|Axolotl (Ambystoma mexicanum)|
I can remember sitting in year 11 biology, way back when, learning about metamorphosis in amphibians. We had a tank in the classroom that had some rather sizable axolotls in it, and I can remember having my mind blown when I was informed that they were effectively stuck half way through metamorphosis. They had limbs like an adult frog or salamander; however, they still had gills much like tadpoles did. So it seemed to me like they were caught in limbo.
For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxin. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time.
Conclusions: Axolotls were selected to become neotenic, so if you want a terrestrial salamander don't get an axolotl and torture it to become one through water deprivation or injections with his only reward being the prospect of a severely shortened life. Buy a different species...