Fig. 1.6.44. A detail from Fig. 1.6.18. Extracellular receptor domains are only rarely apparent in the synaptic cleft after a standard chemical fixation (A – red lines). Compare to the corresponding structures observed in frozen cultured neurons examined by cryo-electron tomography (B, courtesy of Journal of Neuroscience and Tao et al., 2018; DOI: 10.1523/JNEUROSCI.1548-17.2017). Scales = 50 nm. (Neocortex, mouse (A) and a hippocampal neuron, rat (B).)