Synaptology of prefrontal cortical projections to the basolateral amygdala: An electron microscopic study in the rat

Prefrontal projections to the magnocellular basal amygdaloid nucleus (Bmg) of the rat were investigated using Phaseolus vulgaris leucoagglutinin (PHA-L) as an anterograde tracer. Electron microscopic examination revealed that most axon terminals in Bmg labeled by PHA-L injections into the prelimbic area contained round synaptic vesicles and made asymmetric synapses. The great majority of labeled terminals (93%) made synaptic contact with dendritic spines; a few contacts (7%) were seen with thin dendrites. These findings indicate that the main postsynaptic targets of PFC afferents to Bmg are spiny pyramidal neurons, the projection neurons of the baso-lateral amygdala. The morphology of the synapses suggests that they are excitatory.