Annett Rake

Perinatal elevation of hypothalamic insulin, acquired malformation of hypothalamic galaninergic neurons, and syndrome X-like alterations in adulthood of neonatally overfed rats

Overnutrition during critical developmental periods is suggested to be a risk factor for obesity and associated metabolic disorders in later life. Underlying mechanisms are unknown. Neuropeptides are essentially involved in the central nervous regulation of body weight. For instance, hypothalamic galanin (GAL) is a stimulator of food intake and body weight gain. To investigate long-term consequences of early postnatal overfeeding, the normal litter size of Wistar rats (n=10; controls) was reduced from day 3 to day 21 of life to only 3 pups per mother (small litters, SL; overnutrition). Throughout life, SL rats displayed hyperphagia (p<0.01), overweight (p<0.0001), hyperinsulinemia (p<0.01), impaired glucose tolerance (p<0.001), elevated triglycerides (p<0.001), and an increased systolic blood pressure (p<0.05). In adulthood, an increase of GAL-neurons in the arcuate hypothalamic nucleus (ARC) was found (p<0.001), positively correlated to body weight (p<0.001). A second experiment revealed hyperinsulinemia (p<0.001) and increased hypothalamic insulin levels (p<0.05) in SL rats during early postnatal life. Already on day 21 of life, i.e., at the end of the critical hypothalamic differentiation period, in SL rats the number of GAL-neurons was increased in the ARC (p<0.001), showing a positive correlation to body weight and insulin (p<0.05). In conclusion, neonatally acquired persisting malformation of hypothalamic galaninergic neurons, induced by early overfeeding and hyperinsulinism, might promote the development of overweight and syndrome X-like alterations during life.

Elevation of hypothalamic neuropeptide Y-neurons in adult offspring of diabetic mother rats.

We recently reported on an elevation of neurons expressing the main orexigenic peptide neuropeptide Y (NPY) in the arcuate hypothalamic nucleus (ARC) of neonatally hyperinsulinaemic offspring of gestational diabetic mother rats (GD) at weaning. To investigate possible consequences, the long-term outcome of those animals was examined. At adult age, GD offspring showed hyperphagia (p < 0.001), basal hyperinsulinaemia (p < 0.05) and impaired glucose tolerance (p < 0.05), and were overweight (p < 0.01). This was accompanied by an elevated number of NPY neurons (p < 0.001) and galanin neurons (p < 0.001) in the ARC in adult GD offspring under basal conditions. These findings support our hypothesis on perinatally acquired, persisting malformation and/or malprogramming of peptidergic hypothalamic neurons in the offspring of GD mothers, possibly promoting the development of overweight and diabetogenic disturbances during life.

Malformations of Hypothalamic Nuclei in Hyperinsulinemic Offspring of Rats with Gestational Diabetes

Insulin is a potent modulator of central nervous development and is suggested to influence the differentiation and maturation of hypothalamic structures involved in the regulation of body weight and metabolism. Hyperinsulinemic offspring of mothers with impaired glucose tolerance during pregnancy (gestational diabetes, GD) have an increased risk to develop overweight and diabetes mellitus during life, while the underlying pathophysiological mechanisms are still unknown. To investigate the effects of perinatal hyperinsulinism on the organization of hypothalamic regulators of body weight and metabolism, GD was induced in rats by application of streptozotocin on the day of conception (25 mg/kg, i.p.). On the 21st day of life, offspring of GD rats were overweight (p < 0.05) and hyperinsulinemic (p < 0.01). Using computer-assisted morphometric measurements, significantly decreased mean areas of neuronal nuclei and neuronal cytoplasm within the paraventricular hypothalamic nucleus (PVN; p < 0.01) and the ventromedial hypothalamic nucleus (VMN; p < 0.05) were observed in GD offspring. Analysis of topographically distinct parts revealed that these alterations particularly occurred in the parvocellular part of the PVN, as well as in the anterior, central, and dorsomedial part of the VMN. No morphometric alterations were found within the lateral hypothalamic area and the dorsomedial hypothalamic nucleus. In the arcuate hypothalamic nucleus, the mean area of neuronal cytoplasm was decreased (p < 0.05), while the number of neurons expressing tyrosine hydroxylase was clearly elevated (p < 0.002). For astrocytes, a tendency towards an increased glia/neuron ratio was observed in the periventricular hypothalamic area. These observations suggest disturbed differentiation and organization of distinct hypothalamic nuclei and subnuclei, respectively, in hyperinsulinemic offspring of GD rats, possibly leading to dysfunctions of hypothalamic regulators of body weight and metabolism which might contribute to the lifelong increased risk to develop overweight and diabetogenic disturbances.

Hypothalamic insulin and neuropeptide Y in the offspring of gestational diabetic mother rats.

THE offspring of diabetic mothers is at increased risk to develop obesity and diabetogenic disturbances during life. Pathophysiological mechanisms responsible are unclear. Neuropeptide Y (NPY) is an important hypothalamic stimulator of food intake and body weight gain, and its levels are decreased by elevated insulin. In neonatally hyperinsulinaemic offspring of diabetic mother rats, hypothalamic insulin level was significantly increased at birth (p < 0.01). At weaning, i.e. at the end of the critical hypothalamic differentiation period, a significantly increased number of NPY-positive neurons (p < 0.01) appeared in the arcuate hypothalamic nucleus. In conclusion, an increase in the number of NPYergic neurons in the hypothalamus, possibly due to hypothalamic malformation and/or perinatally acquired hypothalamic insulin resistance, might contribute to the development of obesity and metabolic disturbances in the offspring of diabetic mothers.

Increased number of galanin-neurons in the paraventricular hypothalamic nucleus of neonatally overfed weanling rats

Perinatal overfeeding is a risk factor for overweight and diabetes during life. Underlying pathophysiological mechanisms are unclear. The peptide galanin is suggested to stimulate food intake by acting within the paraventricular hypothalamic nucleus (PVN). In early postnatally overfed rats overweight and hyperinsulinemia were observed, accompanied by an increased number of galanin-positive neurons in the PVN at weaning. Our results might indicate malformation of hypothalamic galaninergic neurons due to neonatal overfeeding and hyperinsulinism, respectively, in rats.

Reduction of cholecystokinin-8S-neurons in the paraventricular hypothalamic nucleus of neonatally overfed weanling rats

Cholecystokinin (CCK) is suggested to be involved, e.g. in the central nervous modulation of food intake, possibly by acting within specific hypothalamic nuclei. Perinatal overnutrition predisposes to permanent obesity and hyperphagia, while underlying mechanisms are unclear. By reducing the litter size from the 3rd to 21st day of life, early overnutrition was induced in newborn rats. At weaning, clear overweight (P < 0.001), hyperglycaemia (P < 0.05), hyperinsulinaemia (P < 0.001), and insulin resistance (P < 0.001) occured. These early signs of obesity were associated with a significantly decreased number of CCK-positive neurons in the paraventricular hypothalamic nucleus (P < 0.002). In conclusion, due to neonatal overfeeding malformation of CCKergic neurons at the end of the critical hypothalamic differentiation period occurs. Long-term consequences on CCK-related neuroendocrine regulations could be suggested, including those affecting food intake and body weight gain.

Alterations of hypothalamic catecholamines in the newborn offspring of gestational diabetic mother rats

Catecholamines are essential organizers of the developing brain. Throughout life, they are involved, e.g., in the regulation of body weight and metabolism by specific hypothalamic nuclei, which are suggested to be highly vulnerable to maternal gestational hyperglycemia. By application of streptozotocin (30 mg/kg, i.p.) gestational diabetes (GD) was induced in female rats. On the 1st day of life, male GD offspring were underweight (P<0.05) and hyperglycemic (P<0.05), while on the 21st day of life decreased body weight (P<0.001) and elevated pancreatic insulin (P<0.01) were observed. Using HPLC with electrochemical detection, hypothalamic catecholamines were determined in the newborns, and quantitative immunocytochemistry for tyrosine hydroxylase (TH) was performed. At birth, a tendency towards increased levels of norepinephrine (NE) and dopamine (DA) in the whole hypothalami of GD offspring was observed. In the 21-day-old offspring of GD mothers, NE was significantly increased in the ventromedial hypothalamic nucleus (VMN; P<0.05) and the lateral hypothalamic area (LHA; P<0.05), while DA was significantly elevated in the paraventricular hypothalamic nucleus (PVN; P<0.05) and the LHA (P<0.05). The NE/DA-ratio was found to be decreased in the PVN of GD offspring (P<0.01). Moreover, numerical density of TH-positive neurons was clearly increased within the parvocellular division of the PVN (P<0.0001) as well as in the periventricular hypothalamic area (PER; P<0.05). These data suggest specific alterations of catecholaminergic systems within hypothalamic regulators of body weight and metabolism during early development in the offspring of gestational diabetic mother rats.