Organization of the zona incerta in the macaque: An electron microscopic study

Abstract

Background: The zona incerta (ZI) receives projections from many telencephalic and brainstem structures. On the basis of its connectivity and physiology, this nucleus has been implicated in the control of saccadic eye movements. Because of the complexity of its afferent signals and its simple efferent signal, there must be much local interaction within the ZI to integrate these various afferents. The purpose of this study was to investigate, at the ultrastructural level, whether the ZI contains the anatomical substrata which could subserve the control of eye movements.Methods: Blocks of tissue from the ZI of macaque monkeys were prepared for electron microscopy using standard techniques. Some of these animals were taken specifically for electron microscopy. Others had received injections of tracer substances and were prepared for electron microscopy subsequent to tracer visualization.Results: Cell bodies of medium-large neurons were found in our preparations. They have large nucleoli and relatively small volumes of karyoplasm. Cell bodies and dendrites of all sizes have many synaptic contacts. Three types of synaptic profiles were found, designated Types 1, 2, and 3. Type 1 profiles are symmetrical and contact cell bodies and small dendrites. Type 2 profiles are thought to be presynaptic dendrites and may have symmetrical or asymmetrical contacts. Type 3 profiles are asymmetrical and primarily contact small dendrites. Many synapses contacted vesicle-containing profiles. In some cases, it was clear that these profiles participated in serial synapses on presumptive presynaptic dendrites. Other profiles appeared to be axoaxonic contacts.Conclusions: Afferent and efferent signals are likely to be modulated extensively within the ZI. Therefore, there needs to be complex interactions between neuronal elements of the ZI and its afferents. This study demonstrates that this nucleus possesses the structural substrata to subserve diverse roles, such as the gating of saccadic eye movements.

Inhibitory gain modulation of defense behaviors by zona incerta

“…ZI is a relatively large inhibitory subthalamic nucleus containing multiple sectors and cell types 7 , 17 – 19 . Previous studies have also demonstrated that ZI receives a rich variety of inputs from many brain regions, including multisensory inputs and neuromodulatory inputs that carry information about brain state 2 , 9 , 43 , 44 .…”

“…ZI consists of heterogenous groups of cells, cytoarchitecture of which loosely divide the structure into multiple sectors 7 , 17 , 18 . In rodents, four sectors (rostral, ventral, dorsal, and caudal) of ZI can be defined based on the neurochemical expression pattern 19 .…”

Estrogen‐receptor‐β distribution in the human hypothalamus: Similarities and differences with ERα distribution

“…The zona incerta (ZI) (see Figs. 3, 4) can be considered the most rostral extension of the mesencephalic reticular formation and contains GABA as a major neurotransmitter (Ma et al, 1997) and benzodiazepine binding sites (Najimi et al, 2001). The rostral ZI is continuous with the lateral hypothalamic area and has been implicated in nociceptive and somatosensory perception, locomotion, sexual behavior, feeding and drinking, arousal, and attention (Brown and Grossman, 1980; Edwards and Isaacs, 1991; Heeb and Yahr, 1996; Greco et al, 1996; Ongur and Price, 1998; Iqbal et al, 2001; Mungarndee et al, 2002; Nandi et al, 2002).…”

Organization of the medial pulvinar nucleus in the macaque

“…Material from five adult rhesus monkeys (Macaca mulatta) that had been stained for Nissl substance were used to study the boundaries and general organization of the pulvinar nuclear complex and had been used in previous studies (Ma, 1989;Ma et al, 1990Ma et al, , 1991Ma et al, , 1992Ma et al, , 1997. The monkeys were deeply anesthetized with sodium pentobarbital and perfused through the heart with one of several different fixatives (10% buffered formalin, or 2-4% paraformaldehyde, 0.1-2% glutaraldehyde).…”