The nucleus accumbens (NAc) has emerged as an important part of the neural circuitry regulating d... more The nucleus accumbens (NAc) has emerged as an important part of the neural circuitry regulating depressivelike behaviors. Given that the NAc GABAergic medium spiny neurons project to the ventral pallidum (VP), it is reasonable to suggest that the VP may also be involved in these behaviors. Consequently, we explored the role of the VP GABAergic terminals during depressive-like behaviors in rats using the forced swim test (FST) and the sucrose preference test (SPT). Microdialysis coupled with micellar electrokinetic chromatography was used to monitor in vivo changes of GABA in the VP during the FST. GABA levels significantly increased during day-1 and day-2 during swimming, returning to the pre-swimming levels after the test. Basal concentrations of GABA on day-2 of the FST significantly increased with respect to day-1. In another set of experiments, intra-VP injections of vigabatrin (a GABA transaminase inhibitor) increased extracellular GABA and immobility behaviors in the FST while the direct GABAA receptor antagonist bicuculline reduced immobility behaviors. In the SPT, intra-VP vigabatrin injection significantly reduced preference for sucrose while bicuculline did not produce any change. At the postsynaptic side, we used semiquantitative RT-PCR to measure mRNA expression of 17 GABAA receptor subunits (␣1-␣6, 1-3, ␥2, ␦, , , , and 1-3) in rats subjected to the FST. We found a significant reduction of ␣3 and ␥2 subunit expression and an increase of ␦ subunit expression after day-2 in rats subject to the FST which might enhance tonic inhibition of the VP. Furthermore, immunoblot experiments revealed that protein expression of ␥2 and ␦ subunits changed 6 days after FST in a way similar to mRNA expression. These results suggest that the enhanced VP-GABAergic tone might trigger a low motivational state, anhedonia and a possible memory mechanism for unpleasant experiences.
Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatu... more Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (2 1%) following feeding. Drinking caused
Evidence links dopamine (DA) in the nucleus accumbens (NAc) shell to the ingestion of palatable d... more 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.
Ingestion of different nutrients, such as fats and sugars, normally produces different effects on... more 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 producin...
ABSTRACT Background / Purpose: Previous reports have related the nucleus accumbens (NAc) with beh... more ABSTRACT Background / Purpose: Previous reports have related the nucleus accumbens (NAc) with behavioral depression. Additionally, an important number of GABAergic medium spiny neurons project from the NAc to the ventral pallidum (VP) through the medial forebrain bundle.We studied the VP GABAergic system in behaviorally depressed rats. The inescapable swim test (IST) was employed to induce a behavioral depression-like state on male Sprague-Dawley rats (250-350 g). On day 2 of IST, we measured the mRNA of 17 subunits of the GABA-A receptor (α1-α6, β1-β3, γ2, δ, ε, θ, π, ρ1, ρ2 and ρ3) by semiquantitative RT-PCR. Then, we used immunoblot to explore the synthesis of the GABA-A receptor subunits that showed significant mRNA differences. Finally, we locally injected the GABA-A indirect agonist vigabatrin (0, 5, 10 and 15 µg/0.5 µl); or the direct antagonist bicuculline methbromide (100 ng/0.5 µl), at a flow rate of 0.5 µl/min. Main conclusion: IST induced significant downregulation in transcript level for α3 and γ2 subunits, whereas δ subunit expression was upregulated at day 2. The mRNA of α4, α6, β3, and ρ1 subunits did not express in VP. We did not detect protein expression changes for γ2 and δ subunits at day 2. However, they were evident at day 8 of IST in the same way that changes in transcript expression for γ2 (downregulated) and δ subunits (upregulated). α3 subunit was never detected. VP microinjections of vigabatrin were pro-depressive and bicuculline anti-depressive.The results found by us suggest that GABAergic transmission on the VP seems to be increased during IST, and that it might change the expression pattern of GABA-A receptor subunits. These changes on the GABA-A receptor suggest a possible mechanism of neuronal plasticity underlying helplessness.
Neurosurgery for psychiatric disorders, notably for obsessive-compulsive disorder (OCD), was init... more Neurosurgery for psychiatric disorders, notably for obsessive-compulsive disorder (OCD), was initiated in Venezuela in the decade of 1970, and consisted since that time in the classic stereotactic anterior cingulotomy. In order to know further about the physiopathology of this disorder, we performed intracerebral microdialysis in 2 patients who were operated on. The aim was to measure changes in extracellular neurotransmitters within the basal ganglia. The microdialysis probes were stereotactically placed in the right caudate nucleus and in the dorsomedial nucleus of the right thalamus. The microdialysis was done before the left cingulotomy, during the pause and after the right cingulotomy. Glutamate and gamma-aminobutyric acid (GABA) changes were similar in the caudate nucleus of both patients, whereas in the dorsomedial nucleus the changes were opposite among the 2 patients. Although this study does not bring enough data to explain such differences yet, the existence of dynamic changes in the neurochemistry of the basal ganglia during cingulotomy shows that intracerebral microdialysis can help in the understanding of the pathophysiology of OCD and eventually in the design of new surgeries with better results.
A flexible intravenous microdialysis probe was constructed from Silastic tubing (0.5 mm ID and 1.... more A flexible intravenous microdialysis probe was constructed from Silastic tubing (0.5 mm ID and 1.0 mm OD), with a cellulose hollow fiber tip 0.2 mm in diameter and 25 mm long with a 6,000 mol wt cut off. In vitro tests showed relative recovery rates of 39.1 +/- 1.9% for epinephrine. In vivo tests in freely moving rats, 36 h and 7 days after surgery, showed stable amounts of epinephrine and glucose. After intraperitoneal injections of 2-deoxy-D-glucose, circulating levels of epinephrine and glucose increased significantly. Similar results were obtained several days after implantation of the probe. We conclude that in situations where prolonged blood sampling is necessary, the flexible microdialysis probe provides a reliable means of accessing circulating levels of neuroactive compounds, nutrients, metabolites, and drugs.
The obesity epidemic has been widely publicized in the media worldwide. Investigators at all leve... more 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.
öSystemically administered cholinomimetics or cholinesterase inhibitors can depress behavior in h... more öSystemically administered cholinomimetics or cholinesterase inhibitors can depress behavior in humans and animals, whereas antimuscarinic agents reverse this e¡ect or even produce euphoria. Although these e¡ects have been well documented, the speci¢c brain regions that mediate them remain largely unknown. In the present experiments, muscarinic agonists and antagonists were locally injected into the nucleus accumbens of female Sprague^Dawley rats to test for their e¡ects on behavioral depression in the Porsolt swim test and locomotor activity. Local, microinjections of the drugs in the accumbens elicited behaviors that were similar to the systemic e¡ects reported in other studies. Injection of the non-speci¢c agonist arecoline (40 and 80 Wg) dose-dependently inhibited swimming and escape behavior. This may be mediated in part by accumbens M 1 receptors because blocking these receptors with the speci¢c antagonist pirenzepine (17.5 and 35.0 Wg) did the opposite by increasing swimming. Gallamine (0.13, 0.44, and 0.88 Wg), an antagonist at M 2 receptors, dose-dependently decreased swimming. Two-way microdialysis suggested that this was in part due to the release of ACh by blocking M 2 autoreceptors. Scopolamine, a mixed M 1 /M 2 receptor antagonist, also released ACh but did not decrease swimming, probably because the M 1 receptors were blocked; the drug (1.0 Wg) increased swimming time, much like pirenzepine. With the exception of arecoline, none of the drugs signi¢cantly a¡ected locomotor activity in a photocell cage. Arecoline (40 Wg), which had decreased swimming, reduced activity. The present study suggests that muscarinic receptors in the nucleus accumbens can control immobility in the Porsolt swim test. The onset of immobility may depend on the activation of post-synaptic M 1 receptors.
Premature neonates are born with immature anabolic and catabolic biochemical systems. 1-5 They ca... more Premature neonates are born with immature anabolic and catabolic biochemical systems. 1-5 They cannot synthesize several amino acids and for this reason non-essential amino acids in mature neonates are considered essential in premature neonates thus making parenteral amino acids administration common practice. 6,7 Arginine and citrulline are two of these amino acids. Their essential nature is suggested by the fact that supplements of arginine help to avert necrotizing enterocolitis (NEC) a potentially lethal condition in preterm neonates 8-10 even though some authors do not find a consistent protective effect. 11,12 Citrulline also is an amino acid intimately related to arginine metabolism. 13 The enzyme nitric oxide synthase (NOS) converts arginine into citrulline and produces nitric oxide (NO). 14,15 Citrulline reaction with aspartate to form argininosuccinate is catalyzed by the enzyme argininosuccinate synthetase (ASS). 16 Then the enzyme argininosuccinate lyase (ASL) breaks the molecule of argininosuccinate into fumarate and arginine. 17 Citrulline and arginine supplements protect the tight junctions of intestinal epithelium during ischemic episodes. 18 Therefore supplements of citrulline have been recommended to prevent NEC in preterm neonates. Although low levels of arginine 19-21 and citrulline 22
... 38145. Título: Variación en los niveles extracelulares de Glutamato y GABA en el pálido duran... more ... 38145. Título: Variación en los niveles extracelulares de Glutamato y GABA en el pálido durante la conducta alimentaria y el efecto anoréxico de la cocaína / JacquelinePérez Lu tutor Pedro Rada. Data: 10-Mai-2011. Descrição ...
Popularmente se habla de "adictos a los dulces", sin embargo, nunca se ha estudiado de manera sis... more Popularmente se habla de "adictos a los dulces", sin embargo, nunca se ha estudiado de manera sistemática la existencia de este tipo de adicción a un alimento. Este concepto es de gran importancia cuando en los países desarrollados surge una gran lucha legal contra las grandes cadenas de comida rápida por asegurar, los litigantes, que estas compañías manejan estrategias que favorecen a la adicción y que son responsables de una de las calamidades médicas mas importantes del momento que es la obesidad. La adicción se define como el uso compulsivo e incontrolable de una droga de adicción. Los expertos en el área describen 3 etapas en la adquisición y desarrollo de esta enfermedad. La primera que consiste en el escalamiento y "atracón" de la droga, seguido en una segunda instancia de la dependencia y por último, el deseo imperioso y recaída. A continuación presentaremos un modelo animal de dependencia al azúcar con características muy semejantes a los que se observan con las drogas de adicción y que nos señalan que los sistemas neurales para la conducta alimentaria son probablemente compartidos por las drogas de adicción.
The nucleus accumbens (NAc) has emerged as an important part of the neural circuitry regulating d... more The nucleus accumbens (NAc) has emerged as an important part of the neural circuitry regulating depressivelike behaviors. Given that the NAc GABAergic medium spiny neurons project to the ventral pallidum (VP), it is reasonable to suggest that the VP may also be involved in these behaviors. Consequently, we explored the role of the VP GABAergic terminals during depressive-like behaviors in rats using the forced swim test (FST) and the sucrose preference test (SPT). Microdialysis coupled with micellar electrokinetic chromatography was used to monitor in vivo changes of GABA in the VP during the FST. GABA levels significantly increased during day-1 and day-2 during swimming, returning to the pre-swimming levels after the test. Basal concentrations of GABA on day-2 of the FST significantly increased with respect to day-1. In another set of experiments, intra-VP injections of vigabatrin (a GABA transaminase inhibitor) increased extracellular GABA and immobility behaviors in the FST while the direct GABAA receptor antagonist bicuculline reduced immobility behaviors. In the SPT, intra-VP vigabatrin injection significantly reduced preference for sucrose while bicuculline did not produce any change. At the postsynaptic side, we used semiquantitative RT-PCR to measure mRNA expression of 17 GABAA receptor subunits (␣1-␣6, 1-3, ␥2, ␦, , , , and 1-3) in rats subjected to the FST. We found a significant reduction of ␣3 and ␥2 subunit expression and an increase of ␦ subunit expression after day-2 in rats subject to the FST which might enhance tonic inhibition of the VP. Furthermore, immunoblot experiments revealed that protein expression of ␥2 and ␦ subunits changed 6 days after FST in a way similar to mRNA expression. These results suggest that the enhanced VP-GABAergic tone might trigger a low motivational state, anhedonia and a possible memory mechanism for unpleasant experiences.
Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatu... more Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (2 1%) following feeding. Drinking caused
Evidence links dopamine (DA) in the nucleus accumbens (NAc) shell to the ingestion of palatable d... more 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.
Ingestion of different nutrients, such as fats and sugars, normally produces different effects on... more 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 producin...
ABSTRACT Background / Purpose: Previous reports have related the nucleus accumbens (NAc) with beh... more ABSTRACT Background / Purpose: Previous reports have related the nucleus accumbens (NAc) with behavioral depression. Additionally, an important number of GABAergic medium spiny neurons project from the NAc to the ventral pallidum (VP) through the medial forebrain bundle.We studied the VP GABAergic system in behaviorally depressed rats. The inescapable swim test (IST) was employed to induce a behavioral depression-like state on male Sprague-Dawley rats (250-350 g). On day 2 of IST, we measured the mRNA of 17 subunits of the GABA-A receptor (α1-α6, β1-β3, γ2, δ, ε, θ, π, ρ1, ρ2 and ρ3) by semiquantitative RT-PCR. Then, we used immunoblot to explore the synthesis of the GABA-A receptor subunits that showed significant mRNA differences. Finally, we locally injected the GABA-A indirect agonist vigabatrin (0, 5, 10 and 15 µg/0.5 µl); or the direct antagonist bicuculline methbromide (100 ng/0.5 µl), at a flow rate of 0.5 µl/min. Main conclusion: IST induced significant downregulation in transcript level for α3 and γ2 subunits, whereas δ subunit expression was upregulated at day 2. The mRNA of α4, α6, β3, and ρ1 subunits did not express in VP. We did not detect protein expression changes for γ2 and δ subunits at day 2. However, they were evident at day 8 of IST in the same way that changes in transcript expression for γ2 (downregulated) and δ subunits (upregulated). α3 subunit was never detected. VP microinjections of vigabatrin were pro-depressive and bicuculline anti-depressive.The results found by us suggest that GABAergic transmission on the VP seems to be increased during IST, and that it might change the expression pattern of GABA-A receptor subunits. These changes on the GABA-A receptor suggest a possible mechanism of neuronal plasticity underlying helplessness.
Neurosurgery for psychiatric disorders, notably for obsessive-compulsive disorder (OCD), was init... more Neurosurgery for psychiatric disorders, notably for obsessive-compulsive disorder (OCD), was initiated in Venezuela in the decade of 1970, and consisted since that time in the classic stereotactic anterior cingulotomy. In order to know further about the physiopathology of this disorder, we performed intracerebral microdialysis in 2 patients who were operated on. The aim was to measure changes in extracellular neurotransmitters within the basal ganglia. The microdialysis probes were stereotactically placed in the right caudate nucleus and in the dorsomedial nucleus of the right thalamus. The microdialysis was done before the left cingulotomy, during the pause and after the right cingulotomy. Glutamate and gamma-aminobutyric acid (GABA) changes were similar in the caudate nucleus of both patients, whereas in the dorsomedial nucleus the changes were opposite among the 2 patients. Although this study does not bring enough data to explain such differences yet, the existence of dynamic changes in the neurochemistry of the basal ganglia during cingulotomy shows that intracerebral microdialysis can help in the understanding of the pathophysiology of OCD and eventually in the design of new surgeries with better results.
A flexible intravenous microdialysis probe was constructed from Silastic tubing (0.5 mm ID and 1.... more A flexible intravenous microdialysis probe was constructed from Silastic tubing (0.5 mm ID and 1.0 mm OD), with a cellulose hollow fiber tip 0.2 mm in diameter and 25 mm long with a 6,000 mol wt cut off. In vitro tests showed relative recovery rates of 39.1 +/- 1.9% for epinephrine. In vivo tests in freely moving rats, 36 h and 7 days after surgery, showed stable amounts of epinephrine and glucose. After intraperitoneal injections of 2-deoxy-D-glucose, circulating levels of epinephrine and glucose increased significantly. Similar results were obtained several days after implantation of the probe. We conclude that in situations where prolonged blood sampling is necessary, the flexible microdialysis probe provides a reliable means of accessing circulating levels of neuroactive compounds, nutrients, metabolites, and drugs.
The obesity epidemic has been widely publicized in the media worldwide. Investigators at all leve... more 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.
öSystemically administered cholinomimetics or cholinesterase inhibitors can depress behavior in h... more öSystemically administered cholinomimetics or cholinesterase inhibitors can depress behavior in humans and animals, whereas antimuscarinic agents reverse this e¡ect or even produce euphoria. Although these e¡ects have been well documented, the speci¢c brain regions that mediate them remain largely unknown. In the present experiments, muscarinic agonists and antagonists were locally injected into the nucleus accumbens of female Sprague^Dawley rats to test for their e¡ects on behavioral depression in the Porsolt swim test and locomotor activity. Local, microinjections of the drugs in the accumbens elicited behaviors that were similar to the systemic e¡ects reported in other studies. Injection of the non-speci¢c agonist arecoline (40 and 80 Wg) dose-dependently inhibited swimming and escape behavior. This may be mediated in part by accumbens M 1 receptors because blocking these receptors with the speci¢c antagonist pirenzepine (17.5 and 35.0 Wg) did the opposite by increasing swimming. Gallamine (0.13, 0.44, and 0.88 Wg), an antagonist at M 2 receptors, dose-dependently decreased swimming. Two-way microdialysis suggested that this was in part due to the release of ACh by blocking M 2 autoreceptors. Scopolamine, a mixed M 1 /M 2 receptor antagonist, also released ACh but did not decrease swimming, probably because the M 1 receptors were blocked; the drug (1.0 Wg) increased swimming time, much like pirenzepine. With the exception of arecoline, none of the drugs signi¢cantly a¡ected locomotor activity in a photocell cage. Arecoline (40 Wg), which had decreased swimming, reduced activity. The present study suggests that muscarinic receptors in the nucleus accumbens can control immobility in the Porsolt swim test. The onset of immobility may depend on the activation of post-synaptic M 1 receptors.
Premature neonates are born with immature anabolic and catabolic biochemical systems. 1-5 They ca... more Premature neonates are born with immature anabolic and catabolic biochemical systems. 1-5 They cannot synthesize several amino acids and for this reason non-essential amino acids in mature neonates are considered essential in premature neonates thus making parenteral amino acids administration common practice. 6,7 Arginine and citrulline are two of these amino acids. Their essential nature is suggested by the fact that supplements of arginine help to avert necrotizing enterocolitis (NEC) a potentially lethal condition in preterm neonates 8-10 even though some authors do not find a consistent protective effect. 11,12 Citrulline also is an amino acid intimately related to arginine metabolism. 13 The enzyme nitric oxide synthase (NOS) converts arginine into citrulline and produces nitric oxide (NO). 14,15 Citrulline reaction with aspartate to form argininosuccinate is catalyzed by the enzyme argininosuccinate synthetase (ASS). 16 Then the enzyme argininosuccinate lyase (ASL) breaks the molecule of argininosuccinate into fumarate and arginine. 17 Citrulline and arginine supplements protect the tight junctions of intestinal epithelium during ischemic episodes. 18 Therefore supplements of citrulline have been recommended to prevent NEC in preterm neonates. Although low levels of arginine 19-21 and citrulline 22
... 38145. Título: Variación en los niveles extracelulares de Glutamato y GABA en el pálido duran... more ... 38145. Título: Variación en los niveles extracelulares de Glutamato y GABA en el pálido durante la conducta alimentaria y el efecto anoréxico de la cocaína / JacquelinePérez Lu tutor Pedro Rada. Data: 10-Mai-2011. Descrição ...
Popularmente se habla de "adictos a los dulces", sin embargo, nunca se ha estudiado de manera sis... more Popularmente se habla de "adictos a los dulces", sin embargo, nunca se ha estudiado de manera sistemática la existencia de este tipo de adicción a un alimento. Este concepto es de gran importancia cuando en los países desarrollados surge una gran lucha legal contra las grandes cadenas de comida rápida por asegurar, los litigantes, que estas compañías manejan estrategias que favorecen a la adicción y que son responsables de una de las calamidades médicas mas importantes del momento que es la obesidad. La adicción se define como el uso compulsivo e incontrolable de una droga de adicción. Los expertos en el área describen 3 etapas en la adquisición y desarrollo de esta enfermedad. La primera que consiste en el escalamiento y "atracón" de la droga, seguido en una segunda instancia de la dependencia y por último, el deseo imperioso y recaída. A continuación presentaremos un modelo animal de dependencia al azúcar con características muy semejantes a los que se observan con las drogas de adicción y que nos señalan que los sistemas neurales para la conducta alimentaria son probablemente compartidos por las drogas de adicción.
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