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: The glutamatergic blockage produced by NMDA can restore these signs , such as vacuous chewing movements , tongue protrusions , catalepsy and tremor according to the employed model .
### Output Text:
The glutamatergic blockage produced by <span class="chemical">NMDA</span> can restore these signs , such as vacuous chewing movements , tongue protrusions , catalepsy and tremor according to the employed model . 