Elsevier

Neuroscience

Volume 139, Issue 4, 2006, Pages 1385-1396
Neuroscience

Developmental neuroscience
Absence of Reelin results in altered nociception and aberrant neuronal positioning in the dorsal spinal cord

https://doi.org/10.1016/j.neuroscience.2006.01.042Get rights and content

Abstract

Mutations in reeler, the gene coding for the Reelin protein, result in pronounced motor deficits associated with positioning errors (i.e. ectopic locations) in the cerebral and cerebellar cortices. In this study we provide the first evidence that the reeler mutant also has profound sensory defects. We focused on the dorsal horn of the spinal cord, which receives inputs from small diameter primary afferents and processes information about noxious, painful stimulation. We used immunocytochemistry to map the distribution of Reelin and Disabled-1 (the protein product of the reeler gene, and the intracellular adaptor protein, Dab1, involved in its signaling pathway) in adjacent regions of the developing dorsal horn, from early to late embryonic development. As high levels of Dab1 accumulate in cells that sustain positioning errors in reeler mutants, our findings of increased Dab1 immunoreactivity in reeler laminae I–III, lamina V and the lateral spinal nucleus suggest that there are incorrectly located neurons in the reeler dorsal horn. Subsequently, we identified an aberrant neuronal compaction in reeler lamina I and a reduction of neurons in the lateral spinal nucleus throughout the spinal cord. Additionally, we detected neurokinin-1 receptors expressed by Dab1-labeled neurons in reeler laminae I–III and the lateral spinal nucleus. Consistent with these anatomical abnormalities having functional consequences, we found a significant reduction in mechanical sensitivity and a pronounced thermal hyperalgesia (increased pain sensitivity) in reeler compared with control mice. As the nociceptors in control and reeler dorsal root ganglia are similar, our results indicate that Reelin signaling is an essential contributor to the normal development of central circuits that underlie nociceptive processing and pain.

Section snippets

Animal and tissue preparation

The reeler mice (B6C3Fe -a/a- Reln/rl, Jackson Laboratory, Bar Harbor, ME, USA) were obtained from a breeding colony maintained at UCLA. Mice were studied at embryonic (E12.5–17.5), postnatal (P14-19) and adult (3–6 mo) ages. The adult reeler mutants used for sensory tests were healthy, but displayed ataxia, inability to rear on their hind limbs and were smaller than the wild-type controls. Mice were genotyped using polymerase chain reaction screening as adapted from D’Arcangelo et al. (1996).

Pattern of Reelin expression in the superficial dorsal horn

We used immunocytochemistry in coronal sections from wild-type mice to map and analyze the expression pattern of Reelin and detected Reelin-immunoreactive cells in E12.5 dorsal horn (arrows, Fig. 1A). Labeled neurons were scattered near the base of the dorsal horn, with a few cells located near the dorsal root entry zone. On E13.5, Reelin-labeled cells (arrows, Fig. 1C) were concentrated along the ventrolateral border of the dorsal horn, and by E14.5 they occupied the mediolateral extent of

Discussion

In the present study we used immunocytochemistry to characterize Reelin and Dab1 expression in the developing dorsal horn so as to identify positional errors in regions that process nociceptive information. During embryonic development Reelin and Dab1 are expressed in nearby neurons within the superficial dorsal horn, lateral lamina V, and in the LSN, areas associated with the processing of nociceptive information. In addition to identifying notable positional errors and moderate alterations in

Acknowledgments

This work was supported by the National Science Foundation (IBN-9734550, IOB-0518714, P.E.P.), MARC U*Star Fellowship (S.A.V.), and NICHD MRDD Training Fellowship (A.L.A.). We thank Drs. T. Curran, J. Herz, D. Julius, and S. Magdaleno for their generous antibody gifts. We also thank S. Shields for her assistance with sensory testing, Dr. A. Garfinkel for his statistical advice, and Dr. E. Carpenter for her comments on the manuscript.

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    S.A.V. and A.L.A. contributed equally to this work.

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