[求助]OG-1一些段落不明白!!!

andy7788

Caffeine, the stimulant in coffee, has been called
“the most widely used psychoactive substance on Earth .”
Synder, Daly and Bruns have recently proposed that
caffeine affects behavior by countering the activity in
the human brain of a naturally occurring chemical called
adenosine.
Adenosine normally depresses neuron firing
in many areas of the brain.
It apparently does this by inhibiting the release of neurotransmitters, chemicals that carry nerve impulses from one neuron to the next.
Like many other agents that affect neuron firing,adenosine must first bind to specific receptors on neuronal membranes.
There are at least two classes of these receptors, which have been designated A1 and A2.
Snyder et al propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would.
For many years, caffeine’s effects have been attributed to its inhibition of the production of phosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP.

A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons.
請問這their是指?

Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation.
請大俠來救救我吧~
Q.1 因此,延長periods不懂哪個periods~
Q.2 as might be brought about by a phosphodiesterase inhibitor
這句怎麼理解阿?as是指?為什麼about後又接by?

But Snyder et al point out that the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation.
這邊的those又是指?

Moreover, other compounds that block phosphodiesterase’s activity are not stimulants.

To buttress their case that caffeine acts instead by preventing adenosine binding, Snyder et al compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge adenosine from its receptors in the brains of mice.
請問這邊的instead該怎樣翻譯跟解釋呢?
“In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the
receptors, the higher their ability to stimulate locomotion.”
請問這邊compete該怎樣理解?
Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
effective compounds in both regards.
There were some apparent exceptions to the general
correlation observed between adenosine-receptor binding
and stimulation.
One of these was a compound called 3-isobuty1-1-methylxanthine(IBMX), which bound very
well but actually depressed mouse locomotion.
Snyder et al suggest that this is not a major stumbling block to
their hypothesis.
The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs.
Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.
這邊該怎麼翻譯呢?展示這樣的特質嗎? 都看過以前的討論了~但是還是不太理解~雖然知道這不是閱讀的重點~還是很想了解一下~謝謝各位的幫助!!!^^