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: This prolonged depletion of dopamine in the striatum was antagonized by dizocilpine ( MK - 801 , a non - competitive antagonist of NMDA receptors ) or by LY274614 ( a competitive antagonist of NMDA receptors ) .
### Output Text:
This prolonged depletion of <span class="chemical">dopamine</span> in the striatum was antagonized by <span class="chemical">dizocilpine</span> ( <span class="chemical">MK - 801</span> , a non - competitive antagonist of <span class="chemical">NMDA</span> receptors ) or by <span class="chemical">LY274614</span> ( a competitive antagonist of <span class="chemical">NMDA</span> receptors ) . 