Selective innervation of NK1 receptor-lacking lamina I spinoparabrachial neurons by presumed nonpeptidergic Aδ nociceptors in the rat.

Fine myelinated (Aδ) nociceptors are responsible for fast, well-localised pain, but relatively little is known about their postsynaptic targets in the spinal cord, and therefore about their roles in the neuronal circuits that process nociceptive information. Here we show that transganglionically transported cholera toxin B subunit (CTb) labels a distinct set of afferents in lamina I that are likely to correspond to Aδ nociceptors, and that most of these lack neuropeptides. The vast majority of lamina I projection neurons can be retrogradely labelled from the lateral parabrachial area, and these can be divided into 2 major groups based on expression of the neurokinin 1 receptor (NK1r).

Simultaneous identification of unmyelinated and myelinated primary somatic afferents by co-injection of isolectin B4 and Cholera toxin subunit B into the sciatic nerve of the rat.

Several studies have used the transganglionic tracers cholera toxin subunit B (CTb) and either Bandeiraea simplicifolia isolectin B4 (IB4) or wheat-germ agglutinin (WGA) to label myelinated and unmyelinated afferent fibres respectively. In this study, we aim to determine whether co-injection of CTb and either IB4 or WGA into the sciatic nerve of rat will selectively label myelinated and unmyelinated simultaneously. A double immunofluorescence approach was used to detect these tracers in dorsal root ganglia (DRGs) and afferent fibre terminals in the spinal cord.

Acute and chronic sectioning of fifth lumbar spinal nerve has equivalent effects on the primary afferents of sciatic nerve in rat spinal cord.

The mechanism of neuropathic pain may be associated with sprouting of uninjured primary afferents of peripheral nerves into regions of the spinal cord denervated through peripheral injury. However, this remains controversial. Therefore, the purpose of the present investigation was, first, to determine in detail the central distributions of the unmyelinated primary afferents of each of the L4, L5, and L6 components of sciatic nerve, then to assess the distribution of afferent sciatic terminals following acute and chronic injury to (L5) nerve.

Unmyelinated primary afferents from adjacent spinal nerves intermingle in the spinal dorsal horn: a possible mechanism contributing to neuropathic pain.

Peripheral nerve injury in animals can cause neuropathic pain often expressed in the form of hyperalgesia and allodynia. Spinal nerve ligation, in which the fifth and sixth lumbar (L5 and L6) or only the L5 spinal nerve is ligated and cut, is a model commonly used to produce neuropathic pain. The purpose of the present study was to test whether there is any anatomical evidence to support the suggestion that terminating unmyelinated (C) fibres of injured and adjacent uninjured nerves interact at the level of the spinal dorsal horn.

Peripheral axotomy induces depletion of the vesicular glutamate transporter VGLUT1 in central terminals of myelinated afferent fibres in the rat spinal cord.

Myelinated primary afferent axons use glutamate as their principal neurotransmitter. We have shown previously that central terminals of myelinated tactile and proprioceptive afferents contain the vesicular glutamate transporter VGLUT1. Peripheral nerve injury is known to induce changes in the anatomy, neurochemistry, and physiology of primary afferents.

Do central terminals of intact myelinated primary afferents sprout into the superficial dorsal horn of rat spinal cord after injury to a neighboring peripheral nerve?

In order to investigate whether normal myelinated primary afferent axons sprout into the territories of adjacent injured peripheral nerve fibers in the superficial dorsal horn of the spinal cord, adult rats underwent either sectioning of the saphenous or femoral nerves on one side, or else unilateral denervation of the skin of the posterior thigh. Two weeks later cholera toxin B subunit (CTb), which is normally transported selectively by myelinated somatic primary afferents, was injected into the ipsilateral (intact) sciatic nerve. The relationship between CTb, vasoactive intestinal peptide (VIP), and binding of Bandeiraea simplicifolia isolectin B4 (IB4) was then examined in the ipsilateral dorsal horn of the second to fifth lumbar spinal segments (L2-L5).