CGRP in brain stem motoneurons. Dependent on target innervated?

Effects of endurance and resistance training on calcitonin gene-related Peptide and acetylcholine receptor at slow and fast twitch skeletal muscles and sciatic nerve in male wistar rats

The aim of this study was to investigate effects of endurance and resistance training (ET and RT) on CGRP and AChRs at slow and fast twitch muscles and sciatic nerve in rats. Twenty-five male rats were randomly assigned into three groups including sedentary (SED), endurance training (ET), and resistance training (RT). Animals of ET exercised for 12 weeks, five times/week, and 60 min/day at 30 m/min. Animals of RT were housed in metal cage with 2 m high wire-mesh tower, with water bottles set at the top. 48 h after the last session of training protocol, animals were anaesthetized. The right sciatic nerves were removed; then, Soleus (SOL) and Tibialis anterior (TA) muscles were excised and immediately snap frozen in liquid nitrogen. All frozen tissues were stored at -80°C. Results showed that, after both ET and RT, CGRP content as well as AChR content of SOL and TA muscles significantly increased. But there was no significant difference among groups at sciatic nerve' CGRP content. In conclusion, data demonstrate that ET and RT lead to changes of CGRP and AChR content of ST and FT muscles. The changes indicate to the importance of neuromuscular activity.

The superior olivary complex of the hamster has multiple periods of cholinergic neuron development

Cholinergic neurons of the superior olivary complex share a common embryological and phylogenetic origin with brainstem motor neurons and serve as the major descending efferent pathway either to the cochlea as part of the olivocochlear system or to the cochlear nucleus. In this study, we investigated the developmental expression patterns of choline acetyltransferase (ChAT) and its co-localization with calcitonin gene-related peptide within the superior olivary complex and neighboring brainstem motor nuclei. At embryonic day 12, neurons in the ventral nucleus of the trapezoid body were first to express ChAT. The temporal expression pattern of both ChAT mRNA and immunoreactivity in this periolivary region mimicked motor neurons in the facial and trigeminal motor nuclei. Just before birth, shell neurons surrounding the lateral superior olive expressed ChAT. Neither ChAT-positive periolivary neurons nor shell neurons co-expressed calcitonin gene-related peptide during development or in the adult. Immediately following birth, intrinsic neurons within the lateral superior olive expressed ChAT but not calcitonin gene-related peptide. However, a transient increase in the number of ChAT-positive neurons in the lateral superior olive coincided with the onset of the calcitonin gene-related peptide co-expression within these neurons. We conclude that ChAT expression appears first in periolivary regions containing medial olivocochlear neurons, precedes the expression of calcitonin gene-related peptide in the superior olivary complex, and is co-expressed with calcitonin gene-related peptide within the lateral superior olive containing lateral olivocochlear neurons. These data suggest that the lateral olivocochlear system co-expresses ChAT and calcitonin gene-related peptide, whereas the medial olivocochlear system does not.

alpha-CGRP mRNA levels in motoneurons innervating specific rat muscles

Along with acetylcholine, motoneurons express several neuromodulatory peptides. The most extensively studied of these peptides is calcitonin gene-related peptide (CGRP). CGRP modulates the biochemical, physiological and metabolic properties of skeletal muscle primarily through activation of membrane receptors. Virtually all motor pool contain motoneurons that are immunoreactive for CGRP. The purpose of this study was to determine the proportions of motoneurons that express alpha-CGRP in motor pools innervating muscles with different motor unit compositions. These include the soleus, extensor digitorum longus, tensor fascia latae and the diaphragm muscles as well as the spinal nucleus of the bulbocavernosus. The spinal nucleus of the bulbocavernosus provides innervation to the bulbocavernosus/levator ani muscle complex and the external anal sphincter muscle. The spinal nucleus of the bulbocavernosus contained the greatest proportion of alpha-CGRP mRNA-positive motoneurons, followed in descending rank order by the tensor fascia latae, the extensor digitorum longus, the soleus and the diaphragm motor pools. In addition, significant differences between motor pools were observed in the mean relative alpha-CGRP mRNA level among those motoneurons expressing alpha-CGRP. The highest mean relative alpha-CGRP mRNA level was observed in soleus and the extensor digitorum longus motor pools; followed in descending rank order by the tensor fascia latae, the diaphragm and the spinal nucleus of the bulbocavernosus. We have previously shown that muscle contractile inactivity increases the number of motoneurons that express alpha-CGRP and in the relative mRNA levels. The results of the present study suggest that the proportion of motoneurons within a motor pool that express alpha-CGRP may be closely related to the contractile activity (i.e. activation history) of the target muscle.

Differential expression of alpha-CGRP and beta-CGRP genes within hypoglossal motoneurons in response to axotomy

In this study we have analysed, by in situ hybridization, the expression of the genes for both alpha-CGRP and beta-CGRP in hypoglossal motor nuclei following transection of the left hypoglossal nerve. Our results show that the gene for alpha-CGRP displays a peculiar sequence of regulation (a successive up-down-up-recovery sequence) within ipsilateral hypoglossal motoneurons in response to axotomy. It is initially up-regulated, then down-regulated (displaying mRNA levels below basal), and later again up-regulated before recovery. By contrast, the gene for beta-CGRP displays a successive and distinct up-down-recovery sequence of regulation (it does not display a second increase in mRNA production). The first up-regulation of the alpha-CGRP gene occurs just during the early period of perineuronal glial reaction and the second up-regulation just during the period of delayed astrocyte reaction and muscle reinnervation. Because alpha-CGRP is a neuron-derived factor for many types of cells, including astrocytes and skeletal myocytes, our results suggest that the pleiotropic alpha-CGRP may be a motoneuron-derived trophic signal for both glial and skeletal muscle cells in order to maintain the motoneuron itself and, in consequence, might be of therapeutic interest in treating degenerative disease of motoneurons. beta-CGRP might be redundant within the hypoglossal motoneurons.

Postnatal calcitonin gene-related peptide in the superior olivary complex

The purpose of this study was to investigate quantitatively the distribution of calcitonin gene-related peptide (CGRP)-positive neurons within the superior olivary complex (SOC) at various postnatal ages. In the lateral superior olive (LSO), most if not all, CGRP-positive cells correspond to the cholinergic portion of the lateral olivocochlear system which innervates the cochlea. Brains from 1-day old (P1) through juvenile (P30) hamsters were used. At all ages, CGRP-positive neurons were seen throughout the various nuclei of the SOC. There was a dramatic shift in the distribution of CGRP-positive neurons from being predominantly periolivary to being predominantly confined within the LSO. The number of CGRP-positive neurons clearly increased as a function of increasing age. At the earliest postnatal ages, the LSO contained few if any immunostained cells, whereas at later ages the LSO contained the majority (greater than 70%) of the immunostained cells. Assuming that these CGRP-positive cells within the LSO correspond to olivocochlear neurons, these data suggest that in hamsters the lateral olivocochlear system may be immature at birth up until the second postnatal week.