A GOLGI-STUDY OF DENDRITIC DEVELOPMENT IN THE DORSAL LATERAL GENICULATE-NUCLEUS OF NORMAL FERRETS

The development of neurons in the dorsal lateral geniculate nucleus (dLGN) of pigmented ferrets was studied by using the Golgi-Hortega technique. In adult ferrets, four dLGN cell classes were defined on the basis of somatic and dendritic morphology. Classes 1 and 2 were divided into stellate and oriented subtypes. Class 1 and 4 cells are characterized by filiform appendages, class 2 cells by club-like appendages, and class 3 cells by stalked appendages. At birth, dLGN neurons have simple dendritic arbors. During the first postnatal week, dendritic length and proximal branching density increase markedly. By postnatal day 21 (P21), dendritic morphology begins to take on mature characteristics and by the time of eye opening (P30-P35), most neurons can be classified. Also by that time, dLGN cells are covered with abundant filiform appendages. Developmental changes in appendage density were quantified for class 1 stellate cells. These data reveal that appendage density reaches a peak at P56, decreases sharply until P90, and then gradually declines to mature levels by P180. Elaboration and elimination of transient appendages occurs centrifugally; at maturity appendage density remains greater distally.