Histological characterization and biochemical analysis of paraspinal muscles in neuromuscularly healthy subjects

Introduction: There are no generally accepted histopathological reference values in paraspinal skeletal muscle biopsies. Methods: We examined multifidii muscle biopsies from 20 neuromuscularly healthy subjects using routine histological stains and biochemical analyses of respiratory chain enzymes. Results: Staining showed incomplete myopathic features, such as increased variability in fiber size, type 1 hypertrophy, rounded fiber shape, endomysial fibrosis, and replacement by adipose tissue. Acid phosphatase reaction was positive in up to 35% of the selected muscle fibers. Mitochondrial changes were obvious but revealed no selective age dependence. Reduced complex I, cytochrome c oxidase (COX), and citrate synthase (CS) could be observed. Conclusions: Because the increased variability in morphological details can easily be misinterpreted as myopathic changes, analysis of paraspinal muscles should take into consideration that incomplete myopathic features and reduced oxidative enzyme activities for complex I, COX, and CS are normal variations at this location. Muscle Nerve 52 : 45–54, 2015     

Localization of motoneurons controlling the extraocular muscles of the rat

The localization of extraocular motoneurons in the rat was investigated by injecting horseradish peroxidase and [¹²⁵I]wheat germ agglutinin¹⁷ as retrogade tracer substances into individual eye muscles. The organization of subnuclei was found to be most similar to the rabbit. The subgroups representing the medial rectus and inferior rectus muscles are located in the rostral two thirds of the ipsilateral oculomotor nucleus (nIII) with some medial rectus motoneurons scattered laterally along the edge of the medial longitudinal fasciculus. The motor pool controlling the inferior oblique muscle is located in the middle third of the ipsilateral nIII. The motoneurons of the superior rectus muscles are in the caudal two-thirds of contralateral nIII while the levator palpebrae muscle has a bilateral innervation in the oculomotor nucleus. The motoneurons of the superior oblique are located in the contralateral trochlear nucleus although a few labeled neurons were scattered laterally in amongst the fibers of the medial longitudinal fasciculus. The cell bodies of lateral rectus motoneurons regional separation between the latter and internuclear neurons was found after injecting HRP into the oculomotor nucleus.     

Quantitative morphological analysis of the motoneurons innervating muscles involved in tongue movements of the frog Rana esculenta

We give an account of an effort to make quantitative morphological distinctions between motoneurons of the frog innervating functionally different groups of muscles involved in the movements of the tongue. The protractor, retractor, and inner muscles of the tongue were considered on the basis of their major action during the prey-catching behavior of the frog. Motoneurons were selectively labeled with cobalt lysin through the nerves of the individual muscles, and dendritic trees of successfully labeled neurons were reconstructed. Each motoneuron was characterized by 15 quantitative morphological parameters describing the size of the soma and dendritic tree and 12 orientation variables related to the shape and orientation of the dendritic field. The variables were subjected to multivariate discriminant analysis to find correlations between form and function of these motoneurons. According to the morphological parameters, the motoneurons were classified into three functionally different groups weighted by the shape of the perikaryon, mean diameter of stem dendrites, and mean length of dendritic segments. The most important orientation variables in the separation of three groups were the ellipses describing the shape of dendritic arborization in the horizontal, frontal, and sagittal planes of the brainstem. These findings indicate that characteristic geometry of the dendritic tree may have a preference for one array of fibers over another.     

A comparative study of neck muscle motor neurons in a cricket and a locust

The gross morphology of the neck muscles of a cricket (Gryllus campestris) and their innervation are described and compared with a locust (Schistocerca gregaria). The motor neurons innervating the neck muscles were stained in crickets and locusts with cobalt chloride introduced via the nerve endings in the muscle. The two species show overall similarities, not only in position of the neck motor neurons in suboesophageal, prothoracic, and mesothoracic ganglia but also in motor neuron morphology. However, muscle 60 in the cricket is innervated by a unique motor neuron with its axon in prothoracic nerve 3, instead of sharing motor neurons in suboesophageal nerve 8 and mesothoracic nerve 1 with muscle 59, as in locust. Muscle 62 has the same attachments and innervation with similar motor neurons in cricket and locust but a different mechanical function in the two species. The findings are discussed with respect to possible segmental homologies and to the origins of the muscles as either dorso-ventral or longitudinal. As several muscles share the same motor neurons, we suggest that neck muscle function be described in terms of "behavioural units of action."     

Isolation, characterization, and application of monoclonal antibodies to rat tyrosine hydroxylase

Tyrosine hydroxylase (TH, tyrosine 3-monooxygenase; EC 1.14.16.2) activity in crude extracts of rat pheochromocytoma, rat brain, and bovine adrenal medulla can be immunoprecipitated in an indirect assay by monoclonal antibodies prepared against partially purified rat pheochromocytoma TH. One of these monoclonal antibodies, TH-2D8-2, can be used for immunocytochemical localization of TH in cell bodies, dendrites, and axons in catecholaminergic neurons (e.g., cells in the substantia nigra) of rat brain and in the cell body, neurites, and growth cones of rat pheochromocytoma cells after treatment with nerve growth factor. When linked to Affi-gel 10, this monoclonal antibody can also be used for immunoaffinity purification of rat and bovine TH. These results suggest that TH-2D8-2 is a valuable reagent with which to investigate the localization, physiological regulation, and function of this important enzyme.     

Conduction velocities of alpha-motor fibers innervating human thenar muscles and order of recruitment upon voluntary contraction.

Conduction velocity (CV) of single alpha-motor fibers was measured using a combination of microneurographic and spike-triggered averaging techniques on 7 healthy subjects (aged 25 to 42). Two tungsten microelectrodes were inserted percutaneously into the median nerve at the wrist and 4 to 6 cm more proximally. Motor unit activities recorded from thenar muscles during voluntary isometric contraction with a third microelectrode, were isolated with a window discriminator, and used to trigger an averager. CVs were calculated by dividing the interelectrode distance by the conduction time between unitary activities in the proximally and distally averaged neurograms. The CVs of 100 units ranged between 34 and 66 m/s, with the peak at around 50 m/s. The relationship between CVs and recruitment orders was compared within sets of 2 or 3 units recorded simultaneously. Statistical analysis using a chi 2 test revealed that slower motor units tended to be recruited earlier than faster units (P less than 0.001).     

Dendritic distribution of splenius motoneurons in the cat: comparison of motoneurons innervating different regions of the muscle

The distribution and dendritic organization of splenius motoneurons innervating extrafusal muscle fibers in different regions of the muscle were examined by electrophysiological and intracellular HRP staining techniques. Motoneurons innervating the regions of the splenius muscle supplied by the C2, C3, and C4 peripheral nerves were arranged in three nonoverlapping subnuclei. Reconstructions of the dendritic trees of splenius motoneurons in these three subnuclei showed that there were no major differences in their dendritic distributions. Instead, the dendritic distribution followed a single pattern which was composed of five major dendritic projections. These included a dorsolateral projection to the lateral part of lamina VIII, a lateral projection into the spinal accessory nucleus and beyond the gray-white border, ventral and ventrolateral dendrites in the lateral half of the ventromedial nucleus and the surrounding white matter, medial dendrites which projected both dorsally and ventrally, and finally a conspicuous collection of dendrites which projected rostrally and caudally from the cell body. These results indicate that the dendritic distributions of splenius motoneurons are not related to the segmental position of the motoneuron or the zone of the muscle innervated by the motoneuron. However, a comparison of the dendritic distribution of splenius motoneurons to the dendritic distribution of biventer cervicis-complexus motoneurons indicated that there are major differences in the form of their dendritic trees even though dendrites from both sets of motoneurons share the same territory. As a consequence, although these motoneurons may receive the same connections, the effect of these connections on the excitability of the motoneurons may differ.     

Expansion of the dendritic tree of motoneurons innervating neck muscles of the adult cat after permanent axotomy

The morphologic characteristics of neck motoneurons with intact axons were compared with those of neck motoneurons that had been permanently axotomized for 11 to 17 weeks. Motoneurons were identified antidromically, intracellularly stained with horseradish peroxidase (HRP) and examined after reconstructions of their entire dendritic tree. Axotomized motoneurons differed qualitatively and quantitatively from motoneurons with intact axons. The distal branches of axotomized motoneurons exhibited two novel features: some gave rise to tangled appendages that exhibited growth cone-like specializations resembling lamellipodia and filopodia; others followed a meandering path and had unusually large diameters. These branches showed a discontinuous pattern of staining that was similar to the appearance of myelinated axons stained intra-axonally with HRP. A quantitative analysis of the dendritic trees of 13 completely reconstructed dendritic trees (five axotomized motoneurons and eight motoneurons with intact axons) showed that total dendritic surface area, total dendritic length, and total number of branches increased 38, 34, and 215%, respectively, after axotomy. These measurements were confirmed by comparing the sizes of a larger number of motoneurons (16 axotomized and 21 intact), calculated on the basis of correlations between dendritic tree size and proximal dendritic diameter. We conclude, therefore, that neck motoneurons, in contrast to other types of motoneurons, expand their dendritic trees after axotomy. It is suggested that this expansion is a consequence of two mechanisms: one involves dendritic growth, possibly leading to new synaptic connections; the other causes a conversion of some dendrites into axons. J. Comp. Neurol. 390:392–411, 1998. © 1998 Wiley-Liss, Inc.     

Input-output relationships of identified buccal neurones involved in feeding control in Aplysia

A group of about 28 neurones located in the lateral portion of the caudal face of Aplysia buccal ganglion and projecting into the cerebro-buccal connective were identified by retrograde cobalt staining, and designated as L neurones. It was found that the L neurones did not establish synaptic relations with the known buccal neurones, which are mainly involved in the production of the consummatory phase of feeding, nor with several cerebral neurones tested, including the well-known serotonin giant cell. Neither did they show responses to stimulation of the nerves directed to the buccal mass. On the other hand, the L neurones showed depolarizing responses, with the possible addition of a weak, slower hyperpolarizing phase, to stimulation of the ipsi- and contralateral oesophageal nerves, which innervate the portion of the gut posterior to the buccal mass. These findings, together with several properties of the oesophageal nerve input, suggest that one function of the L cells is to transmit information about gut regions posterior to the buccal mass towards the cerebral ganglia, and that they may mediate the inhibitory influence which in Aplysia is known to be exerted upon feeding by the presence of bulk in the anterior gut. The L neurones showed synaptic responses - consisting mainly or exclusively of depolarizations - to stimulation of the cerebro-buccal connectives. Besides this, large, tonic EPSPs, which often occurred in the 'spontaneous' activity of the L neurones, were found to be generated by spikes that travelled in the cerebro-buccal connective towards the buccal ganglion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Location,morphology, and central projections of mesencephalic trigeminal neurons innervating rat masticatory muscles studied by axonal transport of choleragenoid-horseradish peroxidase

Retrograde and transganglionic transport of horseradish peroxidase conjugated to the B-fragment of cholera toxin (B-HRP) was used to study the location, morphology, and central projections of mesencephalic trigeminal (Me5) neurons innervating rat masticatory muscles. Labeled Me5 cell bodies were found throughout the Me5 nucleus from a level slightly caudal to the trigeminal motor nucleus to the level of the superior colliculus 5 mm further rostrally. Occasionally, labeled Me5 cells were observed in the anterior medullary velum, in the cerebellum, and in the brainstem contralateral to the B-HRP injection. The vast majority of the labeled Me5 cells were pseudounipolar, but multipolar cells were also found. Extensive central projections from labeled Me5 cells could be seen extending from the nucleus of Darkschewitsch rostrally to the C2 segment caudally. Small but consistent projections from Me5 neurons were observed in nuclear islands among the incoming Me5 root fibers. Trigeminal and hypoglossal motor nuclei received direct projections from Me5 cells, but not the facial motor nucleus. The most prominent Me5 projections appeared in the brainstem reticular formation, including the supratrigeminal nucleus. Smaller projections also extended into the main sensory trigeminal nucleus, trigeminal subnucleus oralis, and the nucleus of the solitary tract. © 1993 Wiley-Liss, Inc.     

Proprioception in extraocular muscles of the rat

Stretch receptor afferents from extraocular muscles were found in the rat. Their first-order somata, responding specifically to eye muscle displacements, were restricted to the ipsilateral semilunar ganglion. Over a broad range of stimulus frequencies the sensitivity of receptors increased by a factor of 2.2 per decade with a mean sensitivity of 125 imp. s-1 mm-1 at 1 Hz.     

Organization of motor pools supplying the cervical musculature in a cryptodyran turtle, Pseudemys scripta elegans. II. Medial motor nucleus and muscles supplied by two motor nuclei

In this paper we describe the medial motor nucleus of Pseudemys cervical spinal cord and the motor pools of three neck muscles that exhibit an unusual pattern of innervation. Cells of the medial motor nucleus form a longitudinal column at the dorsomedial gray/white border of the ventral horn from C1 through C8. In Nissl-stained transverse sections they appear fusiform with prominent medially projecting dendrites; in HRP material these dendrites are seen to cross into the contralateral ventral funiculus. Medial nuclear cells vary in size (12-31 micron in diameter) and are often relatively large (greater than 21 micron in diameter). They are significantly larger and more numerous in caudal than in rostral cervical segments. Medial nuclear cells supply three of the cervical muscles examined in this study: mm. retrahens capitis collique (RCCQ), testocervicis, and longus colli. These three muscles differ from other cervical muscles in Pseudemys and from vertebrate limb muscles in that they are supplied in parallel by two populations of motor neurons: the medial and ventral motor nuclei (cf. Yeow and Peterson, '86). Ventral nuclear cells supplying these three muscles are organized into a musculotopic pattern with m. testocervicis motor neurons most medial and m. RCCQ motor neurons lateral; in contrast, the location of medial nuclear motor neurons is invariant with respect to muscle position. HRP-positive medial nuclear cells are sometimes smaller (m. testocervicis) but more often are as large or larger (mm. RCCQ and longus colli) than ventral nuclear cells supplying the same muscles, thus suggesting that they supply extrafusal muscle fibers, perhaps different muscle unit types in the three muscles. Based on the morphology of medial nuclear cells and the probable actions of the muscles they innervate, we hypothesize that the medial motor nucleus may represent a discrete functional system for producing bilaterally synchronous muscle activation, and that this system is accessed by a subset of muscles in the cervical complex.     

Histochemical localisation of a galactose-containing glycoconjugate expressed by sensory neurones innervating different peripheral tissues in the rat

The plant lectin Bandeiraea simplicifolia I-isolectin B4 (BSI-B4) identifies a galactose-containing, membrane-associated glycoconjugate expressed by a discrete subpopulation of unmyelinated primary sensory neurones in the rat. We have previously suggested that BSI-B4 selectively binds to primary sensory neurones that innervate the skin. However, in that study, the tracer diamidino yellow was applied to the cut ends of peripheral nerves to identify neurones innervating particular target tissues. In this study, we have avoided axotomy by retrogradely labelling primary sensory neurones from peripheral tissues using the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbacyanine perchlorate (DiI). DiI was injected into the plantar skin, gastrocnemius muscle, and pyloric region of the stomach in rats. Corresponding ganglia were sectioned, incubated in BSI-B4 conjugated to fluorescein isothiocyanate, and examined with a fluorescence microscope. DiI-labelled cells were identified by red fluorescence within the cytoplasm, whereas cells binding BSI-B4 displayed green fluorescence associated with the plasma membrane and Golgi apparatus. Quantitative analysis revealed that 36.2% of cutaneous neurones, 7.6% of muscle neurones, and 6.8% of visceral neurones expressed the BSI-B4-binding site, indicating that a small but significant proportion of small-diameter primary sensory neurones innervating muscle and viscera also express BSI-B4-binding sites.     

Localization of motoneurons innervating deep and superficial facial muscles in the rat: a horseradish peroxidase and electrophysiologic study

In the rat, distribution of the motoneurons supplying the deep facial muscles (DFM)--the posterior belly of the digastric (VP) and the stylohyoid (SH) muscles--and the superficial facial muscles (SFM) was studied using the horseradish peroxidase (HRP) method and the antidromic field-potential method. The HRP was injected individually into the VP or SH or applied directly to the central end of the facial nerve cut immediately before it enters the parotid gland. Electrical stimulation was administered to the common stem of the branches innervating the VP or SH and to the facial nerve trunk just before entering the parotid gland. Both VP and SH motoneurons were found not in the main but in the accessory facial nucleus, within which the VP motoneurons were more numerous and more dorsorostrally extended than were the SH motoneurons. Motoneurons supplying the SFM were confined within the main facial nucleus. Evidence was found that the distribution of antidromic field potentials evoked by stimulation at the above sites coincided with the distribution of motoneurons supplying either the DFM or SFM obtained from the HRP experiment. In the rat, the accessory and main facial nuclei can be considered to be the mass of motoneurons exclusively innervating the DFM and SFM, respectively.     

Fatigue associated EMG behavior of the first dorsal interosseous and adductor pollicis muscles in different groups of subjects

We have studied the fatigue-associated behavior of surface EMG in two histochemically different muscles of the hand: first dorsal interosseous (FDI) and adductor pollicis (AP; relatively more type I fibers in AP than in FDI). During a fatigue test evoked by electrical stimulation of the ulnar nerve, the mean amplitudes of compound muscle action potentials (M-waves) exhibited the same overall pattern for both muscles: a rapid phase of potentiation followed by a gradual decline. However, if the group of subjects was subdivided on the basis of hand length, significant differences emerged in the reactions of AP: in large hands, no fatigue-associated M-wave decline was seen, whereas in small hands a distinct decline was observed. A possible explanation for this phenomenon might be the presence of a greater amount of EMG contamination from other muscles in smaller hands. In the supposedly “cleaner” recordings from larger hands, significant differences between FDI and AP were observed with regard to their fatigue-associated EMG reactions (M-wave depression in FDI but not in AP). The direction of these differences was in accordance with expectations on the basis of known differences in histochemical fiber type composition. © 1994 John Wiley & Sons, Inc.     

Physiological and morphological characterization of anaxonic non-spiking interneurons in the crayfish motor control system

Spike activity of the motoneurons innervating uropod muscles in crayfish is controlled by anaxonic interneurons located within the terminal (the 6th abdominal) ganglion. These neurons do not generate spikes either spontaneously at the resting potential level or in response to current injection of either polarity. Yet the change in the membrane potential of these non-spiking interneurons caused an increase or decrease in the discharge frequency of motoneuron spikes, depending upon the direction of the membrane potential change. These non-spiking interneurons within the terminal ganglion presumably integrate various descending command signals and select the adequate information to be gated to the motoneurons.     

Sudden loading perturbation to determine the reflex response of different back muscles: a reliability study

In this study we estimate the reliability of reflex response variables to identify the main sources of variability and to estimate appropriate measurement strategies to obtain more reliable measures. Back muscle surface electromyography (EMG) was recorded in healthy males during anteriorly-directed sudden loading perturbations applied to the trunk. Measures of EMG reflex latency and amplitude were obtained. The generalizability theory was used as a framework to estimate the magnitude of the different variance components and the reliability of the measures corresponding to various simulations of different measurement strategies. Reliability of the different variables was poor to moderate (intraclass correlation coefficient range 0-0.62). Averaging scores across homologous muscles and several trials were strategies to achieve more acceptable reliability. The reflex response of back muscles is inherently variable, and a large measurement effort is necessary to obtain reliable and, consequently, valid and responsive estimations of this neuromuscular function.