Anat Cell Biol.  2010 Dec;43(4):340-346. 10.5115/acb.2010.43.4.340.

Ultrastructural analysis of low-threshold mechanoreceptive vibrissa afferent boutons in the cat trigeminal caudal nucleus

• Paik SK
• Choi SK
• Lee JW
• Kim TH
• Ahn DK
• Yoshida A
• Kim YS
• Bae YC

• KMID: 1455349
• DOI: http://doi.org/10.5115/acb.2010.43.4.340

Abstract

Ultrastructural parameters related to synaptic release and their correlation with synaptic connectivity were analyzed in the low-threshold mechanoreceptive vibrissa afferent boutons in laminae III and IV of the trigeminal caudal nucleus (Vc). Rapidly adapting vibrissa afferents were intra-axonally labeled, and quantitative ultrastructural analyses with serial sections were performed on the labeled boutons and their presynaptic endings (p-endings). The volume of the labeled boutons was widely distributed from small to large ones (0.8~12.3 microm3), whereas the p-endings were small and uniform in size. The volume of the labeled boutons was positively correlated with the ultrastructural parameters such as mitochondrial volume (correlation coefficient, r=0.96), active zone area (r=0.82) and apposed surface area (r=0.79). Vesicle density (r=-0.18) showed little correlation to the volume of labeled boutons, suggesting that the total vesicle number of a bouton is proportional to its volume. In addition, the bouton volume was positively correlated with the number of p-endings (r=0.52) and with the number of dendrites postsynaptic to the labeled bouton (r=0.83). These findings suggest that low-threshold mechanoreception conveyed through vibrissa afferents is processed in a bouton size-dependent manner in the Vc, which may contribute to the sensory-motor function of laminae III/IV in Vc.

Keyword

Trigeminal; Low-threshold mechanoreception; Ultrastructure; Synapse; Vibrissa afferent

MeSH Terms

Animals
Cats
Dendrites
Mitochondrial Size
Synapses
Trigeminal Caudal Nucleus

Figure

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  Fig. 1 Light (A, B) and electron (C~E) micrographs showing HRP-labeled vibrissa afferent boutons in the laminae III/IV of the cat trigeminal caudal nucleus (Vc). (A, B) Light micrographs showing the HRP-labeled boutons (arrowheads) in laminae III/IV of Vc. B is an enlargement of boxed area in A. (C) An electron micrograph on a labeled bouton (asterisk) showing a simple synaptic connection with a dendrite (d). (D, E) Electron micrographs on adjacent thin sections showing a labeled bouton (asterisk). The bouton shows an example of complex synaptic arrangement with four dendrites (d1~d4) and presynaptic endings (p1) on adjacent thin sections. Arrows indicate the direction of synaptic transmission. Scale bars, 200 µm in (A); 20 µm in (B) 500 nm in (C~E).

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  Fig. 2 Distribution of the volume of vibrissa afferent boutons and their presynaptic endings (p-endings) in the cat trigeminal caudal nucleus (Vc).

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  Fig. 3 Correlations between the volume of vibrissa afferent boutons and the number of presynaptic endings (p-endings), and between the volume of vibrissa afferent boutons and number of postsynaptic dendrites in the cat trigeminal caudal nucleus (Vc). r, correlation coefficient.

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  Fig. 4 Correlations between the volume of vibrissa afferent boutons and their mitochondrial volume, active zone area, apposed surface area and vesicle density in the cat trigeminal caudal nucleus (Vc). r, correlation coefficient.

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