Intensely positively charged perineuronal nets in the adult rat brain as detected by staining with anionic iron colloid

Full-Scale Label-Free Surface-Enhanced Raman Scattering Analysis of Mouse Brain Using a Black Phosphorus-Based Two-Dimensional Nanoprobe

The brain takes the vital role in human physiological and psychological activities. The precise understanding of the structure of the brain can supply the material basis for the psychological behavior and cognitive ability of human beings. In this study, a fast molecular fingerprint analysis of mouse brain tissue was performed using surface-enhanced Raman scattering (SERS) spectroscopy. A nanohybrid consisting of flake-like black phosphorus (BP) and Au nanoparticles (BP-AuNSs) served as the novel SERS substrate for the spectral analysis of brain tissue. BP-AuNSs exhibited outstanding SERS activity compared to the traditional citrate-stabilized Au nanoparticles, which could be largely ascribed to the plentiful hot spots formed in the BP nanosheet. Rapid, full-scale and label-free SERS imaging of mouse brain tissue was then realized with a scanning speed of 56 ms per pixel. Fine textures and clear contour were observed in the SERS images of brain tissue, which could be well in accordance with the classical histological analysis; however, it could avoid the disadvantages in the processing procedure of tissue section. Additionally, the SERS spectra illustrated plentiful biochemical fingerprint of brain tissue, which indicated the molecular composition of various encephalic regions. The SERS difference spectrum of the left versus right hemisphere revealed the biochemical difference between the two hemispheres, which helped to uncover the psychological and cognitive models of the left and right hemispheres.

Perineuronal nets increase inhibitory GABAergic currents during the critical period in rats

AIM

To investigate inhibitory γ-aminobutyric acid (GABA) ergic postsynaptic currents (IPSCs) and postsynaptic currents (PSCs) in layer IV of the rat visual cortex during the critical period and when plasticity was extended through dissolution of the perineuronal nets (PNNs).

METHODS

We employed 24 normal Long-Evans rats to study GABAA-PSC characteristics of neurons within layer IV of the visual cortex during development. The animals were divided into six groups of four rats according to ages at recording: PW3 (P21-23d), PW4 (P28-30d), PW5 (P35-37d), PW6 (P42-44d), PW7 (P49-51d), and PW8 (56-58d). An additional 24 chondroitin sulfate proteoglycan (CSPG) degradation rats (also Long-Evans) were generated by making a pattern of injections of chondroitinase ABC (chABC) into the visual cortex 1 week prior to recording at PW3, PW4, PW5, PW6, PW7, and PW8. Immunohistochemistry was used to identify the effect of chABC injection on CSPGs. PSCs were detected with whole-cell patch recordings, and GABAA receptor-mediated IPSCs were pharmacologically isolated.

RESULTS

IPSC peak current showed a strong rise in the age-matched control group, peaked at PW5 and were maintained at a roughly constant value thereafter. Although there was a small increase in peak current for the chABC group with age, the peak currents continued to decrease with the delayed highest value at PW6, resulting in significantly different week-by-week comparison with normal development. IPSC decay time continued to increase until PW7 in the control group, while those in the chABC group were maintained at a stable level after an initial increase at PW4. Compared with normal rats, the decay times recorded in the chABC rats were always shorter, which differed significantly at each age. We did not observe any differences in IPSC properties between the age-matched control and penicillinase (P-ase) group. However, the change in IPSCs after chABC treatment was not reflected in the total PSCs or in basic membrane properties in layer IV of the rat visual cortex.

CONCLUSION

Our results demonstrate that rather than rapidly increasing during the critical period for neuronal plasticity, IPSCs in layer IV of rat visual cortex are maintained at an immature level when PNNs are removed by chABC. This suggests that GABA receptor maturation involves the conformation of the CSPGs in PNNs.

Injured mice at the gym: review, results and considerations for combining chondroitinase and locomotor exercise to enhance recovery after spinal cord injury

Exercise provides a number of important benefits after spinal cord injury in clinical studies and animal models. However, the amount of functional improvement in overground locomotion obtained with exercise alone has been limited thus far, for reasons that are still poorly understood. One hypothesis is that the complex network of endogenous extracellular matrix components, including chondroitin sulfate proteoglycans (CSPGs), can inhibit exercise-induced remodeling and limit plasticity of spared circuitry in the adult central nervous system. Recent animal studies have shown that chondroitinase ABC (ChABC) can enhance plasticity in the adult nervous system by cleaving glycosaminoglycan sidechains from CSPGs. In this article we review the current literature on plasticity observed with locomotor training and following degradation of CSPGs with ChABC and then present a rationale for the use of exercise combined with ChABC to promote functional recovery after spinal cord injury. We also present results of a preliminary study that tested the simplest approach for combining these treatments; use of a single intraparenchymal injection of ChABC administered to the lumbar enlargement of mice with voluntary wheel running exercise after a mid-thoracic spinal contusion injury. The results are negative, yet serve to highlight limitations in our understanding of the most effective protocols for combining these approaches. Further work is directed to identify the timing, type, and quantity of exercise and pharmacological interventions that can be used to maximize functional improvements by strengthening appropriate synaptic connections.

Perisynaptic barrier of proteoglycans in the mature brain and spinal cord

Cell bodies and their dendrites of motor neurons, motor-related neurons, and certain other subsets of neurons such as GABAergic interneurons in the mature brain and spinal cord possess intensely negatively charged perineuronal or perisynaptic nets of proteoglycans which are linked to the nerve cell surface glycoproteins. These perineuronal nets of proteoglycans are digested by chondroitinase ABC, hyaluronidase, or collagenase, but not by endo-alpha-N-acetylgalactosaminidase, which is reactive to the nerve cell surface glycoproteins. Aggrecan, versican, neurocan, and brevican are members of a family of chondroitin sulfate proteoglycans that bind to hyaluronan. Neurocan- or brevican-deficient mice showed a regionally heterogeneous composition of proteoglycans in perineuronal nets. Aggrecan glycoforms contribute to the molecular heterogeneity of the perineuronal nets. Proteoglycans such as phosphacan are included in matrix-associated proteoglycans. The extracellular matrix glycoprotein tenascin-R is accumulated in the perineuronal nets. The perineuronal proteoglycans are produced by associated satellite astrocytes just before weaning, while the nerve cell surface glycoproteins are produced by the associated nerve cells at earlier stages after birth. The perineuronal proteoglycans may entrap the tissue fluid and form a perineuronal gel layer which protects the synapses as a "perisynaptic barrier". Degradation of the perineuronal proteoglycans or perisynaptic barrier by treatment with chondroitinase ABC or hyaluronidase reactivates the neuronal plasticity or promotes the functional recovery of a severed nervous system. Another set of perineuronal nets occurs, which are intensely positively charged and contain guanidino compounds. It is considered that these intensely positively charged nets are intermingled with the intensely negatively charged ones of proteoglycans.

The intensely positively charged perineuronal net in the adult rat brain, with special reference to its reactions to oxine, chondroitinase ABC, hyaluronidase and collagenase

Light microscopic observations of healthy adult rat brain sections stained with anionic iron colloid indicated that 5-10% of neurons in the hippocampal subiculum and all neurons in the medial cerebellar nucleus possessed an intensely positively charged perineuronal net. This net was demonstrated to react to oxine, and therefore suggested to consist of guanidino compounds. It was further shown that the intensely positively charged perineuronal net, in accordance with the intensely negatively charged perineuronal net of proteoglycans, was digested by chondroitinase ABC, hyaluronidase, and collagenase, but not by endo-alphaN-acetylgalactosaminidase. This finding suggested that the former positively charged net might be linked to the latter negatively charged one.

Purkinje cells in the adult cat cerebellar cortex possess a perineuronal net of proteoglycans

The Purkinje cells in the adult cat cerebellar cortex were found to possess perineuronal proteoglycans which could be stained with our fine cationic iron colloid and Fujita's highly concentrated aldehyde fuchsin, and digested by chondroitinase ABC/keratanase/ heparitinase and hyaluronidase. The Purkinje cells are surrounded by some collagenous elements which are stained with Gömöri's ammoniacal silver and digested by collagenase. The Purkinje cells also express nerve cell surface glycoproteins which are labeled with lectin Vicia villosa agglutinin and digested by a double treatment with collagenase and endo-alpha-N-acetylgalactosaminidase. Sole digestion by endo-alpha-N-acetylgalactosaminidase never erased the lectin labeling of the nerve cell surface glycoproteins. These findings suggest that the collagenous elements mediate the linkage of the perineuronal proteoglycans to the nerve cell surface glycoproteins. It is presumed that in mice and rats, the perineuronal nets of proteoglycans and nerve cell surface glycoproteins of the Purkinje cells are so thin or coarse that they can not be sufficiently visualized under the light microscope.