Editorial: Development of the hypothalamus

The hypothalamus is the region of the brain in charge of homeostasis as well as homeostatic behaviors like eating and drinking. The anatomical, connectional and physiological complexity of this region matches the importance and intricacy of its functions. Perhaps because of this, research on the developing hypothalamus has lagged behind that on the cortex or hippocampus. The realization that current pathological conditions like, e.g., some forms of obesity, hypertension and hormonal dysfunctions have its origin in developmental alterations of the hypothalamus has turned the focus again on this region. In the present Research Topic we try to give an idea of a variety of approaches, morphological, comparative and genetic, to key developmental questions related to the hypothalamus. In this collection, a focus on essential questions on the nature of this brain region and its specification is obvious. We start logically with papers explaining how the hypothalamus can be subdivided. Differentially with all earlier monographs on the hypothalamus, we reflect here the increasing perception in the field that the classic columnar model is outdated and incompatible with accruing molecular data on the hypothalamus. Many workers are turning to the updated prosomeric model as an instrument for morphologic and causal interpretation. This model has been presented in several articles, and several progressive changes and improvements made to it (Puelles et al. The model proposes that the hypothalamus is the rostralmost part of the neural tube, since the developmental forebrain length axis ends in the terminal wall of the hypothalamus (i.e., the telencephalon is a dorsal outgrowth of the alar hypothalamus). The resulting peduncular and terminal hypothalamic subdivisions of the rostral part of the neural tube are admittedly divergent with those traditionally taught under the columnar viewpoint. The hypothalamus is perhaps the brain region undergoing the most puzzling changes in the model, and this curiously turns out to the advantage of causal explanations. For this reason, the place of the hypothalamus in the prosomeric model and corresponding molecular subdivisions were recently the subject of a long and scholarly book chapter (Puelles et al., 2012). This includes the so-called updated prosomeric model. Here, Puelles and Rubenstein offer a more succint and very clear explanation of the changes introduced in their updated model, tracing their fundament to establish a solid basis of explicit reasonable assumptions, pointing out also some novel morphologic highlights, like the interpretation of the course of the fornix tract, or the newly-defined …