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: A variety of abnormal sensory / motor behaviors associated with electrical discharges recorded from the bilateral brainstem were induced in adult WKY rats by mechanical ( electrode implants ) and DC electrical current stimulations and by acute and chronic administration of cocaine .
### Output Text:
A variety of abnormal sensory / motor behaviors associated with electrical discharges recorded from the bilateral brainstem were induced in adult WKY rats by mechanical ( electrode implants ) and DC electrical current stimulations and by acute and chronic administration of <span class="chemical">cocaine</span> . 