Estrogen has neuroprotective effects in neurodegenerative disorders and models of neuronal damage. The effectiveness of estradiol (EST) (1 mg/kg and 10 mg/kg doses) in cold-induced brain injury (CIB) model was evaluated and compared with standard dexamethasone treatment. Forty-eight male Wistar rats (250-300 g) were randomly divided into 6 groups: sham operated, CIB + no treatment, CIB + 1 mg/kg dexamethasone, CIB + 1 mg/kg EST, CIB + 10 mg/kg EST, CIB + vehicle (ethanol). Rats were placed on stereotaxic frame and a craniotomy of 5 mm diameter was performed on the parietal lob under general anesthesia (ketamine + xylazine). A metal probe of 5 mm diameter was cooled (2 min) in liquid nitrogen (-190 degrees C) and was applied on the craniotomy area for 3 min. The treatment was started immediately after the CIB. Twenty-four hours later the whole brain was isolated and study parameters were assessed. The parameters were tissue wet/dry weight ratio, lipid peroxidation, and histopathological examination of the depth of injury. Both 1 mg/kg dexamethasone and 1 mg/kg EST treatment significantly reduced all the measured injury parameters, whereas 10 mg/kg EST had no effect on any of the parameters. This study shows that EST at lower concentrations is beneficial in this model of cold-induced brain injury. However, the effect of EST is dual and higher concentrations, in contrast, do not affect or even may be detrimental in brain injury. (C) 2010 Elsevier B.V. All rights reserved.