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: METHODS : The effect of pretreatment with trazodone on dexamphetamine - and apomorphine - induced oral stereotypies , on catalepsy induced by haloperidol and apomorphine ( 0 . 05 mg / kg , i . p . ) , on ergometrine - induced wet dog shake ( WDS ) behavior and fluoxetine - induced penile erections was studied in rats .
### Output Text:
METHODS : The effect of pretreatment with <span class="chemical">trazodone</span> on <span class="chemical">dexamphetamine</span> - and <span class="chemical">apomorphine</span> - induced oral stereotypies , on catalepsy induced by <span class="chemical">haloperidol</span> and <span class="chemical">apomorphine</span> ( 0 . 05 mg / kg , i . p . ) , on <span class="chemical">ergometrine</span> - induced wet dog shake ( WDS ) behavior and <span class="chemical">fluoxetine</span> - induced penile erections was studied in rats . 