Biomedical subjects

Dorothy W Gietzen

Publications and source records attributed to Dorothy W Gietzen.

16 recordsLinked to original sources

PubMed2006

Co-localization of phosphorylated extracellular signal-regulated protein kinases 1/2 (ERK1/2) and phosphorylated eukaryotic initiation factor 2alpha (eIF2alpha) in response to a threonine-devoid diet.

The anterior piriform cortex (APC) has been shown to be an essential brain structure for the detection of dietary indispensable amino acid (IAA) deficiency, but little has been known about possible molecular detection mechanisms. Increased phosphorylation of the alpha-subunit of the eukaryotic initiation factor 2alpha (eIF2alpha) has been directly linked to amino acid deficiency in yeast. Recently, we have shown increased phosphorylation of eIF2alpha (p-eIF2alpha) in the rat APC 20 minutes after ingestion of an IAA-deficient meal. We suggest that if phosphorylation of eIF2alpha is an important mechanism in detection of IAA deficiency, then APC neurons that show p-eIF2alpha should also show molecular evidence of potentiation. The present research demonstrates increased expression and co-localization of p-eIF2alpha and phosphorylated extracellular signal-regulated protein kinase 1/2 (p-ERK1/2) in APC neurons, but not in the primary motor or agranular insular cortices in response to an IAA-deficient diet. ERK1/2 is an element of the mitogen-activated protein kinase cascade, an intraneuronal signaling mechanism associated with neuronal activation. The region of the APC that responds to IAA deficiency with increased p-eIF2alpha and p-ERK1/2 labeling ranges from 3.1 to 2.5 mm rostral of bregma. Within this region, only a few neurons respond to IAA deficiency with co-localization of abundant p-eIF2alpha and p-ERK1/2. These chemosensory neurons probably detect IAA deficiency and generate neuronal signaling to other portions of the brain, changing feeding behavior.

Animal Feed↗

PubMed2006

Nutritional homeostasis and indispensable amino acid sensing: a new solution to an old puzzle.

Indispensable amino acids are neither synthesized nor stored in animals and are rapidly depleted when not provided by the diet. To maintain homeostasis, organisms must sense deficiency of an indispensable amino acid and implement a repletion strategy. In rats and birds, the anterior piriform cortex houses the detector, but its mechanism has evaded description for >50 years. Recently, rapid detection of amino acid depletion was shown behaviorally when naïve animals, pre-fed a low nitrogen diet, terminated their first deficient meal within 20 min. The general amino acid control system of yeast, which is activated by amino acid deprivation via deacylated tRNA, was found to be active in rodent brain, showing conservation of amino acid sensory mechanisms across eukaryotic species.

Amino Acids, Essential↗

PubMed2005

Autonomic efferents affect intake of imbalanced amino acid diets by rats.

An anorectic response occurs following ingestion of imbalanced amino acid (IMB) diets. There are three phases to this response: 1, recognition of the IMB diet; 2, conditioned development of an aversion to the IMB diet; and 3, adaptation. Blockade of peripheral serotonin-3 (5-HT3) receptors or vagotomy attenuates Phase 2 of the anorectic response. We investigated whether sympathetic efferents interact with the ventral gastric branch (VGB), by cutting it (X), or with the 5-HT3 receptor in these responses. First, VGBX and sham-operated (SHAM) groups were injected with vehicle or phenoxybenzamine (alpha-blocker), or nadolol (beta-blocker) before introducing the IMB diet. At 3 h suppression of the IMB diet ingestion was unchanged, showing no sympathetic efferent effect on Phase 1. Intake of the IMB diet increased 12-24 h later only in the SHAM+phenoxybenzamine group, so the VGB was necessary for alpha-blockade to enhance IMB diet intake during Phase 2 or possibly Phase 3. On days 2-5, intakes by the SHAM+phenoxybenzamine, VGBX+phenoxybenzamine and VGBX+nadolol groups were elevated. Therefore, alpha-blockade enhanced adaptation alone, but VGBX was necessary for beta-receptor blockade to augment Phase 3 adaptation. Both sympathetic efferents and the VGB are involved in Phases 2-3. Second, rats received vehicle or nadolol or scopolamine (nonselective muscarinic blocker) or pirenzepine (muscarinic M-1 receptor blocker),w+/-tropisetron (5-HT3 blocker). Pirenzepine attenuated the tropisetron effect between 6-9 h, but then pirenzepine and nadolol enhanced the tropisetron effect between 9-12 h. Scopolamine attenuated the tropisetron effect between 9-12 h. While neither experiment showed effects during the recognition phase, the autonomic and serotonergic systems interact in the learned and adaptive responses to IMB diets.

Amino Acids↗

PubMed2005

Uncharged tRNA and sensing of amino acid deficiency in mammalian piriform cortex.

Recognizing a deficiency of indispensable amino acids (IAAs) for protein synthesis is vital for dietary selection in metazoans, including humans. Cells in the brain's anterior piriform cortex (APC) are sensitive to IAA deficiency, signaling diet rejection and foraging for complementary IAA sources, but the mechanism is unknown. Here we report that the mechanism for recognizing IAA-deficient foods follows the conserved general control (GC) system, wherein uncharged transfer RNA induces phosphorylation of eukaryotic initiation factor 2 (eIF2) via the GC nonderepressing 2 (GCN2) kinase. Thus, a basic mechanism of nutritional stress management functions in mammalian brain to guide food selection for survival.

Acylation↗

PubMed2005

Fos-positive neurons are increased in the nucleus of the solitary tract and decreased in the ventromedial hypothalamus and amygdala by a high-protein diet in rats.

Transition from a normal- (NP) to a high-protein (HP) diet induces a rapid depression in food intake and a progressive but incomplete return to the initial intake during the succeeding days. The aim of this study was to determine which CNS regions are involved in the HP diet-induced satiety in rats. Brains were collected from 3 groups of adult rats after habituation to an NP diet (21 d), during the transition phase to a HP diet (2 d), or after habituation to the HP diet (21 d). Fos expression was measured in several brain areas that are involved in the control of food intake (solitary tract nucleus, anterior piriform cortex, lateral hypothalamus, arcuate nucleus, posterior para ventricular nucleus, medio ventral hypothalamus, dorso medial hypothalamus, amygdala, and accumbens nucleus). Changes occurred in the majority of these regions during the transition period from the NP diet to the HP diet. After habituation to the HP diet, significant changes in Fos expression were restricted to an increase in the nucleus of the solitary tract and a decrease in the ventromedial hypothalamus and the cortex of the amygdala. Considering the functional characteristics of these areas, the present results suggest that the vagus nerve conveys the information relative to the quantity of protein ingested, that hypothalamic sites regulate food intake and may alter sympathetic nervous system activity, and that higher brain functions such as memory processing by the limbic system or food reward system are involved in the HP diet-induced satiety in rats.

Adaptation, Physiological↗

PubMed2004

NMDA receptor function within the anterior piriform cortex and lateral hypothalamus in rats on the control of intake of amino acid-deficient diets.

Animals decrease intake of an indispensable amino acid (AA)-deficient or devoid diet, due in part to decreased dietary limiting AA (DLAA) concentrations within the anterior piriform cortex (APC), and to a recognition process that occurs as early as 20 min following exposure to AA deficiencies. Glutamate levels within the APC change in response to AA deficiencies. The APC projects to the lateral hypothalamus (LH), where glutamate acts to stimulate food intake. We hypothesize that the APC, through glutamatergic projections to the LH, inhibits the LH, which signals to reject the AA-deficient or devoid diet, and trigger aversions to the AA-deficient or devoid diet via an ascending pathway to the APC. We examined the effects of (1) bilateral APC and LH blockade of glutamate's NMDA receptors with the antagonist, D-AP5, (2) APC blockade of AMPA receptors with the antagonist, NBQX, to block glutamate transmission from the APC, and (3) direct injection of the agonist, NMDA, into the LH on intake of the AA-deficient, devoid, or corrected diet. Administration of D-AP5 into the APC increased intake of AA-deficient diet by 6 h, but D-AP5 in the LH decreased AA-devoid diet preferentially over AA corrected intake sooner. NBQX in the APC increased AA-deficient diet intake, also at 6 h. NMDA injection into the LH-stimulated intake of the AA corrected diet by 3 h, but did not affect AA-devoid diet intake. Thus, the glutamate receptors in the APC and LH are involved in the feeding responses to AA-deficient diet, albeit with regional differences. We suggest that glutamate mediates the anorectic responses to AA-deficient diets through recognition of AA-devoid diet with the glutamatergic output cells of the APC sending glutamate-based signals for changes in food intake within the LH and through learned avoidance of AA-deficient diet within the APC, as indicated through the more immediate and prolonged periods of activation within the LH and APC, respectively.

Amino Acids↗

PubMed2004

Threonine-imbalanced diet alters first-meal microstructure in rats.

Diets limiting in an essential amino acid have long been known to suppress food intake. The purpose of this study was to examine the microstructure of feeding behavior of rats within the very first meal of an imbalanced diet. Rats were preconditioned for 12 days on a Baseline diet and were then given a test diet with either a corrected amino acid profile or a diet imbalanced with respect to the essential amino acid threonine. Overall, first-meal intake and first-meal duration were robustly and significantly reduced by the Imbalanced diet but not altered by the Corrected diet. The Corrected diet caused an increase in the number of feeding bouts during the first meal. The Imbalanced diet increased the duration of pauses during the first meal. Most rats in the Imbalanced group stopped eating after just 15 min of exposure to the diet, but those still eating after this time tended to have a lower rate of eating compared to those eating the Corrected diet. On the basis of these results, we conclude that changes in microstructure and meal duration contribute to the reduction in food intake upon exposure to amino-acid-deficient diets.

Animal Feed↗

PubMed2004

Phosphorylation of eIF2alpha is involved in the signaling of indispensable amino acid deficiency in the anterior piriform cortex of the brain in rats.

Sensing of indispensable amino acid (IAA) deficiency, an acute challenge to protein homeostasis, is demonstrated by rats as rejection of IAA-deficient diets within 20 min. The anterior piriform cortex (APC) of the brain in rats and birds is essential for this nutrient sensing, and is activated by IAA deficiency. Yet the mechanisms that sense and transduce IAA reduction to signaling in the APC, or indeed in any animal cells, are unknown. Because rejection of a deficient diet within 20 min is too rapid to be explained by transcription-derived signals, brain tissue was taken from rats after 20 min access to either a threonine-basal, -devoid, or -corrected diet and examined for proteins associated with early signaling of IAA deficiency in the yeast model. Western blots and immunohistochemistry showed that the phosphorylation of eukaryotic initiation factor 2-alpha (p-eIF2alpha[Ser51]) and translation of its downstream product, c-Jun, were increased (47%, P < 0.005, and 55%, P < 0.025, respectively) in APC from rats offered devoid, but not corrected diets, compared with those offered basal diets. This was not seen in other brain areas. In cells intensely labeled for cytoplasmic p-eIF2alpha, there was intense fluorescence for c-Jun in the nucleus. Thus, p-eIF2alpha, which is pivotal in the initiation of global protein translation, and its downstream product, the leucine zipper protein, c-Jun, are increased in the mammalian APC within the time frame necessary for the behavioral response. We suggest that p-eIF2alpha and c-Jun participate in signaling nutrient deficiency in the IAA-sensitive neurons of the APC.

Amino Acids, Essential↗

PubMed2004

Diets deficient in indispensable amino acids rapidly decrease the concentration of the limiting amino acid in the anterior piriform cortex of rats.

Diets deficient in an indispensable amino acid have long been known to suppress food intake in rats. Detection of dietary deficiency takes place in the anterior piriform cortex (APC). Recent studies showed that the response to amino acid deficiency takes as little as 15 min to develop, but few data exist to correlate the concentration of amino acids in the APC with this rapid response. The purpose of this study was to measure the concentration of amino acids in the APC in a behaviorally relevant time frame. Rats were preconditioned by consumption of a basal diet for 7-10 d, and then given a test diet with either a control or deficient amino acid profile. Both the threonine- and leucine-deficient diets reliably depleted threonine and leucine concentration in the APC within 30 min, respectively. The control diets and a diet lacking the dispensable amino acid glycine did not lead to amino acid depletion. In combination with previous studies, the present results show that the decrease in the concentration of indispensable amino acids in the APC may be the initial sensory signal for recognition of dietary amino acid deficiency.

Animals↗

PubMed2003

The rapid anorectic response to a threonine imbalanced diet is decreased by injection of threonine into the anterior piriform cortex of rats.

Rats quickly recognize and reject diets deficient in an essential amino acid. The purpose of this study was to determine whether the anterior piriform cortex (APC), the site traditionally recognized as the amino acid chemosensor, plays a role in this early behavior. Rats had cannulae implanted bilaterally into the APC, and were injected with either saline vehicle or 2 nmoles of threonine (n = 6 per group). All rats were then fed a diet imbalanced with respect to threonine. The threonine-injected group had first meals of longer duration and consumed more food. These data conformed to expectations derived from earlier studies of responses to the first meal of an amino acid imbalanced diet. We conclude that the concentration of the dietary limiting amino acid in the APC regulates acceptance and rejection of amino acid deficient diets.

Amino Acids↗

PubMed2003

Effects of amino acid deficiency on monoamines in the lateral hypothalamus (LH) in rats.

Animals decrease intake of an indispensable amino acid deficient diet, due in part to decreased dietary limiting amino acid concentrations within the anterior piriform cortex (APC). In addition to studies supporting a primary role for the APC in this phenomenon, recent studies have shown that the lateral hypothalamus (LH), which receives projections from the APC, also mediates the anorectic response to amino acid deficiency. The neurochemical changes within the LH that accompany the anorexia to amino acid deficiency are unclear. We hypothesized that norepinephrine (NE), dopamine (DA) and serotonin, whose levels are altered in response to amino acid deficiency within the APC, also act within the LH to mediate amino acid deficiency-induced anorexia. We determined that ingestion of an amino acid devoid diet increased concentrations of NE and the serotonin metabolite, 5-hydroxyindoleacetic acid in the LH. The 5-hydroxytryptamine metabolite was increased overall, according to analysis by area under the curve. Individual points reached significance at 130 min; NE was elevated at 170 min. These results suggest that the sustained anorectic response following ingestion of an amino acid devoid diet may be associated with increased activity of the NE and 5-hydroxytryptamine systems in the LH.

Amino Acids↗

PubMed2003

Threonine deprivation rapidly activates the system A amino acid transporter in primary cultures of rat neurons from the essential amino acid sensor in the anterior piriform cortex.

Omnivores show recognition of essential (indispensable) amino acid deficiency by changing their feeding behavior within 20 min, yet the cellular mechanisms of amino acid sensation in eukaryotes are poorly understood. The anterior piriform cortex (APC) of the brain in rats or its analog in birds likely houses the in vivo amino acid chemosensor. Because amino acid transporters adapt rapidly to essential amino acid deficiency in several cell models, we hypothesized that activation of electrogenic amino acid transport in APC neurons might contribute to the function of the amino acid sensor. We evaluated transport systems in primary cultures of neurons from the APC, hippocampus and cerebellum, or glia, incubated in complete or threonine-devoid (deficient) medium. After 10 min in deficient medium, uptake of threonine or a system A-selective substrate, methyl amino-isobutyric acid, was increased 60% in APC neurons only (P < 0.05). These results demonstrated upregulation of system A, an electrogenic amino acid-sodium symporter. This depletion-induced activation required sodium, intact intracellular trafficking, and phosphorylation of signal transduction-related kinases. Efflux studies showed that other transporter types were functional in the APC; they appeared to be altered dynamically in threonine-deficient cells in response to rapid increases in system A activity. The present data provided support for the chemical sensitivity of the APC and its role as the brain area housing the indispensable amino acid chemosensor. They also showed a region-specific, phosphorylation-dependent activation of the system A transporter in the brain in response to threonine deficiency.

Amino Acid Transport System A↗

PubMed2003

Rats rapidly reject diets deficient in essential amino acids.

Omnivores must obtain diets balanced with respect to amino acids to support growth and protein synthesis. The standard paradigm used to study behavioral responses to amino acid deficiency combines deficient diets with dietary novelty. The objective of this study was to examine the effects of amino acid deficiency on the first meal of rats without the confounding effects of novelty. We report on a series of five studies of feeding behavior in rats. Rats were fed low protein diets for 5-7 d and then exposed to diets with and without essential amino acids. Rats consistently demonstrated recognition of essential amino acid deficiency within the first meal by a significant reduction in first meal duration, rejecting the deficient diets after just 12-16 min exposure. This is the first report of a rapid effect of amino acid-deficient diets without the confounding effects of dietary novelty.

Amino Acids, Essential↗

PubMed2002

Role of MAP kinase in signaling indispensable amino acid deficiency in the brain.

Deficiencies of indispensable amino acids (IAAs) appear to be sensed in the anterior piriform cortex (APC) where neurons are activated and potentiated, however, the mediating intracellular signaling mechanisms are largely unexplored. It is postulated that signaling of amino acid deficiency may share many of the same pathways seen with long-term potentiation (LTP). Phosphorylation of mitogen-activated protein kinase (pMAP kinase) has been shown to be a necessary signaling event for the genesis and maintenance of LTP. Immunoperoxidase immunohistochemistry was used to determine the number of neurons showing activation of the MAP kinase signal transduction system. Relative to rats eating a corrected diet, rats consuming threonine-devoid diet showed significantly greater pMAP kinase labeling in the APC, dorsomedial hypothalamus, and the paraventricular hypothalamic nucleus. These are areas previously associated with control of food intake. However, since the dorsomedial hypothalamus and the paraventricular hypothalamic nucleus have not previously been implicated as chemosensory areas for IAAs, phosphorylated MAP kinase expression in these areas may reflect secondary activation.

Animals↗

PubMed2002

GABA(A) and GABA(B) receptors in the anterior piriform cortex modulate feeding in rats.

The effects of GABA(A) and GABA(B) receptors in the anterior piriform cortex (APC) on intake of an amino acid imbalanced diet and a basal diet were evaluated in rats. Administration of muscimol (GABA(A) receptor agonist) to the APC immediately suppressed ingestion of both amino acid imbalanced and basal diets. Central administration of bicuculline (a GABA(A) receptor antagonist) stimulated feeding of the amino acid imbalanced diet but had no effect on intake of the basal diet. The GABA(B) receptor antagonist phaclofen decreased consumption of the basal diet but did not affect consumption of the amino acid imbalanced diet. These findings demonstrate that manipulation of GABA-sensitive cells in the APC can have a pronounced effect on feeding behavior that is not selective to aminoprivic feeding. However, these data suggest that GABA(A) and GABA(B) receptors may function as regulators that are activated by monoaminergic systems and neuropeptides in response to amino acid imbalanced diet intake. Inhibitory effects of GABA(A) and GABA(B) receptors may modulate the pyramidal cells, contributing to the reduced feeding response to the amino acid imbalanced diet. Also, transcription of mRNA for both GABA receptors and the GABA reuptake transporter was affected by a threonine deficient but not a corrected diet, compared to the basal diet. Taken together, these results support the involvement of GABA receptors in the APC in feeding in general and the responses to amino acid deprivation in vivo.

Amino Acids↗

PubMed2002

Transfer ribonucleic acid charging in rat brain after consumption of amino acid-imbalanced diets.

Recognition of an amino acid-imbalanced diet (IMB) is thought to occur in the anterior piriform cortex (APC) of the brain in response to a decrease in the limiting amino acid. We hypothesized that tRNA charging is decreased after ingestion of IMB and that this is part of the mechanism by which a decrease in the limiting amino acid is recognized. We investigated this question by determining levels of charged and uncharged tRNA using the periodate oxidation method and also by using high performance liquid chromatography (HPLC) analysis of amino acids acylated to brain tRNA. Using the periodate method, we found that isoleucyl-tRNA in both whole brain and APC of rats fed an isoleucine-IMB was increased, rather than decreased, in comparison to the basal diet and the corrected diet. Using HPLC analysis, we found that the absolute amount of tRNA charged with the limiting amino acid was not altered by dietary treatment. These two experimental approaches measure different aspects of tRNA charging, but the results clearly indicate that a reduction in tRNA charging is unlikely to be the signal by which a limiting amino acid is recognized in the brain 2 h after ingestion of IMB.

Acylation↗