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Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? for GMAT 2024 is part of GMAT preparation. The Question and answers have been prepared according to the GMAT exam syllabus. Information about Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for GMAT 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer?.

Solutions for Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? in English & in Hindi are available as part of our courses for GMAT. Download more important topics, notes, lectures and mock test series for GMAT Exam by signing up for free.

Here you can find the meaning of Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer?, a detailed solution for Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? has been provided alongside types of Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice Directions: Read the Passage carefully and answer the question as follow.Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeine’s effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exerttheir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But Snyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterase’s activity are notstimulants.To buttress their case that caffeine acts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective compounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.Q.According so Snyder et al, caffeine differs from adenosine in that caffeinea)stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans onlyb)has mixed effects in the brain, whereas adenosine has only a stimulatory effectc)increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrationsd)permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such releasee)inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firingCorrect answer is option 'D'. Can you explain this answer? tests, examples and also practice GMAT tests.