PMC

Comparison of nerve diameter measured photographically from the dissected mouse after fixation and nerve cross-sectional area after excision and microscopic measurement. The line shows a fit by the equation y = 6442e^0.0047x with R² = 0.91

Location of anatomic landmarks relative to the superior edge of the iliac crest. (A) The distance from the iliac crest to the rostral edge of the ipsilateral transverse process (A) was determined for the fifth lumbar (L5) and L6 processes in animals that have six lumbar vertebrae (six LV) and for the L5 of animals with five lumbar vertebrae (five LV). Positive dimensions indicate a rostral direction from the iliac crest. All groups were significantly different. (B) Similar measurements were made for the distances from the iliac crest to the rostral edge of the L5 and L6 superior articular processes of animals with six lumbar vertebrae and the L5 and first sacral (S1) superior articular processes of animals with five lumbar vertebrae. All groups were significantly different. Bars indicate means.

Lumbosacral vertebral column of B6129PF2/J strain mice from the posterior aspect, demonstrating sites of measurement for bony landmarks, with references line drawings. (A) A subject with five symmetric lumbar vertebrae, showing iliac crest (IC), transverse process (TP) of the fifth lumbar vertebra (L5), and the superior articular processes (SAP) of the first sacral (S1) and L5 vertebrae. (B) Similar measurements in a subject with six symmetric lumbar vertebrae. In both images, the dotted line indicates a level 1 mm above the IC. The L5 SAP is always more than 1 mm rostral to the IC, shown in these two animals.

Proportionate contributions of different lumbar spinal nerves to the sciatic nerves of mice (A) and rats (B) of different strains. DBA = DBA/2J strain, F2 = B6129PF2/J, C57 = C57BL/6J, SD = Sprague–Dawley. The sciatic nerve is composed of components from the third lumbar (L3) through L5 levels in mice and the L4 through L6 levels in rats. In all strains, the most caudal segment contributes the least. There are significant differences between strains (shown by brackets) in the contribution of each level. The probability of the main effect for the interaction of strain and segmental level on cross-sectional area is shown in parentheses.

Frequency of hyperalgesia responses (sustained lifting, grooming, shaking, or stomping of the foot) in response to nociceptive mechanical stimulation of the plantar aspect of the hind foot with a pin, in mice (A) and in rats (B). The top panels show the response rate ipsilateral and contralateral to spinal nerve ligation (means ± SD), specifically of the L4 in the mice (n = 11 ANOVA main effect for side, comparing ipsilateral and contralateral, P < 0.001) and L5 in the rats (n = 10, P < 0.001). Positive post hoc comparisons by Bonferroni test are indicated by *. The bottom panels show the response in sham-operated animals (mice n = 5; rats n = 10), which resulted in no difference in response between ipsilateral and contralateral sides.

Fluorescence photomicrographs (inverted) of representative sections from the first lumbar (L1) through L6 dorsal root ganglia of a C57BL/6J strain mice after injection of True Blue retrograde tracer into (A) the sciatic nerve in the thigh and (B) the plantar aspect of the hind paw of two different animals. In these and all other injected mice, positive sensory neuron somata were found predominantly in the L3 and L4 ganglia, with a smaller population in the L5 ganglion. Counts were made after thresholding the image, which was not done for the images shown here. Scale bar indicates 250 µm and applies to all frames.

Segmental distribution of somata of sensory neurons that project to the thigh (A) or the plantar aspect of the hind paw (B), determined by injection of True Blue tracer at these sites. Data are compared between two strains. The animals of the DBA/2J group (DBA; n = 5 for each site) all had five symmetric lumbar vertebrae, while the animals of the C57BL/6J group (C57; n = 5 for each site) all had six symmetric lumbar vertebrae. The patterns of contributions determined this way duplicate the findings of nerve dimensions (). The probability of the main effect for the interaction of strain and segmental level on cell counts is shown in parentheses. Significant differences between groups at a given level are shown by brackets.

Skeletal preparations of mouse and rat vertebral columns and pelvis viewed from the ventral aspect, with reference line drawings. (A) B6129PF2/J strain mouse with five distinct lumbar vertebral segments bilaterally (5/5, i.e. five segments on the left and five on the right). Curved arrows indicate vestigal transverse processes of the fused sixth infra-thoracic vertebra, which is in this case the first sacral (S1) vertebra. (B) C57BL/6J strain mouse with an asymmetric fusion of the sixth lumbar (L6) vertebra (5/6 configuration). On the anatomic left, the L6 transverse process is fused to the ilium and to the sacral ala, leaving a vestigal transverse process (curved arrow), in contrast to the free L6 transverse process on the right (arrowhead). The left side of the L6 vertebral body is fused with the S1 vertebral body (straight arrow). (C) B6129PF2/J strain mouse with five distinct lumbar vertebral segments bilaterally (6/6 configuration). (D) Sprague–Dawley rat with 6/6 lumbar vertebral configuration.

Influence of bony segmentation pattern on proportionate contributions of different lumbar spinal nerves to the sciatic nerves of mice. (A) Animals from all three strains (DBA/2J, B6129PF2/J, C57BL/6J) were grouped to compare those with five lumbar vertebrae on each side (5/5) to those with six on each side (6/6). (B) Animals of the B6129PF2/J (F2) strain with 5/5 a pattern were compared to those with a 6/6 pattern. (C) For animals with asymmetric fusion of all strains, the fused side (Asym five) was compared to the non-fused side (Asym six). The probability of the main effect for the interaction of strain and segmental level on cross-sectional area is shown in parentheses. The n for each group refers to number of sides. Significant differences between groups at a given level are shown by brackets.

Ventral views of dissections and reference drawings made from them, showing the sciatic nerve and its segmental origins. (A) DBA/2J strain mouse with five lumbar bony segments bilaterally. The third lumbar (L3) spinal nerve, together with the L4 and L5 (arrows), contributes to the sciatic nerve. The inset line drawing shows the sites of diameter measurement on the anatomic left side (enlarged). (B) C57BL/6J strain mouse with six lumbar bony segments bilaterally. As with mice with five lumbar vertebrae, the L3, L4, and L5 spinal nerves (arrows) make up the sciatic nerve. (C) In mice, the L5 spinal nerve may appear to make a large contribution (“Before Separation”), but gentle traction pulls the pudendal nerve (arrow) away from the sciatic nerve to expose a typically slight contribution from the L5 spinal nerve to the sciatic nerve (“After Separation”). Dotted lines represent nerves hidden by overlying bone. Dashed lines represent the pelvic bones. (D) Sprague–Dawley strain rat with six lumbar vertebrae. In contrast to the mice, the sciatic nerve is composed of L4 and L5. In other rats, L6 may also contribute to the sciatic nerve.