Partial reversal of anticholinergic amnesia by choline chloride

Life Sciences, Vol. 29, pp. 1317-1323 Printed in the U.S.A.

Pergamon Press

PARTIAL REVERSAL OF ANTICHOLINERGIC AMNESIA BY CHOLINE CHLORIDE Richard C. Mohs, Kenneth L. Davis, Michael I. Levy Psychiatry Service (I 16A) Veterans Administration Medical Center Bronx, N. Y. 10468 and Mount Sinai School of Medicine New York, N. Y. 10029 (Received in final form July 20, 1981)

Summary Twenty young adult males were given tests of memory and mood after receiving choline chloride plus scopolamine, placebo plus scopolamine, and two placebos on separate days in randomized order. Scopolamine caused a marked impairment in performance on a verbal learning task. Pretreatment with choline caused a small but sig~nificant decrease in this impairment and partially reversed the mood changes produced by scopolamine. Although several previous studies have failed to demonstrate that choline has a significant effect on cognition when given alone, the present results indicate that choline can enhance cognition under conditions of cholinergic blockade. This is consistent with preclinical data indicating that cholinergic neurons are most sensitive to precursor availability when they are firing rapidly. There has been considerable interest in the possibility that choline, a precursor to acetylcholine, might be useful for improving memory. Psychopharmacological studies indicate that cholinergic antagonists impair memory (1,2), while cholinesterase iuhibitors (3,4,5) and cholinergic agonists (6) improve memory when given in low doses. Alzheimer's type dementia is associated with a specific loss of cholinergic function (7-10). Since there are no long acting cholinergic agonists or cholinesterase iuhibitors that can safely be administered to humans, attempts to improve memory have focused on choline and phosphatidylcholine. In rats it has been shown that systemic administration of either of these precursors increases brain acetylcholine concentrations (11,12). Choline has also been shown to increase tyrosine hydroxylase activity (15) and homovanillic acid concentrations (14) in the striatum. These effects on dopamine metabolism are antagonized by atropine suggesting that they are a result of increased activity at cholinergic synapses (13,14). Other data, however, appear not to support the conclusion that choline increases cholinergic activity. One stud~ found no significant change in acetylcholine turnover either in cortex or striatum following the acute sevenfold elevation of plasma choline levels (15). Furthermore, clinical studies have failed to demonstrate a significant effect of choline on memory in young adults (16,17), in nondemented elderly people (18,19), or in patients with Alzheimer's disease (20,21). 0024-3205/81/131317-07502.00/0

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Despite these negative clinical data, it remains possible that choline might have a substantial effect on cholinergic activity and therefore on memory under some specific circumstances. Studies with rats suggest that one such circumstance might be when cholinergic receptors are blocked and presynaptic activity is increased. Following the administration of atropine the concentration of acetylcholine is decreased (22,23) and the rate of high affinity choline uptake is increased(24) in rat brain. The decrease in acetylcholine concentration can be prevented by precursor loading with choline (22,23). The present study was designed to determine whether the learning deficit produced by scopolamine can be reversed by precursor loading with choline. Methods Twenty adult males aged 18 to 31 years (mean age 22.5 years) served as subjects. Potential subjects with active medical conditions or a history of psychiatric illness were excluded and all subjects gave informed consent. Subjects were tested in one practice session and three test sessions, separated by at least 48 hours. Table I presents the schedule of procedures for a regular test session. On one test day subjects received choline followed TABLE I Schedule of Procedures for a Test Session Time (min) 0

Procedure Choline (8 gm p.o.) or placebo

+45

Scopolamine (0.43 mg s.c.) or placebo

+75

POMS

+9O

Digit span Word span Six learning trials on list of 24 nouns

by scopol~mlne ICh-Sc conditionl; on another they received placebo followed by scopolamine (P1-Sc condition~; and, on a third they received two placebos (P1-P1 condition). The order of drug conditions was randomized and all testing was double blind. Mood was assessed with the Profile of Mood States (POMS), a 64 item self-rating questionaire (25). Memory was assessed with tests of digit span, word span and free recall for a list of 24 nouns. The digit span test measured the maximum number of digits subjects could recall in order after a single presentation. Word span was tested with the 24 nouns used in the free recall task. The nouns were divided into one set each of 3, 4, and 5 words and 2 sets of 6 words. Each set was presented onceverbally and the longest set recalled completely in correct order was taken as the word span. After the word span test subjects were asked to recall all 24 nouns in any order. The number of words correctly reca/led was the subject's score for the first trial of the free recall test. On each of 5 subsequent trials subjects were first reminded of all words they failed to recall on the previous trial and then tried to recall all 24 words (26). Subjects learned a new list on each

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Choline in Anticholinergic Amnesia

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day. Lists contained 12 concrete, or nigh imagery words (e.g. tree) and 12 abstract or low im~ery words (e.g. franchise) arranged in raudom order. Average im~geryvalues were 6.24 and 2.73 for concrete and abstract words, respectively (27). Average frequencies were 14.6 and 13.4 occurences per million for concrete and abstract words, respectively (28). Results Average digit span scores were 8.15, 7.65 and 7.95 for the P1-P1, Ch-Sc, and P1-Sc conditions, respectively; these means are not significantly different (p > .10). Word span scores were 5.25, 5.10, and 5.05 for the P1-P1, Ch-Sc, and P1-Sc conditions, respectively; again these means are not significantly different (p > .10). Prelimina~ anal~ses of the free recall data indicated that recall did not change significantly from the first to the third test session (p > .20) and that recall was not affected by the order in which drug conditions were admiuistered (p > .I0). Consequently, test da~s and order of drug conditions were not included as factors in subsequent analyses. Figure I presents the total number of words recalled in the three drug conditions. An ANOVA comparing

a uJ 2 2 _1 ._1

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18

n-

14

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..~)"°........ O".......... O

°°°oo°°°°°

s

~

~

2"

I..iJ m D

Z

o ...... <) PLACEBO-PLACEBO

A-----~ CHOLINE-SCOPOLAMINE

2

e - - - - - e PLACEBO-SCOPOLAMINE '

l

I

I

l

1

I

2

3

4

5

6

LEARNING

TRIALS

FIG. 1 Total Number of Words Recalled Correctly From a List of 24 Nouns

the PI-PI condition with the PI-Sc condition indicated that recall was higher in the P1-P1 condition (F (1,19) = 41.2, p ~ .0001), that recall improved over trials (F (5,95) = 160.9, p < .0001) and that recall improved at a faster

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rate over trials in the P1-P1 condition (F (5,95) = 2.6, p < .04). Thus, as expected, scopolamine produced a highly reliable amnesic effect. To determine whether this amnesic effect was partially reversed by choline, a second ANOVA compared the Ch-Sc condition with the P1-Sc condition. This analysis revealed an improvement in recall over trials (F (5~95) = 179.9, p < .0001), no main effect due to drug (F (1,19) = 1.0, p > .05), and a significant interaction between drug conditions and trials (F (5,95) = 5.2, p < .02). As Figure I indicates recall scores were identical in these two drug conditions on trial 1 but recall improved faster in the Ch-Sc condition than in the P1-Sc condition. These significant interactions can be clarified by reference to Table II which presents the amount of new learning in each condition as reflected by the increase in recall over trials. Paired t-tests indicate that increases over trials were gTeater in the P1-P1 condition and in the Ch-Sc condition than in the P1-Sc condition. TABLE II Average Increase in Number of Words Recalled Over Six Trials (Trial 6 Minus Trial I )

Condition

Increase

S.E.M.

P1-PI

12.2

0.7

Ch-Sc

+11.6

0.5

PI-Sc

10.2

0.6

+ p ~ . 0 3 compared with P1-Sc * p ~ .03 compared with P1-P1 Comparison of high and low imagery word recall indicated that high imagery words were easier to recall (F (1,19) = 6.06, p ~ .03) (27), and that scopolamine significantly impaired recall of both kinds of words (p < .001 in both cases). For high ~m~gery words there was a trend for recall to be better in the Ch-Sc condition than in the P1-Sc condition on all trials (F (1,19) = 3.4, P < .08). For low ~ m ~ e r y words there was a significant interaction between drug condition and trials (F (5,95) = 2.8, p ~ .03) reflecting the fact that, on the first three learning trials, recall in the Ch-Sc condition was slightly poorer than recall in the P1-Sc condition while on the last three trials recall was better in the Ch-Sc condition. On the POMS scopolamine alone produced significant increases in self ratings on 4 subscales, tension, depression, fatigue, and confusion, and a significant decrease on one subscale, vigor. Choline produced a significant reversal of scopol~m~ue's effect on only one scale, tension. Discussion The present results indicate that orally a~m~Istered choline can partially reverse the amnesic effects of scopolsmlne. Neither choline nor scopolamine had an effect on the digit and word span tasks which are measures of the capacity of short-term memory (29). This is consistent with previous results demon-

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Choline in Anticholinergic Amnesia

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TABLE llI Mean Scores on the Profile of Mood States Questionaire (~S.E.M.)

POMS Scales

Conditions P1-PI

Ch-Sc

P1-Sc

Tension-anxiety

4.8 + 1.2

#6.4 + 0.7

~ 7 . 8 + 0.8

Depression-dejection

4.6 + 1.8

6.3 -+ 1.4

Anger-hostility

2.7 + 1.1

3.6 + 1.0

~.7

-+ 1.2

4.2 + 0.9 **

Vigor-activity

16.9 + 1.9

10.0 + 1.5

10.1 + 1.8

Fatigue-inertia

4.5 + 2.0

11.6 + 1.7

11.0 _+ 1.3

Confusion-bewilderment

4.7 + 1.4

9.2 + 1.2

~-~9.~ -+ 0.7

** p ~..01 compared with P1-P1 * p < .05 compared with P1-P1 # p < .05 compared with P1-Sc strating that this aspect of memory is unaffected by anticholinergics (I) and cholinomimetics (3). Performance on the free recall task which is a measure of storage of information in long-term memory (29) was impaired by scopolamine and this impairment was partially reversed by choline. Storage into long term memory is known to be very sensitive to fluctuations in central cholinergic activity (1,3) and is known to be severely impaired by damage to the hippocampus (50), an area with substantial cholinergic input (31). This suggests that changes in memory performance produced by scopolamine and choline are mediated by cholinergic synapses in the hippocampus. Several previous studies of the effects of choline have failed to demonstrate a significant effect on memory (16-21). Furthermore, although the effect produced by choline in the present study was statistically significant, it was not large or clinically obvious. This can be contrasted with the results obtained when physostigmine is administered to patients who have received an anticholinergic. Clinically, physostigmine rapidly reverses most of the sedative effects of anticholinergics (52) and experimental studies demonstrate that it reverses about 50-60% of the memory impairment produced by scopol~m~ne (5). In the present study choline did not reverse most of the subjective effects of s c o p o l ~ n e and reversed only about 10-2~% of the learning deficit produced by scopolamine. Thus, although choline does have a significant effect on memory under conditions of cholinergic blockade these effects are small when compared with those of a potent chclincm~metic such as physostigmine. The fact that choline had a significant effect on memory in the present study but not in previous studies when it was administered alone is consistent with preclinical data indicating that choline is most likely to enhance cholinergic

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activity when presynaptic neurons are firing rapidly. As was noted earlier there are conflicting data concerning the effect of choline on basal cholinergic function (33,34). What is clear, however, is that under conditions of cholinergic receptor blockade, when presynaptic neurons increase their rate of firing, choline prevents the normal presynaptic depletion of acetylcholine (22,23,35). These findings together with the present results suggest that precursor loading with choline might be an effective strategy for increasing cholinergic activity under conditions of cholinergic receptor blockade or in other states in which cholinergic neurons are firing at an increased rate. Alzheimer's disease is associated with a dramatic loss of the enzyme needed to synthesize ~cetylcholine presynaptically and a relative sparing of cholinergic receptors (36,37). Thus it is likely that precursors would be effective in Alzheimer's patients only if given in conjunction with another agent that enhanced acetylcholine release. The differential effects of choline on high and low imagery words has no readily apparent explanation. The present results do not confirm the suggestion from a previous study (38) that learning of low imagery words is most likely to be enhanced by increasing cholinergic activity. It may be, however, that the effects of fluctuations in cholinergic activity depend upon characteristics of the information being learned and remembered (39). Acknowledgments This research was supported by the United States Public Health Service grant number AC-02219 from the National Institute on Aging and by the Medical Research Service of the Veterans Administration. References I. D. A. DRACHMAN and M. J. LEAVITT, Arch. Neurol. 30 113-121 (1974). 2. J. S. KETCHUM, F.R. SIDELL, E.B. COW~LL, G.K. AGHAJANIAN, and A.H. FATES, Psychcpharms~ologia 28 121-145 (1973). 3. K.L. DAVIS, R.C. MOHS, J.R. TINKL~NBERG, L.E. HOLLISTER, A. P F ~ A U M , and B.S. KOPELL, Science 2,0.1 272-274 (1978). 4. K.L. DAVIS, R.C. MOHS, and J.R. TIN~Lf.~rBERG, N. Engl. J. Med. 301 946 (1979). 5. D.A. DRACHNAN, Neurology ~_~ 783-790 (1977). 6. N. SITARAM, H. WEINGARTNER, and J.C. GILLIN, Science 20 ! 274-276 (1978). 7. D.M. BOWEN, J.A. SPILLANE, G. CURZON, W. MEIER-RUGE~ P. WHITE, J.J. GOODHARDT, P. IWANGOFF, and A.N. DAVISON, Lancet I 11-14 (1979). 8. P. DAVIES and A.J.F. F~LONEY, Lancet 2 1403 (1976). 9. E.K. PERRY, B.E. TOMLINSON, G. BLESSED, K. BERGMAN, P.H. GIBSON, and R.H. PERRY, Brit. Med. M. --2 1457-1459 (1978). 10. N.R. SIMS, D.M. BOWEN, C.C.T. SMITH, R.H.A. FLACK, A.N. DAVISON, J.S. SNOWD~, and D. NEARY, Lancet, I_ 333-336 (1980). 11. E.L. COHEN and R.J. WURTMAN, Science 1.9.1561-562 (1976). 12. D.R. HAUBRICH. P.F.L. WANG, D.E. CLODY, and P.W. WEDEKING, Life Sci. 17

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Choline in Anticholinergic Amnesia

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