NMDA-dependent proteolysis of presynaptic adhesion molecule L1 in the hippocampus by neuropsin.

Synaptic plasticity requires an activity-dependent, rapid, and long-lasting modification of synaptic character, including morphology and coupling strength. Here we show that a serine protease, neuropsin, directly and specifically modifies the synaptic adhesion molecule L1, which was localized to the presynaptic site of the asymmetric synapse in the mouse hippocampus. Increased neural activity triggered the rapid, transient activation of the precursor form of neuropsin in an NMDA receptor-dependent manner. The activated neuropsin immediately cleaved L1 and released a neuropsin-specific extracellular 180 kDa fragment. This neuropsin-specific L1-cleaving system is involved in NMDA receptor-dependent synaptic plasticity, such as the Schaffer collateral long-term potentiation.

Distribution and densitometry mapping of L1-CAM immunoreactivity in the adult mouse brain--light microscopic observation.

BACKGROUND: The importance of L1 expression in the matured brain is suggested by physiological and behavioral studies showing that L1 is related to hippocampal plasticity and fear conditioning. The distribution of L1 in mouse brain might provide a basis for understanding its role in the brain. RESULTS: We examined the overall distribution of L1 in the adult mouse brain by immunohistochemistry using two polyclonal antibodies against different epitopes for L1. Immunoreactive L1 was widely but unevenly distributed from the olfactory bulb to the upper cervical cord. The accumulation of immunoreactive L1 was greatest in a non-neuronal element of the major fibre bundles, i.e. the lateral olfactory tract, olfactory and temporal limb of the anterior commissure, corpus callosum, stria terminalis, globus pallidus, fornix, mammillothalamic tract, solitary tract, and spinal tract of the trigeminal nerve. High to highest levels of non-neuronal and neuronal L1 were found in the grey matter; i.e. the piriform and entorhinal cortices, hypothalamus, reticular part of the substantia nigra, periaqueductal grey, trigeminal spinal nucleus etc. High to moderate density of neuronal L1 was found in the olfactory bulb, layer V of the cerebral cortex, amygdala, pontine grey, superior colliculi, cerebellar cortex, solitary tract nucleus etc. Only low to lowest levels of neuronal L1 were found in the hippocampus, grey matter in the caudate-putamen, thalamus, cerebellar nuclei etc. CONCLUSION: L1 is widely and unevenly distributed in the matured mouse brain, where immunoreactivity was present not only in neuronal elements; axons, synapses and cell soma, but also in non-neuronal elements.

Identification and characterization of novel human Ca(v)2.2 (alpha 1B) calcium channel variants lacking the synaptic protein interaction site.

The physical interaction between the presynaptic vesicle release complex and the large cytoplasmic region linking domains II and III of N-type (Ca(v)2.2) calcium channel alpha(1)B subunits is considered to be of fundamental importance for efficient neurotransmission. By PCR analysis of human brain cDNA libraries and IMR32 cell mRNA, we have isolated novel N-type channel variants, termed Ca(v)2.2-Delta1 and Delta2, which lack large parts of the domain II-III linker region, including the synaptic protein interaction site. They appear to be widely expressed across the human CNS as indicated by RNase protection assays. When expressed in tsA-201 cells, both novel variants formed barium-permeable channels with voltage dependences and kinetics for activation that were similar to those observed with the full-length channel. All three channel types exhibited the hallmarks of prepulse facilitation, which interestingly occurred independently of G-protein betagamma subunits. By contrast, the voltage dependence of steady-state inactivation seen with both Delta1 and Delta2 channels was shifted toward more depolarized potentials, and recovery from inactivation of Delta1 and Delta2 channels occurred more rapidly than that of the full-length channel. Moreover, the Delta1 channel was dramatically less sensitive to both omega-conotoxin MVIIA and GVIA than either the Delta2 variant or the full-length construct. Finally, the domain II-III linker region of neither variant was able to effectively bind syntaxin in vitro. These results suggest that the structure of the II-III linker region is an important determinant of N-type channel function and pharmacology. The lack of syntaxin binding hints at a unique physiological function of these channels.