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: Among them are glycine transporter - 1 ( GlyT1 ) inhibitors such as SSR103800 , which indirectly enhance NMDA receptor function by increasing the glycine ( a co - agonist for the NMDA receptor ) levels in the synapse .
### Output Text:
Among them are <span class="chemical">glycine</span> transporter - 1 ( GlyT1 ) inhibitors such as <span class="chemical">SSR103800</span> , which indirectly enhance <span class="chemical">NMDA</span> receptor function by increasing the <span class="chemical">glycine</span> ( a co - agonist for the <span class="chemical">NMDA</span> receptor ) levels in the synapse . 