We present chemical, physical, immunohistochemical, and therapeutic evidence that functional deficits caused by neuroinflammation can arise from tissue hypoxia, consistent with an energy crisis in inflamed central nervous system tissue. The neurological deficit was closely correlated with spinal white and gray matter hypoxia. This realization may indicate new avenues for therapy of neuroinflammatory diseases such as MS.

Neurexins are cell-surface molecules that bind neuroligins to form a heterophilic, Ca 2؉ -dependent complex at central synapses. This transsynaptic complex is required for efficient neurotransmission and is involved in the formation of synaptic contacts. In addition, both molecules have been identified as candidate genes for autism. Here we performed mutagenesis experiments to probe for essential components of the neurexin/neuroligin binding interface at the single-amino acid level. We found that in neurexins the contact area is sharply delineated and consists of hydrophobic residues of the LNS domain that surround a Ca 2؉ binding pocket. Point mutations that changed electrostatic and shape properties leave Ca 2؉ coordination intact but completely inhibit neuroligin binding, whereas alternative splicing in ␣-and ␤-neurexins and in neuroligins has a weaker effect on complex formation. In neuroligins, the contact area appears less distinct because exchange of a more distant aspartate completely abolished binding to neurexin but many mutations of predicted interface residues had no strong effect on binding. Together with calculations of energy terms for presumed interface hot spots that complement and extend our mutagenesis and recent crystal structure data, this study presents a comprehensive structural basis for the complex formation of neurexins and neuroligins and their transsynaptic signaling between neurons.calcium ͉ cell adhesion ͉ LNS domain ͉ neurotransmission ͉ synaptogenesis T he heterophilic complex formed by cell adhesion molecules neurexin (Nrxn) and neuroligin (Nlgn) reflects the asymmetric nature of the synapse with presynaptic and postsynaptic specializations (1, 2). Nrxns and Nlgns are essential molecules because they perform important functions in synaptic transmission (3, 4) and differentiation of synaptic contacts (5, 6), and both molecules have been identified as candidate genes for autism (7,8).Nrxns form a family of transmembrane proteins with variable extracellular sequences. Nrxn genes (Nrxn1-3) give rise to ␣-neurexins and shorter ␤-neurexins that contain five (␣-Nrxn) or two (␤-Nrxn) splice sites (SS1-5) (9). Although they share most sequences, the essential role of ␣-Nrxn in neurotransmission cannot be replaced by ␤-Nrxn (10), and one ligand exists for ␣-Nrxn that does not bind to ␤-Nrxn (11). In contrast, Nlgn was discovered by its interaction with ␤-Nrxn (12). The cholinesterase-like adhesion molecule (CAM) domain of Nlgn interacts with the extracellular domain of ␤-Nrxn in a Ca 2ϩ -dependent manner, and binding is facilitated by the splice variation of ␤-Nrxn that lacks an insert in SS4 (13). Nlgn mRNA is also susceptible to splicing, at two positions referred to as A and B (12), including splice variants with no insert in B that bind to all ␤-Nrxns and presumably ␣-Nrxn (14). Therefore, the Nrxn/Nlgn complex involves a domain shared by ␣-and ␤-Nrxns, and any structural characterization needs to account for the Ca 2ϩ dependence and regulation by alternative splicing (15-17).Extracell...

The development of neuronal networks in the brain requires the differentiation of functional synapses. Neurobeachin (Nbea) was identified as a putative regulator of membrane protein trafficking associated with tubulovesicular endomembranes and postsynaptic plasma membranes. Nbea is essential for evoked transmission at neuromuscular junctions, but its role in the central nervous system has not been characterized. Here, we have studied central synapses of a newly generated gene-trap knockout (KO) mouse line at embryonic day 18, because null-mutant mice are paralysed and die perinatally. Although the overall brain architecture was normal, we identified major abnormalities of synaptic function in mutant animals. In acute slices from the brainstem, both spontaneous excitatory and inhibitory postsynaptic currents were clearly reduced and failure rates of evoked inhibitory responses were markedly increased. In addition, the frequency of miniature excitatory and both the frequency and amplitudes of miniature inhibitory postsynaptic currents were severely diminished in KO mice, indicating a perturbation of both action potential-dependent and -independent transmitter release. Moreover, Nbea appears to be important for the formation and composition of central synapses because the area density of mature asymmetric contacts in the fetal brainstem was reduced to 30% of wild-type levels, and the expression levels of a subset of synaptic marker proteins were smaller than in littermate controls. Our data demonstrate for the first time a function of Nbea at central synapses that may be based on its presumed role in targeting membrane proteins to synaptic contacts, and are consistent with the 'excitatory-inhibitory imbalance' model of autism where Nbea gene rearrangements have been detected in some patients.

Optic neuritis is one of the first manifestations of multiple sclerosis. Its pathogenesis is incompletely understood, but considered to be initiated by an auto‐immune response directed against myelin sheaths of the optic nerve. Here, we demonstrate in two frequently used and well‐validated mouse models of optic neuritis that ribbon synapses in the myelin‐free retina are targeted by an auto‐reactive immune system even before alterations in the optic nerve have developed. The auto‐immune response is directed against two adhesion proteins (CASPR1/CNTN1) that are present both in the paranodal region of myelinated nerves as well as at retinal ribbon synapses. This occurs in parallel with altered synaptic vesicle cycling in retinal ribbon synapses and altered visual behavior before the onset of optic nerve demyelination. These findings indicate that early synaptic dysfunctions in the retina contribute to the pathology of optic neuritis in multiple sclerosis.