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: CONCLUSION : We observed that DHEA reduced locomotor activity and increased catalepsy at both doses , while it had no effect on climbing behavior .
### Output Text:
CONCLUSION : We observed that <span class="chemical">DHEA</span> reduced locomotor activity and increased catalepsy at both doses , while it had no effect on climbing behavior . 