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: While some recent studies suggest acute changes in neuroendocrine function , less is known about long - term changes in HPA functionality in recreational users .
### Output Text:
While some recent studies suggest acute changes in neuroendocrine function , less is known about long - term changes in HPA functionality in recreational users . 