Similarities and differences in the innervation of mystacial vibrissal follicle–sinus complexes in the rat and cat: A confocal microscopic study

Abstract

Our confocal three-dimensional analyses revealed substantial differences in the innervation to vibrissal follicle-sinus complexes (FSCs) in the rat and cat. This is the first study using anti-protein gene product 9.5 (PGP9.5) immunolabeling and confocal microscopy on thick sections to examine systematically the terminal arborizations of the various FSC endings and to compare them between two species, the rat and the cat, that have similar-appearing FSCs but different exploratory behaviors, such as existence or absence of whisking. At least eight distinct endings were clearly discriminated three dimensionally in this study: 1) Merkel endings at the rete ridge collar, 2) circumferentially oriented lanceolate endings, 3) Merkel endings at the level of the ring sinus, 4) longitudinally oriented lanceolate endings, 5) club-like ringwulst endings, 6) reticular endings, 7) spiny endings, and 8) encapsulated endings. Of particular contrast, each nerve fiber that innervates Merkel cells at the level of the ring sinus in the rat usually terminates as a single, relatively small cluster of endings, whereas in the cat they terminate en passant as several large clusters of endings. Also, individual arbors of reticular endings in the rat ramify parallel to the vibrissae and distribute over wide, overlapping territories, whereas those in the cat ramify perpendicular and terminate in tightly circumscribed territories. Otherwise, the inner conical body of rat FSCs contains en passant, circumferentially oriented lanceolate endings that are lacking in the cat, whereas the cavernous sinus of the cat has en passant corpuscular endings that are lacking in the rat. Surprisingly, the one type of innervation that is the most similar in both species is a major set of simple, club-like endings, located at the attachment of the ringwulst, that had not previously been recognized as a morphologically unique type of innervation. Although the basic structure of the FSCs is similar in the rat and cat, the numerous differences in innervation suggest that these species would have different tactile capabilities and perceptions possibly related to their different vibrissa-related exploratory behaviors.

Microstructure and innervation of the mystacial vibrissal follicle‐sinus complex in bearded seals, Erignathus barbatus (Pinnipedia: Phocidae)

“…Sections were stained with hematoxylin and eosin, a modified Masson's trichrome stain, a modified Bodian silver stain, or toluidine blue (Armed Forces Institute of Pathology, 1968Pathology, , 1994Reep et al, 2001Reep et al, , 2002. Traditional histocytochemical stains were used because it was not possible to collect samples from remote locations in a manner that would have allowed immunolabeling techniques (e.g., Rice et al, 1997;Ebara et al, 2002). All micrographs were adjusted for brightness and contrast using Adobe Photoshop 7.0.…”

“…Most of our knowledge of vibrissal F-SCs is derived from terrestrial taxa (e.g., Davidson and Hardy, 1952;Melaragno and Montagna, 1953;Andres, 1966;Burgess and Perl, 1973;Gottschaldt et al, 1973;Halata, 1975;Rice et al, 1986Rice et al, , 1993Rice et al, , 1997Ebara et al, 2002). Although the general vibrissal F-SC form is similar among mammals, species-specific differences are evident in both structure and innervation.…”

Empirically inspired simulated electro-mechanical model of the rat mystacial follicle-sinus complex

“…Aspects of FSC anatomy (Dö rfl 1985; Rice et al 1986;Dehnhardt et al 1999;Ebara et al 2002) are distilled in figure 1a. In the rat, the follicle capsule is fairly rigid (Ebara et al 2002), so we modelled it as a rigid component.…”

“…In the rat, the follicle capsule is fairly rigid (Ebara et al 2002), so we modelled it as a rigid component. We conglomerated inner and outer root sheaths such that the whisker base sits within a single elastic sheath (root sheath).…”

Whisker plucking alters responses of rat trigeminal ganglion neurons

“…It remains unknown whether the anatomical structure of nerve endings within the follicle is disturbed by whisker plucking, requiring subsequent re-growth. Regardless of whether or not the re-growth of nerve terminal is required for restoration of function, the circumferential spread of individual nerve endings within the follicle probably remains unchanged because whisker plucking does not affect the angular tuning of NVg neurons (see Rice et al, 1986;Lichtenstein et al, 1990;Ebara et al, 2002). Whisker plucking also likely preserves the physiologic identity of nerve endings and their parent cell bodies as the proportions of SA and RA neurons in the NVg population are equivalent between the plucked and the control groups.…”