Effects of chronic nicotine exposure on Δ9-tetrahydrocannabinol-induced locomotor activity and neural activation in male and female adolescent and adult rats.

RATIONALE: High rates of comorbid tobacco and cannabis use in adolescents and young adults may be related to functional interactions between the nicotinic cholinergic and cannabinoid systems in the brain during development. This study examined the effects of chronic exposure to nicotine (the psychoactive component in tobacco) on acute exposure to delta-9-tetrahydrocannabinol (THC) (the psychoactive component of cannabis). METHODS: Male and female adolescent and adult Sprague-Dawley rats (N = 112) were injected daily with nicotine (1 mg/kg, i.p.) or vehicle for 14 days, followed by a 14-day drug-free period. On test day, rats were injected with THC (5 mg/kg, i.p.) or vehicle, locomotor activity was recorded for 2 h, and brains harvested for c-Fos immunoreactivity (IR). RESULTS: Locomotor activity and c-Fos IR changes induced by THC challenge were altered by nicotine pre-exposure and modified by age and sex. THC-induced suppression of locomotor activity was attenuated by nicotine pre-exposure in adult but not adolescent males. THC-induced suppression of locomotor activity was potentiated by nicotine pre-exposure in female adolescents, with no effects of THC or nicotine observed in female adults. THC increased c-Fos IR in the caudate, nucleus accumbens, stria terminalis, septum, amygdala, hypothalamus, and thalamus. Nicotine pre-exposure potentiated this effect in all regions. Several brain regions showed age and sex differences in c-Fos IR such that expression was greater in adults than adolescents and in females than males. CONCLUSIONS: Chronic nicotine pre-exposure produces lasting effects on cannabinoid-mediated signalling in the brain and on behaviour that are mediated by age and sex. FUNDING SUPPORT: NSERC.

Increased plasma d-lactic acid associated with impaired memory in rats.

AIM: d-Lactic acidosis is associated with memory impairment in humans. Recent research indicates that d-lactic acid may inhibit the supply of energy from astrocytes to neurons involved with memory formation. However, little is known about the effects of increased hind-gut fermentation due to changes in diet on circulating lactic acid concentrations and memory. METHOD: Thirty-six male Wistar rats were fed three dietary treatments: a commercial rat and mouse chow, a soluble carbohydrate based diet or a fermentable carbohydrate based diet. The parameters estimating memory were examined by employing the object recognition test. Physical parameters of fermentation including hind-gut and plasma lactic acid concentrations were examined after sacrifice, either 3 or 21h after feeding. RESULTS: Increased fermentation in the hind-gut of rats, indicated by lower caecum pH, was associated with increased plasma l-lactic acid (r=-0.41, p=0.020) and d-lactic acid (r=-0.33, p=0.087). Memory, being able to discriminate between a familiar and a novel object during the object recognition test, was reduced with increasing plasma d-lactic acid (r=-0.51, p=0.021). CONCLUSIONS: Memory impairment was associated with alterations in plasma d-lactic acid following the fermentation of carbohydrate in the hind-gut. Further work is still required to determine whether these effects are mediated centrally or via direct connections through the enteric nervous system.

Regional distribution of Ginkgo biloba-induced c-Fos immunoreactivity.

A growing literature supports the notion that Ginkgo biloba has cognitive enhancing and anxiolytic properties; however, its effects on neuronal populations have yet to be characterized. The present study used c-Fos immunoreactivity (Fos-IR) to characterize functional activity in selected brain regions following administration of a standardized Ginkgo biloba extract. Because Ginkgo is typically consumed orally, Exp 1 sought to identify patterns of neural activity induced by oral administration. To ensure that the alterations in functional neural activity observed in Exp 1 were not simply due to novel gustatory experience, Exp 2 characterized patterns of Fos-IR following intraperitoneal administration of Ginkgo. Rats were habituated to handling and experimental conditions. In Exp 1, rats self-administered 150 mg/kg Ginkgo or vehicle alone (strawberry jam) orally. In Exp 2, rats were injected with Ginkgo (2.5 or 25 mg/kg, i.p.) or vehicle (0.3% gum Arabic). Animals were anaesthetized and perfused transcardially. Brains were sectioned, immunostained using a c-Fos antibody, then the number of labelled cells was quantified microscopically in selected brain regions. In both experiments Ginkgo increased Fos-IR in numerous brain regions including the insular cortex and amygdala. Intraperitoneal administration induced Fos-IR in some additional regions including the nucleus accumbens and dentate gyrus. Results provide important preliminary data serving to identify several candidate neural sites involved in the cognitive enhancing and anxiolytic effects of Ginkgo biloba.

Repeated exposure to Delta(9)-tetrahydrocannabinol alters heroin-induced locomotor sensitisation and Fos-immunoreactivity.

The present study examined the effect of chronic exposure to Delta(9)-tetrahydrocannabinol (THC) on heroin-induced locomotor sensitisation and Fos-immunoreactivity (Fos-IR). Adult male albino Wistar rats (n=60) were injected intraperitoneally (i.p.) 21 times with vehicle, 0.05, 0.5, or 5.0mg/kg THC (once every 48 h for 41 days). Locomotor activity was assessed for 180 min on pre-exposure days 1, 21, and 41. Following a 2-week washout period, rats were divided into five equal groups (n=12) and injected subcutaneously (s.c.) with vehicle or heroin (0.5mg/kg). Locomotor activity was recorded for 240 min. In drug-naïve rats, heroin significantly increased locomotor activity. THC pre-exposure further increased heroin-induced locomotion. After an interval of 2 weeks, rats pre-exposed to vehicle and 5.0mg/kg THC in the first part of the experiment were randomly assigned to one of four treatment groups (n=6) and injected s.c. with vehicle or 0.5mg/kg heroin and perfused 2h later. Fos-IR was examined in several brain regions. Acute heroin increased Fos-IR in drug-naïve rats in the caudate-putamen (CPu; central, medial and dorsomedial regions), nucleus accumbens (NAC; core and shell regions), bed nucleus of the stria terminalis (BNST), lateral septum, central nucleus of the amygdala (CEA), periaqueductal grey (PAG; dorsolateral, dorsomedial, and lateral), and the Edinger-Westphal nucleus. Pre-exposure to THC significantly increased heroin-induced Fos-IR in the dorsomedial CPu and the NAC (core). Conversely, THC pre-exposure reduced heroin-induced Fos-IR in the BNST, CEA, and the PAG (dorsolateral and lateral). The present study demonstrates that THC pre-exposure increases the locomotor stimulating effects of heroin and provides new evidence for the neural correlates that may underlie cannabinoid and opioid cross-sensitisation.

Impaired learning in adulthood following neonatal delta9-THC exposure.

Cannabis is one of the most commonly used illicit drugs during pregnancy, but little is known about the lasting effects of early-life exposure to this drug. In this study, male Wistar rat pups were treated daily with (-)-delta9-tetrahydrocannabinol (THC; 5 mg/kg, s.c.) or its vehicle between postnatal days (PND) 4 and 14. Drug administration during this early postnatal period in rats is analogous to the third trimester of gestation in humans, which is a major period of synaptogenesis. Rats were subsequently tested drug-free during young adulthood (PND 56) using a two-component food-motivated double Y-maze test. Each trial included distinct spatial discrimination and delayed alternation components, which permitted the simultaneous assessment of reference memory and working memory. Rats were tested for 30 trials/day, 5 days/week for 5 weeks. Results revealed no significant differences between THC- and vehicle-treated rats in the spatial discrimination task. However, compared to vehicle-treated rats, THC-treated rats committed significantly more errors, and required significantly longer to obtain 80% correct over two consecutive days in the delayed alternation task. Results suggest that neonatal THC exposure leads to a specific and lasting deficit in learning in adulthood, which is likely due to impaired working memory function.

Modulation of morphine-induced Fos-immunoreactivity by the cannabinoid receptor antagonist SR 141716.

A growing body of evidence suggests the existence of a functional interaction between opioid and cannabinoid systems. The present study further investigated this functional interaction by examining the combined effects of morphine and the cannabinoid receptor antagonist SR 141716 on Fos-immunoreactivity (Fos-IR), a marker for neural activation. Male albino Wistar rats were treated with SR 141716 (3 mg/kg, intraperitoneally), morphine HCl (10 mg/kg, subcutaneously), vehicle, or SR 141716 and morphine combined (n = 6 per group). Rats were injected with morphine or its vehicle 30-min after administration of SR 141716 or its vehicle and perfused 3 h later. Locomotor activity and body temperature were both increased in the morphine-treated group and SR 141716 significantly inhibited these effects. Morphine increased Fos-IR in several brain regions including the caudate-putamen (CPu), cortex (cingulate, insular and piriform), nucleus accumbens (NAS) shell, lateral septum (LS), bed nucleus of the stria terminalis (BNST), median preoptic nucleus (MnPO), medial preoptic nucleus (MPO), hypothalamus (paraventricular, dorsomedial and ventromedial), paraventricular thalamic nucleus (PV), amygdala (central and basolateral nuclei), dorsolateral periaqueductal gray, ventral tegmental area (VTA), and Edinger-Westphal nucleus. SR 141716 alone increased Fos-IR in the cortex (cingulate, insular and piriform), NAS (shell), LS, BNST, hypothalamus (paraventricular, dorsomedial and ventromedial), PV, amygdala (central, basolateral and medial nuclei), VTA, and Edinger-Westphal nucleus. SR 141716 attenuated morphine-induced Fos-IR in several regions including the CPu, cortex, NAS (shell), LS, MnPO, MPO, paraventricular and dorsomedial hypothalamus, PV, basolateral amygdala, VTA, and Edinger-Westphal nucleus (EW). These results provide further support for functional interplay between the cannabinoid and opioid systems. Possible behavioural and physiological implications of the interactive effects of SR 141716 on morphine-induced Fos-IR are discussed.

A cannabinoid receptor antagonist attenuates conditioned place preference but not behavioural sensitization to morphine.

The present study compared the effects of the cannabinoid receptor antagonist SR 141716 on morphine-induced locomotor sensitization (Experiment 1) and conditioned place preference (CPP, Experiment 2) in male albino Wistar rats. In Experiment 1, rats received seven consecutive daily treatments with morphine (10 mg/kg, SC) in combination with either SR 141716 (0, 0.1, 0.5 or 3.0 mg/kg, IP), or naloxone (10 mg/kg, IP). Three days later, all rats were challenged with a lower dose of morphine (5 mg/kg, SC). Rats pre-treated with morphine showed significantly elevated locomotor activity during the challenge session compared to vehicle-pre-treated animals indicating behavioural sensitization. Prior naloxone, but not SR 141716, co-administration with morphine, significantly attenuated the locomotor sensitization observed. In Experiment 2A, SR 141716 (0.1 mg/kg, IP), co-administered during conditioning, significantly attenuated the place preference produced by morphine (4 mg/kg, SC) in a standard unbiased two compartment place conditioning task. In Experiment 2B, the timing of drug administration and drug doses used were altered to be similar to Experiment 1, such that a comparison between the sensitization and CPP paradigms could be made. Thus, rats were conditioned with morphine (10 mg/kg, SC) combined with SR 141716 (0, 0.1, 0.5 or 3.0 mg/kg, IP) and tested for place preference under the influence of morphine (5 mg/kg, SC). SR 141716 attenuated morphine place preference at a dose (3.0 mg/kg) that did not itself affect place conditioning. Morphine also induced locomotor sensitization in the drug-paired compartment in Experiment 2B which was not blocked by any dose of SR 141716. We conclude that CB1 receptor antagonism modulates the rewarding value of opioids, but not the behavioural sensitization induced by chronic opioid administration.

Evidence for an interaction between CB1 cannabinoid and oxytocin receptors in food and water intake.

Oxytocin and CB(1) cannabinoid receptors independently modulate food intake. Although an interaction between oxytocin and cannabinoid systems has been demonstrated with respect to the cannabinoid withdrawal syndrome, the interaction between these systems in modulating food intake has not yet been examined. The present study had three primary purposes: (1) to determine whether oxytocin and a CB(1) receptor antagonist block food and fluid intake in a supra-additive manner, (2) to determine the relative position of the CB(1) receptors in the chain of control of food intake in relation to the oxytocin system, and (3) to determine whether the increase in fluid intake induced by an oxytocin antagonist is mediated via cannabinoid receptors. Rats were habituated to the test environment and injection procedure, and then received intracerebroventricular (ICV) injections of various combinations of the oxytocin receptor antagonist tocinoic acid, the cannabionid receptor agonist delta(9)-tetrahydrocannabinol (THC), oxytocin, or the cannabinoid receptor antagonist SR 141716. Food and water intake and locomotor activity were then measured for 120 min. When administrated alone, SR 141716 and oxytocin dose-dependently attenuated baseline food intake, while oxytocin but not SR 141716 reduced water intake. Sub-anorectic doses of SR 141716 and oxytocin attenuated baseline feeding beyond what would be expected by the sum of the individual drug effects without affecting baseline water intake. THC stimulated feeding but not water intake. THC-induced feeding was not blocked by oxytocin, however, the oxytocin did attenuate water intake during such feeding. SR 141716 dose-dependently reduced tocinoic-acid-stimulated food intake and partially attenuated water intake. Locomotor activity was not significantly affected by any drug treatments, suggesting that effects on feeding were not due to a non-specific reduction in motivated behaviour. These findings reveal an interaction between cannabinoid and oxytocin systems in food intake. Results further reveal that the oxytocin system effects on water intake are partially mediated via CB(1) receptors, CB(1) receptors are located downstream from oxytocin receptors, and CB(1) receptor signalling is necessary to prevent oxytocin from altering food intake.

Anxiety and aggression associated with the fermentation of carbohydrates in the hindgut of rats.

Lactic acid accumulation in the caecum and colon resulting from the fermentation of carbohydrates can lead to deleterious effects in ruminant and monogastric animals, including humans. In the present study, we examined the behavioural effects of two types of commonly consumed foods: soluble and fermentable carbohydrates (FCs). Thirty-six male Wistar rats were fed either a commercial rat and mouse chow, a soluble carbohydrate (SC)-based diet or an FC-based diet. Social interaction, anxiety, aggression and locomotor activity were examined by employing a social interaction test and a light/dark emergence test, while physical parameters of hindgut fermentation were examined after sacrifice, either 3 or 21 h after feeding. Results showed that anxiety (spending less time in the light compartment during the light/dark emergence test) and aggression (increased fighting during the social interaction test) were increased following raised concentrations of fermentation end products, such as lactic acid and volatile fatty acids (VFAs) in the caecum of rats. These associations occurred regardless of dopamine and 5-HT concentrations in the prefrontal cortex (PFC) and provide evidence supporting a general effect of FCs on behaviour. Possible mechanisms of action along with similarities between a rat and human model of acidosis are discussed.

Evidence for an interaction between CB1 cannabinoid and melanocortin MCR-4 receptors in regulating food intake.

Melanocortin receptor 4 (MCR4) and CB(1) cannabinoid receptors independently modulate food intake. Although an interaction between the cannabinoid and melanocortin systems has been found in recovery from hemorrhagic shock, the interaction between these systems in modulating food intake has not yet been examined. The present study had two primary purposes: 1) to examine whether the cannabinoid and melanocortin systems act independently or synergistically in suppressing food intake; and 2) to determine the relative position of the CB(1) receptors in the chain of control of food intake in relation to the melanocortin system. Rats were habituated to the test environment and injection procedure and then received intracerebroventicular injections of various combinations of the MCR4 receptor antagonist JKC-363, the CB(1) receptor agonist Delta(9)-tetrahydrocannabinol, the MCR4 receptor agonist alpha-MSH, or the cannabinoid CB(1) receptor antagonist SR 141716. Food intake and locomotor activity were then recorded for 120 min. When administrated alone, SR 141716 and alpha-MSH dose-dependently attenuated baseline feeding, whereas sub-anorectic doses of SR 141716 and alpha-MSH synergistically attenuated baseline feeding when combined. Delta(9)-Tetrahydrocannabinol-induced feeding was not blocked by alpha-MSH, whereas SR 141716 dose-dependently attenuated JKC-363-induced feeding. Locomotor activity was not significantly affected by any drug treatment, suggesting that the observed effects on feeding were not due to a nonspecific reduction in motivated behavior. These findings revealed a synergistic interaction between the cannabinoid and melanocortin systems in feeding behavior. These results further suggested that CB(1) receptors are located downstream from melanocortin receptors and CB(1) receptor signaling is necessary to prevent the melanocortin system from altering food intake.

Regional differences in naloxone modulation of Delta(9)-THC induced Fos expression in rat brain.

Recent behavioral and pharmacological research shows extensive interplay between cannabinoid and opioid neurochemical systems. Here we examined the neuroanatomical basis of this interaction using c-fos immunohistochemistry. We compared Fos immunoreactivity in groups of male albino Wistar rats treated with vehicle, Delta(9)-tetrahydrocannabinol (THC, 10 mg/kg, i.p.), naloxone (10 mg/kg, i.p.) or THC and naloxone in combination. Locomotor activity was depressed in both THC treatment groups and moderately inhibited in rats given naloxone alone. Results showed that naloxone inhibited THC-induced Fos immunoreactivity in several key brain regions including the ventral tegmental area, ventromedial and dorsomedial hypothalamus, central caudate-putamen and ventrolateral periaqueductal grey. Conversely, naloxone and THC had an additive effect on Fos immunoreactivity in the central nucleus of the amygdala, the bed nucleus of the stria terminalis (lateral division), the insular cortex, and the paraventricular nucleus of the thalamus. These findings complement earlier pharmacological results showing potent modulation of cannabinoid-induced analgesia, appetite and reward by opioids. The inhibitory effects of naloxone on THC-induced ventral tegmentum, hypothalamic and periaqueductal grey Fos expression point to these structures as key sites involved in cannabinoid-opioid interactions.

The distribution of cannabinoid-induced Fos expression in rat brain: differences between the Lewis and Wistar strain.

Previous studies have suggested that cannabis-like drugs produce mainly aversive and anxiogenic effects in Wistar strain rats, but rewarding effects in Lewis strain rats. In the present study we compared Fos expression, body temperature effects and behavioral effects elicited by the cannabinoid CB(1) receptor agonist CP 55,940 in Lewis and Wistar rats. Both a moderate (50 microg/kg) and a high (250 microg/kg) dose level were used. The 250 microg/kg dose caused locomotor suppression, hypothermia and catalepsy in both strains, but with a significantly greater effect in Wistar rats. The 50 microg/kg dose provoked moderate hypothermia and locomotor suppression but in Wistar rats only. CP 55,940 caused significant Fos immunoreactivity in 24 out of 33 brain regions examined. The most dense expression was seen in the paraventricular nucleus of the hypothalamus, the islands of Calleja, the lateral septum (ventral), the central nucleus of the amygdala, the bed nucleus of the stria terminalis (lateral division) and the ventrolateral periaqueductal gray. Despite having a similar distribution of CP 55,940-induced Fos expression, Lewis rats showed less overall Fos expression than Wistars in nearly every brain region counted. This held equally true for anxiety-related brain structures (e.g. central nucleus of the amygdala, periaqueductal gray and the paraventricular nucleus of the hypothalamus) and reward-related sites (nucleus accumbens and pedunculopontine tegmental nucleus). In a further experiment, Wistar rats and Lewis rats did not differ in the amount of Fos immunoreactivity produced by cocaine (15 mg/kg). These results indicate that Lewis rats are less sensitive to the behavioral, physiological and neural effects of cannabinoids. The exact mechanism underlying this subsensitivity requires further investigation.

Increased anxiety and impaired memory in rats 3 months after administration of 3,4-methylenedioxymethamphetamine ("ecstasy").

Male Wistar rats were administered either (a) a high dose regime of 3,4-methylenedioxymethamphetamine (MDMA) (4 x 5 mg/kg, i.p. over 4 h on each of 2 consecutive days), (b) a moderate dose regime of MDMA (1 x 5 mg/kg on each of 2 consecutive days), (c) D-amphetamine (4 x 1 mg/kg over 4 h on each of 2 days), or (d) vehicle injections. The high MDMA dose regime and the amphetamine treatment both produced acute hyperactivity and hyperthermia. Twelve weeks later, all rats were tested in the drug-free state on a battery of anxiety tests (elevated plus maze, emergence and social interaction tests). A further 2 weeks later they were tested on a novel object recognition memory task. Rats previously given the neurotoxic dose of MDMA showed greater anxiety-like behaviour on all three anxiety tests relative to both controls and D-amphetamine-treated rats. Rats given the moderate MDMA dose regime also showed increased anxiety-like behaviour on all three tests, although to a lesser extent than rats in the high dose group. In the object recognition task, rats given the high MDMA dose regime showed impaired memory relative to all other groups when tested at a 15-min delay but not at a 60-min delay. Rats previously exposed to amphetamine did not differ from saline controls in the anxiety or memory tests. These data suggest that moderate to heavy MDMA exposure over 48 h may lead to increased anxiety and memory impairment 3 months later, possibly through a neurotoxic effect on brain serotonin systems.

Increased motivation for beer in rats following administration of a cannabinoid CB1 receptor agonist.

A series of experiments examined the effects of the cannabinoid CB1 receptor agonist CP 55,940 ((-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hyd roxypropyl)cyclohexanol) on the motivation to consume beer, near-beer (a beer-like beverage containing <0.5% ethanol) and sucrose solutions in rats. The experiments employed a 'lick-based progressive ratio paradigm' in which an ever increasing number of licks had to be emitted at a tube for each successive fixed unit of beverage delivered. Break point, the lick requirement at which responding ceased, was used as an index of motivation. In the first experiment, CP 55,940 (10, 30 or 50 microg/kg) caused a dose-dependent increase in break points for beer (containing 4.5% ethanol v/v) and for near-beer. The highest (50 microg/kg) dose of CP 55,940 also significantly decreased locomotor activity. In the second experiment, CP 55,940 (10 or 30 microg/kg) dose-dependently increased break points in rats licking for 'light' beer (containing 2.7% ethanol v/v) or for a sucrose solution (8.6% w/v) containing the same number of calories as the beer. In the third experiment, the facilitatory effects of CP 55,940 (30 microg/kg) on responding for beer and near-beer were reversed by both the cannabinoid CB1 receptor antagonist SR 141716 (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide hydrochloride) (1.5 mg/kg) and the opioid receptor antagonist naloxone (2.5 mg/kg). Naloxone had a proportionally greater effect on rats licking for beer compared to near-beer, consistent with previous reports of opioid receptor mediation of alcohol craving. These results show that cannabinoids modulate the motivation for beer via both cannabinoid CB1 receptors and opioid receptors. The similar effect of CP 55,940 on the motivation for beer, near-beer and sucrose suggests that the drug effect may reflect a general stimulatory effect on appetite for palatable beverages, although a more specific effect on the desire for alcohol cannot be ruled out.

Nucleus basalis injections of N-methyl-D-aspartate enhance memory of rats in the double Y-maze.

N-methyl-D-aspartate (NMDA) receptors have been implicated in learning and memory. Many findings show that NMDA receptor antagonists impair memory. Few studies, however, have investigated the role of NMDA receptor agonists in mnemonic function. The present study examined the effects of nucleus basalis magnocellularis (nbm) injections of NMDA on memory. Rats were trained in a two-component double Y-maze task consisting of a spatial discrimination and a delayed alternation. Rats (n = 7) were surgically implanted with bilateral cannulae in the nbm prior to maze training. Once trained, animals received bilateral nbm injections (0.5 microl) of saline (0.9%), NMDA (50, 75, and 100 ng/side), and the benzodiazepine receptor partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG 7142; 200 ng/side), in a counterbalanced order. During testing, delays (0, 30, 60 s) were introduced. Nbm FG 7142 or NMDA (50 ng/side) produced an improvement in the delayed alternation task. Results support the hypothesis that nbm NMDA receptors are involved in cognitive processes mediating memory.

The cannabinoid CB1 receptor antagonist SR141716A attenuates the memory impairment produced by delta9-tetrahydrocannabinol or anandamide.

The administration of delta9-tetrahydrocannabinol (THC), the principle psychoactive ingredient in marijuana, or the endogenous cannabinoid anandamide, has been shown to impair recent memory. The purpose of the present investigation was to determine if the cannabinoid CB1 receptor antagonist SR141716A could attenuate THC- or anandamide-induced memory impairment, and to assess the effects on memory of SR141716A alone. Memory was assessed in rats well-trained in a two-component instrumental discrimination task, consisting of a conditional discrimination, and a non-match-to-position to assess recent or working memory. SR141716A (0.0-2.0 mg/kg) had no effect on either the conditional discrimination or the non-match-to-position. However, SR141716A (0.0-2.0 mg/kg) attenuated the memory impairment produced by THC (2.0 or 4.0 mg/kg) as indexed by an enhancement of performance in the non-match-to-position. When administered to rats pretreated with anandamide (2.0 mg/kg), SR141716A (0.0-2.5 mg/kg) impaired performance in the conditional discrimination at the highest dose. This was interpreted as a deficit in some capacity unrelated to memory (e.g., motor impairment). However, lower doses of SR141716A (0.1 and 0.5 mg/kg) attenuated the anandamide-induced impairment of performance in the non-match-to-position without affecting the conditional discrimination. This is the first report that the memory impairment produced by anandamide can be attenuated by a cannabinoid antagonist; results suggest that anandamide-induced memory disruption is mediated by CB receptors.

Delta9-tetrahydrocannabinol, but not the endogenous cannabinoid receptor ligand anandamide, produces conditioned place avoidance.

Although exogenous cannabinoid ligands such as delta9-tetrahydrocannabinol (THC) have been implicated in reward-related learning and aversion, the hedonic effects of the endogenous cannabinoid agonist anandamide (arachidonylethanolamide) have never been assessed. Thus, the effects of anandamide were tested in a place conditioning task. Male Wistar rats received THC (0.0-8.0 mg/kg) or anandamide (0.0-16.0 mg/kg) during conditioning sessions. The half-life of anandamide was increased by pretreatment with the protease inhibitor phenylmethylsulfonyl fluoride (2.0 mg/kg). A significant place aversion was found at the 1.0 and 1.5 mg/kg doses of THC. No significant place conditioning effects were found with anandamide. Locomotor activity during conditioning was significantly decreased by the 1.0, 1.5, 2.0 and 4.0 mg/kg doses of THC as well as the 8.0 and 16.0 mg/kg doses of anandamide. These results fail to implicate the endogenous cannabinoid anandamide in reward-related learning or aversion.

Place conditioning with the dopamine D1-like receptor agonist SKF 82958 but not SKF 81297 or SKF 77434.

While self-administration and place conditioning studies have shown that dopamine D2-like receptor agonists produce reward-related learning, the effects of dopamine D1-like receptor agonists remain equivocal. The present study tested three dopamine D1-like receptor agonists for their ability to induce a place preference. Like control rats treated with amphetamine (2.0 mg/kg i.p.), rats treated with SKF 82958 (+/- -6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1-phenyl-1H- 3-benzazepine hydrobromide; 0.05 but not 0.01, 0.025, 0.075, or 0.10 mg/kg s.c. and/or i.p.) during conditioning showed a significant increase in the amount of time spent on the drug-paired side during the drug free test. Neither SKF 81297 (+/- -6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide; 0.25, 0.50, 1.0, 2.0, and 4.0 mg/kg i.p.) nor SKF 77434 (+/- -7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; 0.20, 1.0, 5.0, and 10.0 mg/kg i.p.) produced place conditioning. Significant increases in locomotion were seen at some doses of all drugs. Results show for the first time that systemic administration of a dopamine D1-like receptor agonist produces a place preference and are consistent with previous findings showing that dopamine D1-like receptor activation produces reward-related learning.

Physostigmine, but not 3,4-diaminopyridine, improves radial maze performance in memory-impaired rats.

The results of some studies suggest that 3,4-diaminopyridine (3,4-DAP), a drug that enhances the release of acetylcholine, may improve memory. The present study examined the ability of 3,4-DAP to reverse the memory impairment produced by scopolamine and the ability of 3,4-DAP and physostigmine to reverse the memory impairment produced by quinolinic acid lesions of the nucleus basalis magnocellularis (nbm) in rats. Mnemonic functioning was assessed with the use of a partially baited eight-arm radial maze. Entries into arms that were never baited were defined as reference memory errors; entries into baited arms from which the food already had been eaten were defined as working memory errors. In Experiment 1, 0.1 mg/kg scopolamine produced a significant increase in working and reference memory errors. Various doses of 3,4-DAP had no significant ameliorative effect on the mnemonic deficit. In Experiment 2, cholinergic function was impaired using a unilateral intra-nbm injection of quinolinic acid (120 nmol in 1.0 microliter). These lesions reduced the levels of the cholinergic marker, choline acetyltransferase, in the cortex by more than 40%. Results showed that the nbm lesion animals were significantly more impaired on the working than reference memory component of the task. Physostigmine (0.01, 0.05, 0.10, 0.20, 0.50 mg/kg) dose-dependently decreased the number of working but not reference memory errors. 3,4-DAP (10(-8), 10(-6), 10(-4), 10(-2), 10(0) mg/kg) had no reliable effect. It was concluded that physostigmine, but not 3,4-DAP, ameliorates memory impairments following decreases in cholinergic function.

Nucleus basalis lesions: implication of basoamygdaloid cholinergic pathways in memory.

Previous studies have shown a lack of association between cortical choline acetyltransferase (ChAT) activity and severity of memory impairment following excitotoxic lesions of the nucleus basalis magnocellularis (NBM). It recently has been proposed that the differential effects of NBM injections of various excitotoxins on amygdaloid and cortical ChAT may explain this result. The present study evaluated the mnemonic effect of unilateral intra-NBM infusions of the excitotoxins phthalic acid and quisqualic acid, which decrease ChAT activity primarily in the amygdala and cortex, respectively. Rats were trained in a double Y-maze, lesioned, and allowed to recover for 1 week prior to memory assessment. Behavioral results showed impaired working but not reference memory following phthalic acid lesions, and no significant effect following quisqualic acid lesions. Biochemical analysis in a second group of subjects confirmed that phthalic acid lesions produced a large decrease in basolateral amygdaloid ChAT, but had little effect on cortical ChAT activity. Conversely, quisqualic acid lesions produced a large decrease in cortical, but not basolateral amygdaloid, ChAT activity. These results suggest that the NBM amygdalopetal cholinergic pathways play a role in mnemonic functioning.