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: Accordingly , intracollicular microinjection of NMDA increased the latency to step down the bar .
### Output Text:
Accordingly , intracollicular microinjection of <span class="chemical">NMDA</span> increased the latency to step down the bar . 