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: Repeated administration of cocaine induces up - regulation of hippocampal NET function .
### Output Text:
Repeated administration of <span class="chemical">cocaine</span> induces up - regulation of hippocampal NET function . 