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: In order to elucidate the role of the catecholaminergic system in the cataleptogenic effect of delta 9 - tetrahydrocannabinol ( THC ) , the effect of pretreatment with 6 - hydroxydopamine ( 6 - OHDA ) or with desipramine and 6 - OHDA and lesions of the locus coeruleus were investigated in rats .
### Output Text:
In order to elucidate the role of the catecholaminergic system in the cataleptogenic effect of <span class="chemical">delta 9 - tetrahydrocannabinol</span> ( <span class="chemical">THC</span> ) , the effect of pretreatment with <span class="chemical">6 - hydroxydopamine</span> ( <span class="chemical">6 - OHDA</span> ) or with <span class="chemical">desipramine</span> and <span class="chemical">6 - OHDA</span> and lesions of the locus coeruleus were investigated in rats . 