Morphometric changes in the dog oculomotor nerve with postnatal growth

Abstract

The aim of the study was to investigate aged-related changes in morphometric features both in the myelinated and unmyelinated fibers of the oculomotor nerve in dogs. According to their age (1, 3, 5, 7 weeks and 4 years) twenty Beagles were classified into five groups (A, B, C, D, and E, respectively). The right intracranial portions of the nerves were processed and analysed by light and electron microscopy. In every nerve, cross-sectional area was calculated. In the myelinated fibers the number, diameter and cross sectional area were calculated, as well as the cross-sectional area and diameter of their axons, and myelin sheath thickness. In unmyelinated fibers the number, cross sectional area and diameter were calculated. Graphical representations for every variable were carried out by mean of frequency histograms. The cross sectional area of the nerve increased in size 4.5 times from group A to group E. From group A to group E the number of myelinated fibres increased significantly 1.5 times and its diameter 2.3 times. The number of unmyelinated fibres decreased in 20% and its diameter 40% from group A to group E. According to the results obtained the oculomotor nerve of the dog has similar structural features than that of other mammal species, and this nerve modifies its morphometry with growth. The results obtained could improve the understanding of those possible pathological conditions that involve morphological alterations of the nerve fibers.