Krabbe disease (KD) is a neurodegenerative disorder caused by the lack of β- galactosylceramidase enzymatic activity and by widespread accumulation of the cytotoxic galactosyl-sphingosine in neuronal, myelinating and endothelial cells. Despite the wide use of Twitcher mice as experimental model for KD, the ultrastructure of this model is partial and mainly addressing peripheral nerves. More details are requested to elucidate the basis of the motor defects, which are the first to appear during KD onset. Here we use transmission electron microscopy (TEM) to focus on the alterations produced by KD in the lower motor system at postnatal day 15 (P15), a nearly asymptomatic stage, and in the juvenile P30 mouse. We find mild effects on motorneuron soma, severe ones on sciatic nerves and very severe effects on nerve terminals and neuromuscular junctions at P30, with peripheral damage being already detectable at P15. Finally, we find that the gastrocnemius muscle undergoes atrophy and structural changes that are independent of denervation at P15. Our data further characterize the ultrastructural analysis of the KD mouse model, and support recent theories of a dying-back mechanism for neuronal degeneration, which is independent of demyelination.

Visual deficits caused by abnormal visual experience during development are hard to recover in adult animals. Removal of chondroitin sulfate proteoglycans from the mature extracellular matrix with chondroitinase ABC promotes plasticity in the adult visual cortex. We tested whether chondroitinase ABC treatment of adult rats facilitates anatomical, functional, and behavioral recovery from the effects of a period of monocular deprivation initiated during the critical period for monocular deprivation. We found that chondroitinase ABC treatment coupled with reverse lid-suturing causes a complete recovery of ocular dominance, visual acuity, and dendritic spine density in adult rats. Thus, manipulations of the extracellular matrix can be used to promote functional recovery in the adult cortex.

Brain cells are immersed in a complex structure forming the extracellular matrix. The composition of the matrix gradually matures during postnatal development, as the brain circuitry reaches its adult form. The fully developed extracellular environment stabilizes neuronal connectivity and decreases cortical plasticity as highlighted by the demonstration that treatments degrading the matrix are able to restore synaptic plasticity in the adult brain. The mechanisms through which the matrix inhibits cortical plasticity are not fully clarified. Here we show that a prominent component of the matrix, chondroitin sulfate proteoglycans (CSPGs), restrains morphological changes of dendritic spines in the visual cortex of adult mice. By means of in vivo and in vitro two-photon imaging and electrophysiology, we find that after enzymatic digestion of CSPGs, cortical spines become more motile and express a larger degree of structural and functional plasticity.

Significance: The control of intracellular Cl ⁻ and pH plays a crucial role in several neuronal functions, and the study of these processes would be helped by tools for their noninvasive optical measurement in vivo. In this study, we have performed combined measurements of Cl ⁻ and pH of individual pyramidal neurons by means of in vivo two-photon imaging, and we provide direct experimental demonstration for the presence of the postnatal developmental shift to lower intraneuronal Cl ⁻ . Moreover, we introduce an approach for dynamic and simultaneous monitoring of intraneuronal Cl ⁻ and pH in vivo. These methods will open a window for the study of the roles of intraneuronal pH and Cl ⁻ in neuronal signaling, plasticity, and disease.

Enriched environment (EE) has been recently shown to affect visual cortex development and plasticity, and to prevent dark rearing effects. The factors mediating EE effects on visual cortical development and plasticity are still unclear. We have investigated whether IGF-1 is involved in mediating EE effects on the developing visual cortex. We show that EE increases the number of IGF-1 positive neurons in the visual cortex at P18. Increasing IGF-1 in the visual cortex of non-EE rats by means of osmotic minipumps implanted at P18 mimics EE effects, accelerating visual acuity development, assessed with Visual Evoked Potentials (VEPs). Blocking IGF-1 action in the visual cortex of EE rats by means of the IGF-1 receptor antagonist JB1 from P18 completely blocks EE action on visual acuity development. These results show that IGF-1 is a key factor mediating EE effects on visual cortical development. We then show that IGF-1 affects GAD65 immunoreactivity in perisomatic innervation and the condensation of Chondroitin Sulphate Proteoglycans (CSPGs) in perineuronal nets (PNNs) in the visual cortex. This suggests that IGF-1 action in mediating EE effects could be exerted through the modulation of intracortical inhibitory circuitry and PNN development.