Microglial activation and vascular responses that are associated with early thalamic neurodegeneration resulting from thiamine deficiency.

Thiamine/vitamin B1 deficiency can lead to behavioral changes and neurotoxicity in humans. This may due in part to vascular damage, neuroinflammation and neuronal degeneration in the diencephalon, which is seen in animal models of pyrithiamine-enhanced thiamine deficiency. However, the time course of the progression of these changes in the animal models has been poorly characterized. Therefore, in this study, the progression of: 1) activated microglial association with vasculature; 2) neurodegeneration; and 3) any vascular leakage in the forebrain during the progress of thiamine deficiency were determined. A thiamine deficient diet along with 0.25 mg/kg/d of pyrithiamine was used as the mouse model. Vasculature was identified with Cd31 and microglia with Cd11b and Iba1 immunoreactivity. Neurodegeneration was determined by FJc labeling. The first sign of activated microglia within the thalamic nuclei were detected after 8 d of thiamine deficiency, and by 9 d activated microglia associated primarily with vasculature were clearly present but only in thalamus. At the 8 d time point neurodegeneration was not present in thalamus. However at 9 d, the first signs of neurodegeneration (FJc + neurons) were seen in most animals. Over 80% of the microglia were activated at 10 d but almost exclusively in the thalamus and the number of degenerating neurons was less than 10% of the activated microglia. At 10 d, there were sporadic minor changes in IgG presence in thalamus indicating minor vascular leakage. Dizocilpine (0.2-0.4 mg/kg) or phenobarbital (10-20 mg/kg) was administered to groups of mice from day 8 through day 10 to block neurodegeneration but neither did. In summary, activated microglia start to surround vasculature 1-2 d prior to the start of neurodegeneration. This response may be a means of controlling or repairing vascular damage and leakage. Glutamate excitotoxicity and vascular leakage likely only play a minor role in the early neurodegeneration resulting from thiamine deficiency. However, failure of dysfunctional vasculature endothelium to supply sufficient nutrients to neurons could be contributing to the neurodegeneration.