On dendrodendritic relations in the dorsal thalamus of the adult cat

Abstract

Golgi analysis of specific and nonspecific nuclei in the dorsal thalamus of adult cats reveals two forms of dendritic specializations. Mossy tuft-like structures are found on the tips of dendrites of most local circuit (L) interneurons and in smaller numbers, on some dendritic termini of thalamocortical (T) relay cells. Long spinelike structures or appendages are present in limited numbers along the dendrite shafts of most L cells. The evidence is suggestive that the mossy tuft bears a presynaptic relation to the dendritic appendage, thereby creating a pattern of dendrodendritic synaptic links throughout dorsal thalamus. Thalamocortical cells also appear to be “plugged in” to this system through their own tuft apparatus. Since electron microscopy has identified two-way synapses in regions of this sort, similar to those originally described in the olfactory bulb, a satisfactory structural basis is provided for inhibition and facilitation and for the rapid spread of rhythmic activity, all via dendritic structures. It is suggested that a system with these structural characteristics could better provide for phenomena such as thalamic synchronous rhythms than synaptic models currently available.