Effects of stimulation of the cingulate gyrus on insulin secretion

Vagally Mediated Gut-Brain Relationships in Appetite Control-Insights from Porcine Studies

Signals arising from the upper part of the gut are essential for the regulation of food intake, particularly satiation. This information is supplied to the brain partly by vagal nervous afferents. The porcine model, because of its sizeable gyrencephalic brain, omnivorous regimen, and comparative anatomy of the proximal part of the gut to that of humans, has provided several important insights relating to the relevance of vagally mediated gut-brain relationships to the regulation of food intake. Furthermore, its large size combined with the capacity to become obese while overeating a western diet makes it a pivotal addition to existing murine models, especially for translational studies relating to obesity. How gastric, proximal intestinal, and portal information relating to meal arrival and transit are encoded by vagal afferents and their further processing by primary and secondary brain projections are reviewed. Their peripheral and central plasticities in the context of obesity are emphasized. We also present recent insights derived from chronic stimulation of the abdominal vagi with specific reference to the modulation of mesolimbic structures and their role in the restoration of insulin sensitivity in the obese miniature pig model.

The effect of loss of the glucose-monitoring neurons in the anterior cingulate cortex: Physiologic challenges induce complex feeding-metabolic alterations after local streptozotocin microinjection in rats

The anterior cingulate cortex (ACC) is interrelated to limbic structures, parts of the central glucose-monitoring (GM) network. GM neurons, postulated to exist here, are hypothesised to participate in regulatory functions, such as the central control of feeding and metabolism. In the present experiments, GM neurons were identified and examined in the ACC by means of the multibarreled microelectrophoretic technique. After bilateral ACC microinjection of streptozotocin (STZ), glucose tolerance tests (GTTs), and determination of relevant plasma metabolite concentrations were performed. Body weights were measured at regular time points during the GTT experiment. Ten percent of the neurons - 30 of 282 recorded cells - responded to the administration of D-glucose, thus, declared to be the GM units. The peak values and dynamics of the GTT blood glucose curves, the plasma metabolite concentrations, and the weight gain were pathologically altered in the STZ treated animals. Our recording experiments revealed the existence of GM neurons in the anterior cingulate cortex. STZ induced selective destruction of these chemosensory cells resulted in feeding and metabolic alterations. The present findings indicate distinguished significance of the cingulate cortical GM neurons in adaptive processes of maintenance of the homeostatic balance.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Blockade of ovulation and release of LH in the rat by electrochemical stimulation of the frontal lobe cortex

The effect of stimulation of the frontal lobe cortex on the release of luteinizing hormone (LH) and ovulation was studied in female rats. Electrochemical stimulation (anodic DC) was applied through monopolar stainless-steel electrodes chronically implanted in the non-anesthetized freely-behaving animals bearing a plastic cannula inserted into the jugular vein for blood sampling. In rats, on the day of proestrus, stimulation (100 uA/30 sec) of the medial cortical surface in the superficial and deep layers of the medial precentral area and of the anterior cingulate area blocked ovulation in about 80% of the animals. A similar effect was seen when the stimulus was applied in the deep layers of the prelimbic and infralimbic areas. On the contrary, stimulation in the superficial layers of these latter two areas, as well as in the superficial and deep layers of the retrosplenial cortex, did not affect normal ovulation. The preovulatory discharge of LH was blocked in the animals which failed to ovulate. The degree of inhibition exerted by the anterior cingulate area and the prelimbic area on ovulation and LH surge was proportional to the amount of current applied. Stimulation of the anterior cingulate area also blocked the release of LH induced by the injection of progesterone into ovariectomized estrogen-primed rats. Furthermore, electrochemical stimulation of the anterior cingulate area inhibited the rise of LH in the serum induced by electrical stimulation of the medial preoptic area of ovariectomized estrogen-injected rats, but it failed to affect that resulting from electrical stimulation of the medial basal hypothalamus. On the other hand, stimulation of the lateral cortical surface and the ventral cortex of the frontal lobe on the day of proestrus affected normal ovulation and LH surge only when the stimulus was applied in the agranular insular area which also exhibited an inhibitory action. It is concluded that certain areas of the frontal lobe cortex related to limbic structures exert an inhibitory influence on ovulation and LH secretion.