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 addition , we observed that the persistent increase in the rat spontaneous locomotion is associated with increased TBARS levels and superoxide generation in submitochondrial particles in the prefrontal cortex , striatum and amygdala .
### Output Text:
In addition , we observed that the persistent increase in the rat spontaneous locomotion is associated with increased TBARS levels and <span class="chemical">superoxide</span> generation in submitochondrial particles in the prefrontal cortex , striatum and amygdala . 