Correlation between plasma levels of arginine and citrulline in preterm and full-term neonates: Therapeutical implications.

BACKGROUND: Preterm neonates exhibit several deficiencies that endanger their lives. Understanding those disturbances will provide tools for the management of preterm neonates. The present work focuses on arginine and citrulline which has been flagged among the biochemical landmarks of prematurity. METHODS: We examined blood samples of preterm newborns as compared with mature neonates to determine the levels of arginine and citrulline by capillary zone electrophoresis with laser induced fluorescence detection (CZE-LIFD). RESULTS: Significantly lower levels of arginine and citrulline were found in preterm neonates than in mature neonates (P<.01). Interestingly there was a highly significant correlation between the two amino acids in mature neonates (P<.0001). Such correlation was present in preterm neonates too (P<.01). Pearson coefficient showed that 60% of the citrulline concentration depends on arginine concentration in mature neonates. Only 20% of the citrulline concentration depends on arginine concentration in preterm neonates. Although the ratio arginine/citrulline was lower in preterm neonates than in mature neonates the difference was not statistically significant. CONCLUSIONS: These results suggest that less arginine is converted to citrulline to form nitric oxide in preterm than in full-term neonates. The result is discussed in terms of the immature enzymatic systems in the preterm neonate.

Physical exercise prevents stress-induced activation of granule neurons and enhances local inhibitory mechanisms in the dentate gyrus.

Physical exercise is known to reduce anxiety. The ventral hippocampus has been linked to anxiety regulation but the effects of running on this subregion of the hippocampus have been incompletely explored. Here, we investigated the effects of cold water stress on the hippocampus of sedentary and runner mice and found that while stress increases expression of the protein products of the immediate early genes c-fos and arc in new and mature granule neurons in sedentary mice, it has no such effect in runners. We further showed that running enhances local inhibitory mechanisms in the hippocampus, including increases in stress-induced activation of hippocampal interneurons, expression of vesicular GABA transporter (vGAT), and extracellular GABA release during cold water swim stress. Finally, blocking GABAA receptors in the ventral hippocampus, but not the dorsal hippocampus, with the antagonist bicuculline, reverses the anxiolytic effect of running. Together, these results suggest that running improves anxiety regulation by engaging local inhibitory mechanisms in the ventral hippocampus.

Opioids in the hypothalamic paraventricular nucleus stimulate ethanol intake.

BACKGROUND: Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists. METHODS: Sprague-Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the mu-receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin (DAMGO), delta-receptor agonist D-Ala-Gly-Phe-Met-NH2 (DALA), or kappa-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN. RESULTS: A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the delta-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the kappa-agonist U-50,488H, which decreased ethanol intake, and the mu-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip. CONCLUSIONS: The delta-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the kappa-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the delta- and kappa-receptors, respectively. These results suggest that enkephalin via the delta-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the kappa-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle.

Sugar and fat bingeing have notable differences in addictive-like behavior.

Ingestion of different nutrients, such as fats and sugars, normally produces different effects on physiology, the brain, and behavior. However, they do share certain neural pathways for reinforcement of behavior, including the mesolimbic dopamine (DA) system. When these nutrients are consumed in the form of binges, this can release excessive DA, which causes compensatory changes that are comparable to the effects of drugs of abuse. In this article, we review data obtained with animal models of fat and sugar bingeing. The concept of "food addiction" is described and reviewed from both clinical and laboratory animal perspectives. Behavioral manifestations of addictive-like behavior and concomitant alterations in DA and opioid systems are compared for sugar and fat bingeing. Finally, in relation to eating disorders and obesity, we discuss how fat may be the macronutrient that results in excess body weight, and sweet taste in the absence of fat may be largely responsible for producing addictive-like behaviors that include a withdrawal syndrome.

Evidence for sugar addiction: behavioral and neurochemical effects of intermittent, excessive sugar intake.

[Avena, N.M., Rada, P., Hoebel B.G., 2007. Evidence for sugar addiction: Behavioral and neurochemical effects of intermittent, excessive sugar intake. Neuroscience and Biobehavioral Reviews XX(X), XXX-XXX]. The experimental question is whether or not sugar can be a substance of abuse and lead to a natural form of addiction. "Food addiction" seems plausible because brain pathways that evolved to respond to natural rewards are also activated by addictive drugs. Sugar is noteworthy as a substance that releases opioids and dopamine and thus might be expected to have addictive potential. This review summarizes evidence of sugar dependence in an animal model. Four components of addiction are analyzed. "Bingeing," "withdrawal," "craving" and "cross-sensitization" are each given operational definitions and demonstrated behaviorally with sugar bingeing as the reinforcer. These behaviors are then related to neurochemical changes in the brain that also occur with addictive drugs. Neural adaptations include changes in dopamine and opioid receptor binding, enkephalin mRNA expression and dopamine and acetylcholine release in the nucleus accumbens. The evidence supports the hypothesis that under certain circumstances rats can become sugar dependent. This may translate to some human conditions as suggested by the literature on eating disorders and obesity.

After daily bingeing on a sucrose solution, food deprivation induces anxiety and accumbens dopamine/acetylcholine imbalance.

Bingeing on sugar may activate neural pathways in a manner similar to taking drugs of abuse, resulting in related signs of dependence. The present experiments test whether rats that have been bingeing on sucrose and then fasted demonstrate signs of opiate-like withdrawal. Rats were maintained on 12-h deprivation followed by 12-h access to a 10% sucrose solution and chow for 28 days, then fasted for 36 h. These animals spent less time on the exposed arm of an elevated plus-maze compared with a similarly deprived ad libitum chow group, suggesting anxiety. Microdialysis revealed a concomitant increase in extracellular acetylcholine and decrease in dopamine release in the nucleus accumbens shell. These results did not appear to be due to hypoglycemia. The findings suggest that a diet of bingeing on sucrose and chow followed by fasting creates a state that involves anxiety and altered accumbens dopamine and acetylcholine balance. This is similar to the effects of naloxone, suggesting opiate-like withdrawal. This may be a factor in some eating disorders.

Accumbens dopamine-acetylcholine balance in approach and avoidance.

Understanding systems for approach and avoidance is basic for behavioral neuroscience. Research on the neural organization and functions of the dorsal striatum in movement disorders, such as Huntington's and Parkinson's Disease, can inform the study of the nucleus accumbens (NAc) in motivational disorders, such as addiction and depression. We propose opposing roles for dopamine (DA) and acetylcholine (ACh) in the NAc in the control of GABA output systems for approach and avoidance. Contrary to DA, which fosters approach, ACh release is a correlate or cause of meal satiation, conditioned taste aversion and aversive brain stimulation. ACh may also counteract excessive DA-mediated approach behavior as revealed during withdrawal from drugs of abuse or sugar when the animal enters an ACh-mediated state of anxiety and behavioral depression. This review summarizes evidence that ACh is important in the inhibition of behavior when extracellular DA is high and the generation of an anxious or depressed state when DA is relatively low.

Sugar Addiction: From Evolution to Revolution.

The obesity epidemic has been widely publicized in the media worldwide. Investigators at all levels have been looking for factors that have contributed to the development of this epidemic. Two major theories have been proposed: (1) sedentary lifestyle and (2) variety and ease of inexpensive palatable foods. In the present review, we analyze how nutrients like sugar that are often used to make foods more appealing could also lead to habituation and even in some cases addiction thereby uniquely contributing to the obesity epidemic. We review the evolutionary aspects of feeding and how they have shaped the human brain to function in "survival mode" signaling to "eat as much as you can while you can." This leads to our present understanding of how the dopaminergic system is involved in reward and its functions in hedonistic rewards, like eating of highly palatable foods, and drug addiction. We also review how other neurotransmitters, like acetylcholine, interact in the satiation processes to counteract the dopamine system. Lastly, we analyze the important question of whether there is sufficient empirical evidence of sugar addiction, discussed within the broader context of food addiction.

A ketogenic diet modifies glutamate, gamma-aminobutyric acid and agmatine levels in the hippocampus of rats: A microdialysis study.

The ketogenic diet (KD) is acknowledged as an unconventional option in the treatment of epilepsy. Several lines of investigation point to a possible role of glutamate and gamma-aminobutyric acid (GABA) as main contributors in this protective effect. Other biomolecules could also be involved in the beneficial consequence of the KD, for example, the diamine agmatine has been suggested to block imidazole and glutamate NMDA receptor and serves as an endogenous anticonvulsant in different animal models of epilepsy. In the present report, we have used microdialysis coupled to capillary electrophoresis to monitor microdialysate levels of GABA, glutamate and agmatine in the hippocampus of rats submitted to a KD for 15days compared to rats on a normal rat chow diet. A significant increase in GABA and agmatine levels while no change in glutamate levels was observed. These results support the notion that the KD modifies different transmitters favoring inhibitory over excitatory neurotransmitters.

Acetylcholine in the accumbens is decreased by diazepam and increased by benzodiazepine withdrawal: a possible mechanism for dependency.

Diazepam is a benzodiazepine used in the treatment of anxiety, insomnia and seizures, but with the potential for abuse. Like the other benzodiazepine anxiolytics, diazepam does not increase dopamine in the nucleus accumbens. This raises the question as to which other neurotransmitter systems are involved in diazepam dependence. The goal was to monitor dopamine and acetylcholine simultaneously following acute and chronic diazepam treatment and after flumazenil-induced withdrawal. Rats were prepared with microdialysis probes in the nucleus accumbens and given diazepam (2, 5 and 7.5 mg/kg) acutely and again after chronic treatment. Accumbens dopamine and acetylcholine decreased, with signs of tolerance to the dopamine effect. When these animals were put into the withdrawal state with flumazenil, there was a significant rise in acetylcholine (145%, P<0.001) with a smaller significant rise in dopamine (124%, P<0.01). It is suggested that the increase in acetylcholine release, relative to dopamine, is a neural component of the withdrawal state that is aversive.

Extracellular glutamate increases in the lateral hypothalamus during meal initiation, and GABA peaks during satiation: microdialysis measurements every 30 s.

Glutamate injected into the lateral hypothalamus can initiate eating, and gamma-aminobutyric acid (GABA) can stop it. This leads to the hypothesis that glutamate inputs are active at the beginning of a meal, and GABA is released at the end. To test this theory, the authors used microdialysis to sample glutamate and GABA simultaneously before, during, and after a meal. Food-deprived rats ate a meal of chow. Glutamate increased during the first third of the meal, then decreased to below baseline while the rats were still eating. GABA also increased at the start of the meal but continued rising and peaked during the last third of the meal. Glutamate may drive a hypothalamic system for eating, and GABA may oppose it.

Cholecystokinin combined with serotonin in the hypothalamus limits accumbens dopamine release while increasing acetylcholine: a possible satiation mechanism.

Serotonin (5-HT) or cholecystokinin (CCK) injected in the hypothalamic paraventricular nucleus (PVN) inhibits feeding, but the mechanism is unknown. Prior research suggests that dopamine (DA) input to the nucleus accumbens (NAc) motivates behavior, and a component of that motivation circuit includes hypothalamic feeding systems. Acetylcholine (ACh) in the NAc, on the other hand, may act in part to inhibit feeding and generate satiety. If so, 5-HT and/or CCK in the PVN should lower extracellular DA or release ACh in the NAc. Rats were prepared with microdialysis probes in the NAc and injectors in the PVN. Serotonin (7.75 microg) or CCK-8 (0.12 microg) injected in the PVN significantly decreased ipsilateral accumbens DA (63 and 73% of baseline, respectively, without effect on ACh). However, 5-HT plus CCK injected in combination decreased DA to 72% (P<0.001) and simultaneously increased extracellular ACh to 128% of baseline (P<0.001). In later tests with the same doses and the same animals, unilateral PVN injections of 5-HT, CCK, or both combined, significantly inhibited food intake in the early dark period. The results suggest that 5-HT in the PVN acts as a neural modulator that primes a hypothalamic satiation system to respond to CCK when the gastrointestinal tract contains food to be digested. The synergistic action of 5-HT plus phasic CCK may then activate a circuit that simultaneously limits DA and releases ACh in the accumbens as part of the satiation process.

Haloperidol abolished glutamate release evoked by photic stimulation of the visual cortex in rats.

There is evidence that systemic administration of haloperidol, a dopamine receptor blocker, attenuates visual cortex evoked potentials. However, there is scarce information on cortical neurochemical changes associated with haloperidol effects on visual function. The present experiment was designed to investigate: (1) the effect of photic stimulation on glutamate release in the visual cortex; and (2) whether systemic administration of haloperidol would affect those neurochemical changes. Microdialysis probes were implanted in the occipital cortex. Glutamate levels were measured every 30 s using capillary zone electrophoresis. Extracellular glutamate levels increased to about 282% 30 s after photic stimulation started and remain elevated for the 3 min that the photic stimulation lasted. Haloperidol (1.5 and 5 mg/kg, i.p.) completely suppressed the increased of glutamate efflux during photic stimulation. Finally, it was also found that the highest dose of haloperidol (5 mg/kg) did not change glutamate basal levels. The results are discussed with reference to possible dopaminergic actions on the visual system function.

Inhibition of cocaine self-administration by fluoxetine or D-fenfluramine combined with phentermine.

Instrumental responding for intravenous cocaine in rats at 85% of free-feeding weight was significantly decreased 50% by D-fenfluramine plus phentermine (D-Fen/Phen, 5 mg/kg of each for 1 day). A similar effect was obtained in normal-weight rats self-administering a cocaine-heroin mixture. Treating normal-weight animals with fluoxetine (5 mg/kg) for 4 days also significantly decreased cocaine self-administration by half, and then adding phentermine caused an additional decrease in cocaine intake. Animals that were well trained to self-administer drug did not self-administer intravenous D-Fen/Phen or Flu/Phen. The present results confirm that serotonergic drugs can decrease cocaine, or cocaine/heroin, self-administration in rats, and that phentermine adds to the effect. Based on related research with the same dose of D-Fen/Phen, it is suggested that effectiveness in reducing cocaine reinforcement is due in part to a satiating effect in which dopamine and acetylcholine are released in the nucleus accumbens.

Ethanol intake is increased by injection of galanin in the paraventricular nucleus and reduced by a galanin antagonist.

Ethanol intake stimulates expression of galanin in several hypothalamic sites, including the paraventricular nucleus. Because injection of galanin in the paraventricular nucleus induces eating, we hypothesized that galanin might also affect ethanol intake. Rats were given ad libitum access to 4% ethanol for 4 weeks and assigned to one of two groups according to levels of ethanol consumption: high levels (>1.5 g/ kg/day) or low levels (<1.0 g/kg/day). In Experiment 1, galanin (1.0 nmol) or Ringer's solution was injected unilaterally into the paraventricular nucleus, with food and water absent during the first 4 h. Galanin significantly increased ethanol intake only in rats that drank high levels of ethanol. In Experiment 2, injection of galanin (0.5 and 1.0 nmol) in the paraventricular nucleus dose-dependently increased ethanol intake with food and water available. The higher dose was also effective in eliciting ethanol intake when tested with food and water absent. In Experiment 3, a test of receptor specificity was provided by injecting rats with the galanin antagonist M-40 (0.5 nmol) or Ringer's solution. Injection of M-40 in the paraventricular nucleus significantly decreased ethanol consumption. In Experiment 4, an anatomic control, with galanin injected 2 mm dorsal to the paraventricular nucleus in the same animals, caused no change in ethanol intake. In conclusion, injection of galanin in the paraventricular nucleus, at a dose known to induce feeding, acted by means of a galanin receptor to potentiate intake of 4% ethanol, even with food and water available as alternate sources of calories and fluid, respectively. Because ethanol can increase expression of galanin mRNA in the paraventricular nucleus, this could set the stage for a positive feedback loop between galanin and ethanol intake.

Cholinergic modulation of food and drug satiety and withdrawal.

Although they comprise only a small portion of the neurons in the region, cholinergic interneurons in the dorsal striatum appear to play an important role in the regulation of various appetitive behaviors, in part, through their interactions with mesolimbic dopamine (DA) systems. In this review, we describe studies that suggest that the activity of cholinergic interneurons in the nucleus accumbens (NAc) and cholinergic projections to the ventral tegmental area (VTA) affect feeding behavior. In vivo microdialysis studies in rats have revealed that the cessation of a meal is associated with a rise in acetylcholine (ACh) levels in the NAc. ACh activation will suppress feeding, and this is also associated with an increase in synaptic accumulation of ACh. Further, we discuss how, in addition to their role in the ending of a meal, cholinergic interneurons in the NAc play an integral role in the cessation of drug use. Another cholinergic system involved in different aspects of appetitive behavior is the projection from the pedunculpontine nuclei directly to the VTA. Activation of this system enhances behaviors through activation of the mesolimbic DA system, and antagonism of ACh receptors in the VTA can reduce drug self-administration. Finally, we discuss the role of accumbens ACh in both drug and palatable food withdrawal. Studies reveal that accumbens ACh is increased during withdrawal from several different drugs of abuse (including cocaine, nicotine and morphine). This rise in extracellular levels of ACh, coupled with a decrease in extracellular levels of DA, is believed to contribute to an aversive state, which can manifest as behaviors associated with drug withdrawal. This theory has also been applied to studies of overeating and/or "food addiction," and the findings suggest a similar imbalance in DA/ACh levels, which is associated with behavioral indications of drug-like withdrawal. In summary, cholinergic neurons play an important role in the modulation of both food and drug intake, as well as the aversive aspects of food- and drug-related addictive behaviors.

In vivo monitoring of cerebral agmatine by microdialysis and capillary electrophoresis.

Agmatine is a putative neurotransmitter in the brain. Current analytical techniques do not allow the detection of agmatine in extracellular fluid, making it difficult to study its physiological role. However, a new method for in vivo monitoring agmatine in the brain was developed. Capillary zone electrophoresis and laser induced fluorescence detection (CZE-LIFD) was used to measure nanomolar concentrations of agmatine in submicroliter sample volumes. This analytical technique proved to detect 0.49 attomole of agmatine improving the sensitivity of previous analytical techniques. On the other hand, the hippocampus is a brain region well known for having a population of agmatine containing neurons. Therefore, intracerebral microdialysis was performed in the hippocampus and agmatine was extracted from the extracellular environment. Detectable amounts of agmatine were found in dialysates from probes located in the hippocampus but not from the probes located in the lateral ventricle. Furthermore, extracellular agmatine was calcium and impulse dependent and depolarization of hippocampal neurons increased extracellular agmatine concentration. The methods reported here are sensitive enough to study the physiological role of brain agmatine in freely moving animals.

Amino acid profile of plasma and cerebrospinal fluid in preeclampsia.

OBJECTIVES: To determine patterns in amino acids (arginine, GABA, glutamate and glutamine) and the diamine (agmatine) in plasma and cerebrospinal fluid (CSF) of mild and severe preeclampsia compared to control patients, using capillary zone electrophoresis to generate methods for refining diagnosis and prognosis and shed light on the pathophysiological mechanisms of preeclampsia. STUDY DESIGN: This is an observational case-control study in pregnant women that attended the emergency ward of the University Hospital, Mérida, Venezuela, during the period April, 2009-April 2010. MAIN OUTCOME MEASURES: Molar concentration of amino acids and diamine in plasma and CSF in control, mild and severe preeclampsia patients. RESULTS: An increase in glutamate plasma levels was observed in mild preeclampsia and even higher in severe patients, while a biphasic response occurred in the CSF samples with a significant increment in mild preeclampsia patients and a decrease in severe preeclampsia patients. GABA significantly decreased both in plasma and CSF in mild preeclampsia with a tendency to return to normal levels in severe preeclampsia patients. Arginine CSF and plasma levels decreased in mild preeclampsia patients and even more in severe preeclampsia while agmatine significantly increased in plasma levels with no changes in CSF. CONCLUSIONS: The results are discussed in terms of molecules that could be used as biomarkers of the severity of the disease and the possible involvement of these substances in the pathophysiology of preeclampsia.

A high-fat meal, or intraperitoneal administration of a fat emulsion, increases extracellular dopamine in the nucleus accumbens.

Evidence links dopamine (DA) in the nucleus accumbens (NAc) shell to the ingestion of palatable diets. Less is known, however, about the specific relation of DA to dietary fat and circulating triglycerides (TG), which are stimulated by fat intake and promote overeating. The present experiments tested in Sprague-Dawley rats whether extracellular levels of NAc DA increase in response to acute access to fat-rich food or peripheral injection of a fat emulsion and, if so, whether this is related to caloric intake or elevated circulating lipids. When rats consumed more calories of a high-fat meal compared with a low-fat meal, there was a significant increase in extracellular accumbens DA (155% vs. 119%). Systemic injection of a fat emulsion, which like a high-fat diet raises circulating TG but eliminates the factor of taste and allows for the control of caloric intake, also significantly increased extracellular levels of DA (127%) compared to an equicaloric glucose solution (70%) and saline (85%). Together, this suggests that a rise in circulating TG may contribute to the stimulatory effect of a high-fat diet on NAc DA.

Feeding behavior as seen through the prism of brain microdialysis.

The knowledge of feeding behavior mechanisms gained through brain microdialysis is reviewed. Most of the chemical changes so far reported concern to the limbic system in rodents. A picture showing increases and decreases of extracellular neurotransmitters correlating to different aspects of feeding behavior is gradually emerging. Depending on the region, the same neurotransmitter may signal opposite aspects of feeding. Dopamine (DA) in the nucleus accumbens (NAC) correlates with food reward, stimulus saliency, and goal directed hyperlocomotion but in the ventromedial hypothalamus DA correlates with satiety and hypolocomotion. The findings accumulated in the last 25 years suggest that the control of a particular function relies on the interaction of several neurotransmitters rather than on a single neurotransmitter. The poor sensitivity of most analytical techniques hinders time and spatial resolution of microdialysis. Therefore, neurochemical correlates of short lasting behaviors are hard to figure out. As new and more sensitive analytical techniques are applied, new neurochemical correlates of feeding show up. Sometimes the proper analytical techniques are simply not available. As a consequence, critical signals such as neuropeptides are not yet completely placed in the puzzle. Despite such limitations, brain microdialysis has yielded a great deal of knowledge on the neurochemical basis of feeding.