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: Additional neuronanatomical studies , including cresyl violet staining , neuronal degeneration methods , and histochemical localization of glial fibrillary acidic protein , suggested that the decrease in the number of GAD mRNA - containing neurons was related to neuronal loss rather than to a decrease in GAD mRNA levels .
### Output Text:
Additional neuronanatomical studies , including <span class="chemical">cresyl violet</span> staining , neuronal degeneration methods , and histochemical localization of glial fibrillary acidic protein , suggested that the decrease in the number of GAD mRNA - containing neurons was related to neuronal loss rather than to a decrease in GAD mRNA levels . 