First formal experiment in endocrinology:


Arnold Adolph Berthold, 1849—Studied roosters


Effects of prepubertal castration of male chick (used to make capons—more tender meat):

      reduces secondary male appearance—

      also affects behavior—


Berthold wanted to know if these extensive effects were dependent on neural connection to the testes. [There was a general appreciation of the role of nerves in functionally connecting different parts of the body, even though neurons had not yet been identified]


Additional results:

1) on autopsy the transplanted testis had re-established a blood supply, but not a neural supply



2) reimplanted or transplanted testis was also approximately 2 times larger than normal:



Question: So, hormones affect behavior (the Mind); Can behavior (the Mind) affect hormones?


Anonymous report to Nature: Self-report on beard growth of an isolated lighthouse keeper

[Nature 226:869-870, 1970]


What is a hormone? Partial Definition: An example of an intercellular chemical signal—a chemical substance, a molecule, that is secreted by one cell of the body and modifies the function of another cell of the body.


Distinction between a hormone and a neurotransmitter:










Chemical Structure














Source (cell type)


















Mode of delivery to target











Most hormones are systemic:


What determines which cells are a target for a systemic hormone?


Why have hormones for intercellular signaling instead of neurotransmitters?