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 intracerebroventricular ( ICV ) administration of ouabain ( a Na ( + ) / K ( + ) - ATPase inhibitor ) in rats has been suggested to mimic some symptoms of human bipolar mania .
### Output Text:
The intracerebroventricular ( ICV ) administration of <span class="chemical">ouabain</span> ( a <span class="chemical">Na</span> ( + ) / <span class="chemical">K</span> ( + ) - ATPase inhibitor ) in rats has been suggested to mimic some symptoms of human bipolar mania . 