Microglial conditioned medium promotes survival and development of cultured mesencephalic neurons from embryonic rat brain

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Abstract
We previously reported that microglial conditioned medium (Mic‐CM) has a neurotrophic effect on cultured rat neocortical neurons [Nakajima et al. (1989): Biomed Res 10:411–423]. In order to investigate the interaction between microglia and neurons in more detail, we determined the effects of Mic‐CM on the primary cultured mesencephalic neurons from 16‐day embryonic rats. The addition of Mic‐CM to the culture medium significantly enhanced the survivability of neurons and promoted neurite extension in a low cell‐density culture condition. In a high cell‐density culture condition, Mic‐CM markedly increased dopamine uptake, which was quantified by assessing the specific [3H]dopamine uptake, and also increased the dopamine content of cultured cells. Furthermore, the number of mesencephalic dopaminergic neurons, which was determined by quantitative analysis of tyrosine hydroxylase (TH)‐immunoreactive cells, increased significantly in the presence of Mic‐CM. These results suggest that Mic‐CM enhances survival or maturation of TH‐positive neurons present in cultures of the embryonic mesencephalon and that these neurotrophic effects may be due to a diffusible factor(s) from microglia.