Ultrastructure of the pulvinar of the squirrel monkey.

Abstract

AbstractThree divisions of the squirrel monkey pulvinar, p. inferior (PI), p. lateralis (PL), and p. medialis (PM), have been studied with light‐ and electron‐microscopic techniques. Two populations of neurons exist. The first neuron is a thalamocortical relay cell (TCR), averaging about 26 μ in diameter, with radial dendritic pattern and thin dendritic appendages. The second is a Golgi type II neuron, about 16 μ average diameter, with more complex dendritic appendages and an axon ramifying in the vicinity of the soma. The TCR: Golgi type II ratio is about 7:3 in PL and PI, and 9:2 in PM.Three types of synaptic terminals are observed: the RS, comprising about 80% of the total population; the RL, comprising about 10%; and the F, comprising about 10%. The first two contain round vesicles and make asymmetrical synaptic contacts, while the third contains both round and flat vesicles and makes symmetrical synaptic contacts. Characteristic groupings of synaptic terminals and dendrites, called “glomeruli”, appear to be organized for structured and efficient interactions. Adhesive contacts are observed between synaptic and non‐synaptic and non‐synaptic structures.Comparisons with other thalamic nuclei are made, and the ultrastructural resemblance among all thalamic nuclei studied thus far is noted. The presence of glomeruli in all is discussed.