Repetitive firing of rat cerebellar parallel fibres after a single stimulation

Abstract

The excitatory postsynaptic currents (EPSCs) evoked in Purkinje cells (PCs) by stimulating parallel fibres (PFs) usually show a single peak, but EPSCs with multiple peaks (polyphasic EPSCs) can be observed in slices from animals older than 15 days. The EPSCs remain polyphasic when the postsynaptic current is reduced (either by reducing the intensity of the PF stimulation or by adding AMPA receptor antagonists) and when the PC membrane potential is made positive. Thus the late peaks are not due to postsynaptic active currents generated in the imperfectly clamped PC, and must arise from repetitive action potentials in the PF. Extracellular recordings from granule cell (GC) somata showed that a single PF stimulation can elicit a doublet or a train of action potentials. Both the late action potentials recorded in the GCs and the late peaks of the polyphasic EPSCs recorded in the PCs were reduced or abolished by paired-pulse stimulation of the PF or by bath application of the GABA A agonist muscimol. The late action potentials in the GCs were also suppressed by local application of muscimol around the cell body. We propose that after a single stimulation of a PF, the antidromic invasion of the ascending axon and the granule cell can trigger a doublet or a burst of action potentials which back-propagate into the PF (except for the first, which finds the PF still in its refractory period). The repetitive activation of the PF by a single stimulation could play a role in the induction of long-term depression.

Information processing in the axon

“…Axonal propagation might also 'bounce back' at a branch point or at the cell body. However, at present, only a handful of examples of reflected propagation have been observed 75,76,87,108,121 . Reflected impulses might limit the spread of the neuronal message and enhance synaptic transmission.…”

“…Our understanding of propagation in mammalian axons is still fragmentary and direct evidence for propagation failures is still controversial 99,101,129,130 . Moreover, evidence for an important role of propagation failures and axonal reflection in information processing in vivo is still scarce 77,108 . A main difficulty in studying propagation along thin unmyelinated axons is their relative complexity and their small size, which make direct electrophysiological recordings almost impossible.…”

Axon Physiology

“…Reflection has not yet been definitively reported in mammalian axons (270), but it has been demonstrated in dendrites. In mitral cells of the mammalian olfactory bulb, both conduction FIG.…”

mGluR1/TRPC3-mediated Synaptic Transmission and Calcium Signaling in Mammalian Central Neurons

“…Remarkably, the frequencies that are most effective in brain slices (Batchelor and Garthwaite 1997) resemble those that are encountered with the stimulation of parallel (Isope et al 2004) or mossy fibers in vivo (Chadderton et al 2004). The slow EPSC is characterized by a characteristic time course: it starts with a latency of 100-200 ms after the stimulation of afferent parallel fibers and lasts for about 1 second (Fig.…”