Abstract:
The cerebellum is known to be the major centre for motor learning in vertebrates. It has
a well-conserved circuit architecture, where a layer of inhibitory neurons, called Purkinje
neurons, receives a copy of the executive signals from the higher motor areas and error
feedback from lower neurons, computes the ‘error’ and tunes the motor execution.
Interestingly, not much is known about how cerebellar output executes motor error
correction. In mammals, the output from the cerebellum is carried by the axons of the
deep cerebellar nuclear cells (DCNs), which project to diverse brain regions, including
the motor thalamus and the reticular formation. In this work, we have looked at the
circuitry encoding cerebellar efferent signals using larval zebrafish as our model. In fish,
Purkinje neurons project onto a group of glutamatergic neurons called the Eurydendroid
cells (ECs), which are thought to be the equivalent of the mammalian DCNs. ECs have
been shown to also project widely within the brain of the fish and thus are likely to play a
critical role in conveying motor error correction information to their targets. However, not
much is known about the inherent activity patterns of these neurons. We performed
spontaneous in-vivo loose patch recordings from ECs of paralyzed zebrafish larvae. We
describe two distinct populations of ECs in terms of their electrophysiological activity i.e.
chatty (consistent/high spiking) and stuttering(irregularly spiking/low spiking). With
pharmacological treatments, we also show that these neurons are inherently spiking.
We also tried to look at the spatial distribution of the two kinds of ECs as a population.
Hence, we performed two-photon calcium imaging and tried to classify the neurons
based on their calcium activity. With further experiments, we hope to dissect the
mechanisms underlying the distinct activity patterns of the two populations and what
their roles might be in terms of cerebellar function. Thereafter, we hope to answer more
general questions about the fundamental nature of the error correction implemented by
the cerebellum.
