Do a google search and you will find the following study:
Effect of Ketamine on Dendritic Arbor Development and Survival of Immature GABAergic Neurons In Vitro
This study was conducted after Jansen's book was revised so the data is not commonly known. It basically shows that even low dose ketamine inhibits Dendritic growth. Especially over long periods. This probably explains the most noticable side-effect of ketamine use... bad short term memory. Dendrite development facilitates memory imprinting.
Lesson, don't do the K while you are studying for finals.
Also keep the hydergine around for any serious K lab work.