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 model group , the expression of P2X3 receptor increased in urothelium and suburothelium , and NK1 receptor increased in suburothelium , while the expression of them in intervention group was lower .
### Output Text:
In model group , the expression of P2X3 receptor increased in urothelium and suburothelium , and NK1 receptor increased in suburothelium , while the expression of them in intervention group was lower . 