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Ramgoolam, K. H.

Publications and source records attributed to Ramgoolam, K. H..

2 recordsLinked to original sources
bioRxiv2022

Capsaicin-induced endocytosis of endogenous presynaptic CaV2.2 in DRG-spinal cord co-cultures inhibits presynaptic function

The N-type calcium channel, CaV2.2 is key to neurotransmission from the primary afferent terminals of dorsal root ganglion (DRG) neurons to their post-synaptic targets in the spinal cord. In this study we have utilized CaV2.2_HA knock-in mice, because the exofacial epitope tag in CaV2.2_HA enables accurate detection and localization of endogenous CaV2.2. CaV2.2_HA knock-in mice were used as a source of DRGs to exclusively study the presynaptic expression of N-type calcium channels in co-cultures between DRG neurons and wild-type spinal cord neurons. CaV2.2_HA is strongly expressed on the cell surface, particularly in TRPV1-positive small and medium DRG neurons. Super-resolution images of the presynaptic terminals revealed an increase in CaV2.2_HA expression and increased association with the post-synaptic marker Homer over time in vitro. Brief application of the TRPV1 agonist, capsaicin, resulted in a significant down-regulation of cell surface CaV2.2_HA expression in DRG neuron somata. At their presynaptic terminals, capsaicin caused a reduction in CaV2.2_HA proximity to and co-localization with the active zone marker RIM 1/2, as well as a lower contribution of N-type channels to single action potential-mediated Ca2+ influx. The mechanism of this down-regulation of CaV2.2_HA involves a Rab 11a-dependent trafficking process, since dominant-negative Rab11a(S25N) occludes the effect of capsaicin on presynaptic CaV2.2_HA expression, and also prevents the effect of capsaicin on action potential induced Ca2+ influx. Taken together, these data suggest that capsaicin causes a decrease in cell surface CaV2.2_HA expression in DRG terminals via a Rab11a-dependent endosomal trafficking pathway.

neuroscience↗
bioRxiv2022

Involvement of CaV2.2 channels and α2δ-1 in hippocampal homeostatic synaptic plasticity

In the mammalian brain, presynaptic CaV2 channels play a pivotal role for synaptic transmission by mediating fast neurotransmitter exocytosis via influx of Ca2+ into the active zone of presynaptic terminals. However, the distribution and modulation of CaV2.2 channels at highly plastic hippocampal synapses remains to be elucidated. Here, we assess CaV2.2 channels during homeostatic synaptic plasticity, a compensatory form of homeostatic control preventing excessive or insufficient neuronal activity during which extensive active zone remodelling has been described. We show that chronic silencing of neuronal activity in mature hippocampal cultures resulted in elevated presynaptic Ca2+ transients, mediated by increased levels of CaV2.2 channels at the presynaptic site. This work focussed further on the role of 2{delta}-1 subunits, important regulators of synaptic transmission and CaV2.2 channel abundance at the presynaptic membrane. We find that 2{delta}-1-overexpression reduces the contribution of CaV2.2 channels to total Ca2+ flux without altering the amplitude of the Ca2+ transients. Levels of endogenous 2{delta}-1 decreased during homeostatic synaptic plasticity, whereas the overexpression of 2{delta}-1 prevented homeostatic synaptic plasticity in hippocampal neurons. Together, this study reveals a key role for CaV2.2 channels and novel roles for 2{delta}-1 during synaptic plastic adaptation.

neuroscience↗