Dendritic organization of class II (inter)neurons in the dorsal lateral geniculate nucleus of the tree shrew: observations based on Golgi, immunocytochemical, and biocytin methods.

In this report we examine the dendritic organization of putative interneurons (class II cells) in different layers of the dorsal lateral geniculate nucleus of the tree shrew. The results show that there is considerable morphological diversity within this class, but that two broad groups can be identified: neurons whose dendrites remain within a layer or its adjacent interlaminar zones (intralaminar class II cells); and neurons whose dendrites cross into an adjacent layer(s) (interlaminar class II cells). The majority of class II cells in every layer have intralaminar dendrites, some of which are oriented along a particular axis, and others that are organized radially. The paired layers (1 and 2, 4 and 5) contain a particular group of intralaminar class II cells that have radially organized dendrites and elaborate claw-like appendages. The dendrites of interlaminar class II cells are organized along lines of projection and extend across as many as four layers. These cells often reside close to or within the interlaminar zones. Overall, the organization of class II cells seems to follow a pattern similar to the class I (relay) cells identified previously. Most have intralaminar dendrites, which presumably underlie the fidelity of signals transmitted from the retina to a particular layer. However, there are also a number of other cells whose processes cross laminar borders, presumably to affect integrative functions within the nucleus.