Ultrastructure of afferents from the zona incerta to the posterior and parafascicular thalamic nuclei of rats

• Published in: Journal of comparative neurology (1911) Vol. 451; no. 1; pp. 33 - 44
• Main Authors: Power, Brian D., Mitrofanis, John
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 09-09-2002
• Subjects: Animals; Biotin - analogs & derivatives; biotinylated dextran; Dextrans; electron microscopy; Fluorescent Dyes; higher order; intralaminar; Intralaminar Thalamic Nuclei - cytology; Male; Microscopy, Electron; Neural Pathways; Neurons, Afferent - ultrastructure; Rats; Rats, Sprague-Dawley - anatomy & histology; Subthalamus - cytology; thalamus
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.10332

We have examined the general ultrastructure of the posterior thalamic (Po) and parafascicular (Pf) nuclei of the dorsal thalamus, together with the ultrastructure of afferents to these nuclei from the zona incerta (ZI). The ZI of Sprague‐Dawley rats was injected with biotinylated dextran (BD) by using stereotaxic coordinates, and the brains were prepared for routine BD histochemistry. The Po and Pf were then dissected free and processed for electron microscopy by using standard methods. A survey of the general ultrastructure of Po and Pf revealed many RS profiles (small with round vesicles) making asymmetric synapses around single, small (distal; 0.5–1.5 μm in diameter) or larger (proximal; 2–4 μm in diameter) dendrites. RL (large with round vesicles) and F type (pleomorphic vesicles) profiles, although sparse, were also observed. Single RLs were seen to envelope proximal dendrites and make asymmetric synapses that usually had a perforated appearance. F type profiles were seen to make symmetric synapses on proximal and sometimes distal dendrites. There were no profiles making synapses on other vesicle‐filled profiles seen, reflecting the scarcity of interneurons in the Po and Pf of rats. Finally, BD‐labeled terminal profiles from the ZI formed a homogeneous population within both the Po and Pf. They were small (1.1 ± 0.2 μm in diameter; n = 238), contained round vesicles, and made asymmetric synapses with proximal (∼75%) and, to a lesser extent, distal (∼25%) dendrites; they formed part of the RS population of the Po and Pf. In conclusion, our results indicate that the ZI imparts a presumably excitatory (asymmetric synapses) input of high efficacy (preference for proximal dendrites) to the Po and Pf of the dorsal thalamus. J. Comp. Neurol. 451:33–44, 2002. © 2002 Wiley‐Liss, Inc.