Parvalbumin (PV), calretinin (CR), calbindin D-28k (CB), stage specific embryonic antigen-4 (SSEA4), and phosphorylated neurofilament 200 (pNF200) have been commonly used as markers for primary afferent neurons with large myelinated (A) fibers but detailed information on the expression of these markers in specific primary afferent fiber types is still lacking. We here examined the fibers that express PV, CR, CB, SSEA4, and pNF200 in the trigeminal ganglion and its peripheral sensory root by light- and electron-microscopic immunohistochemistry and quantitative analysis. We found that all CR-immunopositive (+), CB+, and SSEA4+ fibers and virtually all (98.8%) PV+ fibers were myelinated, most CR+ fibers were large myelinated, whereas most CB+ and SSEA4+ fibers were small myelinated. One half of the PV+ fibers were small myelinated and the other half were large myelinated. Of all pNF200+ fibers, about a third each were small myelinated, large myelinated, and unmyelinated. These findings suggest that PV, CR, CB, and SSEA4 can be used as specific markers for primary afferent neurons with myelinated fibers, but that pNF200 is not suitable as a specific marker for primary afferent neurons with myelinated fibers, and also raise the possibility that PV, CR, CB, and SSEA4 may be expressed in both mechanoreceptive and nociceptive neurons. This article is protected by copyright. All rights reserved.
Cell adhesion molecules play important roles in the development of the nervous system. Among the contactin-associated protein (Caspr; also known as Cntnap) family, which belongs to the neurexin superfamily of proteins, Caspr and Caspr2 are indispensable for the formation and maintenance of myelinated nerves. In contrast, a physiological role for Caspr3 remains to be elucidated. This study examines the expression and localization of Caspr3 in the mouse brain using newly generated Caspr3 antibodies. Caspr3 was expressed abundantly between the first and the second postnatal weeks. During this period, Caspr3 was localized especially to the basal ganglia, including the striatum, external segment of the globus pallidus, and substantia nigra, and no gross abnormalities were apparent in the basal ganglia of Caspr3 knockout mice. In the striatum, Caspr3 was expressed by a subpopulation of medium spiny neurons that constitute the direct and indirect pathways. Caspr3 immunostaining was observed as punctate around the cell bodies as well as in the soma. These Caspr3 signals did not, however, overlap with those of synaptic markers. Our findings suggest that Caspr3 may play an important role in basal ganglia development during early postnatal stages.