Motor Learning and the Cerebellum

SLC26A11 (KBAT) in Purkinje Cells Is Critical for Inhibitory Transmission and Contributes to Locomotor Coordination

Chloride homeostasis determines the impact of inhibitory synaptic transmission and thereby mediates the excitability of neurons. Even though cerebellar Purkinje cells (PCs) receive a pronounced inhibitory GABAergic input from stellate and basket cells, the role of chloride homeostasis in these neurons is largely unknown. Here we studied at both the cellular and systems physiological level the function of a recently discovered chloride channel, SLC26A11 or kidney brain anion transporter (KBAT), which is prominently expressed in PCs. Using perforated patch clamp recordings of PCs, we found that a lack of KBAT channel in PC-specific KBAT KO mice (L7-KBAT KOs) induces a negative shift in the reversal potential of chloride as reflected in the GABA_A-receptor-evoked currents, indicating a decrease in intracellular chloride concentration. Surprisingly, both in vitro and in vivo PCs in L7-KBAT KOs showed a significantly increased action potential firing frequency of simple spikes, which correlated with impaired motor performance on the Erasmus Ladder. Our findings support an important role for SLC26A11 in moderating chloride homeostasis and neuronal activity in the cerebellum.

In vivo analysis of cerebellar Purkinje cell activity in SCA2 transgenic mouse model

Cerebellar Purkinje cells (PCs) are primarily affected in many spinocerebellar ataxias (SCA). In this study we investigated functional activity of PCs in transgenic mouse model of SCA2, a polyglutamine neurodegenerative hereditary disorder. In our studies we used extracellular single-unit recording method to compare spontaneous activity of PCs in age-matched wild-type mice and SCA2-58Q transgenic mice. We discovered that the fraction of PCs with bursting and an irregular pattern of spontaneous activity dramatically increases in aged SCA2-58Q mice compared with wild-type littermates. Small-conductance calcium-activated potassium (SK) channels play an important role in determining firing rate of PCs. Indeed, we demonstrated that intraperitoneal (IP) injection of SK channel inhibitor NS8593 induces an irregular pattern of PC activity in wild-type mice. Furthermore, we demonstrated that IP injection of SK channel-positive modulator chlorzoxazone (CHZ) decreases spontaneous firing rate of cerebellar PCs. Finally, we have shown that IP injections with CHZ normalize firing activity of cerebellar PCs from aging SCA2-58Q mice. We propose that alterations in PC firing patterns is one of potential causes of ataxic symptoms in SCA2 and in other SCAs and that positive modulators of SK channels can be used to normalize activity of PCs and alleviate ataxic phenotype in patients with SCA.

Adult restoration of Shank3 expression rescues selective autistic-like phenotypes

Because ASD is a neurodevelopmental disorder and patients typically display symptoms before the age of three¹, one of the key questions in autism research is whether the pathology is reversible in adults. Here we investigated the developmental requirement of Shank3, one of the most prominent monogenic ASD genes that is estimated to contribute to ~1% of all ASD cases^2–6. SHANK3 is a postsynaptic scaffold protein that regulates synaptic development, function and plasticity by orchestrating the assembly of postsynaptic density (PSD) macromolecular signaling complex^7–9. Disruptions of the Shank3 gene in mouse models have resulted in synaptic defects and autistic-like behaviors including anxiety, social interaction deficits, and repetitive behavior^10–13. We generated a novel Shank3 conditional knock-in mouse model and used it to demonstrate that re-expression of the Shank3 gene in adult led to improvements in synaptic protein composition, spine density and neural function in the striatum. We also provided behavioral evidence that certain behavioral abnormalities including social interaction deficit and repetitive grooming behavior could be rescued, while anxiety and motor coordination deficit could not be recovered in adulthood. Together, these results elucidate the profound impact of post-developmental activation of Shank3 expression on neural function and demonstrate certain degree of continued plasticity in the adult diseased brain.

Evolving Models of Pavlovian Conditioning: Cerebellar Cortical Dynamics in Awake Behaving Mice

Three decades of electrophysiological research on cerebellar cortical activity underlying Pavlovian conditioning have expanded our understanding of motor learning in the brain. Purkinje cell simple spike suppression is considered to be crucial in the expression of conditional blink responses (CRs). However, trial-by-trial quantification of this link in awake behaving animals is lacking, and current hypotheses regarding the underlying plasticity mechanisms have diverged from the classical parallel fiber one to the Purkinje cell synapse LTD hypothesis. Here, we establish that acquired simple spike suppression, acquired conditioned stimulus (CS)-related complex spike responses, and molecular layer interneuron (MLI) activity predict the expression of CRs on a trial-by-trial basis using awake behaving mice. Additionally, we show that two independent transgenic mouse mutants with impaired MLI function exhibit motor learning deficits. Our findings suggest multiple cerebellar cortical plasticity mechanisms underlying simple spike suppression, and they implicate the broader involvement of the olivocerebellar module within the interstimulus interval.

•

Simple spike suppression correlates trial by trial to conditioned eyelid behavior

•

Conditioned stimulus-related complex spikes relate to simple spikes and behavior

•

Molecular layer interneuron (MLI) modulation correlates to behavior

•

Transgenic deficits in MLI input result in partially impaired eyeblink conditioning