Primary afferent input to neurons in laminae III and IV of the rat spinal cord which possess the neurokinin-1 (NK-1) receptor

Naim, Magda Mohamed (1998) Primary afferent input to neurons in laminae III and IV of the rat spinal cord which possess the neurokinin-1 (NK-1) receptor. PhD thesis, University of Glasgow.

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Abstract

Neurokinin-1 receptor-immunoreactivity is present on many neurons in the spinal cord. A population of cells which possess the receptor is located in laminae III and IV and these cells have dorsal dendrites that penetrate the superficial laminae (I and II) of the dorsal horn. Since the dendrites of these neurons traverse several laminae, it has been suggested that they might receive input from different classes of primary afferents that terminate in these laminae. The present study investigated the input which these cells receive from two types of primary afferents: those which contain substance P (and are thought to function as nociceptors) and those with myelinated axons that terminate in laminae III-V (most of which are low-threshold mechanoreceptors). With the immunofluorescence technique and confocal microscopy, all neurons of this type were found to receive contacts from substance P-immunoreactive varicosities and in most cases the contacts onto dorsal dendrites were very numerous. The great majority of substance P-immunoreactive varicosities which formed contacts were also calcitonin gene- related peptide-immunoreactive, indicating that they were of primary afferent origin. Combined confocal and electron microscopy revealed that synapses were present at sites of contacts between substance P-immunoreactive primary afferent boutons and the dendrites of the NK-1 receptor-immunoreactive cells. Some neurons of this type belong to the spinothalamic tract and cells retrogradely-labelled after thalamic injection of cholera toxin B subunit, were therefore examined for the presence of contacts from substance P-immunoreactive axon terminals. The results indicated that the spinothalamic tract neurons which possess the NK-1 receptor and have dorsally directed dendrites also receive contacts from substance P-immunoreactive axonal varicosities onto their dorsal dendrites. By using the transganglionic transport technique, input from myelinated primary afferents which were labelled by injection of cholera toxin B subunit into the sciatic nerve were also examined. Dual-immunofluorescence and confocal microscopy revealed the presence of contacts between labelled primary afferent terminals and all of the NK-1 receptor-immunoreactive cells examined, however these contacts were much less numerous than those which the cells received from substance P-containing primary afferents. Electron microscopy revealed that synapses were present at some of the contacts between the myelinated afferents and the NK-1 receptor-immunoreactive neurons. Since cells of this type were found to receive monosynaptic input from two different classes of primary afferents, (a major input from substance P-containing afferents and a less dense input from myelinated primary afferents) it can be concluded that they are likely to have wide-dynamic-range receptive fields but with a relatively strong nociceptive component.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: A J Todd
Keywords: Neurosciences
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-71352
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 10 May 2019 10:49
URI: http://theses.gla.ac.uk/id/eprint/71352

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