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: METHODS : In this study , we evaluated the performance of dopamine beta - hydroxylase knockout ( Dbh - / - ) mice , which lack norepinephrine ( NE ) , in the elevated plus maze ( EPM ) to examine the contribution of noradrenergic signaling to cocaine - induced anxiety .
### Output Text:
METHODS : In this study , we evaluated the performance of <span class="chemical">dopamine</span> beta - hydroxylase knockout ( Dbh - / - ) mice , which lack <span class="chemical">norepinephrine</span> ( <span class="chemical">NE</span> ) , in the elevated plus maze ( EPM ) to examine the contribution of noradrenergic signaling to <span class="chemical">cocaine</span> - induced anxiety . 