Super-stereotypy II: enhancement of a complex movement sequence by intraventricular dopamine D1 agonists

Genetic disruption of dopamine β-hydroxylase dysregulates innate responses to predator odor in mice

In rodents, exposure to predator odors such as cat urine acts as a severe stressor that engages innate defensive behaviors critical for survival in the wild. The neurotransmitters norepinephrine (NE) and dopamine (DA) modulate anxiety and predator odor responses, and we have shown previously that dopamine β-hydroxylase knockout (Dbh -/-), which reduces NE and increases DA in mouse noradrenergic neurons, disrupts innate behaviors in response to mild stressors such as novelty. We examined the consequences of Dbh knockout on responses to predator odor (bobcat urine) and compared them to Dbh-competent littermate controls. Over the first 10 min of predator odor exposure, controls exhibited robust defensive burying behavior, whereas Dbh -/- mice showed high levels of grooming. Defensive burying was potently suppressed in controls by drugs that reduce NE transmission, while excessive grooming in Dbh -/- mice was blocked by DA receptor antagonism. In response to a cotton square scented with a novel "neutral" odor (lavender), most control mice shredded the material, built a nest, and fell asleep within 90 min. Dbh -/- mice failed to shred the lavender-scented nestlet, but still fell asleep. In contrast, controls sustained high levels of arousal throughout the predator odor test and did not build nests, while Dbh -/- mice were asleep by the 90-min time point, often in shredded bobcat urine-soaked nesting material. Compared with controls exposed to predator odor, Dbh -/- mice demonstrated decreased c-fos induction in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis, but increased c-fos in the locus coeruleus and medial amygdala. These data indicate that relative ratios of central NE and DA signaling coordinate the type and valence of responses to predator odor.

Computational insights on asymmetrical D1 and D2 receptor-mediated chunking: implications for OCD and Schizophrenia

Repetitive thoughts and motor programs including perseveration are bridge symptoms characteristic of obsessive compulsive disorder (OCD), schizophrenia and in the co-morbid overlap of these conditions. The above pathologies are sensitive to altered activation and kinetics of dopamine D 1 and D 2 receptors that differently influence sequence learning and recall. Recognizing start and stop elements of motor and cognitive behaviors has crucial importance. During chunking, frequent components of temporal strings are concatenated into single units. We extended a published computational model (Asabuki et al. 2018), where two populations of neurons are connected and simulated in a reservoir computing framework. These neural pools were adopted to represent D1 and D2 striatal neuronal populations. We investigated how specific neural and striatal circuit parameters can influence start/stop signaling and found that asymmetric intra-network connection probabilities, synaptic weights and differential time constants may contribute to signaling of start/stop elements within learned sequences. Asymmetric coupling between the striatal D 1 and D 2 neural populations was also demonstrated to be beneficial. Our modeling results predict that dynamical differences between the two dopaminergic striatal populations and the interaction between them may play complementary roles in chunk boundary signaling. Start and stop dichotomies can arise from the larger circuit dynamics as well, since neural and intra-striatal connections only partially support a clear division of labor.

Genetic disruption of dopamine β-hydroxylase dysregulates innate responses to predator odor in mice

In rodents, exposure to predator odors such as cat urine acts as a severe stressor that engages innate defensive behaviors critical for survival in the wild. The neurotransmitters norepinephrine (NE) and dopamine (DA) modulate anxiety and predator odor responses, and we have shown previously that dopamine β-hydroxylase knockout (Dbh -/-), which reduces NE and increases DA in mouse noradrenergic neurons, disrupts innate behaviors in response to mild stressors such as novelty. We examined the consequences of Dbh knockout (Dbh -/-) on responses to predator odor (bobcat urine) and compared them to Dbh-competent littermate controls. Over the first 10 min of predator odor exposure, controls exhibited robust defensive burying behavior, whereas Dbh -/- mice showed high levels of grooming. Defensive burying was potently suppressed in controls by drugs that reduce NE transmission, while excessive grooming in Dbh -/- mice was blocked by DA receptor antagonism. In response to a cotton square scented with a novel "neutral" odor (lavender), most control mice shredded the material, built a nest, and fell asleep within 90 min. Dbh -/- mice failed to shred the lavender-scented nestlet, but still fell asleep. In contrast, controls sustained high levels of arousal throughout the predator odor test and did not build nests, while Dbh -/- mice were asleep by the 90-min time point, often in shredded bobcat urine-soaked nesting material. Compared with controls exposed to predator odor, Dbh -/- mice demonstrated decreased c-fos induction in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis, but increased c-fos in the locus coeruleus and medial amygdala. These data indicate that relative ratios of central NE and DA signaling coordinate the type and valence of responses to predator odor.

Influence of the dose of ketamine used on schizophrenia-like symptoms in mice: A correlation study with TH, GAD67, and PPAR-γ

Schizophrenia is a chronic, debilitating mental illness that has not yet been completely understood. In this study, we aimed to investigate the effects of different doses of ketamine, a non-competitive NMDA receptor antagonist, on the positive- and negative-like symptoms of schizophrenia. We also explored whether these effects are related to changes in the immunoreactivity of GAD67, TH, and PPAR-γ in brain structures. To conduct the study, male mice received ketamine (20-40 mg/kg) or its vehicle (0.9 % NaCl) intraperitoneally for 14 consecutive days. We quantified stereotyped behavior, the time of immobility in the forced swimming test (FST), and locomotor activity after 7 or 14 days. In addition, we performed ex vivo analysis of the immunoreactivity of GAD, TH, and PPAR-γ, in brain tissues after 14 days. The results showed that ketamine administration for 14 days increased the grooming time in the nose region at all tested doses. It also increased immobility in the FST at 30 mg/kg doses and decreased the number of rearing cycles during stereotyped behavior at 40 mg/kg. These behavioral effects were not associated with changes in locomotor activity. We did not observe any significant alterations regarding the immunoreactivity of brain proteins. However, we found that GAD and TH were positively correlated with the number of rearing during the stereotyped behavior at doses of 20 and 30 mg/kg ketamine, respectively. GAD was positively correlated with the number of rearing in the open field test at a dose of 20 mg/kg. TH was inversely correlated with immobility time in the FST at a dose of 30 mg/kg. PPAR-γ was inversely correlated with the number of bouts of stereotyped behavior at a dose of 40 mg/kg of ketamine. In conclusion, the behavioral alterations induced by ketamine in positive-like symptoms were reproduced with all doses tested and appear to depend on the modulatory effects of TH, GAD, and PPAR-γ. Conversely, negative-like symptoms were associated with a specific dose of ketamine.

A closer look to neural pathways and psychopharmacology of obsessive compulsive disorder

The intricate neural pathways involved in obsessive-compulsive disorder (OCD) affect areas of our brain that control executive functioning, organization, and planning. OCD is a chronic condition that can be debilitating, afflicting millions of people worldwide. The lifetime prevalence of OCD in the US is 2.3%. OCD is predominantly characterized by obsessions consisting of intrusive and unwanted thoughts, often with impulses that are strongly associated with anxiety. Compulsions with OCD encompass repetitive behaviors or mental acts to satisfy their afflicted obsessions or impulses. While these factors can be unique to each individual, it has been widely established that the etiology of OCD is complex as it relates to neuronal pathways, psychopharmacology, and brain chemistry involved and warrants further exploration.

Spinophilin Limits Metabotropic Glutamate Receptor 5 Scaffolding to the Postsynaptic Density and Cell Type Specifically Mediates Excessive Grooming

BACKGROUND

Grooming dysfunction is a hallmark of the obsessive-compulsive spectrum disorder trichotillomania. Numerous preclinical studies have utilized SAPAP3-deficient mice for understanding the neurobiology of repetitive grooming, suggesting that excessive grooming is caused by increased metabotropic glutamate receptor 5 (mGluR5) activity in striatal direct- and indirect-pathway medium spiny neurons (MSNs). However, the MSN subtype-specific signaling mechanisms that mediate mGluR5-dependent adaptations underlying excessive grooming are not fully understood. Here, we investigated the MSN subtype-specific roles of the striatal signaling hub protein spinophilin in mediating repetitive motor dysfunction associated with mGluR5 function.

METHODS

Quantitative proteomics and immunoblotting were utilized to identify how spinophilin impacts mGluR5 phosphorylation and protein interaction changes. Plasticity and repetitive motor dysfunction associated with mGluR5 action were measured using our novel conditional spinophilin mouse model in which spinophilin was knocked out from striatal direct-pathway MSNs and/or indirect-pathway MSNs.

RESULTS

Loss of spinophilin only in indirect-pathway MSNs decreased performance of a novel motor repertoire, but loss of spinophilin in either MSN subtype abrogated striatal plasticity associated with mGluR5 function and prevented excessive grooming caused by SAPAP3 knockout mice or treatment with the mGluR5-specific positive allosteric modulator VU0360172 without impacting locomotion-relevant behavior. Biochemically, we determined that the spinophilin-mGluR5 interaction correlates with grooming behavior and that loss of spinophilin shifts mGluR5 interactions from lipid raft-associated proteins toward postsynaptic density proteins implicated in psychiatric disorders.

CONCLUSIONS

These results identify spinophilin as a novel striatal signaling hub molecule in MSNs that cell subtype specifically mediates behavioral, functional, and molecular adaptations associated with repetitive motor dysfunction in psychiatric disorders.

Acute Hypobaric Hypoxia Exposure Causes Neurobehavioral Impairments in Rats: Role of Brain Catecholamines and Tetrahydrobiopterin Alterations

Hypoxia is a state in which the body or a specific part of the body is deprived of adequate oxygen supply at the tissue level. Sojourners involved in different activities at high altitudes (> 2500 m) face hypobaric hypoxia (HH) due to low oxygen in the atmosphere. HH is an example of generalized hypoxia, where the homeostasis of the entire body of an organism is affected and results in neurochemical changes. It is known that lower O₂ levels affect catecholamines (CA), severely impairing cognitive and locomotor behavior. However, there is less evidence on the effect of HH-mediated alteration in brain Tetrahydrobiopterin (BH4) levels and its role in neurobehavioral impairments. Hence, this study aimed to shed light on the effect of acute HH on CA and BH4 levels with its neurobehavioral impact on Wistar rat models. After HH exposure, significant alteration of the CA levels in the discrete brain regions, viz., frontal cortex, hippocampus, midbrain, and cerebellum was observed. HH exposure significantly reduced spontaneous motor activity, motor coordination, and spatial memory. The present study suggests that the HH-induced behavioral changes might be related to the alteration of the expression pattern of CA and BH4-related genes and proteins in different rat brain regions. Overall, this study provides novel insights into the role of BH4 and CA in HH-induced neurobehavioral impairments.

In vivo effects of exposure to Golden trumpet Handroanthus chrysotrichus in mice

The Golden trumpet Handroanthus chrysotrichus is a tree that presents beneficial health properties against various diseases. Thus, this study aims to verify the toxicity of H. chrysotrichus bark extract, observing the effects of exposure to this extract in mice. For this, mice were separated in groups: saline (sterile solution .9%); H. chrysotrichus crude extract (HCCE) 10; HCCE 50, and HCCE 100 mg. kg^-1 (p.o.). We analyzed HCCE effects on acute (single exposure) and subchronic protocol (14 days exposure). After both exposures, acute, and subchronic, we collected samples from blood, brain, liver, and kidney tissues for biochemical evaluation. In addition, after subchronic exposure, we performed behavioral tests. Acute exposure caused an increase of lipid peroxidation in liver tissue. Moreover, we observed a significant carbonyl increase in liver and brain tissues from HCCE 50 mg. kg^-1. Kidneys presented carbonyl increase in mice treated with the highest concentration. Besides, creatinine increased in the group of the acute exposure at HCCE 100 mg. kg^-1. Total leukocyte count decreased in all concentrations tested. Sub-chronic exposure at HCCE 100 mg. kg^-1 caused a decrease in the number of crossing and an increase in its self-grooming frequency in the open field test. In this exposure, the brain and liver had a significant increase in carbonyl levels in all concentrations. We concluded that H. chrysotrichus cause behavioral and biochemical alterations in mice. HCCE primary targets seem to be the liver, kidneys, and white cells.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

Yawning and Penile Erection Frequencies Are Resilient to Maternal Care Manipulation in the High-Yawning Subline of Sprague-Dawley Rats

Yawning is a stereotyped behavioral pattern characterized by wide opening of the mouth associated with deep inspiration followed by short expiration. All vertebrate species yawn, but with low frequencies. We obtained two sublines of Sprague–Dawley (SD) rats by a strict inbreeding process: one with a high-yawning frequency (HY) of 20 yawns/h, which is one order of magnitude higher with respect to the low-yawning frequency (LY) subline, with 2 yawns/h. Outbred SD rats had a yawning frequency of 1 yawn/h. HY dams had a different organization of maternal care with respect to that displayed by LY and SD dams because HY dams constructed lower quality nests and had more re-retrieving and atypical retrieving. The aim of this study was to analyze the changes in maternal care using in- and cross-fostering between the sublines and SD dams and to measure spontaneous and dopaminergic-induced yawning, penile erections, grooming and scratching bouts. We also measured the expression of dopamine D₂ receptors in the striatum using Western blot analysis. Our results showed that HY male rats reared by SD or LY dams did not significantly differ in yawning frequencies with respect to HY male rats reared by mothers of their own phenotype. Maternal care did not differ between sublines and SD dams independent of the litter they reared. However, LY rats reared by HY dams showed a significant increase in the number of spontaneous penile erections. Importantly, in-fostered HY male rats had the highest number of yawns induced by systemic administration of (−)-quinpirole supporting that higher maternal care display can influence the frequency of dopaminergic-induced yawning. In fact HY male rats in all conditions yawned more than did LY and SD male rats independent of the dam that raised them supporting a strong influence of genetic background. However SD male rats raised by LY dams showed significantly increased the dopamine D₂ receptor expression. In conclusion, maternal care and the environmental nest conditions during the lactation period did not change the phenotypic characteristics of the yawning sublines supporting that their genetic background is fundamental for the expression of spontaneous or dopaminergic-induced yawning.

Dysregulation of Corticostriatal Connectivity in Huntington's Disease: A Role for Dopamine Modulation

Aberrant communication between striatum, the main information processing unit of the basal ganglia, and cerebral cortex plays a critical role in the emergence of Huntington’s disease (HD), a fatal monogenetic condition that typically strikes in the prime of life. Although both striatum and cortex undergo substantial cell loss over the course of HD, corticostriatal circuits become dysfunctional long before neurons die. Understanding the dysfunction is key to developing effective strategies for treating a progressively worsening triad of motor, cognitive, and psychiatric symptoms. Cortical output neurons drive striatal activity through the release of glutamate, an excitatory amino acid. Striatal outputs, in turn, release γ-amino butyric acid (GABA) and exert inhibitory control over downstream basal ganglia targets. Ample evidence from transgenic rodent models points to dysregulation of corticostriatal glutamate transmission along with corresponding changes in striatal GABA release as underlying factors in the HD behavioral phenotype. Another contributor is dysregulation of dopamine (DA), a modulator of both glutamate and GABA transmission. In fact, pharmacological manipulation of DA is the only currently available treatment for HD symptoms. Here, we review data from animal models and human patients to evaluate the role of DA in HD, including DA interactions with glutamate and GABA within the context of dysfunctional corticostriatal circuitry.

Aberrant self-grooming as early marker of motor dysfunction in a rat model of Huntington's disease

In the study of neurodegenerative diseases, rodent models provide experimentally accessible systems to study multiple pathogenetic aspects. The identification of early and robust behavioural changes is crucial to monitoring disease progression and testing potential therapeutic strategies in animals. Consistent experimental data support the translational value of rodent self-grooming as index of disturbed motor functions and perseverative behaviour patterns in different rodent models of brain disorders. Huntington's disease (HD) is a progressive neurodegenerative disorder, characterized by severe degeneration of basal ganglia, cognitive and psychiatric impairments and motor abnormalities. In the rat species, intrastriatal injection of the excitotoxin quinolinic acid (QA) mimics some of the neuroanatomical and behavioural changes found in HD, including the loss of GABAergic neurons and the appearance of motor and cognitive deficits. We show here that striatal damage induced by unilateral QA injection in dorsal striatum of rats triggers aberrant grooming behaviour as early as three weeks post-lesion in absence of other motor impairments: specifically, both quantitative (frequency and duration) and qualitative (the sequential pattern of movements) features of self-grooming behaviour were significantly altered in QA-lesioned rats placed in either the elevated plus-maze and the open-field. The consistent abnormalities in self-grooming recorded in two different experimental contexts support the use of this behavioural marker in rodent models of striatal damage such as HD, to assess the potential effects of drug and cell replacement therapy in the early stage of disease.

Neurobiology of rodent self-grooming and its value for translational neuroscience

Self-grooming is a complex innate behaviour with an evolutionarily conserved sequencing pattern and is one of the most frequently performed behavioural activities in rodents. In this Review, we discuss the neurobiology of rodent self-grooming, and we highlight studies of rodent models of neuropsychiatric disorders--including models of autism spectrum disorder and obsessive compulsive disorder--that have assessed self-grooming phenotypes. We suggest that rodent self-grooming may be a useful measure of repetitive behaviour in such models, and therefore of value to translational psychiatry. Assessment of rodent self-grooming may also be useful for understanding the neural circuits that are involved in complex sequential patterns of action.

Neuroligin 1 modulates striatal glutamatergic neurotransmission in a pathway and NMDAR subunit-specific manner

Together with its presynaptic partner Neurexin 1 (Nxn1), Neuroligin 1 (NL1) participates in synapse specification and synapse maintenance. We and others have shown that NL1 can also modulate glutamatergic synaptic function in the central nervous system of rodent models. These molecular/cellular changes can translate into altered animal behaviors that are thought to be analogous to symptomatology of neuropsychiatric disorders. For example, in dorsal striatum of NL1 deletion mice, we previously reported that the ratio N-methyl-D-aspartate receptor (NMDAR) mediated synaptic currents to α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR) mediated synaptic currents (NMDA/AMPA) is reduced in medium spiny neuron (MSNs). Importantly, this reduction in NMDA/AMPA ratio correlated with increased repetitive grooming. The striatum is the input nucleus of the basal ganglia (BG). Classical models of this circuitry imply that there are two principal pathways that render distinct and somewhat opposite striatal outputs critical to the function of these nuclei in modulating motor behavior. Thus, we set out to better characterize the effects of NL1 deletion on direct and indirect pathways of the dorsal striatum by genetically labeling MSNs participating in the direct and indirect pathways. We demonstrate that a decrease in NMDAR-mediated currents is limited to MSNs of the direct pathway. Furthermore, the decrease in NMDAR-mediated currents is largely due to a reduction in function of NMDARs containing the GluN2A subunit. In contrast, indirect pathway MSNs in NL1 knockout (KO) mice showed a reduction in the frequency of miniature excitatory neurotransmission not observed in the direct pathway. Thus, NL1 deletion differentially affects direct and indirect pathway MSNs in dorsal striatum. These findings have potential implications for striatal function in NL1 KO mice.

Psychomotor functions at various weeks of chronic renal failure in rats

In chronic renal failure there is a gradual retention of substances in the tissues and body fluids, called as uremic retention toxins, which can bring about a number of biochemical activities in the body. Chronic renal insufficiency also leads to progressive behavioural conflict. Uremic toxins can affect both the central and the peripheral nervous system. Uremic encephalopathy is also associated with problems in cognition and memory. To study the psychomotor functional disorders in rats with progressive chronic renal failure surgical nephrectomy was done by resection method. The animals were grouped into two control groups, Sham control (SC) and normal control (NC) and two uremic groups, moderate uremia (GM) and severe uremia (GS). Psychomotor analysis was done by passive avoidance and open field in these animals at 4, 8, 12, and 16 weeks. After the incubation period, the nephrectomised groups (GM and GS) showed significant changes in exploratory, locomotor and emotional behaviour when compared to the controls (NC and SC). Psychomotor changes involve poor cognition, reduced memory, reduced locomotor activity and decreased exploratory drive and emotional disturbance like increased fear during the initial stages. During the later stages a restless behaviour was noticed, associated with diminished fear.

Mouse models of neurodevelopmental disease of the basal ganglia and associated circuits

This chapter focuses on neurodevelopmental diseases that are tightly linked to abnormal function of the striatum and connected structures. We begin with an overview of three representative diseases in which striatal dysfunction plays a key role--Tourette syndrome and obsessive-compulsive disorder, Rett's syndrome, and primary dystonia. These diseases highlight distinct etiologies that disrupt striatal integrity and function during development, and showcase the varied clinical manifestations of striatal dysfunction. We then review striatal organization and function, including evidence for striatal roles in online motor control/action selection, reinforcement learning, habit formation, and action sequencing. A key barrier to progress has been the relative lack of animal models of these diseases, though recently there has been considerable progress. We review these efforts, including their relative merits providing insight into disease pathogenesis, disease symptomatology, and basal ganglia function.

Acute total sleep deprivation potentiates amphetamine-induced locomotor-stimulant effects and behavioral sensitization in mice

It has been demonstrated that a prolonged period (48 h) of paradoxical sleep deprivation (PSD) potentiates amphetamine (AMP)-induced behavioral sensitization, an animal model of addiction-related neuroadaptations. In the present study, we examined the effects of an acute short-term deprivation of total sleep (TSD) (6h) on AMP-induced behavioral sensitization in mice and compared them to the effects of short-term PSD (6 h). Three-month-old male C57BL/6J mice underwent TSD (experiment 1-gentle handling method) or PSD (experiment 2-multiple platforms method) for 6 h. Immediately after the sleep deprivation period, mice were tested in the open field for 10 min under the effects of saline or 2.0 mg/kg AMP. Seven days later, to assess behavioral sensitization, all of the mice received a challenge injection of 2.0 mg/kg AMP and were tested in the open field for 10 min. Total, peripheral, and central locomotion, and grooming duration were measured. TSD, but not PSD, potentiated the hyperlocomotion induced by an acute injection of AMP and this effect was due to an increased locomotion in the central squares of the apparatus. Similarly, TSD facilitated the development of AMP-induced sensitization, but only in the central locomotion parameter. The data indicate that an acute period of TSD may exacerbate the behavioral effects of AMP in mice. Because sleep architecture is composed of paradoxical and slow wave sleep, and 6-h PSD had no effects on AMP-induced hyperlocomotion or sensitization, our data suggest that the deprivation of slow wave sleep plays a critical role in the mechanisms that underlie the potentiating effects of TSD on both the acute and sensitized addiction-related responses to AMP.

D1 and D2 dopamine receptor antagonists decrease behavioral bout duration, without altering the bout's repeated behavioral components, in a naturalistic model of repetitive and compulsive behavior

Nest building behavior in the pregnant female rabbit (Oryctolagus cuniculus) is a model for compulsive behavior in Obsessive Compulsive Disorder (OCD). This behavior comprises a cycle of repeated, stereotyped components (collecting straw, entering nest box and depositing the straw there, returning to collect more straw), which itself is repeated 80+ times in a single bout that lasts approximately 50min. The bout, in turn, is repeated if necessary, according to the rabbit's perception of whether or not the nest is finished. We administered SCH23390 (5-100μg/kg; D1/D5 antagonist) or raclopride (0.05-1.0mg/kg; D2/D3 antagonist), subcutaneously to day 28 pregnant female rabbits, 30 or 60min before placing straw inside their home cage. At doses that minimally affected ambulatory behavior in open field (5-12.5μg/kg SCH23390, 0.5-1.0mg/kg raclopride), both antagonists dramatically reduced bout duration while not significantly affecting the initiation of straw carrying behavior, the sequential performance of the individual cycle components, maximum cycle frequency, or the total number of bouts performed. These results point to an important role for dopamine neurotransmission for the prolonged expression of a normal, repetitive and compulsive-like behavior. Moreover, the finding that dopamine receptor antagonists decrease the time spent engaged in repetitive behavior (without significantly altering the form of the repetitive behavior itself) suggests a possible explanation for why neuroleptics can be clinically effective for treating OCD.

Repetitive methylphenidate administration modulates the diurnal behavioral activity pattern of adult female SD rats

Diurnal rhythms influence many of the physiological processes that act to maintain homeostasis of the body in response to different environmental changes. Thus, disturbances in diurnal rhythms can lead to various physiological complications. Repeated exposure to psychostimulants may cause long-term effects by disturbing diurnal rhythms. The aim of the present study is to use the open field assay to determine whether repeated exposure to the psychostimulant methylphenidate (MPD) changes diurnal locomotor activity patterns of female adult Sprague-Dawley (SD) rats. As much as 31 female adult SD rats were divided into four groups. On experimental day (ED) 1, all groups were given an injection of saline. On ED 2-7, animals were injected once a day with either saline, or 0.6 mg/kg MPD, or 2.5 mg/kg MPD, or 10 mg/kg MPD depending on the group. On ED 8-10, no injections were given (washout period). On ED 11, animals were treated as they were on ED 2-7. Locomotor movements were recorded using a computerized animal activity monitoring system. The horizontal activity (HA), total distance traveled (TDT), and number of stereotypies (NOS) were analyzed by cosine curve statistical analysis (CCSA) test. The HA and TDT diurnal rhythm activity patterns of ED 2, 7, 8, and 11 were significantly different (p < 0.05) from the control recording of ED 1 according to the CCSA test. The observation obtained in this study suggests that repeated administration of MPD (all doses tested) is able to change diurnal locomotor patterns, which indicates that chronic MPD treatment exerts long-term effects.

Low stress reactivity and neuroendocrine factors in the BTBR T+tf/J mouse model of autism

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. BTBR T+tf/J (BTBR) is an inbred mouse strain that displays robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of autism, including low social interactions, reduced vocalizations in social settings, and high levels of repetitive self-grooming. Autism-relevant phenotypes in BTBR offer translational tools to discover neurochemical mechanisms underlying unusual mouse behaviors relevant to symptoms of autism. Because repetitive self-grooming in mice may be a displacement behavior elevated by stressors, we investigated neuroendocrine markers of stress and behavioral reactivity to stressors in BTBR mice, as compared to C57BL/6J (B6), a standard inbred strain with high sociability. Radioimmunoassays replicated previous findings that circulating corticosterone is higher in BTBR than in B6. Higher basal glucocorticoid receptor mRNA and higher oxytocin peptide levels were detected in the brains of BTBR as compared to B6. No significant differences were detected in corticotrophin releasing factor (CRF) peptide or CRF mRNA. In response to behavioral stressors, BTBR and B6 were generally similar on behavioral tasks including stress-induced hyperthermia, elevated plus-maze, light ↔ dark exploration, tail flick, acoustic startle and prepulse inhibition. BTBR displayed less reactivity than B6 to a noxious thermal stimulus in the hot plate, and less immobility than B6 in both the forced swim and tail suspension depression-related tasks. BTBR, therefore, exhibited lower depression-like scores than B6 on two standard tests sensitive to antidepressants, did not differ from B6 on two well-validated anxiety-like behaviors, and did not exhibit unusual stress reactivity to sensory stimuli. Our findings support the interpretation that autism-relevant social deficits, vocalizations, and repetitive behaviors are not the result of abnormal stress reactivity in the BTBR mouse model of autism.

Dopamine receptor modulation of repetitive grooming actions in the rat: potential relevance for Tourette syndrome

Studies of rodent grooming can provide valuable insight for dopamine contributions to the initiation, organization, and repetition of motor patterns. This information is useful for understanding how brain dysfunctions contribute to movement disorders such as Tourette syndrome and obsessive compulsive disorder, in which patients are driven to reiterate particular movement patterns. In rodents, dopamine D1 receptor stimulation causes a complex behavioral super-stereotypy in the form of excessive production and rigid execution of whole sequences of movements known as syntactic grooming chains. Sequential super-stereotypy of grooming chains may be particularly advantageous for modeling movement sequences and treatments in Tourette syndrome and related disorders. Here, we report that co-administration of haloperidol, one available treatment for Tourette syndrome and primarily a D2 receptor antagonist, prevented D1 stimulation with SKF38393 from inducing sequential super-stereotypy, which manifests as an exaggeration of the tendency to complete all four phases of a syntactic chain in rigid serial order once the first phase has begun. In a separate experiment, we showed that in contrast to acute D1 agonist administration, 39h withdrawal from chronic (3weeks) administration of the D1 antagonist SCH23390 (which has been suggested to increase D1 receptor expression in the basal ganglia) did not elicit sequential super-stereotypy after drug cessation. Instead, rats suddenly removed from repeated SCH23390 spent more time performing simple stereotypies that included intense scratching and biting behaviors. Together, these results have implications for understanding how dopamine receptors facilitate particular stereotypies manifest in animal models of Tourette syndrome and obsessive compulsive disorder.

Social context rapidly modulates the influence of auditory feedback on avian vocal motor control

Sensory feedback is important for the learning and control of a variety of behaviors. Vocal motor production in songbirds is a powerful model system to study sensory influences on behavior because the learning, maintenance, and control of song are critically dependent on auditory feedback. Based on previous behavioral and neural experiments, it has been hypothesized that songs produced in isolation [undirected (UD) song] represent a form of vocal practice, whereas songs produced to females during courtship interactions [female-directed (FD) song] represent a form of vocal performance. According to this "practice versus performance" framework, auditory feedback should be more influential when birds engage in vocal practice than when they engage in vocal performance. To directly test this hypothesis, we used a computerized system to perturb auditory feedback at precise locations during the songs of Bengalese finches and compared the degree to which feedback perturbations caused song interruptions as well as changes to the sequencing and timing of syllables between interleaved renditions of UD and FD song. We found that feedback perturbation caused fewer song interruptions and smaller changes to syllable timing during FD song than during UD song. These data show that changes in the social context in which song is produced rapidly modulate the influence of auditory feedback on song control in a manner consistent with the practice versus performance framework. More generally, they indicate that, for song, as for other motor skills including human speech, the influence of sensory feedback on activity within vocal premotor circuitry can be dynamically modulated.

Impact of serotonin 2C receptor null mutation on physiology and behavior associated with nigrostriatal dopamine pathway function

The impact of serotonergic neurotransmission on brain dopaminergic pathways has substantial relevance to many neuropsychiatric disorders. A particularly prominent role has been ascribed to the inhibitory effects of serotonin 2C receptor (5-HT(2C)R) activation on physiology and behavior mediated by the mesolimbic dopaminergic pathway, particularly in the terminal region of the nucleus accumbens. The influence of this receptor subtype on functions mediated by the nigrostriatal dopaminergic pathway is less clear. Here we report that a null mutation eliminating expression of 5-HT(2C)Rs produces marked alterations in the activity and functional output of this pathway. 5-HT(2C)R mutant mice displayed increased activity of substantia nigra pars compacta (SNc) dopaminergic neurons, elevated baseline extracellular dopamine concentrations in the dorsal striatum (DSt), alterations in grooming behavior, and enhanced sensitivity to the stereotypic behavioral effects of d-amphetamine and GBR 12909. These psychostimulant responses occurred in the absence of phenotypic differences in drug-induced extracellular dopamine concentration, suggesting a phenotypic alteration in behavioral responses to released dopamine. This was further suggested by enhanced behavioral responses of mutant mice to the D(1) receptor agonist SKF 81297. Differences in DSt D(1) or D(2) receptor expression were not found, nor were differences in medium spiny neuron firing patterns or intrinsic membrane properties following dopamine stimulation. We conclude that 5-HT(2C)Rs regulate nigrostriatal dopaminergic activity and function both at SNc dopaminergic neurons and at a locus downstream of the DSt.

Social modulation of sequence and syllable variability in adult birdsong

Birdsong is a learned motor skill that is performed with a high degree of stereotypy in adult birds. Nevertheless, even in species where song "crystallizes" in a form that remains stable over time, there is residual variability. Such variability in well-learned skills is often construed as uncontrolled and irrelevant biological "noise." However, studies in the zebra finch indicate that variability in one song feature--the structure of individual syllables--is actively regulated and may serve a function. When male zebra finches sing alone (undirected song), variability in syllable structure is elevated relative to when they sing to females in a courtship context (female-directed song). This elevated variability is actively introduced to premotor structures controlling syllable production by a forebrain-basal ganglia circuit. Here we test whether social modulation of song variability extends to syllable sequencing, a hierarchically distinct feature of song organization controlled by separate neural substrates from syllable structure. We use Bengalese finches as a model species because, unlike zebra finches, they typically retain substantial moment-by-moment variability in the sequencing of syllables in crystallized adult song. We first show social modulation of previously studied song features, including syllable structure and song tempo. We then demonstrate that variability in syllable sequencing is rapidly modulated by social context with greater variability present in undirected song. These data indicate that the nervous system exerts active control over variability at multiple levels of song organization and support the hypothesis that such variability in otherwise stable adult song serves a function.

Repeated subchronic exposure to phencyclidine elicits excessive atypical grooming in rats

Self-grooming in rodents is stereotypically sequenced and naturally occurs after arousal, novelty, or stress. Grooming expression and syntax resulting from stressful and appetitive conditions were assessed in male Long Evans rats treated daily with 10mg/kg of phencyclidine (PCP) for 15 days. Approximately 20 h after the 1st, the 8th, and/or the 15th injection, grooming was induced with water sprays, a loud sound, or smearing food. Behaviors expressed during the seconds or minutes that followed induction were videotaped and codified. Results showed that subchronic treatment with PCP amplified the grooming response in all stressful and appetitive conditions, but provoked a disorganization of grooming sequences only under the stressful, water condition. Thus, PCP enhanced grooming expression indiscriminately. However, this behavior had to serve both hygienic and stress managing purposes in order for chain sequencing to become disorganized as a consequence of drug treatment. These results suggest that the detailed examination of grooming expression and organization is an appropriate tool to measure stress-induced behavioral sensitization and motor functions in animal models of neuropsychiatric disorders such as schizophrenia.

Dopamine D1 activation shortens the duration of phases in stereotyped grooming sequences

Rats frequently emit grooming actions in a highly stereotyped, syntactic chain in which three distinct phases of facially directed forearm movements are sequentially emitted in a rule-governed pattern and followed by body-directed licking. The present study evaluated the effects of the full dopamine D1 agonist, SKF 81297, and the partial dopamine D1 agonist, SKF 38393, on the duration of individual phases of stereotyped grooming chains. We found that systemic administration of SKF 81297 significantly shortened grooming chain duration. An examination of the fine temporal structure of syntactic grooming chain actions showed that duration changes were correlated with decreased numbers of actions in phases I and IV of the chain. Phases II and III were not changed in duration, although there were some structural distortions introduced. The partial D1 agonist, SKF 38393, had no effect on duration or number of component actions in the grooming chain. Based on these results, we hypothesize that the timing of syntactic grooming phase transitions may involve a D1-mediated internal clock process that is altered by full D1 agonist activation. By this model, SKF 81297 increases the speed of the clock used for the temporal control of grooming actions, and thus shortens phase durations.

Endocannabinoid lipids and mediated system: implications for alcoholism and neuropsychiatric disorders

Several natural lipids have emerged as candidate modulators of central nervous system (CNS) functions. Fatty acid amides and their coupled signaling pathways are known to regulate several physiological and behavioral processes. Recent studies from our laboratory and others also have implicated endogenous marijuana-like brain constituents, endocannabinoids (ECs), and cannabinoid-1 (CB1) receptors in the neural circuitry that mediate drug addiction and neuropsychiatric disorders. Neuroadaptation to chronic ethanol (EtOH) has been shown to involve changes in the EC system. These changes include alterations in the synthesis of EC, their precursors, as well as density and coupling efficacy of CB1 receptors. The evidence for the participation of the EC system in the pathophysiology of various neuropsychiatric disorders is just beginning to evolve. It is of great interest to explore the components of EC system in different areas of the CNS for further understanding of its role in health and disease. This article presents a comprehensive overview of the currently available literature pertaining to the role of the EC system in alcoholism, schizophrenia, depression and/or suicide.

Ethological resolution of behavioural topography and D1-like versus D2-like agonist responses in congenic D5 dopamine receptor mutants: identification of D5:D2-like interactions

The phenotypic ethogram of congenic dopamine D(5) receptor "knockout" mice was evaluated. Each individual topography of behaviour within the natural repertoire was assessed over the extended course of initial exploration of and subsequent habituation to the environment, and following challenge with a series of D(1)-like agonists. Over initial exploration, D(5)-null mice evidenced a modest reduction in locomotion and a modest increase in sifting. Subsequent habituation revealed additional phenotypic effects, primarily overall reduction in grooming and delayed habituation of rearing. Among D(1)-like agonists, A 68930 stimulates both adenylyl cyclase and a putative D(1)-like receptor coupled to stimulation of phospholipase C-mediated phosphoinositide hydrolysis; conversely, SK&F 83959 stimulates phosphoinositide hydrolysis but not adenylyl cyclase while SK&F 83822 stimulates adenylyl cyclase but not phosphoinositide hydrolysis. Though programmed grooming syntax and episodic seizure activity induced by A 68930 and SK&F 83822 were unaltered, grooming induced by SK&F 83959 was reduced in D(5) mutants. Stereotyped, ponderous locomotion induced by the D(2)-like agonist RU 24213 was enhanced in D(5) mutants. Phenotypic and pharmacological characterisation of congenic D(5)-null mice at an ethological level identifies novel functional roles for the D(5) receptor in mediating discrete topographies of behaviour relating to exploration, sequential motor coordination, and how these processes change over the course of interaction with and habituation to the environment. Additionally, they indicate the involvement of phosphoinositide hydrolysis and D(5):D(2)-like interactions in regulating these processes.

Basal ganglia neural mechanisms of natural movement sequences

Natural rodent grooming and other instinctive behavior serves as a natural model of complex movement sequences. Rodent grooming has syntactic (rule-driven) sequences and more random movement patterns. Both incorporate the same movements--only the serial structure differs. Recordings of neural activity in the dorsolateral striatum and the substantia nigra pars reticulata indicate preferential activation during syntactic sequences over more random sequences. Neurons that are responsive during syntactic grooming sequences are often unresponsive or have reverse activation profiles during kinematically similar movements that occur in flexible or random grooming sequences. Few neurons could be categorized as strictly movement related--instead they were activated only in the context of particular sequential patterns of movements. Particular sequential patterns included "syntactic chain" grooming sequences of paw, head, and body movements and also "warm-up" sequences, which consist of head and body/limb movements that precede locomotion after a period of quiet resting (Golani 1992). Activation during warm-up was less intense and less frequent than during grooming sequences, but both sequences activated neurons above baseline levels, and the same neurons sometimes responded to both sequences. The fact that striatal neurons code 2 natural sequences which are made up of different constituent movements suggests that the basal ganglia may have a generalized role in sequence control. The basal ganglia are modulated by the context of the sequence and may play an executive function in the complex natural patterns of sequenced behaviour.

The grooming analysis algorithm discriminates between different levels of anxiety in rats: potential utility for neurobehavioural stress research

Stress has long been known to affect grooming in rodent species, altering both its activity measures and behavioural microstructure. Since stress disturbs a general pattern of self-grooming uninterrupted cephalocaudal progression, the grooming analysis algorithm (Kalueff and Tuohimaa, Brain Res. Protocols, 2004; 15: 151-8) was previously designed for mice to enable the detection of stress by measuring alterations in grooming microstructure in different test situations. Since mice and rats are known to differ in their behaviours, including grooming, the aim of the current study was to test our approach in rats and evaluate the utility of this method for differentiation between high- and low-stress situations. For this, we have developed the rat grooming analysis algorithm (based on ethological analysis of incorrect transitions contrary to the cephalocaudal rule, interrupted grooming activity and the assessment of the regional distribution of grooming) and applied this algorithm to the light-exposed (high stress) and dark-exposed (low stress) groups of rats. Here, we show that the percentage of 'incorrect' transitions between different grooming patterns, the percentage of interrupted grooming bouts and altered regional distribution of grooming (less caudal grooming, more rostral grooming) may be used as behavioural markers of stress in rats. Our results suggest that this method can be a useful tool in neurobehavioural stress research including modelling stress-evoked states, psychopharmacological or behavioural neurogenetics research in rats.

Enhanced binding of dopamine D1receptors in caudate-putamen subregions in High-Yawning Sprague-Dawley rats

Previous reports have shown that the inbred High-Yawning (HY) and Low-Yawning (LY) rats differ in several behavioral characteristics related to mesolimbic and nigrostriatal dopamine (DA) function. To determine if differential expression of DA receptors or DA transporter may mediate the behavioral differences in these two sublines of the Sprague-Dawley rat, we performed a quantitative autoradiography study of the DA D1-like, D2-like, and DA-transporter binding in the basal ganglia and nucleus accumbens. The results show that levels of the D1 binding in the caudate-putamen of the HY rat were higher than in the LY animals, whereas no significant differences in the DA D2 receptors and DA transporter were noted in these sublines. These data suggest that the differences in DA receptors in D1 binding in HY rats may in part have contributed to the behavioral differences related to DA functions such as grooming and penile erection. Our findings are consistent with previous reports showing a decrease in the behavioral responses after systemic administration of DA agonist in LY compared to HY rats.

Sequential super-stereotypy of an instinctive fixed action pattern in hyper-dopaminergic mutant mice: a model of obsessive compulsive disorder and Tourette's

BACKGROUND

Excessive sequential stereotypy of behavioral patterns (sequential super-stereotypy) in Tourette's syndrome and obsessive compulsive disorder (OCD) is thought to involve dysfunction in nigrostriatal dopamine systems. In sequential super-stereotypy, patients become trapped in overly rigid sequential patterns of action, language, or thought. Some instinctive behavioral patterns of animals, such as the syntactic grooming chain pattern of rodents, have sufficiently complex and stereotyped serial structure to detect potential production of overly-rigid sequential patterns. A syntactic grooming chain is a fixed action pattern that serially links up to 25 grooming movements into 4 predictable phases that follow 1 syntactic rule. New mutant mouse models allow gene-based manipulation of brain function relevant to sequential patterns, but no current animal model of spontaneous OCD-like behaviors has so far been reported to exhibit sequential super-stereotypy in the sense of a whole complex serial pattern that becomes stronger and excessively rigid. Here we used a hyper-dopaminergic mutant mouse to examine whether an OCD-like behavioral sequence in animals shows sequential super-stereotypy. Knockdown mutation of the dopamine transporter gene (DAT) causes extracellular dopamine levels in the neostriatum of these adult mutant mice to rise to 170% of wild-type control levels.

RESULTS

We found that the serial pattern of this instinctive behavioral sequence becomes strengthened as an entire entity in hyper-dopaminergic mutants, and more resistant to interruption. Hyper-dopaminergic mutant mice have stronger and more rigid syntactic grooming chain patterns than wild-type control mice. Mutants showed sequential super-stereotypy in the sense of having more stereotyped and predictable syntactic grooming sequences, and were also more likely to resist disruption of the pattern en route, by returning after a disruption to complete the pattern from the appropriate point in the sequence. By contrast, wild-type mice exhibited weaker forms of the fixed action pattern, and often failed to complete the full sequence.

CONCLUSIONS

Sequential super-stereotypy occurs in the complex fixed action patterns of hyper-dopaminergic mutant mice. Elucidation of the basis for sequential super-stereotypy of instinctive behavior in DAT knockdown mutant mice may offer insights into neural mechanisms of overly-rigid sequences of action or thought in human patients with disorders such as Tourette's or OCD.

Grooming analysis algorithm for neurobehavioural stress research

Since rodent self-grooming behaviours are elicited by both comfort and stressful conditions, traditional measures such as duration, latency of onset and the number of bouts may be not suitable to dissociate between these opposite conditions. The aim of the current study was to improve and optimize ethological measurement of self-grooming in neurobehavioural stress research enabling differentiation between stress and no-stress situations. This protocol assists in the correct interpretation of animal grooming behaviours and detection of stress by measuring alterations in grooming microstructure in different test situations. While a general pattern of self-grooming uninterrupted cephalocaudal progression is normally observed in no-stress (comfort) conditions in mice and other rodents, the percentage of "incorrect" transitions between different stages and the percentage of interrupted grooming bouts may be used as behavioural marker of stress. The protocol can be a useful tool in neurobehavioural stress research including modelling stress-evoked states, pharmacological screening of potential antistress drugs or behavioural phenotyping of genetically modified animals.

Punding in Parkinson's disease: its relation to the dopamine dysregulation syndrome

Punding is a term that was coined originally to describe complex prolonged, purposeless, and stereotyped behaviour in chronic amphetamine users. A structured interview of 50 patients with higher dopamine replacement therapy requirements (>800 levodopa equivalent units/day) from 123 unselected patients with Parkinson's disease (PD) from a PD clinic identified 17 (14%) patients with punding. Punding was acknowledged as disruptive and unproductive by the patients themselves, but forcible attempts by family to interrupt the behaviour led to irritability and dysphoria. Punding was associated with very high doses of dopamine replacement therapy often related to a pattern of chronic inappropriate overuse of dopaminergic medication. We believe that this is an underreported, socially disabling phenomenon that is commonly associated with the syndrome of dopamine dysregulation and is phenomenologically distinct from both obsessive-compulsive disorder and mania.

Substantia nigra pars reticulata neurons code initiation of a serial pattern: implications for natural action sequences and sequential disorders

Sequences of movements are initiated abnormally in neurological disorders involving basal ganglia dysfunction, such as Parkinson's disease or Tourette's syndrome. The substantia nigra pars reticulata (SNpr) is one of the two primary output structures of the basal ganglia. However, little is known about how substantia nigra mediates the initiation of normal movement sequences. We studied its role in coding initiation of a sequentially stereotyped but natural movement sequence by recording neuronal activity in SNpr during behavioural performance of 'syntactic grooming chains'. These are rule-governed sequences of up to 25 grooming movements emitted in four predictable (syntactic) phases, which occur spontaneously during grooming behaviour by rats and other rodents. Our results show that neuronal activation in central SNpr codes the onset of this entire rule-governed sequential pattern of grooming actions, not elemental grooming movements. We conclude that the context of sequential pattern may be more important than the elemental motor parameters in determining SNpr neuronal activation.

Ethanol, endocannabinoids, and the cannabinoidergic signaling system

This article represents the proceedings of a symposium at the 2001 annual meeting of the Research Society on Alcoholism in Montreal, Canada. The chairpersons were Appa Hungund and George Koob. The presentations were (1) Role of endocannabinoids in ethanol tolerance, by Appa Hungund; (2) Modulation of cannabinoid receptor and its signal transduction in chronic alcoholism, by B. S. Basavarajappa; (3) Endocannabinoid involvement in the control of appetitive behavior, by George Kunos; (4) Regulation of voluntary ethanol intake by cannabinoid receptor agonists and antagonists in alcohol-preferring sP rats, by Giancarlo Colombo; (5) Role of endogenous cannabinoid system in alcoholism, by Fernado Rodriguez de Fonseca; and (6) Endocannabinoids and dopamine interactions in vivo, by Loren Parsons and George Koob.

Super-stereotypy I: enhancement of a complex movement sequence by systemic dopamine D1 agonists

Peripheral administration of D1 dopamine agonists elicits grooming behavior from rodents. The present study examined grooming behavior and the relative probability and stereotypy of a natural sequence of grooming movements (called a syntactic grooming chain) that follows a predictable fixed pattern of serial order. We compared the amount of grooming behavior vs. the stereotypy of sequential patterns after peripheral administration of either a partial D1 agonist (SKF 38393; 2.5, 5.0, 10, 20 mg/kg), a full D1 agonist (SKF 82958; 0.1, 0.2, 0.5, 1.0 mg/kg; i.p.), a D2 agonist (quinpirole; 5.0, 10 mg/kg), or ACTH (2.0, 5.0 mg/kg). There was a dissociation between the elicited grooming amount, the pattern frequency, and the pattern completion or sequential stereotypy after these drugs. Quinpirole and ACTH both reduced the likelihood that the sequential pattern would be completed in the normal pattern (and reduced the overall amount of grooming). Administration of either SKF 38393 or SKF 82958 increased the tendency to engage in complex stereotyped sequential patterns of grooming (even though only the partial D1 agonist increased the total amount of grooming). In addition, SKF 38393 increased the sequential stereotypy of the already-stereotyped pattern itself (as measured by the probability of completing the stereotyped sequence once it began). Thus, dopamine D1 receptor activation appears to contribute to a kind of sequential super-stereotypy in which a complex, stereotyped behavioral sequence is initiated more frequently and more often goes to completion.