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 present results suggest that blockade of the glycine site of NMDA receptors in the rostral part of the striatum may be mainly responsible for the antiparkinsonian action of this drug .
### Output Text:
The present results suggest that blockade of the <span class="chemical">glycine</span> site of <span class="chemical">NMDA</span> receptors in the rostral part of the striatum may be mainly responsible for the antiparkinsonian action of this drug . 