The free-living nematode Caenorhabditis elegans is a popular model system for studying developmental biology. Here we describe a detailed protocol to high-pressure freeze the C. elegans embryo (either ex vivo after dissection, or within the intact worm) followed by quick freeze substitution. Processed samples are suitable for ultrastructural analysis by conventional electron microscopy (EM) or newer volume EM (vEM) approaches such as Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). The ultrastructure of cellular features such as the nuclear envelope, chromosomes, endoplasmic reticulum and mitochondria are well preserved after these experimental procedures and yield accurate 3D models for visualization and analysis (Chang et al., 2020). This protocol was used in the 3D

Olfactory behavior is among the most fundamental animal behaviors both in the wild and in the laboratory. To elucidate the neural mechanisms underlying olfactory behavior, it is critical to measure neural responses to odorant concentration changes resembling those that animals actually sense during olfactory behavior. However, reproducing the dynamically changing olfactory stimuli to an animal during such measurements of neural activity is technically challenging. Here, we describe technical details and protocols for odor stimulation during calcium imaging of the sensory neurons of the nematode Caenorhabditis elegans. In this system, the neuronal activity of C. elegans is measured using ratiometric calcium imaging during exposure to quantitatively controlled olfactory stimuli over time.