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: Present study clearly suggests that glial activation and post synaptic neurotoxicity are the key factors in STZ induced memory impairment and neuronal cell death .
### Output Text:
Present study clearly suggests that glial activation and post synaptic neurotoxicity are the key factors in <span class="chemical">STZ</span> induced memory impairment and neuronal cell death . 