Discriminative stimulus properties of Cannabis sativa terpenes in rats.

Cannabis is a pharmacologically complex plant consisting of hundreds of potentially active compounds. One class of compounds present in cannabis that has received little attention are terpenes. Traditionally thought to impart aroma and flavor to cannabis, it has become increasingly recognized that terpenes might exert therapeutic effects themselves. Several recent reports have also indicated terpenes might behave as cannabinoid type 1 (CB1) receptor agonists. This study aimed to investigate whether several terpenes present in cannabis produce discriminative stimulus effects similar to or enhance the effects of Δ 9 -tetrahydrocannabinol (THC). Subsequent experiments explored other potential cannabimimetic effects of these terpenes. Rats were trained to discriminate THC from vehicle while responding under a fixed-ratio 10 schedule of food presentation. Substitution testing was performed with the CB receptor agonist JWH-018 and the terpenes linalool, limonene, γ-terpinene and α-humulene alone. Terpenes were also studied in combination with THC. Finally, THC and terpenes were tested in the tetrad assay to screen for CB1-receptor agonist-like effects. THC and JWH-018 dose-dependently produced responding on the THC-paired lever. When administered alone, none of the terpenes produced responding predominantly on the THC-paired lever. When administered in combination with THC, none of the terpenes enhanced the potency of THC, and in the case of α-humulene, decreased the potency of THC to produce responding on the THC-paired lever. While THC produced effects in all four tetrad components, none of the terpenes produced effects in all four components. Therefore, the terpenes examined in this report do not have effects consistent with CB1 receptor agonist properties in the brain.

Generalization of a positive-feature interoceptive morphine occasion setter across the rat estrous cycle.

INTRODUCTION: Interoceptive stimuli elicited by drug administration acquire conditioned modulatory properties of the induction of conditioned appetitive behaviours by exteroceptive cues. This effect may be modeled using a drug discrimination task in which the drug stimulus is trained as a positive-feature (FP) occasion setter (OS) that disambiguates the relation between an exteroceptive light conditioned stimulus (CS) and a sucrose unconditioned stimulus (US). We previously reported that females are less sensitive to generalization of a FP morphine OS than males, so we investigated the role of endogenous ovarian hormones in this difference. METHODS: Male and female rats received intermixed injections of 3.2 mg/kg morphine or saline before each daily training session. Training consisted of 8 presentations of the CS, each followed by access to sucrose on morphine, but not saline sessions. Following acquisiton, rats were tested for generalization of the morphine stimulus to 0, 1.0, 3.2, and 5.4 mg/kg morphine. Female rats were monitored for estrous cyclicity using vaginal cytology throughout the study. RESULTS: Both sexes acquired stable drug discrimination. A gradient of generalization was measured across morphine doses and this behaviour did not differ by sex, nor did it differ across the estrous cycle in females. CONCLUSIONS: Morphine generalization is independent of fluctuations in levels of sex and endogenous gonadal hormones in females under these experimental conditions.

Nicotinic aspects of the discriminative stimulus effects of arecoline.

Despite the evidence that the muscarinic agonist arecoline is a drug of abuse throughout Southeast Asia, its stimulus characteristics have not been well studied. The goal of this work was to understand more about the mediation of discriminative stimulus effects of arecoline. Arecoline (1.0 mg/kg s.c.) was trained as a discriminative stimulus in a group of eight rats. The ability of various cholinergic agonists and antagonists to mimic or antagonize the discriminative stimulus effects of arecoline and to modify its rate-suppressing effects was evaluated. A muscarinic antagonist, but neither of two nicotinic antagonists, was able to modify the discriminative stimulus effects of arecoline, suggesting a predominant muscarinic basis of arecoline's discriminative stimulus effects in this assay. However, both nicotine itself and two nicotine agonists with selective affinity for the α4ß2* receptor (ispronicline and metanicotine) produced full arecoline-like discriminative stimulus effects in these rats. The discriminative stimulus effects of the selective nicotine agonists were blocked by both the general nicotine antagonist mecamylamine and by the selective α4ß2* antagonist, dihydro-beta-erythroidine (DHßE). Surprisingly, only DHßE antagonized the rate-suppressing effects of the selective nicotine agonists. These data indicate a selective α4ß2* nicotine receptor component to the behavioral effects of arecoline. Although the nicotinic aspects of arecoline's behavior effects could suggest that abuse of arecoline-containing material (e.g. betel nut chewing) is mediated through nicotinic rather than muscarinic actions, further research, specifically on the reinforcing effects of arecoline, is necessary before this conclusion can be supported.

Antinociceptive and Discriminative Stimulus Effects of Six Novel Psychoactive Opioid Substances in Male Rats.

Compounds with novel or fentanyl-like structures continue to appear on the illicit drug market and have been responsible for fatalities, yet there are limited preclinical pharmacological data available to evaluate the risk of these compounds to public health. The purpose of the present study was to examine acetyl fentanyl, butyryl fentanyl, 3,4-dichloro-N-[[1-(dimethylamino)cyclohexyl]methyl]benzamide (AH-7921), 1-cyclohexyl-4-(1,2-diphenylethyl)piperazine (MT-45), 4-chloro-N-[1-(2-phenylethyl)-2-piperidinylidene]-benzenesulfonamide (W-15), and 4-chloro-N-[1-[2-(4-nitrophenyl)ethyl]-2-piperidinylidene]-benzenesulfonamide (W-18) for their relative potency to reference opioids and their susceptibility to naltrexone antagonism using the 55oC warm-water, tail-withdrawal assay of antinociception and a morphine drug discrimination assay in male, Sprague-Dawley rats. In the antinociception assay, groups of 8 rats per drug were placed into restraining tubes, their tails were immersed into 40o or 55oC water, and the latency for tail withdrawal was measured with a cutoff time of 15 seconds. In the drug discrimination assay, rats (n = 11) were trained to discriminate between 3.2 mg/kg morphine and saline, subcutaneously, in a two-choice, drug discrimination procedure under a fixed ratio-5 schedule of sucrose pellet delivery. Morphine, fentanyl, and four of the synthetic opioids dose dependently produced antinociception and fully substituted for morphine in the drug discrimination assay with the following rank order of potency: fentanyl > butyryl fentanyl > acetyl fentanyl > AH-7921 > MT45 > morphine. All drugs that produced antinociception or morphine-like discriminative stimulus effects were blocked by naltrexone. W-15 and W-18 did not show antinociceptive or morphine-like discriminative stimulus effects at the doses tested supporting a lack of opioid activity for these two compounds. These findings suggest that butyryl fentanyl, acetyl fentanyl, AH-7941, and MT-45 have abuse liability like other opioid agonists. SIGNIFICANCE STATEMENT: As novel psychoactive substances appear on the illicit drug market, preclinical pharmacological testing is required to assist law enforcement, medical professionals, and legal regulators with decisions about potential public health risks. In this study, four synthetic opioids, acetyl fentanyl, butyryl fentanyl, AH-7921, and MT-45 produced effects similar to fentanyl and morphine and were blocked by naltrexone. These data suggest the four synthetic opioids possess similar abuse liability risks as typical opioid agonists.

Acute vagus nerve stimulation enhances reversal learning in rats.

Cognitive flexibility is a prefrontal cortex-dependent neurocognitive process that enables behavioral adaptation in response to changes in environmental contingencies. Electrical vagus nerve stimulation (VNS) enhances several forms of learning and neuroplasticity, but its effects on cognitive flexibility have not been evaluated. In the current study, a within-subjects design was used to assess the effects of VNS on performance in a novel visual discrimination reversal learning task conducted in touchscreen operant chambers. The task design enabled simultaneous assessment of acute VNS both on reversal learning and on recall of a well-learned discrimination problem. Acute VNS delivered in conjunction with stimuli presentation during reversal learning reliably enhanced learning of new reward contingencies. Enhancement was not observed, however, if VNS was delivered during the session but was not coincident with presentation of to-be-learned stimuli. In addition, whereas VNS delivered at 30 HZ enhanced performance, the same enhancement was not observed using 10 or 50 Hz. Together, these data show that acute VNS facilitates reversal learning and indicate that the timing and frequency of the VNS are critical for these enhancing effects. In separate rats, administration of the norepinephrine reuptake inhibitor atomoxetine also enhanced reversal learning in the same task, consistent with a noradrenergic mechanism through which VNS enhances cognitive flexibility.

Prolonged Treatment with Centella asiatica Improves Memory, Reduces Amyloid-ß Pathology, and Activates NRF2-Regulated Antioxidant Response Pathway in 5xFAD Mice.

BACKGROUND: The medicinal herb Centella asiatica has been long been used for its neuroprotective and cognitive enhancing effects. We have previously shown that two weeks of treatment with a water extract of Centella asiatica (CAW) improves cognition and activates the endogenous antioxidant response pathway without altering amyloid-ß (Aß) plaque burden. OBJECTIVE: Here, we assess the effect of long-term treatment of CAW in the 5xFAD mouse model of Aß accumulation. METHODS: Four-month-old 5xFAD mice were treated with CAW in their drinking water (2 g/L) for three months at which point they underwent cognitive testing as well as analysis of Aß plaque levels and antioxidant and synaptic gene expression. In order to confirm the involvement of the antioxidant regulatory transcription factor NRF2 on the effects of CAW on synaptic plasticity, neurons isolated from 5xFAD mice were also treated with CAW and the targeted inhibitor ML385. RESULTS: Three months of treatment with CAW improved spatial and contextual memory as well as executive function in 5xFAD mice. This improvement was accompanied by increased antioxidant gene expression and a decrease in Aß plaque burden relative to untreated 5xFAD animals. In isolated neurons, treatment with ML385 blocked the effects of CAW on dendritic arborization and synaptic gene expression. CONCLUSION: These results suggest that prolonged CAW exposure could be beneficial in Alzheimer's disease and that these effects likely involve NRF2 activation. Moreover, these findings suggest that targeting NRF2 itself may be a relevant therapeutic strategy for improving synaptic plasticity and cognitive function in Alzheimer's disease.

Discriminative-Stimulus Effects of Synthetic Cathinones in Squirrel Monkeys.

BACKGROUND: Synthetic cathinones display overlapping behavioral effects with psychostimulants (e.g., methamphetamine [MA]) and/or entactogens (e.g., 3,4-methylenedioxymethaphetamine [MDMA])-presumably reflecting their dopaminergic and/or serotonergic activity. The discriminative stimulus effects of MDMA thought to be mediated by such activity have been well characterized in rodents but have not been fully examined in nonhuman primates. METHODS: The present studies were conducted to systematically evaluate the discriminative stimulus effects of 5 abused synthetic cathinones (methylenedioxypyrovalerone [MDPV], α-pyrrolidinovalerophenone [α-PVP], methcathinone [MCAT], mephedrone, and methylone) in adult male squirrel monkeys trained to distinguish intramuscular injections of MA (0.1 mg/kg; n = 4) or MDMA (0.6 mg/kg; n = 4) from vehicle. RESULTS: Each training drug produced dose-dependent effects and, at the highest dose, full substitution. MDMA produced predominantly vehicle-like responding in the MA-trained group, whereas the highest dose of MA (0.56 mg/kg) produced partial substitution (approximately 90% appropriate lever responding in one-half of the subjects) in the MDMA-trained group. MDPV, α-PVP, and MCAT produced full substitution in MA-trained subjects, but, at the same or higher doses, only substituted for MDMA in one-half of the subjects, consistent with primarily dopaminergically mediated interoceptive effects. In contrast, mephedrone and methylone fully substituted in MDMA-trained subjects but failed to fully substitute for the training drug in MA-trained subjects, suggesting a primary role for serotonergic actions in their interoceptive effects. CONCLUSIONS: These findings suggest that differences in the interoceptive effects of synthetic cathinones in nonhuman primates reflect differing compositions of monoaminergic actions that also may mediate their subjective effects in humans.

Sex differences in the discriminative stimulus characteristics of a morphine occasion setter in rats.

The current study investigated whether the stimulus effects of morphine can function as a positive and negative feature in a Pavlovian occasion setting drug discrimination preparation in male and female rats. Sprague-Dawley rats were assigned to a feature positive (FP) or feature negative (FN) training group and all received intermixed morphine (3.2 mg/kg, IP) or saline injections 15 min before 20-min daily training sessions. For FP rats, on morphine sessions, each of eight 15-s white noise (WN) presentations was followed by 4-s access to sucrose (0.01 ml, 26% w/v); on saline sessions, sucrose was withheld. FN rats learned the reverse contingency. FP discrimination was acquired somewhat sooner than FN discrimination, and females, but not males, became sensitized to the locomotor effects of morphine, which did not influence conditioned responding. Rats then entered dose generalization testing. There was no sex difference in dose generalization for FN groups (ED50 1.26 for males and 1.57 for females). Yet for FP rats, the dose response curve for females was shifted to the right compared to males (ED50 0.54 for males and 1.94 for females). FP females exhibited enhanced responding at a dose higher than that of their original training. These findings reveal the need to reassess our notions of drug stimuli that guide appropriate associative behaviours from the perspective of sex differences.

Differential effects of d- and l-enantiomers of govadine on distinct forms of cognitive flexibility and a comparison with dopaminergic drugs.

RATIONALE: There is an urgent need for novel drugs for treating cognitive deficits that are defining features of schizophrenia. The individual d- and l-enantiomers of the tetrahydroprotoberberine (THPB) d,l-govadine have been proposed for the treatment of cognitive deficiencies and positive symptoms of schizophrenia, respectively. OBJECTIVES: We examined the effects of d-, l-, or d,l-govadine on two distinct forms of cognitive flexibility perturbed in schizophrenia and compared them to those induced by a selective D1 receptor agonist and D2 receptor antagonist. METHODS: Male rats received d-, l-, or d,l-govadine (0.3, 0.5, and 1.0 mg/kg), D1 agonist SKF81297(0.1, 0.3, and 1.0 mg/kg), or D2 antagonist haloperidol (0.1-0.2 mg/kg). Experiment 1 used a strategy set-shifting task (between-subjects). In experiment 2, well-trained rats were tested on a probabilistic reversal task (within-subjects). RESULTS: d-Govadine improved set-shifting across all doses, whereas higher doses of l-govadine impaired set-shifting. SKF81297 reduced perseverative errors at the lowest dose. Low/high doses of haloperidol increased/decreased set-shifting errors, the latter "improvement" attributable to impaired retrieval of a previous acquired rule. Probabilistic reversal performance was less affected by these drugs, but d-govadine reduced errors during the first reversal, whereas l-govadine impaired initial discrimination learning. d,l-Govadine had no reliable cognitive effects but caused psychomotor slowing like l-govadine and haloperidol. CONCLUSIONS: These findings further highlight differences between two enantiomers of d,l-govadine that may reflect differential modulation of D1 and D2 receptors. These preclinical findings give further impetus to formal clinical evaluation of d-govadine as a treatment for cognitive deficiencies related to schizophrenia.

Pharmacological Comparison of Mitragynine and 7-Hydroxymitragynine: In Vitro Affinity and Efficacy for µ-Opioid Receptor and Opioid-Like Behavioral Effects in Rats.

Relationships between µ-opioid receptor (MOR) efficacy and effects of mitragynine and 7-hydroxymitragynine are not fully established. We assessed in vitro binding affinity and efficacy and discriminative stimulus effects together with antinociception in rats. The binding affinities of mitragynine and 7-hydroxymitragynine at MOR (Ki values 77.9 and 709 nM, respectively) were higher than their binding affinities at κ-opioid receptor (KOR) or δ-opioid receptor (DOR). [35S]guanosine 5'-O-[γ-thio]triphosphate stimulation at MOR demonstrated that mitragynine was an antagonist, whereas 7-hydroxymitragynine was a partial agonist (Emax = 41.3%). In separate groups of rats discriminating either morphine (3.2 mg/kg) or mitragynine (32 mg/kg), mitragynine produced a maximum of 72.3% morphine-lever responding, and morphine produced a maximum of 65.4% mitragynine-lever responding. Other MOR agonists produced high percentages of drug-lever responding in the morphine and mitragynine discrimination assays: 7-hydroxymitragynine (99.7% and 98.1%, respectively), fentanyl (99.7% and 80.1%, respectively), buprenorphine (99.8% and 79.4%, respectively), and nalbuphine (99.4% and 98.3%, respectively). In the morphine and mitragynine discrimination assays, the KOR agonist U69,593 produced maximums of 72.3% and 22.3%, respectively, and the DOR agonist SNC 80 produced maximums of 34.3% and 23.0%, respectively. 7-Hydroxymitragynine produced antinociception; mitragynine did not. Naltrexone antagonized all of the effects of morphine and 7-hydroxymitragynine; naltrexone antagonized the discriminative stimulus effects of mitragynine but not its rate-decreasing effects. Mitragynine increased the potency of the morphine discrimination yet decreased morphine antinociception. Here we illustrate striking differences in MOR efficacy, with mitragynine having less than 7-hydroxymitragynine. SIGNIFICANCE STATEMENT: At human µ-opioid receptor (MOR) in vitro, mitragynine has low affinity and is an antagonist, whereas 7-hydroxymitragynine has 9-fold higher affinity than mitragynine and is an MOR partial agonist. In rats, intraperitoneal mitragynine exhibits a complex pharmacology including MOR agonism; 7-hydroxymitragynine has higher MOR potency and efficacy than mitragynine. These results are consistent with 7-hydroxymitragynine being a highly selective MOR agonist and with mitragynine having a complex pharmacology that combines low efficacy MOR agonism with activity at nonopioid receptors.

Phencyclidine-induced cognitive impairments in repeated touchscreen visual reversal learning tests in rats.

Reversal learning, a component of executive functioning, is commonly impaired among schizophrenia patients and is lacking effective treatment. N-methyl-ᴅ-aspartate (NMDA) receptor antagonists, such as phencyclidine (PCP), impair reversal learning of rodents. Touchscreen-based pairwise visual discrimination and reversal test is a translational tool to assess reversal learning in rodents. However, to fully exploit this task in testing of novel compounds, it is necessary to perform several reversal learning experiments with trained animals. Firstly, we assessed whether PCP-induced deficits in visual reversal learning in rats would be detectable with a short (5 sessions) reversal learning phase, and whether the short reversal phases could be repeated with novel stimulus pairs. Secondly, we assessed whether the PCP-induced deficits in reversal learning could be seen upon repeated PCP challenges with the same animals. Finally, we tested the effect of a novel compound, a selective α2C adrenoceptor antagonist, ORM-13070, to reverse PCP-induced cognitive deficits in this model. A 4-day PCP treatment at a dose of 1.5 mg/kg/day impaired early reversal learning in male Lister Hooded rats without inducing non-specific behavioral effects. We repeated the reversal learning experiment four times using different stimulus pairs with the same animals, and the PCP-induced impairment was evident in every single experiment. The α2C adrenoceptor antagonist ameliorated the PCP-induced cognitive deficits. Our results suggest that repeated PCP challenges in the touchscreen set-up induce schizophrenia-like cognitive deficits in visual reversal learning, improve throughput of the test and provide a protocol for testing novel drugs.

Serotonergic Innervations of the Orbitofrontal and Medial-prefrontal Cortices are Differentially Involved in Visual Discrimination and Reversal Learning in Rats.

Cross-species studies have identified an evolutionarily conserved role for serotonin in flexible behavior including reversal learning. The aim of the current study was to investigate the contribution of serotonin within the orbitofrontal cortex (OFC) and medial prefrontal cortex (mPFC) to visual discrimination and reversal learning. Male Lister Hooded rats were trained to discriminate between a rewarded (A+) and a nonrewarded (B-) visual stimulus to receive sucrose rewards in touchscreen operant chambers. Serotonin was depleted using surgical infusions of 5,7-dihydroxytryptamine (5,7-DHT), either globally by intracebroventricular (i.c.v.) infusions or locally by microinfusions into the OFC or mPFC. Rats that received i.c.v. infusions of 5,7-DHT before initial training were significantly impaired during both visual discrimination and subsequent reversal learning during which the stimulus-reward contingencies were changed (A- vs. B+). Local serotonin depletion from the OFC impaired reversal learning without affecting initial discrimination. After mPFC depletion, rats were unimpaired during reversal learning but slower to respond at the stimuli during all the stages; the mPFC group was also slower to learn during discrimination than the OFC group. These findings extend our understanding of serotonin in cognitive flexibility by revealing differential effects within two subregions of the prefrontal cortex in visual discrimination and reversal learning.

Central CRF and acute stress differentially modulate probabilistic reversal learning in male and female rats.

Acute stress can have variable and sometimes sex-dependent effects on different executive functions, including cognitive flexibility, some of which may be mediated by increased corticotropin releasing factor (CRF). Previous studies on the effects of stress and CRF on cognitive flexibility have used procedures entailing deterministic rewards, yet how they may alter behavior when outcomes are probabilistic is unclear. The present study examined how acute stress and increased CRF activity alters probabilistic reversal learning (PRL) in male and female rats. Rats learned to discriminate between a 'correct' lever rewarded on 80 % of trials, and an "incorrect" lever delivering reward on 20 % of trials, with reward contingencies reversed after 8 consecutive correct choices. Separate groups received either intracerebroventricular infusions of CRF (3 µg) or restraint stress prior to a PRL session. Experiments examined how these manipulations affected learning when given prior to a one-day acquisition test or during performance in well-trained rats. Exogenous CRF, and to a lesser extent acute stress, impaired motivation across sexes, slowing deliberation times and increasing the number of trials omitted, particularly following a switch in reward contingencies. Neither manipulation significantly altered errors or reversal performance. However, increased CRF activity reduced negative feedback sensitivity. Across manipulations, females showed increased omissions and choice latencies, and were less sensitive to feedback than males. These results reveal the complexity with which stress, CRF, sex, and experience interact to alter aspects of motivation and probabilistic reinforcement learning and provide insight into how CRF activity may contribute to symptoms of stress-related disorders.

Intranasal Insulin Enhances Intracerebroventricular Streptozotocin-Induced Decrease in Olfactory Discriminative Learning via Upregulation of Subventricular Zone-Olfactory Bulb Neurogenesis in the Rat Model.

Olfactory perception and learning play a vital role in the animal's entire life for habituation and survival. Insulin and insulin receptor signaling is well known to modulate the olfactory function and is also involved in the regulation of neurogenesis. A very high density of insulin receptors is present in the olfactory bulb (OB), the brain area involved in the olfactory function, where active adult neurogenesis also takes place. Hence, our study was aimed to explore the effect of intranasal insulin treatment and the involvement of the subventricular zone-olfactory bulb (SVZ-OB) neurogenesis on olfactory discriminative learning and memory in intracerebroventricular streptozotocin (ICV STZ) rat model. Our findings revealed that intranasal insulin treatment significantly increased ICV STZ-induced decrease in the olfactory discriminative learning. No significant change was observed in the post-treatment olfactory memory upon ICV STZ and intranasal insulin treatment. ICV STZ also caused a substantial decline in the SVZ-OB neurogenesis, as indicated by the reduction in the number of 5-bromo-2'-deoxyuridine (BrdU+) cells, BrdU+ Nestin+ cells, and Doublecortin (DCX+) cells, which was reversed by intranasal insulin treatment. Intranasal insulin treatment also increased the number of immature neurons reaching the olfactory bulb (OB) as indicated by an increase in the DCX expression in the OB as compared to the ICV STZ administered group. ICV STZ administration also resulted in the modulation of the expression of the genes regulating postnatal SVZ-OB neurogenesis like Mammalian achaete scute homolog 1 (Mash 1), Neurogenin 2 (Ngn 2), Neuronal differentiation 1 (Neuro D1), and T box brain protein 2 (Tbr 2). Intranasal insulin treatment reverted these changes in gene expression, which might be responsible for the observed increase in the SVZ-OB neurogenesis and hence the olfactory discriminative learning.

Chemogenetics Reveal an Anterior Cingulate-Thalamic Pathway for Attending to Task-Relevant Information.

In a changing environment, organisms need to decide when to select items that resemble previously rewarded stimuli and when it is best to switch to other stimulus types. Here, we used chemogenetic techniques to provide causal evidence that activity in the rodent anterior cingulate cortex and its efferents to the anterior thalamic nuclei modulate the ability to attend to reliable predictors of important outcomes. Rats completed an attentional set-shifting paradigm that first measures the ability to master serial discriminations involving a constant stimulus dimension that reliably predicts reinforcement (intradimensional-shift), followed by the ability to shift attention to a previously irrelevant class of stimuli when reinforcement contingencies change (extradimensional-shift). Chemogenetic disruption of the anterior cingulate cortex (Experiment 1) as well as selective disruption of anterior cingulate efferents to the anterior thalamic nuclei (Experiment 2) impaired intradimensional learning but facilitated 2 sets of extradimensional-shifts. This pattern of results signals the loss of a corticothalamic system for cognitive control that preferentially processes stimuli resembling those previously associated with reward. Previous studies highlight a separate medial prefrontal system that promotes the converse pattern, that is, switching to hitherto inconsistent predictors of reward when contingencies change. Competition between these 2 systems regulates cognitive flexibility and choice.

Behavioral effects of four novel synthetic cathinone analogs in rodents.

A new generation of novel cathinone compounds has been developed as stimulant substitutes to avoid drug control laws and detection of use by blood tests. Dipentylone, N-ethylhexedrone, 4-chloroethcathinone (4-CEC), and 4'-methyl-α-pyrrolidinohexiophenone (MPHP) were tested for in vivo psychostimulant-like effects to assess their abuse liability. Locomotor activity was assessed in an open-field assay using Swiss-Webster mice to screen for locomotor stimulant effects and to identify behaviorally-active dose ranges, times of peak effect, and durations of action. Discriminative stimulus effects were assessed in separate groups of Sprague-Dawley rats trained to discriminate cocaine or methamphetamine from vehicle. Dipentylone, N-ethylhexedrone, 4-CEC, and MPHP dose-dependently increased locomotor activity. Dipentylone, N-ethylhexedrone, and MPHP produced maximal stimulant effects similar to cocaine and methamphetamine. 4-CEC was less efficacious, producing peak stimulant effects of about 74% of that of methamphetamine. The compounds were less potent than methamphetamine and approximately equipotent with cocaine. The doses of cocaine, methamphetamine, dipentylone, and 4-CEC that produced peak effects lasted 2 to 3 h, the peak dose of N-ethylhexedrone lasted 4 h, and the peak dose of MPHP lasted 6 h. All four compounds fully substituted for the discriminative stimulus effects of methamphetamine and cocaine, although full substitution by 4-CEC occurred at doses that substantially decreased response rate. Only 4-CEC fully substituted for MDMA. These data provide evidence that the novel cathinone compounds dipentylone, N-ethylhexedrone, 4-CEC, and MPHP demonstrate potential for abuse as psychostimulants, given their ability to stimulate locomotor activity and their substitution for the discriminative stimulus effects of methamphetamine and cocaine.

Low-dose alcohol: Interoceptive and molecular effects and the role of dentate gyrus in rats.

Alcohol abuse and dependence are world-wide health problems. Most research on alcohol use focuses on the consequences of moderate to high levels of alcohol. However, even at low concentrations, alcohol is capable of producing effects in the brain that can ultimately affect behavior. The current studies seek to understand the effects of low-dose alcohol (blood alcohol levels of ≤10mM). To do so, these experiments utilize a combination of behavioral and molecular techniques to (1) assess the ability of the interoceptive effects of a low dose of alcohol to gain control over goal-tracking behavior in a Pavlovian discrimination task, (2) determine brain regional differences in cellular activity via expression of immediate early genes (IEGs), and (3) assess the role of the dentate gyrus in modulating sensitivity to the interoceptive effects of a low dose of alcohol. Here, we show that intragastric administration of a dose of 0.8 g/kg alcohol produces blood alcohol levels ≤10mM in both male and female Long-Evans rats and can readily be trained as a Pavlovian interoceptive drug cue. In rats trained on this procedure, this dose of alcohol also modulates expression of the IEGs c-Fos and Arc in brain regions known to modulate expression of alcohol interoceptive effects. Finally, pharmacological inactivation of the dentate gyrus with GABA agonists baclofen and muscimol disrupted the ability of a low dose of alcohol to serve as an interoceptive cue. Together, these findings demonstrate behavioral and molecular consequences of low-dose alcohol.

Hesperidin protects against behavioral alterations and loss of dopaminergic neurons in 6-OHDA-lesioned mice: the role of mitochondrial dysfunction and apoptosis.

Hesperidin is a flavonoid glycoside that is frequently found in citrus fruits. Our group have demonstrated that hesperidin has neuroprotective effect in 6-hydroxydopamine (6-OHDA) model of Parkinson's disease (PD), mainly by antioxidant mechanisms. Although the pathophysiology of PD remains uncertain, a large body of evidence has demonstrated that mitochondrial dysfunction and apoptosis play a critical role in dopaminergic nigrostriatal degeneration. However, the ability of hesperidin in modulating these mechanisms has not yet been investigated. In the present study, we examined the potential of a 28-day hesperidin treatment (50 mg/kg/day, p.o.) in preventing behavioral alterations induced by 6-OHDA injection via regulating mitochondrial dysfunction, apoptosis and dopaminergic neurons in the substantia nigra pars compacta (SNpc) in C57BL/6 mice. Our results demonstrated that hesperidin treatment improved motor, olfactory and spatial memory impairments elicited by 6-OHDA injection. Moreover, hesperidin treatment attenuated the loss of dopaminergic neurons (TH+ cells) in the SNpc and the depletion of dopamine (DA) and its metabolities 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum of 6-OHDA-lesioned mice. Hesperidin also protected against the inhibition of mitochondrial respiratory chain complex-I, -IV and V, the decrease of Na + -K + -ATPase activity and the increase of caspase-3 and -9 activity in the striatum. Taken together, our findings indicate that hesperidin mitigates the degeneration of dopaminergic neurons in the SNpc by preventing mitochondrial dysfunction and modulating apoptotic pathways in the striatum of 6-OHDA-treated mice, thus improving behavioral alterations. These results provide new insights on neuroprotective mechanisms of hesperidin in a relevant preclinical model of PD.

Sex, species and age: Effects of rodent demographics on the pharmacology of ∆9-tetrahydrocanabinol.

Cannabis edibles are becoming more common in an increasingly diverse population of users, and the impact of first pass metabolism on cannabis's pharmacological profile across age and sex is not well understood. The present study examined the impact of age, sex and rodent species on the effects of intraperitoneal (i.p.) delta-9-tetrahydrocannabinol (THC) and its primary psychoactive metabolite, 11-OH-THC, in rodent models of psychoactivity and molecular assays of cannabinoid receptor type-1 (CB1) pharmacology. Like oral THC, i.p. THC also undergoes first pass metabolism. In both species and sexes, 11-OH-THC exhibited marginally higher affinity (~1.5 fold) than THC and both served as partial agonists in [35S]GTPγS binding with equivalent potency; 11-OH-THC exhibited slightly greater efficacy in rat brain tissue. In ICR mice, 11-OH-THC exhibited greater potency than THC in assays of catalepsy (7- to 15-fold) and hypothermia (7- to 31-fold). Further, 11-OH-THC was more potent in THC drug discrimination (7- to 9-fold) in C57Bl/6 J mice, with THC-like discriminative stimulus effects being CB1-, but not CB2-, mediated. THC's discriminative stimulus also was stable across age in mice, as its potency did not change over the course of the experiment (~17 months). While sex differences in THC's effects were not revealed in mice, THC was significantly more potent in females Sprague-Dawley rats than in males trained to discriminate THC from vehicle. This study demonstrates a cross-species in the psychoactive effects of i.p. THC across sex that may be related to differential metabolism of THC into its psychoactive metabolite 11-OH-THC, suggesting that species is a crucial design consideration in the preclinical study of phytocannabinoids.

THC and CBD produce divergent effects on perception and panic behaviours via distinct cortical molecular pathways.

Clinical and pre-clinical evidence demonstrates divergent psychotropic effects of THC vs. CBD. While THC can induce perceptual distortions and anxiogenic effects, CBD displays antipsychotic and anxiolytic properties. A key brain region responsible for regulation of cognition and affect, the medial prefrontal cortex (PFC), is strongly modulated by cannabinoids, suggesting that these dissociable THC/CBD-dependent effects may involve functional and molecular interplay within the PFC. The primary aim of this study was to investigate potential interactions and molecular substrates involved in PFC-mediated effects of THC and CBD on differential cognitive and affective behavioural processing. Male Sprague Dawley rats received intra-PFC microinfusions of THC, CBD or their combination, and tested in the latent inhibition paradigm, spontaneous oddity discrimination test, elevated T-maze and open field. To identify local, drug-induced molecular modulation in the PFC, PFC samples were collected and processed with Western Blotting. Intra-PFC THC induced strong panic-like responses that were counteracted with CBD. In contrast, CBD did not affect panic-like behaviours but blocked formation of associative fear memories and impaired latent inhibition and oddity discrimination performance. Interestingly, these CBD effects were dependent upon 5-HT1A receptor transmission but not influenced by THC co-administration. Moreover, THC induced robust phosphorylation of ERK1/2 that was prevented by CBD, while CBD decreased phosphorylation of p70S6K, independently of THC. These results suggest that intra-PFC infusion of THC promotes panic-like behaviour associated with increased ERK1/2 phosphorylation. In contrast, CBD impairs perceptive functions and latent inhibition via activation of 5-HT1A receptors and reduced phosphorylation of p70S6K.