Suprarhinal cortex response to electrical stimulation of the lateral amygdala nucleus in the rat

Electrical stimulation of the lateral amygdala nucleus was found to evoke field potentials and influence unitary activity in the suprarhinal cortex of anesthetized rats. Laminar distributions of the field responses consisted of positive waves in superficial layers, that reversed to electronegatives from a depth of 0.4-0.5 mm. This response was followed by a shallow electropositive wave deeper than 0.7-0.8 mm. Extracellularly recorded units were studied in the posterior agranular insular area of the suprarhinal cortex. The data revealed that stimulation of the lateral amygdala produced a train of small amplitude spikes in association with a negative slow potential. Furthermore, such stimulation invariably elicited an inhibition of the spontaneous firing of large amplitude spikes, in association with a positive slow potential. The onset of this inhibitory response always occurred at longer latency than the excitatory one. The small amplitude spikes may well represent the firing of inhibitory interneurons after lateral amygdala stimulation. The study suggests that a feed-forward system of inhibition appears to be present in the connection between lateral amygdala and posterior agranular insular area of the suprarhinal cortex.