Sphingolipids and DHA Improve Cognitive Deficits in Aged Beagle Dogs

Canine cognitive dysfunction syndrome (CDS) is a disorder found in senior dogs that is typically defined by the development of specific behavioral signs which are attributed to pathological brain aging and no other medical causes. One way of objectively characterizing CDS is with the use of validated neuropsychological test batteries in aged Beagle dogs, which are a natural model of this condition. This study used a series of neuropsychological tests to evaluate the effectiveness of supplementation with a novel lipid extract containing porcine brain-derived sphingolipids (Biosfeen®) and docosahexaenoic acid (DHA) for attenuating cognitive deficits in aged Beagles. Two groups (n = 12), balanced for baseline cognitive test performance, received a daily oral dose of either test supplement, or placebo over a 6-month treatment phase. Cognitive function was evaluated using the following tasks: delayed non-matching to position (DNMP), selective attention, discrimination learning retention, discrimination reversal learning, and spatial discrimination acquisition and reversal learning. The effect of the supplement on brain metabolism using magnetic resonance spectroscopy (MRS) was also examined. A significant decline (p = 0.02) in DNMP performance was seen in placebo-treated dogs, but not in dogs receiving the supplement, suggesting attenuation of working memory performance decline. Compared to placebo, the supplemented group also demonstrated significantly improved (p = 0.01) performance on the most difficult pattern of the spatial discrimination task and on reversal learning of the same pattern (p = 0.01), potentially reflecting improved spatial recognition and executive function, respectively. MRS revealed a significant increase (p = 0.048) in frontal lobe glutamate and glutamine in the treatment group compared to placebo, indicating a physiological change which may be attributed to the supplement. Decreased levels of glutamate and glutamine have been correlated with cognitive decline, suggesting the observed increase in these metabolites might be linked to the positive cognitive effects found in the present study. Results of this study suggest the novel lipid extract may be beneficial for counteracting age-dependent deficits in Beagle dogs and supports further investigation into its use for treatment of CDS. Additionally, due to parallels between canine and human aging, these results might also have applicability for the use of the supplement in human cognitive health.

Contrasting effects of d-amphetamine and atomoxetine on measures of impulsive action and choice

Amphetamine (AMP) and atomoxetine (ATX) represent two of the most widely studied drug treatments used in the investigation of impulsive behaviour. While both drugs have relatively well defined effects in tests designed to investigate impulsive action (e.g. 5-choice task; 5-CSRTT), the effects of both drugs in tests of impulsive choice (e.g. delay discounting) are less consistent. In the present study both AMP and ATX were tested in a rodent gambling task (rGT) and delay discounting in rats separately trained to either an ascending or descending delay schedule. Effects of both drugs were compared to measures of impulsive action (premature (PREM) responses) and perseverative (PSV) responses measured in the 5-choice and rGT tasks. Consistent with previous studies, AMP (0.1-1 mg/kg) increased both PREM and PSV responses, and ATX (0.5-2 mg/kg) reduced both measures in the 5-choice and rGT tasks. At equivalent doses ATX had no reliable effect on choice behaviour in either the rGT or delay discounting suggesting a null effect of this drug on impulsive choice and risky decision making. The effects of AMP were more complex, with a subtle shift in preference to a low risk (P1) choice in the rGT, and an effect on discounting that was unrelated to reinforcer value, but instead dependent on delay sequence and baseline choice preference. One aspect to these outcomes is to highlight the importance of multiple methodological factors when assessing drug effects on complex behaviours such as impulsive choice, and question what are the most appropriate test conditions under which to examine these drugs on discounting.

Low Doses of Psilocybin and Ketamine Enhance Motivation and Attention in Poor Performing Rats: Evidence for an Antidepressant Property

Long term benefits following short-term administration of high psychedelic doses of serotonergic and dissociative hallucinogens, typified by psilocybin and ketamine respectively, support their potential as treatments for psychiatric conditions such as major depressive disorder. The high psychedelic doses induce perceptual experiences which are associated with therapeutic benefit. There have also been anecdotal reports of these drugs being used at what are colloquially referred to as "micro" doses to improve mood and cognitive function, although currently there are recognized limitations to their clinical and preclinical investigation. In the present studies we have defined a low dose and plasma exposure range in rats for both ketamine (0.3-3 mg/kg [10-73 ng/ml]) and psilocybin/psilocin (0.05-0.1 mg/kg [7-12 ng/ml]), based on studies which identified these as sub-threshold for the induction of behavioral stereotypies. Tests of efficacy were focused on depression-related endophenotypes of anhedonia, amotivation and cognitive dysfunction using low performing male Long Evans rats trained in two food motivated tasks: a progressive ratio (PR) and serial 5-choice (5-CSRT) task. Both acute doses of ketamine (1-3 mg/kg IP) and psilocybin (0.05-0.1 mg/kg SC) pretreatment increased break point for food (PR task), and improved attentional accuracy and a measure of impulsive action (5-CSRT task). In each case, effect size was modest and largely restricted to test subjects characterized as "low performing". Furthermore, both drugs showed a similar pattern of effect across both tests. The present studies provide a framework for the future study of ketamine and psilocybin at low doses and plasma exposures, and help to establish the use of these lower concentrations of serotonergic and dissociative hallucinogens both as a valid scientific construct, and as having a therapeutic utility.

Characterization of Amphetamine, Methylphenidate, Nicotine, and Atomoxetine on Measures of Attention, Impulsive Action, and Motivation in the Rat: Implications for Translational Research

Amphetamine (AMP), methylphenidate (MPH), and atomoxetine (ATX) are approved treatments for ADHD, and together with nicotine (NIC), represent pharmacological agents widely studied on cognitive domains including attention and impulsive action in humans. These agents thus represent opportunities for clinical observation to be reinvestigated in the preclinical setting, i.e., reverse translation. The present study investigated each drug in male, Long Evans rats trained to perform either (1) the five-choice serial reaction time task (5-CSRTT), (2) Go/NoGo task, or (3) a progressive ratio (PR) task, for the purpose of studying each drug on attention, impulsive action and motivation. Specific challenges were adopted in the 5-CSRTT designed to tax attention and impulsivity, i.e., high frequency of stimulus presentation (sITI), variable reduction in stimulus duration (sSD), and extended delay to stimulus presentation (10-s ITI). Initially, performance of a large (> 80) cohort of rats in each task variant was conducted to examine performance stability over repeated challenge sessions, and to identify subgroups of "high" and "low" attentive rats (sITI and sSD schedules), and "high" and "low" impulsives (10-s ITI). Using an adaptive sequential study design, the effects of AMP, MPH, ATX, and NIC were examined and contrasting profiles noted across the tests. Both AMP (0.03-0.3 mg/kg) and MPH (1-6 mg/kg) improved attentional performance in the sITI but not sSD or 10-s ITI condition, NIC (0.05-0.2 mg/kg) improved accuracy across all conditions. ATX (0.1-1 mg/kg) detrimentally affected performance in the sITI and sSD condition, notably in "high" performers. In tests of impulsive action, ATX reduced premature responses notably in the 10-s ITI condition, and also reduced false alarms in Go/NoGo. Both AMP and NIC increased premature responses in all task variants, although AMP reduced false alarms highlighting differences between these two measures of impulsive action. The effect of MPH was mixed and appeared baseline dependent. ATX reduced break point for food reinforcement suggesting a detrimental effect on motivation for primary reward. Taken together these studies highlight differences between AMP, MPH, and ATX which may translate to their clinical profiles. NIC had the most reliable effect on attentional accuracy, whereas ATX was reliably effective against all tests of impulsive action.

Effects of 5-HT2C receptor modulation and the NA reuptake inhibitor atomoxetine in tests of compulsive and impulsive behaviour

Drug repositioning has gained strategic value as a reaction to high attrition rates of new drugs as they pass through the clinical development process. The 5-HT2C receptor agonist lorcaserin (Belviq®), and the selective NA reuptake inhibitor atomoxetine (Strattera®) represent two drugs FDA approved for obesity and ADHD respectively. Although both drugs are of differing pharmacological class, each share a property of regulating impulsive behaviours in preclinical studies, and thus represent candidates for consideration in clinical conditions labelled as 'impulsive-compulsive disorders'. The present studies investigated both drugs, as well as the highly selective 5-HT2C agonist CP-809101 in two tests of compulsive action: schedule-induced polydipsia (SIP) and increased perseverative [PSV] (and premature [PREM]) responses emitted during an extended ITI 5-choice task. While lorcaserin (0.06-0.6 mg/kg), CP-809101 (0.1-1 mg/kg) and atomoxetine (0.1-1 mg/kg) each reduced both PREM and PSV measures in the 5-choice task, at equivalent doses only lorcaserin and CP-809101 affected excessive water intake in the SIP task, atomoxetine (0.1-2 mg/kg) was essentially ineffective. Further evidence supporting a role of the 5-HT2C receptor as an important regulator of impulsive-compulsive behaviours, the selective antagonist SB-242084 produced the opposing effects to lorcaserin, i.e promoting both impulsive and compulsive behaviours. The profile of atomoxetine may suggest differences in the nature of compulsive action measured either as non-regulatory drinking in the SIP task, and PSV responses made in a 5-choice task. These studies support the consideration of 5-HT2C receptor agonists, typified by lorcaserin, and atomoxetine as potential treatments for clinical conditions categorised as 'impulsive-compulsive disorders'. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Young to Middle-Aged Dogs with High Amyloid-β Levels in Cerebrospinal Fluid are Impaired on Learning in Standard Cognition tests

Understanding differences in Alzheimer’s disease biomarkers before the pathology becomes evident can contribute to an improved understanding of disease pathogenesis and treatment. A decrease in amyloid-β (Aβ)₄₂ in cerebrospinal fluid (CSF) is suggested to be a biomarker for Aβ deposition in brain. However, the relevance of CSF Aβ levels prior to deposition is not entirely known. Dogs are similar to man with respect to amyloid-β protein precursor (AβPP)-processing, age-related amyloid plaque deposition, and cognitive dysfunction. In the current study, we evaluated the relation between CSF Aβ₄₂ levels and cognitive performance in young to middle-aged dogs (1.5–7 years old). Additionally, CSF sAβPPα and sAβPPβ were measured to evaluate AβPP processing, and CSF cytokines were measured to determine the immune status of the brain. We identified two groups of dogs showing consistently low or high CSF Aβ₄₂ levels. Based on prior studies, it was assumed that at this age no cerebral amyloid plaques were likely to be present. The cognitive performance was evaluated in standard cognition tests. Low or high Aβ concentrations coincided with low or high sAβPPα, sAβPPβ, and CXCL-1 levels, respectively. Dogs with high Aβ concentrations showed significant learning impairments on delayed non-match to position (DNMP), object discrimination, and reversal learning compared to dogs with low Aβ concentrations. Our data support the hypothesis that high levels of CSF Aβ in dogs coincide with lower cognitive performance prior to amyloid deposition. Further experiments are needed to investigate this link, as well as the relevance with respect to Alzheimer’s disease pathology progression.

Enhanced attention and impulsive action following NMDA receptor GluN2B-selective antagonist pretreatment

NMDA GluN2B (NR2B) subtype selective antagonists are currently in clinical development for a variety of indications, including major depression. We previously reported the selective NMDA GluN2B antagonists Ro 63-1908 and traxoprodil, increase premature responding in a 5-choice serial reaction time task (5-CSRTT) suggesting an effect on impulsive action. The present studies extend these investigations to a Go-NoGo and delay discounting task, and the 5-CSRTT under test conditions of both regular (5s) and short (2-5s) multiple ITI (Intertrial interval). Dizocilpine was included for comparison. Both Ro 63-1908 (0.1-1mg/kg SC) and traxoprodil (0.3-3mg/kg SC) increased premature and perseverative responses in both 5-CSRT tasks and improved attention when tested under a short ITI test condition. Ro 63-1908 but not traxoprodil increased motor impulsivity (false alarms) in a Go-NoGo task. Dizocilpine (0.01-0.06mg/kg SC) affected both measures of motor impulsivity and marginally improved attention. In a delay discounting test of impulsive choice, both dizocilpine and Ro 63-1908 decreased impulsive choice (increased choice for the larger, delayed reward), while traxoprodil showed a similar trend. Motor stimulant effects were evident following Ro 63-1908, but not traxoprodil treatment - although no signs of motor stereotypy characteristic of dizocilpine (>0.1mg/kg) were noted. The findings of both NMDA GluN2B antagonists affecting measures of impulsive action and compulsive behavior may underpin emerging evidence to suggest glutamate signaling through the NMDA GluN2B receptor plays an important role in behavioural flexibility. The profiles between Ro 63-1908 and traxoprodil were not identical, perhaps suggesting differences between members of this drug class.

Characterization of the 5-HT2C receptor agonist lorcaserin on efficacy and safety measures in a rat model of diet-induced obesity

The 5-HT2C receptor agonist lorcaserin (Belviq®) has been Food and Drug Administration (FDA) approved for the treatment of obesity. The present study is a back translational investigation into the effect of 28-day lorcaserin treatment in a diet-induced obesity (DIO) model using male, Sprague-Dawley rats. An assessment of drug effect on efficacy and multiple safety endpoints including cardiac function was undertaken. Lorcaserin (1-2 mg/kg SC b.i.d.) significantly reduced percentage body weight gain compared to vehicle-treated controls (VEH: 10.6 ± 0.4%; LOR 1: 7.6 ± 1.2%; LOR 2: 5.4 ± 0.6%). Measurement of body composition using quantitative magnetic resonance (QMR) imaging indicated this change was due to the selective reduction in body fat mass. Modest effects on food intake were recorded. At the completion of the treatment phase, echocardiography revealed no evidence for valvulopathy, that is, no aortic or mitral valve regurgitation. The pharmacokinetics of the present treatment regimen was determined over a 7-day treatment period; plasma C min and C max were in the range 13-160 ng/mL (1 mg/kg b.i.d.) and 34-264 ng/mL (2 mg/kg b.i.d.) with no evidence for drug accumulation. In sum, these studies show an effect of lorcaserin in the DIO model, that in the context of the primary endpoint measure of % body weight change was similar to that reported clinically (i.e., 3.0-5.2% vs. 3.2%). The present studies highlight the translational value of obesity models such as DIO, and suggest that assuming consideration is paid to nonspecific drug effects such as malaise, the DIO model has reasonable forward translational value to help predict clinical outcomes of a new chemical entity.

A back translation of pregabalin and carbamazepine against evoked and non-evoked endpoints in the rat spared nerve injury model of neuropathic pain

The purpose of the present study was twofold. First to characterize endpoints distinct to the reflexive responses to sensory stimuli typically used in neuropathic pain models. A second aim was to evaluate two clinically approved drugs carbamazepine (Tegretol) and pregabalin (Lyrica) against these endpoints with the purpose to backtranslate from the clinical to preclinical setting. The selected neuropathic pain model was the spared nerve injury (SNI) model and the endpoints were burrowing and measures of paw posture in Sprague Dawley rats. As previously described, SNI surgery produced a robust heightened sensitivity to tactile and thermal (cold) stimuli. SNI surgery also produced robust decreases in burrowing and affected multiple measures of paw position. There was no correlation between magnitude of change in burrowing and sensory allodynia within SNI operated rats. Pregabalin (10-30 mg/kg IP) produced a reliable reversal of both tactile and cold allodynia and also the burrowing deficit, with minimal effect on neurological function evaluated using rotorod, beam walking and open field activity. Pregabalin did not affect any measure of paw position. Pharmacokinetic studies conducted in satellite animals identified plasma levels of pregabalin at the 10 mg/kg IP dose to be equivalent to clinically efficacious levels recorded in neuropathic patients (3-6 μg/ml). In contrast carbamazepine (10-60 mg/kg IP) had only a very modest effect against a reflexive (tactile) measure, and no effect against the burrowing deficit. Carbamazepine also affected various measures of neurological function, complicating interpretation of the reflexive measure. Measurement of burrowing appears to detect a behavioural deficit associated with the SNI model, that may be attenuated by pregabalin but not carbamazepine. Overall the present findings support an advantage of pregabalin over carbamazepine in terms of both efficacy and tolerability which is consistent with clinical experience. The inclusion of additional endpoints beyond traditional reflexive behaviours further supports the value of rodent neuropathic pain models, such as the SNI, as behavioural assays to detect new chemical entities to treat this pain condition.

Association and transmission analysis of the FMR1 IVS10 + 14C-T variant in autism

Evidence from the high male to female ratio of individuals with autism as well as suggestive linkage data have implicated the possible involvement of X chromosomal loci in the aetiology of autism. Studies of the FMR1 gene on Xq27 have shown that occasionally individuals, and particularly females, with the [CGG] repeat expansion and methylation mutation may present with autistic symptoms. However, molecular studies suggest that such mutations are not a major cause of autism. Previously, we have screened autism probands for mutations in regions of the FMR1 gene downstream of the [CGG] repeat and identified an intronic variant in the FMR1 gene, IVS10 + 14C-T, which was present at a significantly higher frequency in autistic individuals compared to controls individuals. We have now investigated this variant in a further 136 autism families and 186 control individuals. We have established that the variant is significantly more frequent among East Asian individuals within our affected and control groups (P < 0.0001) and although we observed a trend of higher transmission frequency of the rare allele to affected individuals, there was no significant evidence in either family-based or case/control association studies for this variant in autism (P > 0.05).

The RAY1/ST7 tumor-suppressor locus on chromosome 7q31 represents a complex multi-transcript system

We recently identified a novel gene, RAY1 (FAM4A1), which spans a translocation breakpoint at 7q31 in a patient with autism. This gene has more recently been reported to be a suppressor of tumorigenicity, ST7, although controversy surrounds this observation because subsequent reports have failed to corroborate these findings. Our further analysis of this locus reveals that it is composed of a multigene system that includes two noncoding sense strand genes (ST7OT3 and ST7OT4) that overlap with many alternative forms of the coding RAY1/ST7 transcript, and two noncoding genes on the antisense strand (ST7OT1 and ST7OT2). RAY1/ST7 was determined to have at least three different 5' exons with alternative start codons, one of which seems to be used almost exclusively in the brain. We have also identified a third alternative 3' end of RAY1/ST7 that uses exons from ST7OT3. ST7OT3 spans from intron 10 to exon 14 of RAY1/ST7 and includes several exons. ST7OT4 has at least seven exons and is transcribed on the sense strand between RAY1/ST7 exon 1 and a tropomyosin-like sequence, TPM3L2. ST7OT1 overlaps with the RAY1/ST7 exon 1 and promoter. ST7OT2 spans from RAY1/ST7 intron 9 to intron 1, and has multiple isoforms. We screened the exons of RAY1/ST7 and ST7OT1-3 for sequence variants in 90 unrelated autism probands and identified several rare variants, including a Ile361Val substitution. Although these variants were not observed in a control population, it is unclear whether they contribute to the autistic phenotype. We postulate that the apparent noncoding genes at the RAY1/ST7 locus may be regulatory RNAs. The RAY1/ST7 may generate at least 18 possible isoforms, with many more arising if other sense-strand exons from ST7OT3 and ST7 OT4 are used in a selective and possibly tissue-specific manner.