CaV1 and CaV2 calcium channels mediate the release of distinct pools of synaptic vesicles

Activation of voltage-gated calcium channels at presynaptic terminals leads to local increases in calcium and the fusion of synaptic vesicles containing neurotransmitter. Presynaptic output is a function of the density of calcium channels, the dynamic properties of the channel, the distance to docked vesicles, and the release probability at the docking site. We demonstrate that at Caenorhabditis elegans neuromuscular junctions two different classes of voltage-gated calcium channels, CaV2 and CaV1, mediate the release of distinct pools of synaptic vesicles. CaV2 channels are concentrated in densely packed clusters ~250 nm in diameter with the active zone proteins Neurexin, α-Liprin, SYDE, ELKS/CAST, RIM-BP, α-Catulin, and MAGI1. CaV2 channels are colocalized with the priming protein UNC-13L and mediate the fusion of vesicles docked within 33 nm of the dense projection. CaV2 activity is amplified by ryanodine receptor release of calcium from internal stores, triggering fusion up to 165 nm from the dense projection. By contrast, CaV1 channels are dispersed in the synaptic varicosity, and are colocalized with UNC-13S. CaV1 and ryanodine receptors are separated by just 40 nm, and vesicle fusion mediated by CaV1 is completely dependent on the ryanodine receptor. Distinct synaptic vesicle pools, released by different calcium channels, could be used to tune the speed, voltage-dependence, and quantal content of neurotransmitter release

Stress response varies with plumage colour and local habitat in feral pigeons

International audienceBird populations exposed to different extrinsic conditions often differ in the responsiveness of the hypothalamo–pituitary–adrenal (HPA) axis and thus in corticosterone response that individuals mount when facing stressful events. However, the contribution of genetic variation to among-individual variability in HPA axis responsiveness across different environmental conditions is poorly understood. Melanin-based coloured types provide reliable phenotypic markers of alternative genotypes underlying stress coping styles. Large variations in melanin-based colouration are heritable in feral pigeons. We tested whether melanin-based colouration is associated with variation in corticosterone stress response in feral pigeons. To this end, we examined how corticosterone response varies both within and between differently coloured individuals across different environmental conditions. Differently coloured individuals produced different stress-induced corticosterone levels in relation to their environmental conditions: dark pigeons exhibited a higher corticosterone when originating from rural habitats, while this was not observed in pale pigeons. This suggests that among-population variation in stress response is higher in dark pigeons, this variation possibly reflecting adjustment and/or (epi)genetic adaptation to environmental conditions. In addition, corticosterone response increased with the degree of melanin-based colouration in pigeons originating from rural habitats but not in pigeons originating from more urbanized populations, resulting in the coexistence of alternative stress responses in some populations, but not in others. Our results suggest that species with melanin-based variation in differently urbanized populations along rural–urban gradients are potentially good candidate systems for studying stress coping styles under alternative selective regimes