Anesthetized Long Evans rats show similar protein expression and long-term potentiation as Fischer 344 rats but reduced short-term potentiation in motor cortex

After-effects of anodal transcranial direct current stimulation on the excitability of the motor cortex in rats

PURPOSE

Transcranial direct current stimulation (tDCS) is increasingly seen as a useful tool for noninvasive cortical neuromodulation. A number of studies in humans have shown that when tDCS is applied to the motor cortex it can modulate cortical excitability. It is especially interesting to note that when applied with sufficient duration and intensity, tDCS can enable long-lasting neuroplastic effects. However, the mechanism by which tDCS exerts its effects on the cortex is not fully understood. We investigated the effects of anodal tDCS under urethane anesthesia on field potentials in in vivo rats.

METHODS

These were measured on the skull over the right motor cortex of rats immediately after stimulating the left corpus callosum.

RESULTS

Evoked field potentials in the motor cortex were gradually increased for more than one hour after anodal tDCS. To induce these long-lasting effects, a sufficient duration of stimulation (20 minutes or more) was found to may be required rather than high stimulation intensity.

CONCLUSION

We propose that anodal tDCS with a sufficient duration of stimulation may modulate transcallosal plasticity.

Animal models in spinal cord injury: a review

Multiple neuroprotective agents have shown benefit for the treatment of acute spinal cord injury (SCI) in animal studies. However, clinical trials have, thus far, been uniformly disappointing. This review explores reasons for discrepancies between promising animal studies and disappointing clinical trials and potential barriers to extrapolation of research results from animals to humans. The three major barriers disclosed are: differences in injury type between laboratory-induced SCI and clinical SCI, difficulties in interpreting functional outcome in animals, and inter-species and interstrain differences in pathophysiology of SCI. These barriers can impair the effectiveness of animal models of SCI to predict human outcomes. While some of these barriers can be overcome, others are inherent to the animal models.

Cortical plasticity induced by transcranial magnetic stimulation during wakefulness affects electroencephalogram activity during sleep

BACKGROUND

Sleep electroencephalogram (EEG) brain oscillations in the low-frequency range show local signs of homeostatic regulation after learning. Such increases and decreases of slow wave activity are limited to the cortical regions involved in specific task performance during wakefulness. Here, we test the hypothesis that reorganization of motor cortex produced by long-term potentiation (LTP) affects EEG activity of this brain area during subsequent sleep.

METHODOLOGY/PRINCIPAL FINDINGS

By pairing median nerve stimulation with transcranial magnetic stimulation over the contralateral motor cortex, one can potentiate the motor output, which is presumed to reflect plasticity of the neural circuitry. This paired associative stimulation increases M1 cortical excitability at interstimulus intervals of 25 ms. We compared the scalp distribution of sleep EEG power following paired associative stimulation at 25 ms to that following a control paradigm with 50 ms intervals. It is shown that the experimental manipulation by paired associative stimulation at 25 ms induces a 48% increase in amplitude of motor evoked potentials. This LTP-like potentiation, induced during waking, affects delta and theta EEG power in both REM and non-REM sleep, measured during the following night. Slow-wave activity increases in some frontal and prefrontal derivations and decreases at sites neighboring and contralateral to the stimulated motor cortex. The magnitude of increased amplitudes of motor evoked potentials by the paired associative stimulation at 25 ms predicts enhancements of slow-wave activity in prefrontal regions.

CONCLUSIONS/SIGNIFICANCE

An LTP-like paradigm, presumably inducing increased synaptic strength, leads to changes in local sleep regulation, as indexed by EEG slow-wave activity. Enhancement and depression of slow-wave activity are interpreted in terms of a simultaneous activation of both excitatory and inhibitory circuits consequent to the paired associative stimulation at 25 ms.

Long-term potentiation is associated with changes in synaptic ultrastructure in the rat neocortex

Long-term potentiation (LTP) in the sensorimotor cortex of freely moving rats has been associated with changes in dendritic morphology and dendritic spine density. The current research examined changes in synaptic number and ultrastructure associated with LTP in this cortical region. LTP was induced over a 1 h period and the animals were sacrificed 2 h after the initial stimulation of the LTP group. Synapses within the terminal area of the apical dendrites from layer III pyramidal neurons were quantified by determining the total number of synapses per neuron, the number of excitatory and inhibitory contacts, number of synapses with different curvature subtypes, number of perforated synapses, and synaptic length. Several changes in synaptic morphology of excitatory synapses were revealed but no overall increase in the number of synapses per neuron was evident. Specifically, the induction of LTP was associated with an increased number of excitatory perforated and concave shaped synapses. Increased numbers of perforated concave synapses were also found to be significantly correlated with the degree of potentiation in the LTP animals. These and previous results suggest similar synaptic changes in both the cortex and hippocampus during the early phases of LTP maintenance and distinct synaptic changes during later phases of LTP maintenance.