Pathway-specific alterations in striatal excitability and cholinergic modulation in a SAPAP3 mouse model of compulsive motor behavior

The role of fear and dopamine-striatal pathways in grooming

Fear is a fundamental emotion that triggers rapid and automatic behavioral response. Fear is known to suppress reward-seeking behaviors, interrupt previous activities to prioritize defensive responses and lead to rapid switch to defensive reactions. Dopamine (DA) plays a complicated role in the choice and performance of actions and it has a potential interaction of innate actions with the presence of fear. Here, in a series of experiments we explore the role of the different DA striatal pathways in mediating grooming, an innate behavior comprised of a structured sequence of repetitive actions, with or without the presence of fear. Using chemogenetics, we specifically inhibited the DA pathways projecting to the dorsolateral striatum (DLS), dorsomedial striatum (DMS), and ventral striatum (VS), while mice were engaged in a behavioral paradigm inducing grooming during the presentation of a fear related cue. We found that fear related cues consistently reduced grooming proportions and shortened induced grooming bouts, regardless of DA manipulation, indicating prioritization of freezing behavior in fearful contexts. This also suggests that fear responses may be mediated through pathways independent of DA-based action selection. The role of DA, however, varies depending on the specific striatal pathway. Inhibiting DLS DA input delayed grooming initiation and reduced grooming when competing with freezing. In contrast, DMS DA input had no effect on grooming, while inhibition of VS mesolimbic DA input increased grooming proportions and duration. These findings underscore the distinct and sometimes opposing roles of different DA-striatal pathways in modulating innate behaviors. We discuss potential implications of this duality in DA function for both theoretical and clinical fields.

Advancing Obsessive-Compulsive Disorder Research: Insights from Transgenic Animal Models and Innovative Therapies

Obsessive-compulsive disorder (OCD) is a prevalent, chronic, and severe neuropsychiatric disorder that leads to illness-related disability. Despite the availability of several treatments, many OCD patients respond inadequately, because the underlying neural mechanisms remain unclear, necessitating the establishment of many animal models, particularly mouse models, to elucidate disease mechanisms and therapeutic strategies better. Although the development of animal models is ongoing, there remain many comprehensive summaries and updates in recent research, hampering efforts to develop novel treatments and enhance existing interventions. This review summarizes the phenotypes of several commonly used models and mechanistic insights from transgenic models of OCD, such as knockout mouse models. In addition, we present the advantages and limitations of these models and discuss their future in helping further understand the pathophysiology and advanced treatment. Here, we highlight current frontline treatment approaches for OCD, including neuromodulation and surgical interventions, and propose potential future directions. By studying gene mutations and observing phenotypes from available OCD animal models, researchers have classified the molecular signatures of each model reminiscent of changes in brain areas and neural pathways, with the hope of guiding the future selection of the most appropriate models for specific research in the OCD field.

Synchronous activation of striatal cholinergic interneurons induces local serotonin release

Striatal cholinergic interneurons (CINs) activate nicotinic acetylcholine receptors on dopamine axons to extend the range of dopamine release. Here we show that synchronous activation of CINs induces and extends the range of local serotonin release via a similar mechanism. This process is exaggerated in the hypercholinergic striatum of a mouse model of OCD-like behavior, implicating CINs as critical regulators of serotonin levels in the healthy and pathological striatum.

Astrocyte Gi-GPCR signaling corrects compulsive-like grooming and anxiety-related behaviors in Sapap3 knockout mice

Astrocytes are morphologically complex cells that serve essential roles. They are widely implicated in central nervous system (CNS) disorders, with changes in astrocyte morphology and gene expression accompanying disease. In the Sapap3 knockout (KO) mouse model of compulsive and anxiety-related behaviors related to obsessive-compulsive disorder (OCD), striatal astrocytes display reduced morphology and altered actin cytoskeleton and Gi-G-protein-coupled receptor (Gi-GPCR) signaling proteins. Here, we show that normalizing striatal astrocyte morphology, actin cytoskeleton, and essential homeostatic support functions by targeting the astrocyte Gi-GPCR pathway using chemogenetics corrected phenotypes in Sapap3 KO mice, including anxiety-related and compulsive behaviors. Our data portend an astrocytic pharmacological strategy for rescuing phenotypes in brain disorders that include compromised astrocyte morphology and tissue support.

Experience-dependent grooming microstructure alterations and gastrointestinal dysfunction in the SAPAP3 knockout mouse model of compulsive behaviour

BACKGROUND

Compulsive- and anxiety-like behaviour can be efficiently modelled in SAPAP3 knockout (KO) mice, a preclinical model of relevance to obsessive-compulsive disorder (OCD). Although there is emerging evidence in the clinical literature of gastrointestinal dysfunction in OCD, no previous studies have investigated gut function in preclinical models of relevance to OCD. Similarly, the effects of voluntary exercise (EX) or environmental enrichment (EE) have not yet been explored in this context.

METHOD

We comprehensively phenotyped the SAPAP3 KO mouse model, including the assessment of grooming microstructure, anxiety- and depressive-like behaviour, and gastrointestinal function. Mice were exposed to either standard housing (SH), exercise (EX, provided by giving mice access to running wheels), or environmental enrichment (EE) for 4 weeks to investigate the effects of enriched housing conditions in this animal model relevant to OCD.

FINDINGS

Our study is the first to assess grooming microstructure, perseverative locomotor activity, and gastrointestinal function in SAPAP3 KO mice. We are also the first to report a sexually dimorphic effect of grooming in young-adult SAPAP3 KO mice; along with changes to grooming patterning and indicators of gut dysfunction, which occurred in the absence of gut dysbiosis in this model. Overall, we found no beneficial effects of voluntary exercise or environmental enrichment interventions in this mouse model; and unexpectedly, we revealed a deleterious effect of wheel-running exercise on grooming behaviour. We suspect that the detrimental effects of experimental housing in our study may be indicative of off-target effects of stress-a conclusion that warrants further investigation into the effects of chronic stress in this preclinical model of compulsive behaviour.

Cortico-basal ganglia plasticity in motor learning

One key function of the brain is to control our body's movements, allowing us to interact with the world around us. Yet, many motor behaviors are not innate but require learning through repeated practice. Among the brain's motor regions, the cortico-basal ganglia circuit is particularly crucial for acquiring and executing motor skills, and neuronal activity in these regions is directly linked to movement parameters. Cell-type-specific adaptations of activity patterns and synaptic connectivity support the learning of new motor skills. Functionally, neuronal activity sequences become structured and associated with learned movements. On the synaptic level, specific connections become potentiated during learning through mechanisms such as long-term synaptic plasticity and dendritic spine dynamics, which are thought to mediate functional circuit plasticity. These synaptic and circuit adaptations within the cortico-basal ganglia circuitry are thus critical for motor skill acquisition, and disruptions in this plasticity can contribute to movement disorders.

Obsessive-compulsive disorder induced by donepezil in a patient with Alzheimer's disease

Background

Donepezil, an acetylcholinesterase inhibitor commonly used to treat Alzheimer's disease (AD), is generally well tolerated. There have been no previous reports on donepezil-induced obsessive-compulsive disorder (OCD).

Case Presentation

The patient, a retired man in his 70s diagnosed with AD, displayed OCD symptoms following donepezil initiation, exacerbating post-stroke-specifically, a cerebral infarction in the right posterior limb of the internal capsule. Remarkably, the symptoms abated upon discontinuation of donepezil.

Conclusion

Caution should be exercised when using donepezil in patients with a history of stroke.

Striatal insights: a cellular and molecular perspective on repetitive behaviors in pathology

Animals often behave repetitively and predictably. These repetitive behaviors can have a component that is learned and ingrained as habits, which can be evolutionarily advantageous as they reduce cognitive load and the expenditure of attentional resources. Repetitive behaviors can also be conscious and deliberate, and may occur in the absence of habit formation, typically when they are a feature of normal development in children, or neuropsychiatric disorders. They can be considered pathological when they interfere with social relationships and daily activities. For instance, people affected by obsessive-compulsive disorder, autism spectrum disorder, Huntington's disease and Gilles de la Tourette syndrome can display a wide range of symptoms like compulsive, stereotyped and ritualistic behaviors. The striatum nucleus of the basal ganglia is proposed to act as a master regulator of these repetitive behaviors through its circuit connections with sensorimotor, associative, and limbic areas of the cortex. However, the precise mechanisms within the striatum, detailing its compartmental organization, cellular specificity, and the intricacies of its downstream connections, remain an area of active research. In this review, we summarize evidence across multiple scales, including circuit-level, cellular, and molecular dimensions, to elucidate the striatal mechanisms underpinning repetitive behaviors and offer perspectives on the implicated disorders. We consider the close relationship between behavioral output and transcriptional changes, and thereby structural and circuit alterations, including those occurring through epigenetic processes.