Functional Coupling between mGluR1 and Ca_v3.1 T-Type Calcium Channels Contributes to Parallel Fiber-Induced Fast Calcium Signaling within Purkinje Cell Dendritic Spines

Abstract

T-type voltage-gated calcium channels are expressed in the dendrites of many neurons, although their functional interactions with postsynaptic receptors and contributions to synaptic signaling are not well understood. We combine electrophysiological and ultrafast two-photon calcium imaging to demonstrate that mGluR1 activation potentiates cerebellar Purkinje cell Ca v 3.1 T-type currents via a G-protein-and tyrosine-phosphatase-dependent pathway. Immunohistochemical and electron microscopic investigations on wild-type and Ca v 3.1 gene knock-out animals show that Ca v 3.1 T-type channels are preferentially expressed in Purkinje cell dendritic spines and colocalize with mGluR1s. We further demonstrate that parallel fiber stimulation induces fast subthreshold calcium signaling in dendritic spines and that the synaptic Ca v 3.1-mediated calcium transients are potentiated by mGluR1 selectively during bursts of excitatory parallel fiber inputs. Our data identify a new fast calcium signaling pathway in Purkinje cell dendritic spines triggered by short burst of parallel fiber inputs and mediated by T-type calcium channels and mGluR1s.

Intermediate conductance calcium-activated potassium channels modulate summation of parallel fiber input in cerebellar Purkinje cells

“…Although KCCN4 mRNA has been detected in the cerebellar Purkinje cell layer (23), KCa3.1 expression has not been reported in CNS neurons (3). Of the three Cav3 channel isoforms expressed in Purkinje cells (13,14,24), Cav3.2 is preferentially blocked by 100 μM Ni 2+ (16), as found for the evoked AHP (Fig. 1A).…”

“…As a result, parallel fiber-evoked EPSPs surpassed spike threshold within 5-10 stimuli to reliably generate spike output. We found no role for mGluR1 receptor activation (14) or presynaptic endocannabinoid receptors (32), as neither JNJ16259685 nor the CB1 receptor blocker AM-251 occluded the effect of Ni 2+ (n = 4) during these stimuli. In addition, the parallel fiber-evoked EPSP paired-pulse ratio was unaffected by either Ni 2+ (n = 7, P = 0.95) or TRAM-34 (n = 7, P = 0.582) (Fig.…”

“…In contrast, low voltage-activated (LVA) Cav3 (T-type) Ca 2+ channels that are active during the subthreshold interspike interval (12)(13)(14) have not been associated with any specific KCa channel. We now report that KCa3.1 channels are expressed in cerebellar Purkinje cells and act to shape the parallel fiber EPSP waveform, providing unique evidence for a functional role for KCa3.1 channels in a CNS neuron.…”

T-type channel blockade impairs long-term potentiation at the parallel fiber–Purkinje cell synapse and cerebellar learning

“…The biophysical properties of low-voltage activated calcium channels allow them to be activated by subthreshold synaptic inputs and thus participate in synaptic integration and signaling. Indeed, we have previously shown that T-type channels are activated by synaptic activity at the PF-PC synapse (11,22). Furthermore, they can contribute to the intrinsic firing behavior of neurons (23,24).…”

“…PCs bear different voltage-dependent Ca channels including P/Q-type (6)(7)(8) and T-type channels (9,10). The spines of PCs contain a high density of Ca V 3.1 T-type channels (11), which can be readily activated by typical bursts of PF activity that occur during sensory stimulation (12)(13)(14). To date, the function of the PF to PC synapse plays a pivotal role in cerebellar motor learning, probably involving bidirectional changes of its strength (1)(2)(3).…”