Lithium treatment prevents stress-induced dendritic remodeling in the rodent amygdala

Amygdala function is altered in patients with bipolar disorder (BD), but may be normalized by treatment with mood stabilizers. Lithium remains the most effective mood stabilizing therapy for BD, but the relevance of its neuroprotective effects in pre-clinical studies to clinical outcomes is unknown, and the targeting of amygdalar neurons by therapeutic interventions for BD has not yet been examined. Chronic stress in rodents increases activation of the amygdala and induces dendritic hypertrophy, thus providing a quantifiable marker of neuronal structural pathology that may be reversed by lithium treatment. Rats underwent restraint stress for 21 days, with or without concurrent administration of lithium in their diet. The overall length and complexity of neuronal dendritic arbors of principal pyramidal neurons in the basolateral amygdala were quantified using Golgi-Cox impregnation and three-dimensional neuron tracing. Lithium treatment prevented stress-induced increases in dendritic branching of amygdalar pyramidal neurons by reducing total dendritic length (18.0%; P=0.006) and the number of dendritic branch points (21.0%; P=0.02). Despite its protective effect when administered during stress, lithium did not alter amygdalar dendritic morphology when administered to non-stressed control rats. Our results demonstrate that lithium attenuates structural remodeling in the amygdala during stress, but has contrasting effects on neuronal morphology under pathological versus healthy conditions. This may reflect an ability of lithium to stabilize excitatory neurotransmission in the amygdala of individuals with BD, reducing the need for compensatory adjustments of dendritic architecture.