Biomedical subjects

G Bosco

Publications and source records attributed to G Bosco.

At least 19 recordsLinked to original sources

PubMed2001

DNA replication control through interaction of E2F-RB and the origin recognition complex.

The E2F transcription factor and retinoblastoma protein control cell-cycle progression and DNA replication during S phase. Mutations in the Drosophila dE2F1 and dDP genes affect the origin recognition complex (DmORC) and initiation of replication at the chorion gene replication origin. Here we show that mutants of Rbf (an retinoblastoma protein homologue) fail to limit DNA replication. We also show that the dDP, dE2F1 and Rbf proteins are located in a complex with DmORC, and that dE2F1 and DmORC are bound to the chorion origin of replication in vivo. Our results indicate that dE2F1 and Rbf function together at replication origins to limit DNA replication through interactions with DmORC.

Animals↗

PubMed2000

Information processing in the spinocerebellar system.

The purpose of this study was to determine whether sensory information about limb kinematics relayed to the cerebellum over spinocerebellar pathways may be modified at the cerebellar level. We tested this by recording from dorsal spinocerebellar tract (DSCT) and Purkinje cells under the same experimental conditions in which the hindlimbs of anesthetized cats were passively moved through a series of step-like movement cycles. A population analysis of the response behavior showed that DSCT neurons encode a combination of limb axis position and movement velocity, whereas the Purkinje cells located in the DSCT cerebellar target areas encode limb axis velocity and position independently. We conclude from this that the cerebellum may somehow extract a velocity component from the afferent input signal.

Action Potentials↗

PubMed2000

Sensory representation of passive movement kinematics by rat's spinocerebellar Purkinje cells.

In this paper we examined Purkinje cells' sensory representations of kinematic parameters of passive movements imposed to the forelimb of anesthetized rats. Simple spike Purkinje cell activity was recorded while the rat's ipsilateral forearm was moved passively along circular footpaths at two different speeds. We found that the activity of 35.33% (165/467) of the neurons was significantly modulated during movement cycles. A multivariate regression analysis indicated that movement direction was the predominant factor in determining Purkinje cell activity, whereas movement velocity (i.e. the combination of movement direction and speed) was represented to a much lesser degree. Based on this result, we might suggest that a cortical efferent copy is necessary to the cerebellum in order to elaborate a movement velocity signal.

Action Potentials↗

PubMed2000

Distribution of spinocerebellar Purkinje cell responses to passive forelimb movements in the rat.

We recorded Purkinje cell activity throughout the spinocerebellum of anaesthetized rats while imposing circular passive movements to the unrestrained forelimb. The aim was to understand the type of processing of sensory information occurring at the level of the cerebellar cortex, on the basis that precerebellar sensory neurons have been shown to represent whole limb movement parameters better than single joint movements. We observed that neurons representing sensory aspects of arm movements were scattered throughout the spinocerebellar cortex without a distinct segregation from those that did not respond, albeit the relative density of responsive and unresponsive neurons was quite variable and depended on the area of the cortex. Furthermore, Purkinje cells that responded significantly to the arm movement cycles all showed the same response pattern consisting of a firing rate increase during the downward extension of the arm. These results are discussed as suggesting a coordinate framework for the representation of proprioceptive information in the cerebellum congruent to that observed for encoding motor parameters.

Animals↗

PubMed2000

Reference frames for spinal proprioception: limb endpoint based or joint-level based?

Many sensorimotor neurons in the CNS encode global parameters of limb movement and posture rather than specific muscle or joint parameters. Our investigations of spinocerebellar activity have demonstrated that these second-order spinal neurons also may encode proprioceptive information in a limb-based rather than joint-based reference frame. However, our finding that each foot position was determined by a unique combination of joint angles in the passive limb made it difficult to distinguish unequivocally between a limb-based and a joint-based representation. In this study, we decoupled foot position from limb geometry by applying mechanical constraints to individual hindlimb joints in anesthetized cats. We quantified the effect of the joint constraints on limb geometry by analyzing joint-angle covariance in the free and constrained conditions. One type of constraint, a rigid constraint of the knee angle, both changed the covariance pattern and significantly reduced the strength of joint-angle covariance. The other type, an elastic constraint of the ankle angle, changed only the covariance pattern and not its overall strength. We studied the effect of these constraints on the activity in 70 dorsal spinocerebellar tract (DSCT) neurons using a multivariate regression model, with limb axis length and orientation as predictors of neuronal activity. This model also included an experimental condition indicator variable that allowed significant intercept or slope changes in the relationships between foot position parameters and neuronal activity to be determined across conditions. The result of this analysis was that the spatial tuning of 37/70 neurons (53%) was unaffected by the constraints, suggesting that they were somehow able to signal foot position independently from the specific joint angles. We also investigated the extent to which cell activity represented individual joint angles by means of a regression model based on a linear combination of joint angles. A backward elimination of the insignificant predictors determined the set of independent joint angles that best described the neuronal activity for each experimental condition. Finally, by comparing the results of these two approaches, we could determine whether a DSCT neuron represented foot position, specific joint angles, or none of these variables consistently. We found that 10/70 neurons (14%) represented one or more specific joint-angles. The activity of another 27 neurons (39%) was significantly affected by limb geometry changes, but 33 neurons (47%) consistently elaborated a foot position representation in the coordinates of the limb axis.

Action Potentials↗

PubMed2000

Reference frames for spinal proprioception: kinematics based or kinetics based?

This second paper of the series deals with another issue regarding sensorimotor representations in the CNS that has received much attention, namely the relative weighting of kinematic and kinetic representations. The question we address here is the contribution of muscle tension afferent information in dorsal spinocerebellar tract (DSCT) sensory representations of foot position. In five anesthetized cats, we activated major hindlimb muscle groups using electrical stimulation of ventral root filaments while passively positioning of the left hind foot throughout its workspace. In general, as the parameters of the joint angle covariance planes indicated, muscle stimulation did not significantly change hindlimb geometry. We analyzed the effects of the muscle stimulation on DSCT neuronal activity within the framework of a kinematic-based representation of foot position. We used a multivariate regression model described in the companion paper, wherein indicators of the experimental condition were added as firing rate predictors along with the limb axis length and orientation to account for possible effects of muscle stimulation. The results indicated that the response gain of 35/59 neurons studied (59%) was not changed by the muscle activations, although most neurons showed some change in their overall firing level with stimulation of one or more muscles. Most of the neurons responded to pseudorandom stimulation of the same muscle groups with complex temporal patterns of activity. For a subpopulation of 42 neurons, we investigated the extent to which their representation of foot position was affected by a rigid constraint of the knee joint and at least one type of muscle stimulation. Although they could be divided into four subgroups based on significance level cutoffs for the constraint or stimulation effect, these effects were in fact quite distributed. However, when we examined the preferred directions of spatial tuning relative to the limb axis position, we found it was unchanged by muscle stimulation for most cells. Even in those cases in which response gain was altered by muscle stimulation, the cell's preferred direction generally was unaltered. The invariance of preferred direction with muscle stimulation lead us to the conclusion that the reference frame for DSCT coding may be based primarily on limb kinematics.

Action Potentials↗

PubMed2000

C-Fos expression in the basilar pontine nuclei and reticulotegmental nucleus of the rat following lateral cerebellar nucleus stimulation.

The present study was carried out with the aim to observe whether, in the rat, the electric activation of the projection form the cerebellar lateral nucleus (LN) to the basilar pontine nuclei (BPN) and to the reticulotegmental nucleus (RtTg) is capable to induce the c-Fos expression. In particular, we compared the effects of a continuous LN stimulation at low-frequency (tonic stimulation) with those induced by high frequency pulse trains (phasic stimulation). The observed results show that the stimulation of LN induces c-Fos expression in a significant fraction of neurons in the contralateral BPN and RtTg. It was also observed that phasic stimulation was slightly more capable in producing c-Fos expression with respect to the tonic stimulation. Furthermore, systemic injection of MK-801, a non-competitive antagonist of the NMDA receptor, reduced the LN-induced c-Fos expression in BPN and RtTg. In contrast, GYKI 52466, an AMPA/kainate receptor antagonist, did not change the LN driven induction of c-Fos in both BPN and RtTg.

Animals↗

PubMed1999

Cortical control of cerebellar dentato-rubral and dentato-olivary neurons.

The cortical input of 117 dentate nucleus neurons projecting either to the red nucleus (73 cells) or to the inferior olive (44 units) was studied electrophysiologically in rats. The majority of cells in both groups responded to electrical stimulation of discrete sites of the contralateral motor cortex. However, activation latencies from the same cortical focus were shorter for neurons projecting to the red nucleus than for olivary-projecting neurons. Principal components analysis pointed out significant differences between the two neuronal subgroups also in the temporal pattern of activity. These results suggest that a motor command might be transmitted through parallel independent channels to cerebellar neurons projecting to different regions of the brainstem.

Animals↗

PubMed1999

On the relation of rat's external cuneate activity to global parameters of forelimb posture.

Using anesthetized adult rats, we studied the relationships between the activity of cells belonging to the external cuneate nucleus (ECN) and passive forelimb positions. In essence, we sought to distinguish between a representation of limb position based on local limb parameters (individual joint angles, for example) or a representation based on more global parameters such as the length and the orientation of the limb axis. Using multivariate regression analyses we found that most neurons showed strong linear relationships with the length and the orientation of the limb axis. Relationships to individual joint angles were, instead, rather weak and in most cases not significant. This result implies an extensive integration of sensory information at the level of second order sensory neurons.

Animals↗

PubMed1999

ORC localization in Drosophila follicle cells and the effects of mutations in dE2F and dDP.

We isolated mutations in Drosophila E2F and DP that affect chorion gene amplification and ORC2 localization in the follicle cells. In the follicle cells of the ovary, the ORC2 protein is localized throughout the follicle cell nuclei when they are undergoing polyploid genomic replication, and its levels appear constant in both S and G phases. In contrast, when genomic replication ceases and specific regions amplify, ORC2 is present solely at the amplifying loci. Mutations in the DNA-binding domains of dE2F or dDP reduce amplification, and in these mutants specific localization of ORC2 to amplification loci is lost. Interestingly, a dE2F mutant predicted to lack the carboxy-terminal transcriptional activation and RB-binding domain does not abolish ORC2 localization and shows premature chorion amplification. The effect of the mutations in the heterodimer subunits suggests that E2F controls not only the onset of S phase but also origin activity within S phase.

Animals↗

PubMed1999

Low sensitivity of dorsal spinocerebellar neurons to limb movement speed.

This paper reports the effect of limb movement speed on dorsal spinocerebellar tract (DSCT) activity recorded while the cat hindlimb was passively moved through two types of foot trajectories (figure eight and step cycle) at different speeds. While nearly all the DSCT neurons sampled (151/159; 94.5%) were significantly modulated by the direction of foot movement in these trajectories, they were only modestly influenced by movement speed. We quantified the speed effect and also accounted for intrinsic cell variability by computing a variability index (VI) between pairs of responses to trajectories made either at the same or at different speeds. The distribution of same-speed VIs across cells indicated a mean variability of about 10% over a trajectory cycle, whereas the two-speed distributions indicated a mean change of about 25% for a two- to fourfold change in movement speed. We also examined the relative contribution of movement speed to the activity of each DSCT cell by means of a multivariate regression model that also included as predictors the position, movement direction, and interactions between movement and position. We found that 28 of 103 (27.2%) neurons were not sensitive to movement speed. The rest were modulated in varying degrees by changes in speed, and the speed modulation depended on limb position for most of them (54/75). Overall, DSCT speed sensitivity resembles the 0.3-power relationship used to describe the velocity sensitivity of muscle spindles for large muscle stretches. We examined this by recording muscle spindle activity during these passive foot trajectories and found that their speed sensitivity was within the range observed for the DSCT and explained by the 0.3-power law. In total, movement speed accounted for about 15% of the variance in DSCT activity across cells, while the directional component of movement accounted for about 45%. The results suggest a separate processing of sensory information about the two components of movement velocity: namely, its direction and magnitude.

Animals↗

PubMed1998

Telomere maintenance is dependent on activities required for end repair of double-strand breaks.

Telomeres are functionally distinct from ends generated by chromosome breakage, in that telomeres, unlike double-strand breaks, are insulated from recombination with other chromosomal termini [1]. We report that the Ku heterodimer and the Rad50/Mre11/Xrs2 complex, both of which are required for repair of double-strand breaks [2-5], have separate roles in normal telomere maintenance in yeast. Using epistasis analysis, we show that the Ku end-binding complex defined a third telomere-associated activity, required in parallel with telomerase [6] and Cdc13, a protein binding the single-strand portion of telomere DNA [7,8]. Furthermore, loss of Ku function altered the expression of telomere-located genes, indicative of a disruption of telomeric chromatin. These data suggest that the Ku complex and the Cdc13 protein function as terminus-binding factors, contributing distinct roles in chromosome end protection. In contrast, MRE11 and RAD50 were required for the telomerase-mediated pathway, rather than for telomeric end protection; we propose that this complex functions to prepare DNA ends for telomerase to replicate. These results suggest that as a part of normal telomere maintenance, telomeres are identified as double-strand breaks, with additional mechanisms required to prevent telomere recombination. Ku, Cdc13 and telomerase define three epistasis groups required in parallel for telomere maintenance.

Antigens, Nuclear↗

PubMed1998

Spinocerebellar Purkinje cells and rat forelimb postures: a direction-dependent activity.

On anesthetized adult rats, we examined the possibility that the discharges of spinocerebellar Purkinje cells (PCs) are modulated by passive limb positioning. The rat forelimb was passively placed in four different sagittal positions while the simple spike spontaneous activity of single PCs was recorded; recordings started 5 s after the reaching of the posture and the forelimb remained at each position for at least 30 s. Although the activity of the PCs did not reflect the forelimb position, it showed hysteresis that depended in a cosine fashion on the direction of the preceding movement. This implies that the directional sensitivity of spinocerebellar PCs is persistent, since the activity levels were almost constant throughout the recording time.

Action Potentials↗

PubMed1998

Spatial organization of proprioception in the cat spinocerebellum. Purkinje cell responses to passive foot rotation.

This study examines the spinocerebellar locations of Purkinje cells that responded to passive foot rotations at the ankle joint in anaesthetized cats. Using a novel approach for mapping the locations of recorded cells from several animals onto an unfolded two-dimensional representation of the cortex, we found that cells distributed throughout the anterior-posterior extent of the spinocerebellar cortex, except in the most medial parts corresponding to zones a and b, were responsive to ankle joint rotation. The cell distributions revealed a clustering according to their response amplitudes, which showed evidence for both parasagittal and transverse banding.

Animals↗

PubMed1998

Chromosome break-induced DNA replication leads to nonreciprocal translocations and telomere capture.

In yeast, broken chromosomes can be repaired by recombination, resulting in nonreciprocal translocations. In haploid cells suffering an HO endonuclease-induced, double-strand break (DSB), nearly 2% of the broken chromosome ends recombined with a sequence near the opposite chromosome end, which shares only 72 bp of homology with the cut sequence. This produced a repaired chromosome with the same 20-kb sequence at each end. Diploid strains were constructed in which the broken chromosome shared homology with the unbroken chromosome only on the centromere-proximal side of the DSB. More than half of these cells repaired the DSB by copying sequences distal to the break from the unbroken template chromosome. All these events were RAD52 dependent. Pedigree analysis established that DSBs occurring in G1 were repaired by a replicative mechanism, producing two identical daughter cells. We discuss the implications of these data in understanding telomerase-independent replication of telomeres, gene amplification, and the evolution of chromosomal ends.

Chromosomes, Fungal↗

PubMed1997

Minimally invasive coronary artery bypass grafting on a beating heart.

BACKGROUND: We reviewed our experience with left internal mammary artery (LIMA)-to-left anterior descending artery (LAD) anastomosis on a beating heart through a left anterior small thoracotomy. METHODS: This procedure was performed in 343 of 358 scheduled patients; in 15 (4.2%) the LAD was not suitable or was too small. The chest was opened in the fourth (127, 37.0%) or fifth (197, 57.4%) intercostal space, or both (19, 5.6%); the length of the harvested LIMA was 4-15 cm. The LAD was occluded by means of two 4-0 Prolene (Ethicon, Somerville, NJ) sutures, both snared on a small piece of silicone tubing. The anastomosis was performed with two 8-0 Prolene sutures. In the early postoperative period all patients underwent angiography or a doppler flow assessment of the LIMA or both. RESULTS: In 310 patients the LIMA was connected directly to the LAD; to elongate the LIMA, in 30 patients an inferior epigastric artery and in 3 patients a saphenous vein was used. In 2 patients the diagonal branch was also grafted using an inferior epigastric artery from the LIMA. Three patients (0.9%) died during the first 30 days after the operation, and 4 other patients (1.2%) died after the first month. Twenty-five patients (7.3%) were reoperated on because of anastomotic or conduit failure, 18 (5.2%) early and 7 (2.1%) late; one additional patient had a late percutaneous transluminal coronary angioplasty for anastomotic stenosis. At a mean of 9.5 +/- 5.7 months of follow-up, 336 patients (98.0%) were alive, asymptomatic with or without medical treatment, and without cardiac events. COMMENT: Left internal mammary artery-to-LAD anastomosis performed on a beating heart through a left anterior small thoracotomy is a procedure that can be performed with low risk and acceptable midterm results in selected patients.

Adult↗

PubMed1997

LDL apheresis in a homozygous familial hypercholesterolemic child aged 4.5.

Preliminary experience with the efficacy and safety of dextran sulfate cellulose low-density lipoprotein (LDL) apheresis for the treatment of a 4.5-year-old girl with homozygous familial hypercholesterolemia and coronary artery disease is reported. The decrease of the most atherogenic apolipoprotein B-containing lipoproteins, low-density lipoprotein (LDL) and lipoprotein(a) (Lp [a]), were in the ranges of 63.1-68.7%, and 52.5-58.6%, respectively. The child tolerated LDL apheresis without any clinically significant complications. Therefore, she was submitted to a long-term program of treatment at intervals of 15 days. The experience suggests the possibility of an early beginning of extracorporeal treatment with LDL apheresis in children severely affected by homozygous or double heterozygous familial hypercholesterolemia.

Blood Component Removal↗

PubMed1997

Representation of multiple kinematic parameters of the cat hindlimb in spinocerebellar activity.

Dorsal spinocerebellar tract (DSCT) neurons have been shown to transmit signals related to hindlimb position and movement direction in the anesthetized cat. Because both parameters may be encoded by single neurons, we examined the extent to which their representations might occur sequentially or simultaneously by recording unit activity while the hindlimb was moved passively in the sagittal plane by a robot arm. A center-out/out-center paradigm moved the foot 2 cm from a given position radially to eight positions located 45 degrees apart, holding each position for 8 s. Another paradigm moved the foot along various paths to 20 positions distributed throughout most of the limb's workspace. With each paradigm, we could assess the activity related to foot position and the direction of movement to each position. Modulation of unit activity evoked by center-out/out-center movements was determined for each 1-s postmovement interval by use of a cosine tuning model that specified modulation amplitude and preferred direction. Of 125 units tested, 82.4% were significantly modulated (P < 0.05) according to this model. We assessed the relative contributions of position and movement by taking advantage of the fact that directional modulation following out-center movements to a common position could only be related to the movement, whereas that following the center-out movements related to both position and movement. The results suggested a simultaneous modulation by these two parameters. Each cell could be characterized by a similar preferred direction for position or movement modulation and the distribution of preferred directions across cells clustered significantly along an axis close to the limb axis. When the limb axis was rotated, the unit preferred directions rotated similarly, on average. Unexpectedly, we found the activity of more than half the cells to be modulated for > or = 8 s after out-center movements, implying a persistent movement-related activity well after a movement is completed. These findings were confirmed and extended with the second paradigm by using a multivariate regression model that included terms for position, movement, and their multiplicative interaction. The activity of 81.3% of the 97 neurons tested fit the model (R2 > 0.4, P < .0001); 31.6% were modulated exclusively by foot position, and 58.2% simultaneously by both position and movement, with significant interaction. We conclude from our results that DSCT neurons may be modulated simultaneously by limb position and movement, and their preferred directions tend to align with the limb axis. The modulation is interactive such that movement modulation amplitude depends on limb position, and many cells also retain a memory trace of recent movements. The results are discussed in terms of a possible role for the DSCT in encoding limb compliance.

Animals↗