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 magnitude of transformation of the microglia assessed by the number of intersections was significantly higher in the PDN groups than in controls in the prefrontal cortex ( moderate - dose , 24 . 1 ; high - dose , 23 . 6 ; controls 18 . 7 ; p < 0 . 01 ) and striatum ( moderate - dose 25 . 6 ; high - dose 26 . 3 ; controls 18 . 9 ; p < 0 . 01 ) , but not in hippocampus .
### Output Text:
The magnitude of transformation of the microglia assessed by the number of intersections was significantly higher in the <span class="chemical">PDN</span> groups than in controls in the prefrontal cortex ( moderate - dose , 24 . 1 ; high - dose , 23 . 6 ; controls 18 . 7 ; p < 0 . 01 ) and striatum ( moderate - dose 25 . 6 ; high - dose 26 . 3 ; controls 18 . 9 ; p < 0 . 01 ) , but not in hippocampus . 