PubMed Health⌕ Search

Biomedical subjects

J D White

Publications and source records attributed to J D White.

At least 19 recordsLinked to original sources
PubMed1992

Limbic seizures increase cyclophilin mRNA levels in rat hippocampus.

Limbic seizures lead to dramatic and specific modulation of mRNA levels for many genes in the hippocampus including immediate early, growth factor and neuropeptide genes. In the present study, the influence of hilus lesion (HL)-induced seizures on the abundance of mRNA coding for cyclophilin, a peptide prolyl isomerase, in rat hippocampus was analyzed. By nuclease protection analysis a significant increase in cyclophilin mRNA levels was observed in the hippocampal dentate gyrus/CA1 subfield following HL-induced seizures. The increase began 6 h post-HL, reached a maximum (2.5-fold) at 12 h post-HL and returned to control values by 48 h post-HL. Cyclophilin mRNA levels remained stable in the cerebral cortex throughout the same seizure and post-seizure activity time span.

Amino Acid Isomerases↗
PubMed1992

Hypothalamic neuropeptide Y gene expression in rats on scheduled feeding regimen.

Recent evidence suggests that neuropeptide Y (NPY) is an important signal in the neural circuitry that controls feeding behavior. Previously we observed that in rats entrained to 4 h daily scheduled feeding regimen (SFR), NPY content and release in the paraventricular nucleus (PVN) was elevated but decreased rapidly in association with food consumption. In the present study, we investigated the pattern of hypothalamic NPY gene expression in SFR rats before and after food consumption by measuring the content of preproNPY mRNA in the medial basal hypothalamus (MBH). Adult male rats were maintained on either ad libitum diet (control) or on SFR. Rats were killed before food presentation at 11.00 h and at the end of 4 h food consumption at 15.00 h. The levels of preproNPY mRNA in the MBH were determined by solution hybridization/RNase protection assay using a cRNA probe complementary to rat NPY precursor mRNA. We observed that, as compared to that in control rats on ad libitum diet, preproNPY mRNA levels in the MBH were increased two-fold in the SFR rat at 11.00 h and remained elevated even after 4 h of food consumption. These results show a simultaneous enhancement in PVN NPY release and hypothalamic gene expression in advance of scheduled feeding time, but food intake rapidly decreases PVN NPY release and content, with little impact on hypothalamic gene expression.

Animals↗
PubMed1992

Steroidal regulation of hypothalamic neuropeptide Y release and gene expression.

Neuropeptide Y (NPY) readily stimulates the release of hypothalamic LHRH and pituitary LH release in intact and gonadal steroid-primed gonadectomized rats. We have now tested the hypothesis that the release and synthesis of hypothalamic NPY may be regulated by gonadal steroids. To measure the effects of gonadal hormones on NPY release, a permanent push-pull cannula was implanted in the anterior pituitary (AP) of sham castrated (controls) or castrated (CAST) male rats, and 1 week later, the AP was perfused with artificial cerebrospinal fluid over a 3-4 h period. NPY concentrations in the perfusates collected at 10-min intervals were measured by RIAs. The NPY release pattern in the AP was episodic in both intact and CAST rats, and the frequency of NPY episodes was similar in two groups. However, the amount of NPY detected in the AP of CAST rats was significantly less than that of intact rats because the mean rate of release and the amplitude of NPY episodes in the perfusates of CAST rats were significantly reduced. This observation of attenuated hypothalamic NPY output in vivo and previous evidence of decreased hypothalamic NPY contents after CAST implied that the synthesis of hypothalamic NPY may be regulated by testicular secretions. Therefore, the effects of testosterone (T)-replacement on preproNPY messenger RNA (mRNA) in the medial basal hypothalamus (MBH) was evaluated. Rats were CAST and received either empty or T-filled Silastic capsules sc. Two weeks later, the level of perproNPY mRNA in the MBH was determined by solution hybridization/ribonuclease protection assay using a complementary RNA probe complementary to the rat NPY precursor mRNA. We observed that the levels of preproNPY mRNA were 2-fold higher in the MBH of T-replaced CAST as compared to control CAST rats. These findings are consistent with the hypothesis that gonadal steroids enhance the neurosecretory activity of hypothalamic NPYergic neurons, and for the first time reveal a coupling between the level of gene expression and the secretion of a neuropeptide involved in the regulation of hypothalamic LHRH and pituitary LH release.

Animals↗
PubMed1992

Inhibition of hypothalamic neuropeptide Y gene expression by insulin.

Insulin acts in the brain to suppress feeding, whereas neuropeptide Y (NPY) has the opposite effect. Since fasting lowers plasma insulin levels and increases hypothalamic synthesis of NPY, we proposed that insulin may inhibit hypothalamic NPY gene expression. To test this hypothesis, we used RIA and in situ hybridization histochemistry to determine if centrally administered insulin could reduce levels of both NPY and its messenger RNA (mRNA) in discreet hypothalamic regions during fasting. Three groups of Long-Evans rats were entered into a 72-h study protocol. One group was fed ad libitum during this period, while the others were fasted. Fed rats received intracerebroventricular (icv) injections of saline vehicle at 12-h intervals, whereas fasted groups received icv vehicle alone or with insulin (4 mU/12 h). In vehicle-only treated rats, fasting significantly increased expression of preproNPY mRNA in the arcuate nucleus to 179 +/- 20% of fed controls. Administration of icv insulin during fasting abolished this increase (99 +/- 14% of fed controls; P less than 0.05 vs. fasted, vehicle-treated rats). Central insulin administration during fasting also reduced immunoreactive NPY concentrations in samples punched from the paraventricular nucleus (PVN) (875 +/- 122 pg/punch) to levels below vehicle-only treated rats (1396 +/- 435 pg/punch; P less than 0.05), similar to free-feeding control values (814 +/- 170 pg/punch). By comparison, neither fasting nor central insulin administration altered NPY levels in four other hypothalamic regions (supraoptic, ventromedial, dorsomedial, and arcuate nuclei). Continuous icv insulin infusion at a lower dose (2 mU/day) produced a similar result during a shorter period (48 h) of food deprivation in Wistar rats. In this study, central insulin infusion also inhibited the fasting-related increase in arcuate preproNPY mRNA levels and did not affect plasma glucose or insulin levels. This suggests that insulin acts locally to inhibit hypothalamic NPY mRNA expression. We conclude that the increase of levels of NPY in the PVN and preproNPY mRNA in the arcuate nucleus during fasting are inhibited by icv insulin. Fasting, therefore, increases NPY biosynthesis along an arcuate nucleus-PVN pathway in the hypothalamus via a mechanism dependent on low insulin levels.

Animals↗
PubMed1991

Toxicity and kinetics of [3H]microcystin-LR in isolated perfused rat livers.

Isolated rat livers were perfused for 60 min with either 0.3 or 0.5 microgram/ml (initial volume, 119 ml) of [3H]microcystin-LR at a constant flow of 10 ml/min in a recirculating system. During the 60-min exposure, toxin caused stimulation of glycogenolysis, liver engorgement, and cessation of bile flow. Electron micrographs of liver showed dilation of bile canaliculi and the space of Disse. loss of sinusoidal lining architecture, and decreased hepatocyte intercellular contacts. Although hepatocytes did not exhibit overt necrosis, mitochondria were hydropic, occasionally encircled by whorls of rough endoplasmic reticulum, and desmosomal tonofilaments were decreased on the plasma membrane lateral surface. Isolated mitochondria displayed inhibition of state 3 respiration and a 50-60% decrease in the respiratory control index, characteristic of hydropism. Distribution of radiolabel was 1.7% to bile, 79% to perfusate, and 16% to liver. Two to four percent was recovered in perfusate that leaked from the surface of the liver. Of the radiolabel found in bile and perfusate, 78 and 100% were associated with parent toxin, respectively. The radiolabel in liver, associated with the cytosolic fraction (S-100), corresponded to parent toxin (15%) and to a more-polar component(s) (85%). The elimination half-life from perfusate was 130 +/- 10 min (0.5 microgram/ml) and the hepatic extraction ratio 0.07 +/- 0.01. Although the calculated hepatic extraction ratio was low, there was a significant accumulation of microcystin in the liver. Many toxic effects of microcystin in the perfused liver mimicked those observed in the whole animal, suggesting that this model can be used as an alternative to whole animals for screening of potential therapeutic agents.

Animals↗
PubMed1990

Increased hypothalamic content of preproneuropeptide-Y messenger ribonucleic acid in streptozotocin-diabetic rats.

Neuropeptide-Y (NPY) is a 36-amino acid C-terminally amidated peptide found within the hypothalamus that can potently stimulate carbohydrate feeding. Moreover, the hypothalamic content of NPY can be modulated by peripheral hetabolic status. To further evaluate the regulation of NPY synthesis in states of altered metabolic homeostasis, we measured the hypothalamic content of prepro-NPY mRNA in streptozocin (STZ)-diabetic, STZ-diabetic insulin-replaced, and control rats by both nuclease protection and in situ hybridization analyses. Adult male Sprague-Dawley rats received a single injection of STZ (100 mg/kg, ip) or citric acid (control). Beginning 72 h later one group of STZ-treated animals received daily injections of insulin (4 U Ultralente/day). All animals were killed 17-19 days after STZ or control treatment. STZ-treated animals were hyperglycernic and showed growth failure compared to control rats. Glycemic control was restored by insulin replacement, as was partial growth. Nuclease protection analysis revealed an approximately 3- to 4-fold increase in prepro-NPY mRNA levels in the samples from STZ-treated rats vs. control. This increase was returned to control values by insulin replacement. In situ hybridization analysis revealed the STZ-induced increase in hypothalamic prepro-NPY mRNA was detectable in the arcuate nucleus at levels that were in agreement with the nuclease protection results, but that NPY expression in other brain regions appeared to be either unaffected or decreased after STZ treatment. These data suggest that hypothalamic NPY expression is modulated by peripheral metabolic status and provide further explanation for the hyperphagia accompanying STZ-induced diabetes.

Animals↗
PubMed1990

Increased hypothalamic content of preproneuropeptide Y messenger ribonucleic acid in genetically obese Zucker rats and its regulation by food deprivation.

Neuropeptide Y (NPY) is a potent orexigenic agent capable of producing hyperphagia and obesity. NPY-containing neurons project from the hypothalmic arcuate nucleus to the paraventricular nucleus, an area known to be sensitive to the orexigenic effects of NPY. In this study we investigated the possibility that preproNPY messenger RNA (mRNA) content may be altered in obese Zucker rats compared to that of their lean littermates. Total RNA was isolated from hypothalamic dissections from male and female, obese and lean Zucker rats. RNA was also isolated from dissections of: olfactory bulb, entorhinal cortex, hippocampus, and striatum of female obese and lean rats. PreproNPY mRNA content was determined by solution hybridization-RNase protection analysis. The results revealed a 2- to 3-fold increase in preproNPY mRNA levels in the hypothalamus of obese animals compared to lean. The increase was observed in both sexes and was specific to the hypothalamus. In situ hybridization localized this increase to the arcuate nucleus. An additional RNase protection study was pursued to investigate the effects of 72 h food deprivation on hypothalamic preproNPY mRNA levels in lean and obese animals. Lean animals displayed an approximate 2-fold increase in preproNPY mRNA content, whereas obese animals showed no significant increase after food deprivation. These data are consistent with the hypothesis that NPY projections within the hypothalamus are involved in regulating feeding behavior and weight gain, and that disturbed regulation of hypothalamic NPY expression may play a role in the etiology of obesity in the genetically obese Zucker rat.

Animals↗
PubMed1990

Influence of food deprivation in the rat on hypothalamic expression of growth hormone-releasing factor and somatostatin.

Food deprivation in the rat is associated with a reduction in serum GH levels characterized by suppression of high amplitude GH bursts and a decrease in the duration of secretory episodes. The mechanism(s) mediating this response is unknown. The present studies were designed to evaluate the role of hypothalamic factors potentially responsible for abnormal GH dynamics in food-deprived rats by measuring hypothalamic prepro-GH-releasing factor (GRF) and preprosomatostatin (SRIF) mRNA and peptide levels in adult male Sprague-Dawley rats after 72 h of food deprivation or free access to food. Hypothalamic prepro-GRF mRNA was reduced 80% in food-deprived rats compared to that in fed controls (P less than 0.001), while GRF content was unchanged. Levels of prepro-SRIF mRNA in food-deprived rats were similar to those in controls, as was hypothalamic SRIF content. The time course of hypothalamic prepro-GRF mRNA reduction was determined in groups of rats food-deprived for 24, 48, or 72 h and revealed a significant (30%) reduction of prepro-GRF mRNA (P less than 0.05 vs. fed) by 24 h, with maximal reduction (80%) by 48 h. Refeeding groups of animals for up to 72 h after they had been food-deprived for 72 h resulted in restoration of prepro-GRF mRNA levels to 50% of control levels by 24 h (P less than 0.05 vs. fed) and a return to control values by 48 h. These data suggest that decreased GRF gene expression and possibly GRF release play a major role in the loss of pulsatile GH secretion seen in this model of nutrient deprivation.

Animal Feed↗
PubMed1989

Comparison of in vivo and in vitro toxic effects of microcystin-LR in fasted rats.

The toxic effects of microcystin-LR, a cyclic heptapeptide isolated from the cyanobacterium Microcystis aeruginosa, were studied in the fasted rat model and in subcellular fractions from fasted, toxin-treated and control rats. Hepatotoxic effects of a lethal dose (100 micrograms/kg) were examined 15-90 min post-injection. Elevations of serum enzymes, particularly sorbitol dehydrogenase, specific for liver mitochondria, correlated with hepatic damage. Electron micrographs showed progressive cellular disruption, including dilation of rough endoplasmic reticulum, incorporation of cellular components into cytolysosomes, hydropic mitochondria devoid of electron-opaque deposits, loss of desmosome-associated intermediate filaments, disruption of sinusoidal architecture and, ultimately, lysis of hepatocytes. The appearance of hydropic mitochondria correlated with loss of coupled electron transport. Changes in plasma membrane-associated cytoskeletal filaments correlated with loss of desmosome tonofilaments. In contrast to in vivo exposure to microcystin-LR, in vitro exposure to toxin had no effect on mitochondria or cytoskeletal filaments, suggesting that the toxic effects observed in vivo were indirect and may be dependent on bioactivation of the toxin or a cascade of events not supported in in vitro models.

Adenosine Diphosphate↗
PubMed1988

Second messenger mechanisms governing opiate peptide transmitter regulation in the rat adrenal medulla.

Decreasing transsynaptic activity through surgical adrenal denervation or by medullary explantation, increases Leu-enkephalin immunoreactivity (Leu-Enk) and preproenkephalin mRNA (prepro-EK). Membrane depolarization prevents this rise. To determine whether depolarizing effects are mediated by intracellular movement of calcium ions, explanted medullae were depolarized in the presence of EGTA or the calcium ion 'channel' blockers D600 or verapamil. Inhibition of Ca2+ influx prevented the effects of KCl-induced depolarization on the rise in Leu-Enk and on prepro-EK. Increasing intracellular Ca2+ with the ionophore A23187, in the absence of depolarizing agents, reproduced the effects of depolarization. By contrast, medullae grown in the presence of A23187, but in Ca2+-free medium, showed similar increases in prepro-EK mRNA and Leu-Enk, indicating an absolute requirement for Ca2+. In addition, KCl-inhibitory effects could be partially blocked by the calmodulin and protein kinase-C antagonist, trifluoperazine. However, KCl effects were not antagonized by the preferential calmodulin inhibitors W7, W13 or calmidizolium even at doses 10-fold higher than required to prevent calmodulin-dependent effects. Thus, these data suggest that inhibitory effects of transsynaptic activity and membrane depolarization on adrenal enkephalin occurs through Ca2+ and perhaps through a protein kinase-C dependent pathway, mechanisms known to augment catecholamine biosynthesis. It appears then that the same or similar molecular mechanisms can result in differential regulation of these co-localized transmitter systems.

Adrenal Medulla↗