Short-term memory: Facilitation and disruption with cholinergic agents

Phystology and Behavtor, Vol l l, pp 571-575. Brain Research Pubhcatmns Inc , 1973 Prmted in the U S.A

Short-Term Memory: Facilitation and Disruption with Cholinergic Agents HERBERT P ALPERN AND JOHN G MARRIOTT

Department o f Psychology, Unil,erstty o f Colorado, Boulder, Colorado 80302 and hlstitute for Behavioral Genetws, Umversity o f Colorado, Boulder, Colorado 80302

( R e c e i v e d 13 M a r c h 1 9 7 3 ) ALPERN, H P AND J. G MARRIOTT Short-term memory facthtatton and dtsruptton with chohnergtc agents PHYSIOL BEHAV. 11(4) 5 7 1 - 5 7 5 , 1973 -Male mice (C57BI~/6 strain) trained in a T-maze to develop a successive reversal learning set were delayed-response tested at several intervals When treated with scopolamine, behavior was impaired at all Intervals; however, physostlgmlne faclhtated performance at the longer intervals The lmpalrlnent and faclhtatlon were most probably due to the actions of the chohnerglc agents upon the expression of short-term memory, and it was concluded that the chohnerglc synapse was necessary for short-term memory Short-term memory Chohnerglc drugs Scopolamine Inbred mice

Memory facilitation

Memory disruption

Physostlgnune

is n o t clear t h a t t h e drugs were o p e r a t i n g u p o n the u n d e r lying STM process as o p p o s e d to s o m e o t h e r p e r f o r m a n c e variable [ 1 0 , 2 3 ] . The p r e s e n t s t u d y was designed to e x a m i n e the role o f c h o h n e r g l c t r a n s m i s s i o n in STM The efficacy of m e a s u r i n g STM in mice w i t h t h e delayed r e s p o n s e p r o c e d u r e e m p l o y e d has b e e n a d e q u a t e l y d e m o n s t r a t e d [1,2] The t e c h n i q u e involved t r a i n i n g mice to develop a simple successive reversal l e a r n i n g set, t h e n to provide t h e m with a unit of i n f o r m a t i o n ( t h e signal to reverse), and finally to d e t e r m i n e t h e l e n g t h of tame for w h i c h t h a t i n f o r m a t i o n (as i n d e x e d b y reversal b e h a v i o r ) could be r e t a i n e d

R E C E N T e v i d e n c e suggests t h a t m e m o r y processes Involve t h e a c t i o n o f specific t r a n s m i t t e r s u b s t a n c e s in t h e c e n t r a l n e r v o u s s y s t e m . N a m e l y , c h o h n e r g l c b l o c k i n g a g e n t s [ 7, 15, 16, 29, 3 3 ] , a n t l c h o h n e r s t e r a s e c o m p o u n d s [7, 8, 9, 11, 16, 28, 29, 30, 33] a n d adrenerglc d e p l e t o r s [12, 13, 21, 22, 25, 26, 32] have b e e n s h o w n to alter r e t e n t i o n in r o d e n t s on a variety o f d i f f e r e n t tasks and e x p e r i m e n t a l p r o c e d u r e s . The clearest d e m o n s t r a t i o n t h a t the u n d e r l y i n g m e m o r y was a f f e c t e d b y these agents has b e e n p r e s e n t e d b y D e u t s c h and his associates w h o have s h o w n t h a t l o n g - t e r m m e m o r y can be s y s t e m a t i c a l l y m a n i p u l a t e d w i t h c h o h n o lytm as well as a n t l c h o h n e s t e r a s e c o m p o u n d s [ 7 ] . Some c a u t i o n , h o w e v e r , s h o u l d be used in a t t r i b u t i n g t h e s e results to effects o n a p a r t i c u l a r n e u r a l t r a n s m i t t i n g s y s t e m , since t h e drugs used in these studies have a m u l t i p l i c i t y o f effects in a d d i t i o n to t h e i r specific chollnerglc a n d / o r adrenerglc a c t i o n s [ 1 4 , 3 1 ] This c o m m e n t is m o s t r e l e v a n t to ,nvestigatlons e m p l o y i n g a single dosage o f a p a r t i c u l a r agent, or even a single agent In studies e m p l o y i n g several comp o u n d s , espemally drugs p u r p o r t e d to have o p p o s i n g a c t i o n s , xt is less likely t h a t o t h e r n o n s p e c i f i c effects could a c c o u n t for c o r r e p o n d l n g a l t e r a t i o n s in b e h a v i o r C u r r e n t t h e o r i e s of m e m o r y p o s t u l a t e in a d d i t i o n to l o n g - t e r m m e m o r y a s h o r t - t e r m m e m o r y (STM) process perslstmg for several s e c o n d s or m i n u t e s [5, 6, 17, 18] A l t h o u g h chohnergac b l o c k i n g agents have b e e n s h o w n to have a d e l e t e r i o u s effect u p o n delayed response b e h a v i o r , it

METHOD

A mmals T w e n t y 60-day-old naive male mice of t h e C 5 7 B L / 6 strain bred in o u r l a b o r a t o r y were used. When n o t b e h a v iorally tested, t h e mice were given access to m o u s e c h o w a n d w a t e r ad lib

Apparatus A white were 9 cm

T-maze, described elsewhere [ 1 , 2 ] , c o n s t r u c t e d f r o m Plexlglas was used. The start r u n w a y ' s d i m e n s i o n s 29 1/2 x 4 x 9 cm and each arm m e a s u r e d 21 x 4 x A l u m i n u m sheet m e t a l lined the i n t e r i o r walls of

~Thls investigation was supported by National Institute of Mental Health Grants MH 11167 and MH 20574-01 and National Institute for General Medical Sciences Grant GM 14547 We thank Donald Rossmelsl for assistance in testing the animals 571

572 b o t h arms o f the maze The grid floor and the a l u m i n u m lining the walls o f the maze were c o n n e c t e d to a grid scrambler and an alternating current shock source w h i c h delivered 3 ma to a 10 K resistance

A L P E R N AND M A R R I O T T

"FABLE 1 DAILY

EXPERIMENTAL PROCEDURE DURING RESPONSE TESTING

DELAYED

Proc'edut e

The mice, individually housed during daily runs, were trained to develop a successive reversal set by the following p r o c e d u r e A f t e r p l a c e m e n t in the start r u n w a y , the animal had 2 5 sec to e n t e r the correct alley b e f o r e the grids in the start runway and the grids, as well as the a l u m i n u m lining, m the Incorrect arm were e l c t n f i e d A c o r r e c t i o n p r o c e d u r e allowed the animal to escape into the correct alley, if necessary, and exit into its holding cage One half sec before the grids were electrified a 4000 Hz, 105 db t o n e , d e h v e r e d from a speaker located directly above the choice p o i n t , was s o u n d e d to alert the animal to the i m m i n e n t shock Animals wine initially trained to chose one arm until shock was successfully avoided on 5/6 consecutive trials with an lntertrial interval o f 5 rain Training was t e r m i n a t e d at this point on half o f the days On alternate days a second disCrllninatlon reversal was a d m i n i s t e r e d and the previously correct position became the p u n i s h e d p o s i t i o n The animals were reversed each day from the last position learned on the previous day When each animal could reliably reverse its behavior lnaklng no m o r e than 1 error in three consecutive days on the first reversal p r o b l e m (reveisal set criterion), delayed response testing began (One animal was discarded for falling to attain the leversai set criterion) Here the basic p r o c e d u r e r e m a i n e d the same h o w e v e r , each day (1) every m o u s e was injected l n t r a p e n t o n e a l l y with either the vehicle (09<; sallneL the c h o l i n o l y t l c c o m p o u n d s c o p o l a m m e h y d r o b r o m l d e (0 5 mg/kg or 2 lng/kg), or the antIcholinesterase c o m p o u n d p h y s o s t l g m l n e sahcylate ( 0 0 5 mg/kg or 0 2 mg/kg), (2) one-half h o u r after Injection, every animal was given a trial with the d l s c r n m n a t i o n reversed f r o m that of the previous day (stgn-trlal}, thus, the cue signalling the reversal on the sign-trial was f o o t s h o c k for c h o o s i n g m c o r rectly, (3) every animal was next tested for reversal behavior after the sign-trial at one o f the selected delay intervals lelther 2, 15, 20 or 25 mln), and on this trial an error was scored if the a m m a l e n t e r e d the incorrect alley, (4) presenting trials every 5 lnln, the inlce were t h e n trained oil this d i s c r i m i n a t i o n until a 5/6 criterion was reached (see Table 11 Animals were initially tested at the 2 lnln delay interval For the first two days of testing at this interval, animals received lust the vehicle Then the low, followed by the high dosage of s c o p o l a m i n e were each a d m i n i s t e r e d for two successive days The animals n e x t advanced to the I5 mln interval Again, the vehicle was p r e s e n t e d for two successive days For the n e x t two days, half o f tile mice received the low dosage of s c o p o l a m i n e followed by two days of the high dosage The vehicle was again a d m i n i s t e r e d for two consecutive days and these animals were n e x t treated for two days with the low dosage o f p h y s o s t i g m i n e , f o l l o w e d by two days o f the high dosage The o t h e r half o f the animals were Sllmlarly t r e a t e d , howe~er, o r d e r o f administration o f the drugs was reversed The p a t t e r n of drug p r e s e n t a t i o n was always vehicle - low dose - high dose in order to minimize possible c o n f o u n d i n g influences caused by lncolnplete m e t a b o h s l n of the drugs, t h e r e b y carrying their effects over into the n e x t testing session (An analysis

1

Injection

One-halt

hour

prior to maze r u n n i n g anllnal

rejected x~lth rather ~ahne, scopolamine, or phy~osttgmme 2

Sign-trial

Anmlal given single trial m maze with dlscrmmratmn reversed from that learned last on pre~mns day

3

Dela3

Animal detained m holding cage either 2 15, 20 or 25 mm

4

Test trml

A.nllllal gl'~en second trial 111 maze to d e t e r n n n e

retention o) dlscrmnnatmn reversal signalled on flr,t trial 5

Training to Criterion

3tnlind[ given trials spaced 5 mill a p a r t until 5 / 6

correct a~o~dances achieved On alternate days tralmng

on

~e~.ond

discrimination

reversal

admlnlqered

of variance with r e p e a t e d measures of the error scores for the first and second day at each drug and c o n t r o l c o n d i t i o n s h o w e d no differences b e t w e e n days; thus, additive drug effects if p r e s e n t , appear neghglble ) The 20 mln interval followed, and the regimen for drug a d m i n i s t r a t i o n was identical to that e m p l o y e d at 15 mln, e x c e p t t h a t half of tile animals which received s c o p o l a m i n e first at the 15 m m interval received p h y s o s t i g m i n e first at this interval, e t c , m order to c o u n t e r b a l a n c e the o r d e r of drug p r e s e n t a t i o n Lastly, animals were tested at the 25 rain delay Here, vehicle days were followed by p h y s o s t l g m l n e days with a procedure identical to that e m p l o y e d at 2 m m The delay intervals were n o t r a n d o m l y p r e s e n t e d b u t were progressively lengthed to m a x i m i z e stable p e r f o r m a n c e across days and minimize disruptive influences caused by daily change of the interval Our previous work indicates no improvem e n t in p e r f o r m a n c e at any of the intervals tested as a result o f practice acro,~s several days or weeks [ 1 ] , therefore, a r a n d o m i z e d design with respect to p r e s e n t a t i o n of the delay intervals was not dictated A d d i t i o n a l l y , prior to delayed response testing at each of the intervals, the animals were given one practice session, w i t h o u t injection, at the respective delays This session was e m p l o y e d to minimize any disruptive influeiaces caused by changing the delay interval These data were not included in any o f the analyses RESUL~IS

Animals averaged 15 2 reversals in attaining the reversalset criterion In agreement with prevxous studies [ 1 , 2 ] , maximal r e t e n t i o n o f i n f o r m a t i o n a c q m r e d on the sign-trial o c c u r r e d at the 2 mln delay and then d e c a y e d progresmvely to chance levels at 25 mln when the animals were injected with the vehicle alone c o n t r o l days (sohd black bars, Fig 1 F3,~4 = 3 67, p < 0 025 for the interval effect). Binomial testb, with an e x p e c t e d p r o b a b i l i t y o f 0 5 [ 2 7 ] , used to d e t e r m i n e w h e t h e r p e r f o r m a n c e at each interval was slgnlfl-

SHORT-TERM

100 90

MEMORY

573

I'

SCOPOLAMINE

II

80

.5 mg/kg

70 CO W CO Z

Control

2 mg/kg

60

0

0_ r.O Ill rr t--

50 40

0i l l

nr" r'r"

0

PHYSOSTIGMINE 90

0 t-Z W

o

0:: W 0_

80

Control .05 mg/kg ~----'~.2 mg/kg

70 60 50 40 2 min.

15 min,

20 min.

25 min.

FIG 1 The percentage of correct responses at each of the delay intervals after treatment with physiological saline (control), scopolamine, and physostlgmme

574

ALPERN AND MARRIOTT

c a n t l y b e t t e r t h a n c h a n c e r e s p o n d i n g , i n d i c a t e d significant r e t e n t i o n at 2 rain (p
ones used in this s t u d y , c o n s t a n t n e u r o p h y s l o l o g i c a l effects have b e e n r e p o r t e d for d u r a t i o n s of 3 0 - 6 0 m l n F o r physostigmlne t h e n e u r o p h y s l o l o g l c a l effects were i n i t i a t e d 3 - 7 rain a f t e r i n j e c t i o n and persisted for 3 0 - 6 0 m l n [4] F o r s c o p o l a m i n e the o n s e t of the effects o c c u r r e d w i t h i n 30 rain and lasted 2 0 - 2 5 m i n [19] Since s c o p o l a m i n e has central depressant as well as p e r i p h e r a l m o t o r effects, it IS c o n c e i v a b l e t h a t these actions could have i m p a i r e d p e r f o r m a n c e A similar Investigation to the one r e p o r t e d here ( u n p u b l i s h e d ) i n d i c a t e d t h a t p e n t o b a r b i t a l in a d e p r e s s a n t dosage (20 m g / k g ) has n o effect u p o n delayed r e s p o n d i n g . F u r t h e r m o r e , 50 m g / k g of p r o p r a n o l o l , w h i c h p r o d u c e d b l a t a n t m o t o r defects, and m e t h s c o p o l a m t n e h y d r o b r o m i d e (4 m g / k g ) w h i c h is only peripherally active, did n o t i m p a i r delayed r e s p o n d i n g . Overall, t h e evidence does n o t s u p p o r t the I n t e r p r e t a t i o n t h a t t h e results o b t a i n e d were due to the drugs' actions u p o n n o n m e m o r y factors These drugs also i n f l u e n c e long-term m e m o r y [8, 9, 11, 15, 16, 28, 29, 33] and m i g h t have p r o d u c e d changes in reversal b e h a v i o r b y acting u p o n r e t e n t i o n of the p o s i t i o n learned o n the previous day Persistence o n the p o s i t i o n learned previously or a s p o n t a n e o u s reversal t e n d e n c y m i g h t have a c c o u n t e d for these results I n s p e c t i o n of t h e data o n t h e sign-trial, h o w e v e r , w h e n t h e animals selected an arm of the maze p r e s u m a b l y o n the basis of m e m o r y from the p r e c e d i n g day, i n d i c a t e d no differences, i e., n o persistence or s p o n t a n e o u s reversing as a result of e i t h e r drug a d m i n i s t r a t i o n C o n s e q u e n t l y , t h e d r u g s ' actions u p o n long-term m e m o r y do n o t a p p e a r responsible for the observed a l t e r a t i o n s in r e t e n t i o n Since the chollnergic agents so effectively and s y s t e m a t i cally m a n i p u l a t e d the e x p r e s s i o n o f STM, It appears t h a t the c h o h n e r g l c s y s t e m is necessary for STM At the 25-mIn delay interval, w h e n c o n t r o l p e r f o r m a n c e was n o t d i f f e r e n t from chance, t h e higher dosage o f p h y s o s t i g m l n e r e s t o r e d correct r e s p o n d i n g to 80% Moreover, t h e low dosage of s c o p o l a m i n e i m p a i r e d p e r f o r m a n c e a c o n s t a n t a m o u n t at each of the intervals sampled (15% at 2 rain, 13% at 15 rain, and 15% at 20 man), whereas the higher dosage prod u c e d c h a n c e r e s p o n d i n g (total d i s r u p t i o n ) at each of these intervals. T h a t the m o s t efficient expression of STM is related to an o p t i m a l level of c h o h n e r g l c acitlvity is also s u p p o r t e d b y these results The high dosage of p h y s o s t i g m l n e t h a t restored p e r f o r m a n c e at the 25-rain delay interval was n o t effective at 20 mln However, the low dosage was m o s t effective at 20 min The sensitivity of the s y n a p t l c m e c h a nism to the effects o f p h y s o s t i g m l n e appears to decline as the STM trace decays Prior to t h e decay of the STM trace, the lower dosages increased the s t r e n g t h o f the trace When the trace was m i n i m a l , however, t h e higher dose was required to restore the activity of STM These d a t a s u p p o r t c o m p a r a b l e r e p o r t s c o n c e r n i n g o p t i m a l levels of c h o h n e r g l c activity in long-term m e m o r y [7]

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6. 7. 8.

9

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11

12.

13.

14

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16 17 18 19

MEMORY

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20

21

22

23.

24. 25

26

27 28 29

30

31.

32.

33

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