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: RESULTS : We found that cocaine dose - dependently increased anxiety - like behavior in control ( Dbh + / - ) mice , as measured by a decrease in open arm exploration .
### Output Text:
RESULTS : We found that <span class="chemical">cocaine</span> dose - dependently increased anxiety - like behavior in control ( Dbh + / - ) mice , as measured by a decrease in open arm exploration . 