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: Contribution of the glycine site of NMDA receptors in rostral and intermediate - caudal parts of the striatum to the regulation of muscle tone in rats .
### Output Text:
Contribution of the <span class="chemical">glycine</span> site of <span class="chemical">NMDA</span> receptors in rostral and intermediate - caudal parts of the striatum to the regulation of muscle tone in rats . 