Clozapine Increases Nestin Concentration in the Adult Male Rat Hippocampus: A Preliminary Study.

Patients with schizophrenia, and rodent models of the disease, both exhibit suppressed neurogenesis, with antipsychotics possibly enhancing neurogenesis in pre-clinical models. Nestin, a cytoskeletal protein, is implicated in neuronal differentiation and adult neurogenesis. We hypothesized that schizophrenia pathogenesis involves nestin downregulation; however, few studies have related nestin to schizophrenia. We assessed nestin protein concentration, prepulse inhibition (PPI), and social interaction in the MK-801 model of schizophrenia, with or without antipsychotic (clozapine) treatment. Adult male Sprague-Dawley rats were intraperitoneally administered saline or MK-801 (0.1 mg/kg) to produce a schizophrenia-like phenotype, with concomitant subcutaneous injections of vehicle or clozapine (5 mg/kg). PPI was assessed on days 1, 8, and 15, and social interaction was assessed on day 4. Hippocampus tissue samples were dissected for Western blotting of nestin concentration. MK-801 alone did not alter nestin concentration, while clozapine alone enhanced hippocampal nestin concentration; this effect was not apparent in animals with MK-801 and clozapine co-administration. MK-801 also produced schizophrenia-like PPI disruptions, some of which were reversed by clozapine. Social interaction deficits were not detected in this model. This is the first report of clozapine-induced enhancements of hippocampal nestin concentration that might be mediated by NMDA receptors. Future studies will explore the impact of neurodevelopmental nestin concentration on symptom onset and antipsychotic treatment.

Place field repetition and spatial learning in a multicompartment environment.

Recent studies have shown that place cells in the hippocampus possess firing fields that repeat in physically similar, parallel environments. These results imply that it should be difficult for animals to distinguish parallel environments at a behavioral level. To test this, we trained rats on a novel odor-location task in an environment with four parallel compartments which had previously been shown to yield place field repetition. A second group of animals was trained on the same task, but with the compartments arranged in different directions, an arrangement we hypothesised would yield less place field repetition. Learning of the odor-location task in the parallel compartments was significantly impaired relative to learning in the radially arranged compartments. Fewer animals acquired the full discrimination in the parallel compartments compared to those trained in the radial compartments, and the former also required many more sessions to reach criterion compared to the latter. To confirm that the arrangement of compartments yielded differences in place cell repetition, in a separate group of animals we recorded from CA1 place cells in both environments. We found that CA1 place cells exhibited repeated fields across four parallel local compartments, but did not do so when the same compartments were arranged radially. To confirm that the differences in place field repetition across the parallel and radial compartments depended on their angular arrangement, and not incidental differences in access to an extra-maze visual landmark, we repeated the recordings in a second set of rats in the absence of the orientation landmark. We found, once again, that place fields showed repetition in parallel compartments, and did not do so in radially arranged compartments. Thus place field repetition, or lack thereof, in these compartments was not dependent on extra-maze cues. Together, these results imply that place field repetition constrains spatial learning.

Therapeutic potential of gamma entrainment using sensory stimulation for cognitive symptoms associated with schizophrenia.

Schizophrenia is a complex neuropsychiatric disorder with significant morbidity. Treatment options that address the spectrum of symptoms are limited, highlighting the need for innovative therapeutic approaches. Gamma Entrainment Using Sensory Stimulation (GENUS) is an emerging treatment for neuropsychiatric disorders that uses sensory stimulation to entrain impaired oscillatory network activity and restore brain function. Aberrant oscillatory activity often underlies the symptoms experienced by patients with schizophrenia. We propose that GENUS has therapeutic potential for schizophrenia. This paper reviews the current status of schizophrenia treatment and explores the use of sensory stimulation as an adjunctive treatment, specifically through gamma entrainment. Impaired gamma frequency entrainment is observed in patients, particularly in response to auditory and visual stimuli. Thus, sensory stimulation, such as music listening, may have therapeutic potential for individuals with schizophrenia. GENUS holds novel therapeutic potential to improve the lives of individuals with schizophrenia, but further research is required to determine the efficacy of GENUS, optimize its delivery and therapeutic window, and develop strategies for its implementation in specific patient populations.

Orally administered Cannabigerol (CBG) in rats: Cannabimimetic actions, anxiety-like behavior, and inflammation-induced pain.

Cannabigerol (CBG) is a phytocannabinoid found in cannabis that is promoted for medical use and other health benefits, but current empirical data on the behavioral effects of CBG are lacking. The purpose of this study was to evaluate the effects of a wide dose range of orally administered CBG on outcomes related to its potential cannabimimetic effects (cannabinoid tetrad), as well as effects on anxiety-like behavior, inflammation and related pain hypersensitivity. In a series of experiments, male and female Sprague Dawley rats received oral CBG (per os [p.o.]) or vehicle prior to testing of effects on 1) the cannabinoid tetrad (30-600 mg/kg, p.o.): assessments of locomotor activity, body temperature, antinociception (tail flick test), and catalepsy (bar test); 2) acoustic startle response (ASR) test of anxiety-like behavior (30-300 mg/kg, p.o.); 3) carrageenan-induced inflammation (paw edema), hyperalgesia (Hargreaves test), and allodynia (von Frey test) tests (10-60 mg/kg, p.o.). Positive control groups were administered THC (0-30 mg/kg, p.o.) for the cannabinoid tetrad assay, the benzodiazepine lorazepam (0-3 mg/kg, intraperitoneal [i.p.]) for the ASR test, or the opioid analgesic morphine (0-10 mg/kg, i.p.) for the carrageenan-induced inflammation and pain hypersensitivity tests. CBG did not produce cannabimimetic actions in the tetrad, but increased locomotor activity at the highest doses (300-600 mg/kg). THC produced typical dose-related cannabimimetic effects. CBG did not produce anxiolytic effects in the ASR test, while groups pretreated with lorazepam showed reductions in ASR. Finally, pretreatment with CBG prior to an intraplantar injection of carrageenan did not prevent the induction of an acute inflammatory state (i.e., increased paw edema and associated hyperalgesia and allodynia). In contrast, morphine alleviated hyperalgesia and allodynia induced by intraplantar carrageenan but did not affect the development of paw edema. In sum, these data do not support the use of oral CBG for anxiety or inflammatory pain.

Evaluating Potential Anxiolytic Effects of Minor Cannabinoids and Terpenes After Acute and Chronic Oral Administration in Rats.

Background: Cannabis and its primary psychoactive constituent delta-9-tetrahydrocannabinol (D9-THC) produce biphasic, dose-dependent effects on anxiety. In addition to D9-THC, cannabis contains other "minor" cannabinoids and terpenes with purported therapeutic potential for the treatment of anxiety. Empirical data on potential therapeutic effects of these compounds is limited. The current study evaluated the effects of selected minor cannabinoids and terpenes in a battery of tests sensitive to anxiolytic and anxiogenic drugs. Methods: In Experiment 1, adult male Sprague Dawley rats (N=7-8/group) were administered acute oral doses of one of five minor cannabinoids: delta-8-tetrahydrocannabinol (D8-THC; 10 mg/kg), tetrahydrocannabivarin (32 mg/kg), cannabidiolic acid (32 mg/kg), cannabidivarin (32 mg/kg), and cannabigerol (100 mg/kg), or one of five terpenes: D-limonene (17 mg/kg), ⍺-pinene (100 mg/kg), ⍺-terpineol (10 mg/kg), bisabolol (100 mg/kg), and ß-caryophyllene (17 mg/kg), or vehicle (medium-chain triglycerides [MCT] oil). Ethyl alcohol was tested as an active comparator. Thirty minutes post-administration, the marble burying test, the three-chamber social interaction test, and the novelty-induced hypophagia test were completed; motor activity was assessed throughout testing. Experiment 2 examined the potential anxiolytic effects of minor cannabinoids when administered chronically; rats administered MCT oil or minor cannabinoids in Experiment 1 continued receiving once-daily doses for 21 days and were assessed using the same test battery after 7, 14, and 21 days of administration. Results and Conclusions: When compared to vehicle, acute administration of bisabolol and D-limonene increased the amount of food consumed and bisabolol-, D-limonene-, ⍺-pinene-, and ß-caryophyllene decreased percent time spent in the outer zone in the novelty-induced hypophagia test, suggestive of an anxiolytic effect. Only ethanol increased social interaction. After acute administration, anxiogenic effects in the marble burying test were observed for D8-THC, but not for other minor cannabinoids and terpenes. Throughout chronic administration, only D8-THC displayed anxiogenic effects in the novelty-induced hypophagia test. The other cannabinoids did not show anxiolytic or anxiogenic effects in any of the tests at the doses or times tested. The minor cannabinoids and terpenes did not impair or stimulate general motor activity. These data provide a foundation for future studies investigating cannabinoid/terpene interactions.

Cannabis Vapor Exposure Alters Neural Circuit Oscillatory Activity in a Neurodevelopmental Model of Schizophrenia: Exploring the Differential Impact of Cannabis Constituents.

Cannabis use is highly prevalent in patients with schizophrenia and worsens the course of the disorder. To understand how exposure to cannabis changes schizophrenia-related oscillatory disruptions, we investigated the impact of administering cannabis vapor containing either Δ9-tetrahydrocannabinol (THC) or balanced THC/cannabidiol (CBD) on oscillatory activity in the neonatal ventral hippocampal lesion (NVHL) rat model of schizophrenia. Male Sprague Dawley rats underwent lesion or sham surgeries on postnatal day 7. In adulthood, electrodes were implanted targeting the cingulate cortex (Cg), the prelimbic cortex (PrLC), the hippocampus (HIP), and the nucleus accumbens (NAc). Local field potential recordings were obtained after rats were administered either the "THC-only" cannabis vapor (8-18% THC/0% CBD) or the "Balanced THC:CBD" cannabis vapor (4-11% THC/8.5-15.5% CBD) in a cross-over design with a 2-week wash-out period between exposures. Compared to controls, NVHL rats had reduced baseline gamma power in the Cg, HIP, and NAc, and reduced HIP-Cg high-gamma coherence. THC-only vapor exposure broadly suppressed oscillatory power and coherence, even beyond the baseline reductions observed in NHVL rats. Balanced THC:CBD vapor, however, did not suppress oscillatory power and coherence, and in some instances enhanced power. For NVHL rats, THC-only vapor normalized the baseline HIP-Cg high-gamma coherence deficits. NHVL rats demonstrated a 20 ms delay in HIP theta to high-gamma phase coupling, which was not apparent in the PrLC and NAc after both exposures. In conclusion, cannabis vapor exposure has varying impacts on oscillatory activity in NVHL rats, and the relative composition of naturally occurring cannabinoids may contribute to this variability.

The Impact of Sex, Circadian Disruption, and the ClockΔ19/Δ19 Genotype on Alcohol Drinking in Mice.

Shift work is associated with increased alcohol drinking, more so in males than females, and is thought to be a coping mechanism for disrupted sleep cycles. However, little is presently known about the causal influence of circadian rhythm disruptions on sex differences in alcohol consumption. In this study, we disrupted circadian rhythms in female and male mice using both environmental (i.e., shifting diurnal cycles) and genetic (i.e., ClockΔ19/Δ19 mutation) manipulations, and measured changes in alcohol consumption and preference using a two-bottle choice paradigm. Alcohol consumption and preference, as well as food and water consumption, total caloric intake, and weight were assessed in adult female and male ClockΔ19/Δ19 mutant mice or wild-type (WT) litter-mates, housed under a 12-hour:12-hour light:dark (L:D) cycle or a shortened 10-hour:10-hour L:D cycle. Female WT mice (under both light cycles) increased their alcohol consumption and preference over time, a pattern not observed in male WT mice. Compared to WT mice, ClockΔ19/Δ19 mice displayed increased alcohol consumption and preference. Sex differences were not apparent in ClockΔ19/Δ19 mice, with or without shifting diurnal cycles. In conclusion, sex differences in alcohol consumption patterns are evident and increase with prolonged access to alcohol. Disrupting circadian rhythms by mutating the Clock gene greatly increases alcohol consumption and abolishes sex differences present in WT animals.

Cannabis Use and Mental Illness: Understanding Circuit Dysfunction Through Preclinical Models.

Patients with a serious mental illness often use cannabis at higher rates than the general population and are also often diagnosed with cannabis use disorder. Clinical studies reveal a strong association between the psychoactive effects of cannabis and the symptoms of serious mental illnesses. Although some studies purport that cannabis may treat mental illnesses, others have highlighted the negative consequences of use for patients with a mental illness and for otherwise healthy users. As epidemiological and clinical studies are unable to directly infer causality or examine neurobiology through circuit manipulation, preclinical animal models remain a valuable resource for examining the causal effects of cannabis. This is especially true considering the diversity of constituents in the cannabis plant contributing to its effects. In this mini-review, we provide an updated perspective on the preclinical evidence of shared neurobiological mechanisms underpinning the dual diagnosis of cannabis use disorder and a serious mental illness. We present studies of cannabinoid exposure in otherwise healthy rodents, as well as rodent models of schizophrenia, depression, and bipolar disorder, and the resulting impact on electrophysiological indices of neural circuit activity. We propose a consolidated neural circuit-based understanding of the preclinical evidence to generate new hypotheses and identify novel therapeutic targets.

Discordant Effects of Cannabinoid 2 Receptor Antagonism/Inverse Agonism During Adolescence on Pavlovian and Instrumental Reward Learning in Adult Male Rats.

The endocannabinoid system is responsible for regulating a spectrum of physiological activities and plays a critical role in the developing brain. During adolescence, the endocannabinoid system is particularly sensitive to external insults that may change the brain's developmental trajectory. Cannabinoid receptor type 2 (CB2R) was initially thought to predominantly function in the peripheral nervous system, but more recent studies have implicated its role in the mesolimbic pathway, a network largely attributed to reward circuitry and reward motivated behavior, which undergoes extensive changes during adolescence. It is therefore important to understand how CB2R modulation during adolescence can impact reward-related behaviors in adulthood. In this study, adolescent male rats (postnatal days 28-41) were exposed to a low or high dose of the CB2R antagonist/inverse agonist SR144528 and Pavlovian autoshaping and instrumental conditional behavioral outcomes were measured in adulthood. SR144528-treated rats had significantly slower acquisition of the autoshaping task, seen by less lever pressing behavior over time [F (2, 19) = 5.964, p = 0.010]. Conversely, there was no effect of adolescent SR144528 exposure on instrumental conditioning. These results suggest that modulation of the CB2R in adolescence differentially impacts reward-learning behaviors in adulthood.

Adolescent neurodevelopment and substance use: Receptor expression and behavioral consequences.

Adolescence is the transitional period between childhood and adulthood, during which extensive brain development occurs. Since this period also overlaps with the initiation of drug use, it is important to consider how substance use during this time might produce long-term neurobiological alterations, especially against the backdrop of developmental changes in neurotransmission. Alcohol, cannabis, nicotine, and opioids all produce marked changes in the expression and function of the neurotransmitter and receptor systems with which they interact. These acute and chronic alterations also contribute to behavioral consequences ranging from increased addiction risk to cognitive or neuropsychiatric behavioral dysfunctions. The current review provides an in-depth overview and update of the developmental changes in neurotransmission during adolescence, as well as the impact of drug exposure during this neurodevelopmental window. While most of these factors have been studied in animal models, which are the focus of this review, future longitudinal studies in humans that assess neural function and behavior will help to confirm pre-clinical findings. Furthermore, the neural changes induced by each drug should also be considered in the context of other contributing factors, such as sex. Further understanding of these consequences can help in the identification of novel approaches for preventing and reversing the neurobiological effects of adolescent substance use.

EXTENDED ATTENUATION OF CORTICOSTRIATAL POWER AND COHERENCE AFTER ACUTE EXPOSURE TO VAPOURIZED Δ9 TETRAHYDROCANNABINOL IN RATS.

INTRODUCTION: Over 14% of Canadians use cannabis, with nearly 60% of these individuals reporting daily or weekly use. Inhalation of cannabis vapour has recently gained popularity, but the effects of this exposure on neural activity remain unknown. In this study, we assessed the impact of acute exposure to vapourized Δ9-tetrahydrocannabinol (THC) on neural circuit dynamics in rats. OBJECTIVES: We aimed to characterize the changes in neural activity in the dorsal striatum (dStr), orbitofrontal cortex (OFC), and prefrontal cortex (PFC), after acute exposure to THC vapour. METHODS: Rats were implanted with electrode arrays targeting the dStr, OFC, and PFC. Rats were administered THC (or vehicle) using a Volcano® vapourizer and local field potential recordings were performed in a plexiglass chamber in a cross-over design with a week-long washout period. RESULTS: Decreased spectral power was observed within the dStr, OFC, and PFC in the gamma range (>32-100 Hz) following vapourized THC administration. Most changes in gamma were still present 7 days after THC administration. Decreased gamma coherence was also observed between the OFC-PFC and dStr-PFC region-pairs. CONCLUSION: A single exposure to vapourized THC suppresses cortical and dorsal striatal gamma power and coherence, effects that appear to last at least a week. Given the role of gamma hypofunction in schizophrenia, these findings may provide mechanistic insights into the known psychotomimetic effects of THC.