Slide 10 of 25
Notes:
Positive contrast is created by the heavy metals that react and bind with organic molecules in the tissue and thus are able to deflect and scatter electrons. It is achieved by use of uranium salts and lead salts. Positive contrast is normally used on sectioned material. Here you see the image of the place of contact between two neurons - synapse. The pre-terminal contains numerous vesicles that are filled with neuromediators, substances that are released from the terminal and change the properties of the membrane of the neighboring neuron.
Uranyl ions strongly react with phosphate and amino groups, so that proteins and nucleic acids are highly stained.
Lead ions are believed to bind to negatively charged components, such as hydroxyl groups and osmium-reacted areas. Thus lipids are especially well-stained with lead ions.
