Chondroitin Sulfate Expression in Perineuronal Nets After Goldfish Spinal Cord Lesion

Link Protein 1 Is Involved in the Activity-Dependent Modulation of Perineuronal Nets in the Spinal Cord

One of the challenges of the mature nervous system is to maintain the stability of neural networks while providing a degree of plasticity to generate experience-dependent modifications. This plasticity-stability dynamism is regulated by perineuronal nets (PNNs) and is crucial for the proper functioning of the system. Previously, we found a relation between spinal PNNs reduction and maladaptive plasticity after spinal cord injury (SCI), which was attenuated by maintaining PNNs with activity-dependent therapies. Moreover, transgenic mice lacking the cartilage link protein 1 (Crtl1 KO mice) showed aberrant spinal PNNs and increased spinal plasticity. Therefore, the aim of this study is to evaluate the role of link protein 1 in the activity-dependent modulation of spinal PNNs surrounding motoneurons and its impact on the maladaptive plasticity observed following SCI. We first studied the activity-dependent modulation of spinal PNNs using a voluntary wheel-running protocol. This training protocol increased spinal PNNs in WT mice but did not modify PNN components in Crtl1 KO mice, suggesting that link protein 1 mediates the activity-dependent modulation of PNNs. Secondly, a thoracic SCI was performed, and functional outcomes were evaluated for 35 days. Interestingly, hyperreflexia and hyperalgesia found at the end of the experiment in WT-injured mice were already present at basal levels in Crtl1 KO mice and remained unchanged after the injury. These findings demonstrated that link protein 1 plays a dual role in the correct formation and in activity-dependent modulation of PNNs, turning it into an essential element for the proper function of PNN in spinal circuits.

Perineuronal Nets: Subtle Structures with Large Implications

Perineuronal nets (PNNs) are specialized structures of the extracellular matrix that surround the soma and proximal dendrites of certain neurons in the central nervous system, particularly parvalbumin-expressing interneurons. Their appearance overlaps the maturation of neuronal circuits and the closure of critical periods in different regions of the brain, setting their connectivity and abruptly reducing their plasticity. As a consequence, the digestion of PNNs, as well as the removal or manipulation of their components, leads to a boost in this plasticity and can play a key role in the functional recovery from different insults and in the etiopathology of certain neurologic and psychiatric disorders. Here we review the structure, composition, and distribution of PNNs and their variation throughout the evolutive scale. We also discuss methodological approaches to study these structures. The function of PNNs during neurodevelopment and adulthood is discussed, as well as the influence of intrinsic and extrinsic factors on these specialized regions of the extracellular matrix. Finally, we review current data on alterations in PNNs described in diseases of the central nervous system (CNS), focusing on psychiatric disorders. Together, all the data available point to the PNNs as a promising target to understand the physiology and pathologic conditions of the CNS.

Net gain and loss: influence of natural rewards and drugs of abuse on perineuronal nets

Overindulgence, excessive consumption, and a pattern of compulsive use of natural rewards, such as certain foods or drugs of abuse, may result in the development of obesity or substance use disorder, respectively. Natural rewards and drugs of abuse can trigger similar changes in the neurobiological substrates that drive food- and drug-seeking behaviors. This review examines the impact natural rewards and drugs of abuse have on perineuronal nets (PNNs). PNNs are specialized extracellular matrix structures that ensheathe certain neurons during development over the critical period to provide synaptic stabilization and a protective microenvironment for the cells they surround. This review also analyzes how natural rewards and drugs of abuse impact the density and maturation of PNNs within reward-associated circuitry of the brain, which may contribute to maladaptive food- and drug-seeking behaviors. Finally, we evaluate the relatively few studies that have degraded PNNs to perturb reward-seeking behaviors. Taken together, this review sheds light on the complex way PNNs are regulated by natural rewards and drugs and highlights a need for future studies to delineate the molecular mechanisms that underlie the modification and maintenance of PNNs following exposure to rewarding stimuli.

The Role and Modulation of Spinal Perineuronal Nets in the Healthy and Injured Spinal Cord

Rather than being a stable scaffold, perineuronal nets (PNNs) are a dynamic and specialized extracellular matrix involved in plasticity modulation. They have been extensively studied in the brain and associated with neuroprotection, ionic buffering, and neural maturation. However, their biological function in the spinal cord and the effects of disrupting spinal PNNs remain elusive. The goal of this review is to summarize the current knowledge of spinal PNNs and their potential in pathological conditions such as traumatic spinal cord injury (SCI). We also highlighted interventions that have been used to modulate the extracellular matrix after SCI, targeting the glial scar and spinal PNNs, in an effort to promote regeneration and stabilization of the spinal circuits, respectively. These concepts are discussed in the framework of developmental and neuroplastic changes in PNNs, drawing similarities between immature and denervated neurons after an SCI, which may provide a useful context for future SCI research.

Chondroitin sulfate expression around motoneurons changes after complete spinal transection of neonatal rats

Hind limb locomotor activity spontaneously recovers after complete spinal transection (CST) in neonatal rats, but the mechanisms underlying the recovery are poorly understood. The perineuronal net (PNN) surrounding the neuronal cell bodies comprises an extracellular matrix that regulates neuronal plasticity during development. Here, we examined the expression of chondroitin sulfate (CS), a major component of the PNN, on motoneurons after CST in neonatal rats, and compared it with that in juvenile rats, in which hindlimb locomotor activity does not recover spontaneously. The spinal cord was transected at the mid-thoracic level in neonatal (postnatal day 5 [P5] and P10) and juvenile (P15 and P20) rats. Two weeks after CST, the percentage of motoneurons surrounded by chondroitin sulfate C (CS-C) - positive structures was significantly lower in rats with CST at P10 than in intact rats, and tended to be higher in rats with CST at P15 than in intact rats. The percentage of motoneurons with CS-A - positive structures was significantly lower in rats with CST at P15 than in intact rats. These findings suggest that CS-A and CS-C are differentially expressed in the PNNs in rats with CST. The decrease in CS-C - positive PNNs might facilitate the formation of new synaptic contacts to motoneurons, resulting in the recovery of the hindlimb locomotor activity in rats with CST during the neonatal period.

Expression of matrix metalloproteinases during axonal regeneration in the goldfish spinal cord

Spinal cord injury in fish produces fibrous scar, but spontaneous axonal regeneration beyond the scar sometimes occurs. A previous study revealed that regenerating axons enter the scar through tubular structures with laminin, and that an increased number of axons within the tube is coincident with enlargement of the tube diameter and reduction of the fibrous scar area. The present study investigated the expression of matrix metalloproteinases (MMPs) that might play a role in the degradation of the extracellular matrix in fibrous scar tissue and in the remodeling of tubular structures. Spinal hemisection produced fibrous scar tissue in the lesion center, surrounded by nervous tissue. Two weeks after spinal lesioning, MMP-9 was expressed in some regenerating axons in the fibrous scar tissue. MMP-14 was expressed in the regenerating axons, as well as in glial processes in the fibrous scar tissue. MMP-2 was suggested to be expressed in mast cells in the fibrous scar. The mast cells were in contact with fibroblasts, and in close proximity to the basement membrane of tubular structures surrounding the regenerating axons. The present findings suggest that several MMPs are involved in axon regenerating processes following spinal cord injury in goldfish. MMP-9 and MMP-14 expressed in the regenerating axons might degrade extracellular matrix and support axonal growth deep into the fibrous scar tissue. MMP-14 expressed in glial cells and MMP-2 expressed in mast cells might also provide a beneficial environment for axonal regeneration, leading to successful motor recovery.

Chondroitin sulfate expression around spinal motoneurons during postnatal development in rats

Perineuronal nets are extracellular matrix structures that surround neuronal cell bodies and their proximal dendrites in the central nervous system. Chondroitin sulfate proteoglycans, which contain chondroitin sulfates (CSs) are major components of perineuronal nets. CSs are considered to have inhibitory roles in neural plasticity, although the effects differ according to their sulfation pattern. In the present study, we investigated the expression of the CS subtypes CS-A and CS-C surrounding spinal motoneurons in different postnatal periods to explore the potential influence of altered CS sulfation patterns on spinal development. CS-A-positive structures were observed around motoneurons in the cervical, thoracic, and lumbar segments as early as postnatal day (P) 5. Most motoneurons were covered with CS-A-positive structures during the first 2 postnatal weeks. The percentage of motoneurons covered with CS-A-positive structures decreased after P20, becoming lower than 70% in the cervical, and lumber segments after P35. CS-C-positive structures were occasionally observed around motoneurons during the first 2 postnatal weeks. The percentage of motoneurons covered with CS-C-positive structures increased after P20, becoming significantly higher after P25 than before P20. The expression pattern of Wisteria Floribunda agglutinin-positive structures around motoneurons was similar to that of the CS-C-positive structures. The present findings revealed that CS-A and CS-C are differentially expressed in the extracellular matrix surrounding motoneurons. The altered sulfation pattern with increased CS-C expression is associated with the maturation of perineuronal nets and might lead to changes in the motoneuron plasticity.