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: Specifically , WSP mice may have lower sensitivity to cholinergic convulsants compared with WSR because of postsynaptic receptor desensitization brought on by higher activity of cholinergic neurons .
### Output Text:
Specifically , WSP mice may have lower sensitivity to cholinergic convulsants compared with WSR because of postsynaptic receptor desensitization brought on by higher activity of cholinergic neurons . 