The dopamine D1 receptor agonist SKF-82958 effectively increases eye blinking count in common marmosets

Effects of DPTQ, a novel positive allosteric modulator of the dopamine D1 receptor, on spontaneous eye blink rate and spatial working memory in the nonhuman primate

RATIONALE

Dopamine (DA) signaling through the D1 receptor has been shown to be integral to multiple aspects of cognition, including the core process of working memory. The discovery of positive allosteric modulators (PAMs) of the D1 receptor has enabled treatment modalities that may have alternative benefits to orthosteric D1 agonists arising from a synergism of action with functional D1 receptor signaling.

OBJECTIVES

To investigate this potential, we have studied the effects of the novel D1 PAM DPTQ on a spatial delayed response working memory task in the rhesus monkey. Initial studies indicated that DPTQ binds to primate D1R with high affinity and selectivity and elevates spontaneous eye blink rate in rhesus monkeys in a dose-dependent manner consistent with plasma ligand exposures and central D1activation.

RESULTS

Based on those results, DPTQ was tested at 2.5 mg/kg IM in the working memory task. No acute effect was observed 1 h after dosing, but performance was impaired 48 h later. Remarkably, this deficit was immediately followed by a significant enhancement in cognition over the next 3 days. In a second experiment in which DPTQ was administered on days 1 and 5, the early impairment was smaller and did not reach statistical significance, but statistically significant enhancement of performance was observed over the following week. Lower doses of 0.1 and 1.0 mg/kg were also capable of producing this protracted enhancement without inducing any transient impairment.

CONCLUSIONS

DPTQ exemplifies a class of D1PAMs that may be capable of providing long-term improvements in working memory.

Ecopipam for Tourette Syndrome: A Randomized Trial

BACKGROUND AND OBJECTIVES

All US Food and Drug Administration-approved medications for Tourette syndrome are antipsychotics, and their use is limited by the risk of weight gain, metabolic changes, and drug-induced movement disorders. Several small trials suggest that ecopipam, a first-in-class, selective dopamine 1 receptor antagonist, reduces tics with a low risk for these adverse events. This trial sought to further evaluate the efficacy, safety, and tolerability of ecopipam in children and adolescents with moderate to severe Tourette syndrome.

METHODS

This was a multicenter, randomized, double-blind, placebo-controlled, phase 2b trial. Subjects aged ≥6 to <18 years with a baseline Yale Global Tic Severity Score Total Tic Score of ≥20 were randomly assigned 1:1 to ecopipam (n = 76) or placebo (n = 77). The primary endpoint was mean change over 12 weeks in the Yale Global Tic Severity Score Total Tic Score. The Clinical Global Impression of Tourette Syndrome Severity was the secondary endpoint. Safety and tolerability were evaluated at each study visit.

RESULTS

Total tic scores were significantly reduced from baseline to 12 weeks in the ecopipam group compared with placebo (least squares mean differences -3.44, 95% confidence interval -6.09 to -0.79, P = .01). Improvement in Clinical Global Impression of Tourette Syndrome Severity was also greater in the ecopipam group (P = .03). More weight gain was seen in subjects assigned to placebo. No metabolic or electrocardiogram changes were identified. Headache (15.8%), insomnia (14.5%), fatigue (7.9%), and somnolence (7.9%) were the most common adverse events.

CONCLUSIONS

Among children and adolescents with TS, ecopipam reduces tics to a greater extent than placebo, without observable evidence of common antipsychotic-associated side effects.

Effect of dopamine receptor-related compounds on naive common marmosets for auditory steady state response

Abnormalities of auditory steady state responses (ASSR) and the effects of antipsychotic drugs on ASSR have been investigated in patients with schizophrenia. It is presumed that effects of drugs do not directly reflect on ASSR, because of ASSR abnormalities associated with schizophrenia. Therefore, to investigate the direct effect of drugs on ASSR, we established an ASSR evaluation system for common marmosets in a naïve state. Dopamine D1 receptor stimulation (SKF-81297, 2 mg/kg, intraperitoneal) significantly increased evoked power (EP) at 40 Hz. The phase locking factor (PLF) was increased significantly at 20, 30, 40, and 80 Hz. However, the administration of a dopamine D1 receptor antagonist (SCH-39166, 0.3 mg/kg intraperitoneal) resulted in a significant decrease in EP and PLF at 30 Hz. Dopamine D2 receptor stimulation (quinpirole, 1 mg/kg, intramuscular) tended to increase EP and induced power (IP) at all frequencies, and a significant difference was observed at 30 Hz IP. There was no change in PLF at all frequencies. In addition, dopamine D2 receptor blockade (raclopride, 3 mg/kg, intraperitoneal) reduced EP and PLF at 30 Hz. Subcutaneous administration of the serotonin dopamine antagonist, risperidone (0.3 mg/kg), tended to increase IP and decrease PLF, but not significantly. Taken together, it is possible to compare the differences in the mode of action of drugs on ASSR using naïve non-human primates.

The confounding effects of eye blinking on pupillometry, and their remedy

Pupillometry, thanks to its strong relationship with cognitive factors and recent advancements in measuring techniques, has become popular among cognitive or neural scientists as a tool for studying the physiological processes involved in mental or neural processes. Despite this growing popularity of pupillometry, the methodological understanding of pupillometry is limited, especially regarding potential factors that may threaten pupillary measurements' validity. Eye blinking can be a factor because it frequently occurs in a manner dependent on many cognitive components and induces a pulse-like pupillary change consisting of constriction and dilation with substantive magnitude and length. We set out to characterize the basic properties of this "blink-locked pupillary response (BPR)," including the shape and magnitude of BPR and their variability across subjects and blinks, as the first step of studying the confounding nature of eye blinking. Then, we demonstrated how the dependency of eye blinking on cognitive factors could confound, via BPR, the pupillary responses that are supposed to reflect the cognitive states of interest. By building a statistical model of how the confounding effects of eye blinking occur, we proposed a probabilistic-inference algorithm of de-confounding raw pupillary measurements and showed that the proposed algorithm selectively removed BPR and enhanced the statistical power of pupillometry experiments. Our findings call for attention to the presence and confounding nature of BPR in pupillometry. The algorithm we developed here can be used as an effective remedy for the confounding effects of BPR on pupillometry.

The Effects of Eating a High Fat Diet on Sensitivity of Male and Female Rats to Methamphetamine and Dopamine D1 Receptor Agonist SKF 82958

Rats eating high fat chow are more sensitive to the behavioral effects of dopaminergic drugs, including methamphetamine and the dopamine D2/D3 receptor agonist quinpirole, than rats eating standard chow. However, limited work has explored possible sex differences regarding the impact of diet on drug sensitivity. It is also unknown whether eating high fat chow enhances sensitivity of rats to other dopamine (e.g., D1) receptor agonists. To explore these possibilities, male and female Sprague-Dawley rats eating standard laboratory chow (17% kcal from fat) or high fat chow (60% kcal from fat) were tested once per week for 6 weeks with dopamine D1 receptor agonist SKF 82958 (0.01-3.2 mg/kg) or methamphetamine (0.1-3.2 mg/kg) using cumulative dosing procedures. Eating high fat chow increased sensitivity of male and female rats to methamphetamine-induced locomotion; however, only female rats eating high fat chow were more sensitive to SKF 82958-induced locomotion. SKF 82958-induced eye blinking was also marginally, although not significantly, enhanced among female rats eating high fat chow, but not males. Further, although dopamine D2 receptor expression was significantly increased for SKF 82958-treated rats eating high fat chow regardless of sex, no differences were observed in dopamine D1 receptor expression. Taken together, the present study suggests that although eating high fat chow enhances sensitivity of both sexes to dopaminergic drugs, the mechanism driving this effect might be different for males versus females. These data further demonstrate the importance of studying both sexes simultaneously when investigating factors that influence drug sensitivity. SIGNIFICANCE STATEMENT: Although it is known that diet can impact sensitivity to some dopaminergic drugs, sex differences regarding this effect are not well characterized. This report demonstrates that eating a high fat diet enhances sensitivity to methamphetamine, regardless of sex; however, sensitivity to dopamine D1 receptor agonist SKF 82958 is increased only among females eating high fat chow, but not males. This suggests that the mechanism(s) driving diet-induced changes in drug sensitivity might be different between sexes.

Spontaneous eye blink rate and dopamine synthesis capacity: preliminary evidence for an absence of positive correlation

Dopamine is central to a number of cognitive functions and brain disorders. Given the cost of neurochemical imaging in humans, behavioural proxy measures of dopamine have gained in popularity in the past decade, such as spontaneous eye blink rate (sEBR). Increased sEBR is commonly associated with increased dopamine function based on pharmacological evidence and patient studies. Yet, this hypothesis has not been validated using in vivo measures of dopamine function in humans. To fill this gap, we measured sEBR and striatal dopamine synthesis capacity using [¹⁸F]DOPA PET in 20 participants (nine healthy individuals and 11 pathological gamblers). Our results, based on frequentist and Bayesian statistics, as well as region‐of‐interest and voxel‐wise analyses, argue against a positive relationship between sEBR and striatal dopamine synthesis capacity. They show that, if anything, the evidence is in favour of a negative relationship. These results, which complement findings from a recent study that failed to observe a relationship between sEBR and dopamine D2 receptor availability, suggest that caution and nuance are warranted when interpreting sEBR in terms of a proxy measure of striatal dopamine.

Spontaneous Eye Blink Rate (EBR) Is Uncorrelated with Dopamine D2 Receptor Availability and Unmodulated by Dopamine Agonism in Healthy Adults

Spontaneous eye blink rate (EBR) has been proposed as a noninvasive, inexpensive marker of dopamine functioning. Support for a relation between EBR and dopamine function comes from observations that EBR is altered in populations with dopamine dysfunction and EBR changes under a dopaminergic manipulation. However, the evidence across the literature is inconsistent and incomplete. A direct correlation between EBR and dopamine function has so far been observed only in nonhuman animals. Given significant interest in using EBR as a proxy for dopamine function, this study aimed to verify a direct association in healthy, human adults. Here we measured EBR in healthy human subjects whose dopamine D2 receptor (DRD2) availability was assessed with positron emission tomography (PET)-[18F]fallypride to examine the predictive power of EBR for DRD2 availability. Effects of the dopamine agonist bromocriptine on EBR also were examined to determine the responsiveness of EBR to dopaminergic stimulation and, in light of the hypothesized inverted-U profile of dopamine effects, the role of DRD2 availability in EBR responsivity to bromocriptine. Results from 20 subjects (age 33.6 ± 7.6 years, 9F) showed no relation between EBR and DRD2 availability. EBR also was not responsive to dopaminergic stimulation by bromocriptine, and individual differences in DRD2 availability did not modulate EBR responsivity to bromocriptine. Given that EBR is hypothesized to be particularly sensitive to DRD2 function, these findings suggest caution in using EBR as a proxy for dopamine function in healthy humans.

A Study of Deep CNN-Based Classification of Open and Closed Eyes Using a Visible Light Camera Sensor

The necessity for the classification of open and closed eyes is increasing in various fields, including analysis of eye fatigue in 3D TVs, analysis of the psychological states of test subjects, and eye status tracking-based driver drowsiness detection. Previous studies have used various methods to distinguish between open and closed eyes, such as classifiers based on the features obtained from image binarization, edge operators, or texture analysis. However, when it comes to eye images with different lighting conditions and resolutions, it can be difficult to find an optimal threshold for image binarization or optimal filters for edge and texture extraction. In order to address this issue, we propose a method to classify open and closed eye images with different conditions, acquired by a visible light camera, using a deep residual convolutional neural network. After conducting performance analysis on both self-collected and open databases, we have determined that the classification accuracy of the proposed method is superior to that of existing methods.

Beyond eye gaze: What else can eyetracking reveal about cognition and cognitive development?

This review provides an introduction to two eyetracking measures that can be used to study cognitive development and plasticity: pupil dilation and spontaneous blink rate. We begin by outlining the rich history of gaze analysis, which can reveal the current focus of attention as well as cognitive strategies. We then turn to the two lesser-utilized ocular measures. Pupil dilation is modulated by the brain's locus coeruleus-norepinephrine system, which controls physiological arousal and attention, and has been used as a measure of subjective task difficulty, mental effort, and neural gain. Spontaneous eyeblink rate correlates with levels of dopamine in the central nervous system, and can reveal processes underlying learning and goal-directed behavior. Taken together, gaze, pupil dilation, and blink rate are three non-invasive and complementary measures of cognition with high temporal resolution and well-understood neural foundations. Here we review the neural foundations of pupil dilation and blink rate, provide examples of their usage, describe analytic methods and methodological considerations, and discuss their potential for research on learning, cognitive development, and plasticity.

Spontaneous eye blink rate as predictor of dopamine-related cognitive function-A review

An extensive body of research suggests the spontaneous eye blink rate (EBR) is a non-invasive indirect marker of central dopamine (DA) function, with higher EBR predicting higher DA function. In the present review we provide a comprehensive overview of this literature. We broadly divide the available research in studies that aim to disentangle the dopaminergic underpinnings of EBR, investigate its utility in diagnosis of DA-related disorders and responsivity to drug treatment, and, lastly, investigate EBR as predictor of individual differences in DA-related cognitive performance. We conclude (i) EBR can reflect both DA receptor subtype D1 and D2 activity, although baseline EBR might be most strongly related to the latter, (ii) EBR can predict hypo- and hyperdopaminergic activity as well as normalization of this activity following treatment, and (iii) EBR can reliably predict individual differences in performance on many cognitive tasks, in particular those related to reward-driven behavior and cognitive flexibility. In sum, this review establishes EBR as a useful predictor of DA in a wide variety of contexts.

The atypical antipsychotic blonanserin reverses (+)-PD-128907- and ketamine-induced deficit in executive function in common marmosets

Antagonism of the dopamine D3 receptor is considered a promising strategy for the treatment of cognitive impairment associated with schizophrenia. We have previously reported that the atypical antipsychotic blonanserin, a dopamine D2/D3 and serotonin 5-HT2A receptor antagonist, highly occupies dopamine D3 receptors at its antipsychotic dose range in rats. In the present study, we evaluated the effects of blonanserin on executive function in common marmosets using the object retrieval with detour (ORD) task. The dopamine D3 receptor-preferring agonist (+)-PD-128907 at 1mg/kg decreased success rate in the difficult trial, but not in the easy trial. Since the difference between the two trials is only cognitive demand, our findings indicate that excess activation of dopamine D3 receptors impairs executive function in common marmosets. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by (+)-PD-128907 in the difficult trial. This finding indicates that blonanserin has beneficial effect on executive function deficit induced by activation of the dopamine D3 receptor in common marmosets. Next, and based on the glutamatergic hypothesis of schizophrenia, the common marmosets were treated with the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine. Ketamine at sub-anesthetic doses decreased success rate in the difficult trial, but not in the easy trial. Blonanserin at 0.1mg/kg reversed the decrease in success rate induced by ketamine in the difficult trial. The findings of this study suggest that blonanserin might have beneficial effect on executive dysfunction in patients with schizophrenia.