Spiny interneurons identified in the normal mouse spinal cord show alterations in the Wobbler mouse: a model for inherited motoneuron disease

Presumed interneurons are described in the Golgi-impregnated cervical spinal cord taken from normal phenotype and motoneuron-diseased mice of the Wobbler mouse strain (NFR/wr), as well as from the spinal cord of two related normal mouse strains (C57B1/6N and NFR/N). The interneurons, distributed throughout Rexed's laminae V-VIII, are characterized by numerous spines clustered along the distal dendrites. Quantitatively, the soma size (μm2) of the interneurons in the Wobbler specimens studied late in the motoneuron disease is smaller than that measured in the pair-matched (3-week-old) normal phenotype littermates. Early in the disease, the spine density (number of spines per 100 μm length dendrite) is greater compared with the normal phenotype littermates, perhaps implying that sprouting may occur. At a later stage in the disease process, the spine density does not differ significantly. However the increase in the spine density expected with advancing age is not observed for the Wobbler interneurons. It is proposed that perhaps the normal age-related proliferation of spines is impaired in the Wobbler mice. Since the measurements for spine length are lower in the Wobbler interneurons studied late in the motoneuron disease compared with the pair-matched (3-month-old) normal phenotype littermates, the normal age-related lengthening of the spines seems to be lacking. In addition, the spine length measured in the normal phenotype littermates is significantly greater compared with the normal mice (NFR/N, C57B1/6N). Thus the growth patterns of the spines may differ in the Wobbler mouse strain compared with the normal (C57B1/6N, NFR/N) mouse strains. It is proposed that the Wobbler motoneuron disease affects interneurons as well as motoneurons.

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).

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.

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.

Alteration in the levels of thyrotropin releasing hormone, substance P and enkephalins in the spinal cord, brainstem, hypothalamus and midbrain of the Wobbler mouse at different stages of the motoneuron disease

The present study was undertaken to quantify selected neuropeptides (thyrotropin releasing hormone, substance P, methionine and leucine enkephalin) in the cervical spinal cord and other regions of the central nervous system of Wobbler mice by radioimmunoassays during several stages of the motoneuron disease compared with age- and sex-matched normal phenotype littermates. In Wobbler spinal cord, thyrotropin releasing hormone is higher early in the disease, whereas in the brainstem it is higher at a later stage. Substance P in spinal cord is also higher late in the disease. Leucine enkephalin levels are greater at all stages in diseased spinal cord and brainstem, but methionine enkephalin increases only late in the disease. Highly significant increases of the peptides (except thyrotropin releasing hormone) appear in hypothalamus and midbrain only late in the motoneuron disease. Regression analyses show that thyrotropin releasing hormone in spinal cord and brainstem decreases normally with age in the control mice and at a faster rate related to the extent of motor impairment in Wobbler mice. Thyrotropin releasing hormone and methionine enkephalin in the Wobbler brainstem correlate (P less than 0.05) with the progress of the motoneuron disease. Methionine enkephalin increases faster in Wobbler brainstem and decreases faster in control spinal cord with age. The increase of leucine enkephalin in the Wobbler spinal cord correlates significantly with age and with the progress of the disease, but leucine enkephalin declines slightly with age in the controls. The changes of substance P in spinal cord and brainstem do not correlate significantly with the progress of the disease. In the hypothalamus, increasing values for substance P in control specimens and enkephalins in Wobbler specimens are significantly correlated with age. However, in the midbrain, higher methionine and leucine enkephalin levels are significantly associated with age only in the control mice. Alterations of neuropeptides in the Wobbler mouse spinal cord and brainstem may result from the degeneration of bulbospinal raphe neurons projecting to the ventral spinal cord, or from primary afferent or interneuronal nerve terminals. The data imply that the neuronal degeneration process in the Wobbler motoneuron disease is not limited to motoneurons. In the spinal cord, the data support our previous hypothesis that neuronal sprouting presynaptic to the motoneurons may account for increased neuropeptide concentrations. Alternatively, synthesis and/or degradation of these peptides may be altered. In addition, it is proposed that enkephalinergic neurons may develop abnormally in Wobbler mice. The early increase of leucine enkephalin in the Wobbler spinal cord possibly indicates its importance in the etiology of the motoneuron disease.

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

The Wobbler mouse possesses an inherited form of motoneuron disease that expresses itself most dramatically in the forelimbs. Previous immunocytochemical (ICC) studies have shown that neuronal processes containing substance P (SP), thyrotropin releasing hormone (TRH) and serotonin (5-HT) seem to sprout in the ventral horn of the cervical spinal cord taken from the Wobbler mouse. By radioimmunoassay, increased concentrations of spinal SP, TRH, and 5-HT, as well as leucine and methionine enkephalins (LE, ME) have been documented. The present ICC study quantifies the numbers of neuronal processes in the Wobbler cervical spinal cord and brainstem which contain SP, 5-HT, LE, ME and other neuropeptides (cholecystokinin, CCK; neuropeptide Y; galanin; calcitonin gene-related peptide, CGRP). It is proposed that those processes that sprout early in the mononeuron disease (5-HT, LE, ME, CCK and also TRH according to other studies) may be involved in the etiology. In addition, it is hypothesized that the loss of CGRP within the ventral horn may represent the loss of a trophic factor that is important to the survival motoneurons and may influence the increase of fiber densities around the dying motoneurons.

Reduced branching and length of dendrites detected in cervical spinal cord motoneurons of Wobbler mouse, a model for inherited motoneuron disease

The Wobbler mouse (wr) has been proposed as a model for human inherited motoneuron disease (infantile spinal muscular atrophy). The primary defect is thought to be in the motoneurons. Therefore we undertook a survey of the qualitative and quantitative changes occurring in the cervical spinal motoneurons of Wobbler mice during a late stage of the motoneuron disease compared with age- and sex-matched normal phenotype (NFR/wr) littermates. The Rapid Golgi Method was applied. In control and Wobbler mice, four types of neurons were identified according to their dendritic patterns: multipolar, tripolar, bipolar, and unipolar cells. Unipolar cells were observed more often in the Wobbler specimens than the controls and may represent a final stage in the degeneration of other cell types with greater numbers of primary dendrites. Medium (300-999 microns 2) and large (greater than 1,000 microns 2) impregnated neurons (presumably alpha-motoneurons) showed strong indications of cell degeneration, including statistically significant reductions in the measurements for dendritic length, distribution, and branching, as well as the number of spines. In contrast, the small (less than 300 microns 2) neurons showed only mild signs of degeneration, including slight reductions in dendritic length, but no significant differences appeared in the distribution and branching of dendrites, or in the number of spines. Instead, a small increase could be detected in the number of primary and secondary dendritic branches emanating from the small neurons, as well as in the number of dendritic spines. These findings suggest that sprouting may occur to a slight extent. Although previous studies document that swelling with subsequent vacuolation of motoneurons is the predominant feature characterizing the Wobbler disease, the mean soma area (microns 2) calculated for the impregnated neurons of the Wobbler specimens showed no significant difference from the controls. It is hypothesized that the advanced signs of the Wobbler motoneuron disease are primarily reflected in the degeneration of the dendrites and spines on the medium and large alpha-motoneurons. The small neurons (presumably a mixed population of gamma-motoneurons, interneurons, and Renshaw cells) possess dendrites and spines that seem to be less affected, and instead show signs of sprouting.

Measurement of neuropeptides in the brain and spinal cord of Wobbler mouse: a model for motoneuron disease

The Wobbler mouse (wr) exhibits the loss of motoneurons especially in the cervical spinal cord, and thus has been studied as a model for human motoneuron diseases. Wobbler mice selected at various ages and stages during the disease process show increased levels of thyrotropin releasing hormone and substance P in spinal cord and brainstem (medulla). Enkephalins (methionine and leucine) also increase in the spinal cord and brainstem. Somatostatin increases in hypothalamus, perhaps accounting partly for the small size of this mutant mouse via its effect on growth hormone.

Selective decrease of immunoreactive tyrosine hydroxylase in nigrostriatum of adult male rats after N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment

Several laboratories have reported that N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine causes damage to the nigral dopamine neurons of man, monkey, and mouse. Controversial data suggest that a rat model of Parkinsonism may be possible. Although loss of dopamine cells has not been detected in the rat brain, our immunocytochemical studies show that immunoreactive tyrosine hydroxylase, the rate-limiting enzyme which synthesizes dopamine, is significantly reduced in concentration, or its antigenicity altered, in substantia nigra/pars compacta as well as the caudate nucleus. Optical density measurements demonstrate the reduction or alteration of immunoreactive tyrosine hydroxylase in nigro-striatal neurons, indicating that axonal terminals, as well as parent perikarya, may be sensitive to the drug. After treatment, abnormal morphological remodelling may result in the affected neuronal processes, perhaps indicating sublethal toxicity, followed by slow recovery. Despite the lack of nigral cell death, it is proposed that the present data support the use of the rat as a model to investigate the early effects of Parkinsonism induced by this agent, and the biological mechanisms of cellular recovery.

Substance P neurons sprout in the cervical spinal cord of the wobbler mouse: a model for motoneuron disease

The mutant mouse, wobbler, possesses a recessively inherited degeneration of motoneurons and other ventral horn cells in the cervical spinal cord, and therefore it has been proposed as an animal model of human motoneuron disease. Affected mice have been identified by behavioral tests that also determined the extent of the motor deficit. The results from these tests were combined and used to define distinct stages of the disease process that could then be correlated histochemically with the amount of acetylcholinesterase (AChE) staining in the cervical spinal cord. AChE is used as a marker for cholinergic neurons and is known to hydrolyze the neuropeptide modulator substance P (SP). SP, a peptide neuromodulator of primary afferent transmission in the dorsal horn, excites motoneurons in the ventral horn, and may possess secondary functions in neuronal maintenance. Therefore, the levels of immunoreactive (IR) SP and AChE were examined in an attempt to determine the possible interaction between these factors in motoneuron degeneration. By enzyme histochemistry, the cervical spinal cord, taken from wobbler mice at behaviorally identified stages of the motor deficit, exhibited decreased levels of AChE throughout the ventral horn. The decrease detected in the AChe staining intensity was linear and correlated with the decrease in the number of AChE-positive cells in the ventral cervical spinal cord, as the motor deficit progressed. Presumably, the continual decrease in AChE staining represents the degeneration of cholinergic perikarya and neuronal processes in the ventral horn as the motoneuron disease proceeds. At two well-established stages of the motor deficit, the amount of immunoreactive SP increased in the ventral horn compared with the control mice. The elevated levels of immunoreactive SP suggest sprouting may have occurred preceding, or in response to, the motoneuron degeneration. Several additional hypotheses are discussed in respect to phenomena that might contribute to the increase of immunoreactive SP in the degenerating ventral horn of the wobbler mouse.

Differential immunostaining for substance P in Huntington's diseased and normal spinal cord: significance of serial (optimal, supra-optimal and end-point) dilutions of primary anti-serum in comparing biological specimens

Using immunocytochemistry (ICC), the number of immunoreaction products (IRPs) visualized for the peptide substance P (SP) appears reduced within the human spinal cord (also substantia nigra) taken at autopsy from cases diagnosed with Huntington's disease (HD) compared with the non-HD cases (Vacca 1983). The reductions of SR-IRPs become apparent in the HD specimens when primary anti-SP serum is applied to the tissue sections at "supra-optimal" dilutions; that is, dilutions greater than the "optimal" dilutions which visualize maximal numbers of SP-IRPs and concomitantly give maximal staining intensity. Curiously, the application of "optimal" dilutions to the HD and non-HD specimens visualizes equivalent numbers of SP-IRPs; therefore, the qualitative and quantitative differences between the specimens become masked. Applying "supra-optimal" dilutions of the anti-SP serum unmasks the difference, and also reveals different end-points for the immunostain deposited in each type of specimen. In both the HD and non-HD specimens, two sizes of SP-IRPs could be identified, large (3 micron) and small (0.7 micron). Presumably they mark two different categories of axons defined by caliber (e.g., C-type and A gamma), or origin (e.g., sensory intrinsic, or supraspinal). Alternatively the large SP-IRPs label tangentially-cut or large axons and nerve terminals. In the present report, counts of the large and small SP-IRPs visualized in the HD and the non-HD specimens have been plotted against the serial dilutions (optimal, supra-optimal and end-point) of the primary anti-SP serum used for ICC. The graphs which result, describe a "titration curve" characteristic for the large SP-IRPs in each specimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of immunoreactive substance P and enkephalins in rat spinal cord after electroacupuncture

A form of electrically-induced analgesia known as electroacupuncture was administered to rats bilaterally at the point "Huan-tiao." Compared with untreated rats, treated rats showed altered pain thresholds characterized as low, intermediate, and high. From immunocytochemical studies, the spinal cords taken from the treated rats exhibited differences in immunoreactivity for substance P (SP), methionine- and leucine-enkephalins (ME and LE respectively). By densitometry, the altered levels of immunoreactive (IR) peptides correlated with the pain thresholds in specific ways. That is, high pain threshold correlated with the visualization of increased IR-SP adn IR-LE within neuronal processes throughout the dorsal horn substantia gelatinosa. In the same specimens, decreased IR-ME could be seen. In contrast, low pain threshold correlated with decreased IR-SP and IR-ME. IR-LE showed a concomitant decrease in the medial substantia gelatinosa region, and slight, insignificant changes laterally. The data suggest that different degrees of analgesia induced by electroacupuncture result from the variable release of SP, ME, and LE in spinal regions associated with nociception. In terms of current models of pain processing, the data do not entirely support an axo-axonic interaction between enkephalin interneurons and SP terminals. Some modifications and an alternative model are considered.