Three-dimensional microanatomy of longitudinal lanceolate endings in rat vibrissae

Abstract

The longitudinal lanceolate endings are ubiquitous sensory terminals in the sinus and nonsinus hairs of mammals that form a palisade around the hair follicle. To analyze how the nerve endings detect hair movements, the present study re-examined their fine structure and relationships with surrounding connective tissue in rat vibrissae by using a combination of three methods: immunohistochemistry for S-100 protein, scanning electron microscopy of NaOH-macerated specimens, and transmission electron microscopy of serial sections. Observations showed the lanceolate endings to be represented by triplet units with a flattened axon terminal flanked on each side by a Schwann cell lamella, as reported previously. Two distinct parts were discriminated in the lanceolate ending: a principal portion in which the axon terminal protruded numerous fine fingers from between the Schwann cell coverings, and an apical cone that enclosed a large axon finger in an attenuated Schwann sheath. Long foot processes of Schwann cells fanned out distally from each apical cone. The principal portions of the lanceolate endings were firmly linked to the surrounding connective tissue by the narrow edges equipped with axon fingers, suggesting their continuous deformation by sustained hair deflections. In contrast, the apical cones were freely suspended in an amorphous matrix with only the end feet of the Schwann cell projections attached to rigid tissue elements. This part of the ending was proposed as a possible transducer site to generate rapidly adapting receptor potentials, both retreating and overshooting during the acceleration and deceleration phases of a given vibrissal movement.

Morphology and chemical characteristics of subepithelial laminar nerve endings in the rat epiglottic mucosa

“…Thus, the laminar endings should be mechanoreceptors as previously suggested (Yamamoto et al 1998). The direction of the endings should not correlate to the body axis, and be twodimensionally spread in every direction, unlike the muscle spindles and lanceolate receptors that are arranged in axes with muscle fiber and sinus hair, respectively (Schoultz and Swett 1974;Takahashi-Iwanaga 2000). The epiglottic laminar endings may be activated by mucosal tension in every direction, which is produced by pressure changes of laryngeal lumen but not by changes of unidirectional airflow.…”

“…Ultrastructure of axon terminals of the laminar endings Small axoplasmic projections from the sheath of terminal Schwann cells in the laminar ending have been reported in Pacinian corpuscles, Ruffini endings and lanceolate endings, and are directly in contact with connective tissue fibers to anchor the axon terminals (Spencer and Schaumburg 1973;Maeda et al 1999;Takahashi-Iwanaga et al 1997;Takahashi-Iwanaga 2000). In the laminar endings, small projections occasionally appeared but continuous spike-like projections that were observed in Ruffini endings and lanceolate endings were not observed.…”

“…Immunohistochemically, it has been reported that morphological organization of terminal Schwann cells was observed by immunohistochemistry for S-100 protein in Ruffini and lanceolate endings (Maeda et al 1989;Sato et al 1988;Takahashi-Iwanaga 2000). Furthermore, scanning electron microscopy with alkaline maceration method revealed that the terminal Schwann cells were closely associated with axon terminals (Takahashi-Iwanaga 2000;Takahashi-Iwanaga et al 1997). In the laryngeal laminar endings, morphology of terminal Schwann cells has been simply mentioned (Yamamoto et al 1998).…”

“…Generally, axon terminals of uncapsulated mechanoreceptors are ensheathed by cytoplasmic processes of terminal Schwann cells in several mechanoreceptors: Golgi tendon organs, Ruffini endings, lanceolate endings of the sinus hair, and nerve endings in tracheal smooth muscle (Schoultz and Swett 1974;Takahashi-Iwanaga 2000;Takahashi-Iwanaga et al 1997;Yamamoto et al 1994). The exact function of terminal Schwann cells is unknown, but these cells may be involved with glia-neuronal interaction by ATP response via P2Y purinoceptor (Takahashi-Iwanaga and Habara 2004).…”

Development of Innervation to Maxillary Whiskers in Mice

“…The sensory information that arises from these receptors is used by the animal in various behavioral tasks. The peripheral innervation pattern and the central projections of the maxillary whiskers have been extensively studied in several species (Patrizi and Munger, 1966;Dykes, 1975;Macintosh, 1975;Halata and Munger, 1980;Dörfl, 1985;Rice et al, 1985Rice et al, , 1986Dehnhardt et al, 1999;Takahashi-Iwanaga, 2000). One striking feature of the vibrissal follicle central projection is the presence of a precise somatotopic map between individual whiskers and their central terminations in the trigeminal sensory nuclei, thalamic nuclei, and somatosensory cortex (Woolsey and van der Loos, 1970;Woolsey et al, 1975;Rice et al, 1985;van der Loos, 1976;Belford and Killackey, 1979).…”