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: Those drugs with strong affinity for 5 - hydroxytryptamine1a receptors were able to reverse catalepsy .
### Output Text:
Those drugs with strong affinity for <span class="chemical">5 - hydroxytryptamine1a</span> receptors were able to reverse catalepsy . 