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

Abstract

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.

Keywords: Gilles de la Tourette syndrome; Huntington’s disease; autism spectrum disorder; cell-type specificity; epigenetics; obsessive-compulsive disorder; repetitive behavior; striatum.

Figure 1

Toward a multi-level understanding of striatal dysfunctions underlying repetitive behaviors in neurodevelopmental, neuropsychiatric and neurodegenerative diseases (i.e., Obsessive-Compulsive Disorder, Autism Spectrum Disorder, premanifest Huntington’s Disease and Gilles de la Tourette Syndrome).

Figure 2

Multiscale evidence for striatal circuitry alterations underlying repetitive behaviors. Diseases like (A) Obsessive-Compulsive Disorder, OCD, (B) Autism Spectrum Disorder, ASD, (C) premanifest Huntington’s Disease, (preHD) and (D) Gilles de la Tourette Syndrome, GTS, despite having different etiologies, all share repetitive behaviors as a core symptom in affected patients. Changes at the molecular and cellular level can lead to dysfunctional structural and functional connectivity across the striatal circuitry. (A) In OCD, alterations in the electrophysiological properties of dSPNs, iSPNs and astrocytes, can lead to a direct vs. indirect pathway imbalance. (B) In ASD, complex alterations at the molecular and cellular level, as well as structural and functional connectivity have been associated with the emergence of repetitive behaviors. (C) In premanifest HD, loss of matrix and striosomes cellular identity, as well as altered connectivity between cortical and striatal regions have been reported, at very early stages of the disease. (D) In GTS alterations at the cellular and circuit level lead to a scenario where disinhibition of the direct pathway could be the underlying cause of uncontrollable tics. dSPN, direct spiny projection neuron; iSPN, indirect spiny projection neuron; CIN, Cholinergic interneuron; FSI, Fast spiking interneuron; SNc, Substantia nigra pars compacta; GPe, External globus pallidus; GPi, Internal globus pallidus; STN, Subthalamic nucleus; DMS, Dorsomedial striatum; DLS, Dorsolateral striatum; VS, Ventral striatum.