Expression of the inducible nitric oxide synthase in distinct cellular types after traumatic brain injury: an in situ hybridization anal immunocytochemical study
T. Petrov et al., Expression of the inducible nitric oxide synthase in distinct cellular types after traumatic brain injury: an in situ hybridization anal immunocytochemical study, ACT NEUROP, 100(2), 2000, pp. 196-204
The Marmarou's acceleration traumatic brain injury (TBI) model, in situ hyb
ridization and immunocytochemistry were utilized to study the temporal expr
ession of the inducible form of nitric oxide synthase (iNOS) mRNA and prote
in in different cellular compartments of the rat brain. Four hours followin
g TBI, expression of iNOS was observed in the endothelial cells of cerebral
blood vessels, macrophages and many cortical and hippocampal neurons. In t
he cortex labeled neuronal and nonneuronal cells were primarily found in th
e superficial layers. In the hippocampus the strongest neuronal labeling wa
s observed in the CA1 and CA3 (lateral part) regions. By 24 h post TBI endo
thelial cells no longer expressed iNOS mRNA, and the macrophage and neurona
l INOS expression was reduced by 30-50%. The reduction was assessed by auto
mated quantitation of the silver grains that occupy individual cellular pro
files using an image analysis system. Immunocytochemistry revealed de novo
iNOS synthesis in non-neuronal cells at the different time points, thus par
alleling the changes in iNOS mRNA expression. In contrast, iNOS immunoreact
ivity in neurons was not observed before 24 h post TBI, suggesting failure
of iNOS protein translation at 4 h after trauma. The results demonstrate co
mplex spatial and temporal patterns of iNOS expression in discrete cellular
populations, indicating different times of nitric oxide synthesis (and rel
ease) following TBI. Uncoupling of iNOS mRNA and protein synthesis in neuro
ns suggests differential synthesis of nitric oxide in these cells as compar
ed to non-neuronal cellular populations after trauma.