Maybe I should clarify what neuro-receptors are:

In cell biology, the receptor is a structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance. There are many receptors.

To take an example, there is substance P, a molecule that acts as a messenger for the sensation of pain (those of us with FMS/CFS have an over-abundance of substance P). The receptor for substance P is a unique harbor on the cell surface where substance P docks. Without this receptor, substance P cannot dock and cannot deliver its message of pain.

Putting it very simplistically: In my case, there is a receptor for chemicals that include those similar to iron; where these chemicals dock and deliver. If iron has filled that receptor, other chemicals that are similar are not able to deliver their cargo. Among those chemicals similar to iron are at least one of my medications.

For a more technical definition see http://www.answers.com/topic/receptor .