Calcitonin Gene‐related Peptide (CGRP)‐like Immunoreactivity and CGRP mRNA in Rat Spinal Cord Motoneurons after Different Types of Lesions

Abstract

By use of the indirect immunofluorescence (IF) technique, radioimmunoassay (RIA) and in situ hybridization (ISH) histochemistry, the staining pattern, content and expression of calcitonin gene-related peptide (CGRP) in lumbar motoneurons of normal rats and rats subjected to sciatic nerve transection (SNT), ventral root transection (VRT), low thoracic spinal cord transection (SCT) alone or in combination with a subsequent SNT, as well as rats subjected to chemical lesioning of 5-hydroxytryptamine (5-HT) neurons by 5,7-dihydroxytryptamine (5,7-DHT), were studied. We here confirm that a large number of the lumbar motoneurons normally contain CGRP-like immunoreactivity (LI) and CGRP mRNA. SNT induced a transient increase in CGRP-LI, with a peak at days 2 - 5 after lesion, and normalized levels again after approximately 2 - 3 weeks. Comparable results were obtained with IF and RIA. This increase is probably a consequence of increased CGRP synthesis, since a parallel up-regulation of CGRP mRNA levels was seen. A normalization of CGRP mRNA did not occur during the period studied, despite an apparent normalization of peptide levels after 2 weeks, and this may in turn be due to an increased turnover and/or release of CGRP. The up-regulation of CGRP is probably caused by the axon injury itself, since a similar cellular reaction with respect to CGRP was observed in motoneurons subjected to VRT. However, SNT, which also lesions dorsal root afferents and causes a decline in CGRP-LI in the dorsal horn, induced an increase in CGRP-LI in motoneurons on the contralateral side also. Thus, it may be that severance of dorsal root afferents and/or changes in reflex activity may also influence the production of CGRP in motoneurons. SCT, which severs all descending synaptic input to the motor nucleus and causes a paralysis of muscles innervated by motoneurons below the lesion, resulted in a marked decline in both content of CGRP-LI (IF and RIA) and expression of CGRP mRNA. However, treatment with 5,7-DHT, which lesions 5-HT neurons, including those giving rise to the bulbospinal serotoninergic pathway, did not cause any dramatic changes in motor behaviour but induced an increase in both motoneuron content of CGRP-LI and expression of CGRP mRNA. In rats first subjected to SCT, which depresses CGRP, followed 2 weeks later by SNT, we found a marked increase in both content of CGRP-LI (IF and RIA) and expression of mRNA coding for CGRP. In summary our results show that the cellular production of the CGRP peptide, normally expressed in motoneurons, is influenced in a complex way by motoneuron injury as well as changes in the afferent input. There also appear to be important differences in the expression of CGRP in small (gamma) and large (alpha) motoneurons as well as between motoneurons of different nuclei, in normal as well as axotomized rats.

Differential regulation of trophic factor receptor mRNAs in spinal motoneurons after sciatic nerve transection and ventral root avulsion in the rat

“…Because the quantitative data are based on the relation between signaling in motoneurons on operated vs. nonoperated sides, any contralateral changes induced by the lesion could have an influence on the results. Such changes have been described for, e.g., GAP-43 and CGRP in motoneurons (Piehl et al, 1991;Lindå et al, 1992;Booth and Brown, 1993). However, scrutinizing single glasses containing cords from all survival times did not reveal any significant differences in grain density in contralateral motoneurons for any of the probes used in this study.…”

Choline acetyltransferase and calcitonin gene-related peptide immunoreactivity in motoneurons after different types of nerve injury

“…Previous studies, on cranial and spinal motoneurons have determined how cellular levels of either ChAT (Lams et al, 1988;Armstrong et aI., 1991) or CGRP (Streit et al, 1989;Arvidsson et al, 1990;Haas et al, 1990;Dumoulin et al, 1991;Piehl et al, 1991;Saika et al, 1991) are affected by peripheral axotomy. This study is the first to quantify immunoreactive changes in proteins in the hypoglossal nucleus after different types of nerve injury and to compare enzyme and neuropeptide levels to the extent of peripheral reinnervation.…”

“…As a putative trophic factor, CGRP appears in late prenatal development, increases rapidly, then decreases to adult levels of reduced immunoreactivity by the end of the fourth postnatal week (Kubota et al, 1988). Immunocytochemical and biochemical data have demonstrated an increase of CGRP after axotomy of cranial (Streit et al, 1989;Haas et al, 1990;Dumoulin et al, 1991;Saika et al, 1991) and spinal (Arvidsson et al, 1990;Noguchi et al, 1990;Piehl et al, 1991) motoneurons. In contrast to these findings, decreased acetylcholine (ACh) content in the axotomized neuron has been inferred from sharp decreases in choline acetyltransferase (CHAT), the enzyme that catalyzes ACh synthesis (Lares et al, 1988;Armstrong et al, 1991).…”

Glucose‐dependent insulinotropic polypeptide (GIP) and its receptor (GIPR): Cellular localization, lesion‐affected expression, and impaired regenerative axonal growth

“…The observed lesion-associated induction of both GIP and GIPR mRNAs in the ventral spinal cord indicates a putative role of the GIP/GIPR system as a mediator of injury responses for injured motor neurons. Spinal motor neurons are considered to have a peptidergic identity (Gibson et al, 1984), and it has been demonstrated that peptide expression in motor neurons is highly plastic, insofar as mRNA levels are up-regulated after axotomy (Piehl et al, 1991). In fact, it is well established that several neuropeptides exhibiting important neurotrophic actions were up-regulated in response to nerve injury (Hokfelt et al, 2000;Bosse et al, 2001Bosse et al, , 2006.…”