Projection neurons of the basolateral amygdala: a correlative Golgi and retrograde tract tracing study.

This study analyzed the projection neurons of the anterior subdivision of the rat basolateral amygdaloid nucleus (BLa) by correlating the morphology of Golgi-stained neurons with the morphology of neurons that were retrogradely labeled by injections into the main terminal fields of BLa. In each animal multiple injections of horseradish peroxidase (HRP) and wheat germ agglutinin-conjugated HRP were made into the prefrontal cortex and rostral striatum. These injections labeled approximately 85% of BLa neurons. The great majority of labeled neurons were the same shape and relative size as the pyramidal (class I) neurons described in previous Golgi studies. The unlabeled neurons appeared to correspond to the nonpyramidal (class II and class III) neurons described in Golgi studies. Thus this investigation provides experimental evidence that the pyramidal neurons are the main projection neurons of BL, whereas most of the nonpyramidal cells are local circuit neurons.