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: Furthermore , the effects are mediated through dopamine rather than norepinephrine and do not require the carotid sinus baroreceptors .
### Output Text:
Furthermore , the effects are mediated through <span class="chemical">dopamine</span> rather than <span class="chemical">norepinephrine</span> and do not require the carotid sinus baroreceptors . 