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Three‐dimensional reconstruction of scleral cold thermoreceptors of the cat eye
Author(s) -
Heppelmann Bernd,
Gallar Juana,
Trost Brigitte,
Schmidt Robert F.,
Belmonte Carlos
Publication year - 2001
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.1403
Subject(s) - thermoreceptor , free nerve ending , anatomy , biology , sclera , sensory system , nociceptor , vesicle , transduction (biophysics) , biophysics , receptor , neuroscience , membrane , nociception , biochemistry , genetics
Sensory endings that respond to local cooling were identified electrophysiologically in the cat's sclera. Functionally identified scleral thermal fibers were then used to analyze the structural characteristics of cold receptor endings. Four Aδ units sensitive to controlled cooling of their scleral receptive fields were recorded. The receptive areas were mapped, demarcated with pins and examined electron microscopically using extensive three‐dimensional reconstructions. The supporting tissue within the receptive areas of cold units consisted of dense collageneous tissue with a small number of blood vessels that were either veins or capillaries. Aδ nerve fibers were found within these tissue blocks presumably corresponding with cold sensitive fibers. Small nerves and single nerve fibers devoid of a perineurium were found in all parts of the tissue, only occasionally passing a blood vessel. The terminal portions showed axonal swellings all along the unmyelinated segment filled with mitochondria, glycogen particles, and some vesicles. About 30% of the terminal axonal membrane is not covered by Schwann cells. In the unmyelinated distal portion, the mitochondrial content ranged from 0.012 to 0.038 μm 3 mitochondrial volume per μm 2 nerve fiber membrane. In comparison with sensory endings in the cat's knee joint, cold receptors in the cat sclera showed many similarities in their three‐dimensional structure with polymodal nociceptor endings of the knee joint but contain less mitochondria. This suggests that cold sensory endings do not require specialized cellular processes for the transduction of cold stimuli, as is the case for multimodal transduction and sensitization in the terminal portion of polymodal nociceptors. J. Comp. Neurol. 441:148–154, 2001. © 2001 Wiley‐Liss, Inc.