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 the pinealectomized chick , pretreatment with dopamine increased the duration of catatonia ( DOC ) after ketamine , but pretreatment with norepinephrine did not .
### Output Text:
In the pinealectomized chick , pretreatment with <span class="chemical">dopamine</span> increased the duration of catatonia ( DOC ) after <span class="chemical">ketamine</span> , but pretreatment with <span class="chemical">norepinephrine</span> did not . 