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: Additionally , in models of prolonged status epilepticus the pars reticulata of substantia nigra ( SNR ) suffers from a massive lesion which may arise from a massive metabolic derangement and hyperexcitation developing in the activated SNR .
### Output Text:
Additionally , in models of prolonged status epilepticus the pars reticulata of substantia nigra ( SNR ) suffers from a massive lesion which may arise from a massive metabolic derangement and hyperexcitation developing in the activated SNR . 