Cerebellar Purkinje cells exhibit a unique type of synaptic plasticity, namely, long-term depression (LTD). When two inputs to a Purkinje cell, one from a climbing fiber and the other from a set of...

https://www.physiology.org/doi/pdf/10.1152/physrev.2001.81.3.1143

Cerebellar Long-Term Depression: Characterization, Signal Transduction, and Functional Roles

Movement, the fundamental component of behavior and the principal extrinsic action of the brain, is produced when skeletal muscles contract and relax in response to patterns of action potentials ge...

/pdf/synaptic-control-of-motoneuronal-excitability-104bymieik.pdf

Synaptic Control of Motoneuronal Excitability

Pathologic tremors occur when the normal, continuous pattern of muscle activation is replaced by relatively synchronous bursting. This article discusses the possible roles of stretch reflex and central oscillators in producing tremor. The gain and conduction delay in some reflex arcs places the stretch reflex close to oscillation in some muscles during normal operation. Within the brain, cells in the thalamic relay nuclei and inferior olive contain a set of ionic conductancies in the cell membrane that can interact to produce oscillations in membrane potential. This tendency is exaggerated by hyperpolarizing or depolarizing the cell away from the normal resting potential. The activity of neighboring cells can be coupled (by electrotonic gap junctions in the olive and by recurrent axonal projections from the reticular nucleus in the thalamus), thus a large population of cells can oscillate together and exert a powerful rhythmic influence on motor output.

Physiology and Anatomy of Possible Oscillators in the Central Nervous System

The objective of this project was to examine the influence of stimulus waveform and frequency on extracellular stimulation of neurons with their cell bodies near the electrode (local cells) and fibers of passage in the CNS. Detailed computer-based models of CNS cells and axons were developed that accurately reproduced the dynamic firing properties of mammalian motoneurons including afterpotential shape, spike-frequency adaptation, and firing frequency as a function of stimulus amplitude. The neuron models were coupled to a three-dimensional finite element model of the spinal cord that solved for the potentials generated in the tissue medium by an extracellular electrode. Extracellular stimulation of the CNS with symmetrical charge balanced biphasic stimuli resulted in activation of fibers of passage, axon terminals, and local cells around the electrode at similar thresholds. While high stimulus frequencies enhanced activation of fibers of passage, a much more robust technique to achieve selective activation of targeted neuronal populations was via alterations in the stimulus waveform. Asymmetrical charge-balanced biphasic stimuli, consisting of a long-duration low-amplitude cathodic prepulse phase followed by a short-duration high-amplitude anodic stimulus phase, enabled selective activation of local cells. Conversely, an anodic prepulse phase followed by a cathodic stimulus phase enabled selective activation of fibers of passage. The threshold for activation of axon terminals in the vicinity of the electrode was lower than the threshold for direct activation of local cells, independent of the stimulus waveform. As a result, stimulation induced trans-synaptic influences (indirect depolarization/hyperpolarization) on local cells altered their neural output, and this indirect effect was dependent on stimulus frequency. If the indirect activation of local cells was inhibitory, there was little effect on the stimulation induced neural output of the local cells. However, if the indirect activation of the local cells was excitatory, attempts to activate selectively fibers of passage over local cells was limited. These outcomes provide a biophysical basis for understanding frequency-dependent outputs during CNS stimulation and provide useful tools for selective stimulation of the CNS.

https://www.physiology.org/doi/pdf/10.1152/jn.2002.88.4.1592

Extracellular stimulation of central neurons: influence of stimulus waveform and frequency on neuronal output.

Microcircuitry and function of the inferior olive

A new combination of WGA-HRP anterograde tracing and GABA immunocytochemistry applied to afferents of the cat inferior olive at the ultrastructural level.

F. Calkoen

Papers

A new combination of WGA-HRP anterograde tracing and GABA immunocytochemistry applied to afferents of the cat inferior olive at the ultrastructural level.

The distribution of GABA in lumbar motoneuronal cell groups. A quantitative ultrastructural study in rat.