Intracerebral dopaminergic transplantation has been accepted as a viable treatment option of Parkinson`s disease. However, despite the abundant data regarding the fate of the transplanted neurons, little is known of the glial reaction following transplantation.
In the present study, we investigate the reaction of host microglial cells to intracerebral transplantation of embryonic dopaminergic cells in a rodent model of Parkinson`s disease. By means of immunohistochemistry, we compare the characteristics of the microglial reaction in different zones surrounding the intrastriatal grafts, with those in areas of mechanical influence by the transplantation instrument only at two distinct time points.
Data shows that activated microglia is present around grafts, as well as around areas of mechanical influence. Activated ameboid microglial cells are present along the graft-host interface on day 28 following transplantation. This finding stands out against the reaction around areas of mechanical influence only, in which on day 28 the microglial cells tend to have a more quiescent morphology. Surprisingly, the quantitative characteristics of microglial recruitment are significantly lower around grafts, compared to the respective zones around areas of mechanical influence.
Our findings of fewer, but more active cells around grafts, are suggestive of a prolonged activation of host microglial cells by transplanted tissue. Because no graft rejection is present, this can be explained with modification of microglial reaction by grafted cells. An equilibrium between neuroprotective and proinflammatory microglia exists around grafts, and it is crucial for the synaptic integration of transplanted cells. Further clarification of mechanisms of microglial activation following transplantation could potentially contribute to the development of novel neuroprotective strategies.
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