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: The cataleptogenic effect of THC was significantly reduced in rats treated with 6 - OHDA and in rats with lesions of the locus coeruleus but not in rats treated with desipramine and 6 - OHDA , as compared with control rats .
### Output Text:
The cataleptogenic effect of <span class="chemical">THC</span> was significantly reduced in rats treated with <span class="chemical">6 - OHDA</span> and in rats with lesions of the locus coeruleus but not in rats treated with <span class="chemical">desipramine</span> and <span class="chemical">6 - OHDA</span> , as compared with control rats . 