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: Therefore , the present study was carried out to investigate the effect of chronic curcumin administration on phenobarbitone - and carbamazepine - induced cognitive impairment and oxidative stress in rats .
### Output Text:
Therefore , the present study was carried out to investigate the effect of chronic <span class="chemical">curcumin</span> administration on <span class="chemical">phenobarbitone</span> - and <span class="chemical">carbamazepine</span> - induced cognitive impairment and oxidative stress in rats . 