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: Participation of a bulbospinal serotonergic pathway in the rat brain in clonidine - induced hypotension and bradycardia .
### Output Text:
Participation of a bulbospinal serotonergic pathway in the rat brain in <span class="chemical">clonidine</span> - induced hypotension and bradycardia . 