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: Involvement of locus coeruleus and noradrenergic neurotransmission in fentanyl - induced muscular rigidity in the rat .
### Output Text:
Involvement of locus coeruleus and noradrenergic neurotransmission in <span class="chemical">fentanyl</span> - induced muscular rigidity in the rat . 