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: Thus , the absence of D2R lowers the threshold for seizures induced by both glutamate and acetylcholine .
### Output Text:
Thus , the absence of D2R lowers the threshold for seizures induced by both <span class="chemical">glutamate</span> and <span class="chemical">acetylcholine</span> . 