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: It may be concluded that , like other tricyclic antidepressants studied previously , TRI given repeatedly increases the responsiveness of brain dopamine D2 and D3 ( locomotor activity but not stereotypy ) as well as alpha1 - adrenergic receptors to their agonists .
### Output Text:
It may be concluded that , like other tricyclic <span class="chemical">antidepressants</span> studied previously , <span class="chemical">TRI</span> given repeatedly increases the responsiveness of brain <span class="chemical">dopamine</span> D2 and D3 ( locomotor activity but not stereotypy ) as well as alpha1 - adrenergic receptors to their agonists . 