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 expression of arginine vasopressin ( AVP ) gene in the paraventricular ( PVN ) and supraoptic nuclei ( SON ) was investigated in rats with lithium ( Li ) - induced polyuria , using in situ hybridization histochemistry and radioimmunoassay .
### Output Text:
The expression of <span class="chemical">arginine vasopressin</span> ( <span class="chemical">AVP</span> ) gene in the paraventricular ( PVN ) and supraoptic nuclei ( SON ) was investigated in rats with <span class="chemical">lithium</span> ( <span class="chemical">Li</span> ) - induced polyuria , using in situ hybridization histochemistry and radioimmunoassay . 