Evidence for synaptic stripping by cortical microglia.
Recent studies have described significant demyelination and microglial activation in the cerebral cortex of brains from multiple sclerosis patients. To date, however, experimental models of cortical demyelination or cortical inflammation have not been extensively studied. In this report we describe focal cortical inflammation induced by stereotaxic injection of killed bacteria (BCG), followed 1 month later by subcutaneous injection of the same antigen, a protocol that overcomes the immune privilege of the cortex. Intracerebral BCG injection produced focal microglial activation at the injection site (termed acute lesion). Ten days after peripheral challenge (termed immune-mediated lesion), larger areas and higher densities of activated microglia were found near the injection site. In both paradigms, activated microglia and/or their processes closely apposed neuronal perikarya and apical dendrites. In the immune-mediated lesions, approximately 45% of the axosomatic synapses was displaced by activated microglia. Upon activation, therefore, cortical microglial migrate to and strip synapses from neuronal perikarya. Since neuronal pathology was not a feature of either the acute or immune-mediated lesion, synaptic stripping by activated microglia may have neuroprotective consequences.
Trapp
Bruce D
BD
Department of Neurosciences, Lerner Research Institute, The Cleveland Clinic, Cleveland, OH 44195, USA. trappb@ccf.org
Wujek
Jerome R
JR
Criste
Gerson A
GA
Jalabi
Walid
W
Yin
Xinghua
X
Kidd
Grahame J
GJ
Stohlman
Stephen
S
Ransohoff
Richard
R
D000818:Animals; D001500:BCG Vaccine / Q000276:immunology / Q000633:toxicity; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D018932:Chemokine CCL2 / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005620:Freund's Adjuvant / Q000494:pharmacology; D007150:Immunohistochemistry; D007249:Inflammation / Q000139:chemically induced; D008297:Male; D017628:Microglia / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D051381:Rats; D011917:Rats, Inbred Lew; D013569:Synapses / Q000378:metabolism / Q000502:physiology*
D001500:BCG Vaccine; C491766:Ccl2 protein, rat; D018932:Chemokine CCL2; D005620:Freund's Adjuvant