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: Moreover , the dopaminergic control of epilepsy - induced neurodegeneration seems to be mediated by distinct interactions of D2R signaling with these two neurotransmitters .
### Output Text:
Moreover , the dopaminergic control of epilepsy - induced neurodegeneration seems to be mediated by distinct interactions of D2R signaling with these two neurotransmitters . 