title: Electron microscopy of the subthalamic nucleus in the baboon. I. Synaptic organization of the subthalamic nucleus in the baboon.
abstract: Our study of the synaptic organization of the baboon subthalamic nucleus has revealed at least nine different types of synapses. Most frequently encountered is the type I (F) axo-dendritic or axo-somatic synapse. It is characterized by scattered flat vesicles and many large mitochondria. The axon terminal is either elongated, tubule shaped (type IF en passant), and undergoes many short button-like en passant junctions with a parallel running dendrite, or it is spindle shaped with similar synaptic contacts (type IFa). In other cases a more compact bouton forms many short junctions at the same time with a dendrite and a beak-shaped spine springing from it. A smaller bouton with flat vesicles, which show a tendency to fuse together (type IIF) usually undergoes slightly asymmetric contacts with two vesicles-free dendrites between which they frequently appear wedged. Three types of boutons with small, round vesicles have extended asymmetric contacts forming elongated (type III), star-shaped (type IV), or oval (type V) synapses. The latter form contacts mostly with dendritic terminals or spines. Another type of synapses contain larger, pale, pleomorphic vesicles (VI (SO)): The bouton is more compact and often in contact with a dendritic terminal. Type VII (LO) shows a looser arrangement of vesicles intermingled with more dense core vesicles. Type VIII (F) is a dendritic terminal with loosely arranged, flat vesicles and is in contact either with a type VI or with a type VII P bouton. Finally, there is an axo-spinous microsynapse type IX, which partly degenerates after contralateral pallidum externum coagulation. A few axon preterminals filled with dense core vesicles do not undergo synaptic contacts.
mesh_terms: D000818:Animals; D004027:Diencephalon / Q000166:cytology / Q000648:ultrastructure; D005260:Female; D008297:Male; D008854:Microscopy, Electron; D009474:Neurons / Q000648:ultrastructure; D010215:Papio / Q000033:anatomy & histology*; D013569:Synapses / Q000648:ultrastructure*