Insect visceral muscle. Fine structure of the proctodeal muscle fibres

The fine structure of the longitudinal muscle fibres of the cockroach proctodeum was investigated by electron microscopy. The fibre is separated incompletely into fibrils, the resting sarcomere length is variable: about 5·8 to 7·3 μm, and the A- and I-bandings are not always clear in longitudinal sections. The ratio of thin and thick filaments at the overlapped region is about 4·1:1 when relaxed, and about 9·8:1 when fully contracted. The myofilament array is not well organized.The previously observed prolonged time course of muscle contraction seems to correlate with the present observations on the poorly developed sarcoplasmic reticulum and irregular distribution of transverse tubules. The Z-bands are irregularly aligned and discontinuous in longitudinal sections. The Z-band structure was studied in relation to the supercontractility. It was found that at maximal isotonic contraction (about 25 per cent rest length) the myofilaments pass through the expanded Z-regions.     

Muscle fibre growth dynamics in diploid and triploid rainbow trout

The effect of triploidy on muscle fibre growth was determined by comparing hyperplasia and hypertrophy of white muscle fibres in all-female, diploid and triploid rainbow trout Oncorhynchus mykiss (100–400 mm total length). Conventional morphometry and protein and DNA concentrations were used to assess muscle fibre hyperplasia and hypertrophy in white muscle samples derived from an anterio-dorsal location. Muscle fibre distributions were significantly different between triploids and diploids in trout <300 mm. The proportion of fibres <20 μm was higher in diploids than in triploids and the proportion of fibres in the 20–40 μm category was higher in triploids than in diploids. This indicates that the hyperplastic fibres of triploids are larger than those of diploids. Larger hyperplastic fibres in triploids are probably due to the combined effect of increased nuclear size in triploids and the relatively high nucleus: cell ratio observed in small muscle fibres. These larger fibres may be less favourable to cellular metabolic exchange because of their smaller surface area to volume ratios, and perhaps account for reduced viability and growth observed in triploids during early life stages. On the other hand, the lack of difference in the distribution of fibres <20 μm between diploids and triploids at larger body size ranges (301–400 mm) imply that triploid trout may have higher rates of new fibre recruitment and growth capacity at these sizes. There was no difference between diploid and triploid trout in the mean size of muscle fibres; however, the number of fibres per unit area was reduced by 10% in triploids. No differences were observed in protein or DNA concentrations in muscle tissues between the two genetic groups. Since triploid nuclei have 1·5 times more DNA than diploid nuclei, this deviation from the expected muscle DNA concentration (1·3–1·4 times more DNA in triploids when the 10% reduction in fibre density is considered) suggests that the number of nuclei per muscle fibre is reduced. In both diploids and triploids, mean fibre size increased with body length while fibre density decreased. Similarly, protein concentration in the muscle tissue increased and DNA concentration declined with increasing body length. Protein/DNA ratio was strongly and positively correlated with fibre size. These results demonstrate that changes in DNA and protein concentrations can be used to assess hyperplasia and hypertrophy in muscle tissues. However, the morphometric procedure provides better insight into muscle fibre growth as it enables the direct visualization and analysis of muscle fibre distribution patterns.     

Fine structure of the alary muscles of the American cockroach

The alary muscles of the cockroach, Periplaneta americana, are striated with an A-band of 3·0 to 3·5 μm long. Each muscle fibre was 10 to 12 μm in diameter and Z-lines appeared as small discrete units staggered throughout the sarcoplasm. Mitochondria were conspicuously located near the Z-line areas and were absent from the middle portion of the sarcomere. A transverse membrane system was present which formed dyad structures with a relatively sparse sarcoplasmic reticulum. Cockroach alary muscles were innervated by axons containing electron-dense granules of near 100 nm in diameter. These are thought to be typical of ‘neurosecretory’ axons based on their ultrastructural appearance.     

CORRELATION OF FINE STRUCTURE AND PHYSIOLOGY OF THE INNERVATION OF SMOOTH MUSCLE IN THE GUINEA PIG VAS DEFERENS

An electron microscope study of the innervation of smooth muscle of the guinea pig vas deferens was undertaken in order to find a structural basis for recent electrophysiological observations. The external longitudinal muscle coat was examined in transverse section. Large areas of the surfaces of adjacent muscle cells were 500 to 800 A apart. Closer contacts were rare. A special type of close contact suggested cytoplasmic transfer between neighbouring cells. Groups of non-myelinated axons from ganglia at the distal end of the hypogastric nerve ramified throughout the muscle. Some small axon bundles and single axons lay in narrow fissures within closely packed muscle masses. Many axons contained "synaptic vesicles." About 25 per cent of the muscle fibres in the plane of section were within 0.25 µ of a partly naked axon; of these 15 per cent were within 500 A of the axon, and about 1 per cent made close contact (200 A) with a naked axon. It is unlikely that every muscle fibre is in close contact with an axon, and it is not possible for every fibre to have many such contacts. Muscle fibres are probably activated by both diffusion of transmitter from naked portions of axons a fraction of a micron distant, and electrotonic spread of activity from neighbouring cells.     

Effect of particle size on the anthelmintic efficacy of mebendazole against Nippostrongylus brasiliensis in the rat.

The effect of reduction in particle size on the anthelmintic efficacy of mebendazole (methyl 5 (6)- benzoyle 1–2 benzimidazole carbamate) was studied in rats undergoing a primary infection with N. brasiliensis. A single oral treatment with fine ground mebendazole (particle size spectrum—54·95 per cent of particles less than 10·62 μ dia.; 86·06 per cent less than 21·27 μ) removed more than 98 per cent of adult worms from the intestine at a dose rate of 12·5 mg/kg body wt. On the other hand the best result achieved with coarse ground mebendazole (18·47 per cent of particles less than 10·62 μ dia; 42·26 per cent less than 21·27 μ dia) was 58 per cent of adult worms removed at a dose rate of 100 mg/kg body wt. It was also shown that fine ground mebendazole adversely affected migrating third stage larvae of N. brasiliensis.     

Myotube production in fast myotomal muscle is switched-off at shorter body lengths in male than female Atlantic halibut Hippoglossus hippoglossus (L.) resulting in a lower final fibre number

A sampling method is described to determine accurately the number of fast myotomal muscle fibres (N_F) in a large flatfish species, the Atlantic halibut Hippoglossus hippoglossus. An unusual feature of the fast myotomal muscle is the presence of internalized strips of slow muscle fibres. In fish of 1·5–3·5 kg (n = 24), the total cross‐sectional area (A_TC) of fast muscle was 18% greater in the dorsal than ventral myotomal compartments (P < 0·05), whereas there was no significant difference between left‐ and right‐hand sides of the body. Due the bilateral asymmetry, muscle blocks (5 × 5 × 5 mm) were prepared to systematically sample each myotomal quadrant (dorsal, ventral, left‐ and right‐side) and the diameters of 150 fast fibres measured per block. Smooth non‐parametric probability functions were fitted to a minimum of 800 measurements of fibre diameter per quadrant (n = 5). There were no significant differences in the distribution of muscle fibre diameters between myotomal compartments and therefore N_F could be estimated from a single quadrant. The number of blocks required to estimate N_F with a repeatability of ±2·5% increased from six at 300 g body mass to 17 at 96·5 kg, caused by variation within and between blocks. Gompertz curves were fitted to measurements of fibre number and fork length (L_F). The estimated final fibre number was 8·96 × 10⁵ (7·99–9·94 × 10⁵, 95% CI) for males and 1·73 × 10⁶ (1·56–1·90 × 10⁶, 95% CI) for female fish. The estimated L_F for cessation of fibre recruitment in the fast muscle of female fish (1775 mm) was almost twice that in males (810 mm), reflecting their greater ultimate body size.     

Muscle fibre types and size distribution in sub-antarctic notothenioid fishes

The presumptive tonic muscles fibres of Cottoperca gobio, Champsocephalus esox, Harpagifer bispinis, Eleginops maclovinus, Patagontothen tessellata, P. cornucola and Paranotothenia magellanica stained weakly or were unstained for glycogen, lipid, succinic dehydrogenase (SDHase) and myosin ATPase (mATPase) activity. Slow, intermediate and fast twitch muscle fibres, distinguished on the basis of the pH stability of their mATPases, showed intense, moderate and low staining activity for SDHase, respectively. Slow fibres were the major component of the pectoral fin adductor profundis muscle. The proportion of different muscle fibre types varied from the proximal to distal end of the muscle, but showed relatively little variation between species. The myotomes contained a lateral superficial strip of red muscle composed of presumptive tonic, slow twitch and intermediate fibres, thickening to a major wedge at the horizontal septum. All species also had characteristic secondary dorsal and ventral wedges of red muscle. The relative abundance and localization of muscle fibre types in the red muscle varied between species and with body size in the protandric hermaphrodite E. maclovinus. The frequency distribution of diameters for fast twitch muscle fibres, the major component of deep white muscle, was determined in fish of a range of body sizes. The absence of fibres <20 μm diameter was used as a criterion for the cessation of muscle fibre recruitment. Fibre recruitment had stopped in P. tessellata of 13·8 cm L_T and E. maclovinus of 32·8 cm L_T, equivalent to 49 and 36·5% of their recorded maximum sizes respectively. As a result in 20‐cm P. tessellata, the maximum fibre diameter was 300 μm and 36% of fibres were in excess of 200 μm. The unusually large maximum fibre diameter, the general arrangement of the red muscle layer and the extreme pH lability of the mATPase of fast twitch fibres are all common characters of the sub‐Antarctic and Antarctic Notothenioids, including Cottoperca gobio, the suggested sister group to the Notothenidae.     

On the Polarization and Innervation of the Pars Inferior Sensory Epithelia of the Herring Labyrinth

The macula sacculi and the macula lagenae of the herring, Clupea harengus L., were examined by light microscopy, the macula lagenae is large compared to what is normal among non-ostariophysan fishes, the morphological polarization of the hair cells in the inferior maculae shows a pattern which is similar to that usually seen in teleost fishes. The fibres in the nerves supplying the macula sacculi and the macula lagenae were counted and their diameters measured. The ramulus saccularis is divided in two separate ramuli innervating populations of hair cells with different morphological polarization. The saccular rostral nerve trunk contains 1800–2300 fibres, with 1300–1800 fibres in the caudal nerve trunk. The lagenar nerve is composed of 2100–4000 fibres. The fibre diameters are 1–14 μm in all ramuli. Silver staining of the nerve axoplasm reveals a unique differentiation of the maculae, which can be divided into a central area surrounded by a peripheral part. The hair cells in the central area are innervated by thick nerve fibres (5–14 μm diameter) as well as a few thin nerve fibres (about 1 μm diameter), while the receptor cells in the peripheral area are exclusively innervated by thin fibres having diameters of 2 μm or less.     

Changes in muscle structure associated with somatic growth in Idiosepius pygmaeus, a small tropical cephalopod

Mantle muscle tissue of Idiosepius pygmaeus was examined to describe changes in structure and organization associated with growth. Growth in I. pygmaeus|DD was a function of both an increase in muscle fibre number and fibre size within muscle blocks. Continuous fibre production over the observed life span of I. pygmaeus was indicated by the presence of very small muscle fibres (< 1.0 μm in diameter) in substantial proportions in all sizes of individuals. Muscle blocks became larger as animals increased in size, although new muscle blocks were generated in all sizes of individuals. Mantle muscle fibres had a maximum size of 11 μm. Therefore, for an individual to continue increasing muscle block sizes, new fibres must be produced. This is further evidence of continuous fibre production throughout the size range of I. pygmaeus examined. The relative rates of muscle fibre generation and fibre growth depended on the size of the animal and position along the mantle (anterior, mid or posterior mantle). The predominance of small fibres and blocks at the anterior end of the mantle suggested that this was the primary growth region. Mitochondriapoor and mitochondria-rich muscle fibres from small individuals had much larger mitochondrial cores than muscle fibres from larger animals. Changes in the muscle structure are discussed with respect to the metabolic and energetic requirements of I. pygmaeus , and how these may change with growth.     

Changes in the sciatic nerve of the rabbit and its tissue constituents during development

Abstract— A segment, defined by gross anatomic boundaries, which comprises most of the sciatic nerve was dissected from rabbits aged from birth to 1 yr. The mean and standard deviation of the variance determined for the weights of pairs of nerve units removed from single animals of an age group did not exceed 2·7 per cent and 12·3 per cent respectively of the average weight of the two nerve units which were the values determined for a group of newborn animals. During the period from birth to one year of age, the weight and length of the nerve unit increased 47- and 6-fold respectively while the animal's weight increased 78-fold. Whereas the nerve unit length increased little after 8 weeks, its weight and that of the whole animal continued to increase up to 1 year. Estimations of nucleic acids in the nerve unit from adult animals gave values of 54 μg DNA-P and 25 μg RNA-P per g fresh weight. During the period birth to 1 yr the absolute amount of DNA in the nerve unit increased 11-fold, 71 per cent of this having occurred by 6 weeks of age. The absolute amount of RNA increased 11 -fold by 8 weeks of age and remained constant thereafter. During the period birth to 1 yr, the proportion of the nerve constituents accounted for by lipid-free solids remained constant at 10 per cent, while lipids increased from 5 to 18 per cent and tissue water declined from 84 to 71 per cent. Changes in some lipid classes were examined also. Increases of absolute content in the nerve unit over the first year and concentrations on a fresh weight basis attained in year-old animals were as follows: cholesterol, 132-fold and 86 mg/g; triglyceride 554-fold and 43·2 mg/g; total phospholipid, 85-fold and 61 mg/g; cerebroside 205-fold and 28 μmol/g; sulphatide, 154-fold and 10 μmol/g; monogalactosyl diglyceride, 31-fold and 0·6 μmol/g. The ratio cholesterol/phospholipid/galactolipid in whole nerve units from adult animals was 2·0/2·1/1·0 and the change in this ratio in the first year was compatible with enrichment of myelin in galactolipid during myelination. The ratio of cerebroside to sulphatide increased from 2·0 to 2·6 during this period. Increases in absolute content and concentrations attained for sialic acid-containing components representing cell surface constituents were as follows: ganglioside sialic acid, 33-fold, and 83 μg/g; glycoprotein sialic acid, 57-fold and 371 μg/g. The quantitative pattern of ganglioside fractions separated by thin-layer chromatography in one direction resembled that of whole brain and was the same at all ages studied. The changes reported reflect a composite picture of changes in a variety of cell membranes indicative of marked variation during development in quantity and composition of membranes.     

Explosive development of pectoral muscle fibres in large juvenile blue catfish Ictalurus furcatus

As part of an effort on scaling of pectoral spines and muscles, the basis for growth was examined in six pectoral muscles in juvenile blue catfish Ictalurus furcatus, the largest catfish in North America. Fibre number increases slowly in fish from 13·0 to 26·4 cm in total length, doubles by 27·0 cm and remains stable in larger individuals. Simultaneously, mean fibre diameter decreases by half, caused by the addition of new small fibres, before increasing non‐linearly in larger fish. The orders of magnitude disparity between the size at hatching and the size of large adults may have selected for rapid muscle fibre addition at a threshold size.     

Elongation of duplex DNA by recA protein

recA protein, which is essential for the recombination process in Escherichia coli, was incubated in the presence of 5′-γ-thiotriphosphate with circular plasmid pBR_βG containing small single-stranded gaps. Stable complexes were formed which appear in the electron microscope as fibres with a diameter about five times that of naked DNA. Complex formation appears to be a co-operative process whereby the average rise per base-pair with respect to the fibre axis increases from 3·39 ± 0·08 Å to 5·20 ± 0·18 Å. The elongation of DNA by about 50% is compatible with an unwinding of the double helix and an intercalating mode of binding of recA and/or 5′-γ-thiotriphosphate to DNA.     

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.     

Growth and multiplication of white skeletal muscle fibres in carp larvae in relation to somatic growth rate

A morphometric analysis of white axial muscle of common carp Cyprinus carpio was undertaken in order to quantify increase in fibre size, fibre nuclei and fibre number in relation to somatic growth rate during early life. In fast-growing carp larvae fed zooplankton, length and height of fibres from the central part of dorsolateral muscle increased at the same rate (0.75) relative to the total length of the larvae during the first 2 weeks of feeding. During this period, the number of nuclei per fibre increased threefold while the number of nuclei per unit fibre surface remained constant. In fast-growing larvae fed a formulated diet, the total cross-sectional area of one epaxial quadrant of white muscle and the total area of white fibres increased at almost the same rate (3.15; 3.23) relative to larval total length during the first 28 days of exogenous feeding. The total number of white fibres increased faster (2.07) relative to the total length of larvae than the mean area of white fibres (1.16). Hyperplasia accounted for 64% of muscle growth in these larvae. The proportion of fibres with a width < 10 μm decreased from 72% at first feeding to 14% 28 days later, while the proportion of fibres with a width >20 μm which was 0% at first feeding increased up to 34% in the same time. The recruitment of new white fibres seemed to be almost the same in the whole muscle quadrant at first feeding and 18 or 28 days later but, 8 days after first feeding, a transient significant recruitment of new fibres was shown at the apex of the myotome. Comparisons between fast- and slow-growing groups of larvae showed that for a given larval total length: (1) the mean width of central white fibres was higher and the proportion of central fibres with a width <10 μm was lower in slow-growing larvae than in fast-growing ones; (2) the total number of white fibres was lower for a higher total cross-sectional area of white muscle in slow-growing larvae than in fast-growing ones. These results suggest that, in Cyprinus carpio larvae, slow-growing conditions are related to a decreased contribution of hyperplasia to muscle growth.     

The lattice arrangement of the collagen fibres in the submucosa of the rat small intestine: scanning electron microscopy

Summary The three-dimensional architecture of the submucosal collagen fibres of the rat (3 weeks old) small intestine was examined by scanning electron microscopy using a selective microdissection method. The main framework of the submucosa was composed of two arrays of collagen fibre bundles running diagonally around the intestinal wall, one set in a clockwise direction, the other counterclockwise. These fibre bundles were about 5 m in diameter and were oriented at a range of angle ± 30°–50° to the longitudinal axis of the intestine. With the advantage of the SEM observation it was demonstrated that these fibres in different arrays did not constitute two separate layers but interwove to form a unified lattice sheet. An irregular network of fine collagen fibrils over the main framework was also seen. The significance of their arrangement is discussed with respect to the skeletal function of the submucosa in the intestine.     

Pathological changes in the microstructure of longissimus lumborum muscle from five breeds of pigs

The aim of the study was to determine the extent of histopathological changes in m. longissimus lumborum of PL, PLW, Duroc, Pietrain, and Pu?awska pigs (N = 30 per breed) aged 210 days. Changes in fibre size (atrophy, hypertrophy - giant fibres), changes in fibre shape (angular fibres), degenerative lesions (necrosis with phagocytosis) and connective tissue hypertrophy were evaluated. The percentage of individual pathological changes in m. longissimus lumborum of the analysed pig breeds was relatively low. Significantly more normal fibres were found in the muscles of Pu?awska compared to Pietrain pigs. Muscle fibre atrophy was the most frequent and extensive histopathological change. The muscles of Pu?awska pigs had significantly fewer atrophic, giant and angular fibres, significantly less necrosis with phagocytosis, and less animals with connective tissue hypertrophy compared to the other pig breeds. On the other hand, Pietrain pigs were characterized by a greater number of animals with giant fibres and a significantly higher proportion of giant fibres compared to the other breeds. Also the diameter of giant fibres was the largest in Pietrain, intermediate in PL and PLW, and the smallest in Duroc and Pulawska pigs. Moreover, current findings indicate that giant fibres may arise from each muscle fibre type (I, IIA and IIB). It is concluded that selection of pigs for increased leanness contributes to the incidence of histopathological changes, which may decrease pork quality.     

The Fine Structure of Degenerating Nerve Fibers, their Sheaths, and their Terminations in the Central Nerve Cord of the Cockroach (Periplaneta americana)

The connectives above and below the second thoracic ganglion and nerves to and from the mesothoracic leg were severed in Periplaneta americana. Isolated ganglia and severed nerve cord were examined in the electron microscope. In the connectives, sheaths of degenerating fibers remain continuous but become thicker and more dense. There is increase in number and more haphazard disposition of the neuroglial processes which ensheath the axons. The cytoplasm contains vacuoles. Dense droplets normally intercalated between the layers of neuroglial processes ensheathing the axons are strikingly increased in number. The axoplasm with its organelles forms dense clumps. Mitochondria in axons are enlarged, the intramitochondrial matrix is more dense, and the internal folds are disorganized. In ganglia, mitochondrial changes in terminal parts of the axons appear similar to those described in the parent axons in the connective. The synaptic portions of nerve fibers appear very dense. Alterations of the sheath are minimal. Synaptic particles in the degenerating axoplasmic coagulum undergo only slight morphological changes and are still present up to 6 days after severance of their nerve fibers. It is difficult to assess whether there are any alterations in the total number of synaptic particles during degeneration.     

Kinetics of microtubule formation after cold disaggregation of the mitotic apparatus

The rate of spindle-fiber reformation following cold treatment of the giant amoeba, Chaos carolinensis, has been determined and used to test a single growth point, subunit incorporation model of microtubule assembly. Mitotic apparatuses isolated at one-minute intervals after rewarming contain progressively longer spindle fibers; re-assembly begins at the kinetochore region, proceeds at a rate of 1·5 μm per minute, then slows as the normal length of 5 μm is approached. From information on microtubule ultrastructure, the total number of 40-Å subunits in mitotic apparatuses per amoeba, and hence the concentration released during disassembly, was calculated to be 1·0 × 10¹⁵ molecules per cm³. Calculation of diffusion and assembly kinetics indicates that this concentration of microtubule subunits is equal to the concentration required to produce a growth rate of 1·5 μm per minute by diffusion of single subunits to one assembly point per microtubule.     

Fine structure and axonal organization in the buccal ganglia nerves ofAplysia (Mollusca,Gastropoda)

Summary The morphology of theAplysia buccal nerves and connectives has been studied by electron microscopic analysis. In these nerves the fine structure of the elements (connective sheath, glia, axons and their vesicular and cytoplasmatic content) is similar to that of other molluscan nerves. Some features seem to be comparable to other invertebrate groups such as Crustacea and Annelida. The axons have been divided into four classes on the basis of their calibre, and each type has been counted in all the nerves. The number of axons relating to identified buccal neurons is discussed. Finally, some speculations about relationships between buccal ganglia and peripheral regions connected by buccal nerves are proposed.     

Ultrastructure of calcitonin gene-related peptide-and substance P-like immunoreactive nerve fibres in the carotid body and carotid sinus of the guinea pig

Summary Previous studies have demonstrated that substance P-(SP) and calcitonin gene-related peptide-like immunoreactivities (CGRP-LI) coexist in sensory nerve fibres in the guinea-pig carotid body and carotid sinus. In the present study the ultrastructure of these nerve fibres was investigated by means of single-and double-labelling immunocytochemistry. In both, carotid body and carotid sinus immunoreactive fibres were unmyelinated axons of small dianeter (0.12–0.56 m). At the subcellular level, SP-and CGRP-LI were colocalized in intra-axonal dense core vesicles, suggesting corelease and simultaneous action of these two compounds. SP/CGRP-LI nerve fibres within the carotid body were mainly found in the interparenchymal connective tissue, but also occurred in relationship to blood vesslesl and nests of glomus cells. Neither in the carotid body not in the carotid sinus, SP/CGRP-LI axons corresponded to the large terminals which are generally considered to represent the main chemoreceptor and baroreceptor endings, respectively. Thus, SP/CGRP-LI fibres either belong to the chemo-and baroreceptors of the C-fibre class or constitute a fibre population not directly involved in conduction of baro-and chemoreflexes.This study was supported by the DFG, grant He 919/6-2