Differences in the corticofugal facilitating effect on evoked potentials in the neostriatum of rats and monkeys

Identical facilitation of the primary response to peripheral stimuli in rats and monkeys has been induced by local superficial cooling of the cortex in the somatosensory area S1. Higher facilitation of the evoked potentials was observed in the neostriatum of rats. Correlation of the evoked potentials with primary responses was more significant with respect to temporal than amplitude parameters. In monkeys, "cool" facilitation of the cortical primary response did not result in facilitation of the evoked potential in the neostriatum. Temporal correlation between the primary response and the evoked potential was less significant, whereas correlation in the amplitude was absent. The data obtained indicate the existence of differences in functional organization of corticofugal influences upon the neostriatum in rodents and primates.     

Tapering of human nerve fibres

To determine the tapering of human nerve fibres, rostral and caudal root pieces of cauda equina nerve roots were removed and nerve fibre diameter distributions were constructed for 4 myelin sheath thickness ranges for the two sites, and compared with each other. The reduction of the group diameter in the different alpha-motoneuron groups was 0.2 % per 13 cm. Accounting for systematic errors, there may be even less tapering. An identified single nerve fibre showed no tapering. Further, there is indication that gamma-motoneurons, preganglionic sympathetic and parasympathetic fibres and skin afferents also reduce their fibre diameter by 0.2 % per 13 cm or less. Consequently, a nerve fibre with a diameter of 10 microm would be reduced to approximately 9.8 microm at 1m from the cell soma. Preganglionic parasympathetic fibres were found to be represented in roots S1 to S5. At similar distances from the spinal cord, the mean diameter of ventral root alpha1-motoneuron (FF) axons increased from the thoracic towards the lumbo-sacral region before decreasing again in the lower sacral region. Usually no alpha1-motoneuron axons were found in S5 roots. The diameter distribution of unmyelinated nerve fibres of a ventral S5 root showed three peaks at 0.25, 0.95 and 1.2 microm. The unmyelinated fibres with diameters around 0.25 microm may represent parasympathetic fibres. In six selected areas of the ventral S5 root, 6.6 times more unmyelinated nerve fibres than myelinated fibres were found on the average.     

Observations on the primary sensory ending of tenuissimus muscle spindles in the cat

Summary The arrangement of preterminal and terminal axon branches in the primary sensory endings of cat tenuissimus muscle spindles was studied using whole-mount and serial-section techniques. Although in every case one firstorder preterminal branch was supplied exclusively to the bag₁ type of intrafusal muscle fibre, the preterminal branching patterns differed considerably in detail.Terminals varied widely in size and location. Their precise form varied according to their position on the intrafusal muscle fibres rather than their relationship to preterminal branches. Terminals derived from separate preterminal branches remained separate and did not fuse with themselves or each other. Individually bag₁ fibres had most terminals, chain fibres least. The surface of the muscle fibres were differentially indented by the terminals, least in bag₁ fibres and most in chain fibres.The results are discussed in relation to mechanosensory transduction and to the factors involved in determining the form of the primary ending.     

Characteristics of paravertebral muscles – fibre type distribution pattern in the pika, Ochotona rufescens (Mammalia: Lagomorpha)

The evolution of the locomotor apparatus in vertebrates is marked by major reorganizations in trunk's musculature. The hypothesized functions of mammalian back muscles in the literature are discussed under consideration of the distribution and proportion of oxidative, type‐I‐fibres, oxidative‐glycolytic, type‐IIa‐fibres and glycolytic, type‐IIb‐fibres in paravertebral muscles of a small mammal. The fibre type distribution was examined from a complete series of histological sections maintaining topographical relationships between the muscles as well as within the muscle, in order to establish the overall distribution pattern. The deep and short muscles showed the highest percentage of oxidative fibres. The larger, superficial paravertebral muscles contained the highest percentage of glycolytic fibres. Two muscles were intermediate in their proportion of fibre types. All epaxial muscles together can be interpreted as an antigravity muscle–complex counteracting enduringly against the rebound tendency caused by gravitation, comparable with antigravity muscles in limbs. A gradient from deep to superficial, or a clear regionalization of oxidative muscle fibres in central deep regions around a large intramuscular tendon was found in the m. spinalis and the m. quadratus lumborum, respectively. Concepts of the function of human back muscles as those of A. Bergmark (1989: Acta Orthop. Scand. 230 , 1) or S.G.T. Gibbons & M.J. Comerford (2001: Orthop. Division Rev. March/April, 21) were exposed to be more general within mammals. Functional specializations of different muscles and muscle parts are discussed under the consideration of evolutionary reorganization of the paravertebral musculature in tetrapods. Along the cranio‐caudal axis, the percentage of oxidative fibres was decreased in caudal direction within the same muscles, whereas the proportion of glycolytic fibres was increased. Therefore, classifications of muscles as ‘glycolytic’ or ‘oxidative’ based on biopsies or analyses of single cross‐sections may result in wrong interpretations. Changes in the proportions of the fibre type distribution pattern were mostly due to oxidative and glycolytic fibre types, whereas the percentage of oxidative‐glycolytic fibres had only minor influence. A significant positive correlation between the cross‐sectional area of the single fibre and its percentage in the area investigated were observed for oxidative fibres, whereby the size was positive correlated to the proportion of the oxidative fibres.     

Comparative aspects of muscle fibre size and succinic dehydrogenase distribution in the longissimus dorsi muscle of several species of East African mammals

The distribution of succinic dehydrogenase enzyme activity was investigated in frozen sections of longissimus dorsi muscle taken from several species of East African game animal (giraffe, hartebeest, wildebeest, oryx, gerenuk and dik-dik) as well as local zebu cattle. Muscle fibres were classified as red (high succinic dehydrogenase activity), white (low activity) or intermediate. The mean diameter and percentage distribution of each fibre type were noted as well as the overall mean muscle fibre diameter (MFD) for each species. The diameters of red muscle fibres were found to be between 54 and 62% of the diameters of the white muscle fibres for all species with MFD differences between species being up to over 100%. The variation in MFD was found to be significantly and positively correlated with live weight, when zebu values were omitted. It was found that the variation in MFD was significantly related to the diameter of muscle fibre types and not to the percent distribution of these fibre types.     

Muscle spindle receptors

Summary The depolarization of the sensory terminals of muscle spindle primary endings is studied in terms of a simplified core conductor model of the system. The terminals branching from a group Ia afferent fibre have different geometrical structures, depending on whether they innervate the nuclear bag or the nuclear chain intrafusal fibres of a muscle spindle.The depolarization of the two different structures as a function of space and time is analysed by digital simulation technique. The studies indicate that the tapered core conductor model of the bag-fibre terminals responds faster than a uniform system similar to the terminals innervating the nuclear chain fibres. The steady state response, on the other hand, appears to supply a more effective depolarization in the case of a uniform system with otherwise equivalent parameters.The results suggest that the bag fibre terminals are best suited for converting dynamical stimuli into an electrical signal, whilst the chain fibre terminals seem to yield a more effective steady state response. The results are discussed in relation to the functional properties of the mammalian muscle spindles and in relation to the earlier proposed models of the mechanical system represented by the two types of intrafusal muscle fibres.     

The Organization of the lamina ganglionaris of the prawn,Pandalus borealis (Kröyer)

The Lamina ganglionaris (first optic neuropile) of the decapod crustacean Pandalus borealis has its optic cartridges (synaptic compartments) arranged in horizontal rows. Each optic cartridge contains seven receptor axon terminals and the branching axis fibres of five monopolar second order neurons. Four types of monopolar neurons are classified. Their cell bodies are arranged in two layers. The inner layer contains the cell bodies of exclusively one of these types, and each cartridge is invaded by two neurons of this neuron type (type M 1:a and M 1:b). The outer layer contains the cell bodies of the remaining three types (M 2, M3 and M4). One gives rise to a large radially branched axis fibre in the centre of the cartridge. The other two have wide branches which may make inter-cartridge contacts, one proximally and the other distally in the plexiform layer, which is clearly bistratified. The receptor axons terminate in two levels corresponding to these strata. Two sets of tangenital fibres form networks in the proximal and the mid-portion of the lamina. Both networks have fibres with primary branches in the vertical plane and secondary branches in the horizontal plane. The fibres of the networks are derived from axons that pass from the second optic neuropile, the medulla externa.     

Ultrastructural transformation of fast chicken muscle fibres induced by nerve cross-union

Summary The fast posterior latissimus dorsi (PLD) muscle of newly hatched chickens was transposed and cross-innervated by the slow-type nerve originally innervating the anterior latissimus dorsi (ALD) muscle. The innervation and the ultrastructure of the cross-innervated posterior latissimus dorsi (PLD-X) muscle was investigated from one week up to 18 months after the operation and compared with that of the control fast (PLD-C) and control slow (ALD-C) muscles. All nerve terminals in the PLD-X muscle were of the slow type. Yet the degree of ultrastructural transformation differed from fibre to fibre. Only about 30% of PLD-X fibres had transformed ultrastructure closely resembling the control slow fibres. In this group of maximally altered fibres, the myofibrils had large diameters, wide Z lines and indistinct M lines as the control slow fibres. The amount of mitochondria was increased to levels found in control slow fibres. The mean percentage of triads was also comparable to that of control slow fibres, being approximately by two thirds lower than in control fast fibres.The differences in the degree of ultrastructural transformation are presumably due to different plasticity of muscle cells at the time of cross-innervation. In the transposed PLD-X muscles large areas undergo degeneration and regeneration. It is suggested that an almost complete changeover of the fibre type is only brought about after cross-innervation of newly differentiating muscle cells, whereas partial alteration occurs after reinnervation of young myofibres.The skillful technical assistance of Dr. Z. Liková, Mrs. M. Sobotková, Ing. M. Doubek and Mr. H. Kunz is gratefully acknowledged.     

The Role of the Neuronal Network in Functional Evolution of the Mammalian Telencephalon

During evolution of the vertebrate telencephalon the analyzing-synthesizing function was divided between two structures: the screen one, optimal for mechanisms of discrete analysis of information, and the neuronal network, in which cortical, functionally specialized modules can create the generalized equivalent of their activity. In the screen and reticular structures, each of these mechanisms got a possibility of developing independently without restricting functional capabilities of the other one. This resulted in formation of two telencephalon structures developing in parallel and functionally related, the cortex and the neostriatum. Experimental data indicate that the neuronal network of neostriatum is a field for interaction of corticofugal signals. These signals form neuronal mosaics reflecting the dynamics of cortical activity as combination patterns. Thereby, in neostriatum, corticofugal signals spread over a large surface of the cortex are transformed into their three-dimensional equivalent similar to population coding of information that takes place in the brain sensory structures. The established system of interrelationships between the cortex and the neostriatum turned out to be rather universal and economic. As a result, a broad spectrum of functional brain capabilities that we can see in various representatives of mammals was formed during a relatively short time with the minimum of structural changes, mainly quantitative in character.     

Primary afferent depolarization of C fibres in the spinal cord of the cat

The excitability of primary afferent terminals of cutaneous C fibres was tested in the spinal cord of decerebrated cats. C fibre terminal excitability was decreased in the spinal state, and increased by conditioning volleys that activated only A fibres of another cutaneous nerve and by stimulating hair mechanically. It is suggested that C fibre input and therefore nociceptive information to the central nervous system is susceptible to presynaptic control by segmental and suprasegmental mechanisms.     

Connections of the representational area of the distal section of the forelimb in the rat sensorimotor cortex

Using horseradish peroxidase, studies have been made on the distribution of retrogradely labeled nervous cells in the sensorimotor cortex of rats. The enzyme was injected into electrophysiologically identified zone of representation of the distal part of the forelimb in areas S2 and S1. It was found that this zone in S2 contains afferent connections mainly from representation of the same extremity in S1 and only a few afferents from other areas of S1, S2 and M1 of the same hemisphere. Single labeled neurones were found in areas S2, S1 and M1 of the contralateral hemisphere. Representation of the forelimb in S1 receives mainly cortical afferents from the same region of S1 and from single cells of homologous zones S2 of the same and S1 of the contralateral hemisphere. Connections from S1 to S2 are more numerous than the opposite ones. In contrast to cats and monkeys, in rats afferent cortical fibers to zone S2 pass not only from the third layer, but also from the fifth and sixth layers of the cortex. It is suggested that during progressive development of the neocortex in mammals, the increase in the degree of separation of neurones (which give origin to corticofugal and cortical connections) among different layers of the cortex takes place.     

Dedifferentiation and remodeling of motor endplates following experimental localized lesions of muscle fibers

Local anaesthetics, cardiotoxin and mechanical injuries may cause necrosis of muscle fibres while leaving the motor nerve fibres and their terminals intact. With local injuries to mouse muscles carried out by freezing or cutting we made a point of preserving both the nerve terminals and the muscle fibre portions on which these terminals were located. It was thus possible to follow the changes induced at endplates by these lesions. Within two or three days of the freezing or cutting, the muscle fibres underwent very different degrees of regression of the contractile material and T-system. The neuromuscular junctions also underwent changes, principally affecting their postsynaptic portion, in particular the folds of the subneural apparatus. After dedifferentiation of subsynaptic areas, we observed sprouting of the nerve terminal on muscle fibres which survived the amputation of one end and formed actively new myofibrils. This sprouting restored synaptic connections at the original sites, but with new structural features and correlative changes in the distribution of cholinergic receptors and cholinesterases. It is probable that after a phase of involution followed by a phase of recovery, the injured muscle fibres triggered off the nerve terminal sprouting which led to the remodelling of the endplates.     

Automated cytometry of muscle fibre sections: size and spatial distribution of the four fibre types in young and adult rats.

An automated cytometry program was applied to the extensor digitorum longus muscle of young and adult rats. Lesser diameter and spatial distribution of about 4000 fibres were measured in digital images from ATPase-stained muscle sections. All fibre types grow thicker with age, but the coefficient of variation of the diameter is age-independent. At both ages, 2B fibres have the largest mean diameter and are most frequent. 2A fibres in young rats present a diameter smaller or equal to type 1 but then show a faster increase in size; their relative number increases from 20 to 28%. Consequently type 2A displays the most important change with age. The spatial distribution of fibres is mathematically expressed; most images show a random distribution of type 1 and type 2 fibres. Taking into account the variation of fibre size of each type, the number of fibres which should be measured in order to reach a specified precision was calculated.     

LDH isoenzymes in the axial muscle of the sharks Galeus melastomus and Etmopterus spinax

The lactate dehydrogenase isoenzyme patterns have been studied in the axial muscles of the sharks Etmopterus and Galeus. Samples from red, intermediate and white muscle fibres were run separately on a polyacrylamide slab-gel. Both sharks have three isoenzymes; all three are present in the red and intermediate fibres, while the white fibres contain only the two slowest-moving isoenzymes. The red fibres of both sharks contain most of the fastest-moving isoenzyme.
The isoenzymes have a high tolerance towards urea; the slow moving isoenzyme is inhibited at about 2 m urea, the next isoenzyme at 4-6 M urea, and some activity of the fast-moving isoenzyme is still present at 10 M urea in the incubation medium. The LDH distribution in the fibre types is studied by histochemistry on frozen sections.     

Fibre autoradiography of repair and replication in DNA from single cells: the effect of DNA synthesis inhibitors

DNA fibre autoradiography, after incorporation of high specific activity 3H-thymidine and 3H-deoxycytidine, has been used to investigate repair in DNA fibres from single cells following UV, or methyl-methane sulphonate (MMS) treatment. Asynchronously growing human fibroblasts, leucocytes, and HeLa cells at different phases of the cell cycle have been investigated. Isotope incorporation in repair could be differentiated from that involved in replication by the distribution and density of silver grains along the DNA fibres. Grain distribution due to repair was continuous over long stretches of the fibres and was at a low density, occasionally interspersed with short slightly denser segments. Replication labelling on the other hand, was dense and usually in short tandem segments. Repair labelling was of a similar overall density in fibres from a single cell, but differed in intensity from cell to cell. In mutagen treated Go (leucocytes) or G1 (HeLa cells), repair labelling was not increased by the presence of the DNA inhibitors, hydroxyurea (HU) or 5-fluorodeoxyuridine (FUdR). Repair was not detectable in S cells however, without the use of these inhibitors to reduce endogenous nucleoside production. FUdR enhanced the repair labelling in S cells only slightly, while HU increased it beyond that observed in UV irradiated, HU treated, G1 cells. The intensity of repair labelling in fibres from mutagen treated S cells appears to be proportional to the degree of reduction of DNA chain elongation in replicons.     

The hypothalamo-hypophysial system in acipenseridae

Summary The distribution of adrenergic and peptidergic (Gomori-positive) structures of the hypophysial neuro-intermediate complex in Acipenseridae has been studied by means of light, fluorescence, and electron microscopy. Adrenergic fibres (B-fibres) and their terminals have been detected in the neurohypophysis of these fishes. The terminal swellings of B-fibres as well as the terminals of the neurosecretory peptidergic fibres (A₁ and A₂) make contact with the basement membrane of the connective tissue layer separating the neurohypophysis from the intermediate lobe. Capillaries are situated within this layer and, therefore, the main part of the fibre terminals is in contact with the pericapillary space. The release of catecholamines from the adrenergic terminals into the capillaries connected with the general circulation is supposed. The diffusion of catecholamines through the connective tissue layer into the parenchyma of the intermediate lobe is also suggested. Hence, the glandular activity of the intermediate lobe seems to be under the dual control of adrenergic and peptidergic elements of the hypothalamus.The authors wish to express their deep appreciation to G. M. Persov, Dr. Sc. Biol., Head of the Laboratory of Experimental Ichthyology, Petershof Biological Institute of the University of Leningrad, for the material supplied for fluorescence microscopy, and to Mr. G. V. Sabinin for photographic services.     

Distribution of synaptic boutons in the mesencephalic trigeminal nucleus of the rat--a quantitative electron-microscopical study.

The distribution of synapses and synaptic bouton types in the mesencephalic trigeminal (Me5) nucleus was examined in a quantitative electron-microscopical study. Of 588 terminal boutons that were counted in the compact caudal part of the Me5 nucleus, less than 8% formed synapses on the somata of the predominantly unipolar Me5 neurons. About 79% formed synapses on fibres located between the Me5 somata, while about 13% of the vesicle-containing terminals had no clear synaptic specialization. All of these non-synaptic terminals were G type boutons, with pleomorphic and large characteristic dense-core vesicles. Approximately 60% of the axosomatic synapses were of the S type, containing spherical vesicles and an asymmetrical or symmetrical synaptic specialization. About 20, respectively 15% of the axosomatic synapses, were of the F, respectively P type; both are symmetrical synapse types containing either a majority of flat or pleomorphic vesicles. Less than 10% of the axosomatic synapses were of the G type. Although some proportional differences were noted, an almost similar bouton type distribution pattern was found for the axodendritic synapses suggesting that the axosomatic and axodendritic synapses in the Me5 nucleus are part of the same afferent fibre plexus covering the Me5 nucleus.     

Analysis of retted and non retted flax fibres by chemical and enzymatic means

Flax fibres (Linum usitatissimum L.) were subjected to chemical and enzymatic analysis in order to determine the compositional changes brought about by the retting process and also to determine the accessibility of the fibre polymers to enzymatic treatment. Chemical analysis involved subjecting both retted and non retted fibres to a series of sequential chemical extractions with 1% ammonium oxalate, 0.05 M KOH, 1 M KOH and 4 M KOH. Retting was shown to cause minimal weight loss from the fibres but caused significant changes to the pectic polymers present. Retted fibres were shown to have significantly lower amounts of rhamnogalacturonan as well as arabinan and xylan. In addition the average molecular mass of the pectic extracts was considerably lowered. Enzyme treatment of the 1 M KOH extracts with two different enzymes demonstrated that the non retted extract contained a relatively high molecular weight xylan not found in the retted extract. Treatment of the 1 M KOH extracts and the fibres with Endoglucanase V from Trichoderma viride demonstrated that while this enzyme solubilised cellulose as well as xylan and xyloglucan oligomers from the extract, it had limited access to these polymers on the fibre. MALDI-TOF MS analysis of the material solubilised from the extract suggested that the xylan was randomly substituted with 4-O-methyl glucuronic acid moieties. The xyloglucan was shown to be of the XXXG type and was substituted with galactose and fucose units. The enzyme treatments of the fibres demonstrated that the xylan and xyloglucan polymers in the fibres were not accessible to the enzyme but that material which was entrapped by the cellulose could be released by the hydrolysis of this cellulose.     

Development of muscle spindles deprived of fusimotor innervation

Summary Muscle spindles of limb muscles were deefferented in neonatal rats by sectioning ventral roots or by removal of the lumbosacral spinal cord.Ten to 56 days after the operation, muscle spindles were examined in the medial gastrocnemius, extensor digitorum longus and soleus muscles. The differentiation of muscle spindles was not affected by deefferentation. The number of spindles in the investigated muscles was not reduced. Intrafusal fibres increased in number from two at birth to four per spindle on the average, as in normal muscles. The characteristic ultrastructural distinctions of nuclear bag and nuclear chain fibres developed as under normal conditions. However, intrafusal fibres atrophied slowly after fusimotor denervation, their polar zones becoming reduced in diameter by about 25% in comparison with control fibre diameters. Spindle capsules, on the other hand, increased in size and attained diameters comparable with normal spindles, appearing even somewhat distended.As intrafusal fibres degenerate after complete denervation at birth (Zelená, 1957), but differentiate in the absence of fusimotor innervation, it can be concluded that sensory nerve terminals induce and support their development. It is assumed that the morphogenetic influence of sensory terminals is mediated by release and uptake of a trophic substance at the synaptic junction. The occurrence of light and dense core vesicles in the sensory terminals and of coated invaginations and vesicles at both the axonal and plasma membrane speak in favour of such a possibility.The authors wish to thank Mrs. M. Sobotková, Dr. Z. Liková, Mr. H. Kunz and Ing. M. Doubek for their skillful technical assistance.     

Morphological changes in continuously stretched skeletal muscles in sheep

The effects of continuous elongation of skeletal muscles were studied on six sheep who underwent a lengthening osteotomy of the right tibia. Open muscle biopsies were taken from the biceps femoris muscle preoperatively (Group A), after 5 weeks of bone distraction (Group B) and after another 5 weeks without further distraction (Group C). The size and distribution of type 1 (slow-twitch) and type 2 (fast-twitch) muscle fibres were determined from sections stained for myofibrillar ATPase activity. All sections were also evaluated by light microscopy, especially with regard to myopathic changes. The type 2 fibres showed a significant decrease in size from group A to B and from group B to C. The reduction in fibre size from group A to C was 44.2%. The type 1 fibres, on the other hand, showed no significant differences in mean fibre size between the groups. However, there were considerable individual variations in type 1 fibre size between the groups. The distribution of both fibre types was similar in groups A and B (appr. 17% type 1 fibres) whereas the relative number of type 1 fibres was reduced to 12.4% in group C (P less than 0.01). Myopathic changes, i.e. muscle fibre necroses, were not seen in any of the groups. It is concluded that the type 2 fibre atrophy is mainly caused by muscular inactivity during the postoperative period, but an additional effect of continuous stretching of the muscle cannot be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)