Archives of Psychiatry and Psychotherapy Volume 3, Issue 3, September 2001 pages 37-51
The behavioural effects of the transcranial magnetic brain stimulation (TMS) in a rat: a comparison with electroshocks 1
T om asz Z y s s h2, A n d rzej Z ię b a 2, Je rz y V etu lan i3, Ja c e k M a m c z a rz 3, A d a m R o m a n 3, Jo a n n a M i k a 3
1EEG and Evoked Potentials Unit, D epartm ent o f Neurology, U niversity Hospital, Cracow 2 Departm ent o f Psychiatry, M edical College, Jagellonian University, Cracow
3 Institute o f Pharm acology, Polish A cadem y o f Sciences, Cracow
Som e experim ental studies suggest that stim ulation o f the central nervous system with strong magnetic fie ld pulses (transcranial magnetic stimulation = TMS) evokes functional and structural changes analogous to those, which take place during electroconvulsive therapy (ECT/ECS).
The aim o f our study was to compare the effects o f the prolonged (long-time) repetitive rapid-rate TMS and chronic electroconvulsive shocks on rat behaviour in som e tests:
Open Field, Tail Flick, Apom orphine H yperactivity and P o rso lts Forced Swim Test.
None o f the animals exposed to rTM S show ed sym ptom s o f convulsive seizure, which was present in ECS. The Open Field Test show ed that neither acute nor chronic rTM S or ECS disturbed general locom otor activity o f animals. Chronic ECS evoked analgesia - extend
ing the latency o f tail flic k (46%). Tail Flick Test show ed presence o f nociceptive effect after acute and chronic rTM S (respectively 24 and 21%> o f control values). Both rTM S (m ax 58% in 30 mitt o f the stim ulation f o r the strongest stim ulation regime) and even stronger EC S (max 92%) intensified am pom orphine-induced hyperactivity o f animals.
P o rso lt’s Forced Swim Test show ed the highest shortening o f im m obility time after ECS (up to 50% o f control values) and slightly lower activity after rTM S (up to 29%). The effect depended on rTM S param eters.
The results obtained proved that rTM S and ECS evoke som e antidepressant responses in behavioural tests on rats, but rTM S evokes fe w e r side effects.
Key words', transcranial magnetic stimulation, electroshocks, behavioural tests, rat Introduction
In 1992 w e p ublished theoretical and m odel assum ptions regarding the possible application o f the neuro-physiological technique o f transcranial m agnetic stim ulation (TM S) in treatm ent o f depression [1], A s a new, physical m eth o d o f depression treat
m ent, TM S m ethod can substitute electroconvulsive therapy, w hich, despite its high 1 The w ork w as supported by research grants o f Collegium M edicum , Jagiellonian U niversity DN- BNS/501 /K L /139/L/97 and W1/K1/295/L/98, and the K BN grant 1159/T11/95/09,
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clinical effectiveness, is basically applied as a secondary choice m ethod. The superiority o f TM S consists o f the fact that the antidepressant effect is obtained in a painless w ay n ot burdening the patient and it does n o t require evoking a convulsive seizure, w hich is unavoidable in the E C T m ethod [2],
Since that year, the m eth o d has been applied in several hospitals all over the w orld in about 250 patients [3, 4, 5, 6]. A s an experim ental m eth o d o f treatm ent, TM S w as u sed m ostly in patients w ith a drug-resistant form o f depression. A t the present m o m ent, clinical exam inations according to the protocols o f the third research phase are being conducted (exam inations in larger and diversified groups o f patients aim ed at determ ining the relation betw een safety and therapeutic effectiveness o f the m ethod).
The results o f clinical exam inations seem satisfactory, though they undoubtedly require testing, especially in a different group than that w ith drug-resistant depression.
Contrary to the classical research procedures applied in testing new pharm acological m eans including anti-depressant drugs, TM S m ethod w as n o t subm itted to sufficient basic tests on anim als. D epending on the kin d o f research m ethods, w e distinguish fo u r types o f ex perim ental investigations: (neuro)structural investigations, neuro- physiological investigations, bio-chem ical m ethods and behavioural tests [7, 8, 9].
O nly eight w orks have been published regarding the application o f all these m ethods to anim als, and it is a highly insufficient num ber in com parison to a large num ber o f anim al studies on each psychopharm acological drug [10, 11, 12, 13, 14, 15, 16]. We need n o t discuss the n ecessity o f conducting experim ents on anim als. T hey not only allow for evaluation o f the biological effectiveness o f a n ew anti-depressant drug o f physical m ethod like E C T o r TM S (bio-chem ical and behavioural m odels), they also enable us to assess safety. This w ork presents the results o f behavioural investiga
tions, in w hich we perform ed a com parison o f TM S and E C T techniques in several behavioural tests (consisting in evaluation o f the an im al’s behaviour), w hich are used in classical pharm acology for evaluation o f psychotropic d ru g s’ activity.
Goal
The aim o f this study w as to com pare the influence o f repetitive prolonged rap id rate transcranial m agnetic stim ulation (rTM S; this type o f m agnetic stim ulation is ascribed the highest anti-depressant effectiveness) and electroconvulsive stim ulation (ECS) in rats. In our w ork, we w anted to exam ine w hether the alternative m agnetic field w e applied w ould give in behavioural tests sim ilar results to those observed in rats after ECS o r different ones.
Material and method
The experim ents w ere carried out on 114 m ale W istar rats, w eighing 250-300 g, kept five rats p e r cage in standard conditions (tem perature 22-23°C; 12-12 h dark-light cycle, food and w ater - ad libitum ). The investigations com prised three experim ents, in w hich w e applied different param eters o f the m agnetic field (frequency, duration o f a single session, num ber o f stim ulation sessions).
M agnetic stim ulation w as conducted using a prototype m agnetic stim ulator M S -3 designed in E lectro-technology Institute in W arsaw and constructed in Z D A N iA at
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 3 9
the A cadem y o f M ining and M etallurgy in Cracow. This stim ulator generates an im pulsive m agnetic field w ith m axim um induction value 1.6 T and m axim um frequency f=100H z. D ue to the coil cooling system , total train tim e could am ount to several m inutes2. A nim als subm itted to m agnetic stim ulation w ere place in special cage-tubes for their im m obilisation during the several m in u tes’ stim ulation. The coil was placed im m ediately above the an im a l’s head (Fig 1.).
Fig. 1. A p p earan ce o f stim u latin g coil (core coil w ith w a te r cooling) an d it location ov er the cage fo r r a t im m obilization r a t d u rin g rT M S stim ulation (real size p ro portion).
The action o f m agnetic stim ulation was com pared w ith the action o f electroshocks applied to the anim als - w ithout anaesthetisation - w ith the use o f ear electrodes (clips).
The electroshock m achine ZK -2 generated electric current w ith the follow ing param eters: 1=150m A , f=50H z, t=0.5s. The sam e param eters o f electroshock stim ulation were used in each experim ent. TM S or ECS w ere applied once a day, every second day, i.e., three tim es a week, and their total num ber depended upon the routine (regim e) o f a given experim ent.
The third group consisted o f control anim als, not subm itted to any kind o f stim u
lation, but rem aining in the sam e room as the other tw o groups. T hus, all groups o f anim als w ere exposed to acoustic artefacts generated by the m agnetic stim ulator w hile it was on. E ach group consisted o f eight (experim ent N o 1; see below ) or nine (experim ents N o 2 and 3) anim als. In som e experim ents (No 2 and 3), in w hich dif
ferent param eters o f m agnetic stim ulation TM S were exam ined, we used several o f third groups (TM S1, TM S2, TM S3).
We used the follow ing behavioural tests to estim ate stim ulation effects: "open field”
and "tail-flick” tests (both in the experim ent N o. 1); apom orphine stereotypy test (ex
perim ent N o. 2); and P o rso lt’s forced sw im m ing test (experim ent N o. 3). C onducting o f three separate experim ents was connected w ith the necessity o f exam ining different
2 A ntidepressant activity is seen mostly in a prolonged, i.e. longer than one minute, magnetic stim u
lation. The presently accessible standard m agnetic stim ulators ensure constant stim ulation lasting 10-15 sec. In clinical investigations, this short train duration is overcom e by application o f several 10-sec trains divided by several m inute long intervals needed for cooling the coil e.g. in a container filled w ith ice.
Tomasz Zyss et al.
param eters o f stim ulation as w ell as w ith the high sensitivity o f behavioural tests and the possibility o f their interference i f m ore than one w ere conducted the sam e day.
B ehavioural tests w ere carried out the d ay after that w hen the m agnetic stim ulation procedure w as perform ed.
Examination of motor activity in the “open field” test
The test consists in observing the activity o f an animal placed in a special experiment chamber - “an open field” . Both the general m otor activity (e.g., the distance covered in a given time) and other elements o f behaviour like standing on hind legs, defaecations, urinations, scratching, etc., are evaluated.
Initially, the animal, which is placed in a new environment for the first time, examines actively the area o f the “open field”. This activity may be connected w ith certain cogni
tive needs o f the animal, and it m ay correspond to cognitive activity, curiosity or interest o f a man, who has come to a new place formerly unknown to him. After a time, when the animal gets acquainted w ith the place, the interest lessens and the m otor activity usually decreases. The activity level achieves a stable value, which is more or less constant for a given individual and is connected w ith its basic m otor activity (temper) [17, 18, 19, 20],
In the experiment, we used a chamber consisting o f four neighbouring “open fields”
(arenas) 50x50x50 cm in size. A video camera placed above the “open fields” recorded simultaneously m otor activity o f four animals. We perform ed evaluation o f their m otor activity during the first ten minutes after their being placed in the chamber. The “open field” test was carried out after the first and the ninth Tm and EC stimulation. The rats were stimulated w ith the magnetic field o f the following parameters:
B = 1.6 T; f = 30 Hz; t = 330 s; n = 9; N = 89100 impulses = 90 Kimp (kilo-impuls
es).
Video-recording was analysed w ith “EYE” software, w hich allows for tracking o f a white spot (the rat) on the background o f the dark arena o f the “open field”, through reg
istering o f the anim al’s co-ordinates. Later, “TRACK-ANALYZER” software measured automatically the distance covered by the animal in the watch-time (it was the only aspect o f m otor activity that was taken into account in our experiment).
Analgesic effects in the “tail-flick” test
Tests evaluating the influence o f the examined drug on the pain threshold are used in psycho-neuro-pharm acological research. “Tail-flick” test is one o f these. This test consists in measuring the latency o f pain reaction, i.e., duration o f pain stimulus applied to the skin o f the anim al’s tail, till the reaction o f its removal (flick) beyond the area o f the stimulus action. Special instruments are used to generate pain stimulus o f changeable strength. In our experiment, the stimulus was generated by a beam o f intensive light (like sunrays converged by a lens) applied from an A n a l g e s i a M e t e r A p p a r a t u s (mod. 3 3IITC, Inc.) Landing, N.I.
The start o f the stimulus turns on a time meter, which is stopped by a photocell impulse at the moment o f the tail flick [19, 2 1 , 2 2 , 2 3 , 2 4 ],
The “tail-flick” test, like the “open field” test was performed after the first EC and TM stimulations. Due to its m uch greater invasiveness (application o f a pain stimulus), it was perform ed at least 3-4 hours after the examination o f spontaneous m otor activity. Since we perform ed the “tail-flick” test within the frames o f the same experiment, the magnetic field used in stimulation had the same parameters as those given above:
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 41
B = 1.6 T; f = 30 Hz; t = 3 3 0 s; n = 9; N = 89100 impulses = 90 Kimp.
Motor hyperactivity after apomorphine
Psychopharm acological studies indicate that application o f apomorphine (in 1-16 mg/kg doses) - leading to stimulation o f dopaminergic receptors - triggers o ff a set o f stereotypical behaviours like licking, biting, climbing cage walls as well as hypothermia.
In lower doses (<1 mg/kg) apomorphine intensifies locomotor activity without evoking stereotypical symptoms. The effects o f m otor action o f apomorphine are neutralised by neuroleptics. On the other hand, antidepressant drugs as w ell as ECS sessions intensify stereotypy and m otor hyperactivity induced by apomorphine. Certain differences in the influence o f antidepressant drugs and ECS on apomorphine induced hypothermia allow for application o f a test to detect those antidepressants, w hich intensify noradrenergic neurotransmission [7, 9, 12, 25, 26, 27],
The anim als’ m otor activity was examined in special photo-mechanic actometers [28], 15 minutes after a dose o f 0.5 mg/kg o f apomorphine was hypodermically injected. We investigated motor activity for 30 minutes, recording the activity after 10,20 and 30 minutes o f examination. In the test we applied magnetic stimulation according to two regimes that differed in the num ber o f stimulations:
TMS 1: B 1.6 T: f 20 1 Iz: I 300 s: n = 9; N = 54 Kimp.
TMS 2: B = 1.6 T; f 201 Iz: t = 3 0 0 s; n = 1 8 ; N = 1 0 8 Kimp.
The regime that included 18 stimulation sessions was the only one in w hich stimula
tions were conducted every day and not every second day. Besides, two control groups took part in the experiment: 1) animals not submitted to any stimulation, w hich received a dose o f apomorphine (called control proper), and 2) animals (conventionally called naive), which were not stimulated w ith EC or TM either, and which received saline injections.
The described selection o f control groups is a standard procedure used in pharmacologi
cal tests.
Porsolt’s forced swimming test
The forced swimming test developed by Porsolt is a highly predictive m ethod used in the studies on antidepressant drugs [29], A n animal is forced to swim in a container (for a rat it is a cylindrical glass jar: h = 40 cm; 2r = 18 cm and water level at 15 cm above bot
tom; water temperature = 25°C), w hich it cannot leave. Initially, it manifests high motor activity. A fter a time, however, it assumes a characteristic posture o f immobility, executing only minimum movement necessary to keep its head above w ater surface. The test is con
ducted on two subsequent days. On the fist day the animal in placed in the water container for fifteen minutes to adopt to the test. On the second day, it is placed in w ater again, and its swimming time is measured during five minutes. The examination itself consists in measuring the active swimming period during a several minutes log observation.
It is known that drugs w ith antidepressant potential decrease the immobility period [20, 3 0 ,3 1 ,3 2 ],
In our experiment, Porsolt’s test was executed after the 9th or 18th TMS session and after 9 ECS sessions. We applied different stimulation frequencies and stimulation times.
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Finally, due to different parameters o f stimulation, TMS technique was used in three groups o f animals, as shown in the list below:
TMS I: B = 1.6 T; f = 20 Hz; t = 300 s; n = 9; N = 54 Kimp.
TM S II; B = 1.6 T; f = 20 H z; t = 300 s; n = 18; N =108 K im p.
TM S III: B = 1.6 T; f = 30 H z; t = 330 s; n = 9; N = 90 K im p.
The investigations were conducted in the Institute o f Pharm acology o f the Polish A cadem y o f Sciences in Cracow. Statistical significance o f the results was estim ated on the basis o f the unifactor variance analysis and t-S tudent test for independent variables.
Results
“ O p en field” te st
F igure one show s the m ean distance covered by anim als from all groups during the ten m inutes w hen th e ir m o to r activity was recorded. The “open field” test show ed that n either ECS n o r TM S influenced effectively the anim als’ m o to r activity. B oth after the first and the ninth stim ulation session, the m o to r activity o f the stim ulated rats increased, but this phenom enon was not statistically significant. A particularly m arked m o to r activation was registered after the first stim ulation session (by 48% for ECS and by 60% for TM S; p>0,05). This can be explained w ith the anim als’ reaction to a com pletely new and rather stressing situation o f the new ly started experim ent. A fter nine stim ulation sessions, the anim als were well adjusted to the three-w eek-long ex-
a fte r 1st stim u la tio n a fte r 9th stim u la tio n
Fig. 2 R a ts’ m o to r activity in th e “ open field” test a fte r a single an d prolonged eiectroconvuisive shocks (EC S) an d tra n s c ra n ia i m agnetic stim ulation (TM S); each column represents x ± s e m; groups are equal in number, n = 8; NS = no statistical signifi-
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 4 3
perim ent, hence their m otor activity was not connected w ith the stim ulating procedure
>
be confirm ed by the activity o f the control group anim als, w hose activity after the first day o f the experim ent was nearly tw ice as high as after the experim ent term ination.
E xecution o f the test 24 hours after stim ulation show ed that, e.g., the particularly high increase o f the ra ts’ activity after m agnetic stim ulation was not connected w ith the rebound effect after the 5.5 m inutes long im m obilisation (Fig. 2).
The "o p en field” test proved that neither ECS nor TM S - w hile preserving the sam e tendency (increase o f the anim als ’ m otor activity) - disturbed the rats ’ locom otor activity. Thus, none o f the techniques m anifested tachythym oleptic action, w hich, in clinical conditions, can be an undesirable side effect o f antidepressant drugs.
“ T ail-flick” te st
Figure 2 show s the results o f the "tail-flick” test. The test m anifested that both a single TM S stim ulation and a w hole series o f such stim ulations (9) led to a consider-
a fte r 1st stim u la tio n a f te r 9 th stim u la tio n Fig. 3 P ain th resh o ld in ra ts m easured in th e “tail-flick” te st a fte r single and prolonged electroconvulsive shocks (EC S) a n d tra n s c ra n ia l m agnetic stim ulation (TM S); each column represents x ± s e m; groups are equal in number, n = 8; *=p<0.05;
***=p <0.001; NS = no statistical significance.
able decrease o f the tail-flick latency. This effect (hyperalgesia; low ering o f the pain threshold) seem ed to persist during the w hole experim ent, since it decreased the la
tency o f p ain reaction after the first and the n inth m agnetic stim ulation session by 24%
and 21% respectively (p<0.05). A reverse effect was observed after E C T stim ulation, but statistical significance w as attained only after a series o f stim ulations. Statistical calculations show that nine ECS sessions evoked analgesia, considerably prolonging
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the tail-flick latency by ca. 46% (p<0.01) (Fig. 3).
T he analgesic action o f the E C T series, i.e., disturbance (disappearance) o f pain reaction can be interpreted as an undesirable phenom enon resulting from - at least - functional deterioration o f the central nervous system . The reverse effect observed after m agnetic stim ulation, i.e., acceleration o f the reaction to a pain stim ulus - im portant, am ong others, fo r self-defence - seem s a beneficial phenom enon, but its clinical im plications require further consideration.
A p o m o rp h in e in d u c e d h y p e ra c tiv ity
Figure 3 shows the results o f influence ofT M S and ECS on m otor hyperactivity after apom orphine (cum ulative diagram). The anim als from the "naive” group m anifested the low est m otor activity; apom orphine injection in the control p roper evoked m ore than tw ice as high locom otor activity. The latter group was a control for the groups subjected to stim ulation procedures. Statistical analysis show ed that electroshocks considerably intensifies the apom orphine induced m otor hyperactivity. The activity intensification after ECS was significant at each o f the three tim e points in the test (by 62, 75 and 92% respectively fo r the 10th, 20th and 30th m inute o f the test). The influence o fT M S
e a.
■ I
3
Fig. 4 Influence o f re p eate d electroconvulsive shocks (E C S) an d tra n s c ra n ia l m agnetic stim ulation (TM S) on ra ts ’ m o to r activity a fte r ad m in istratio n o f ap o m o r
phine - cum ulative d ia g ra m ; each point represents x ± s e m; groups are equal in number, n = 8; black marker = statistical significance on the level: *= p<0.05; **= p<0.01; ***=
pO.OOl ; white marker = NS = no statistical significance. Legend: TMS 1 : b = 1.6 T; f = 20 Hz; t = 300 s; n = 9; N = 54 Kimp.; TMS 2: B = 1.6 T; f = 20 Hz; t = 300 s; n = 18; N
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 4 5
w as slightly w eaker and clearly dependent upon the num ber o f stim ulation sessions.
W hen w e applied only 9 stim ulation sessions, statistically significant intensification o f m otor activity (41% ; p< 0.05) w as achieved as late as the 30lh m inute o f the test. The m ore intensive m agnetic stim ulation procedure (tw ice as high num ber o f stim ulation sessions, stim ulation applied every day) allow ed us to achieve statistical significance after 20 m inutes o f the test (45% ; p< 0.0) A fter the subsequent ten m inutes o f the test, this effect w as even stronger (58% ; p< 0.01) (Fig. 4).
Thus, in the test o f m otor hyperactivity after apom orphine, TM S m anifested action sim ilar to that o f ECT; it w as dependent upon the dose o f the applied m agnetic field.
P o r s o lt’s te s t
P o rso lt’s test confirm ed that EC stim ulation led to the greatest decrease o f im m obil
ity latency (by 50% ; p < 0 .0 0 1 ). This m eans that anim als subjected to electroconvulsive stim ulation rem ained active on the w ater surface for the longest time. T his carries sim ple and understandable clinical im plications. The decrease o f im m obility latency in P o rso lt’s “forced sw im m ing” test w as also observed after application o f a series o f
c o i r v l TT.TS1 TMS2 TMS 3 ECS
Fig. 5 S hortening o f ra ts ’ im m obility tim e in P o rso lt’s “ forced sw im m ing” test after prolonged electroconvulsive stim ulation (ECS) an d tra n sc ra n ia l m agnetic stim ulation (TM S); each column represents x ± s e m ; groups are equal in number, n= 8; *= p<0.05;
**=p<0.01; ***=p<0.001; NS = no statistical significance. Legend: TMS I: B = 1.6 T, f
= 20 Hz, t = 300 s, n = 9, N = 54 Kimp.; TMS II: B = 1.6 T, f = 2 0 H z ,t = 300 s, n = 18, N = 108 Kimp.; TMS III: B = 1.6 T, f = 3 0 H z ,t = 330 s, n = 9, N = 90 Kimp.; ECS: 1 = 150 mA, f = 50 Hz, t = 0.5 s, n = 9
m agnetic stim ulations. The action o f TM S w as slightly w eaker than that o f ECS, though it w as also statistically significant. The decrease ofim m obility time afterT M S depended upon the frequency and tim e o f stim ulation, and the frequency param eter seem ed to be m ore im portant. So, as com pared w ith the control group, im m obility latency w as
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shortened by 8%, 22% (p<0.05) and 29% (p< 0.01) respectively after m agnetic stim ula
tion according to the procedures TM S I, TM S II and TM S III (Fig. 5).
T hus, we show ed that the transcranial stiulation technique (TM S) evokes effects sim ilar to those achieved after ECS in the test highly correlated w ith clinical action o f antidepressant drugs. B esides, we proved a correlation betw een the dose o f the applied m agnetic field expressed b y param eters like frequency and stim ulation tim e, and the value o f the obtained biological result (response). O u r second observation seem s to confirm the existence o f correlation betw een the dose and the result, w hich w as also observed in the test o f m o to r hyperactivity after apom orphine.
Discussion
T he influence o f m agnetic fields (or the so-called m agnetic com ponent o f electro
m agnetic fields - EM ) on hum ans and anim als has been studied for several decades. The aim o f these studies w as to prove - o r disprove - the influence o f artificial, industrial EM fields on behaviour o f living organism s, their m otor activity and cognitive functions included. The obtained results, how ever, w ere neither consistent n o r univocal.
T he researchers m ost often observed an increase o f m o to r activity in anim als under the influence o f m agnetic stim ulation. A s early as in 1960, B am o th y and B am o th y d e tected over 50% locom otor activation in m ice after stim ulation w ith the field o f intensity am ounting to hundredth parts o f tesla [after 33]. The increase o f m o to r activation in anim als w as detected w ith the use the “open field” test [34, 35, 36, 37, 38]. N um erous w orks, however, claim ed no influence o f a m agnetic field on a 24-hour m odel o f anim al m o to r activity [34, 36]. W ith the use o f N akam ura and T h o en en ’s test allow ing for evaluation o f an im als’ irritability on a conventional scale, M row iec et al. [40] w ere not able to detect differences betw een rats subjected to m agnetic stim ulation and control rats. D espite a relatively long tim e o f exposure (up to 72 hours) and a strong field (1.5 T), D avis et al. [39] w ere not able to obtain changes o f locom otor activity in m ice.
Some authors also reported an inhibiting influence o f m agnetic stim ulation. To estim ate activity, M row iec et al. [40] u sed the “o pen field’ test and the “hole” test, in w hich ep i
sodes o f a ra t’s crossing over, looking into, clim bing up, w ashing and defecating w ere counted during three m inutes in a special experim ental container. In the “open field”
test, the authors show ed that the activity o f rats subjected to m agnetic stim ulation o f 0.01 T and 40H z decreased. T his decrease w as observed bo th after the first stim ulation and after 7 days o f exposition. The activity o f the stim ulated anim als becam e equal to that o f control anim als in the second w eek o f the experim ent. O bservations m ade in the first and second w eek after term ination o f a 14 days long stim ulation procedure did n o t show any difference in locom otor activity o f the tw o groups o f anim als. In turn, N orekian et al. [41 ] detected a prolonged reaction tim e in rats subjected to stim ulation, b u t this effect persisted fo r less than one hour after exposition.
The hitherto conducted studies on the influence o f m agnetic field on m em ory, attention and generally understood cognitive functions in anim als are not univocal either. E xperim ental w orks indicate both im provem ent and deterioration o f co g n i
tive functions u nder the influence o f exposition to m agnetic field. U sing the field o f
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 4 7
induction = 1 0 m T and frequency = 40 H z, M row iec et al. [40] reported a consider
able im provem ent o f spatial m em ory evaluated in the “w ater labyrinth” test. Innis et al. [after 33] found that the applied m agnetic field did not influence significantly the process o f m em orisation. The results o f L ev in e’s and B lu n i’s w orks [42] even indicated a considerably decreased ability to learn distinguish the left side from right one in m ice after their being exposed to m agnetic field. C ieslar et al. [43] detected a change in ra ts’ reactivity to a pain stim ulus, in the form o f a m ild analgesic effect.
O ther behavioural sym ptom s in anim als, connected w ith their exposure to m agnetic field, w ere also described [44, 45].
A ll the studies m entioned above described behavioural action o f m agnetic field w hose param eters (induction, increase rate) did not allow for a specific stim ulation o f the central nervous system neurons. T his field w as not able to bring about de
polarisation o f nervous cell m em brane, subsequently evoking its stim ulation. This becam e possible as late as the 1980s. In 1982, Poison et al. perform ed an effective m agnetic stim ulation o f brain in experim ental anim als [after 2], and in 1985, B arker at al. executed first clinical experim ents on hum ans. T hus, the new neuro-physiological technique called transcranial m agnetic stim ulation (TM S) w as w orked out. Its first and m ajor application w as neurological diagnostics. In 1992, a hypothesis w as form ulated, w hich described a possibility to apply TM S in psychiatry, as a therapeutic m ethod in treatm ent o f depression - alternative to electroconvulsive therapy [1]. M erely a few clinical centres started research on using TM S in the depressive syndrom e therapy. Also, several experim ents on anim als were perform ed. The num ber o f hitherto conducted and published behavioural on TM S activity in anim als - as contrasted w ith the num ber o f basic studies on new ly synthesised chem ical substances w ith probable antidepressant action - is lim ited to a m ere three [12, 25, 46].
In 1994, Fleischm ann et al. w ere the first to conduct a behavioural experim ental study on anim als. T hey perform ed a com parison o f effects o f TM S and ECS in rats - in the test o f apom orphine evoked stereotypy [12]. In their research, they applied tw o kinds o f m agnetic stim ulation: a) w ith the use o f a “ slow ” stim ulator M agstim 200:
f= 0.2 H z, 2x25 im pulses w ith a ten m in u tes’ break, for ten days (“ single pulse” TM S
= spTM S) and b) w ith the use o f a “rapid” stim ulator C adw ell R apid R ate Stim ulator:
f = 25 H z, 50 im pulses (2 s) for seven days (“repetitive rapid rate” TM S = rTM S). To evoke m otor stereotypy they adm inistered 0.25 and 0.5 m g o f apom orphine p e r kg o f b o d y w eight. T hey observed an increase o f apom orphine induced m otor stereotypy w hen m agnetic stim ulation o f 25 H z frequency w as applied (results on the threshold o f statistical significance). TM S stim ulation w ith 0.2 H z frequency did not give signifi
cant results. T hese results confirm ed that m agnetic stim ulation o f the brain can evoke behavioural effects sim ilar to those, w hich occur after electroconvulsive stim ulation, but w ithout a convulsive effect. TM S stim ulation w ith frequencies am ounting to several tens o f H z (rTM S) w as m ore effective than that w ith the frequency < 1 H z (spTM S).
O ne year later (1995), F leish m an n ’s group presented further results o f their stud
ies [15]. This tim e they used exclusively the rTM S stim ulator (C adw ell R apid Rate Stim ulator; B = 2.3 T; f = 25 Hz; t = 2 s; n = 50 im pulses daily; N = 7-10 days). To evaluate the action o f TM S they used apom orphine stereotypy test and P o rso lt’s forced
Tomasz Zyss et al.
sw im m ing test. M agnetic stim ulation increased the a n im als’ stereotypical activity (m easured in special points) fo r each dose o f apom orphie (0.25, 0.5 and 1 m g/kg o f body w eight) though it w as only after the sm allest dose that the difference betw een TM S stim ulated anim als an d control ones w as statistically significant. P o rso lt’s test confirm ed that T M S, like electroconvulsive stim ulation, shortened the im m obility period. The antidepressant-like effect after TM S w as only slightly w eaker that that, w hich w as achieved after ECS.
D uring the international congress on transcranial m agnetic stim ulation that took palce in G ottingen in 1998, K eck et al. [46] presented the results o f their behavioural and endocrinological research conducted on rats. U sing another stim ulator, also w ork
ing in rT M S routine (D antec M ag Pro; B = ?; f = ?; t = ?; n = 300 im pulses daily; N
= 6 w eeks), they found shortening o f im m obility period in P o rso lt’s test. O n the other hand, they did n o t detect - after a series o f TM S - disturbances in the an im als’ learn ing an d cognitive functions (M o rris’s w ater labyrinth) o r em otional sphere (social interaction tests).
In 1997 our team also published the results o f com parative research on the TM S and ECS techniques, in w hich we u sed several behavioural tests [16]. T hen w e used a prototype stim ulator M S2 (B = 0.1 T; f = 50 H z; t = 5 m in). We found that in the forced sw im m ing test, im m obility tim e w as shortened after TM S and even stronger so after ECS. B oth TM S and ECS decreased the basic m o to r activity. EC stim ulation dim inished cognitive activity and TM S did not. O nly electroconvulsive stim ulation induced analgesia, prolonging tail flick latency.
O ur present studies have confirm ed our earlier observations and broadened our know ledge o f TM S action in behavioural experim ents on rats. In general, we could recognise high safety o f the TM S technique. D uring none o f the experim ents, i.e., at none o f the applied stim ulation param eters o f the m agnetic field, could w e evoke a convulsive seizure in any o f the rats w hile this phenom enon w as observed at each case o f EC stim ulation. T his tim e, n either electroconvulsive stim ulation n o r m agnetic stim ulation, applied once o r repeatedly, disturbed the an im als’ basic m o to r activity
“open field” . R epeated EC stim ulation disturbed pain excitability threshold, leading to prolonged latency o f p ain reaction (tail flick test). T his can be explained, i.a., w ith after shock functional disturbances o f the central nervous system (connected w ith the opioid /?/ system ) and seem s to be clinically disadvantageous. A n opposite effect w as observed after one as w ell as several transcranial m agnetic stim ulations. C linical im portance and im plications o f hyperalgesia after TM S require further study and e x planation. The apom orphine induced m otor hyperactivity test and P orsolt’s test show ed that TM S w orked in a sim ilar w ay as ECS did: it intensified apom orphine stim ulated m o to r activity and shortened the im m obility tim e during the forced sw im m ing. The effect after TM S w as slightly w eaker than after ECS. The latest tw o tests revealed a correlation betw een the param eters o f m agnetic stim ulation (generally understood dose) and its effect. The conducted experim ents show ed that TM S, like EC S, evokes in rats certain responses, w hich suggest its antidepressant action, b u t brings less undesirable side effects. B asic studies on antidepressant effects o f transcranial m agnetic stim ulation
The behavioural effects o f the transcranial magnetic brain stim ulation (TM S) in a rat 4 9
should be continued [4 7 ,4 8 ], M oreover, they should cover n o t only other behavioural tests corresponding w ith anim al m odels o f depression, bu t also bio-chem ical exam ina
tions (receptor system s, cAM P, channels, e.g., calcium channels, etc.).
Conclusions
1. Transcranial m agnetic stim ulation (TM S), like EC S, does n o t disturb basic m otor activity in anim als.
2. E lectroconvulsive shocks - u sually after repetitive application - led to disappear
ance o f pain reaction, w hile single and repetitive transcranial m agnetic stim ulations induced hyperalgesia.
3. B oth TM S and ECS intensified m otor activity in anim als stim ulated before w ith adm inistration o f apm orphine.
4. TM S and, even stronger, ECS shortened im m obility tim e in the forced sw im m ing test.
5. The dose o f the applied field (param eters) considerably influenced the behavioural effect o f stim ulation m easured w ith the apom orphine induced m otor hyperactivity test an d P o rso lt’s test.
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