Neurocognitive dysfunction and pharmacological intervention using guanfacine in a rhesus macaque model of self-injurious behavior

Scientific rationale for the use of α2A-adrenoceptor agonists in treating neuroinflammatory cognitive disorders

Neuroinflammatory disorders preferentially impair the higher cognitive and executive functions of the prefrontal cortex (PFC). This includes such challenging disorders as delirium, perioperative neurocognitive disorder, and the sustained cognitive deficits from "long-COVID" or traumatic brain injury. There are no FDA-approved treatments for these symptoms; thus, understanding their etiology is important for generating therapeutic strategies. The current review describes the molecular rationale for why PFC circuits are especially vulnerable to inflammation, and how α2A-adrenoceptor (α2A-AR) actions throughout the nervous and immune systems can benefit the circuits in PFC needed for higher cognition. The layer III circuits in the dorsolateral PFC (dlPFC) that generate and sustain the mental representations needed for higher cognition have unusual neurotransmission and neuromodulation. They are wholly dependent on NMDAR neurotransmission, with little AMPAR contribution, and thus are especially vulnerable to kynurenic acid inflammatory signaling which blocks NMDAR. Layer III dlPFC spines also have unusual neuromodulation, with cAMP magnification of calcium signaling in spines, which opens nearby potassium channels to rapidly weaken connectivity and reduce neuronal firing. This process must be tightly regulated, e.g. by mGluR3 or α2A-AR on spines, to prevent loss of firing. However, the production of GCPII inflammatory signaling reduces mGluR3 actions and markedly diminishes dlPFC network firing. Both basic and clinical studies show that α2A-AR agonists such as guanfacine can restore dlPFC network firing and cognitive function, through direct actions in the dlPFC, but also by reducing the activity of stress-related circuits, e.g. in the locus coeruleus and amygdala, and by having anti-inflammatory actions in the immune system. This information is particularly timely, as guanfacine is currently the focus of large clinical trials for the treatment of delirium, and in open label studies for the treatment of cognitive deficits from long-COVID.

Nonhuman primate abnormal behavior: Etiology, assessment, and treatment

Across captive settings, nonhuman primates may develop an array of abnormal behaviors including stereotypic and self-injurious behavior. Abnormal behavior can indicate a state of poor welfare, since it is often associated with a suboptimal environment. However, this may not always be the case as some behaviors can develop independently of any psychological distress, be triggered in environments known to promote welfare, and be part of an animal's coping mechanism. Furthermore, not all animals develop abnormal behavior, which has led researchers to assess risk factors that differentiate individuals in the display of these behaviors. Intrinsic risk factors that have been identified include the animal's species and genetics, age, sex, temperament, and clinical condition, while environmental risk factors include variables such as the animal's rearing, housing condition, husbandry procedures, and research experiences. To identify specific triggers and at-risk animals, the expression of abnormal behavior in captive nonhuman primates should be routinely addressed in a consistent manner by appropriately trained staff. Which behaviors to assess, what assessment methods to use, which primates to monitor, and the aims of data collection should all be identified before proceeding to an intervention and/or treatment. This article provides guidance for this process, by presenting an overview of known triggers and risk factors that should be considered, steps to design a comprehensive evaluation plan, and strategies that might be used for prevention or treatment. It also outlines the tools and processes for assessing and evaluating behavior in an appendix. This process will lead to a better understanding of abnormal behavior in captive primate colonies and ultimately to improved welfare.

Improving transparency-A call to include social housing information in biomedical research articles involving nonhuman primates

The social setting of animal subjects in the research environment has known effects on a variety of dependent measures used in biomedical research. Proper evaluation of the robustness of published research is dependent upon transparent, detailed, and accurate reporting of research methods, including the animals' social housing conditions. However, to date, most research articles utilizing nonhuman primates (NHPs) provide only partial data on this topic, hampering transparency, and reproducibility. Therefore, we call for the inclusion of information pertaining to the social aspects of the animals' housing conditions in publications involving NHPs to improve transparency. We argue that including this information in scientific publications is crucial for the interpretation of research findings in the appropriate context and for understanding unexplained variability in study findings. Finally, the inclusion of this information in publications will additionally familiarize scientists with how other researchers conducting similar studies are housing their animals and will encourage them to consider the implications of various housing conditions on their research outcomes.

Neuromodulation of prefrontal cortex cognitive function in primates: the powerful roles of monoamines and acetylcholine

The primate prefrontal cortex (PFC) subserves our highest order cognitive operations, and yet is tremendously dependent on a precise neurochemical environment for proper functioning. Depletion of noradrenaline and dopamine, or of acetylcholine from the dorsolateral PFC (dlPFC), is as devastating as removing the cortex itself, and serotonergic influences are also critical to proper functioning of the orbital and medial PFC. Most neuromodulators have a narrow inverted U dose response, which coordinates arousal state with cognitive state, and contributes to cognitive deficits with fatigue or uncontrollable stress. Studies in monkeys have revealed the molecular signaling mechanisms that govern the generation and modulation of mental representations by the dlPFC, allowing dynamic regulation of network strength, a process that requires tight regulation to prevent toxic actions, e.g., as occurs with advanced age. Brain imaging studies in humans have observed drug and genotype influences on a range of cognitive tasks and on PFC circuit functional connectivity, e.g., showing that catecholamines stabilize representations in a baseline-dependent manner. Research in monkeys has already led to new treatments for cognitive disorders in humans, encouraging future research in this important field.

A Rhesus Monkey Model of Non-suicidal Self-Injury

Non-suicidal self-injury (NSSI) is a type of behavioral pathology seen not only in a variety of clinical conditions but also among non-clinical populations, particularly adolescents and young adults. With the exception of rare genetic conditions that give rise to self-harming behaviors, the etiology of NSSI and the events that trigger specific episodes of this behavior remain poorly understood. This review presents the features of an important, extensively studied animal model of NSSI, namely spontaneously occurring self-injurious behavior (SIB) in rhesus macaque monkeys. We compare and contrast rhesus monkey SIB with NSSI with respect to form, prevalence rates, environmental and biological risk factors, behavioral correlates, proposed functions, and treatment modalities. Many parallels between rhesus monkey SIB and NSSI are demonstrated, which supports the validity of this animal model across several domains. Determining the etiology of spontaneously occurring SIB in monkeys, its underlying biological mechanisms, and which pharmacological agents are most effective for treating the disorder may aid in identifying potential risk factors for the occurrence of NSSI in humans and developing medications for severe cases that are resistant to conventional psychotherapeutic approaches.

Self-Injurious behavior in rhesus macaques: Issues and challenges

Some monkeys housed in research facilities develop abnormal behavior ranging from stereotypic to the more serious condition of self-injurious behavior (SIB). We initially sought to understand how and why monkeys engaged in SIB and more importantly why only a small percentage of laboratory monkeys, with seemingly similar housing and background, developed this disorder. Of particular importance was the recognition that different pathways might lead to SIB and that strong individual differences would affect the manifestation of this disorder and the response to treatment. We developed a comprehensive plan to identify effective treatment and prevention strategies. We started with characterizing the disorder in terms of prevalence and types of environments in which it was found. We then conducted observations on a cohort of SIB and control monkeys to identify conditions associated with SIB (e.g., disordered sleep) as well as clinical disease states and congenital defects that could be precipitating factors. We examined the environmental events that triggered episodes of SIB in monkeys with the disorder and evaluated three models that might explain the reinforcement contingencies associated with SIB, including tension reduction, self-stimulation, and social communication. Possible treatments for SIB such as environmental enrichment, social housing, and pharmacotherapy were tested by our group and others. To date, no single treatment has been found to abolish SIB, and each of these treatments is impacted by individual differences. To develop possible prevention strategies, we examined colony management and health records to find risk factors for SIB. These risk factors generalized to other facilities, and considerable effort was expended by all behavioral managers at these facilities to reduce early life stress exposure, to minimize the length of individual cage housing by emphasizing pair housing, and to reduce the possible stressfulness of various veterinary/medical procedures by implementing positive reinforcement training.

Brain PET Imaging: Value for Understanding the Pathophysiology of HIV-associated Neurocognitive Disorder (HAND)

PURPOSE OF REVIEW

The purpose of this review is to summarize recent developments in PET imaging of neuropathologies underlying HIV-associated neurocognitive dysfunction (HAND). We concentrate on the recent post antiretroviral era (ART), highlighting clinical and preclinical brain PET imaging studies.

RECENT FINDINGS

In the post ART era, PET imaging has been used to better understand perturbations of glucose metabolism, neuroinflammation, the function of neurotransmitter systems, and amyloid/tau protein deposition in the brains of HIV-infected patients and HIV animal models. Preclinical and translational findings from those studies shed a new light on the complex pathophysiology underlying HAND. The molecular imaging capabilities of PET in neuro-HIV are great complements for structural imaging modalities. Recent and future PET imaging studies can improve our understanding of neuro-HIV and provide biomarkers of disease progress that could be used as surrogate endpoints in the evaluation of the effectiveness of potential neuroprotective therapies.

Disabling the Gβγ-SNARE interaction disrupts GPCR-mediated presynaptic inhibition, leading to physiological and behavioral phenotypes

G protein-coupled receptors (GPCRs) that couple to G_i/o proteins modulate neurotransmission presynaptically by inhibiting exocytosis. Release of Gβγ subunits from activated G proteins decreases the activity of voltage-gated Ca²⁺ channels (VGCCs), decreasing excitability. A less understood Gβγ-mediated mechanism downstream of Ca²⁺ entry is the binding of Gβγ to SNARE complexes, which facilitate the fusion of vesicles with the cell plasma membrane in exocytosis. Here, we generated mice expressing a form of the SNARE protein SNAP25 with premature truncation of the C terminus and that were therefore partially deficient in this interaction. SNAP25Δ3 homozygote mice exhibited normal presynaptic inhibition by GABA_B receptors, which inhibit VGCCs, but defective presynaptic inhibition by receptors that work directly on the SNARE complex, such as 5-hydroxytryptamine (serotonin) 5-HT_1b receptors and adrenergic α_2a receptors. Simultaneously stimulating receptors that act through both mechanisms showed synergistic inhibitory effects. SNAP25Δ3 homozygote mice had various behavioral phenotypes, including increased stress-induced hyperthermia, defective spatial learning, impaired gait, and supraspinal nociception. These data suggest that the inhibition of exocytosis by G_i/o-coupled GPCRs through the Gβγ-SNARE interaction is a crucial component of numerous physiological and behavioral processes.

The Effect of Treatment with Guanfacine, an Alpha2 Adrenergic Agonist, on Dopaminergic Tone in Tobacco Smokers: An [11C]FLB457 PET Study

Guanfacine, a noradrenergic alpha2a agonist, reduced tobacco smoking in a 4-week trial and in animal models has been shown to reduce cortical dopamine release, which is critically involved in the reinforcing effect of tobacco smoking. We measured amphetamine-induced extrastriatal dopamine release before and after treatment with guanfacine with [11C]FLB457, a dopamine D2/D3 receptor radiotracer, and positron emission tomography (PET). Sixteen tobacco smokers had one set of [11C]FLB457 PET scans on the same day, one before and one at 2.5-3 h after amphetamine (0.4-0.5 mg/kg, PO). A subset (n=12) then underwent guanfacine treatment (3 mg/day for 3 weeks) and the set of scans were repeated. [11C]FLB457-binding potential (BPND) was measured pre- and post amphetamine in extrastriatal brain regions. The fractional change in BPND after vs before amphetamine (Δ BPND) is an indirect measure of DA release and was compared between the untreated and guanfacine-treated conditions. Guanfacine treatment attenuated amphetamine-induced DA release; however, the change was due to a global 8% decrease in baseline BPND from the untreated to the guanfacine-treated condition. Chronic guanfacine treatment reduced [11C]FLB457 BPND in tobacco smokers, suggesting an increase in dopaminergic tone. Guanfacine-induced normalization of dopamine signaling may be an important mesocortical mechanism contributing to its ability to aid in tobacco smoking cessation.

Rhesus macaques (Macaca mulatta) displaying self-injurious behavior show more sleep disruption than controls

Self-injurious behavior (SIB) is a pathology observed in both humans and animals. In humans, SIB has been linked to various mental health conditions that are also associated with significant sleep disruption. In rhesus macaques, SIB consists of self-directed biting which can range from mild skin abrasions to wounds requiring veterinary care. However, only one study suggests possible sleep disruption in macaques with SIB. We evaluated sleep disruption using a noninvasive system (infra-red camera and a video surveillance program) which created videos for every movement over the nighttime hours. Nighttime activity was examined in 13 macaques (three females) of which six were classified as having SIB (one female). Each monkey was studied for a total of 6 nights spanning a period of 4 months. Measures included total movement time (TMT), time moving in the first hour (HR1), time moving in the last hour (HR11), and number of videos <10 secs, ≥10 secs, and ≥30 secs in length. Overall, SIB monkeys had higher TMT (p < 0.01), higher HR1 (p<0.001), and generated more videos ≥10 secs (p < 0.01) and ≥30 secs (p < 0.01). Thus, SIB monkeys showed significant sleep disruption. A four-fold difference between SIB and control monkeys in the ≥30 secs videos revealed many more significant awakenings in the SIB group. Overall higher nighttime activity, in the first hour but not in the last hour, is consistent with sleep-onset insomnia in humans. Whether increased nighttime activity contributes to the SIB condition during the day or, conversely, SIB causes higher nighttime activity remains undetermined.

Ranking Cognitive Flexibility in a Group Setting of Rhesus Monkeys with a Set-Shifting Procedure

Attentional set-shifting ability is an executive function underling cognitive flexibility in humans and animals. In humans, this function is typically observed during a single experimental session where dimensions of playing cards are used to measure flexibility in the face of changing rules for reinforcement (i.e., the Wisconsin Card Sorting Test (WCST)). In laboratory animals, particularly non-human primates, variants of the WCST involve extensive training and testing on a series of dimensional discriminations, usually in social isolation. In the present study, a novel experimental approach was used to assess attentional set-shifting simultaneously in 12 rhesus monkeys. Specifically, monkeys living in individual cages but in the same room were trained at the same time each day in a set-shifting task in the same housing environment. As opposed to the previous studies, each daily session began with a simple single-dimension discrimination regardless of the animal’s performance on the previous session. A total of eight increasingly difficult, discriminations (sets) were possible in each daily 45 min session. Correct responses were reinforced under a second-order schedule of flavored food pellet delivery, and criteria for completing a set was 12 correct trials out of a running total of 15 trials. Monkeys progressed through the sets at their own pace and abilities. The results demonstrate that all 12 monkeys acquired the simple discrimination (the first set), but individual differences in the ability to progress through all eight sets were apparent. A performance index (PI) that encompassed progression through the sets, errors and session duration was calculated and used to rank each monkey’s performance in relation to each other. Overall, this version of a set-shifting task results in an efficient assessment of reliable differences in cognitive flexibility in a group of monkeys.

Guanfacine Extended Release: A New Pharmacological Treatment Option in Europe

Children/adolescents with attention-deficit/hyperactivity disorder (ADHD) may have a poor or inadequate response to psychostimulants or be unable to tolerate their side-effects; furthermore, stimulants may be inappropriate because of co-existing conditions. Only one non-stimulant ADHD pharmacotherapy, the noradrenaline transporter inhibitor atomoxetine, is currently approved for use in Europe. We review recent advances in understanding of the pathophysiology of ADHD with a focus on the roles of catecholamine receptors in context of the α2A-adrenergic receptor agonist guanfacine extended release (GXR), a new non-stimulant treatment option in Europe. Neuroimaging studies of children/adolescents with ADHD show impaired brain maturation, and structural and functional anomalies in brain regions and networks. Neurobiological studies in ADHD and medication response patterns support involvement of monoaminergic neurotransmitters (primarily dopamine and noradrenaline). Guanfacine is a selective α2A-adrenergic receptor agonist that has been shown to improve prefrontal cortical cognitive function, including working memory. The hypothesized mode of action of guanfacine centres on direct stimulation of post-synaptic α2A-adrenergic receptors to enhance noradrenaline neurotransmission. Preclinical data suggest that guanfacine also influences dendritic spine growth and maturation. Clinical trials have demonstrated the efficacy of GXR in ADHD, and it is approved as monotherapy or adjunctive therapy to stimulants in Canada and the USA (for children and adolescents). GXR was approved recently in Europe for the treatment of ADHD in children and adolescents for whom stimulants are not suitable, not tolerated or have been shown to be ineffective. GXR may provide particular benefit for children/adolescents who have specific co-morbidities such as chronic tic disorders or oppositional defiant disorder (or oppositional symptoms) that have failed to respond to first-line treatment options.

Rhesus macaques (Macaca mulatta) with self-injurious behavior show less behavioral anxiety during the human intruder test

Self-injurious behavior (SIB) has been linked to anxiety in the human literature, but relatively few studies have explored this link in rhesus macaques. A widely used behavioral assessment of anxiety, the human intruder test (HIT), employs the mildly stressful stimulus of an unfamiliar experimenter to assess anxious behavior in macaques. The HIT was conducted on 59 (20 male) laboratory housed rhesus macaques, 30 with a record of SIB (10 male). If monkeys with SIB have a more anxious phenotype, they should show stronger reactions to the HIT. However, contrary to our predictions, monkeys with SIB did not show higher levels of anxious behavior compared to controls. They spent significantly less time showing anxious behavior and displayed little aggression in response to the stare of the intruder. SIB and control monkeys did not differ in a range score (number of unique behaviors expressed per phase); however, SIB monkeys had a lower change score (total number of behaviors expressed including repetitions) than controls. In general, monkeys that paced regardless of SIB status, showed a reduction in pacing when the intruder entered the room. Possible explanations for the failure of SIB monkeys to show increased anxiety in the HIT include greater exposure of SIB monkeys to unfamiliar humans because of their condition, evidence for a subtype of SIB which is not anxiety related, and/or the presence of comorbid depressive-like symptoms. Am. J. Primatol. 79:e22569, 2017. © 2016 Wiley Periodicals, Inc.