Cation-binding sites in trigeminal ganglia and maxillary nerve: unusual reactivity of perikarya, stem axons and satellite cells

Effects of trifluoperazine and amiloride on the extrusion of axoplasmic Ca++ by rapidly adapting and slowly adapting type I cutaneous mechanoreceptors: an electron-microscopic study using the oxalate-antimonate method

Influences of Ca++ transport inhibitors on the extrusion of cytosolic Ca++ from axon terminals of oral mucosal mechanoreceptors were cytochemically studied through the use of trifluoperazine (TFP), a Ca++ pump inhibitor, and amiloride, a Na+/Ca++ exchanger inhibitor. Palates of Mongolian gerbils were isolated after perfusion with normal, TFP-containing, or amiloride-containing HEPES-buffered saline, and then mechanically stimulated in the same buffer. Cytosolic Ca++ in axon terminals at 2 min after the stimulation was visualized by means of an oxalate-antimonate method using microwave fixation, and then evaluated electron-microscopically. TFP was found to inhibit the Ca++ extrusion from axon terminals of Meissner corpuscles, but not from those of Merkel cell-axon complexes. Conversely, amiloride severely reduced the Ca++ extrusion from axon terminals of Merkel cell-axon complexes, but not from those of Meissner corpuscles. These results suggest that cytosolic Ca++ extrusion from axon terminals of rapidly adapting and slowly adapting type I mechanoreceptors is regulated by a Ca++ pump and an Na+/Ca++ exchanger, respectively.

Ultrastructural and cytochemical evidence for single impulse initiation zones in vestibular macular nerve fibers of rat

Cupric ion-ferricyanide labeling methods and related ferrocyanide-stained tissues were used to locate and characterize, at the ultrastructural level, presumptive impulse initiation zones in the three types of vestibular macular nerve fibers. Large-diameter, M-type vestibular nerve fibers terminate in a calyx at the heminode, and labeling is coextensive with the base of the calyx. Intermediate, M/U-type nerve fibers have short, unmyelinated preterminal segments that sometimes bifurcate intramacularly, and small-diameter, U-type nerve fibers have long, unmyelinated preterminal axons and up to three branches. Preterminals of these nerve fibers display ultrastructural heterogeneity that is correlated with labeling patterns for sodium channels and/or associated polyanionic sites. They have a nodelike ultrastructure and label heavily from near the heminode to the base of the macula. Their intramacular branches, less organized ultrastructurally, label only slightly. Results indicate that vestibular nerve fibers have one impulse initiation zone, located near the heminode, that varies in length according to nerve fiber type. Structural heterogeneity may favor impulse conduction in the central direction, and length of the impulse initiation zone could influence nerve discharge patterns.

Spatial and morphological differentiation of trigger zones in afferent fibers to the teleost utricle

A morphological correlate of the trigger site (the locus of action potential initiation) was identified in afferent axons of the utricle in the ear of two species of teleost fish. These sites were identified by the ferric-ferrocyanide (Prussian blue) cytochemical procedure and they were correlated with the geometries of afferent intraepithelial arbors as visualized by means of a silver stain. The intraepithelial arbors of afferent fibers show regional distributions that correlate with axon diameter and Prussian blue staining. Afferent axons with diameters greater than 4-5 microns only innervate the striola regions of the epithelium and terminate as one of two distinct types of intraepithelial arbors. Afferent axons with diameters smaller than 4 microns are ubiquitously distributed throughout the epithelium. Arbors that stained by Prussian blue within the utricular epithelium are restricted to the striolar regions. These arbors possess nodal-like membrane in different branches as postsynaptic membrane. Afferents that innervate hair cells in the extrastriolar epithelial regions stained with Prussian blue only at the extraepithelial terminal heminode. The postsynaptic membrane of these afferents is passive or dendritic-like.

Membrane heterogeneity in sensory receptors of rat vibrissae: Merkel receptors differ from other nerve endings

The cupric/ferrocyanide reaction was used to analyse cation-binding sites in rat vibrissae. The heminode of the last myelinated segment had moderate staining. No staining of any complex receptor was found except for Merkel receptors. Both the Merkel cell and associated nerve ending were stained except for their apposed cell membranes, suggesting either reciprocal membrane specialization at that site, or prevention of cupric/ferrocyanide penetration into the space between the two cells.