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: Together , the data suggests that functional antagonism of sigma receptors is capable of attenuating a number of cocaine - induced behaviors .
### Output Text:
Together , the data suggests that functional antagonism of sigma receptors is capable of attenuating a number of <span class="chemical">cocaine</span> - induced behaviors . 