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: Neuropeptide - Y ( NPY ) is expressed by granule cells and mossy fibres of the hippocampal dentate gyrus during experimental temporal lobe epilepsy ( TLE ) .
### Output Text:
Neuropeptide - Y ( NPY ) is expressed by granule cells and mossy fibres of the hippocampal dentate gyrus during experimental temporal lobe epilepsy ( TLE ) . 