GABAB receptor auxiliary subunits modulate Cav2.3-mediated release from medial habenula terminals

Abstract

The synaptic connection from medial habenula (MHb) to interpeduncular nucleus (IPN) is critical for emotion-related behaviors, and uniquely expresses R-type Ca2+ channels (Cav2.3) and auxiliary GABAB receptor (GBR) subunits, the K+-channel tetramerization domain-containing proteins (KCTDs). Activation of GBRs facilitates or inhibits transmitter release from MHb terminals depending on the IPN subnucleus, but the role of KCTDs is unknown. We therefore examined the localization and function of Cav2.3, GBRs, and KCTDs in this pathway in mice. We show in heterologous cells that KCTD8 and KCTD12b directly bind to Cav2.3 and that KCTD8 potentiates Cav2.3 currents in the absence of GBRs. In the rostral IPN, KCTD8, KCTD12b and Cav2.3 co-localize at the presynaptic active zone. Genetic deletion indicated a bidirectional modulation of Cav2.3-mediated release by these KCTDs with a compensatory increase of KCTD8 in the active zone in KCTD12b-deficient mice. The interaction of Cav2.3 with KCTDs therefore scales synaptic strength independent of GBR activation.

The Number and Distinct Clustering Patterns of Voltage-Gated Calcium Channels in Nerve Terminals

“…The quantitative analysis of the gold particle distribution suggests that all subtypes of Ca V 2 channels are accumulated in the AZs of presynaptic boutons. However, Cav2.3 has a high density in the surroundings of AZ too, which gradually decreases with distance from the AZ ( Bhandari et al, 2021 ), whereas Cav2.1 shows very low density in the extra-AZ areas ( Figure 1D ).…”

“…Thus, the density of Ca V 2.1 at AZs is estimated to be (1,320 channels × 0.92)/3.33 µm 2 = 365 channels/µm 2 , and the Ca V 2.1 (Éltes et al, 2017). Right, labeling for Ca V 2.3 (5 nm) and AMPA-type glutamate receptor (panAMPA, 15 nm) at an mHb-IPN synapse in the mouse brain (Bhandari et al, 2021) Perimeter release model, multiple SVs are positioned at the perimeter of a Ca V 2 channel cluster (Nakamura et al, 2015).…”

“…However, SDS-FRL relies on random fracturing of frozen slices, making the identification of labeled profiles more difficult compared with volume data obtained by the three-dimensional reconstruction of serial sections. SDS-FRL has been utilized for quantitative analysis of the nanoscale distribution of Ca V 2 channels at the AZs in rodent brains ( Holderith et al, 2012 ; Indriati et al, 2013 ; Baur et al, 2015 ; Nakamura et al, 2015 ; Éltes et al, 2017 ; Kusch et al, 2018 ; Luján et al, 2018a , b ; Rebola et al, 2019 ; Eguchi et al, 2020 ; Kleindienst et al, 2020 ; Bhandari et al, 2021 ). Figure 1C shows the examples of the replica labeling for Ca V 2.1, 2.2, and 2.3 on presynaptic boutons in different synapses ( Éltes et al, 2017 ; Bhandari et al, 2021 ).…”

“…SDS-FRL has been utilized for quantitative analysis of the nanoscale distribution of Ca V 2 channels at the AZs in rodent brains ( Holderith et al, 2012 ; Indriati et al, 2013 ; Baur et al, 2015 ; Nakamura et al, 2015 ; Éltes et al, 2017 ; Kusch et al, 2018 ; Luján et al, 2018a , b ; Rebola et al, 2019 ; Eguchi et al, 2020 ; Kleindienst et al, 2020 ; Bhandari et al, 2021 ). Figure 1C shows the examples of the replica labeling for Ca V 2.1, 2.2, and 2.3 on presynaptic boutons in different synapses ( Éltes et al, 2017 ; Bhandari et al, 2021 ). The quantitative analysis of the gold particle distribution suggests that all subtypes of Ca V 2 channels are accumulated in the AZs of presynaptic boutons.…”

“…Middle , labeling for Ca V 2.2 at an IN-CA3 PN synapse in the mouse hippocampus ( Éltes et al, 2017 ). Right , labeling for Ca V 2.3 (5 nm) and AMPA-type glutamate receptor (panAMPA, 15 nm) at an mHb-IPN synapse in the mouse brain ( Bhandari et al, 2021 ). Cyan indicates AZ areas.…”