Neuronal arrangement in the auditory field L of the neostriatum of the starling.

Light microscopic investigations show that nerve cells of the field L in the starling neostriatum are dispersed into small groups forming unit-like clusters. Isolated neurons occur between these neuronal clusters. Electron microsceopy demonstrates that the neurons occurring in small clusters are not separated by intervening glial processes, but only by a normal intercellular space. In each neuronal cluster large areas of direct somato-somatic and dendro-somatic appositions exist. In areas of somato-somatic apposition, the plasma membranes of adjoining neurons show specialized junctional zones. These junctional zones resemble desmosoid puncta adhaerentia. In areas of dendro-somatic apposition the neuronal plasma membranes approach each other more closely, but do not show any specialized junctional zone. The clustering of neurons without glial separation and the presence of junctional zones between these neurons are discussed.