A comparative study of the mammalian amygdala: a Golgi study of the basolateral amygdala

The lateral (LA), basolateral (BL) and basomedial (BM) amygdaloid nuclei were compared in the guinea pig (Cavia porcellus), rabbit (Oryctolagus cuniculus) fox (Vulpes vulpes) and pig (Sus scrofa) by using the Golgi techniques. The interspecific comparisons of the individual basolateral nuclei have shown that the neuronal structure in each of them is extremely stable and remains almost unchanged in the series of animals studied. The only difference is the size of the basolateral neurons, which increases with the increasing size of the brain. Moreover, the intraspecific comparisons revealed that in all the animals studied LA, BL and BM form a fairly homogenous mass of cells in which similar cell types are present. The most numerous neurons in all basolateral nuclei are the spiny cells that often show a pyramidal or semi-pyramidal appearance (the Type I cells). Many of these have conical cell bodies and easily recognisable "apical" and "basal" dendrites. The Type II neurons are the most common variety of non-pyramidal cell and have round cell bodies and smooth or sparsely spined dendrites. The axons of these cells often form a dense terminal field that remains in the vicinity of the parent soma. The Type III cells, which are only occasionally seen, are small spine-sparse neurogliaform neurons with a few extremely delicate beaded dendrites and a poorly branching local axon. These neurons were only located in LA and BL.