The Effects Of Lisdexamfetamine On Prefrontal Cortex-mediating Executive Function And Visual Discrimination Learning And The Underlying Neural Mechanisms

BackgroundCognitive enhancers are a group of drugs that enhance cognitive function under normal and,or disease conditions.D-amphetamine,the most classical cognitive enhancer,was used to improve alertness,body reaction and working efficiency in healthy individuals who are engaging in certain vocations.However,d-amphetamine is rapidly absorbed into blood and dramatically increase catecholamine neurotransmitter dopamine（DA）and Noradrenaline（NE）release.The immediate-release pharmacokinetic and neurochemical characteristics induced by d-amphetamine produce narrow effective window,greater variability among individuals and potential addiction in mediating cognition,which extremely limited its application.Lisdexamfetamine,the first prodrug acting on the catecholamine system,is synthesized by covalently linking d-amphetamine to the amino acid l-lysine.After administration,lisdexamfetamine was hydrolyzed by erythrocyte peptidase and releases d-amphetamine,the actual pharmacological metabolite.Because of the rate-limiting step,the vivo pharmacokinetic profile is significantly different from that of d-amphetamine.Pre-clinical and clinical evidences have showed lower addictive potential of lisdexamfetamine.Currently,lisdexamfetamine has been proved to treated attention deficit and hyperactivity disorder（ADHD）and binge-eating disorder.However,the effects of lisdexamfetamine on the core elements of execeutive function（including attention,working memory,cognitive flexibility）,and other higher in-order cognition,such as visual discrimination（including spatial location discrimination and image discrimination）under normal condition still unknown.Thus,the aim of presented study is to explore the effects and characteristics of lisdexamfetamine on execeutive function and visual discrimination.Our study can provide experimental evidences for lisdexamfetamine to be a novel effective and lower addicted cognitive enhancer.Due to the different in vivo release pattern of d-amphetamine and lisdexamfetamine,we compared the difference of d-amphetamine and lisdexamfetamine in cognition improvement,as well as the underlying association to the pharmacokinetic and neurochemical profiles.Our research also accumulate evidences of beneficial pharmacokinetic and neurochemical characteristics of amphetamine type psychostimulants when they play obvious effects to cognition improvement.MethodsThis study was divided into two parts.（1）The first part was to compare the effects of d-amphetamine and lisdexamfetamine on the three core cognitive domains of executive function as well as the underlying mechanisms.We established Y-maze spontaneous alternation task-lower working memory load and Trial-unique delayed nonmatching task（TUNL）-higher working memory load to reflect spatial working memory;5-Choice Serial Reaction Time Task（5-CSRTT）to reflect sustained attention and inhibitory control;visual discrimination（VD）based reversal learning task to reflect intra-dimension cognitive flexibility.Further,we explored the underlying mechanisms from pharmacokinetic and neurochemical profiles of both drugs using liquid chromatography combined with mass spectrometry and in vivo microdialysis combined with high performance liquid chromatography-electrochemical detection.（2）The second part was to compared the effects of d-amphetamine and lisdexamfetamine on visual discrimination,including spatial position discrimination and image information discrimination.Given the durg targets of pre-synaptic DAT and NET,and the involvement of glutamate receptor in learning and memory,we further analyzed the protein expression of DAT and NET pre-synaptically,as well as the distribution of glutamate receptor post-synaptically.ResultsPart 1 The effects and mechanisms of d-amphetamine and lisdexamfetamine on m PFC-mediating executive function（1）Effects of d-amphetamine and lisdexamfetamine on working memory.Based on Y-maze spontaneous alternation task,d-amphetamine ranges from 0.2to 13.5 mg/kg did not significantly increase the percentage of spontaneous alternation in rats,while 4.5 mg/kg lisdexamfetamine significantly enhanced it.The results suggested that lisdexamfetamine improved spatial working memory of rats under low cognitive load,while d-amphetamine failed to improve it.Based on TUNL task,under higher pattern separation,0.15 mg/kg d-amphetamine and 1.0 mg/kg lisdexamfetamine significantly improved the correct accuracy under 12 s ITI.The results suggested that both d-amphetamine and lisdexamfetamine enhanced working memory maintenance under certain higher cognitive load condition.（2）Effects of d-amphetamine and lisdexamfetamine on sustained attention and inhibitory control.Based on 5-CSRTT,under higher attention,high intensity complex task environment,0.5 mg/kg d-amphetamine significantly increased the percentage of correct and shortened the correct response latency,but also significantly increased impulsive behavior.Unlike d-amphetamine,lisdexamfetamine ranges from 0.1 to 1.0mg/kg significantly improved the percentage of correct,while all the doses failed to increase impulsive response.Under high-impulsive environment,0.5 mg/kg d-amphetamine significantly increased impulsive behavior,while lisdexamfetamine did not significantly affect it.Above all,in comparison to d-amphetamine,lisdexamfetamine significantly improve attention with no significant effects to impulsivity.（3）Effects of d-amphetamine and lisdexamfetamine on cognitive flexibility.According to visual discrimination based reversal learning task,1.5 mg/kg d-amphetamine and 3.0 mg/kg lisdexamfetamine both significantly improved the percentage of correct,suggesting that both of drugs enhanced intra-dimension cognitive flexibility.3.1.6 The mechanisms of d-amphetamine and lisdexamfetamine in mediating executive function（4）The pharmacokinetic characteristics of d-amphetamine and lisdexamfetamineThe results showed that 0.5-4.5 mg/kg d-amphetamine rapidly released after administration(t_maxwas about 15 min)and quickly eliminated(t_1/2was about 90 min).The fold of C_maxamong plasma free amphetamine base was consistent with the fold of injection doses.In comparison with d-amphetamine,lisdexamfetamine ranges from1.0 to 4.5 mg/kg slowly released(t_maxwas about 60 min)and slowly eliminated(t_1/2was about 160 min).The fold of C_maxamong plasma free amphetamine base was less than the fold of injection doses,suggesting the rate-limiting step converting lisdexamfetamine to amphetamine exist.The exposure profile of both drugs in cognition and reward-associated brain zones were similar to that in plasma.（5）The nuerochemical profile of d-amphetamine and lisdexamfetamineD-amphetamine with 0.5 and 4.5 mg/kg rapidly increased DA level rapidly 30 min after administration and then decreased rapidly.Unlike d-amphetamine,lisdexamfetamine with 1.0 and 4.5 mg/kg slowly increased DA and reached the maximum 60 min after administration,the peak value was lower than that of d-amphetamine but the duration was longer than d-amphetamine.Part 2 The effects and mechanisms of d-amphetamine and lisdexamfetamine on visual discrimination learning.（1）Effects of d-amphetamine and lisdexamfetamine on spatial recognition memory.Based on two-trial Y-maze delayed alternate task,0.2-4.5 mg/kg d-amphetamine failed to significantly increase the percentage of novel arm visits and retention.In the contrary,4.5 mg/kg lisdexamfetamine significantly increased both the percentage of novel arm visits and retention.The results suggested that lisdexamfetamine improved spatial location discrimination.（2）Effects of d-amphetamine and lisdexamfetamine on image information discrimination.Based on visual discrimination learning task,we compared the acute effects of single administration of d-amphetamine and lisdexamfetamine on different discrimination stage.D-amphetamine failed to significantly increase discrimination accuracy neither early stage（day 4）nor late stage（day 9）.On the contrary,0.1 and 1.0mg/kg lisdexamfetamine significantly improved the percentage of correct at both stages,with no effects to the accuracy of the second day.In addition,chronic administration with 1.0 mg/kg lisdexamfetamine significantly improved the learning efficiency and shorten the training times required for learning.Our results showed acute treatment with lisdexamfetamine significantly enhanced discrimination accuracy,chronic administration can improve the learning efficiency.（3）Effects of d-amphetamine and lisdexamfetamine on catecholamine transporters and glutamate distribution.Single treatment with d-amphetamine ranges from 0.05 to 0.5 mg/kg and lisdexamfetamine ranges from 0.1 to 1.0 mg/kg significantly decreased the expression of DAT and NET;chronic administration with 1.0 mg/kg lisdexamfetamine significantly enhanced the membranous/cytosolic ration in Hip,whereas had no effects to AMPA receptors distribution.Conclusions（1）For the core domains of executive function,d-amphetamine only enhance working memory and sustained attention under certain task environment.In the oppose,lisdexamfetamine improve working memory and attention under both lower and higher cognitive load condition,with no effects to impulsive responses.Both of drugs can improve intra-dimension cognitive flexibility.Our results suggests lisdexamfetamine produces a wider and safer effective window than d-amphetamine in cognition improvement.（2）D-amphetmine elicit repaid increase of amphetamine base in plasma and brain,which further increase DA level quickly.In the contary,lisdexamfetamine produces lower amplitude and sustained-release pattern of free amphetamine base in plasma and brain,with the similar profile to DA release pattern.Our results suggest the lower amplitude and sustained-release pattern of DA induced by lisdexamfetamine is more benefit to executive enhancement than the immediate-release DA pattern by d-amphetamine.（3）Single treatment with lisdexamfetamine significantly improve visual discrimination,which may due to the inhibition of pre-synaptic catecholamine trasporters;chronic treatment with lisdexamfetamine significantly enhance the learning efficiency,which may link to the increasing membranous distribution of NMDA receptors in Hip.Above all,in comparison to d-amphetamine,lisdexamfetamine is more reasonable to become the ideal cognitive enhancer;the lower magnitude,sustained-release pattern of catecholamine neurotransmitters are more benefit for cognitive enhancement.