Development of microglia in the chick embryo spinal cord: implications in the regulation of motoneuronal survival and death.
The role of microglia during normal development of the nervous system is still not well understood. In the present study, a chick embryo model was used to examine the development of microglia in the spinal cord and characterize their changes in response to naturally occurring and pathological death of motoneurons (MNs). The microglial response to MN axotomy and the effects of microglial activation on MN survival were also studied. We found that: 1) macrophages/microglial cells were present in the spinal cord at early developmental stages (E3) and that they were recruited after normal and induced MN apoptosis; 2) although many microglial cells were seen phagocytosing apoptotic bodies, a proportion of dying cells were devoid of engulfing microglia; 3) axotomy of mature MNs was accompanied by microglial activation in the absence of MN death; 4) excitotoxic (necrotic) MN death provoked a rapid and massive microglial recruitment with phagocytic activity; 5) lipopolysaccharide-induced microglial activation in vivo resulted in the death of immature, but not mature, microglia; and 6) overactivation of microglia modulated the survival of mature MNs, either by killing them or by enhancing their vulnerability to die in response to a mild injury. Taken together, these observations indicate that normal microglia do not play an active role in triggering apoptosis of developing MNs. Rather, they act as phagocytes for the removal of dying cells during the process of programmed cell death.
Calderó
Jordi
J
Unitat de Neurobiologia Cel.lular, Departament de Medicina Experimental, Facultat de Medicina, Universitat de Lleida and Institut de Recerca Biomèdica de Lleida (IRBLLEIDA), Catalonia, Spain. jordi.caldero@mex.udl.cat
Brunet
Núria
N
Ciutat
Dolors
D
Hereu
Marta
M
Esquerda
Josep E
JE
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D019771:Axotomy; D002038:Bungarotoxins / Q000633:toxicity; D002452:Cell Count; D016923:Cell Death / Q000187:drug effects / Q000502:physiology*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology*; D002642:Chick Embryo; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000633:toxicity; D008070:Lipopolysaccharides / Q000633:toxicity; D008262:Macrophage Activation / Q000187:drug effects / Q000502:physiology; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D017628:Microglia / Q000187:drug effects / Q000502:physiology*; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009336:Necrosis / Q000503:physiopathology; D009498:Neurotoxins / Q000633:toxicity; D010587:Phagocytosis; D013116:Spinal Cord / Q000187:drug effects / Q000196:embryology* / Q000503:physiopathology; D013997:Time Factors
D002038:Bungarotoxins; D008070:Lipopolysaccharides; D009498:Neurotoxins; D007608:Kainic Acid