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: RATIONALE : 5 - Hydroxytryptamine , via stimulation of 5 - HT 2C receptors , exerts a tonic inhibitory influence on dopaminergic neurotransmission , whereas activation of 5 - HT 2A receptors enhances stimulated DAergic neurotransmission .
### Output Text:
RATIONALE : <span class="chemical">5 - Hydroxytryptamine</span> , via stimulation of <span class="chemical">5 - HT</span> 2C receptors , exerts a tonic inhibitory influence on dopaminergic neurotransmission , whereas activation of <span class="chemical">5 - HT</span> 2A receptors enhances stimulated DAergic neurotransmission . 