Dietary protein alters age-induced change in hypothalamic GABA and immune response

Dietary variation of protein–carbohydrate: Effect on hypothalamic and hippocampal GABA–glutamate in relation to aging

Dietary protein variation has been found to alter brain regional neurochemistry with aging. In the present investigation, we studied the effect of short-term treatment of protein-carbohydrate variable diet to rat on hypothalamic and hippocampal gamma-amino butyric acid (GABA)-glutamate metabolism with increase of age. Exposure of male albino rats with diet containing normal protein (20%)-normal carbohydrate (68%) increased GABA metabolism and decreased glutamate metabolism in both hypothalamus and hippocampus with the increase of age. GABA-glutamate metabolism of rats having low protein (8%)-high carbohydrate (80%) diet for short-term period (STP), was activated in young age (3 months) and decreased in old age (18 months) in both the brain regions. On the contrary, intake of high protein (50%)-low carbohydrate (38%) diet under similar condition decreased GABA-glutamate metabolism in both hypothalamus and hippocampus of young brain and increased only in hypothalamus of aged brain. In hippocampus of aged brain the same diet decreased glutamate metabolism without changing its GABA metabolism. These results suggest that an age-associated change in GABA-glutamate metabolism depends on the amount of dietary protein and carbohydrate and also on the brain region.

Long-term exposure of variable dietary protein-to-carbohydrate ratio: effect on brain regional glutamatergic activity with age

Glutamatergic activity of hypothalamus and hippocampus of young (3 months) male albino rats having normal diet [protein (20%)-carbohydrate (68%)] was increased with the increase of age. Long-term (60 consecutive days) feeding of low protein (8%)-high carbohydrate (80%) diet (LP-HC) increased glutamatergic activity in these brain regions of young rats and decreased that in aged (18 months). On the contrary, supplementation of high protein (50%)-low carbohydrate (38%) diet (HP-LC) under similar condition decreased glutamatergic activity in those brain regions of young and increased that in aged brain regions. Thus, prolonged exposure of LP-HC diet may damage young brain; whereas, HP-LC diet under similar condition causes excitotoxicity to aged brain. Therefore, considering the present scenario in relation to metabolism and receptor activity of glutamatergic system, it may be suggested that long-term consumption of LP-HC and HP-LC diets modulate the brain regional glutamatergic activity reversibly with age.

Dietary protein deficiency in pregnant mice and offspring

Previous studies suggest an association between dermal contact hypersensitivity and preterm delivery. We hypothesized that dietary protein deficiency produces cell-mediated immune hypersensitivity in pregnant animals and their offspring akin to those known to produce tissue damage. We compared the effects of feeding a 20% protein diet (controls) to those of feeding a 10% protein (deficient) diet ad libitum to pregnant BALB/c mice. We measured dermal contact sensitivity to 2,4-dinitrofluorobenzene (DNFB) by the increment in ear skin thickness (swelling) 72 h after immunization and parity by the number of viable pups delivered. Dams fed the protein-deficient diet ingested less food, gained less weight and delivered fewer viable pups than the dams fed the control diet. Greater DNFB-stimulated increment in ear skin thickness was found in the protein-deficient mothers and in their offspring than in the control mothers and their offspring. We conclude that dietary protein deficiency limits parity and induces immune hypersensitivity. These findings suggest the potential for dietary protein deficiency to activate a T-cell-mediated branch of the immune response that may put pregnant animals at risk for preterm delivery.

Kudzu Root Extract Suppresses Voluntary Alcohol Intake and Alcohol Withdrawal Symptoms in P Rats Receiving Free Access to Water and Alcohol

Alcohol-preferring (P) rats, given free choice to drink water or 15% alcohol, drank 7-10 g of alcohol/kg/day, giving blood alcohol values ranging from 16 to 24 mg/dL. Body weight and food and total fluid intake values in control and alcohol-drinking P rats did not differ significantly, while water intake was inversely related to the amount of alcohol consumed. Alcohol withdrawal after 50 days of alcohol drinking caused withdrawal symptoms such as hypersensitivity, poor landing coordination, and tremors. A daily 0.5, 0.75, and 1.0 g/kg dose of kudzu root (KdR) did not affect body weight and food and water intake values in control (no alcohol) P rats. Subchronic feeding of relatively higher KdR doses (0.75 and 1.0 g/kg) caused a 25-30% reduction in weight gain. The 0.5 g/kg KdR dose caused a 50-60% reduction in alcohol consumption, abolished the development of alcohol withdrawal symptoms, but did not affect blood alcohol levels. The higher KdR doses did not further reduce alcohol consumption. Alcohol suppressed the weight-reducing effects of KdR. The KdR extract used in this study contained 150 mg/g of puerarin, 13 mg/g of daidzin, 4 mg/g of daidzein, 3 mg/g of genistin, 0.2 mg/g of genistein, and 1 mg/g of glycetin. Blood and liver samples contained mostly puerarin and a trace amount of daidzein that may have been formed by the hydrolysis of daidzin by liver enzymes. An important observation was that brain samples obtained from KdR-fed or alcohol + KdR-fed rats did not contain any of the KdR isoflavones. Thus, KdR isoflavones suppressed alcohol drinking and withdrawal symptoms without entering the brain.

Cerebral GABA release and GAD activity in protein- and tryptophan-restricted rats during development

To evaluate the effects on the GABAergic system, Wistar rats were raised on a chronically protein- and tryptophan-restricted diet with 8% protein, based on either Purina chow or corn. There was a significant decrease in both body and cerebral weight in the restricted animals compared with the control group fed with a 23% protein diet. In animals fed mainly corn, glutamic acid decarboxylase (GAD) activity increased significantly at the ages studied (14, 30, and 60 days) in the cerebral cortex and hippocampus. In the same way, gamma-aminobutyric acid (GABA) release decreased significantly in early life in both brain regions, then increased in 30-60-day-old animals corn-fed predominantly in the cerebral cortex. The reduction in GABA release may be attributable to a decrease in GABAergic cell density, which could induce an over-activation of 5-hydroxytryptamine (5-HTergic) receptors, leading in turn to the observed enhancement of GAD activity. Taken together, these results may represent a plastic response by GABAergic neurons to (5-HTergic under-stimulation in mainly corn-fed animals.