One-week exposure to a free-choice high-fat high-sugar diet does not disrupt blood-brain barrier permeability in fed or overnight fasted rats.

Objectives: The hypothalamus lies adjacent to the third ventricle and is in close proximity with the median eminence (ME), a circumventricular organ with an incomplete blood-brain barrier (BBB) which controls direct entry of nutrients into the brain. The blood-CSF barrier of the hypothalamus shows dynamic changes upon neuroendocrine events and adjusts permeability with the tight junction (TJ) complex. It has been shown that chronic exposure to a high-fat diet (HFD) affects BBB permeability. HFD also induces leptin resistance and alters neuropeptide expression in the arcuate nucleus (Arc) of the hypothalamus starting early during overnutrition. We hypothesized altered integrity of the BBB to occur after exposing rats to a free-choice high-fat high-sugar (fcHFHS) diet for 1 week. Methods: We measured diffusion of Evans blue dye over the ME and assessed expression of the TJ proteins ZO-1, claudin-5, and occludin in the tanycytic wall of the third ventricle. Furthermore, we assessed protein expression of glucose transporter 1 (GLUT-1), which is highly expressed in the Arc-ME complex and facilitates glucose transport over the BBB. Results: fcHFHS-fed rats increased caloric intake compared to control, however, there was no effect of the fcHFHS diet on permeability of the BBB, nor changes in protein expression of tight TJ proteins or GLUT-1. Fasting acutely affects the BBB and we hypothesized that exposure to the fcHFHS diet affects the BBB differently compared to chow after fasting. We did not, however, find any differences in Evans blue diffusion nor protein expression between chow- and fcHFHS-fed rats when fasted overnight. Conclusions: We conclude that short-term consumption of a fcHFHS diet does not change permeability or diffusion in the hypothalamus barrier in ad libitum fed or fasted rats.

Infusion of fluoxetine, a serotonin reuptake inhibitor, in the shell region of the nucleus accumbens increases blood glucose concentrations in rats.

The brain is well known to regulate blood glucose, and the hypothalamus and hindbrain, in particular, have been studied extensively to understand the underlying mechanisms. Nuclei in these regions respond to alterations in blood glucose concentrations and can alter glucose liver output or glucose tissue uptake to maintain blood glucose concentrations within strict boundaries. Interestingly, several cortico-limbic regions also respond to alterations in glucose concentrations and have been shown to project to hypothalamic nuclei and glucoregulatory organs. For instance, electrical stimulation of the shell of the nucleus accumbens (sNAc) results in increased circulating concentrations of glucose and glucagon and activation of the lateral hypothalamus (LH). Whether this is caused by the simultaneous increase in serotonin release in the sNAc remains to be determined. To study the effect of sNAc serotonin on systemic glucose metabolism, we implanted bilateral microdialysis probes in the sNAc of male Wistar rats and infused fluoxetine, a serotonin reuptake inhibitor, or vehicle after which blood glucose, endogenous glucose production (EGP) and glucoregulatory hormones were measured. Fluoxetine in the sNAc for 1h significantly increased blood glucose concentrations without an effect on glucoregulatory hormones. This increase was accompanied by a higher EGP in the fluoxetine infused rats compared to the controls. These data provide further evidence for a role of sNAc-serotonin in the regulation of glucose metabolism.