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: Behavioral effects of pubertal anabolic androgenic steroid exposure in male rats with low serotonin .
### Output Text:
Behavioral effects of pubertal anabolic androgenic <span class="chemical">steroid</span> exposure in male rats with low <span class="chemical">serotonin</span> . 