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: Here , we investigated the effects of CCK - 8 on long - term potentiation ( LTP ) in the lateral perforant path ( LPP ) - granule cell synapse of rat dentate gyrus ( DG ) in acute saline or morphine - treated rats .
### Output Text:
Here , we investigated the effects of <span class="chemical">CCK - 8</span> on long - term potentiation ( LTP ) in the lateral perforant path ( LPP ) - granule cell synapse of rat dentate gyrus ( DG ) in acute saline or <span class="chemical">morphine</span> - treated rats . 