ABSTRACT
Remyelination of the CNS is necessary to restore neural function in a number of demyelinating conditions. Schwann cells, the myelinating cells of the periphery, are candidates for this purpose because they have more robust regenerative properties than their central homologs, the oligodendrocytes. Although the ability of Schwann cells to remyelinate the CNS has been demonstrated, their capacity to enter the adult spinal cord in large numbers and effect functional recovery remains uncertain. We used cholera toxin B-subunit conjugated to saporin to demyelinate the rat lumbar spinal cord, remove macroglia, and produce paraplegia. After the removal of oligodendrocyte and astrocyte debris by invading macrophages, there was a spontaneous entry of Schwann cells into the spinal cord, along with axonal remyelination and concomitant functional recovery from paraplegia occurring within 75 d. The Schwann cells appeared to enter the dorsal funiculi via the dorsal root entry zone and the lateral funiculi via rootlets that had become adherent to the lateral spinal cord after the inflammation. In the following weeks, Schwann cell myelin surrounding central axons was progressively replaced by oligodendrocyte myelin without lapse in motor function. Our results show that endogenous Schwann cells can reverse a severe neurological deficit caused by CNS demyelination and enable later oligodendrocyte remyelination.
Subject(s)
Demyelinating Diseases/pathology , Immunotoxins , N-Glycosyl Hydrolases , Paraplegia/pathology , Recovery of Function , Schwann Cells/pathology , Spinal Cord/pathology , Animals , Astrocytes/drug effects , Astrocytes/pathology , Cell Count , Cholera Toxin/administration & dosage , Cholera Toxin/chemistry , Cholera Toxin/metabolism , Demyelinating Diseases/chemically induced , Demyelinating Diseases/complications , Demyelinating Diseases/metabolism , Female , G(M1) Ganglioside/metabolism , Injections, Spinal , Lumbosacral Region , Macrophages/pathology , Male , Myelin Sheath/pathology , Oligodendroglia/drug effects , Oligodendroglia/pathology , Paraplegia/etiology , Paraplegia/rehabilitation , Plant Proteins/administration & dosage , Plant Proteins/chemistry , Rats , Rats, Sprague-Dawley , Ribosome Inactivating Proteins, Type 1 , Saporins , Spinal Cord/metabolism , Substance P/chemistryABSTRACT
To obtain rapidly inducible and reversible expression of transgenes in the forebrain of the mouse, we have combined the reverse tetracycline-controlled transactivator (rtTA) system with the CaMKIIalpha promoter. We show that doxycycline induces maximal gene expression in neurons of the forebrain within 6 days and that this expression can be reversed by removal of doxycycline. Using calcineurin as a test transgene, we show that doxycycline-induced expression impairs both an intermediate form of LTP (I-LTP) in the hippocampus and the storage of spatial memory. The reversibility of the rtTA system in turn allowed us to examine the effects of the transgene on memory retrieval after normal storage had occurred. This examination suggests that retrieval requires some of the same molecular components required for storage.
Subject(s)
Gene Expression Regulation/physiology , Memory/physiology , Prosencephalon/drug effects , Tetracycline/pharmacology , Trans-Activators/drug effects , Animals , Anti-Bacterial Agents/pharmacology , Calcineurin/genetics , Calcium-Calmodulin-Dependent Protein Kinase Type 2 , Calcium-Calmodulin-Dependent Protein Kinases/genetics , Dose-Response Relationship, Drug , Doxycycline/pharmacology , Maze Learning/physiology , Mice , Mice, Transgenic , Neural Pathways/drug effects , Promoter Regions, Genetic , Prosencephalon/metabolism , Trans-Activators/biosynthesisABSTRACT
To investigate the role of phosphatases in synaptic plasticity using genetic approaches, we generated transgenic mice that overexpress a truncated form of calcineurin under the control of the CaMKIIalpha promoter. Mice expressing this transgene show increased calcium-dependent phosphatase activity in the hippocampus. Physiological studies of these mice and parallel pharmacological experiments in wild-type mice reveal a novel, intermediate phase of LTP (I-LTP) in the CA1 region of the hippocampus. This intermediate phase differs from E-LTP by requiring multiple trains for induction and in being dependent on PKA. It differs from L-LTP in not requiring new protein synthesis. These data suggest that calcineurin acts as an inhibitory constraint on I-LTP that is relieved by PKA. This inhibitory constraint acts as a gate to regulate the synaptic induction of L-LTP.
Subject(s)
Calcineurin/physiology , Long-Term Potentiation/physiology , Action Potentials/physiology , Animals , Calcineurin/genetics , Cyclic AMP-Dependent Protein Kinases/pharmacology , Cyclic AMP-Dependent Protein Kinases/physiology , Electric Stimulation , Enzyme Inhibitors/pharmacology , Excitatory Postsynaptic Potentials/physiology , Female , Gene Expression/genetics , Gene Expression/physiology , Gene Expression Regulation/genetics , Gene Expression Regulation/physiology , Genetic Engineering , Hippocampus/chemistry , Hippocampus/metabolism , Long-Term Potentiation/drug effects , Long-Term Potentiation/genetics , Male , Mice , Mice, Inbred CBA , Mice, Mutant Strains , Mice, Transgenic , Phosphoprotein Phosphatases/antagonists & inhibitors , Phosphoric Monoester Hydrolases/physiology , Protein Biosynthesis , Proteins/drug effects , Pyramidal Cells/physiology , Recombinant Proteins/genetics , Stimulation, Chemical , Synapses/physiology , Synaptic Transmission/genetics , Synaptic Transmission/physiology , Transgenes/genetics , Transgenes/physiologyABSTRACT
Seven docking predictions were made with the LIGIN program. In six cases the location of the binding pocket was identified correctly by systematically docking everywhere within the protein structure. In two cases the ligand was docked to within 1.8 A RMSD of the experimentally determined structure. LIGIN has not been optimized to deal with highly flexible ligands that dock at the surface of proteins. Consequently, in three cases the exposed part of the ligand was docked poorly, although the buried parts were docked well, and made similar atomic contacts with the protein as in the experimentally determined structure.
