Expansion of medical marijuana use in the US and the recently successful decriminalization of recreational marijuana in two States elevates interest in the specific cognitive effects of Δ9tetrahydrocannabinol (Δ9THC), the major psychoactive constituent of marijuana. Controlled laboratory studies in nonhuman primates provide mixed evidence for specific effects of Δ9THC in learning and memory tasks, with a suggestion that frontal-mediated tasks may be the most sensitive. In this study, adult male rhesus monkeys were trained on tasks which assess reversal learning, extradimensional attentional shift learning and spatial delayed-response. Subjects were challenged with 0.1–0.5 mg/kg Δ9THC, i.m., in randomized order and evaluated on the behavioral measures. Peak plasma levels of Δ9THC were observed 30 min after 0.2 mg/kg (69 ± 29 ng/ml) and 60 min after 0.5 mg/kg (121 ± 23 ng/ml) was administered and behavioral effects on a bimanual motor task persisted for up to 2 h after injection. An increase in errors-to-criterion (ETC) associated with reversal learning was further increased by Δ9THC in a dose-dependent manner. The increase in ETC associated with extradimensional shifts was not affected by Δ9THC. Spatial delayed-response performance was impaired by Δ9THC in a retention-interval-dependent manner. Overall the pattern of results suggests a more profound effect of Δ9THC on tasks mediated by orbitofrontal (reversal learning) versus dorsolateral (extradimensional shifts) prefrontal mechanisms.
"However, similar to Y-maze performance, there was no effect of chronic CP treatment, strengthening the selectivity of its action on PPI. Thus, although previous studies have shown involvement of both the endocannabinoid system and BDNF in memory formation and consolidation (Papaleo et al., 2011; Panlilio et al., 2012; De Bitencourt et al., 2013; Wright et al., 2013), in our protocol including chronic CP treatment followed by a 2-week washout, there were no such effects. Future studies could include the acute effects of cannabinoid receptor stimulation on memory function in BDNF HET mice and controls after chronic pre-treatment with CP, similar to the PPI studies presented here. "
[Show abstract][Hide abstract] ABSTRACT: Reduced brain-derived neurotrophic factor (BDNF) signaling has been shown in the frontal cortex and hippocampus in schizophrenia. The aim of the present study was to investigate whether a BDNF deficit would modulate effects of chronic cannabis intake, a well-described risk factor for schizophrenia development. BDNF heterozygous mice (HET) and wild-type controls were chronically treated during weeks 6, 7, and 8 of life with the cannabinoid receptor agonist, CP55,940 (CP). After a 2-week delay, there were no CP-induced deficits in any of the groups in short-term spatial memory in a Y-maze task or novel object recognition memory. Baseline prepulse inhibition (PPI) was lower but average startle was increased in BDNF HET compared to wild-type controls. Acute CP administration before the PPI session caused a marked increase in PPI in male HET mice pre-treated with CP but not in any of the other male groups. In females, there were small increases of PPI in all groups upon acute CP administration. Acute CP administration furthermore reduced startle and this effect was greater in HET mice irrespective of chronic CP pre-treatment. Analysis of the levels of [(3)H]CP55,940 binding by autoradiography revealed a significant increase in the nucleus accumbens of male BDNF HET mice previously treated with CP but not in any of the other groups or in the caudate nucleus. These results show that BDNF deficiency and chronic young-adult cannabinoid receptor stimulation do not interact in this model on learning and memory later in life. In contrast, male "two hit" mice, but not females, were hypersensitive to the effect of acute CP on sensorimotor gating. These effects may be related to a selective increase of [(3)H]CP55,940 binding in the nucleus accumbens, reflecting up-regulation of CB1 receptor density in this region. These data could be of relevance to our understanding of differential "two hit" neurodevelopmental mechanisms in schizophrenia.
[Show abstract][Hide abstract] ABSTRACT: Cognition deficits in schizophrenia remain an untreated area, and one in which R&D investment by pharmaceutical companies is high. However, whilst many preclinical assays demonstrate pro-cognitive activity with new drugs, in the main, this has not yet translated successfully to the clinic. In an attempt to address this and reduce the high attrition rate for drugs in the clinic, selected preclinical researchers are re-focusing their efforts on the development and validation of more translational assays. The attentional set-shifting task is an example of such an assay, which has been back-translated from the clinic to a preclinical setting. Here we review its application in schizophrenia research across humans and animals, specifically with regards to the neural basis underlying cognitive performance, the various disease-like or symptom models employed in rodents to mimic cognitive dysfunction in schizophrenia, and the resulting impact of drug treatment on executive function. Using the attentional set-shifting task, we highlight the potential promise a more translational approach can bring, whilst demonstrating the need for closer alignment in the validation and integration of this task to fully realize this promise.
Current pharmaceutical design 12/2013; 20(31). DOI:10.2174/1381612819666131216114909 · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although human alcoholics exhibit lasting cognitive deficits, it can be difficult to definitively rule out pre-alcohol performance differences. For example, individuals with a family history of alcoholism are at increased risk for alcoholism and are also behaviorally impaired. Animal models of controlled alcohol exposure permit balanced group assignment, thereby ruling out the effects of pre-existing differences. Periadolescent male rhesus macaques (N = 5) consumed alcohol during 200 drinking sessions (M F) across a 10-month period (mean daily alcohol consumption: 1.38 g/kg/day). A control group (N = 5) consumed a fruit-flavored vehicle during the same period. Spatial working memory, visual discrimination learning and retention and response time behavioral domains were assessed with sub-tests of the Monkey CANTAB (CAmbridge Neuropsychological Test Automated Battery). Spatial working memory performance was impaired in the alcohol group after 120 drinking sessions (6 mo) in a manner that depended on retention interval. The chronic alcohol animals were also impaired in retaining a visual discrimination over 24 hrs when assessed 6-8 weeks after cessation of alcohol drinking. Finally, the presentation of distractors in the response time task impaired the response time and accuracy of the chronic alcohol group more than controls after 6 months of alcohol cessation. Chronic alcohol consumption over as little as 6 months produces cognitive deficits, with some domains still affected after acute (6-8 wks) and lasting (6 mo) discontinuation from drinking. Animals were matched on alcohol preference and behavioral performance prior to exposure, thus providing strong evidence for the causal role of chronic alcohol in these deficits.
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