Labelling of cervical and thoracic spinal neurones following injection of horseradish peroxidase in the leg muscles of rats

Locations of the motor endplate band and motoneurons innervating the sternomastoid muscle in the rat

Sternocleidomastoid (SCM) is a long muscle with two bellies, sternomastoid (SM) and cleidomastoid (CM) in the lateral side of the neck. It has been widely used as muscle and myocutaneous flap for reconstruction of oral cavity and facial defects and as a candidate for reinnervation studies. Therefore, exact neuroanatomy of the SCM is critical for guiding reinnervation procedures. In this study, SM in rats were investigated to document banding pattern of motor endplates (MEPs) using whole-mount acetylcholinesterase (AChE) staining and to determine locations of the motoneurons innervating the muscle using retrograde horseradish peroxidase (HRP) tracing technique. The results showed that the MEPs in the SM and CM were organized into a single band which was located in the middle portion of the muscle. After HRP injections into the MEP band of the SM, ipsilaterally labeled motoneurons were identified in the caudal medulla oblongata (MO), C1, and C2. The SM motoneurons were found to form a single column in lower MO and dorsomedial (DM) nucleus in C1. In contrast, the labeled SM motoneurons in C2 formed either one (DM nucleus), two [DM and ventrolateral (VL) nuclei], or three [DM, VL, and ventromedial (VM)] columns. These findings are important not only for understanding the neural control of the muscle but also for evaluating the success rate of a given reinnervation procedure when the SM is chosen as a target muscle.

Three-dimensional topography of the motor endplates of the rat gastrocnemius muscle

Spatial distribution of motor endplates affects the shape of the electrical activity recorded from muscle. In order to provide information for realistic models of action potential propagation within muscles, we assembled three-dimensional maps of the motor endplates of the rat medial gastrocnemius (MGM) and lateral gastrocnemius (MGL) muscles. The maps were assembled from histological cross sections stained for acetylcholinesterase activity. Within MGL, the motor endplates formed three columns along its longitudinal axis. Within MGM, the motor endplates were arranged in a leaf-like body that shifted obliquely from proximal to distal. As inferred from the proximo-distal distribution of the cross-sectional projection area, the majority of the motor endplates were concentrated in the middle of MGL and in the distal third of MGM. Regions of maximal motor endplate concentration are considered most suitable for injections of neuroactive substances, such as neuronal tracers. The assembled maps of the gastrocnemius muscles can be used as guides for such injections within the motor endplate zones.

Morphological changes of the soleus motoneuron pool in chronic midthoracic contused rats

This study investigated the morphological features of the soleus motoneuron pool in rats with chronic (4 months), midthoracic (T8) contusions of moderate severity. Motoneurons were retrogradely labeled using unconjugated cholera toxin B (CTB) subunit solution injected directly into the soleus muscle of 10 contused and 6 age- and sex-matched, normal controls. Morphometric studies compared somal area, perimeter, diameter, dendritic length, and size distribution of labeled cells in normal and postcontusion animals. In normal animals, motoneurons with a mean of 110.4 +/- 5.2 were labeled on the toxin-injected side of the cord (left). By comparison, labeled cells with a mean of 93.0 +/- 8.4 (a 16% decrease, P = 0.006) were observed in the chronic spinal-injured animals. A significantly smaller frequency of very small (area, approximately 100 microm2) and medium (area, 545-914 microm2) neurons, and a significantly higher frequency of larger (area, >914 microm2) neurons was observed in the labeled soleus motoneuron pools of injured animals compared with the normal controls. Dendritic bundles in the contused animals were composed of thicker dendrites, were arranged in more closely aggregated bundles, and were organized in a longitudinal axis (rostrocaudal axis). Changes in soleus motoneuron dendritic morphology also included significant decrease of total number of dendrites, increased staining, hypertrophy of primary dendrites, and significant decreased primary, secondary, and tertiary branching. The changes in size distribution and dendritic morphology in the postcontusion animals possibly resulted from cell loss and transformation of medium cells to larger cells and/or injury-associated failure of medium cells to transport the immunolabel.

Vitamin E affects quantitative age changes in lumbar motoneurons and in their peripheral projections

Vitamin E deficiency was previously found to induce plastic changes in the number of primary sensory neurons and in motoneuron peripheral field projections. In this work, quantitative changes in motoneurons of lumbar segments, in nerve fibres constituting ventral roots and in innervating leg motor fibres were studied in normal and vitamin E deficient rats from 1 to 5 months of age. The number of lumbar motoneurons was found to decrease, while there were no changes in the number of ventral root fibres. An increase in the number of innervating leg motor fibres was observed during ageing in control rats; in vitamin E deficient rats the number of fibres in the ventral roots did not change, as occurred in controls, but the decrease in the number of motoneurons was smaller and the number of innervating leg motor fibres increased further in comparison to the controls. The findings are consistent with the idea that vitamin E deficiency causes a decrease in motoneuron death or, alternatively, that it induces some process partially compensating naturally occurring motoneuron death.

Triceps surae motoneuron morphology in the rat: a quantitative light microscopic study

The rat is now the model of choice for many studies of motor function. However, little quantitative information on the structure of rat motoneurons is available. In conjunction with efforts to define the physiologic and anatomic substrates of operantly conditioned plasticity in the spinal cord, 13 physiologically identified triceps surae motoneurons in the rat lumbar spinal cord were labeled intracellularly with horseradish peroxidase and completely reconstructed and measured with a computer-based neuron-tracing system. Somata were all located in the ventral horn of lumbar segments 4-5, had an average diameter of 35 microns, and had 6-12 dendrites. Dendrites ramified throughout the ventral horn and also penetrated the white matter. Their spread was greater in the rostrocaudal and dorsoventral directions (1.53 +/- 0.24 mm and 1.35 +/- 0.23 mm, respectively) than in the mediolateral direction (0.85 +/- 0.14 mm). Regardless of soma location, dendritic fields usually extended throughout the ipsilateral coronal cross-section of the ventral horn. As a result, the ventral or lateral extent of the field was correlated strongly with the soma's distance from the ventral or lateral border, respectively, of the ventral horn. Furthermore, although soma locations in the coronal plane varied widely, the centers of the dendritic fields tended to cluster near the center of the ventral horn. Dendrites constituted 96.2-98.4% (mean +/- SD = 97.3 +/- 0.7%) of the total neuronal surface area. Each of the 104 dendrites studied had an average of 13 branch points and 27 segments. First-order segment diameters ranged from 1.4 to 11.7 microns (mean +/- SD = 5.3 +/- 2.1 microns). Total dendritic length, surface area, volume, number of dendritic segments, and maximum segment order were correlated strongly with diameter of the first-order segment. Proceeding distally between branch points, the mean decrease in dendritic diameter (i.e., tapering) +/- the standard deviation was 22 +/- 8% of the proximal diameter. The average ratio +/- the standard deviation of the sum of the average diameters of each daughter segment raised to the 1.5 power to the average diameter of the parent segment raised to the 1.5 power (i.e., Rall's ratio; Rall, 1959) was 0.87 +/- 0.08. In comparison with cat alpha-motoneurons, rat motoneurons had smaller soma diameters, fewer dendrites, smaller total surface areas, and shorter total dendritic lengths. However, the number of terminations per dendrite was similar in the two species, so that rat motoneurons had more terminations per unit dendritic length.(ABSTRACT TRUNCATED AT 400 WORDS)

All peroneal motoneurons of the rat survive crush injury but some fail to reinnervate their original targets

This is a quantitative study of the motoneuronal population of the rat's common peroneal nerve following severe crush injury of the sciatic nerve or its component branches. The crush was performed unilaterally under anesthesia for 60 seconds with hemostat jaws covered with tubing to form a smooth, 2 mm long, injured zone. Recovery from injury was allowed for 14 to 188 days. It was measured behaviorally using the sciatic functional index (SFI) and electrophysiologically by comparing the conduction velocity and amplitudes of evoked muscle action potentials prior to injury, and again after injury just before the nerve was labeled with horseradish peroxidase (HRP), and/or its wheat germ agglutinin conjugate (WGA-HRP), 48-72 hours before sacrifice. The motoneurons were retrogradely labeled on both sides so that the uninjured side might serve as a control. On the injured side the nerves were labeled either distal or proximal to the crush site. The tibialis anterior muscles on both sides were removed and weighted. Spinal segments L2 to L6 were cut in serial, frozen cross-sections. HRP reaction products were formed using TMB as the chromogen. The normal peroneal nerve was found to contain 634 +/- 26 motoneurons (22 cases). The number of motoneurons labeled 5-15 mm distal to the injury site (22 cases) was 535 +/- 69 or 84.4% of normal. In 12 cases in which the nerve was labeled 5 mm proximal to the injury normal population numbers (648 +/- 30) were found. These counts demonstrated that the unlabeled 15.6% in the distal labeled cases had not vanished as a result of cell death. Instead, the unlabeled group was composed mainly of small motoneurons whose axons probably had not regenerated distal to the crushed zone. Mean soma size of injured neurons increased to maximum 3-6 weeks after injury and then gradually decreased in size over the following weeks to nearly normal values. This transient increase in size was due to two factors: 1) soma swelling in response to axonal injury, and 2) absence of many small motoneurons, presumably gamma-motoneurons, which were either incapable of, or prevented from, regenerating beyond the injury zone long after larger motoneurons had reinnervated their targets. SFI scores, muscle weights, and amplitude ratios of evoked potentials recovered to control values by 70-80 days post-injury. Conduction velocities remained 20-25% below normal at the end of 80 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Explanation for the labeling of cervical motoneurons in young rats following the introduction of horseradish peroxidase into the calf

This study was carried out to determine whether cervical motoneurons, labeled following the introduction of horseradish peroxidase into the rat hind leg, belong to the cutaneous trunci motoneuron pool. The cutaneous trunci is a superficial muscle that extends from the axilla, over the flank, and into the thigh. Its nerve supply is derived from the brachial plexus. In experimental animals, horseradish peroxidase was either injected directly into the right gastrocnemius muscles, or applied to gelfoam and implanted over the calf muscles in the right leg of 5-, 10-, 15-day-old and adult rats. In control animals the cutaneous trunci was denervated prior to the administration of horseradish peroxidase. Labeled cervical motoneurons were present in the 5-, 10-, and 15-day-old but not the adult experimental groups and were located within the predetermined confines of the cutaneous trunci motoneuron pool. No labeling of cervical motoneurons was observed in any of the control groups in which the cutaneous trunci muscle was denervated. The most likely explanation for the labeling of cervical motoneurons in young rats was the local diffusion of horseradish peroxidase from the calf to the thigh, where it entered the cutaneous trunci muscle and was taken up by some of its motoneurons. The absence of such labeling in adult rats was probably due to the presence of connective tissue barriers to diffusion and to the greater distance between the site of horseradish peroxidase application and the cutaneous trunci muscle, which prevented the tracer from reaching the cutaneous trunci muscle and labeling its motoneurons.

Spinal cord projections from hindlimb muscle nerves in the rat studied by transganglionic transport of horseradish peroxidase, wheat germ agglutinin conjugated horseradish peroxidase, or horseradish peroxidase with dimethylsulfoxide

The spinal cord projections of four different groups of hindlimb muscle nerve branches--the medial and lateral gastrocnemius nerves, muscle branches of the deep peroneal nerve, muscle branches of the femoral nerve, and a nerve to the hamstring muscles--were studied with transganglionic transport of horseradish peroxidase (HRP) in the rat. The influence of varying the postoperative survival (3, 6, and 10 days) and of using wheat germ agglutinin-HRP conjugate (WGA-HRP), or HRP with dimethylsulfoxide (DMSO) instead of free HRP was studied for the gastrocnemius nerves. After 3 days' survival following application of HRP to the gastrocnemius nerves, fine granular labeling was found mainly in lamina V in L4-5, and coarse granular labeling was found in Clarke's column as far caudally as L2, and in laminae VI and VII predominantly in Th12-L2. After 6 or 10 days' survival, the fine labeling in lamina V was sparse or absent, whereas the coarse labeling appeared to remain or to be only slightly reduced in Clarke's column and in laminae VI and VII. No labeling suggestive of terminals was observed in laminae I-III from the gastrocnemius nerves. Except for sparse labeling in lamina I in some of the cases and some minor differences rostrocaudally, the spinal distribution of labeling was similar to that from the other nerves investigated. The distribution of labeling obtained after application of WGA-HRP or HRP with DMSO to the gastrocnemius nerves was very similar to that obtained with free HRP after 3 days' survival. The results indicate that the spinal cord projections of hindlimb muscle nerves in the rat distribute mainly in the deep part of the dorsal horn and in the intermediate zone. Furthermore, the lack of labeling suggestive of terminals in laminae I-III from the gastrocnemius nerves suggests, in conflict with earlier findings in the cat, that primary afferent fibers from muscles do not necessarily terminate in these laminae in the rat. The results suggest, furthermore, that fine granular labeling found in lamina V represents fine-calibered afferent fibers. Finally, the similar spinal projection patterns of the different muscle nerves investigated suggest either a less developed or an essentially different somatotopic organization for muscle afferents compared to cutaneous afferents, as revealed in earlier studies.

Localization of motoneurons innervating individual abdominal muscles of the cat

The motor pools of the individual abdominal muscles of the cat were localized in studies by using either intramuscular injections of horseradish peroxidase (HRP) to retrogradely label abdominal motoneurons or electrical microstimulation of the ventral horn at different segmental levels to produce localized twitches of the abdominal muscles. The segmental distribution of each motor pool was as follows: rectus abdominis, T4-L3; external oblique, T6-L3; transverse abdominis, T9-L3; and internal oblique, T13-L3. The differences in the rostral extents of the individual motor pools reflect the greater rostral extents of the different muscles (rectus abdominis greater than external oblique greater than transverse abdominis greater than internal oblique). Labeled motoneurons were also found at other segmental levels; however, it was concluded that this labeling occurred because of spread of HRP from the injected muscle since localized abdominal muscle twitches could not be produced by electrical stimulation in these regions. In addition, control experiments showed that HRP can spread from the injected muscle and identified the sources of some of this spurious labeling. Motoneurons labeled after injections into the four abdominal muscles overlapped extensively on transverse sections of the spinal cord; however, rectus abdominis motoneurons were located more medially than the others from about T11 to L3. Soma diameters ranged between 12 and 41 microns (average 24-26 microns per cat). In summary, this study has provided a systematic description of the innervation of the individual abdominal muscles of the cat.

Motoneurons of the rat sciatic nerve

The sciatic nerve of the rat is a commonly used model for studies on nerve injury, regeneration, and recovery of function. To interpret the changes that occur in a neuron population subsequent to peripheral nerve injury, and to compare different repair procedures, it is essential to have a complete and accurate understanding of the population's normal cellular constituents and their locations. This study reports on the numbers, sizes, and topographic distributions of the motoneuron populations of individual branches of the rat sciatic nerve (peroneal, tibial, sural, and the medial and lateral gastrocnemius nerves), as determined by retrograde transport of HRP (or WGA-HRP) from cut proximal nerve ends isolated in wax to prevent spread of the tracer substance. Optimal labeling of motoneurons was evident between 42 and 73 h of survival. Reconstructions were made from 40-micron serial sections of spinal segments L6 through L2, usually in the coronal plane. Accurate motoneuron counts were obtained by detailed reconstructions in which an accounting of all "split cell" fragments was made to avoid double cell counts. The sciatic nerve of the albino rat contains a total population of about 2005 +/- 89 motoneurons. The tibial nerve contained 982 +/- 36 cells or 49% of the total. The common peroneal nerve contained 31% or 632 +/- 27 motoneurons. The medial and lateral gastrocnemius nerve branches contained collectively 322 +/- 16 (16%). The sural nerve accounted for only 68 +/- 10 motoneurons (3%). The sciatic motoneurons form a continuous, compact cell column in the dorsolateral quadrant of the ventral horn extending from rostral L6 into the caudal third of L3 over a longitudinal distance of about 6.3 to 7.5 mm. This fusiform column shows its greatest width, 0.5 mm, in mid-L4. Within this compartment motoneurons of each branch of the sciatic occupy spatially distinct subcompartments. Their relative positions are described in detail.

Sexual differences in the distribution of substance P immunoreactive fibers in the ventral horn of the rat lumbar spinal cord

The distribution of substance P (SP) in the rat spinal cord was investigated by peroxidase-anti-peroxidase immunocytochemistry combined with retrograde horseradish peroxidase (HRP) labeling via the cremaster muscle. In the male rats, a dense network of SP immunoreactive (SP-IR) fibers and terminals was detected in the ventral column of the L1 and L2 segments (Vent L1-2) with a different density and extent from the other segmental levels. These fibers and terminals were accumulated within and around the nucleus centromedialis lumbaris (CM) of the L1 and L2 segments. However, in the female rats, SP-IR fibers and terminals were sparse in the Vent L1-2 without particular segmental differences. HRP-positive motoneurons were located in the CM and surrounded by SP-IR fibers and terminals. These results indicate that the Vent L1-2 of the rat spinal cord shows sexual dimorphism with respect to the regional distribution of SP-IR fibers and terminals, and that motoneurons that innervate the cremaster muscle are innervated by dense SP-IR fibers and terminals.

Absence of postnatal death among motoneurones supplying the inferior gluteal nerve of the rat

Motoneurones innervating the caudal part of the gluteus maximus muscle of 0-2 day, 10-12 day and 2-3-month-old rats were labelled by a half-hour application of a solution of 30% horseradish peroxidase (HRP) and 2% lysophatidylcholine delivered by suction electrode to the cut inferior gluteal nerves. The numbers of motoneurones labelled 24-48 h later were not significantly different in the 3 age groups (mean = 58.75, 54.0, 57.5, respectively). When a simple 30% HRP solution was used in adult rats, the number of motoneurones labelled was significantly less (mean = 48.75). In contrast, application of 0.5 microliter of HRP in a pledget of gelfoam to either the cut or uncut inferior gluteal nerve of neonates labelled large numbers of motoneurones, presumably by diffusion into nearby muscles. It is concluded that no death of motoneurones innervating the gluteus maximus muscle occurs postnatally, and that spread of HRP to neighbouring muscles can give rise to spuriously high motoneurone counts in neonates, and that incomplete uptake or transport of HRP in adults can lead to incorrectly low counts.

The organization of motoneurons in the turtle lumbar spinal cord

The distribution of motoneurons in the lumbosacral spinal cord of the turtle Pseudemys scripta elegans was studied by using the technique of retrograde transport of horseradish peroxidase. A total of 19 different hindlimb muscles were injected with varying amounts of horseradish peroxidase. The resulting distribution of labeled motoneurons was studied in both longitudinal and transverse sections of spinal cord. Motoneurons innervating a particular hindlimb muscle are clustered in longitudinally arranged motorpools. Motorpools of different muscles can show considerable overlap in both the rostrocaudal and transverse planes. The distribution of the various motorpools demonstrates a somatotopic organization of motoneurons within the lumbar spinal cord. Motoneurons innervating more distally positioned muscles are generally found in the more caudal segments, while motoneurons supplying proximal muscles are distributed throughout almost the whole lumbosacral intumescence. Motoneurons innervating anterodorsally positioned muscles are found in the ventrolateral part of area IX in the ventral horn, while more dorsomedially positioned motoneurons innervate the posteroventral muscles. These features are consistent with observations in other tetrapods, although the somatotopic representation of motoneurons is more evident in higher vertebrates such as chicken and cat. The observed motorpool distribution is discussed in relation to the presumed ontogeny of the spinal cord and hindlimb muscles and also in relation to the functions of the investigated muscles.

The distribution of afferent fibers from the gastrocnemius-soleus muscle in the dorsal horn of the cat, as revealed by the transport of horseradish peroxidase

The transganglionic transport of horseradish peroxidase (HRP) was used to examine the distribution of afferent fibers from the gastrocnemius-soleus (GS) muscle in the dorsal horn of the cat. Intense labeling was consistently observed in lamina I (in segments L4 to S3) and in the lateral portion of lamina V (segments L6 and S1-3), but not to any significant extent in laminae II-IV. These terminal fields were ascribed to the small-diameter (group III/IV) GS afferent fibers.

Cervical cord neurons labeled by horseradish peroxidase application to the sciatic nerve in the rat

After horseradish peroxidase (HRP) application to the proximal cut end of the sciatic nerve in rats aged 3-10 days, HRP-labeled neuronal cell bodies were found ipsilaterally in the ventrolateral region of the ventral horn in the cervical enlargements of the spinal cord. Such labeled neurons were occasionally seen in rats aged 15 days, but not seen at all in rats aged 60-90 days. The labeling was presumably the result of a retrograde transneuronal axonal transport of HRP applied to the sciatic nerve.

Motor neuron columns in the lumbar spinal cord of the rat

The location in the rat spinal cord of motor neurons innervating 23 muscles or muscle groups of the hind limb has been determined by using retrograde transport of horseradish peroxidase. The motor neurons supplying a single muscle form a discrete longitudinal column in the lateral ventral horn. The columns extend through up to three adjacent spinal segments and their longitudinal location varies by as much as one segment in different animals. The relative positions of the columns supplying different muscles and their transverse location in the spinal cord are very consistent between individuals and a stereotaxic map has been constructed. This is briefly compared with descriptions from other species. Counts of the numbers of motor axons in seven different muscles nerves have been made with the aid of acetylcholinesterase histochemistry to identify the motor component. The numbers of motor neuron somata labelled with horseradish peroxidase are on average 70% of the axon counts.