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: PCPA significantly and substantially depleted 5 - HT and 5 - HIAA in all brain regions examined .
### Output Text:
<span class="chemical">PCPA</span> significantly and substantially depleted <span class="chemical">5 - HT</span> and <span class="chemical">5 - HIAA</span> in all brain regions examined . 