An excitatory ventromedial hypothalamus to paraventricular thalamus circuit that suppresses food intake

It is well recognized that ventromedial hypothalamus (VMH) serves as a satiety center in the brain. However, the feeding circuit for the VMH regulation of food intake remains to be defined. Here, we combine fiber photometry, chemo/optogenetics, virus-assisted retrograde tracing, ChR2-assisted circuit mapping and behavioral assays to show that selective activation of VMH neurons expressing steroidogenic factor 1 (SF1) rapidly inhibits food intake, VMH SF1 neurons project dense fibers to the paraventricular thalamus (PVT), selective chemo/optogenetic stimulation of the PVT-projecting SF1 neurons or their projections to the PVT inhibits food intake, and chemical genetic inactivation of PVT neurons diminishes SF1 neural inhibition of feeding. We also find that activation of SF1 neurons or their projections to the PVT elicits a flavor aversive effect, and selective optogenetic stimulation of ChR2-expressing SF1 projections to the PVT elicits direct excitatory postsynaptic currents. Together, our data reveal a neural circuit from VMH to PVT that inhibits food intake.

Orexins (hypocretins): novel hypothalamic peptides with divergent functions

The hypothalamus is the most important region in the control of food intake and body weight. The ventromedial "satiety center" and lateral hypothalamic "feeding center" have been implicated in the regulation of feeding and energy homeostasis by various studies of brain lesions. The discovery of orexin peptides, whose neurons are localized in the lateral hypothalamus and adjacent areas, has given us new insight into the regulation of feeding. Dense fiber projections are found throughout the brain, especially in the raphe nucleus, locus coeruleus, paraventricular thalamic nucleus, arcuate nucleus, and central gray. Orexins mainly stimulate food intake, but by the virtue of wide immunoreactive projections throughout the brain and spinal cord, orexins interact with various neuronal pathways to potentate divergent functions. In this review, we summarize recent progress in the physiological, neuroanatomical, and molecular studies of the novel neuropeptide orexins (hypocretins).Key words: orexins (hypocretins), hypothalamus, lateral hypothalamus, feeding behavior, energy homeostasis, neurons.

Amino Acid Imbalance and Diet Preference in the Hypothalamic–Hyperphagic Rat

Diet selection by control and hypothalamic–hyperphagic rats was recorded to examine the hypothesis that the plasma amino acid pattern may act as a satiety signal with respect to the decreased food intake associated with amino acid unbalanced diets. Rats were offered choices between: (a) protein-free and imbalanced diets; (b) imbalanced and corrected diets; (c) corrected and basal diets. Although selection by control and operated rats differed with respect to choice a, selection behaviors were comparable for choices b and c. Plasma amino acid patterns were similar in control and operated rats indicating that the same potential satiety signal was present in both groups. Since the "satiety center" was ablated in operated rats, it would seem that if plasma amino acid patterns serve as a satiety signal, this signal must act in some manner other than on the ventromedial area of the hypothalamus.