In addition, here the expression of the protein was assessed by measuring the density

of pixels of AQP4 immunoreactivity in astrocytes of the WM, GL, PL and ML in CHIR-99021 mouse separate, whereas in the study by Wen and co-workers (1999) AQP4 expression was evaluated by immunoblotting of the membrane fraction of the whole cerebellum. We attribute such discrepancies to differences in the methodological design. The P. nigriventer venom exposure caused differential upregulation of the AQP4 in astrocytes, depending on the region considered, the time after envenoming and the age of animals. Soon after 2 h of envenomation AQP4 expression increased by 83% in the GL and 44% in ML of P14 animals and 60% in GL of adults. These figures changed after 24 h to a 77.5% increase in astrocytes Sotrastaurin ic50 of the WM and 101.6% in the ML of P14 rats and 103% in WM, 52% in ML and 91.8% in the GL of 8-week-old rats. Under present experimental condition, the two-way analysis of variance

confirmed that the time after envenomation influenced strongly the upregulation of the protein induced by PNV exposure, which seems logical since the local venom concentration probably decreased due to venom clearance from tissue. The two-way analysis of variance also demonstrated that animal age also influenced the region-related differences observed in the expression of AQP4 in the cerebellum in response to PNV. We found that the PNV affected more intensely AQP4 expression in the ML of P14 than in adults, whereas the opposite occurred for the WM where the PNV effect induced a stronger upregulation

of AQP4 in adults relative to P14. As shown, despite the preponderance of increased AQP4 in astrocytes of the gray matter over those of the white matter, the data suggest that the protein may be mediating distinct events in the two compartments promoting mainly K+ buffering in the former and fluid homeostasis in the latter. A plausible explanation for the regional differences between white and gray matter in the expression of AQP4 in adult and P14 animals over time is to date unclear. The white matter and gray matter contain two gross populations of Non-specific serine/threonine protein kinase astrocytes which are distinct in their morphology and functional characteristics. Protoplasmic astrocytes confined within the gray matter have profuse and short branched processes which encase synaptic contacts, which suggest that AQP4 in such astrocytes could have a key role in neural activity. Fibrous astrocytes of the white matter have fewer but lengthier, although less ramified, processes whose distal endings establish close contact with nodes of Ranvier of myelinated nerve fibers (Wang and Bordey, 2008). In this case, the AQP4 would be suggestively, but not exclusively, engaged in Na+/K+ pump regulation. The distal endfeet of both types of astrocytes shield the microvasculature of the BBB, hence the role of AQP4 would be involved mainly in water balance (Nico et al., 2002).