Morphometric Changes in the Dog Trochlear Nerve with Growth

The objective of this work was to analyse changes in morphometric characteristics related to growth in the trochlear nerve in dogs. Twenty beagles, split into four dog age groups (A, 7 days; B, 21 days; C, 35 days; D, 49 days and E, 4 years), were used. The right intracranial portion of the nerve was analysed by light and electron microscopy. The nerve cross‐sectional area was calculated. Number, diameter and cross‐sectional area of unmyelinated and myelinated fibres were also calculated. In myelinated fibres, the corresponding axon area and diameter and myelin sheath thickness were also calculated. The number of myelinated and unmyelinated fibres was 1070.25 ± 112.07 and 592.25 ± 467.53 in group A, 1367 ± 57.98 and 143.67 ± 54.37 in group B, 1574.20 ± 299.50 and 151.67 ± 51.73 in group C, 1340.33 ± 151 and 127 ± 48.75 in group D and 1476 ± 260.71 and 284 ± 101.82 in group E. The mean diameter for myelinated and unmyelinated fibres was 4.37 ± 0.17 μm and 0.41 ± 0.08 μm for group A; 6.21 ± 0.12 μm and 0.30 ± 0.03 μm for B; 6.90 ± 0.91 μm and 0.32 ± 0.03 μm for C; 7.86 ± 1.19 μm and 0.32 ± 0.02 μm for D; 10.63 ± 0.50 μm and 0.30 ± 0.01 μm for E, respectively. This nerve possesses similar structural and ultrastructural features to the same nerve in other species and modifies its morphometry with growth. Results could enhance the understanding of pathological disorders.