Spike doublets in neurons of the lateral amygdala: mechanisms and contribution to rhythmic activity

A majority of projection neurons in the lateral amygdala generate oscillatory spike firing in the theta-frequency range, largely due to intrinsic membrane properties. Here we report on the occurrence of spike doublets in about 70% of these cells. Spike doublets consisted of a fast initial and a second slower component, which were mediated by sodium- and calcium-dependent mechanisms, respectively. With increased level of depolarization, there was a gradual transition of fast action potentials, regular alternation of fast action potentials and spike doublets, regular spike doublets, and high-threshold oscillations. Fast Fourier transforms demonstrated the rhythmic nature of spike doublets at around 3 Hz with an intra-doublet frequency of 25-80 Hz. Spike doublets may thus contribute to the overall rhythmicity in the membrane potential patterns of projection cells and support the integration of synaptic input signals.