title: Neonatal capsaicin treatment prevents the normal postnatal withdrawal of A fibres from lamina II without affecting fos responses to innocuous peripheral stimulation.
abstract: The development of spinal cord sensory pathways has been investigated in postnatal day (P) 21 rat pups following neonatal capsaicin treatment. Capsaicin-induced destruction of C fibres was confirmed by 62% loss of Isolectin B4 (IB4)-binding and an 86% loss of calcitonin gene-related peptide (CGRP)-immunoreactive small diameter dorsal root ganglion cells. Neonatal capsaicin treatment prevented the normal withdrawal of choleragenoid-horseradish peroxidase (B-HRP)-labelled A fibres from lamina II (substantia gelatinosa) to deeper laminae postnatally. A fibre terminals projected more dorsally, extending into 43% of lamina II compared to vehicle-treated littermates. A small cell loss in, and/or shrinkage of, substantia gelatinosa cannot account for this. These support the concept of a competitive interaction between A and C fibre afferents to establish final terminal fields. However the continued exuberant A fibre termination in capsaicin-treated rats did not lead to continued c-fos induction in the superficial dorsal horn by innocuous stimulation. In normal development, exuberant A fibre terminals coincide with c-fos activation in lamina II by innocuous skin stimulation [23]. Despite the continued presence of exuberant A fibre terminals, c-fos was not induced by innocuous peripheral stimulation in P21 capsaicin-treated rats implying that these superficial terminals do not activate lamina II neurons in the same way as in the neonate.
authors.affiliation: Department of Anatomy and Developmental Biology, University College London, Gower Street, WC1E 6BT, London, UK. c.tornsey@ucl.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Torsney
authors.forename: J
authors.initials: J
authors.lastname: Meredith-Middleton
authors.forename: M
authors.initials: M
authors.lastname: Fitzgerald
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015415:Biomarkers; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D002211:Capsaicin / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D005727:Ganglia, Spinal / Q000166:cytology / Q000254:growth & development*; D009413:Nerve Fibers, Myelinated / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009475:Neurons, Afferent / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D010812:Physical Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis*; D051381:Rats; D013376:Substantia Gelatinosa / Q000166:cytology / Q000254:growth & development*
chemical_list: D015415:Biomarkers; D016760:Proto-Oncogene Proteins c-fos; D015740:Calcitonin Gene-Related Peptide; D002211:Capsaicin