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Kumar et al: Effect of antiepileptics on learning and memory Original Article
Effect of lamotrigine, levetiracetam and phenytoin on learning and
memory in albino rats
Kumar S1, Singh H2, Sharma J3

1
ABSTRACT
Dr Subodh Kumar
MD, Senior Resident, Pharmacology Background: Epilepsy is one of the most prevalent non-communicable
AIIMS, New Delhi, India neurologic diseases leading to significant disability and mortality. Complaints of impaired learning and memory are common in patients of epilepsy. Anti- 2Dr Harmanjit Singh
epileptic drugs (AEDs) may further enhance this impairment. So the present MD, Senior Resident, Pharmacology study was carried out on albino rats to evaluate the effect of AEDs on learning AIIMS, New Delhi, India and memory. Email: [email protected] Objective: To assess the effect of lamotrigine, levetiracetam and phenytoin on
3Dr Janardan Sharma
learning and memory in albino rats. Professor Material and Methods: Albino rats of about 150 -200 gm of either sex were
Pharmacology of Therapeutics treated with drugs for 15 days and assessed for effect on learning behavior and RIMS, Ranchi, India again treated for next 15 days after which they were assessed for retention behavior (memory) on Morris water maze and Elevated plus maze. The data Received: 03-12-2013 was statistically analyzed by applying Mann- Whitney test. Revised: 25-01-2014 Result: Phenytoin and lamotrigine caused significant impairment of learning
Accepted: 02-02-2014 whereas levetiracetam had no statistically significant effect on learning. Phenytoin also caused significant impairment of memory whereas lamotrigine Correspondence to: and levetiracetam did not cause statistically significant impairment of memory. Dr Harmanjit Singh
Conclusion: Learning was impaired by phenytoin and lamotrigine but not by
9968118472 levetiracetam which has novel mechanism of action. Phenytoin resulted in memory impairment on Morris water maze but no impairment on elevated plus maze and no other drug caused this effect. KEY WORDS: Anti epileptic drugs, learning, memory, elevated plus maze, morris
water maze commonly used AEDs have some effect on Epilepsy is one of the most prevalent non- cognitive function. The effect become communicable neurologic diseases leading substantial when crucial functions are to significant disability and mortality. [1] involved. For example learning in children, Complaints of impaired learning and driving ability in adults or when already- memory are common in patients of vulnerable functions are involved, such as epilepsy. Anti – epileptic drugs (AEDs) may memory in elderly patients. further enhance this impairment. [2] So Many new AEDs like oxcarbazepine, study of effect of AEDs on learning and memory is of particular importance. gabapentin, tiagabine, topiramate and Learning and memory are most levetiracetam have been introduced into important part of cognition. So impairment clinical practice within the last decade. of learning and memory function can also Most of these new drugs are as effective as be stated in terms of impaired cognition. All the old AEDs (phenytoin, Phenobarbital). In IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory general newer AEDs seem to be better phenytoin which is effective against both tolerated than the older drugs. The new partial seizures and generalized tonic clonic AEDs might produce less impairment of seizures with that of lamotrigine which is cognitive functions but this aspect has not currently considered first line drug against been systematically studied3. So there is a both partial as well as generalized tonic need to systematically assess the role of clonic seizure, and levetiracetam the newest drug in the group used as an impairment in epileptic patient. [3] The adjunct in partial seizures. [8] study comparing the effect of newer and This study was undertaken to assess relatively older drug will be of particular the effect of anti – epileptic drugs on importance since it will reveal the relative learning and memory in albino rats with the difference of impairment caused by these aims and objective of the study as following drugs, so it will be very helpful in choosing 1. To observe the effect on learning and the drug for the treatment. memory of three drugs i.e. lamotrigine, It is important to understand that levetiracetam and phenytoin. whether the impairment is caused by the 2. To compare the effect on memory and disease itself or by the AEDs so that further learning of newer anti epileptic drugs i.e. preventive measures will be taken. But it is lamotrigine & levetiracetam with older anti difficult to distinguish between impairment epileptic drug i.e. phenytoin. associated with the disorder and those attributable to the drugs used for Material and Methods
treatment. In an attempt to isolate the This study was done in the cognitive deficits associated with the drugs themselves, this study investigates the Therapeutics, Rajendra Institute of Medical effects of antiepileptic compounds on learning and memory in normal animals. Institutional Animal Ethics Committee Barbiturates and benzodiazepines (IAEC), RIMS, Ranchi was taken prior to the are known to impair cognition in healthy start of this study. volunteers as well as patients with epilepsy. 24 healthy albino rats of about 150 - Carbamazepine, phenytoin, and valproate 200 gm in weight were divided in four have been reported to adversely affect groups (control, phenytoin, lamotrigine & cognition to a similar extent, although the levetiracetam) of six animals each. Each magnitude of the effects of these three animal was placed in separate cages. drugs appears to be less than that of barbiturates and benzodiazepines. [4] The temperature, humidity and feeding were effects of newer AEDs are less well studied, but several reports have suggested that The doses of the drug were newer AEDs such as lamotrigine and determined on the basis of ratio of surface levetiracetam may have fewer effects on area of rat and man (0.018). Thus doses in cognition than do older drugs. [5-7] rat were calculated by multiplying the This study compared cognitive absolute human dose by a factor of 0.018. impairment caused by one of the more Then each animal was weighed one week commonly used anti epileptic drug, before the experiment and absolute dose IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory was calculated according to their body base is placed in middle of any fixed quadrant. To hide the platform water is Separate suspension of each drugs added to a level 2 cm above the platform. were prepared by mixing the drug in normal The room should have potential extra maze saline with gum acacia. All the three drugs cues that help to navigate the tank. were made to strength of 10mg/ml by Procedure
mixing 100mg of the respective drugs with Rats were placed in the water at a 10ml of normal saline. Only freshly designated starting location and the time to prepared drugs were used each day. The find the hidden platform from the starting control group received 0.5 ml of normal point is defined as "Escape Latency". Each rat was tested for four trials/day with inter trial period of two minute during which All the drugs were given orally with a bent they were placed in their home cage. stainless steel feeding needle specially Selection criteria – The rats for water maze made for rats. The lumen size of the feeding were preselected. Rats that do not go to the visible platform on training and testing trials in the allotted time of 120 seconds were All the rats received respective treatment excluded from the study. Also, animals that for the period of 15 days after which they refuse to search for the hidden platform were examined for their learning behavior during training and float on the water were on Morris water maze and elevated plus removed from the study. maze for five consecutive days (day1 to day Elevated Plus Maze (EPM)
5). The rats again received all the respective It is a validated method to test parameters treatment for next 15 days after which they of learning and memory [10, 11] to evaluate were examined again (on day 20) on Morris spatial long term memory in rodents. water maze and elevated plus maze to Introduced by Pellow (1985) in rats based evaluate retention of past event (memory). on apparent natural aversion of rodents to open and high spaces. Based on this etoh et Morris water maze (MWM)
al. has demonstrated that transfer latency The Morris water maze is one of the most was markedly shortened if the animal had previously experienced entering in closed neuroscience for studying the psychological arm, and this shortening has been related processes and neural mechanisms of spatial to memory process. Apparatus for rat learning and memory. It has gained a consist of two open (50 x 10 cm) and two position at the very core of contemporary enclosed arms (50x10x40 cm). The entire neuroscience research. [9] maze is elevated to a height of 50 cm. It Consist of a large circular tank of Procedure
diameter 1.8- 2.0 m and 0.4-0.5m in height. The rats were placed at the edge of open The pool is filled with water and rendered arm with facing away from the closed arm. opaque by addition of non toxic color. The Transfer latency is the elapsed time tank is marked off into four quadrants, i.e. between the time the animal is placed in North, South, East & West. An escape the open arm and the time in which all its platform of 13 cm square size with heavy leg have crossed a line marking initiation of IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory closed arms. Each rat was examined significant impairment of memory on MWM twice/day on successive open arm and time (Table2, day 20). But there was no to reach in closed arm was noted by statistically significant impairment as stopwatch. Selection criteria- The animals compared to lamotrigine group (Table 2, 3). were preselected and those who don't Levetiracetam versus Others
cross the line in 120s were excluded from the experiment. The data was collected and significant impairment in learning as effects on transfer latency time after compared to control group on MWM (Table administration of drug were compared with 2; day1-5). But it was found to impair each drugs and control. learning on day 4 in elevated plus maze Data entry was done on MS EXCEL (Table3). It has no significant effect on and ‘SPSS version 17' software was used for memory on both MWM as well as EPM data analysis. Mann- Whitney test was (Table 2, 3; day20). used to compare the effect of the drugs on Lamotrigine versus Others
different groups. Mann-Whitney test is a Lamotrigine causes significant impairment non parametric test used to compare two in learning compared to the control on both independent groups of sampled data. A non MWM and EPM (Table2, 3; day1-5). parametric test was applied in this study as Lamotrigine causes significant impairment the sample size in this study is less than 30 as compared to levetiracetam group in as well as the data is not normally distributed since a cut off time of 120s has significant impairment in EPM (Table3). been set prior in selection criteria. P<0.05 There is no significant difference between was considered significant. the impairment caused by lamotrigine group compared to phenytoin group except on day 5 in EPM (Table3). Phenytoin versus Others
But lamotrigine fails to show any Phenytoin causes significant impairment in learning compared to the control as well as memory as compared to control on both with levetiracetam group on both MWM & MWM (Table1) as well as EPM (Table2).
EPM (Table 2, 3; day1-5). It also causes
Table 1: Escape & Transfer latency time (i.e the time to reach the target) on Morris water maze and
elevated plus maze respectively

Morris water maze(Escape latency time) Elevated plus maze(Transfer latency time) levetiracetam lamotrigine Control levetiracetam lamotrigine 34.80±5.81 41.08±4.75 37.87±4.36 40.58±3.25 70.66±14.56 89.25±14.60 75.83±12.01 21.33±7.22 34.79±5.81 21.33±7.22 32.08±3.28 29.58±3.73 44.33±13.67 63.00±13.11 14.95±1.76 30.75±1.95 19.04±1.27 30.75±1.95 17.25±1.31 12.66±1.35 24.25±6.92 11.91±1.05 20.87±4.09 10.91±1.06 21.33±7.22 7.95±0.44 19.16±5.09 10.25±0.85 Day20 15.00±1.95 29.03±1.95 19.70±1.72 22.07±2.43 80.83±13.71 89.58±14.37 76.00±12.02 Each value represents the Mean±SEM of six animals after taking averages of four trials /day IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory


Table 2: Significant levels (p value) obtained after day wise comparison of change in escape latency
time (drug versus control and drug versus drug) on MWM

Phenytoin Vs
Lamotrigine
Control
Levetiracetam
Control
Phenytoin Vs
Lamotrigine
Phenytoin Vs
Lamotrigine
* indicates significant values (P<0.05) using Mann-Whitney test Table 3: Significant levels (p value) obtained after day wise comparison of change in transfer latency
time (drug versus control and drug versus drug) on EPM
Phenytoin Vs
Lamotrigine
Levetiracetam
Phenytoin Vs
Lamotrigine
Phenytoin Vs
Lamotrigine
* indicates significant values (P<0.05)

Discussion
permits assessment of the effects of AEDs Determining the effects of AEDs on cognitive function in nonepileptic subjects, complexities of the disease state. Cognition both human and laboratory animals, in individuals with epilepsy may be IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory influenced by several factors, including effects in healthy volunteers or in patients basic neuropathology and the frequency with epilepsy. [18] The present result differs and severity of seizures. The present study from these previous studies. The present compared the effects of three AEDs on study indicated that lamotrigine also causes learning in nonepileptic rats. Phenytoin is one of the most widely prescribed anti learning compared to control. There is no seizure compounds. It was the first anti epileptic compound which have non sedative action at ordinary doses and that phenytoin. The cause of this difference in led to its extensive use. Recent evidence result from previous literature is not known. suggests that despite the success in But since both phenytoin and lamotrigine controlling these types of seizures, mainly acts by blocking Na+ channels and phenytoin has profoundly negative effects thus preventing repetitive firing in neurons, on learning and memory processes. [12, 13] the result obtained in this study can be The results in this study are consistent with explained on the basis of their similar these findings. Thus, these data suggest mechanism of action. Thus it suggests that that there is an apparent learning and further research in this field is warranted to establish the fact. maintenance on phenytoin. There is a need This work showing impact of drugs to carefully investigate when prescribing phenytoin, lamotrigine and levetiracetam this drug, particularly in vulnerable on learning and memory is important population like children, where long-term especially when the drugs are used in: developmental considerations need to be a. Children in whom process of learning and accounted for as well [14] and older adults memory is in process of development. particularly for their driving ability. b. Old aged persons where memory is Little is known as yet about the impaired due to senile degeneration, effects of levetiracetam on cognitive whether these drugs can precipitate memory loss or senile dementia is still a volunteers, levetiracetam had less effect on performance than did carbamazepine or c. In neurological condition presenting with oxcarbazepine. [15] In patients with epilepsy, retardation-whether add-on therapy with levetiracetam was these drugs will further accentuate the reported not to produce significant changes in cognitive performance. [16] In fact, Cramer The purpose of the present study et al. [17] reported that add-on therapy with was to evaluate the effects of AEDs on levetiracetam improved performance on learning and memory as measured by the Cognitive Functioning. The findings in Morris water maze and elevated plus maze these studies are consistent with above task in nonepileptic rats. The major finding studies as levetiracetam did not cause a of the present study is that statistically significant impairment learning 1. Learning was impaired by the Na+ channel and memory in comparison to the control blockers i.e. phenytoin and lamotrigine but group. Lamotrigine has been reported not not by levetiracetam which has novel to produce statistically significant cognitive mechanism of action. IJMDS www.ijmds.org July 2014; 3(2)

Kumar et al: Effect of antiepileptics on learning and memory 2. The effect of these drugs on memory is not 5. Martin R, Kuzniecky R, Ho S, very clear from the present study as no Hetherington H, Pan J, Sinclair K, et al. drug has shown any statistically significant impairment on memory except for gabapentin, and lamotrigine in healthy phenytoin which has shown impairment only on Morris water maze but no young adults. Neurology1999;52:321–7. impairment on elevated plus maze. 6. Bootsma HP, Aldenkamp AP, Diepman L, In brief, it can be suggested that Hulsman J, Lamnrechts D, Leenan L, et though the conclusion mentioned as above al. The Effect of Antiepileptic Drugs on are in partial correlation of older work, Cognition: Patient Perceived Cognitive further research in this line is needed in large number of subjects to stamp the Levetiracetam in Clinical Practice, effect of these drugs on learning and memory. Epilepsia 2006;47:24-7. 7. Gomer B, Wagner K, Frings L, Sar J, References
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