Search

We studied the activity of single neurons in the pre-supplementary motor area (pre-SMA) of macaque monkeys as they performed two visuomotor tasks, called the visual fixation task and the visual fixation-blink task. Both tasks involved a sequence of three visual stimuli, red followed by yellow and green. The tasks differed in that the latter one had a gap within the period of the red stimulus, called a "blink". The tasks were performed in two modes, one of which included movements of both the arm and eye and the other of which involved only eye movements. In the arm-eye mode, the monkeys had to press a bar and fixate the red stimulus that appeared after bar press. To receive a reward, both the bar press and visual fixation had to be maintained until the green stimulus triggered bar release. In the eye mode, bar press and bar release were eliminated from the task. Of the 42 neurons active during the visual fixation task, 15 showed task-related activity in both arm-eye and eye modes, and our analysis focused on these cells. We found that the introduction of the blink in visual fixation-blink task abolished the task-related activity of these cells over the course of 2-4 trials. This finding suggests a role for the pre-SMA in reflecting progression of trials as an updating of motor instruction., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

The objective was to study whether repetitive transcranial magnetic stimulation (rTMS) of the motor cortex could induce modification of peripheral blood lactate values. Nineteen young healthy volunteers were included; during the study, all subjects were at rest, sitting on a comfortable armchair. The muscular activation was evaluated by continuous electromyographic record. TMS was performed by using a circular coil at the vertex. Resting motor threshold (rMT) was defined as the lowest TMS intensity able to induce motor responses of an amplitude >50 microV in the relaxed contralateral target muscle in approximately 50% of 20 consecutive stimuli. Venous blood lactate values were measured before, immediately after and 10 min after a single session of low frequencies (1Hz for 15 min) rTMS (LF rTMS) or high frequency (20 Hz for 15 min) rTMS (HF rTMS). As expected, LF rTMS induced a decrease of motor cortex excitability, whereas HF rTMS evoked an increase of motor cortex excitability. However, in the present investigation we observed that both conditions are associated to a significant increase of blood lactate. Since in our experimental conditions we can exclude a muscular production of lactate, the significant increment of peripheral blood lactate values, observed 10 min after the end of the rTMS session, is probably due to the crossing by brain-produced lactate of the blood-brain barrier.

By using retrograde double-labeling techniques, we analyzed the topography of projections from the lateral reticular nucleus (LRN) to the anterior and posterior lobes of the cerebellum, with the aim to investigate whether LRN projections to the two lobes come from different neurons or from branching axons of the same cells. We observed that about 4/5 of afferents the cerebellar cortex come from the ipsilateral LRN and about 1/5 from the contralateral nucleus. Furthermore, magnocellular division of LRN projects mainly to the anterior lobe, whereas parvicellular part primarily to the posterior lobe. The double-labelled cells were very numerous (about 1/3) and were located throughout the LRN, with the higher incidence in the magnocellular division and the lower in the subtrigeminal part.

We studied in vitro the effects of Tiagabine on genomic DNA of cortical rat astrocytes. To evaluate DNA damage, we used a relatively simple technique called Single Cell Gel Electrophoresis or Comet assay. Tiagabine was dissolved in culture medium and added at concentration of 1, 10, 20 and 50 microg/ml on 12-day old cultured astrocytes. In presence of 1 and 10 microg/ml of Tiagabine, no DNA damage was observed after 48 h of treatment. A moderate DNA damage was instead observed for cells exposed to 20 microg/ml of antiepileptic drug. Finally, DNA fragmentation was more evident after treatment with 50 microg/ml of Tiagabine. We conclude that Tiagabine, at the usual recommended doses, does not appear to influence negatively the cortical rat astrocytes, inducing DNA fragmentation only at very high concentrations.

Biological effects of tiagabine, a new antiepileptic drug, were analyzed on cultures of rat's cortical astrocytes. Tiagabine was added to the cultures at concentrations of 1 and 10 microg/ml, correspondent to therapeutic range; cell viability (tetrazolium salt assay and lactic dehydrogenase release), maturation and differentiation (glutamine synthetase activity) and presence of stress conditions (reactive oxygen species formation, inducible nitric oxide synthetase expression and 70 kDa heath shock protein production) were tested. Our results indicate that the addition of Tiagabine to primary astrocytes not only did not change significantly the examined metabolic activities but also seems to exert a protective action against oxidative stress. Thus, our data reinforce the idea that Tiagabine may be considered an effective promising drug in the treatment of epilepsy.

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.

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.

We studied in vivo the influences exerted by the retrorubral field (RRF) on the on commissural-evoked CA1 pyramidal cell excitability in the rat hippocampal formation (HF). The stimulation of RRF before the activation of the contralateral CA3 area evoked in all the studied rats a reduction in amplitude of the evoked population spike in the CA1 pyramidal cell body layer of both the dorsal and the ventral HF. No significant differences in the intensity of the inhibitory effect were observed between dorsal and ventral parts of the HF. The stimulation of the ipsilateral RRF reduced the amplitude of the evoked population spike in a higher degree with respect to the contralateral side. Since these side-to-side differences were significant, it can be concluded that the RRF-induced inhibitory effect is stronger on the ipsilateral CA1 pyramidal cells. The inhibitory effect appears within 0.1 s of stimulating the RRF, reaches its maximal effect around 0.4-0.5 s following the conditioning train and returned to its control size after 5 s.

In adult cats, with mesencephalic decerebration sparing the cerebral peduncles and ablation of the sensorimotor cortex, changes in firing of single cells of subthalamic nucleus (STN) were analyzed upon stimulation of ipsilateral medullary pyramidal tract (PT). Twenty-two out of 44 of the STN cells exhibited, following PT stimulation, discharge changes that in the greatest part of cases (91%) were excitatory in nature. Excitations, always followed by inhibitory rebound, appeared with latency values compatible with a monosynaptic linkage.

The pyramidal tract (PT) and the red nucleus (RN) of cats were stimulated electrically to identify by antidromic invasion PT and non-PT neurons projecting from cortical areas 4 and 6 to the RN. A main result was that the input to RN is much stronger from PT neurons than that of non-PT neurons in area 4, and vice versa in area 6.

In cats with C4-T2 unilateral dorsal rhizotomy, stimulation of interpositus nucleus of the cerebellum, ipsilateral to the deafferented side, elicits in forelimbs single muscle contractions, which display threshold, latencies and spatial-temporal characteristics similar to those of the muscular responses produced in the other forelimb, upon stimulation of interpositus nucleus of the intact side. Motor effects induced by the interpositus nucleus-stimulation on the deafferented side disappear following red nucleus lesions. Single muscle contractions triggered from interpositus nucleus are, therefore, mediated by impulses impinging on alpha-motoneurons, via the rubrospinal pathway.