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: On the other hand , pretreatment with p - chlorophenylalamine ( 3 X 320 mg / kg i . p . , 24 hr ) , a serotonin depletor , caused no significant change in the hyperactivity .
### Output Text:
On the other hand , pretreatment with <span class="chemical">p - chlorophenylalamine</span> ( 3 X 320 mg / kg i . p . , 24 hr ) , a <span class="chemical">serotonin</span> depletor , caused no significant change in the hyperactivity . 