The Stucture and Function of Eimer's Organ in the Mole

Abstract

THE STRUCTURE AND FUNCTION OF EIMER’S ORGAN IN THE MOLE

Paul D. Marasco

Dissertation under the direction of Kenneth C. Catania This study examines the structure and function of Eimer’s organ in the mole. Eimer’s organ is a complex, well organized, and densely innervated mechanosensory structure found on the nose of the mole. Eimer’s organs appear to allow the mole make rapid sensory discriminations of objects. Labeling with AM1-43, substance P, neurofilament 200 and DiI revealed innervation patterns indicating that mechanosensory and nociceptive function is segregated to separate afferents within Eimer’s organ. Transmission electron microscopy revealed that the central column of Eimer’s organ may mechanically transduce stimuli and the intraepidermal free nerve endings do not appear to be active within the outer layer of the skin. The peripheral free nerve endings were structurally distinct from their central column counterparts and they were unmyelinated. The receptors in Eimer’s organ were similar in morphology to those found in a range of other mammalian skin. Electrophysiological examination revealed that the receptive fields for receptors in Eimer’s organ were small and response properties were consistent with an SA-1 receptor class, an FA-2 class. A second rapidly adapting class was hypothesized to represent activity of the mechanosensory free nerve endings. Most receptors were directionally sensitive and highly phase locked. Some receptors responded best when stimulated at a velocity matching the velocity of the nose in during foraging. The results support the hypothesis that Eimer's organ is a mechanosensory structure that functions to detect small surface features and textures by encoding and integrating deflection information for multiple Eimer's organs during brief touches.