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PubMed1989

Specificities of afferents reinnervating cat muscle spindles after nerve section.

1. We have made quantitative assessments of the sensory reinnervation and recovery of peroneus brevis muscle spindles following section and epineurial repair of the common peroneal nerve. After 6-50 weeks recovery, single-unit, dorsal-root recordings were made of the responses to ramp-and-hold or sinusoidal stretch of the reinnervated spindles, which were subsequently examined in teased, silver preparations. 2. Assessments of recovery used data obtained from cross-union experiments in which foreign afferents (including Ib) were given the opportunity of reinnervating spindles in the absence of their native (Ia, spindle II) afferents; and from an examination of tenuissimus spindles reinnervated by Ia and spindle II afferents in the absence of Ib afferents. These studies revealed: (i) that regenerating Ib afferents can terminate in sites originally occupied by the endings of Ia or spindle II afferents, and respond to stretch like normal Ia and spindle II afferents; (ii) that Ib and spindle II afferents reinnervating spindles are histologically identical apart from diameter range; and (iii) that some cutaneous afferents can reinnervate spindles and give highly abnormal, phasic stretch responses. 3. Recovery of afferents reinnervating spindles was marked by increases in conduction velocity and proportions firing tonically, but their firing rates at the three phases of ramp-and-hold stretch were considerably lower than normal and showed no tendency to increase. 4. Some relatively fast afferents that gave spindle II-type responses were identified as Ib afferents reinnervating secondary-ending sites; conversely, some relatively slow afferents that gave Ia-type responses were identified as spindle II afferents reinnervating primary-ending sites. 5. The estimated loss of spindle afferents from tenuissimus after nerve section (52% Ia, 49% spindle II) was considerably less than the estimated loss of these afferents from peroneus brevis after section of the common peroneal nerve (79% Ia, 86% spindle II). The proportion of spindles in tenuissimus reinnervated by free-ending afferents was also much lower (22%) than in peroneus brevis (73%). These differences are partly attributed to the greater size and degree of afferent complexity of the common peroneal nerve. 6. Similar proportions of spindles in peroneus brevis were reinnervated by Ia and Ib afferents after both partial (27% Ia, 20% Ib) and complete (21% Ia, 20% Ib) section of the common peroneal nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1995

Spindle waves are propagating synchronized oscillations in the ferret LGNd in vitro.

1. The cellular features of propagation of spindle waves and a bicuculline-induced slow oscillation through sagittal slices of the ferret dorsal lateral geniculate nucleus (LGNd) maintained in vitro were examined with simultaneous extracellular and intracellular recordings from up to eight sites. Spindle waves typically propagated along the long axis (dorsal-ventral) of the sagittal slice at a speed of 0.3-1.5 mm/s and were synchronized along the line of projection between the perigeniculate nucleus (PGN) and the A, A1, and C laminae. 2. Spindle waves can be initiated with local electrical stimulation or can occur spontaneously in any part of the LGNd/PGN. On initiation of a spindle wave, spindle waves propagate away from the site of initiation. Spindle waves may propagate only locally or may collide with other spindle waves. Collision of spindle waves is associated with synchronization of the two network oscillations, and the spindle waves do not propagate past one another. 3. Repetitive electrical stimulation reveals that spindle wave generation and propagation exhibit a relative refractory period of between 7 and 14 s in vitro. Stimulation at rates of less than the refractory period results in the generation of abbreviated local spindle waves at the stimulation site, but not in the propagation of this spindle wave into adjacent regions of the slice. 4. Local block of non-N-methyl-D-aspartate (non-NMDA) excitatory amino acid receptors in the PGN with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) prevents the propagation of spindle waves across the point of application, indicating that the excitation of PGN neurons by thalamocortical cells is essential to the propagation of these oscillations. The local antagonism of non-NMDA receptors in the PGN results in the dorsal and ventral aspects of the LGNd slice behaving as independent spindle wave generators, even if before application of CNQX they were not. 5. Activation of a burst discharge in a single PGN neuron can result in the generation of a full spindle wave and the propagation of this spindle wave both dorsally and ventrally through the slice away from the activated PGN neuron. The ability of a burst of action potentials in a PGN neuron to generate a spindle wave is suppressed immediately after the generation of a spindle wave, but slowly returns over a 7- to 14-s period corresponding to the relative spindle wave refractory period.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2003

Visualization of the metaphase II meiotic spindle in living human oocytes using the Polscope enables the prediction of embryonic developmental competence after ICSI.

BACKGROUND: Meiotic spindles in living human oocytes can be visualized by the Polscope. This study investigated the relationship between the presence/location of the spindle in metaphase II (MII) oocytes and developmental competence of embryos in vitro. METHODS: The spindles in 626 MII oocytes were examined by the Polscope and divided into six groups (A-F) based on the presence or absence of the spindles and the angle between the spindle and the first polar body. After ICSI, the fertilization and embryo development were evaluated. RESULTS: Meiotic spindles were imaged in 523 oocytes (83.5%), while 103 (16.5%) did not have a visible spindle (group F). The majority of oocytes (68.8%) had the spindle directly beneath or adjacent to the first polar body (groups A and B: 48.2 and 20.6%). Oocytes in group C (11.2%) had the spindle located between 60 and 120 degrees angle away from the first polar body, those in group D (2.4%) had the spindle located between 120 and 180 degrees angle and those in group E (1.1%) had the spindle located at 180 degrees angle to the first polar body. The fertilization and embryonic development were similar in the oocytes with spindles regardless of spindle position. However, the rate of high quality embryos was significantly higher in the oocytes (64.2%) with visible spindles than in the oocytes (35.9%) without spindle and multipronuclear proportion showed a slight tendency to increase in oocytes without spindles. (10.7 versus 5.9%, P = 0.12; NS). CONCLUSIONS: the presence of a bi-refringent meiotic spindle in human oocytes by using the Polscope can predict a higher embryonic developmental competence. However, the relative position of the spindle within the oocyte doesn't appear to influence the developmental potential of embryos.

Adult↗

PubMed1990

Kinetic analysis of mitotic spindle elongation in vitro.

Studies of mitotic spindle elongation in vitro using populations of diatom spindles visualized with immunofluorescence microscopy have shown that the two interdigitating half-spindles are driven apart by an ATP-dependent process that generates force in the zone of overlap between half-spindles. To characterize further the system responsible for spindle elongation, we observed spindle elongation directly with polarized light or phase-contrast video-microscopy. We report that the kinetics of spindle elongation versus time are linear. A constant rate of spindle elongation occurs despite the continuous decrease in length of the zone of overlap between half-spindles. The average rate of spindle elongation varies as a function of treatment, and rates measured match spindle elongation rates measured in vivo. When spindles elongated in the presence of polymerizing tubulin (from bovine brain), the extent of elongation was greater than the original zone of half-spindle overlap, but the rate of elongation was constant. No component of force due to tubulin polymerization was found. The total elongation observed in the presence of added tubulin could exceed a doubling of original spindle length, matching the elongation in the intact diatom. The linear rate of spindle elongation in vitro suggests that the force transducer for anaphase B is a mechanochemical ATPase, analogous to dynein or myosin, and that the force for spindle elongation does not arise from stored energy, e.g. in an elastic matrix in the midzone. Additionally, on the basis of observations described here, we conclude that the force-transduction system for spindle elongation must be able to remain in the zone of microtubule overlap during the sliding apart of half-spindles, and that the transducer can generate force between microtubules that are not strictly antiparallel.

Adenosine Triphosphate↗

PubMed2006

Adaptation of rat soleus muscle spindles after 21 days of hindlimb unloading.

Spindle discharges are affected by muscle unloading, and changes in passive stiffness of the muscle-tendon unit may contribute to the changes in spindle solicitation. To test this hypothesis, we determined the spindle sensitivity from electroneurograms of the soleus nerve, and, concomitantly, we measured the incremental passive muscle tension. Both measurements were done from ramp and hold stretches imposed to the soleus muscle after the Achilles tendon was severed. The ratio between the spindle sensitivity and the passive stiffness gave a "spindle efficacy index" (SEI). The experiments were conducted on control rats (C, n = 12) and on rats that had undergone hindlimb unloading (HU, n = 12) for 21 days. The muscle threshold lengths for electroneurogram to discharge (neurogram length, Ln) and for detecting passive tension (slack length, Ls) were determined, and, when these lengths differed, the stretches were imposed at these two initial lengths. The contralateral muscles were used to count muscle spindles and spindle fibers (ATPase staining) and to identify MyHC isoforms by immunostaining. Ln and Ls values were identical for the C muscles, while after HU, Ln was significantly shorter than Ls, which indicated that spindle afferents were more sensitive since they discharged before any passive tension was developed by the soleus muscle. At Ln, spindle sensitivity and passive stiffness did not differ for C and HU muscles. Consequently, when calculated at this relatively short initial muscle length, the SEI was maintained (or even slightly increased) after HU. This held under dynamic conditions (ramp phase of the stretch) and under static conditions (hold phase of the stretch). At Ls, the dynamic and static incremental stiffness values increased significantly after HU. Under dynamic conditions, the spindle sensitivity also increased after HU but to a less degree than incremental stiffness, which led to a significant decrease in SEI. Under static conditions, the spindle sensitivity presented a high increase, and, consequently, SEI was not modified. These functional changes were associated with structural adaptations: HU did not alter the total number of muscle spindles, but the number of spindles containing three nuclear chain fibers increased significantly. The main change in intrafusal MyHC content concerned the slow type I MyHC isoform. In conclusion, after a period of muscle unloading, the spindle discharges were maintained or even enhanced in several experimental conditions. This may be due to a better transmission of the external stretch to muscle spindles through stiffer elastic structures but also to own muscle spindle adaptations which reinforce the spindle sensitivity, notably under static conditions.

Adaptation, Physiological↗

PubMed1986

Physiological and ultrastructural analysis of elongating mitotic spindles reactivated in vitro.

We have developed a simple procedure for isolating mitotic spindles from the diatom Stephanopyxis turris and have shown that they undergo anaphase spindle elongation in vitro upon addition of ATP. The isolated central spindle is a barrel-shaped structure with a prominent zone of microtubule overlap. After ATP addition greater than 75% of the spindle population undergoes distinct structural rearrangements: the spindles on average are longer and the two half-spindles are separated by a distinct gap traversed by only a small number of microtubules, the phase-dense material in the overlap zone is gone, and the peripheral microtubule arrays have depolymerized. At the ultrastructural level, we examined serial cross-sections of spindles after 1-, 5-, and 10-min incubations in reactivation medium. Microtubule depolymerization distal to the poles is confirmed by the increased number of incomplete, i.e., c-microtubule profiles specifically located in the region of overlap. After 10 min we see areas of reduced microtubule number which correspond to the gaps seen in the light microscope and an overall reduction in the number of half-spindle microtubules to about one-third the original number. The changes in spindle structure are highly specific for ATP, are dose-dependent, and do not occur with nonhydrolyzable nucleotide analogues. Spindle elongation and gap formation are blocked by 10 microM vanadate, equimolar mixtures of ATP and AMPPNP, and by sulfhydryl reagents. This process is not affected by nocodazole, erythro-9-[3-(2-hydroxynonyl)]adenine, cytochalasin D, and phalloidin. In the presence of taxol, the extent of spindle elongation is increased; however, distinct gaps still form between the two half-spindles. These results show that the response of isolated spindles to ATP is a complex process consisting of several discrete steps including initiation events, spindle elongation mechanochemistry, controlled central spindle microtubule plus-end depolymerization, and loss of peripheral microtubules. They also show that the microtubule overlap zone is an important site of ATP action and suggest that spindle elongation in vitro is best explained by a mechanism of microtubule-microtubule sliding. Spindle elongation in vitro cannot be accounted for by cytoplasmic forces pulling on the poles or by microtubule polymerization.

Actomyosin↗

PubMed2005

Spindle positions and their distributions in in vivo and in vitro matured mouse oocytes.

BACKGROUND: This study was carried out to compare spindle locations and their developmental competencies both in vivo and in vitro in matured mouse oocytes. Spindle locations were identified using a polscope. Since meiotic spindles in living oocytes are highly birefringent, their structures can be viewed non-invasively by using a polscope. METHODS: In vivo matured metaphase II oocytes were collected from the oviducts of mice. Immature oocytes were collected from mouse ovaries, and then cultured in YS medium until the first polar body (PB) extrusion. In vitro and in vivo matured oocytes were classified into four categories according to their spindle positions relative to the first PB (0 degrees , 0-90 degrees , 90-180 degrees and without a spindle image), and rates of fertilization and blastocyst formation were assessed. In vivo matured oocytes with a 0 degrees spindle disposition relative to PB were cultured in vitro for 24 h, and then their spindle positions were re-assessed. RESULTS: Most in vivo matured oocytes (89.1%) had a 0 degrees spindle position. Only 6 and 3% of oocytes had spindle positions of 0-90 degrees and 90-180 degrees , respectively. No spindle image was observed in 2%. However, most in vitro matured oocytes (83.1%) had a 0-90 degrees spindle position and, in contrast, only 6.5% of these oocytes had a 0 degrees spindle position. The rate of fertilization and blastocyst rate were significantly higher for in vivo matured oocytes than in vitro matured oocytes (87.1 versus 64.9% and 76.1% versus 66.0%, respectively, P<0.05 for each). We also observed that 71.7% of the in vivo matured oocytes with the 0 degrees spindle position showed a spindle position change to 0-90 degrees after 24 h of culture. These oocytes had a poor fertilization rate (43%) and a zero blastocyst rate. CONCLUSION: In vitro matured mouse oocytes showed quite different spindle positions compared with in vivo matured oocytes. Moreover, in vivo matured oocytes cultured for 24 h had a spindle position distribution that was similar to that of in vitro matured oocytes. The different spindle positions observed in in vivo and in vitro matured oocytes may reflect differences in their cytoplasmic maturation processes. These findings have implications regarding the lower developmental competency of in vitro matured oocytes.

Animals↗

PubMed2001

Spindle cell and mixed spindle/lymphocytic thymomas: an integrated clinicopathologic and immunohistochemical study of 81 cases.

Forty-three cases of spindle cell thymoma (medullary, WHO type A) and 38 cases of mixed spindle/lymphocytic thymoma (WHO type AB) were studied for their clinicopathologic and immunohistochemical characteristics. Three histologic patterns of spindle cell thymoma were observed: short-spindled (57%), long-spindled (31%), and micronodular (12%). The short-spindled variant was composed of oval to short spindle cells commonly arranged in a hemangiopericytic or microcystic pattern. The long-spindled variant chiefly consisted of fibroblast-like epithelial cells mimicking fibrohistiocytic neoplasms. The micronodular variant was characterized by small nests of short spindle cells dispersed among a lymphoid stroma with frequent germinal centers. All kinds of spindle cell could be admixed with lymphocyte-rich "cortex"-like areas to constitute mixed spindle/lymphocytic thymomas. Immunohistochemically, the epithelial cells in up to 70% of the short-spindled and long-spindled variants of spindle cell thymoma and 90% of mixed spindle/lymphocytic thymomas were positive for CD20, whereas the epithelial cells in all micronodular spindle cell thymomas were negative. All of the spindle cell thymomas and most of the mixed spindle/lymphocytic thymomas in this study were found in stages I and II. Follow up of the patients did not disclose relapse or mortality directly resulting from the tumors. However, the prognosis of stage I and II spindle cell and mixed spindle/lymphocytic thymomas did not significantly differ from those of stage I and II thymomas of other types by a stage-matched survival analysis. Our data showed that spindle cell and mixed spindle/lymphocytic thymomas are distinctive in histologic pattern and immunohistochemical profile. When interpreted within the context of staging, spindle cell and mixed spindle/lymphocytic thymomas presenting in stages I and II most likely behave in an indolent fashion.

Adult↗

PubMed2003

Occurrence of periodic sleep spindles within and across non-REM sleep episodes.

Sleep spindles have been reported to occur both as single events and periodically in sequences. However, there is no systematic description about the occurrence of spindles in sequences in relation to time of night. The aim of the present study was to examine the temporal occurrence of periodic sleep spindles during the night. Sleep spindles of 19 healthy subjects were selected visually. A minimum of three consecutive spindles was required to form a spindle sequence. A 5-second upper time interval limit was applied as the longest duration between spindles belonging to a spindle sequence. The number of spindles and time occupied by spindle sequences increased from the first to the fourth non-REM (NREM) sleep episode. Within NREM sleep episodes, the number of spindles and spindle sequences dominated at the beginning. In the first two NREM sleep episodes with high slow-wave activity (SWA), there were few spindle sequences and they decreased with increasing SWA. In the third and fourth NREM sleep episode with less SWA, there were more spindle sequences and they were more evenly distributed. It is possible that in the first NREM sleep episodes, hyperpolarization of the thalamocortical cells deepens so rapidly that the NREM sleep level, where spindle sequences arise, is passed and spindle sequences are not formed. Spindle sequences could be regarded as markers of the evolution of the NREM sleep process and their lack or excess in relation to time of night and NREM sleep episode can hopefully be used to indicate changes in brain mechanisms behind NREM sleep.

Adult↗

PubMed1981

Autosomal spindle fibres influence subsequent sex-chromosome movement in crane-fly spermatocytes.

In meiosis-I crane-fly spermatocytes 3 autosomal half-bivalents move to each pole in anaphase while the 2 sex-chromosomal univalents remain at the equator. The sex chromosomes move to opposite poles only after the autosomes reach the poles; the sex chromosomes start to move polewards about 25 min after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex cin after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex cin after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex chromosome that remained at the equator would normally have moved to the pole associated with the irradiated autosomal spindle fibre. In the second, both sex chromosomes moved to the same pole, always that of the non-irradiated side. These effects occurred whether or not autosomal anaphase movement was blocked by the irradiation. There was no wavelength dependence for altering sex-chromosome movements. Sex-chromosome movements were altered only when at least one sex-chromosomal spindle fibre was adjacent to the irradiated autosomal spindle fibre; when neither sex chromosome had a spindle fibre adjacent to the irradiated autosomal spindle fibres the chromosomes always moved normally. Irradiation of sex-chromosomal spindle fibres during sex-chromosomal anaphase showed short blockages of movement (usually 5-8 min), and then complete recovery. Direct irradiation of sex-chromosomal spindle fibres (without irradiating autosomal spindle fibres) when the autosomes were in anaphase but the sex chromosomes were in metaphase never caused abnormal sex-chromosome movements. These results eliminate the possibility that when we irradiated autosomal spindle fibres that were adjacent to sex-chromosomal spindle fibres the sex-chromosomal spindle fibres were irradiated inadvertently and were unable to recover from the damage. We suggest that the irradiations of autosomal spindle fibres alter a control system involved in "turning on' sex-chromosomal spindle fibre motors, rather than directly altering the motors. We suggest that interactions between spindle fibres are somehow involved in this control system.

Animals↗

PubMed2004

Poly(ADP-ribose) is required for spindle assembly and structure.

The mitotic spindle is typically thought of as an array of microtubules, microtubule-associated proteins and motors that self-organizes to align and segregate chromosomes. The major spindle components consist of proteins and DNA, the primary structural elements of the spindle. Other macromolecules including RNA and lipids also associate with spindles, but their spindle function, if any, is unknown. Poly(ADP-ribose) (PAR) is a large, branched, negatively charged polymeric macromolecule whose polymerization onto acceptor proteins is catalysed by a family of poly(ADP-ribose) polymerases (PARPs). Several PARPs localize to the spindle in vertebrate cells, suggesting that PARPs and/or PAR have a role in spindle function. Here we show that PAR is enriched in the spindle and is required for spindle function--PAR hydrolysis or perturbation leads to rapid disruption of spindle structure, and hydrolysis during spindle assembly blocks the formation of bipolar spindles. PAR exhibits localization dynamics that differ from known spindle proteins and are consistent with a low rate of turnover in the spindle. Thus, PAR is a non-proteinaceous, non-chromosomal component of the spindle required for bipolar spindle assembly and function.

Animals↗

PubMed2002

Spindle observation in living mammalian oocytes with the polarization microscope and its practical use.

The meiotic spindle is crucial for normal chromosome alignment and separation of maternal chromosomes during meiosis. Conventional methods to image spindles rely on fixation and transmission electron microscope or immunofluorescence staining and fluorescence microscope, so they provide limited value to studies of spindle dynamics and human clinical in vitro fertilization. A new orientation-independent polarized light microscope, the LC Polscope, was used to examine the bi-refringent spindles in living mammalian oocytes. It was found that spindles could be imaged with the Polscope in living oocytes in all mammals so far examined, including hamster, mouse, cattle, human, and rat. The first polar body did not accurately predict the spindle location in most metaphase II oocytes. Intracytoplasmic sperm injection (ICSI) could be performed by monitoring spindle position. Studies in humans indicated that, aftr ICSI, higher fertilization and embryonic developmental rates could be achieved in oocytes with than without bi-refringent spindles. Because spindles in most mammalian oocytes are extremely sensitive to slight changes in temperature, maintenance of temperature at 37 degrees C is crucial for normal spindle function. As chromosomes#10; are usually associated with microtubule fibers in the spindles, the position of chromosomes could be indirectly located by imaging spindles. Removing spindles under the Polscope can achieve an enucleation#10; efficiency rate of 100% in mouse oocytes. The Polscope can also be used to examine the spindle dynamics, detect spindle morphology, predict chromosome misalignment, and perform spindle transfer.

Animals↗

PubMed2003

Meiotic spindle location and identification and its effect on embryonic cleavage plane and early development.

BACKGROUND: To examine the relationship between the meiotic spindle, the first cleavage plane and any resulting influence on embryonic development parameters. METHODS: Sibling oocytes (n = 246) were allocated to either a control [polar body (PB)-aligned] or a treatment (spindle-aligned) microinjection group by use of a random numbers table. Spindles were identified by PolScope((R)) and the early embryo development parameters, and angle of first cleavage plane in relation to a defined animal-vegetal pole were analysed. RESULTS: Most oocytes (92.7%) had a visible spindle at the time of microinjection; however, 62.6% of first PBs (1PBs) were not located above the spindle (average deviation 37.3 +/- 33.2 degrees; range 0-176.6), with 6.9% of 1PBs in the opposite hemisphere to the spindle. The second PBs (2PBs) can also have an unpredictable deviation from the position of the meiotic spindle (12.5 +/- 16.7 degrees; range 0-91.8). This increased when the 1PB was above the spindle, forming a physical barrier to extrusion (average 24.7 +/- 16.1 degrees; range 7.9-91.8). Embryos developing from the spindle-aligned microinjection group had significantly more blastomeres per embryo (P = 0.044), a higher morphology score per embryo (P = 0.008) and a significantly higher average embryo score parameter (P = 0.003), with more embryos developing without any detectable fragmentation (P < 0.05) than the PB-aligned control group. Non-fragmented embryos undergo meridional cleavage, with a small angle between the spindle location and first cleavage plane (16.4 +/- 14.0 degrees ) compared with embryos with some degree of fragmentation (P = 0.002). This angle increased with the degree of fragmentation, with worst quality embryos having a spindle:cleavage angle of 45.1 +/- 17.7 degrees. CONCLUSIONS: The 1PB and, to a lesser degree, the 2PB can be unreliable predictors of the exact meiotic spindle location in human oocytes. Embryos from spindle-aligned oocytes have an increase in all measured development parameters over control siblings. When the animal pole is defined as the meiotic spindle location, non-fragmented embryos tend to develop from a meridional cleavage; with the most fragmented embryos developing from a more equatorial initial cleavage plane. This study proposes that the spindle accurately marks the animal pole in human oocytes, and provides evidence linking the meiotic spindle location to the first cleavage plane and resulting early embryo development parameters in human embryos.

Adult↗

PubMed2003

[Histochemical study of the sensory endings of muscle spindles in rat longissimus muscles].

Most studies concerning the structure and function of muscle spindles have utilized the hind limbs of experimental animals. However, little is known about muscle spindles of the back muscles. The purpose of this study was to investigate the sensory innervation of muscle spindles of the paravertebral muscle in the rat. The subjects were 10 normal male rats. The longissimus muscles were isolated and frozen in cooled isopentane (-160 degrees C), and serial transverse sections were made with a cryostat. Histochemical preparations were then made using nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) stain and modified Gomori-trichrome stain. The muscle spindles in each segment were identified microscopically by observing the equatorial and polar regions. NADH-TR staining was employed to distinguish nuclear bag1, nuclear bag2, and nuclear chain intrafusal muscle fibers. A total of 20 spindle poles were surveyed. The mean polar length of intrafusal fibers as well as that of each region (A, B, and C) were measured. NADH-TR staining also demonstrated the terminal sites of sensory fibers along intrafusal fibers. All spindle poles surveyed were innervated by secondary sensory fibers in addition to primary sensory fibers. Eight spindle poles were intermediate type muscle spindles that were innervated by one primary sensory fiber and one secondary sensory fiber. Twelve spindle poles were complex type muscle spindles that were innervated by one primary sensory fiber and multiple secondary sensory fibers. The mean length of the A region was 223.1+/-37.9 microm (n=8) for intermediate type spindles and 493.8+/-157.0 microm (n=12) for complex type spindles. The length of the A region was significantly longer in the complex type spindles than in the intermediate type spindles (p<0.001). The results suggest that the innervations of secondary sensory fibers were well developed in the longissimus muscle spindles in the rat. The morphological features of muscle spindles of the longissimus muscle may represent the structural basis for qualitatively different afferent discharges that relate to the characteristic types of locomotion served by paravertebral muscles.

Animals↗

PubMed1979

Chromosome movement and spindle birefringence in locally heated cells: interaction versus local control.

A microheater was used to produce a temperature gradient within the mitotic spindle of living cells. The slope of the temperature gradient was estimated from thermal conductivity calculations and confirmed by measurements of spindle birefringence and by experiments on striated muscle. When the microheater was placed at one spindle pole or at one group of kinetochores, the gradient was steep enough to cause a large difference in birefringence between the two half-spindles, but the velocity of chromosome movement in anaphase was nearly the same in the warmer and cooler half-spindles. When the heater was shifted from the pole toward the interzone, the average velocity of chromosome movement increased approximately two-fold but was, again, nearly uniform in the two half-spindles. The rate of spindle elongation was especially sensitive to the site of heating, increasing ten-fold when the heater was shifted from the pole to the interzone. Regardless of heater position, the rate of chromosome movement was determined largely by the temperature of the coolest spindle region--chromosomes in the warmer half-spindle moved more slowly than expected from estimates of the temperature in that region. Since the microheater produces a substantial temperature gradient within the spindle, the near uniformity of chromosome velocity in both half-spindles must be due to some biological property of the spindle. Two very different explanations for the results are considered the most likely. According to one explanation, the near uniformity of velocity in both half-spindles is determined by the structure of the interpolar spindle, while changes in velocity involve force producers located both in the half-spindles and in the interzone. On the other explanation, the velocity is nearly the same in both half-spindles because the force producers are located exclusively in the interzone (Margolis et al., 1978).

Anaphase↗

PubMed1975

Barbiturate spindle activity in functionally corresponding thalamic and cortical somato-sensory areas in the cat.

(1) Spontaneous barbiturate spindles were recorded from a locus in the thalamic nucleus ventralis postero-lateralis (VPL) and the corresponding projection area in the somato-sensory cortex (SI) in the cat. (2) Type I spindles32 recorded from such sites in the thalamus and cortex, regarded as being functionally on line, were cross-correlated. The analysis gave high negative cross-correlation coefficients, indicating that a considerable degree of wave synchrony existed between the spindles. Maximal wave synchrony was present in the first and middle part of the spindle. (3) The thalamo-cortical spindle wave synchrony was reduced by a small displacement of the cortical electrode within the somato-sensory cortex. Starting with a very lightly anaesthetized animal, small amounts of barbiturate did not influence the size of the cortical area which had spindles in synchrony with the thalamic spindles. (4) Spindles recorded from a VPL locus and from its cortical projection site started simultaneously. When the thalamic and cortical electrodes were positioned functionally off line this spindle coincidence decreased. The intervals between the spindle onsets increased with increasing off line positions of the electrodes. Those few thalamic and cortical spindles which occurred simultaneously showed no, or only weak, spindle wave synchrony. (5) These data suggest a point-to-point topographical relation between thalamic and cortical loci engaged in barbiturate spindle activity. (6) Type I and type II spindles32 differed with respect to spindle characteristics (amplitude, duration, incidence) and also with respect to corresponding thalamic rhythmic activity. These spindle types are, therefore, probably produced by different mechanisms. We suggest that type II spindles represent a purely cortical process initiated by type I spindles.

Animals↗

PubMed1997

Spindle oscillations during cortical spreading depression in naturally sleeping cats.

Spindling activity characterizes the EEG of animals and humans in the early stages of resting sleep. Spindles are defined as waxing and waning rhythmic waves at 7-14 Hz that recur periodically every 3-10 s. Spindling originates in the thalamus, but a role for the cerebral cortex in triggering and synchronizing thalamic spindles was shown by stimulation of the contralateral cortex avoiding antidromic activation of thalamocortical axons and by diminished coherency of thalamic spindles after hemidecortication. Spontaneous spindles under barbiturate anesthesia are waxing and waning but under ketamine-xylazine anesthesia or when evoked by strong stimuli spindle waves are almost exclusively waning, i.e. they start with maximum amplitude and then decrease progressively. Waxing and waning of spindles has been ascribed to progressive entrainment of units into the oscillation followed by a progressive desynchronization. Therefore, exclusively waning spindles would be produced by an initial high synchrony in the corticothalamic network. Such a situation is observable upon strong stimulation or, spontaneously, when spindles are paced by the slow cortical oscillation and preceded by a strong corticothalamic drive. We have conducted experiments in naturally sleeping cats to verify the occurrence of two patterns of spindle oscillations and to test the role of the cortex in synchronizing and shaping spindles. We have found that indeed two types of spindles (waxing and waning or mostly waning) occur in naturally sleeping animals. We also demonstrate that during cortical spreading depression spindles are less synchronous and only of the waxing and waning type. As cortical activity recovers, waning spindles reappear and are preceded by electroencephalogram deflections which are related to corticothalamic depolarizing inputs. Our results strongly support the hypothesis of the role of the cerebral cortex in shaping and synchronizing thalamically generated spindles.

Animals↗

PubMed1995

The impact of chromosomes and centrosomes on spindle assembly as observed in living cells.

We analyzed the role that chromosomes, kinetochores, and centrosomes play in spindle assembly in living grasshopper spermatocytes by reconstructing spindles lacking certain components. We used video-enhanced, polarization microscopy to distinguish the effect of each component on spindle microtubule dynamics and we discovered that both chromosomes and centrosomes make potent and very different contributions to the organization of the spindle. Remarkably, the position of a single chromosome can markedly affect the distribution of microtubules within a spindle or even alter the fate of spindle assembly. In an experimentally constructed spindle having only one chromosome, moving the chromosome to one of the two poles induces a dramatic assembly of microtubules at the nearer pole and a concomitant disassembly at the farther pole. So long as a spindle carries a single chromosome it will persist normally. A spindle will also persist even when all chromosomes are detached and then removed from the cell. If, however, a single chromosome remains in the cell but is detached from the spindle and kept in the cytoplasm, the spindle disassembles. One might expect the effect of chromosomes on spindle assembly to relate to a property of a specific site on each chromosome, perhaps the kinetochore. We have ruled out that possibility by showing that it is the size of chromosomes rather than the number of kinetochores that matters. Although chromosomes affect spindle assembly, they cannot organize a spindle in the absence of centrosomes. In contrast, centrosomes can organize a functional bipolar spindle in the absence of chromosomes. If both centrosomes and chromosomes are removed from the cell, the spindle quickly disappears.

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