The hippocampus

Figure 1. Coronal slice through the transverse axis of the hippocampus. The black lines trace the classic ‘trisynaptic loop’. The red lines depict other important pathways in the hippocampus, including the direct projections from entorhinal cortex (EC) to all three CA fi elds, the feedback to the EC via the subiculum, the recurrent collateral circuitry of CA3, and the feedback projection from CA3 to DG. For simplicity, many other details of the connectivity of the hippocampus are omitted. Where next for the study of anhydrobiosis? Studies have largely relied on detecting gene upregulation upon exposure to desiccation. This approach will fail to identify constitutively expresssed genes that are important for anhydrobiotic survival but whose expression does not change during desiccation and rehydration. We still do not understand why some nematodes, for example, do not survive desiccation, while others can survive immediate exposure to extreme desiccation, and yet others require preconditioning at a high relative humidity. A comparative approach is likely to be informative, as has recently been published comparing the genomes of P. vanderplanki and its desiccation-intolerant relative P. nubifer.