In BM, LPS significantly increased the release of NO, TNF-a and IL-1b. Interestingly, LPS did not induce a statistically significant increase in the release TNF-a and IL-1b in SCM, and levels of all three of these pro-inflammatory cytokines in media from activated SCM were significantly reduced relative to BM. Conversely IL-6 and IL10 release by LPS-activated SCM exhibited a non-significant trend towards higher release than BM. LPS activation was also associated with an increase in phagocytic activity of BM but not SCM. Overall, our findings suggest that SCM exhibit a less inflammatory and phagocytic phenotype than BM in response to activation with LPS. Interestingly, a recent in vivo study using fluorescence assisted cell sorting demonstrated that expression levels of the surface receptors CD45 and CD11b are higher in spinal microglia than brain microglia in naı ¨ve mice. In cells sorted three days after viral infection with Theiler’s murine encephalomyelitis virus, surface receptors were upregulated in spinal microglia compared to brain microglia. Combined with our findings, these data suggest that the activating stimulus and local environment interact to determine the phenotypic response of microglia. For example, microglia from neonatal cortex and hippocampus are more neurotoxic than those from striatum, thalami or brainstem. Notably, microglia from neonatal striatum have a more ramified morphology and reduced release of proinflammatory effectors relative to cortical microglia. However, the morphological and functional heterogeneity of BM vs. SCM has not previously been assessed. Given that SCM can affect the fate of neurons during development and after spinal cord injury, an understanding of the functional response properties of spinal microglia is important. Primary SCM cultures are not common in the literature and have not been characterized to the extent of BM primary cultures. Mild trypsinization is an established protocol for isolation of primary BM, with higher yields than isolation via shaking, but has not been well validated for use in SCM. Here, we demonstrate that mild trypsinization can also be used to isolate microglia from mixed glial cultures derived from neonatal rat spinal cord tissue. IL-1b has a more typical inflammatory and neurotoxic profile, and inhibition of IL-1b reduces neuronal tissue damage after brain injury. Similarly, NO is an inflammatory and neurotoxic mediator known to contribute the lesion growth in spinal cord injury, stroke, and brain injury by the reactive metabolite perioxynitrite. As such, the relative reduction in the release of pro-inflammatory effectors by SCM relative to BM suggests that SCM might have a less neurotoxic profile after activation by LPS in vitro. It is well known that IL-6 and IL-10 are upregulated after an injury or disease in CNS and that microglia are capable of releasing IL-6 and IL-10.