In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The obtained data revealed that BCNU administration resulted in deterioration of learning and short - term memory ( STM ) , as measured by using radial arm water maze , accompanied with decreased hippocampal glutathione reductase ( GR ) activity and reduced glutathione ( GSH ) content .
### Output Text:
The obtained data revealed that <span class="chemical">BCNU</span> administration resulted in deterioration of learning and short - term memory ( STM ) , as measured by using radial arm water maze , accompanied with decreased hippocampal <span class="chemical">glutathione</span> reductase ( GR ) activity and reduced <span class="chemical">glutathione</span> ( <span class="chemical">GSH</span> ) content . 