Somatostatin-like immunoreactivity in non-pyramidal neurons of the human entorhinal region.

The distribution of somatostatin-immunoreactive cells and processes throughout the human entorhinal region and subjacent white matter was examined either by the unlabelled antibody-enzyme method or by the avidin-biotin method. The brain slices were obtained at autopsy with a short post-mortem delay. The majority of somatostatin immunoreactive nerve cells was found in the inner principal layer and subjacent white matter. In addition, individually scattered immunoreactive neurons were observed in both the outer principal layer and lamina dissecans. The immunoreactive perikarya varied in shape and ranged in size from 10 to 30 micron. Without exception the neurons could be classified as belonging to the group of non-pyramidal neurons. Each neuron gave rise to a few thick dendrites and a thin axon with a beaded appearance. In the adult human brain, the pattern formed by lipofuscin granules deposited in the nerve cells can be considered characteristic for the type of the neuron. Therefore, immunoreactive perikarya were documented, destained of chromogen and restained to demonstrate lipofuscin pigment and basophilic substance. It became evident from these studies that the previously immunoreactive cells were characterized by a large rounded and eccentrically located nucleus, sparse basophilic substance and, in most cases, a lack of lipofuscin granules. A few of the immunoreactive cells were laden with coarse pigment granules. The findings permit classification of entorhinal somatostatin-immunoreactive neurons as either non-pigmented or pigment-laden non-pyramidal neurons.