Regarding the endogenous opioid system and its relation to human anxiety, Donald Klein and I just submitted a review paper on this central subject.
We have well-controlled experimental data relating endogenous opioid dysfunction to panic anxiety. We expect to publish these shortly.
On the bench side, look out for Luiz Schenberg's illuminating rat studies.
Our work-in-progress can be previewed here, at the panic cyber conference:
