myparkinsons.co.uk

Arvid Carlsson,Nobel Lecture A Half -Century of Research

Bioscience Reports, Vol. 21, No. 6, December 2001 ( 2002)
NOBEL LECTURE 8 DECEMBER, 1999
A Half-Century of Neurotransmitter Research: Impact on
Neurology and Psychiatry
Arvid Carlsson
BEGINNINGS
My encounter with dopamine followed upon an incredible sequence of fortunate
events. I had been working on calcium metabolism, using radioactive isotopes, which
had then just become commercially available. This work had resulted in my doctoral
thesis in 1951 and a series of subsequent papers, including two doctoral theses by
students of mine. It had become somewhat visible internationally, resulting for
example, in an invitation to a Gordon Conference in New England in 1955. The
reason why I left this research field was that in connection with a competition for
an associate professorship in pharmacology the expert committee let me know that
in their opinion calcium metabolism did not occupy a central position in pharmacology.
I therefore turned to Professor Sune Bergstro¨m who was at that time head
of the Department of Physiological Chemistry of the University of Lund, Sweden.
This Department was located in the same building as our Pharmacology Department.
Professor Bergstro¨m had already been very helpful in several instances when
I had a professional problem of some kind. Incidentally, Dr. Bengt Samuelsson was
at that time working with Professor Bergstro¨m in the same Department. Thus the
three Swedes who were to become Nobel laureates in the period 1980–2000, happened
to be working under the same roof for a few years.
I asked Sune Bergstro¨m if he could help me to get in touch with an outstanding
American laboratory working in the area of biochemical pharmacology, which I felt
had a great future. He wrote to his friend Dr. Bernard Witkop, a highly talented
chemist working in the National Institutes of Health in Bethesda, MD. This letter
was forwarded via the late Dr. Sidney Udenfriend, to his boss the late Dr. Bernard
1Department of Pharmacology, University of Gothenburg, Gothenburg, Sweden.
 The Nobel Foundation 2000
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0144-8463
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1200-0691
0  2002 Plenum Publishing Corporation
692 Carlsson
Fig. 1. Bernard B. Brodie (1907–1989).
B. Brodie (Fig. 1), head of the famous Laboratory of Chemical Pharmacology of
the National Heart Institute. That is how I came to work under Dr. Brodie for
about five months, starting in August 1955. The timing of my arrival there was
extremely fortunate. Brodie and his colleagues had just a few months before made
a breakthrough discovery, namely that the administration of reserpine, a recently
introduced antipsychotic and antihypertensive drug, caused the virtually complete
disappearance of serotonin from the brain and other tissues (Pletscher et al., 1955,
1956, Fig. 2).
Fig. 2. Brain level of serotonin four hours after various intravenous doses of reserpine. From
Pletscher et al.(1956).
A Half-Century of Neurotransmitter Research 693
‘‘APPRENTICE TO GENIUS’’
Brodie was a remarkably charismatic and intensive person. He was generally
called Steve Brodie. This referred to a saloon keeper named Steve Brodie, who at
the beginning of the previous century had jumped off the Brooklyn Bridge in order
to win a bet. Bernard Brodie, too, was a sensation seeker who in his youth had
started on a career as a boxer but later switched to become an organic chemist. He
then confined his sensation seeking to non-physical adventures. He liked to call
himself a gambler. He had gained a tremendous reputation as a pioneer in the area
of drug metabolism and should perhaps rightly be called the father of modern biochemical
pharmacology. A large number of his apprentices, coming from various
parts of the world, later became prominent figures in pharmacology (see Kanigel,
1986, ‘‘Apprentice to Genius’). In the 1950s, after hearing about the sensational
clinical actions of the new antipsychotic drugs and the ability of the hallucinogenic
LSD to block serotonin effects on various peripheral organs he decided to enter the
field of psychopharmacology. While knowing very little about the brain he had a
tremendous trump card in being able to determine for the first time serotonin and
similar molecules in the brain, using the prototype of a new instrument developed
in his own lab together with Sidney Udenfriend and Dr. Robert Bowman. This
instrument, the spectrophotofluorimeter, was to replace previous bioassays and to
revolutionize drug research and neurotransmitter pharmacology for several decades.
This research soon led to the breakthrough discovery just mentioned, that is,
the depletion of serotonin stores by reserpine treatment. For the first time a bridge
seemed to have been built between the biochemistry of the brain and some important
brain functions, with some obvious neuropsychiatric implications.
Brodie and his colleagues, especially Dr. Parkhurst Shore, generously introduced
me into the new analytical methods and the use of the new instrument. I
proposed to Brodie that we investigate the effect of reserpine on the catecholamines
in view of their chemical similarity to serotonin. But Brodie thought this would be
waste of time. He was so sure that serotonin was the target to focus upon.
A ‘‘ROSETTA STONE’’?
But I felt that a look at the catecholamines might be worth while. To get started
quickly I would then need a partner specialized in the catecholamine field. Again I
was incredibly lucky. Of all the people working in that field at the time the most
clever partner in such a project was located in my home University, the University
of Lund: Professor Nils-A° ke Hillarp (Fig. 3). I wrote to him from Bethesda and
proposed a collaboration, and he agreed. Thus a most fruitful collaboration started,
lasting until his untimely death in 1965. Hillarp’s personality was different from that
of Brodie in many respects, but they were similar in terms of brilliance, charisma
and intensity. His background was histology and histochemistry, but his knowledge
extended far into physiology and biochemistry.
In the spring of the following year Hillarp and I got the first results. We demonstrated
the depletion of catecholamines from the adrenal medulla of rabbits following
treatment with reserpine (Carlsson and Hillarp, 1956). This was before I had
694 Carlsson
Fig. 3. Hillarp. Photo: Georg Thieme.
acquired my own miracle instrument, the so-called Aminco-Bowman Spetrophotofluorimeter.
The only instrument we had for the determination of catecholamines
was a colorimeter, using the method of von Euler and Hamberg (1949). But we did
not need any instrument because the absence of a color development in the samples
from reserpine-treated rabbits could be seen with the naked eye.
The same results were obtained when we analyzed heart and brain, in the latter
case using our new instrument. We also found that sympathetic nerves no longer
responded to nerve stimulation following reserpine treatment, apparently due to
depletion of transmitter (Carlsson et al., 1957a). Thus depletion of catecholamines
could be the cause of the behavioral inhibition induced by reserpine. To investigate
this we gave DOPA (3,4-dihydroxyphenylalanine) to reserpine-treated animals and
thus discovered the dramatic reversal of the reserpine-induced syndrome by this
catecholamine precursor (Carlsson et al., 1957b, Fig. 4). The reason we used the
precursor was that the catecholamines are unable to penetrate from the blood into
the brain, because of the blood-brain barrier.
We then analyzed the brains of DOPA-treated animals and much to our disappointment
we were unable to detect any restoration of noradrenaline levels. Experiments
with monoamine oxidase inhibitors clearly showed that a monoamine rather
than DOPA itself was responsible for the behavioral response, and thus we were
forced to look for the intermediate in the conversion of DOPA to noradrenaline:
dopamine.
At that time dopamine was considered to be without any interest because of its
low physiological activity, when tested on various smooth-muscle preparations. We
had to develop a method for determining dopamine because no such method was
A Half-Century of Neurotransmitter Research 695
Fig. 4. Rabbits treated with reserpine (5 mg
kg intravenously) before (top) and after
DL-DOPA (200 mg
kg intravenously, bottom). From Carlsson (1960). Photo: Tor
Magnusson.
available at the time (Carlsson and Waldeck, 1958). We could then show that dopamine
occurs normally in the brain in an amount somewhat higher than that of
noradrenaline, that it is brought to disappear by reserpine treatment, and that the
antireserpine action of DOPA is closely correlated to the restoration of dopamine
levels in the brain. We also showed that the restoration of serotonin levels by treatment
with its precursor 5-hydroxytryptophan did not lead to any reversal of the
reserpine syndrome (Carlsson et al., 1958).
The classical method in physiology to prove a function of a natural constituent,
is to remove the constituent in question and demonstrate a loss of function, and
then to reintroduce the constituent, and demonstrate a restoration of the same function.
We thought we had done this in the case of dopamine. We could easily exclude
possible alternative explanations, such as a role of noradrenaline and serotonin and
a direct action of L-DOPA.
In fact, our enthusiasm made us think that now we had found the Rosetta stone
that would give us access to the chemical language of the brain.
Later we found the unique distribution of dopamine in the brain, with an accumulation
in the basal ganglia, that is structures known to be involved in motor
functions. This, taken together with the fact that a characteristic side effect of reserpine
is to mimic very faithfully the syndrome of Parkinsonism and to induce a similar
symptomatology in animals, led us to conclude that depletion of dopamine will
696 Carlsson
induce the Parkinson syndrome and that treatment with L-DOPA will alleviate that
syndrome by restoring the dopamine level. All this I presented at the First International
Catecholamine Symposium in October, 1958 (Carlsson, 1959; Bertler and
Rosengren, 1959).
A BATTLE IN LONDON
A year and a half later, in March 1960, a Ciba Foundation Symposium on
Adrenergic Mechanisms was held in London (Vane et al., 1960). I then presented
the same data and some additional support obtained from studies on the action of
monoamine oxidase inhibitors. At this meeting practically all of the most eminent
experts in this area participated. The central figure was Sir Henry Dale, a Nobel
Laureate aged 85 but still remarkably vital. He dominated the scene, and the participants,
many of whom were his former students, treated him with enormous respect,
like school children their headmaster, although many of them had indeed reached a
mature age.
To better understand how our dopamine story was received at this meeting it
may be useful to recapitulate briefly the development following Otto Loewi’s discovery
of chemical transmission in the frog heart (Loewi, 1921). During the following
decades evidence accumulated, supporting the existence of chemical transmission
in various parts of the peripheral nervous system. Dale and his collaborators played
an important role here. They had, however, been fiercely attacked by a number
of neurophysiologists, who argued in favor of an electrical transmission across the
synapses. The most eminent proponent of this view was Sir John Eccles. The debates
between Dale and Eccles had been quite vivid, as witnessed by several attendants of
these debates between what was called ‘‘the sparks’’ and ‘‘the soup’. Despite the
sometimes harsh wordings the debates between Dale and Eccles over the years ended
in mutual respect and admiration, as clearly indicated in the correspondence of more
than twenty years between the two (see Katz, 1996, Girolami et al., 1994). Doubts
about a chemical transmission were particularly strongly expressed concerning the
central nervous system. In the mid 1950s, however, Eccles had placed one foot in
the ‘‘soup’’ camp, based on his own observation that a recurrent collateral of the
motor neurone, impinging on the so-called Renshaw cells, seemed to operate by
cholinergic transmission. This was, however, a very special case, given the fact that
motor neurons are cholinergic. Apart from this finding, as pointed out by McLennan
(1963) in his monograph ‘‘Synaptic Transmission,’’ there was no evidence in favor
of chemical transmission in the central nervous system.
At this meeting in London the debate that followed upon our paper entitled
‘‘On the biochemistry and possible functions of dopamine and noradrenaline in the
brain’’ and a subsequent special discussion session, revealed a profound and nearly
unanimous skepticism regarding our points of view. Our data as such were not
questioned. Actually some confirmatory animal experiments were reported at the
meeting, and I referred to a paper by Degkwitz et al. (1960), in which an antireserpine
action of DOPA in humans was reported.. Dale expressed the view that
L-DOPA is a poison, which he found remarkable for an amino acid. Marthe Vogt
A Half-Century of Neurotransmitter Research 697
concluded that the views expressed by Brodie and us regarding a function of serotonin
and catecholamines, respectively, in the brain would not have a long life.
W. D. M. Paton referred to some unpublished experiments indicating that the
catecholamines are located in glia. In his concluding remarks John Gaddum stated
that at this meeting nobody had ventured to speculate on the relation between catechol
amines and the function of the brain. But this was what I had insisted upon
throughout the meeting, so the clear message to me was that I was nobody!
In retrospect I believe almost everybody would agree that our story and its
implications were straight forward and obvious. How come that these eminent
experts rejected the whole thing? I have no definite answer. Clearly the pharmacologists
had great difficulty in accepting that dopamine could be an agonist in its own
right, given its poor physiological effect on smooth-muscle preparations. The idea
of DOPA being a mysterious poison probably came out of some experiments
reported at the meeting where large doses of this amino acid, given to experimental
animals together with a monoamine oxidase inhibitor, could cause paralysis, convulsions
and death. In addition, I believe that the previous ‘‘sparks-and-soup’’
debates still had some impact. In these debates some elaborate criteria for a neurotransmitter
had been formulated. Our data were of a different kind and these criteria
were not applicable.
In this regard I and my collaborators, like my mentor Steve Brodie, simply had
the advantage of being ignorant and not so much burdened by dogma.
A PARADIGM SHIFT
But it wouldn’t be long until the scene would change dramatically. Hillarp also
attended the London meeting. On our trip back to Sweden we agreed we should
increase our efforts to convince the world that chemical transmission does indeed
exist in the brain. Our idea was that Hillarp join me to work full time on research
in our new and well-equipped Department of Pharmacology of the University of
Go¨ teborg, where I had been appointed professor and chairman the year before. We
managed to obtain a grant from the Swedish Medical Research Council to set Hillarp
free from his teaching duties in Lund. He could start full-time research in Go¨ teborg
already in the autumn of 1960.
We felt that the ability of catecholamines to yield fluorescent conversion products
might be useful for their visualization in the microscope. We first tried a modifcation
of the trihydroxyindole method (Carlsson et al., 1961). It worked beautifully
for the adrenal medulla but not in other tissues. Hillarp then turned to another
reaction that had been used for the quantitative assay of indoleamines, using formaldehyde
as a reagent. Together with his skillful research assistant, the late Georg
Thieme he worked out a model system, in which they managed to optimize the
reaction conditions. (These experiments were reported by Falck et al., 1962). Subsequently,
together with his former student Bengt Falck, Hillarp used air-dried preparations
of iris and mesenterium, and discovered that the reaction worked
beautifully, thus permitting the visualization of noradrenaline in adrenergic nerves
and serotonin in mast cells in the fluorescence microscope. This led to an intense
collaboration between our Department of Pharmacology in Go¨teborg and Hillarp’s
698 Carlsson
Fig. 5. Group picture, taken January 1965, showing the group of young researchers recruited by Hillarp
after his move to the Karolinska Institute in 1962. From Dahlstro¨m and Carlsson (1986). Photo: Lennart
Nilsson.
original Department of Histlogy in Lund, and finally, after Hillarp’s move to take
over the Chair of Histology at the Karolinska Institute in 1963, with an enthusiastic
group of young students in his new Department (see Fig. 5). Thus within a few years
the neuronal localization of dopamine, noradrenaline and serotonin in the central
and peripheral nervous system was clearly established (Fig. 6). Moreover, the major
Fig. 6. Dopaminergic cell bodies in rat substantia nigra. Green fluorescence developed following treatment
with formaldehyde vapour. Courtesy of Annica Dahlstro¨m.
A Half-Century of Neurotransmitter Research 699
Fig. 7. Monoaminergic pathways in brain. From Fuxe
and Ande´n (1966).
monoaminergic pathways could be mapped (Fig. 7), and the site of action of the
major psychotropic drugs clarified (see Dahlstro¨m and Carlsson, 1986, Carlsson
1966, Fig. 8).
As mentioned, a large number of people were engaged in this effort. Sadly, many
of these people have passed away, in many cases prematurely. Among these Georg
Fig. 8. Scheme of monoaminergic synapse, with the sites of action of major classes of psychotropic
drugs indicated.. From Carlsson (1966).
700 Carlsson
Fig. 9. Thieme (1926–1996). Fig. 10. Margit Lindqvist (1924–1978).
Thieme (Fig. 9) has already been mentioned. Margit Lindqvist (Fig. 10), a very skilful
laboratrory assistant, who matured to become a qualified research worker, played an
enormous role already from the outset of my scientific career. Nils-Erik Ande´n (Fig.
11) and Jan Ha¨ggendal (Fig. 12) were originally students of mine who became outstanding
pharmacologists and largely contributed to characterize both central and peripheral
monoaminergic transmission (for some of their early work, see Ande´n,
Carlsson and Ha¨ggendal, 1969). Hans Corrodi (Fig. 13), a very skilful organic chemist,
who moved to Sweden because of his love for the mountains in Northern Sweden, contributed
much to clarify the chemistry of the formaldehyde histofluorescence method
and to many other projects, especially the development of the first selective serotonin
reuptake inhibitor SSRI, see below).
In February 1965 an international symposium entitled ‘‘Mechanisms of Release
of Biogenic Amines’’ was held in Stockholm (v. Euler et al., 1966), with most of the
major figures of that research field participating. In his Introductory Remarks Professor
Uvna¨s mentioned that ‘‘. . . these amines play an important role as chemical
mediators in the peripheral and central nervous system. . . .’’ None of the participants
of this symposium expressed any doubt on this point. It looks as though a paradigm
shift had taken place between 1960 and 1965.
It goes without saying that the concept of chemical transmission has had a
profound impact on practically every aspect of brain research. In so far as neurology
and psychiatry are concerned, a couple of examples are summarized below.
‘‘AWAKENINGS’’
Following our above-mentioned proposal of a role of dopamine in Parkinsonism,
some important parallel and apparently independent developments took
A Half-Century of Neurotransmitter Research 701
Fig. 11. Nils-Erik Ande´n (1937–1990). Fig. 12. Jan Ha¨ggendal (1932–1992).
Fig. 13. Hans Corrodi (1929–1974).
702 Carlsson
place in Austria, Canada and Japan. These will now be briefly commented upon,
starting out with Austria.
Later in the same year as the Symposium on Adrenergic Mechanisms, there
appeared in Klinische Wochenschrift a paper in German, describing a marked
reduction of dopamine in the brains of deceased patients who had suffered from
Parkinson’s disease and postencephalitic Parkinsonism (Ehringer and Hornykiewicz,
1960). This was soon followed by a paper by Birkmayer and Hornykiewicz (1961),
in which a temporary improvement of akinesia was reported following a single intravenous
dose of L-DOPA to Parkinson patients.
As far as I can gather from an autobiography of Hornykiewicz (1992) as well
as a personal communication from him, the following had happened. I wish to
mention this in some detail, because it illustrates how the interaction of different
minds can lead to important progress. In 1958 Hornykiewicz was approached by a
mentor Professor Lindner or, according to a different version, by his chief Professor
Bru¨ cke, who tried to persuade him to analyze the brain of a Parkinson patient, which
the neurologist Walter Birkmayer wanted to be analyzed for serotonin. Presumably
Birkmayer had been impressed by Brodie’s already mentioned discovery in 1955 of
the depletion of this compound by reserpine, and in contrast to many neurologists
at that time he was aware of its possible implications. Shortly afterwards, in 1959,
Hornykiewicz read about our work on dopamine and its role in the Parkinson syndrome.
He then decided to include dopamine and noradrenaline in the study. In
fact, in the subsequent work serotonin had to be left out initially because of some
technical problems.
Hornykiewicz and his postdoctoral fellow Ehringer were now facing a challenge,
because they had no adequate equipment to measure dopamine. But they
managed to overcome this problem by using the purification of the brain extracts
by ion exchange chromatography that our research group had worked out. The
subsequent measurement was performed using the colorimetric method of Euler and
Hamberg. Although this method by itself is highly unspecific, specificity could be
obtained by using our purification step together with our finding that dopamine is
by far the dominating catecholamine in the basal ganglia, where it occurred in high
concentrations. They had to work up several grams of tissue and to concentrate the
extracts by evacuation to dryness. Following this heroic procedure they were richly
rewarded, because the samples from the Parkinsonian brains, in contrast to the
controls, turned out to be colorless, as revealed by the naked eye!
The corresponding development of Parkinson research in Canada is summarized
in a paper by Barbeau et al. (1962), presented at a meeting in Geneva in September
the previous year. The main findings of the Canadian workers was a
reduction of the urinary excretion of dopamine in Parkinson patients and an alleviation
of the rigidity of such patients following oral treatment with L-DOPA.
In Japan some remarkable progress was made, which has not been adequately
paid attention to in the Western countries (see reviews by Nakajima 1991, and Foley
2000). In a lecture on the 5th of August, 1959, less than a year after my lecture at
the International Catecholamine Symposium mentioned above, the basic concept
regarding the role of dopamine in the basal ganglia in Parkinson’s disease was presented
by I. Sano (1959). In this lecture data on the distribution of dopamine in the
A Half-Century of Neurotransmitter Research 703
human brain were presented for the first time. In a lecture in Tokyo on the 6 February,
1960, Sano reported on reduced amounts of dopamine in the basal ganglia of
a Parkinson patient, analyzed post mortem, and in the same year he published a
paper describing alleviation of rigidity in a Parkinson patient following intravenous
administration of DL-DOPA (Sano, 1960).
Thus treatment of Parkinson patients with DOPA was initiated simultaneously
in three different countries only a few years after the discovery of the anti-reserpine
action of this agent and the subsequent formulation of the concept of a role of
dopamine in extrapyramidal functions. While this treatment led to results of great
scientific interest, it took several years until it could be implemented as routine treatment
of Parkinson patients. The reason was that the treatment regimens used
initially were inadequate and led to but marginal improvement of questionable
therapeutic value (Hornykiewicz, 1966). It remained for George Cotzias (1967) to
develop an adequate dose regimen. After that L-DOPA treatment rapidly became
the golden standard for the treatment of Parkinson’s disease.
When I had seen Cotzias’ impressive film demonstrating the effect of escalating
oral doses of L-DOPA at a meeting in Canada I hastened back to Go¨teborg and
initiated studies together with Drs. Svanborg, Steg and others, which quickly confirmed
Cotzias’ observations (Ande´n et al., 1970), like in many other places at the
same time. This success story was soon afterwards told to the general public by
Oliver Sacks in ‘‘Awakenings’’ (Sacks, 1973), which became a bestseller and was
also made into a movie.
ROLE OF SEROTONIN IN DEPRESSION: ZIMELIDINE,
THE FIRST SSRI
The so-called tricyclic antidepressants, with imipramine as the prototype, were
serendipitously discovered in the late 1950s, thanks to Kuhn, a psychiatrist and a
keen clinical observer. In the early 1960s these agents were found to block the reuptake
of noradrenaline by nerve terminals, thus enhancing the adrenergic transmission
mechanism. In 1968 we discovered that many antidepressants also could block the
reuptake of serotonin (Carlsson et al. 1968), and this prompted us to develop a
compound that selectively blocked the reuptake of serotonin without acting on noradrenaline.
Such agents are now known as SSRIs. This first agent was called zimelidine,
whose preclinical properties we first described in Berntsson et al. (1972).
Zimelidine turned out to be an active antidepressant agent with a very favorable
side effect profile (Carlsson et al., 1981), apart from a very rare, but serious side
effect, presumably based on an immunological mechanism, that led to its withdrawal
from the market. But zimelidine was followed by several other SSRIs, among which
Prozac is especially well known, not least because of a bestseller titled ‘‘Listening to
Prozac,’’ authored by P. D. Kramer (1993). In this book Prozac is stated to be able
to treat not only patients with depression and a variety of anxiety disorders, as had
previously been amply demonstrated for many SSRIs, but also to be able to change
the personality of people with psychological problems. Kramer was especially astonished
by the fact that disturbances, which would have taken several months of psychotherapy
to control, could be alleviated within a few days of treatment with Prozac.
704 Carlsson
This favorable action, making people feel and function better, even if they were not
mentally ill in the conventional sense, is a fascinating but, needless to say, controversial
issue. Less controversial is probably the 25% reduction in suicide rates in
Sweden in the 1990s, apparently related to the introduction of the SSRIs (Isacsson
2000). In any event the SSRIs represent a major therapeutic advance as well as a
milestone in rational drug development (Carlsson, 1999).
The development of zimelidine was based on our discovery that certain antihistamines
are serotonin-reuptake blocking agents, albeit non-selective. The most
powerful agents among these were the pheniramines and diphenhydramine (Carlsson
et al., 1969). We started out from the pheniramines and developed zimelidine. The
Lilly scientists started out from our diphenhydramine data and developed Prozac,
which was found to act very much like zimelidine, though devoid of its serious side
effect.
DOPAMINERGIC STABILIZERS—A NOVEL PHARMACOLOGIC
PRINCIPLE
In 1963 Margit Lindqvist and I presented the first evidence supporting the view
that the most important group of antipsychotic agents, represented by agents such
as chlorpromazine and haloperidol, act by blocking receptors for dopamine, and to
some extent also receptors for noradrenaline (Carlsson and Lindqvist, 1963, Fig.
14). This conclusion has later been confirmed and extended in numerous laboratories,
and techniques have been developed to screen for such agents in test tube
Fig. 14. Accumulation of of the basic catecholamine metabolites normetanephrine and
3-methoxytyramine, enhanced by treatment with major neuroleptic agents following
monoamine oxidase inhibition. From Carlsson and Lindqvist 1963.
A Half-Century of Neurotransmitter Research 705
experiments. One might have expected then that this should have led to the development
of drugs with stronger efficacy and less side effects. Unfortunately, this has
not happened.
We have hypothesized that the cause of this failure is that treatment with dopamine
receptor antagonists can hardly avoid the serious and unpleasant side effects
induced by dopamine hypofunction. Even though there is evidence of elevated dopaminergic
activity in schizophrenia, this may be limited to psychotic episodes. In fact,
we may be dealing with an instability of the dopamine release rather than a continuously
elevated baseline. Thus, between psychotic episodes, the patient would then
suffer from a dopaminergic hypofunction, especially during treatment with the currently
used antipsychotic agents, showing up as a severe disturbance of the reward
system and of cognition, and also as motor disturbances. This may make it impossible
to attain an adequate dose level (for discussion and references, see Carlsson et
al., 2001).
We believe that we can now get around this problem by using a new principle
of intervention that we call dopaminergic stabilization. The underlying mechanism
is complicated but in principle it rests on the existence of mutually antagonistic
subpopulations of dopamine D2 receptors, as regards the final functional outcome.
For example, the presynaptically located dopaminergic autoreceptors are inhibitory
on the overall dopaminergic activity. Dopaminergic stabilizers are dopamine D2
antagonists or partial D2 agonists capable of occupying mutually opposing receptor
subpopulations in such proportions as to leave the normal baseline dopaminergic
activity level essentially unchanged. This leads to stabilization by dampening fluctuations
of dopamine release, simply because fewer dopamine receptors are unoccupied
and thus available for the endogenous neurotransmitter.
Using the dopaminergic stabilizer (−)-OSU6162 (Fig. 15), developed by our
research group, partly in collaboration with Upjohn (now merged into Pharmacia
Fig. 15. Chemical structure of (−)-OSU6162.
706 Carlsson
Fig. 16. Stabilizing action of (−)-OSU6162 in rats.. Filled bars: no treatment with (−)-
OSU6162. Open bars: (−)-OSU6162. ‘‘Ctr’. Actively exploring control rats. ‘‘hab’: Rats
habituated to their environment. ‘‘d-amph’: rats treated with d-amphetamine. Note.
Treatment with one and the same dose of (−)-OSU6162 can induce stimulation of
behavior when baseline activity is low (habituated rats) and inhibition when the activity
is high (d-amphetamine pretreatment).
Corporation), we have demonstrated the stabilization phenomenon in experimental
animals (Fig. 16) and, in preliminary clinical studies, its pharmacotheraputic potential
in L-DOPA-induced dyskinesias in Parkinson patients, in Huntington’s disease
(Fig. 17), and in schizophrenia (Tedroff et al., 1999, Ekesbo, 1999, Gefvert et al.,
2000).
The partial dopamine receptor agonist preclamol ((−)–3-PPP) has likewise a
dopaminergic stabilizer profile. This agent was discovered by our research group
and is in development in collaboration with Dr. Tamminga and her colleagues at
the Maryland Psychiatric Research Center (Lahti et al., 1988).
Our experience with dopaminergic stabilizers suggests that research into neurotransmitter
pathophysiology has until now focussed too much on the hyper- versus
hypofunction dichotomy. Although the instability concept is by no means new, there
has not been much of a goal- directed strategy aiming to stabilize neurocircuits
involved in neuropsychiatric disorders. Our preliminary data suggest that such an
approach can lead to enormous gains in the treatment of a great variety neurological
and psychiatric disorders.
OUTLOOK
During the past half-century brain research has been dominated by biochemical
approaches, in contrast to the previous half-century, which had a strong electrophysiological
emphasis. This switch is understandable in view of the entrance of
A Half-Century of Neurotransmitter Research 707
Fig. 17. Choreatic events at baseline and following 0.5 mg
kg (−)-OSU6162 as
an intravenous infusion during 30 minutes to a patient with Huntington’s disease.
From Tedroff et al. (1999).
the neurohumoral transmission concept into brain research in conjunction with the
spectacular progress of molecular biology. However, it must be recognized that the
brain is not a chemical factory but an extremely complicated survival machine. In
order to bring all the forthcoming biochemical observations into a meaningful
framework it will prove necessary to emphasize more strongly aspects of neurocircuits
and connectivity and to do so both at the microscopic and macroscopic level.
For example, the old questions dealing with neurocircuits within a cerebral region
such as the cortex and those addressing the interaction between the different regions
will in all probability come into focus more strongly in order to make full use of the
new knowledge gained from neurotransmitter physiology and molecular biology.
Here the new imaging techniques in conjunction with advanced computer-dependent
statistics involving pattern recognition derived from a wealth of data with great
complexity will probably prove extremely useful and very much help to bridge the
gap between animal and human observations. If nothing else, such approaches will
help to reveal the enormous width of our present ignorance of the human brain.
ACKNOWLEDGEMENTS
During my scientific career I have had the privilege to work with hundreds of
other research workers, highly qualified technicians and other personnel, to whom I
owe a lot. Only about forty of these people are mentioned in this text including the
reference list. Sadly, a considerable number of these people have passed away, in
many cases prematurely. Some of these, to whom I have a special debt of gratitude,
have been commemorated with pictures.
708 Carlsson
Throughout my professional career I have enjoyed excellent working conditions,
first for almost two decades at the University of Lund, Sweden, and thereafter,
for four decades, at the University of Gothenburg. My 5-month visit to the
National Institutes of Health had obviously a decisive and extremely positive impact
on my career.
I have received generous support from numerous sources, among which the
following need to be mentioned specially: The Swedish Medical Research Council,
The Swedish Board of Technical Development, The Knut och Alice Wallenberg
Foundation, and during the critical late 1950s and early 1960s, U.S. Air Force and
National Institutes of Health, U.S.A., and more recently from the Theodore & Vada
Stanley Foundation, U.S.A. In addition I have enjoyed a fruitful collaboration with
generous financial support from several major pharmaceutical companies, especially
Astra
Ha¨ssle, Sweden, The Upjohn Company, U.S.A, Organon, The Netherlands
and Aventis (previously Hoechst Marion Roussel), Germany.
To express in a few words my debt of gratitude to my wife Ulla-Lisa and to
the rest of my family is not possible. Here I wish to refer to my autobiography
(Carlsson, 1998), in which I have also had the opportunity to go into further detail
in several other respects.
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February 5, 2015 - Posted by Chris | History