Motor coordination and spatial orientation are affected by neurofilament maldistribution: correlations with regional brain activity of cytochrome oxidase

 NFH-LacZ transgenic mice are characterized by an early accumulation of the neurofilament cytoskeleton in the cell bodies of neurons with age-associated abnormalities of motor neurons and cerebellar Purkinje cells. In comparison to normal littermate controls, irrespective of age (3 and 12–20 months), NFH-LacZ transgenic mice had a lower number of rears in an open field, deficiencies in some motor-coordination tests, and a higher number of quadrant entries and escape latencies while swimming toward a visible platform. Decreased cytochrome oxidase activity in the lateral reticular nucleus of NFH-LacZ mice was associated with poor performance in two motor coordination tests. Lower metabolic activity in the lateral reticular nucleus may be secondary to previously described cerebellar abnormalities, leading to deficient motor control. The dramatic cytoskeletal perturbation characterizing NFH-LacZ mice affects only selective neuronal populations and results in selective behavioral deficits, which can be correlated with regional brain metabolic activity. Received: 10 July 1998 / Accepted: 28 December 1998     

Regional brain variations of cytochrome oxidase activity and motor coordination in Girk2(Wv) (Weaver) mutant mice

The Girk2(Wv) (weaver) phenotype, caused by a mutated inward rectifying potassium channel, is characterized by degeneration of cerebellar granule cell population as well as midbrain dopamine-containing cells of the nigrostriatal pathway. To investigate the regional brain metabolic consequences of this combined pathology, cytochrome oxidase (CO) activity was measured by histochemistry from brain regions of wild-type and homozygous Girk2(Wv) mutant mice and correlated with motor performances. CO activity of Girk2(Wv) mutants was abnormal in cerebellar cortex, dentate nucleus, and brainstem regions (medial and lateral vestibular nuclei, prepositus, superior colliculus, lateral cuneiform nucleus, and reticular nuclei) implicated in the gaze system. CO activity increased in midbrain dopaminergic regions after correcting for tissue density, regions with severe depletion of tyrosine hydroxylase activity. Forebrain regions were relatively spared in term of CO activity, except for subthalamic nucleus, lateral geniculate nucleus, and cortical eye field. Similarly to the Rora(sg) cerebellar mutant, metabolic alterations in cerebellar and vestibular regions were linearly correlated with poor motor coordination, underlining the sensitivity of these tests to cerebellar dysfunction.     

Impaired motor skills on static and mobile beams in lurcher mutant mice

 The cerebellum plays a role in various sensorimotor learning tasks. The purpose of the present studies was to evaluate sensorimotor skills in a spontaneous mouse mutant with cerebellar cortical atrophy. Lurcher mutant mice, characterized by massive losses of cerebellar granule cells and Purkinje cells, were assessed on two static beams varying in width and on an accelerating rotorod. On the static beams, lurcher mutants were deficient in stable positioning while immobile. Contrary to normal mice, they retreated backwards involuntarily and clung off-balance to the side of the beams. However, lurcher mutants were not deficient in segment crossings, body turns, latencies before crossing the first segment, and time spent in motion. There was an improvement over days in static stable positioning on both beams. On the rotorod, although lurcher mutants fell sooner and were inferior to controls in maximal speed of rotation achieved, there was an improvement on both measures across days. Moreover, retention of this motor skill was normal. These results indicate that, although lurcher mutants are limited in their capacity to execute motor coordination tasks, postural sensorimotor learning is not abolished in the absence of cerebellar cortical output neurons. Received: 26 July 1996 / Accepted: 25 February 1997     

Regional brain variations of cytochrome oxidase activity and motor co-ordination in staggerer mutant mice

A mutant mouse with cerebellar cortical atrophy, staggerer, was examined in tests of motor activity and co-ordination as well as in regional brain metabolism as assessed by cytochrome oxidase activity. Compared with non-ataxic controls, staggerer mutants had inferior performances in the open field, the wooden beam, the wooden edge, and the rotorod tests. An increase in cytochrome oxidase activity in the deep cerebellar nuclei and in some cerebellar efferent regions, such as the lateral vestibular nucleus, the parvicellular red nucleus, and the ventral tegmental area, was found in staggerer mutant mice. Abnormally high cytochrome oxidase activity in the interpositus and the dentate nuclei was linearly correlated with poor performance on the wooden beam and on the rotorod. High cytochrome oxidase activity in the lateral vestibular nucleus was also associated with poor performance on the wooden beam. Moreover, high cytochrome oxidase activity in the fastigial nucleus was associated with poor performance on the wooden beam but with high motor activity in the open field. These results indicate that a lack of innervation of Purkinje cells to the deep cerebellar nuclei is in part the cause of motor co-ordination deficits in staggerer mutant mice.     

Absence of an association between motor coordination and spatial orientation in lurcher mutant mice

Lurcher mutant mice were impaired in spatial orientation and motor coordination in comparison to normal mice. Both groups improved across days in both invisible and visible water maze platform conditions. Contrary to normal mice, lurcher mutants did not improve over days in terms of the time taken to reach a side-bar in a motor coordination test, an indication of defective motor learning. However, lurchers were able to stay on the bar longer across days. These results indicate that motor learning deficits in this cerebellar-damaged animal are not absolute but dependent on the type of measurement attempted. There was no correlation between motor coordination and spatial orientation for normal mice. A similar absence of correlation was noted for lurcher mutants, except for falling latencies in the coat-hanger test during the middle of training.     

Regional brain variations of cytochrome oxidase activity in spontaneously hypertensive mice

To explore the central disturbances resulting from blood pressure changes, spontaneously hypertensive mice (SHM) were compared to normotensive controls for cytochrome oxidase (CO) activity, an index of oxidative capacity in the central nervous system and a marker of long-term regional brain metabolism and neuronal activity. In all brain areas presenting significant enzymatic variations, only increases in CO activity were found in SHM, particularly the central autonomic network. However, only specific regions were affected, namely the insular cortex and the hypothalamic nuclei principally involved in high-order autonomic control. Altered limbic structures included the lateral septum, various hippocampal subregions, as well as prelimbic cortex. CO activity was also elevated in several forebrain regions, including those directly connected to the limbic system, such as the nucleus accumbens, the claustrum, and dorsomedial and reticular thalamic nuclei, as well as subthalamic and ventrolateral thalamic nuclei. In the brainstem, the only regions affected were the locus coeruleus, site of noradrenergic cell bodies, the trigeminal system, and four interconnected regions: the inferior colliculus, the paramedial reticular formation, the medial vestibular, and the cerebellar fastigial nuclei. These data show that specific regions modulating sympathetic nerve discharge are activated in young adult SHM, possibly due to mitochondrial dysfunction and excitotoxicity.     

Effects of corticosterone synthesis inhibitor metyrapone on anxiety-related behaviors in Lurcher mutant mice

Beyond their motor impairments, the cerebellar Lurcher mutant mice show an alteration of the anxiety-related behaviors we called “behavioral disinhibition”. This is characterized by a low avoidance towards the open arms of the elevated plus-maze device paradoxically combined with a dramatic blood corticosterone level rise induced by the exposure to the experimental conditions. The present study was aimed at determining if the disinhibition of the mutants could be caused by their stress-induced high corticosterone rate. For this purpose, we compared the behaviors of Lurcher and control mice in the elevated plus-maze test after injection of either 2-methyl-1.2-di-3-pyridil-1-propanone (metyrapone; 75 mg/kg), a corticosterone synthesis inhibitor, or vehicle alone (Tween 80, 5%). Our results showed that metyrapone, although efficiently reducing their blood corticosterone rate, provoked only modest modifications of the anxiety-related behaviors in mice of both genotypes. As a result, the behavioral distance between the Lurcher and control mice slightly decreased, without being totally abolished. Thus, it seems that the behavioral disinhibition of the mutants is caused only in part by their stress-provoked high corticosterone level. As a complementary hypothesis, we propose that the behavioral disturbances observed in the Lurcher mice also might arise from dysfunctions of the neural pathways connecting the cerebellum with some limbic structures known to be highly involved in the regulation of emotions.     

Consequences of altered cerebellar input for the cortical regulation of motor coordination, as reflected in EEG potentials

The cerebellum is certainly involved in fine coordination of movements, but has no efferences of its own to the muscles. Thus, it can exert its influence only via other cerebral areas that have those efferences. This study investigated in patients with cerebellar atrophy how cortical motor areas are affected by dysfunction of the cerebellum. The main question was whether the patients’ slow cortical electroencephalogram (EEG) potentials during key-press preparation and execution would be generally altered or would be specifically altered when fine coordination was needed. In the coordination task, right- and left-hand keys had to be pressed simultaneously with different forces, under visual feedback. Control tasks were to press with both hands equally or with one hand only. The patients indeed had a performance deficit in the coordination task. Their cortical EEG potentials were already drastically reduced in the simple tasks, but were enhanced by the same amount as in healthy subjects when more coordination was needed. These results suggest that the cerebellum is not exclusively active in fine coordination, but is generally involved in any kind of preparatory and executive activity, whereas the motor cortex becomes more active with fine coordination. The role of the cerebellum might be to provide the motor cortex with information needed for coordinating movements. In cerebellar atrophy, this altered input may be sufficient for the motor cortex in controlling simple tasks, but not for complex ones. Received: 4 November 1998 / Accepted: 14 April 1999     

Load compensation during homologous and non-homologous coordination

Two-limb coordination of homologous and non-homologous effectors was examined during isofrequency (1:1) and multifrequency (2:1) conditions. The coordination patterns involved flexion and extension movements in the sagittal plane and were performed under unloaded and single-limb (right arm) loaded conditions. Previous studies suggested that the lower degree of 1:1 synchronization observed during nonhomologous as compared to homologous coordination results from natural differences in biophysical (inertial) properties. Elaborating on this idea, adding weight to the right arm was hypothesized to modulate its inertial characteristics, rendering homologous limbs more dissimilar and nonhomologous limbs more similar by enhancing and decreasing their inertial differences, respectively. Therefore, the observations made during unloaded conditions were predicted to be completely reversed during loaded conditions. Findings revealed that during 1:1 coordination (experiment 1) single-limb loading resulted in a decreased relative phase stability, whereas relative phase accuracy depended upon the limb combination. In particular, phase-locking was more accurately maintained for loaded homologous than for nonhomologous limbs, whereas loading the nonhomologous limbs resulted in a deterioration of the quality of synchronization. These findings suggest that there is an additional explanation of differential coordination capabilities among limb combinations. It is hypothesized that the neural networks subserving the control centers of the homologous limbs are more tightly connected than those of the nonhomologous effectors, allowing 1:1 synchronization to be more successfully preserved in the face of (load) perturbations. During 2:1 coordination (experiment 2), the loading procedure disturbed the coordination dynamics across all limb combinations. That no differential effect of loading on effector combination was observed is possibly a result of the fact that only an initial level of practice was studied in which optimal relative phase dynamics are still being explored for both homologous and nonhomologous limbs. Received: 7 May 1997 / Accepted: 16 January 1998     

Mss51p, a putative translational activator of cytochrome c oxidase subunit-1 (COX1) mRNA, is required for synthesis of Cox1p in Saccharomyces cerevisiae

 Mutants of Saccharomyces cerevisiae that lack a functional MSS51 gene are respiratory deficient due to the absence of cytochrome c oxidase subunit 1 (Cox1p). It has been previously suggested, but not formally proven, that Mss51p is required for translational activation of COX1 mRNA, rather than being involved in a subsequent step in the synthesis of Cox1p or its assembly into cytochrome c oxidase. Pulse-chase labelling experiments now show that the absence of detectable levels of Cox1p in mss51-null strains is indeed due to the lack of synthesis of Cox1p, and is not caused by reduced stability of the protein. To gain more insight into the exact function of Mss51p, we determined the subcellular localization of the protein. We were able to show that an epitope-tagged version of Mss51p (Mss51HA) complements the mutation and can be localized in mitochondria, where it is firmly associated with the mitochondrial inner membrane. In addition, we characterized the previously identified mutant allele mss51-3. Sequence analysis revealed the presence of a short open reading frame upstream of MSS51 resulting from the creation of an extra ATG startcodon. Received: 3 December 1999 / 5 January 2000     

Regional variations of cytochrome oxidase activity in the central auditory system of Relnrl-Orl (reeler) mutant mice

Despite preserved cell differentiation, the Reln(rl-Orl) phenotype comprises laminar abnormalities of cell position in auditory cortex and dorsal cochlear nucleus. The metabolic consequences of the cell ectopias were determined by estimating cytochrome oxidase (CO) activity, a marker of neuronal activity. CO activity increased in the granular cell layer of dorsal cochlear nucleus, trapezoid body nucleus, intermediate lateral lemniscus, central and external inferior colliculus, and pyramidal cell layer of primary auditory cortex. On the contrary, CO activity decreased in the superficial molecular layer of dorsal cochlear nucleus as well as in the medioventral periolivary nucleus. These metabolic variations are discussed in terms of their possible relation to morphologic anomalies observed in the mutant.     

Interlimb coordination in patients with Parkinson’s disease: motor learning deficits and the importance of augmented information feedback

 The basal ganglia have traditionally been associated with motor control functions and this view has prevailed since the late nineteenth century. Recent experimental studies suggest that this neuroanatomical system is also critically involved in motor learning. In the present study, motor learning/transfer capabilities were compared between patients with Parkinson’s disease and a group of normal elderly people. Subjects practiced a bimanual coordination task that required continuous flexion-extension movements in the transverse plane with a 90° phase offset between the forearms. During acquisition, augmented visual feedback of the relative motions was provided in real time. The findings revealed improvements in the bimanual coordination pattern across practice in both groups when the augmented concurrent feedback was present. However, when transferred to performance conditions in which the augmented information was withheld, performance deteriorated (relative to the augmented condition) and this effect was more prevalent in the Parkinson patients. More specifically, no improvement in interlimb coordination was observed under nonaugmented feedback conditions across practice. Instead, a drift toward the preferred in-phase and anti-phase coordination patterns was evident. The present findings suggest that Parkinson patients can improve their performance on a new motor task, but they remain strongly dependent on augmented visual information to guide these newly acquired movements. The apparent adoption of a closed-loop control mode is accompanied with decreases in movement speed in order to use the feedback to ensure accuracy. When the augmented feedback is withheld and the movement pattern is to be controlled by means of intrinsic information feedback sources, performance is severely hampered. The findings are hypothesized to indicate that learning/transfer is affected in Parkinson patients who apparently prefer some constancy in the environmental contingencies under which practice takes place. The present findings are consistent with the notion that the basal ganglia form a critical neuroanatomical substrate for motor learning. Received: 7 December 1995 / Accepted: 12 August 1996     

Spatiotemporal reorganization of electrical activity in the human brain associated with a timing transition

We used a 61-channel electrode array to investigate the spatiotemporal dynamics of electroencephalographic (EEG) activity related to behavioral transitions in rhythmic sensorimotor coordination. Subjects were instructed to maintain a 1:1 relationship between repeated right index finger flexion and a series of periodically delivered tones (metronome) in a syncopated (anti-phase) fashion. Systematic increases in stimulus presentation rate are known to induce a spontaneous switch in behavior from syncopation to synchronization (in-phase coordination). We show that this transition is accompanied by a large-scale reorganization of cortical activity manifested in the spatial distributions of EEG power at the coordination frequency. Significant decreases in power were observed at electrode locations over left central and anterior parietal areas, most likely reflecting reduced activation of left primary sensorimotor cortex. A second condition in which subjects were instructed to synchronize with the metronome controlled for the effects of movement frequency, since synchronization is known to remain stable across a wide range of frequencies. Different, smaller spatial differences were observed between topographic patterns associated with synchronization at low versus high stimulus rates. Our results demonstrate qualitative changes in the spatial dynamics of human brain electrical activity associated with a transition in the timing of sensorimotor coordination and suggest that maintenance of a more difficult anti-phase timing relation is associated with greater activation of primary sensorimotor areas. Received: 3 September 1998 / Accepted: 3 March 1999     

Group-I introns in the cytochrome c oxidase genes of Dictyostelium discoideum : two related ORFs in one loop of a group-I intron, a cox1/2 hybrid gene and an unusually large cox3 gene

 The DNA sequences of cytochrome oxidase (subunits 1, 2 and 3) genes of the cellular slime mold Dictyostelium discoideum mitochondria were determined. The genes for subunits 1 and 2 have a single continuous ORF (COX1/2) which contains four group-I introns. The insertion sites of the two group-I introns (DdOX1/2.2 and DdOX1/2.3) coincide with those of fungal and algal group-I introns, as well as a liverwort group-I intron, in the cytochrome oxidase subunit 1. Interestingly, intron DdOX1/2.2 has two free-standing ORFs in a loop (L8) which have similar amino-acid sequences and are homologous to ai4 DNA endonuclease (I-Sce II) and bi4 RNA maturase found in group-I introns of Saccharomyces cerevisiae mitochondrial DNA. Two group-I introns (DdOX1/2.3 and DdOX1/2.4) also have a free-standing ORF in loop 1 and loop 2, respectively. These results show that these group-I introns and the intronic ORFs have evolved from the same ancestral origin, but that these ORFs have been propagated independently. Received: 1 May / 16 September 1996     

A mutation in cytochrome oxidase subunit 2 restores respiration of the mutant pet ts1402

The yeast PET1402/OXA1 gene encoding a 44.8-kDa protein is required for mitochondrial biogenesis. Substitution of Leu240 to serine in the protein results in an accumulation of the precursor form of the mitochondrially encoded subunit 2 of cytochrome oxidase (Cox2) and temperature-sensitive respiration. This temperature sensitivity can be suppressed by a mutation in the cox2 gene changing Ala189 of the Cox2 protein to proline. In the cox2-ts1402 double mutant respiration is restored without removal of the Cox2 pre-sequence. The suppression suggests an interaction of the Pet1402 protein with the cytochrome oxidase complex. Antibodies raised against the predicted C-terminus and the tagged N-terminus of the Pet1402 protein reacted with a 37-kDa polypeptide. This protein, present in the mitochondrial fraction, is localized within the inner membrane. The difference in size can be explained by the removal of the predicted mitochondrial-targeting sequence from the Pet1402 protein. The mitochondrial localization of the protein points to a direct interaction with the cytochrome oxidase complex. Received: 4 December 1996 / 26 January 1997     

Eye-hand coordination in uni- and bimanual goal-oriented tasks

 Two different drawer tasks were investigated with the aim of assessing the role of eye movements in well-coordinated hand movements. In an unimanual step-tracking task, which had a predictive and an unpredictive movement, a two-way repeated-measures ANOVA showed a significant effect of prediction on the onset of grip-force (GF) rate (300±39 ms for the predictive condition versus 394±53 ms for the non-predictive condition, P<0.0001). Correlation coefficients, computed from the eye and the hand movements were low for the right and the left hand. The saccade was more coupled with the visual step change than with the action of the hand per se. In a second bimanual pull-and-pick task, the instruction was to pull a drawer with the left hand from a closed position to a LED-cued open position and then to grasp and reinsert a small peg in the drawer with the right hand. Correlation coefficients, computed from the latencies of saccades and of the leading left hand or of the right hand, were significant in four of five subjects. Intermanual correlations were significant in all five subjects. In conclusion, we found that the initial saccade in the unimanual task was best related with the visual step change, but was poorly correlated with the pulling/pushing hand. In the bimanual task, a moderate, but significant temporal coupling between the eyes and hand events was observed. This coupling was, however, less tight than that between both hands. Received: 24 August 1998 / Accepted: 13 January 1999     

Patterns of cytochrome oxidase activity in areas 17, 18 and 19 of the visual cortex of cats and kittens

Summary The laminar pattern of cytochrome oxidase activity was studied in visual cortical areas 17,18 and 19 in adult cats and kittens, following electrophysiological determination of the boundaries of these areas in all but the youngest animals. The patterns of cytochrome oxidase staining and the cytoarchitectonic appearances of areas 17, 18 and 19 were compared. At all ages activity was especially high in the region of layers IV and VI in areas 17 and 18, and was low in all laminae in area 19. The results suggest that the degree of cytochrome oxidase activity in these regions of the visual cortex may be related to the strength and type of projection that they receive from the lateral geniculate nucleus. The cytochrome oxidase technique is a useful means of defining the 18/19 border, and may help locate the boundary between areas 17 and 18, in both adult cats and kittens.     

Cloning and characterization of KlCOX18, a gene required for activity of cytochrome oxidase in Kluyveromyces lactis

We describe the isolation and initial characterization of KlCOX18, a gene that is essential for the assembly of a functional cytochrome oxidase in the yeast Kluyveromyces lactis. Cells carrying a recessive nuclear mutation in this gene are respiratory deficient and contain reduced levels of cytochromes a and a ₃ . The KlCOX18 gene has been cloned by complementation of the respective nuclear mutation, sequenced, and disrupted. KlCOX18 is located on chromosome II and contains an open reading frame of 939 base pairs. The corresponding protein exhibits 70.4% similarity to the Cox18p of Saccharomyces cerevisiae. It contains three possible membrane-spanning domains and a putative amino-terminal mitochondrial import sequence. The strain carrying a null mutation in KlCOX18 does not grow on non-fermentable carbon sources and is deficient in both cytochrome c oxidase and respiratory activity. It is proposed that KlCox18p, like its S. cerevisiae counterpart, provides an important function at a later step of the cytochrome oxidase assembly pathway. Received: 25 March / 3 July 1997     

Prehension movements and motor development in children

 The maturation of manual dexterity and other sensorimotor functions was assessed with various behavioural tests. In healthy children (age 4–5 years) and in adults, the kinematics of reaching and grasping, a bimanual task and fast repetitive tapping movements were analysed. Furthermore a comprehensive motor function score (MOT), probing agility and balance, was evaluated. In the prehension task, the straightness of the reaching trajectories increased with age. Children opened their grip relatively wider than adults, thus grasping with a higher safety margin. The speed of both tapping and bimanual movements increased with age, and higher scores were reached in the MOT. Although the different behavioural tests sensitively indicated maturational changes, their results were generally not correlated, i.e. the outcome of a particular test could not predict the results of other tasks. Hence there is no simple and uniform relationship between different behavioural data describing maturation of sensorimotor functions. Received: 20 July 1998 / Accepted: 11 December 1998     

Neuronal activity related to eye-hand coordination in the primate premotor cortex

To test the functional implications of gaze signals that we previously reported in the dorsal premotor cortex (PMd), we trained two rhesus monkeys to point to visual targets presented on a touch screen while controlling their gaze orientation. Each monkey had to perform four different tasks. To initiate a trial, the monkey had to put his hand on a starting position at the center of the touch screen and fixate a fixation point. In one task, the animal had to make a reaching movement to a peripheral target randomly presented at one of eight possible locations on a circle while maintaining fixation at the center of this virtual circle (central fixation + reaching). In the second task, the monkey maintained fixation at the location of the upcoming peripheral target and, later, reached to that location. After a delay, the target was turned on and the monkey made a reaching arm movement (target fixation + reaching). In the third task, the monkey made a saccade to the target without any arm movement (saccade). Finally, in the fourth task, the monkey first made a saccade to the target, then reached to it after a delay (saccade + reaching). This design allowed us to examine the contribution of the oculomotor context to arm-related neuronal activity in PMd. We analyzed the effects of the task type on neuronal activity and found that many cells showed a task effect during the signal (26/60; 43%), set (16/49; 33%) and/or movement (15/54; 28%) epochs, depending on the oculomotor history. These findings, together with previously published data, suggest that PMd codes limb-movement direction in a gaze-dependent manner and may, thus, play an important role in the brain mechanisms of eye-hand coordination during visually guided reaching. Received: 10 September 1998 / Accepted: 19 March 1999