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: Acute treatment with apomorphine caused disruption of prepulse inhibition ( PPI ) in controls and in rats that had undergone either maternal deprivation or corticosterone treatment , but was surprisingly absent in rats that had undergone the combined early and late stress .
### Output Text:
Acute treatment with <span class="chemical">apomorphine</span> caused disruption of prepulse inhibition ( PPI ) in controls and in rats that had undergone either maternal deprivation or <span class="chemical">corticosterone</span> treatment , but was surprisingly absent in rats that had undergone the combined early and late stress . 