Decreased immunoreactive (IR) calcitonin gene-related peptide correlates with sprouting of IR-peptidergic and serotonergic neuronal processes in spinal cord and brain nuclei from the Wobbler mouse during motoneuron disease

Alterations in the number of motoneurons containing immunoreactive calcitonin gene-related peptide(CGRP)& choline acetyltransferase(ChAT) in the cervical spinal cord of the wobbler mouse during the development of the motoneuron disease

The Wobbler mouse (wr) has been studied as a model for inherited human motoneuron diseases (MNDs). Using behavioral tests for forelimb power, walking, climbing, and the “clasp-like reflex” response, the progress of the MND can be categorized into early (Stage 1, age 21 days) and late (Stage 4, age 3 months) stages. Age-and sex-matched normal phenotype littermates (NFR/wr) were used as controls (Stage 0), as well as mice from two related wild-type mouse strains: NFR/N and a C57BI/6N. Using behavioral tests, we also detected pre-symptomatic Wobblers at postnatal ages 7 and 14 days. The mice were anesthetized and perfusion-fixed for immunocytochemical (ICC) of CGRP and ChAT in the spinal cord (C3 to C5).

Using computerized morphomety (Vidas, Zeiss), the numbers of IR-CGRP labelled motoneurons were significantly lower in 14 day old Wobbler specimens compared with the controls (Fig. 1). The same trend was observed at 21 days (Stage 1) and 3 months (Stage 4). The IR-CGRP-containing motoneurons in the Wobbler specimens declined progressively with age.

Neurodegenerative changes are prevented by Erythropoietin in the pmn model of motoneuron degeneration

Motoneuron diseases are fatal neurodegenerative disorders characterized by a progressive loss of motoneurons, muscle weakness and premature death. The progressive motor neuronopathy (pmn) mutant mouse has been considered a good model for the autosomal recessive childhood form of spinal muscular atrophy (SMA). Here, we investigated the therapeutic potential of Erythropoietin (Epo) on this mutant mouse. Symptomatic or pre-symptomatic treatment with Epo significantly prolongs lifespan by 84.6% or 87.2% respectively. Epo preserves muscle strength and significantly attenuates behavioural motor deficits of mutant pmn mice. Histological and metabolic changes in the spinal cord evaluated by immunohistochemistry, western blot, and high-resolution (1)H-NMR spectroscopy were also greatly prevented by Epo-treatment. Our results illustrate the efficacy of Epo in improving quality of life of mutant pmn mice and open novel therapeutic pathways for motoneuron diseases.

Effects of assisted feeding on Wobbler mouse motoneuron disease and on serotonergic and peptidergic sprouting in the cervical spinal ventral horn

The Wobbler mouse is used as a model of human motoneuron disease (MND). During the disease progress, the significant loss of motoneurons in cervical spinal cord and cranial motor nuclei leads to the progressive loss of motor function in the forelimb, head, and neck regions. The loss of cutting and chewing ability that results in the inability to feed properly might lead to a lower mean body weight (b. wt.) that is generally one-half that of the normal phenotype littermate controls. Nutritional deficit might also influence neuronal processes sprouting in the cervical spinal ventral horn. To determine whether nutritional deficits contribute to the wt. loss, and influence the progress of MND as well as its sprouting phenomenon, Wobbler and normal phenotype control littermates were dropper-fed three times daily on a regular laboratory diet of Rat Chow. Weight measurements and behavioral tests were taken to monitor the disease. Immunocytochemisty of serotonin, substance P, and leucine enkephalin were conducted in the cervical spinal cord to investigate if any alteration occurred on the previously reported values in ad lib-fed animals. Organ wts. were measured to determine where nutritional benefit was incurred. Although mean wt. loss in Wobblers was reduced, wt. differed significantly from the control values after dropper feeding. However, the progress of the disease or alteration of neurotransmitters containing neuronal processes were not affected by nutritional factors. Therefore, nutritional intake affects wt. gain, but is not a primary consideration in the progress of MND. Behavioral deficits and neurotransmitter alterations are probably directly caused by motoneuron losses.

Increase in fiber density for immunoreactive serotonin, substance P, enkephalin and thyrotropin-releasing hormone occurs during the early presymptomatic period of motoneuron disease in Wobbler mouse spinal cord ventral horn

The Wobbler mouse is a useful small animal model for the study of human motoneuron diseases. Besides showing the loss of motoneurons when the symptoms are expressed around the age of 3 weeks, we have also demonstrated the presumed 'sprouting' of neuronal processes in the cervical spinal ventral horn which contain immunoreactive (IR) serotonin (5-HT), substance P (SP) and methionine and leucine enkephalins (ME, LE), as well as thyrotropin-releasing hormone (TRH). This occurs during the symptomatic period when IR-5-HT, ME and LE sprout at Stage 1, around the age of 3 weeks, whereas IR-SP sprouts only at a late stage (stage 4) of the disease (at age 3 months). The present investigation shows that the presumed sprouting occurs even before the appearance of symptoms and prior to significant motoneuron losses. IR-5-HT containing neuronal processes sprout by postnatal day 7, whereas IR-SP, -ME, -LE, and -TRH processes sprout by day 14. Hypothetically the early sprouts may contribute to the loss of motoneurons. They also respond to ciliary and brain derives neurotrophic factors cotreatment. IR-SP neuronal processes, although they sprout by day 14, show normal fiber density by the time symptoms appear (stage 1, age 21 days). However the SP sprouting is biphasic and a significant increase in number also occurs at an advanced stage of the disease (stage 4, age 3 months).

A novel behavioral method to detect motoneuron disease in Wobbler mice aged three to seven days old

The Wobbler mouse possesses an inherited autosomal recessive form of motoneuron disease. The most characteristic abnormality is the degeneration of motoneurons, mostly in the cervical spinal cord, and in the brain stem cranial motor nuclei. The underlying pathology shows up as symptoms that are only detectable confidently around the time of weaning (age 3 weeks). We now report a new method designed to identify presymptomatic Wobbler mice by behavioral and statistical approaches. We measured body weight, righting reflex (RR) and gender to examine whether these parameters have an impact on the status of the disease before age 3 weeks. Using a total of 341 NFR/wr strain pups, we found a strong association between RR and the Wobbler disease status (p<0.0001) between postnatal days 3 to 7, and achieved greater than 97% correct classification of Wobblers. Therefore the measurement of RR allows the early detection of the affected Wobbler (wr/wr) mice with a minimum of error. This method has been used in our laboratory for immunocytochemical studies that show the early sprouting of immunoreactive serotonin and peptidergic fibers in the cervical spinal ventral horn by postnatal days 7 and 12 respectively. The early detection of Wobbler mice thus facilitates significant new understanding regarding the pathogenesis of motoneuron disease. We can now examine potentially therapeutic approaches which may be more effective than when administered in the symptomatic weanlings (work in progress).

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Neuron volume in the ventral horn in Wobbler mouse motoneuron disease: a light microscope stereological study

Previous pathological reports have indicated that swollen and vacuolated motoneuron cell bodies are the most predominant feature characterising Wobbler mouse motoneuron disease, but there has been little supportive evidence using area measurements. The present study focuses on the possible role of changes in neuronal nuclear and perikaryal volumes in the cervical spinal cord ventral horn, using new and traditional stereological probes which provide unbiased estimates of volume. Semithin sections from the ventral horn of Wobbler mice and age and sex-matched phenotypically normal littermates were examined at 2 ages (young and old). The young Wobbler group had significantly larger volume weighted mean perikaryal volumes compared with age-matched controls, reflecting the presence of large swollen cells characteristic of this group; this situation was reversed in the control group. Number-weighted perikaryal volume estimates in the old Wobbler group were smaller than in age-matched controls. The variation in perikaryal volume was greatest in the young Wobbler group in which the coefficient of variation was 127%. The mean number weighted and volume weighted mean nuclear volumes were significantly smaller in the old Wobbler group compared with age-matched controls and young Wobbler groups. The application of new stereological probes has enabled us to document more precisely these changes in neuronal structure in the Wobbler mutant mouse.

Changes in receptor levels for thyrotropin releasing hormone, serotonin, and substance P in cervical spinal cord of Wobbler mouse: a quantitative autoradiography study during early and late stages of the motoneuron disease

Receptor levels for thyrotropin releasing hormone (TRH) measured by quantitative autoradiography in the Wobbler mouse cervical spinal cord show receptor losses that may relate to the inherited loss of motoneurons, most pronounced late (at Stage 4) in the motoneuron disease. An age-related decrease of TRH and serotonin (5-HT) receptors can be seen in the ventral horn of the control specimens (normal phenotype littermate and wild-type alike). However, this pattern is missing for substance P (SP) receptors from the wild-type specimens. Therefore the age-related decrease of SP receptors detected in the Wobbler mouse strain may identify a strain-related defect in SP neuronal/receptor developmental patterns. A higher level of TRH receptors was measured in the Wobbler dorsal horn at an early stage (Stage 1) in the motoneuron disease compared with the control specimens. The data are discussed in relation to an aberrant neuronal sprouting that occurs around the degenerating motoneurons in the ventral horn during the course of the motoneuron disease.

Identification of thyrotropin-releasing hormone receptor mRNA in the Leydig cells of the mouse testis by in situ hybridization

Thyrotropin-releasing hormone receptor (TRH-R) mRNA was detected in cryostat sections of the mouse testis using biotinylated oligonucleotides complementary to the cDNA encoding the mouse pituitary TRH-R by in situ hybridization. Hybridization signals were detected exclusively in the Leydig cells. The intensity of the signal was probe-concentration dependent. This result suggests that testicular TRH may serve as an autocrine regulator of reproductive function and development via TRH-R in a fashion that is similar or identical to that in the pituitary.

Lecithinized superoxide dismutase retards wobbler mouse motoneuron disease

Gene mutations of Cu/Zn superoxide dismutase (SOD) have been discovered in familial amyotrophic lateral sclerosis (ALS). Oxidative stress also plays a role in the pathogenesis of sporadic ALS. Whether antioxidant therapy is beneficial in this fatal disease is now crucial. We have shown that SOD treatment improves neuromuscular dysfunction and morphological changes in wobbler mouse motoneuron disease. Progressive spinal motor neuronopathy and axonopathy, predominantly in the cervical cord, occur at postnatal age 3-4 weeks, leading to muscle weakness and contracture of the forelimbs in this animal. These motor deficits rapidly increase by postnatal age 6-8 weeks, and then slowly progress. Wobbler mice were given two doses daily of phosphatidyl choline-bound Cu/Zn SOD (PC-SOD, 10(4), 10(5) U/kg) or a vehicle solution by intraperitoneal injection from postnatal 3-4 to postnatal 7-8 weeks of age. PC-SOD treatment attenuated progression of motor dysfunction, prevented denervation muscle atrophy, and delayed degeneration of spinal motoneurons in wobbler mice. This raises the possibility that PC-SOD may have therapeutic potential in human motoneuron disease.

Increase in alpha-CGRP and GAP-43 in aged motoneurons: a study of peptides, growth factors, and ChAT mRNA in the lumbar spinal cord of senescent rats with symptoms of hindlimb incapacities

Sprague-Dawley rats develop progressive motor dysfunctions during the third year of life. We use this as a model to examine possible neuronal mechanism(s) that may cause motor impairments occuring during aging. In this study we have used indirect immunofluorescence histochemistry (IF) and in situ hybridization histochemistry (ISH) to study quantitatively and qualitatively the staining pattern and mRNA expression of calcitonin gene-related peptide (alpha-CGRP), growth-associated protein 43 (GAP-43), and acidic fibroblast growth factor (aFGF) in spinal lumbar motoneurons of young adult (2-3 months) and aged (30 months) Sprague-Dawley rats. In addition, mRNAs encoding choline acetyltransferase (ChAT), beta-CGRP, and cholecystokinin (CCK) were analyzed. All aged rats used in this study disclosed symptoms of hindlimb incapacity, ranging from mild weight-bearing insufficiency to paralysis of the hind limbs. The symptoms were confined to the musculature of the hindlimb and hip regions. Only a small number (approximately 15%) of the large motoneurons that innervate the hindlimb muscles were lost in those aged rats that had clinical symptoms of hindlimb motor incapacities. The remaining motoneurons expressed ChAT mRNA at levels similar to those of young adult rats. The vast majority of these motoneurons showed increased mRNA levels for alpha-CGRP and GAP-43. Aged motoneurons contained more CGRP like immunoreactivity (LI), but the number of immunoreactive neurons was smaller than in adult rats. GAP-43-LI could be detected in motoneurons in aged, but not in adult, rats. GAP-43-LI was always colocalized with CGRP-LI in aged motoneurons. Studies of individual aged rats revealed that the increase of GAP-43 mRNA-positive cell bodies occurred in cases with the most severe clinical symptoms, whereas the increase in alpha-CGRP was even evident in rats with mild symptoms. No alterations in content of aFGF-LI or aFGF mRNA could be detected in the aged rat, and the content of CCK and beta-CGRP mRNAs was also normal. The usefulness of this rat model for studies of neuromuscular aging and possible functional roles for GAP-43 and CGRP in plastic and regenerative processes during aging are discussed.

Histometric effects of ciliary neurotrophic factor in wobbler mouse motor neuron disease

We investigated the histological effects of ciliary neurotrophic factor on degenerating motor neurons, their axons, and skeletal muscles in 68 wobbler mice with motor neuron disease. Treatment consisted of recombinant rat or human ciliary neurotrophic factor (or a vehicle solution), 1-mg/kg subcutaneous injection, three times per week for 4 weeks after the clinical diagnosis. The number of motor neurons immunoreactive for calcitonin gene-related peptide was higher in mice receiving rat ciliary neurotrophic factor (p < 0.03), although the number of choline acetyltransferase-reactive neurons was the same in both treated and untreated control groups. Treatment did not prevent vacuolar degeneration of motor neurons. In mice treated with human ciliary neurotrophic factor, the percentage of axons undergoing acute axonal degeneration (myelin ovoids) was smaller in the entire C5 ventral root (p < 0.02) and in the musculocutaneous nerve (p < 0.04), and the number of myelinated nerve fibers was 30% higher in both nerves (p < 0.01 and p < 0.04, respectively) than in controls. In ciliary neurotrophic factor-treated mice, the biceps muscle weight was 20% greater, the mean muscle fiber diameter was 30% larger, and the number of atrophied muscle fibers was 75% lower than that in the vehicle-treated wobbler mice (p < 0.001 for all three results). The number of terminal axonal branching points and the mean length of motor end-plates were also higher in the ciliary neurotrophic factor-treated mice (p < 0.001 and p < 0.02, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in acetylcholinesterase and choline acetyltransferase activities and neuropeptide levels in the ventral spinal cord of the Wobbler mouse during inherited motoneuron disease

Enzymatic assays for acetylcholine esterase (AChE) and choline acetyltransferase (ChAT) were applied to dorsal and ventral cervical spinal cord regions taken from the Wobbler mouse, a model for inherited motoneuron disease. Early in the disease, ChAT (but not AChE) activity is significantly greater compared with the control littermate specimens. The high ChAT activity correlates with the high thyrotropin releasing hormone (also leucine-enkephalin) concentrations measured in the Wobbler ventral horn early in the disease. Late in the motoneuron disease, both AChE and ChAT activities are significantly lower than in the control littermate specimens. These data correlate with the high substance P, methionine and leucine enkephalin concentrations measured in the Wobbler ventral horn late in the motoneuron disease.

Thyrotropin-releasing hormone (TRH) neurons sprout in cervical spinal cord of Wobbler mouse

The present study was undertaken to quantify the immunocytochemical changes for thyrotropin-releasing hormone (TRH) within the ventral horn of the cervical spinal cord from Wobbler (wr/wr) mice selected at postnatal ages 3 weeks to 5 months compared with the normal phenotype (NFR/wr) littermates as well as mice from two related normal mouse strains: the NFR/N parent strain, and the closely related C57B1/6N mouse strain. The immunoreactive (IR) neuronal processes containing TRH appeared in all specimens within Rexed's laminae VIII, IX, and X. Compared with the normal (C57B1/6N, NFR/N) specimens, the pair-matched normal phenotype (NFR/wr) and Wobbler (wr/wr) specimens possessed significantly greater numbers of IR-TRH containing processes at every age studied. Compared with the normal phenotype (NFR/wr) specimens, greater numbers of IR-TRH containing processes appeared in the ventral horn region studied from the Wobbler (wr/wr) specimens taken early (Stage 1) as well as later (Stages 3 and 4) in the motoneuron disease. An age-related decline in the number of IR-TRH processes was apparent among the specimens from the Wobbler mouse strain (NFR/wr, wr/wr), but not the normal (NFR/N, C57B1/6N) mouse strains. The data suggest that TRH may play a significant role in the Wobbler disease, possibly even before the symptoms become apparent. In addition strain-related differences exist which may be important to the etiology of the Wobbler disorder.

Decrease of enkephalins in cerebellum during Wobbler mouse motoneuron disease

The Wobbler mouse possesses an inherited motoneuron disease, which expresses itself primarily at cervical spinal levels and in cranial motor nuclei. Cell degeneration is sporatic and negligible in other motor regions of the brain (e.g., cerebellum, corpus striatum). However, enkephalin concentrations are consistently lower in the Wobbler cerebellum throughout the motoneuron disease, whereas substance P concentrations are significantly higher late in the disease compared with the normal phenotype littermates. The data imply that early changes in enkephalin (also shown for leucine enkephalin in the spinal cord and brainstem) may be important to the etiology of the Wobbler disorder. Like the late increase of substance P, this may reflect a yet-to-be described response to parent cell degeneration in the raphe nuclei. TRH remained unchanged in Wobbler cerebellum and corpus striatum, wherein the other peptides studied herein also maintained similar concentrations to the normal phenotype littermates.