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: Pretreatment with either VPU ( 50 and 100 mg / kg ) or VPA ( 300 and 600 mg / kg ) completely abolished pilocarpine - evoked increases in extracellular glutamate and aspartate .
### Output Text:
Pretreatment with either <span class="chemical">VPU</span> ( 50 and 100 mg / kg ) or <span class="chemical">VPA</span> ( 300 and 600 mg / kg ) completely abolished <span class="chemical">pilocarpine</span> - evoked increases in extracellular <span class="chemical">glutamate</span> and <span class="chemical">aspartate</span> . 