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: The present results demonstrate that CCK - 8 attenuates the effect of morphine on hippocampal LTP through CCK2 receptors and suggest an ameliorative function of CCK - 8 on morphine - induced memory impairment .
### Output Text:
The present results demonstrate that <span class="chemical">CCK - 8</span> attenuates the effect of <span class="chemical">morphine</span> on hippocampal LTP through CCK2 receptors and suggest an ameliorative function of <span class="chemical">CCK - 8</span> on <span class="chemical">morphine</span> - induced memory impairment . 