What is the kindling effect and how does it relate to bipolar disorder?

Good question: Kindling is the phenomenon noted in 1960s where a small stimulus to the brain repeated over time produced a grand mal seizure. Continued stimulus resulted in spontaneous seizures. In bipolar disorder, the thinking is that the illness gets worse and harder to treat with each episode. Initial episodes might be triggered by stress, over time cycles are more freq and spontaneous. So treat early.

Kindling: Is a phenomenon that results in increased sensitivity of the nervous system due to repeated causative events. It is mostly applied to alcohol withdrawal, where repeated withdrawals cause more severe withdrawal symptoms. Another example is use of multiple small stimulations to induce seizures in epilepsy. Kindling in bipolar do can be viewed as development of tolerance to medications with time.