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 Dbh - / - mice had normal baseline performance in the EPM but were completely resistant to the anxiogenic effects of cocaine .
### Output Text:
The Dbh - / - mice had normal baseline performance in the EPM but were completely resistant to the anxiogenic effects of <span class="chemical">cocaine</span> . 