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 contrary , the cataleptogenic effect of haloperidol was significantly reduced in rats treated with desipramine and 6 - OHDA but not in rats treated with 6 - OHDA or in rats with lesions of the locus coeruleus .
### Output Text:
On the contrary , the cataleptogenic effect of <span class="chemical">haloperidol</span> was significantly reduced in rats treated with <span class="chemical">desipramine</span> and <span class="chemical">6 - OHDA</span> but not in rats treated with <span class="chemical">6 - OHDA</span> or in rats with lesions of the locus coeruleus . 