Cocaine-Induced Preference Conditioning: a Machine Vision Perspective

Perineuronal Net Microscopy: From Brain Pathology to Artificial Intelligence

Perineuronal nets (PNN) are a special highly structured type of extracellular matrix encapsulating synapses on large populations of CNS neurons. PNN undergo structural changes in schizophrenia, epilepsy, Alzheimer's disease, stroke, post-traumatic conditions, and some other brain disorders. The functional role of the PNN microstructure in brain pathologies has remained largely unstudied until recently. Here, we review recent research implicating PNN microstructural changes in schizophrenia and other disorders. We further concentrate on high-resolution studies of the PNN mesh units surrounding synaptic boutons to elucidate fine structural details behind the mutual functional regulation between the ECM and the synaptic terminal. We also review some updates regarding PNN as a potential pharmacological target. Artificial intelligence (AI)-based methods are now arriving as a new tool that may have the potential to grasp the brain's complexity through a wide range of organization levels-from synaptic molecular events to large scale tissue rearrangements and the whole-brain connectome function. This scope matches exactly the complex role of PNN in brain physiology and pathology processes, and the first AI-assisted PNN microscopy studies have been reported. To that end, we report here on a machine learning-assisted tool for PNN mesh contour tracing.

Role of Perineuronal nets in the cerebellar cortex in cocaine-induced conditioned preference, extinction, and reinstatement

Perineuronal nets (PNNs) are cartilage-like structures of extracellular matrix molecules that enwrap in a net-like manner the cell-body and proximal dendrites of special subsets of neurons. PNNs stabilize their incoming connections and restrict plasticity. Consequently, they have been proposed as a candidate mechanism for drug-induced learning and memory. In the cerebellum, PNNs surround Golgi inhibitory interneurons and both inhibitory and excitatory neurons in the deep cerebellar nuclei (DCN). Previous studies from the lab showed that cocaine-induced conditioned memory increased PNN expression in the granule cell layer of the posterior vermis. The present research aimed to investigate the role of cerebellar PNNs in cocaine-induced conditioned preference. For this purpose, we use the enzyme chondroitinase ABC (ChABC) to digest PNNs at different time points of the learning process to ascertain whether their removal can affect drug-induced memory. Our results show that PNN digestion using ChABC in the posterior vermis (Lobule VIII) did not affect the acquisition of cocaine-induced conditioned preference. However, the removal of PNNs in Lobule VIII -but not in the DCN- disrupted short-term memory of conditioned preference. Moreover, although PNN digestion facilitated the formation of extinction, reinstatement of cocaine-induced conditioned preference was encouraged under PNN digestion. The present findings suggests that PNNs around Golgi interneurons are needed to maintain cocaine-induced Pavlovian memory but also to stabilize extinction memory. Conversely, PNN degradation within the DCN did not affect stability of cocaine-induced memories. Therefore, degradation of PNNs in the vermis might be used as a promising tool to manipulate drug-induced memory.

When the front fails, the rear wins. Cerebellar correlates of prefrontal dysfunction in cocaine-induced memory in male rats

Reciprocal pathways connecting the cerebellum to the prefrontal cortex provide a biological and functional substrate to modulate cognitive functions. Dysfunction of both medial prefrontal cortex (mPFC) and cerebellum underlie the phenotypes of several neuropsychiatric disorders that exhibit comorbidity with substance use disorder (SUD). In people with SUD, cue-action-reward associations appears to be particularly strong and salient, acting as powerful motivational triggers for craving and relapse. Studies of cue reactivity in human with SUD have shown cerebellar activations when drug-related cues are presented. Our preclinical research showed that cocaine-induced conditioned preference increases neural activity and upregulates perineuronal nets (PNNs) around Golgi interneurons in the posterior cerebellar cortex. In the present investigation, we aimed at evaluating cerebellar signatures of conditioned preference for cocaine when drug learning is established under mPFC impairment. We used lidocaine to temporarily inactivate in male rats either the Prelimbic (PL) or the Infralimbic (IL) cortices during cocaine-induced conditioning. The inactivation of the IL, but not the PL, encouraged the acquisition of preference for cocaine-related cues, increased posterior cerebellar cortex activity, and upregulated the expression of PNNs around Golgi interneurons. Moreover, IL impairment not only increased vGluT2- and vGAT-related activity around Golgi cells but also regulated PNNs differently on subpopulations of Golgi cells, increasing the number of neurogranin+ PNN-expressing Golgi cells. Our findings suggest that IL dysfunction may facilitate the acquisition of cocaine-induced memory and cerebellar drug-related learning hallmarks. Overall, IL perturbation during cocaine-induced Pavlovian learning increased cerebellar activity and drug effects. Importantly, cerebellum involvement requires a contingent experience with the drug, and it is not the effect of a mere inactivation of IL cortex.

Time-dependent regulation of perineuronal nets in the cerebellar cortex during abstinence of cocaine-self administration

RATIONALE

The probability of structural remodeling in brain circuits may be modulated by molecules of perineuronal nets (PNNs) that restrict neuronal plasticity to stabilize circuits. Animal research demonstrates that addictive drugs can remodel PNNs in different brain regions, including the cerebellum.

OBJECTIVE

This study aimed to investigate the effects of short versus extended access to cocaine self-administration on PNN expression around Golgi interneurons in the cerebellar cortex after different periods of abstinence.

METHODS

After 1 week of training (2 h/day), Sprague-Dawley rats self-administered cocaine daily for 20 days under short (ShA) or extended (LgA) access. PNN expression in the cerebellum was assessed after 1 day, 7 days, and 28 days of forced abstinence. PNNs were immunolabeled using Wisteria floribunda agglutinin (WFA) and captured by confocal microscopy.

RESULTS

WFA intensity increased in PNN-bearing Golgi neurons over the abstinence period and a higher proportion of more intense PNNs were formed throughout the first month of abstinence. After the first 24 h of cocaine abstinence, however, we found a reduction in WFA intensity in the cerebellar cortex of rats with ShA to cocaine as compared to naïve animals. When comparing with naïve rats, LgA rats showed consistent PNN upregulation at 28 days of cocaine abstinence.

CONCLUSIONS

Our results suggest that cocaine self-administration produces modifications in PNN that enhance conditions for synaptic plasticity in the cerebellar cortex. These modifications are revealed shortly after the cessation of drug intake but PNNs become more intense during protracted abstinence in the LgA group, pointing to the stabilization of drug-induced synaptic changes. These findings indicate that extended access to cocaine self-administration dynamically regulates conditions for plasticity in the cerebellum during abstinence.