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Open Access Research

Lamina I NK1 expressing projection neurones are functional in early postnatal rats and contribute to the setting up of adult mechanical sensory thresholds

Sharon HW Man, Sandrine M Géranton* and Stephen P Hunt

Author Affiliations

Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, UK

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Molecular Pain 2012, 8:35  doi:10.1186/1744-8069-8-35

Published: 27 April 2012

Abstract

Background

A small proportion of lamina I neurons of the spinal cord project upon the hindbrain and are thought to engage descending pathways that modulate the behavioural response to peripheral injury. Early postnatal development of nociception in rats is associated with exaggerated and diffuse cutaneous reflexes with a gradual refinement of responses over the first postnatal weeks related to increased participation of inhibitory networks. This study examined the postnatal development of lamina I projection neurons from postnatal day 3 (P3) until P48.

Results

At P3, a subset of lamina I neurons were found to express the neurokinin 1 (NK1) receptor. Using fluorogold retrograde tracing, we found that the NK1 positive neurons projected upon the parabrachial nucleus (PB) within the hindbrain. Using c-fos immunohistochemistry, we showed that lamina I and PB neurons in P3 rats responded to noxious stimulation of the periphery. Finally, ablation of lamina I neurons with substance-P saporin conjugates at P3 resulted in increased mechanical sensitivity from P45 onwards compared to control animals of the same age.

Conclusions

These results suggest that the lamina I pathway is present and functional at least from P3 and required for establishing and fine-tuning mechanical sensitivity in adult rats.

Keywords:
Lamina 1; Projection neurones; Parabrachial nucleus; c-fos; NK1; Formalin; Postnatal rat; Substance-P saporin; Mechanical sensory thresholds