Neuroreceptor kinetics in rats repeatedly exposed to quinpirole as a model for OCD

Correlation between compulsive behaviors and plastic changes in the dendritic spines of the prefrontal cortex and dorsolateral striatum of male rats

Obsessive-compulsive disorder (OCD) is a mental affliction characterized by compulsive behaviors often manifested in intrusive thoughts and repetitive actions. The quinpirole model has been used with rats to replicate compulsive behaviors and study the neurophysiological processes associated with this pathology. Several changes in the dendritic spines of the medial prefrontal cortex (mPFC) and dorsolateral striatum (DLS) have been related to the occurrence of compulsive behaviors. Dendritic spines regulate excitatory synaptic contacts, and their morphology is associated with various brain pathologies. The present study was designed to correlate the occurrence of compulsive behaviors (generated by administering the drug quinpirole) with the morphology of the different types of dendritic spines in the mPFC and DLS. A total of 18 male rats were used. Half were assigned to the experimental group, the other half to the control group. The former received injections of quinpirole, while the latter rats were injected with physiological saline solution, for 10 days in both cases. After the experimental treatment, the quinpirole rats exhibited all the parameters indicative of compulsive behavior and a significant correlation with the density of stubby and wide neckless spines in both the mPFC and DLS. Dendritic spines from both mPFC and DLS neurons showed plastic changes correlatively with the expression of compulsive behavior induced by quinpirole. Further studies are suggested to evaluate the involvement of glutamatergic neurotransmission in the neurobiology of OCD.

Towards zebrafish models to unravel translational insights of obsessive-compulsive disorder: A neurobehavioral perspective

Obsessive-compulsive disorder (OCD) is a chronic and debilitating illness that has been considered a polygenic and multifactorial disorder, challenging effective therapeutic interventions. Although invaluable advances have been obtained from human and rodent studies, several molecular and mechanistic aspects of OCD etiology are still obscure. Thus, the use of non-traditional animal models may foster innovative approaches in this field, aiming to elucidate the underlying mechanisms of disease from an evolutionary perspective. The zebrafish (Danio rerio) has been increasingly considered a powerful organism in translational neuroscience research, especially due to the intrinsic features of the species. Here, we outline target mechanisms of OCD for translational research, and discuss how zebrafish-based models can contribute to explore neurobehavioral aspects resembling those found in OCD. We also identify possible advantages and limitations of potential zebrafish-based models, as well as highlight future directions in both etiological and therapeutic research. Lastly, we reinforce the use of zebrafish as a promising tool to unravel the biological basis of OCD, as well as novel pharmacological therapies in the field.

Potential therapeutic mechanism of deep brain stimulation of the nucleus accumbens in obsessive-compulsive disorder

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) (NAc-DBS) is an effective solution to refractory obsessive-compulsive disorder (OCD). However, evidence for the neurobiological mechanisms of OCD and the effect of NAc-DBS is still lacking. One hypothesis is that the electrophysiological activities in the NAc are modulated by DBS, and another hypothesis is that the activities of neurotransmitters in the NAc are influenced by DBS. To investigate these potential alterations, rats with quinpirole (QNP)- induced OCD were treated with DBS of the core part of NAc. Then, extracellular spikes (SPK) and local field potentials (LFP) in the NAc were recorded, and the levels of relevant neurotransmitters and related proteins were measured. Analysis of SPK revealed that the firing rate was decreased and the firing pattern was changed after NAc-DBS, and analysis of LFP showed that overall power spectral density (PSD) levels were reduced after NAc-DBS. Additionally, we found that the relative powers of the theta band, alpha band and beta band were increased in OCD status, while the relative powers of the delta band and gamma band were decreased. This pathological pattern of power distribution was reformed by NAc-DBS. Furthermore, we found that the local levels of monoamines [dopamine (DA) and serotonin (5-HT)] and amino acids [glutamate (Glu) and gamma-aminobutyric acid (GABA)] in the NAc were increased in OCD status, and that the expression of the two types of DA receptors in the NAc exhibited an opposite change. These abnormalities could be reversed by NAc-DBS. These findings provide a more comprehensive understanding about the function of the NAc in the pathophysiology of OCD and provide more detailed evidence for the potential effect of NAc-DBS.

Structural and functional MRI of altered brain development in a novel adolescent rat model of quinpirole-induced compulsive checking behavior

Obsessive-compulsive disorder (OCD) is increasingly considered to be a neurodevelopmental disorder. However, despite insights in neural substrates of OCD in adults, less is known about mechanisms underlying compulsivity during brain development in children and adolescents. Therefore, we developed an adolescent rat model of compulsive checking behavior and investigated developmental changes in structural and functional measures in the frontostriatal circuitry. Five-weeks old Sprague Dawley rats were subcutaneously injected with quinpirole (n = 21) or saline (n = 20) twice a week for five weeks. Each injection was followed by placement in the middle of an open field table, and compulsive behavior was quantified as repeated checking behavior. Anatomical, resting-state functional and diffusion MRI at 4.7T were conducted before the first and after the last quinpirole/saline injection to measure regional volumes, functional connectivity and structural integrity in the brain, respectively. After consecutive quinpirole injections, adolescent rats demonstrated clear checking behavior and repeated travelling between two open-field zones. MRI measurements revealed an increase of regional volumes within the frontostriatal circuits and an increase in fractional anisotropy (FA) in white matter areas during maturation in both experimental groups. Quinpirole-injected rats showed a larger developmental increase in FA values in the internal capsule and forceps minor compared to control rats. Our study points toward a link between development of compulsive behavior and altered white matter maturation in quinpirole-injected adolescent rats, in line with observations in pediatric patients with compulsive phenotypes. This novel animal model provides opportunities to investigate novel treatments and underlying mechanisms for patients with early-onset OCD specifically.