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 a series of five experiments , the modulating role of naloxone on a scopolamine - induced retention deficit in a passive avoidance paradigm was investigated in mice .
### Output Text:
In a series of five experiments , the modulating role of <span class="chemical">naloxone</span> on a <span class="chemical">scopolamine</span> - induced retention deficit in a passive avoidance paradigm was investigated in mice . 