Biomedical subjects

M S Rioult-Pedotti

Publications and source records attributed to M S Rioult-Pedotti.

5 recordsLinked to original sources

PubMed2000

Learning-induced LTP in neocortex.

The hypothesis that learning occurs through long-term potentiation (LTP)- and long-term depression (LTD)-like mechanisms is widely held but unproven. This hypothesis makes three assumptions: Synapses are modifiable, they modify with learning, and they strengthen through an LTP-like mechanism. We previously established the ability for synaptic modification and a synaptic strengthening with motor skill learning in horizontal connections of the rat motor cortex (MI). Here we investigated whether learning strengthened these connections through LTP. We demonstrated that synapses in the trained MI were near the ceiling of their modification range, compared with the untrained MI, but the range of synaptic modification was not affected by learning. In the trained MI, LTP was markedly reduced and LTD was enhanced. These results are consistent with the use of LTP to strengthen synapses during learning.

Animals↗

PubMed1998

Strengthening of horizontal cortical connections following skill learning.

Learning a new motor skill requires an alteration in the spatiotemporal pattern of muscle activation. Motor areas of cerebral neocortex are thought to be involved in this type of learning, possibly by functional reorganization of cortical connections. Here we show that skill learning is accompanied by changes in the strength of connections within adult rat primary motor cortex (M1). Rats were trained for three or five days in a skilled reaching task with one forelimb, after which slices of motor cortex were examined to determine the effect of training on the strength of horizontal intracortical connections in layer II/III. The amplitude of field potentials in the forelimb region contralateral to the trained limb was significantly increased relative to the opposite 'untrained' hemisphere. No differences were seen in the hindlimb region. Moreover, the amount of long-term potentiation (LTP) that could be induced in trained M1 was less than in controls, suggesting that the effect of training was at least partly due to LTP-like mechanisms. These data represent the first direct evidence that plasticity of intracortical connections is associated with learning a new motor skill.

Action Potentials↗

PubMed1997

Intrinsic NMDA-induced oscillations in motoneurons of an adult vertebrate spinal cord are masked by inhibition.

Low-frequency membrane potential oscillations were induced in motoneurons (MNs) of isolated hemisected frog spinal cords during N-methyl-D-aspartate (NMDA) application. Oscillations required the presence of physiological Mg2+ and preincubation with strychnine, whereas incubation with bicuculline or phaclofen was not effective. Oscillations were evident in intracellular recordings from single MNs and simultaneous extracellular recordings from lumbar ventral roots. In Mg(2+)-free solution, MNs exhibited irregular transient membrane potential depolarizations that were blocked by D,L-2-amino-5-phosphonopentanoic acid (APV) but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Generation and maintenance of membrane potential oscillations required specific NMDA receptor activation. Oscillations were antagonized by APV but not by CNQX. Strychnine preincubation was required for NMDA to induce oscillations, but was not critical in maintaining them, because oscillations persisted after removal of strychnine. Therefore oscillations are suggested to be an inherent property of the spinal neuronal circuitry. Tetrodotoxin (TTX) blocked spike activity and had a bimodal effect on membrane potential oscillations. Oscillations initially were blocked by TTX, but reappeared spontaneously after 10-40 min. This suggests that maintenance of oscillations, once evoked, does not involve MN firing. Na+ entry through TTX-insensitive Na+ channels and/or NMDA receptor channels, trans-membrane Ca2+ flux, Ca2+ release from intracellular stores, and Ca2+ activated K+ channels were critical in controlling the amplitude and frequency of membrane potential oscillations. It is hypothesized that these unmasked intrinsic oscillations in adult frog spinal cord MNs may represent a premetamorphic spinal oscillator involved in tadpole swimming that becomes suppressed during metamorphosis as strychnine-sensitive inhibition becomes more pronounced.

Animals↗

PubMed1991

The influence of noise on quantal EPSP size obtained by deconvolution in spinal motoneurons in the cat.

1. The amplitudes of quantal components that make up single-fiber excitatory postsynaptic potentials (EPSPS) were determined by a deconvolution technique and by simulation studies and were compared with the background noise. 2. A strong correlation was found between the sizes of EPSP quantal components and the standard deviation of the noise from which the data were extracted by deconvolution. A similar correlation was then shown in published data from several other laboratories. 3. EPSPS having amplitudes less than 100 microV were recorded that had little or no variance in their amplitudes. Most of these EPSPS showed a much smaller peak variance than would be expected if they fluctuated among amplitudes in steps of approximately 100 microV--the proposed mean value for the amplitude of the quantal EPSP. 4. Deconvolution of simulated data with the maximum likelihood algorithm resulted in the suppression of components less than 1.5 SD of the background noise. The remaining components were approximately equally spaced. No way was found to detect this error, and rejection of deconvolved data with components less than 1.5 noise SD did not eliminate it. The resulting erroneous data showed a strong correlation between the amplitudes of the components obtained and the noise standard deviation. 5. It is concluded that at least some EPSPS generated by single Ia-afferents on motoneurons are composed of quantal components significantly less than 100 microV and that deconvolution procedures are not capable of detecting such small components.

Action Potentials↗

PubMed1988

The cervico-ocular reflex in intact and chronically labyrinthectomized frogs.

Eye movements in response to horizontal oscillation of the body against the stationary head (cervico-ocular reflex) were measured with search coils in the frequency range between 0.02 and 1.0 Hz in intact and chronica bilaterally labyrinthectomized frogs. The evoked eye movements were compensatory in direction but only about 1-2% of the amplitude of the stimulus (+/- 5-20 degrees). In chronic bilaterally labyrinthectomized frogs (n = 5) very similar response characteristics were measured. The very small amplitudes of these responses in controls and in frogs with removed labyrinthine organs render this reflex functionally irrelevant for both gaze stabilization and recovery from dynamic vestibular deficits after a loss of labyrinthine function.

Animals↗