BACKGROUND: Hexahydrocannabinol (HHC) is a new psychoactive substance known for its mind-altering effects and temporary legal status. It is widely used in parts of the Europe and United Kingdom as a legal alternative to ∆9-tetrahydrocannabinol, yet little research has explored its effects and safety. This study examined how HHC is processed in the body, its toxicity, and its impact on behavior in male Wistar rats. METHODS: A 1:1 mixture of (9R)-HHC and (9S)-HHC was administered via intragastric gavage at doses of 1, 5, and 10 mg/kg. Behavioral effects were assessed using the open field test and the prepulse inhibition of acoustic startle response. RESULTS: Two hours after the highest dose (10 mg/kg), peak concentrations of HHC were detected in blood and brain tissue. The Organization for Economic Co-operation and Development 423 toxicity test classified HHC as a Category 4 substance, estimating a lethal dose of 1000 mg/kg. Compared to controls (administered by sunflower oil), 10 mg/kg HHC reduced movement, increased anxiety, and impaired sensory processing. CONCLUSIONS: Overall, HHC crosses the blood-brain barrier, exhibits mild toxicity, and induces behavioral effects similar to tetrahydrocannabinol. Its dose-dependent anxiogenic properties and impact on information processing highlight the importance of the appropriate dosing in any potential therapeutic use.

• Keywords
• acute toxicity, behavior, hexahydrocannabinol, pharmacokinetics, rat,
• Publication type
• Journal Article MeSH

BACKGROUND: Elevated brain levels of kynurenic acid (KYNA), a metabolite in the kynurenine pathway, are associated with cognitive dysfunctions, which are nowadays often considered as fundamental characteristics of several psychopathologies; however, the role of KYNA in mental illnesses, such as schizophrenia, is not fully elucidated. This study aimed to assess KYNA levels in the prefrontal cortex (PFC) of rats prenatally treated with methylazoxymethanol (MAM) acetate, i.e., a well-validated neurodevelopmental animal model of schizophrenia. The effects of an early pharmacological modulation of the endogenous cannabinoid system were also evaluated. METHODS: Pregnant Sprague-Dawley rats were treated with MAM (22 mg/kg, ip) or its vehicle at gestational day 17. Male offspring were treated with the cannabinoid CB1 receptor antagonist/inverse agonist AM251 (0.5 mg/kg/day, ip) or with the typical antipsychotic haloperidol (0.6 mg/kg/day, ip) from postnatal day (PND) 19 to PND39. The locomotor activity and cognitive performance were assessed in the novel object recognition test and the open field test in adulthood. KYNA levels in the PFC of prenatally MAM-treated rats were also assessed. RESULTS: A significant cognitive impairment was observed in prenatally MAM-treated rats (p < 0.01), which was associated with enhanced PFC KYNA levels (p < 0.05). The peripubertal AM251, but not haloperidol, treatment ameliorated the cognitive deficit (p < 0.05), by normalizing the PFC KYNA content in MAM rats. CONCLUSIONS: The present findings suggest that the cognitive deficit observed in MAM rats may be related to enhanced PFC KYNA levels which could be, in turn, mediated by the activation of cannabinoid CB1 receptor. These results further support the modulation of brain KYNA levels as a potential therapeutic strategy to ameliorate the cognitive dysfunctions in schizophrenia.

• Keywords
• AM251, Haloperidol, Kynurenine Pathway, Novel object recognition test, Peripubertal treatment, Schizophrenia,
• MeSH
• Antipsychotic Agents pharmacology   MeSH
• Haloperidol pharmacology   MeSH
• Cognitive Dysfunction metabolism   drug therapy   MeSH
• Rats MeSH
• Kynurenic Acid * metabolism   MeSH
• Methylazoxymethanol Acetate * analogs & derivatives   MeSH
• Disease Models, Animal MeSH
• Piperidines pharmacology   MeSH
• Rats, Sprague-Dawley * MeSH
• Prefrontal Cortex * metabolism   drug effects   MeSH
• Pyrazoles pharmacology   MeSH
• Receptor, Cannabinoid, CB1 metabolism   MeSH
• Schizophrenia * metabolism   drug therapy   MeSH
• Pregnancy MeSH
• Prenatal Exposure Delayed Effects * metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Pregnancy MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AM 251 MeSH Browser
• Antipsychotic Agents MeSH
• Haloperidol MeSH
• Kynurenic Acid * MeSH
• Methylazoxymethanol Acetate * MeSH
• Piperidines MeSH
• Pyrazoles MeSH
• Receptor, Cannabinoid, CB1 MeSH

Adolescent exposure to cannabinoids as a postnatal environmental insult may increase the risk of psychosis in subjects exposed to perinatal insult, as suggested by the two-hit hypothesis of schizophrenia. Here, we hypothesized that peripubertal Δ9-tetrahydrocannabinol (aTHC) may affect the impact of prenatal methylazoxymethanol acetate (MAM) or perinatal THC (pTHC) exposure in adult rats. We found that MAM and pTHC-exposed rats, when compared to the control group (CNT), were characterized by adult phenotype relevant to schizophrenia, including social withdrawal and cognitive impairment, as revealed by social interaction test and novel object recognition test, respectively. At the molecular level, we observed an increase in cannabinoid CB1 receptor (Cnr1) and/or dopamine D2/D3 receptor (Drd2, Drd3) gene expression in the prefrontal cortex of adult MAM or pTHC-exposed rats, which we attributed to changes in DNA methylation at key regulatory gene regions. Interestingly, aTHC treatment significantly impaired social behavior, but not cognitive performance in CNT groups. In pTHC rats, aTHC did not exacerbate the altered phenotype nor dopaminergic signaling, while it reversed cognitive deficit in MAM rats by modulating Drd2 and Drd3 gene expression. In conclusion, our results suggest that the effects of peripubertal THC exposure may depend on individual differences related to dopaminergic neurotransmission.

• Keywords
• dopamine D2/D3 receptors, methylazoxymethanol acetate, psychopathology, Δ9-tetrahydrocannabinol,
• MeSH
• Dopamine metabolism   MeSH
• Rats MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Prefrontal Cortex drug effects   metabolism   MeSH
• Receptors, Dopamine D3 metabolism   MeSH
• Schizophrenia * chemically induced   MeSH
• Pregnancy MeSH
• Dronabinol * toxicity   MeSH
• Prenatal Exposure Delayed Effects * metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Pregnancy MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Dopamine MeSH
• Receptors, Dopamine D3 MeSH
• Dronabinol * MeSH

In agreement with the neurodevelopmental hypothesis of schizophrenia, prenatal exposure of Sprague-Dawley rats to the antimitotic agent methylazoxymethanol acetate (MAM) at gestational day 17 produces long-lasting behavioral alterations such as social withdrawal and cognitive impairment in adulthood, mimicking a schizophrenia-like phenotype. These abnormalities were preceded at neonatal age both by the delayed appearance of neonatal reflexes, an index of impaired brain maturation, and by higher 2-arachidonoylglycerol (2-AG) brain levels. Schizophrenia-like deficits were reversed by early treatment [from postnatal day (PND) 2 to PND 8] with the CB1 antagonist/inverse agonist AM251 (0.5 mg/kg/day). By contrast, early CB1 blockade affected the behavioral performance of control rats which was paralleled by enhanced 2-AG content in the prefrontal cortex (PFC). These results suggest that prenatal MAM insult leads to premorbid anomalies at neonatal age via altered tone of the endocannabinoid system, which may be considered as an early marker preceding the development of schizophrenia-like alterations in adulthood.

• Keywords
• 2-arachidonoylglycerol (2-AG), AM251, MAM model, cannabinoid CB1 receptor, endocannabinoid system, schizophrenia,
• MeSH
• Rats MeSH
• Methylazoxymethanol Acetate * MeSH
• Disease Models, Animal MeSH
• Rats, Sprague-Dawley MeSH
• Receptor, Cannabinoid, CB1 MeSH
• Schizophrenia * chemically induced   drug therapy   genetics   MeSH
• Pregnancy MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Pregnancy MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Methylazoxymethanol Acetate * MeSH
• Receptor, Cannabinoid, CB1 MeSH

Clinical studies consistently report structural impairments (i.e.: ventricular enlargement, decreased volume of anterior cingulate cortex or hippocampus) and functional abnormalities including changes in regional cerebral blood flow in individuals suffering from schizophrenia, which can be evaluated by magnetic resonance imaging (MRI) techniques. The aim of this study was to assess cerebral blood perfusion in several schizophrenia-related brain regions using Arterial Spin Labelling MRI (ASL MRI, 9.4 T Bruker BioSpec 94/30USR scanner) in rats. In this study, prenatal exposure to methylazoxymethanol acetate (MAM, 22 mg/kg) at gestational day (GD) 17 and the perinatal treatment with Δ-9-tetrahydrocannabinol (THC, 5 mg/kg) from GD15 to postnatal day 9 elicited behavioral deficits consistent with schizophrenia-like phenotype, which is in agreement with the neurodevelopmental hypothesis of schizophrenia. In MAM exposed rats a significant enlargement of lateral ventricles and perfusion changes (i.e.: increased blood perfusion in the circle of Willis and sensorimotor cortex and decreased perfusion in hippocampus) were detected. On the other hand, the THC perinatally exposed rats did not show differences in the cerebral blood perfusion in any region of interest. These results suggest that although both pre/perinatal insults showed some of the schizophrenia-like deficits, these are not strictly related to distinct hemodynamic features.

• MeSH
• Circle of Willis diagnostic imaging   drug effects   embryology   MeSH
• Hippocampus blood supply   diagnostic imaging   drug effects   embryology   MeSH
• Rats MeSH
• Humans MeSH
• Magnetic Resonance Angiography methods   MeSH
• Methylazoxymethanol Acetate toxicity   MeSH
• Disease Models, Animal MeSH
• Cerebrovascular Circulation drug effects   MeSH
• Neurogenesis drug effects   MeSH
• Schizophrenia chemically induced   diagnosis   MeSH
• Sensorimotor Cortex blood supply   diagnostic imaging   drug effects   embryology   MeSH
• Behavior Observation Techniques MeSH
• Pregnancy MeSH
• Dronabinol toxicity   MeSH
• Prenatal Exposure Delayed Effects chemically induced   diagnostic imaging   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Male MeSH
• Pregnancy MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Methylazoxymethanol Acetate MeSH
• Dronabinol MeSH