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: However , the observation that antagonists of the glutamate N - methyl - D - aspartate ( NMDA ) receptor produce schizophrenic - like symptoms in humans has led to the idea of a dysfunctioning of the glutamatergic system via its NMDA receptor .
### Output Text:
However , the observation that antagonists of the <span class="chemical">glutamate</span> <span class="chemical">N - methyl - D - aspartate</span> ( <span class="chemical">NMDA</span> ) receptor produce schizophrenic - like symptoms in humans has led to the idea of a dysfunctioning of the glutamatergic system via its <span class="chemical">NMDA</span> receptor . 