Abstract
The receptive field of a neuron reflects its function. For example, for parallel fiber (PF) inputs in C3 zone the cerebellar cortex, the excitatory and inhibitory receptive fields of a Purkinje cell (PC) have different locations, and each location has a specific relationship to the location of the climbing fiber (CF) receptive field of the PC. Previous studies have shown that this pattern of input connectivity to the PC and its afferent inhibitory interneurons can be fundamentally disrupted by applying direct electrical stimulation to the PFs, paired or unpaired with CF activation, with protocols that induce plasticity in these synapses. However, afferent fiber stimulation, which is typically used in experimental studies of plasticity, set up highly artificial input patterns at the level of the recipient cells, raising the issue that these forms of plasticity potentially may not occur under more natural input patterns. Here we used skin stimulation to set up spatiotemporally more realistic afferent input patterns in the PFs to investigate whether these input patterns are also capable of inducing synaptic plasticity using similar protocols that have previously been described for direct PF stimulation. We find that receptive field components can be added to and removed from PCs and interneurons following brief periods of skin stimulation. Following these protocols, the receptive fields of mossy fibers were unchanged. These findings confirm that previously described plasticity protocols may have a functional role also for more normal patterns of afferent input.
Highlights
The efficacy of a synaptic contact is typically subjected to bidirectional plasticity, i.e., it can be both potentiated and depressed (Malenka and Bear, 2004)
A climbing fibers (CF)-dependent signal in interneurons was predicted from the fact that the parallel fiber (PF) receptive field of interneurons overlapped that of the local CF (Ekerot and Jorntell, 2001), and from the observation that CF activation converted a PF-stimulation protocol that induced receptive field reduction to a protocol that induced to receptive field expansion (Jorntell and Ekerot, 2002, 2003), most likely corresponding to LTD and LTP, respectively, of PF input to interneurons (Rancillac and Crepel, 2004; Smith and Otis, 2005; Dean et al, 2010)
Interneurons were identified by having large extracellular spikes in the molecular layer (Figure 1A; which Purkinje cell (PC) lack) and by their lack of complex spikes (Csp) both spontaneously and in responses evoked www.frontiersin.org www.frontiersin.org from the inferior olive (IO)
Summary
The efficacy of a synaptic contact is typically subjected to bidirectional plasticity, i.e., it can be both potentiated and depressed (Malenka and Bear, 2004). PF-LTP that lead to a reversal of the CF induced PF-LTD in PCs was demonstrated in vitro (Lev-Ram et al, 2002, 2003; Coesmans et al, 2004). PF activation alone, in a protocol that mimicked a PF-LTD protocol but omitted the CF activation, led to spectacular receptive field increases in PCs (Jorntell and Ekerot, 2002). A CF input to interneurons and its mode of activation was demonstrated (Jorntell and Ekerot, 2002, 2003; Szapiro and Barbour, 2007). Due to a lack of recordings, a picture of the potential functional roles of the interneurons in vivo has only recently emerged (Jorntell et al, 2010)
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