Neuronal expression of macrophage colony stimulating factor in Purkinje cells and olfactory mitral cells of wild-type and cerebellar-mutant mice

Macrophage colony stimulating factor (M-CSF) is known to be the most effective growth factor for macrophage and microglial proliferation. In the brain tissue system, M-CSF is mainly produced in astrocytes and microglia, but is not known to occur in neurons. In the present paper, we examined the distribution of neurons expressing M-CSF in the mouse brain by immuno-histochemistry and in situ hybridization. We observed M-CSF immunoreactivity in both the cerebellum and the olfactory bulb. These positive cells were found to be Purkinje cells in the cerebellum, and mitral cells in the olfactory bulb. M-CSF mRNA expression was also confirmed to occur in these cells. Purkinje cells of reeler and weaver mutants showed M-CSF expression as seen in wild-type mice; however, those in the staggerer mutant did not. This expression in wild-type mice first appeared at postnatal day 7 and continued stably thereafter. When Purkinje cells were deprived of their climbing fibre innervation by inferior cerebellar pedunculotomy or by transplantation of cerebellar anlagen into the anterior eye chamber, the expression of M-CSF remained unchanged. These data indicate that expression of M-CSF in Purkinje cells is controlled by an intrinsic mechanism and could, therefore, be a new marker of postnatal development in rodent cerebella. The absence of M-CSF expression in the staggerer mutant is possibly due to developmental arrest in the early postnatal period.