The effect of neonatal capsaicin treatment on the CGRP-immunoreaction in the trigeminal subnucleus caudalis of mice

Abstract

The calcitonin-gene related peptide (CGRP) is a primary afferent neurotransmitter in the trigeminal system. Although a neonatal administration of capsaicin eliminates substance P (SP)-mediated nociceptive responses to induce a permanent functional reduction in C-fibers, little information is available regarding changes in CGRP-immunoreaction in mice undergoing neonatal capsaicin treatment (CP mice). This study examined postnatal changes in the distribution of CGRP-immunoreaction in the trigeminal subnucleus caudalis and trigeminal ganglion of CP mice by immunohistochemical technique and a quantitative analysis. Immunohistochemistry for CGRP in the subnucleus caudalis (Vc) demonstrated two dense distributions of neurons in the CP mice as well as naïve mice: in the marginal layer and the region 400-600 μm deep. The quantitative analysis revealed no significant difference in the density of CGRP immunoreaction between naïve and CP mice 1-8 weeks of age. In the trigeminal ganglion of both groups, the size distribution of CGRPpositive neurons displayed a distribution pattern with one peak in 200-300 μm 2 at week 1 and with two peaks in 200-300 μm 2 and 600-700 μm 2 at week 8 but no significant difference in neural density existed between these regions. When double staining in the naïve mice with CGRP or SP and VR1, a capsaicin receptor, was done, many trigeminal ganglion neurons co-expressed SP-and VR1-immunoreactions, but rarely exhibited CGRP/VR1-co-localization. Taken together with previous data, these current observations suggest that CGRP containing afferent neurons possibly performs differing roles in nociceptive afferent input transmission within the Vc from SP-containing neurons in mice.Calcitonin gene-related peptide (CGRP), widely distributed in central and peripheral nervous systems, has diverse functions including that as a primary afferent neurotransmitter. This neuropeptide is involved in nociception, as strongly suggested by experimental findings that a cyclooxygenese inhibitor attenuated a release of CGRP from the trigeminal nucleus caudalis (17), and that a bath application of CGRP also produced a slow action potential in dorsal root ganglion cells (20). Indeed, an intravenous administration of CGRP induces headache in migraineurs (19). In addition to the nociceptive function, CGRP enhances excitations of wide dynamic range neurons caused by NMDA or AMPA receptor agonist, suggesting a nociceptive modulation role of CGRP (8). Substance P (SP) is also a slow acting neurotransmitter that serves as a modulator of nociceptive transmission (36). CGRP is released from Aδ-and C-fibers while SP is from C-fibers (3,22,23).

Primary trigeminal afferents are the main source for stimulus-induced CGRP release into jugular vein blood and CSF

“…We treated newborn rats with subcutaneously administered capsaicin, a method that has repeatedly been shown to destroy most of the pain-transmitting C-fibres (17). Experimental work in mice shows no difference in TNC with respect to CGRP immunoreactivity between capsaicin and vehicle after several weeks (28). This is in line with our CGRP PCR and immunohistochemistry data.…”

Immunohistochemical characterization of calcitonin gene-related peptide in the trigeminal system of the familial hemiplegic migraine 1 knock-in mouse

“…Pictures were taken on the same day to prevent the decrease of fluorescence intensity over time. Following acquisition of images at ×50 magnification, with unchanged linear properties, Image J (National Institutes of Health, Bethesda, MD) was used for densitometric analysis of CGRP fibers in each hemisection as previously described (39,40). Results are expressed as median and interquartile (IQ) ranges per hemisection for each animal group.…”

Distribution of CGRP in the minipig brainstem

“…CGRP has also been implicated in other physiological actions (hyperthermia, locomotor activity, social behavior, the regulation of astrocytes, glucose metabolism, increases in the number of acetylcholine receptors at the level of the neuromuscular junction, etc) (Batten et al, ; de Souza et al, ; Gibson et al, ; New and Mudge, ; Raynaud et al, ). The colocalization of CGRP with substance P or with gamma‐aminobutiric acid (GABA) and the presence of CGRP in intrinsic neurons of the brainstem have also been reported (Aita et al, ; Batten et al, ; Maison et al, ). It is also known that motor neurons containing CGRP located in the nucleus ambiguus project to the striated muscle of the larynx and pharynx, but CGRP immunoreactivity is absent from vagal preganglionic motor neurons projecting to structures in the chest and abdomen (McWilliam et al, ).…”