressful stimuli during adolescence significantly increased the vulnerability to ethanol consumption induced by maternal separation. These results clearly demonstrated that exposure to early life stress increased the vulnerability to ethanol consumption, potentiated the effects of stressful stimuli exposure during adolescence on ethanol consumption and modified the expression of key targets involved in the response to stress, ethanol reinforcing properties and cognitive processes.