The rostromedial zona incerta is involved in attentional processes while adjacent LHA responds to arousal: c-Fos and anatomical evidence.

Neurons producing melanin-concentrating hormone (MCH) are located in the tuberal lateral hypothalamus (LHA) and in the rostromedial part of the zona incerta (ZI). This distribution suggests that rostromedial ZI shares some common features with the LHA. However, its functions with regard to arousal or feeding, which are often associated with the LHA, have not been thoroughly investigated. This study analyses the responses in the tuberal LHA and adjacent rostromedial ZI after experiments related to arousal, exploration, food teasing and ingestive behavior. Specific aspects of the connections of the rostromedial ZI were also studied using retrograde and anterograde tract-tracing approaches. The rostromedial ZI is activated during exploratory and teasing experiments. It receives specific projections from the frontal eye field and the anterior pole of the superior colliculus that are involved in gaze fixation and saccadic eye movements. It also receives projections from the laterodorsal tegmental nucleus involved in attention/arousal. By contrast, the tuberal LHA is activated during wakefulness and exploratory behavior and reportedly receives projections from the medial prefrontal and insular cortex, and from several brainstem structures such as the periaqueductal gray. We conclude that the rostromedial ZI is involved in attentional processes while the adjacent tuberal LHA is involved in arousal.

Different distributions of preproMCH and hypocretin/orexin in the forebrain of the pig (Sus scrofa domesticus).

Neurons producing melanin-concentrating hormone (MCH) or hypocretin/orexin (Hcrt) have been implicated in the sleep/wake cycle and feeding behavior. Sleep and feeding habits vary greatly among mammalian species, depending in part of the prey/predatory status of animals. However, the distribution of both peptides has been described in only a limited number of species. In this work, we describe the distribution of MCH neurons in the brain of the domestic pig. Using in situ hybridization and immunohistochemistry, their cell bodies are shown to be located in the posterior lateral hypothalamic area (LHA), as expected. They form a dense cluster ventro-lateral to the fornix while only scattered cells are present dorsal to this tract. By comparison, Hcrt cell bodies are located mainly dorsal to the fornix. Therefore, the two populations of neurons display complementary distributions in the posterior LHA. MCH projections are, as indicated by MCH-positive axons, very abundant in all cortical fields ventral to the rhinal sulcus, as well as in the lateral, basolateral and basomedial amygdala. In contrast, most of the isocortex is sparsely innervated. To conclude, the distribution of MCH cell bodies and projections shows some very specific features in the pig brain, that are clearly different of that described in the rat, mouse or human. In contrast, the Hcrt pattern seems more similar to that in these species, i.e. more conserved. These results suggest that the LHA anatomic organization shows some very significant interspecies differences, which may be related to the different behavioral repertoires of animals with regard to feeding and sleep/wake cycles.