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: Acute morphine ( 30mg / kg , s . c . ) treatment significantly attenuated hippocampal LTP and CCK - 8 ( 1ug , i . c . v . ) restored the amplitude of PS that was attenuated by morphine injection .
### Output Text:
Acute <span class="chemical">morphine</span> ( 30mg / kg , s . c . ) treatment significantly attenuated hippocampal LTP and <span class="chemical">CCK - 8</span> ( 1ug , i . c . v . ) restored the amplitude of PS that was attenuated by <span class="chemical">morphine</span> injection . 