3.1 BLA astrocytes were activated in rats with DNP
Within 3 days following an i.p. injection of STZ, blood glucose levels were significantly higher in the diabetic rats than in the control rats (Fig. 1A). All STZ-treated rats exhibited polydipsia, polyuria and polyphagia. Although food and water intake significantly increased, body weights of the STZ-treated rats were profoundly reduced (Fig. 1B). In addition, mechanical allodynia was consistently present in the diabetic rats, compared with the control rats, 7 days after STZ injection, indicating that the diabetic rats developed mechanical allodynia (Fig. 1C).
Anxiety-like behavior is a common comorbidity of chronic neuropathic pain. Next, we assessed the effect of STZ-induced chronic pain on anxiety-like behavior in rats. In the open field test, the total distance of the rats in the open field and the distance in the central area of the open field differ significantly between DNP rats and controls (Fig. 1E-1G). In the elevated plus maze test, we observed DNP rats significantly reduced the number of entries into the open arms and the time spent in the open arms compared to controls (Fig. 1H-1J).
To investigate the dynamic changes in astrocytes in the BLA of the diabetic rats that displayed tactile allodynia, BLA tissues were taken by perfusion, and immunofluorescence histochemical staining was performed. The distribution of astrocytes in the control, day 3 and day 7 groups was reduced, and the immunofluorescence intensity was weak. However, 14 days after STZ injection, we observed a large number of GFAP-labeled astrocytes in the BLA, and the intensity of immunofluorescence was markedly enhanced, reaching a peak at 21 days and lasting at least 28 days (Fig. 1K-1M). The significantly increased expression of GFAP in the BLA after the development of DNP suggests a potential role of BLA astrocytes in the pathogenesis of DNP.