Saeed AW, Ribeiro-Da-Silva A (2007) Changes in neurokinin-1 receptor expression in populations of spinal lamina I neurons in rats lacking non-peptidergic nociceptive fibers. Neuroscience 2007 Abstracts 821.4/FF19. Society for Neuroscience, San Diego, CA.
Summary: Neurokinin-1 receptor (NK-1r)-containing lamina I projection neurons are deeply involved in the transmission of pain-related information to the brain. Previous studies have shown that lamina I neurons can be classified morphologically into fusiform, pyramidal and multipolar cells, and that these types differ in functional properties, with the pyramidal type being non-nociceptive. Our laboratory has shown not only a considerable increase in immunoreactivity for the NK-1r in animals with CFA-induced arthritis but also a de novo expression of these receptors by pyramidal neurons (Almarestani et al., Soc.Neurosci.Abstr., Program # 249.11, 2006). Based on this, we deemed it interesting to study whether pyramidal neurons would also express NK-1r in an animal model in which we have previously shown a drastic increase in NK-1r expression but no augmented nociceptive responses. To achieve this, we injected, under anesthesia, saporin (SAP) conjugated to the lectin IB4 into the left sciatic nerve of male Sprague Dawley rats to selectively lesion the non-peptidergic nociceptive C-fibers. Animals were sacrificed from 2 weeks to 2 months post-lesion. Horizontal sections of spinal segments L5 and L6 were cut and processed for IB4 binding and NK-1r immunoreactivity using immunofluorescence. Examination of IB4-SAP treated rats at several time points post-lesion revealed increased expression of NK-1r by lamina I cells of the fusiform and multipolar types on the side ipsilateral to the lesion, compared to the contralateral side and to controls. However, pyramidal cells seldom expressed the NK-1r in both control and lesioned animals. Surprisingly, we also observed a direct innervation of lamina I neurons by IB4-positive neurons in control animals, which did not occur ipsilaterally in lesioned animals. These observations support the concept that increased activity by the peptidergic nociceptive afferents may be important in the maintenance of nociceptive responses in the absence of non-peptidergic fibers.
Related Products: IB4-SAP (Cat. #IT-10)