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: In conclusion , MT induction halts BCNU - induced hippocampal toxicity as it prevented GR inhibition and GSH depletion and counteracted the increased levels of TNFalpha , MDA and caspase - 3 activity with subsequent preservation of cognition .
### Output Text:
In conclusion , <span class="chemical">MT</span> induction halts <span class="chemical">BCNU</span> - induced hippocampal toxicity as it prevented GR inhibition and <span class="chemical">GSH</span> depletion and counteracted the increased levels of TNFalpha , <span class="chemical">MDA</span> and caspase - 3 activity with subsequent preservation of cognition . 