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: Increasing the brain serotonin levels by the administration of 5 - hydroxytryptophan ( 80 - 160 mg / kg ) in combination with a peripheral decarboxylase inhibitor resulted in an inhibition of the muscimol effect .
### Output Text:
Increasing the brain <span class="chemical">serotonin</span> levels by the administration of <span class="chemical">5 - hydroxytryptophan</span> ( 80 - 160 mg / kg ) in combination with a peripheral decarboxylase inhibitor resulted in an inhibition of the <span class="chemical">muscimol</span> effect . 