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Home , Dopamine (medication), Neurotransmitter

NSCASCPERSPECTIVE CLASSIC PNAS

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Solomon H. Snyder1 The Solomon H. Snyder Department of , Department of and Molecular Sciences, and Department of and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205

Edited by Leslie Lars Iversen, University of Oxford, Oxford, United Kingdom and approved September 20, 2011 (received for review September 1, 2011)

In the early 1970s, receptors for acting via second messengers had not been identified biochemically nor were there definitive links to such messengers. The discovery by John W. Kebabian and of a dopamine-sensitive adenyl cyclase, accordingly, was a giant step forward. The investigators first characterized the in sympathetic ganglia wherein dopamine- producing cells link pre- and post-synaptic . Then, in the corpus , the brain area enriched in dopamine, they delineated the enzyme’s properties and showed that it was inhibited by drugs, leading to a large body of research on dopamine as a mediator of antipsychotic drug action and putative roles for this transmitter in the pathophysiology of .

n the early 1970s, a reasonable amount was known about the bio- I chemistry of neurotransmitters. A few chemical transmitters were ac- cepted—, , , and GABA. There were hints that certain common amino acids such as glutamate and , besides their roles in general and protein syn- thesis, might also be neurotransmitters. However, this hint was still a controversial area. In 1970, Chang and Leeman (1) had isolated and sequenced in the brain as a that stimulates sal- ivary secretion, but there was little else to argue for as transmitters. The explosion of peptide transmitters that commenced with the isolation of enke- Fig. 1. Photographs of John W. Kebabian (Left) and Paul Greengard (Right) in the 1970s at about the phalins was several years in the offing (2). of their pioneering work on dopamine-activating adenylate cyclase. Gases such as , carbon mon- oxide, and hydrogen sulfide as endogenous biologically active substances were not transmitter and drug receptors in the mid- Why did Kebabian and Greengard (5) even fantasized. 1970s came as a surprise (4). and Kebabian et al. (6) choose to explore The of acetylcholine, sero- For neurotransmitters that act by dopamine rather than a better character- tonin, norepinephrine, and GABA had opening channels, such as acetylcholine ized transmitter such as norepinephrine or been elucidated, and their degradative at the , transmitter serotonin? Dopamine is the metabolic pathways had been established. Their re- recognition was presumed to be trans- precursor of norepinephrine, differing lease by was generally accepted. formed into an opening or closing of ion only in the absence of a hydroxyl at the Synaptic inactivation by an enzyme in the channels. For the biogenic , such as β-position, which is added by the enzyme case of acetylcholine and for amines and norepinephrine and serotonin, the picture dopamine β- hydroxylase (Fig. 2). Specu- amino acids, by into the nerve was murkier. Hence, the work of Kebabian lation that dopamine might be a biolog- endings that had released them seemed on and Greengard (5) and Kebabian et al. (6) ically active molecule in its own right came solid ground. However, molecular charac- (Fig. 1) implying that dopamine in the in the late 1950s when Carlsson et al. terization of the most important element of superior cervical ganglion and the brain’s (8) used the recently developed spec- fl synaptic transmission, transmitter receptors, acts through a trophoto uorometric techniques for mea- was still unattained, at least in the brain. coupled to a cAMP-forming enzyme—ad- suring biogenic amines to uncover ex- It was generally assumed that neuro- enylate cyclase—was a giant step forward. tremely high concentrations of dopamine transmitters bound to receptor proteins on How did Kebabian and Greengard (5) in the caudate nucleus of the brain, vastly postsynaptic membranes. Several inves- and Kebabian et al. (6) come to explore greater than norepinephrine levels in this tigators had identified the receptor protein adenylate cyclase as a target for the syn- region. Dopamine became clinically rele- for the actions of acetylcholine in the aptic effects of a ? The vant when Hornykiewicz (9) discovered electric organ of the electric eel through deep background for this work comes from its depletion in the caudate nucleus of the binding of radiolabeled α-bungarotoxin the pioneering efforts of Sutherland and (3). However, the receptor in these elec- Rall (7) that discovered cAMP as a second Author contributions: S.H.S. wrote the paper. tric organs comprises 20% of membrane molecule for a number of hor- The author declares no conflict of interest. protein, about 1 million as dense as mones. Sutherland and Rall (7) then This article is a PNAS Direct Submission. fi what would be expected in the brain. Thus, identi ed adenylate cyclase as a cAMP- See Classic Article “Dopamine-sensitive adenylate cyclase few investigators anticipated ever under- forming enzyme, which could be activated in caudate nucleus of rat brain, and its similarity to the standing neurotransmitter receptors in by , each with its own distinctive ‘’” on page 2145 in issue 8 of volume 69. the brain at a biochemical level, and the receptor coupled somehow to a unitary See Classic Profile on page 18872. identification by binding of neuro- adenylate cyclase. 1E-mail: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1114346108 PNAS | November 22, 2011 | vol. 108 | no. 47 | 18869–18871 Downloaded by guest on September 26, 2021 dopamine in the ganglion, and possibly elsewhere in the , may be mediated by stimulating the synthesis of -3′,5′-monophosphate” (5). The superior cervical ganglion is an ideal tissue for investigating synaptic transmission, with a single presynaptic and a single postsynaptic along with small interneurons linking the pre- and postsynaptic elements. Greengard then proceeded to the more challenging caudate nucleus, the area of highest dopamine DOPA density in the brain (8). He used similar strategies as in the ganglion. In homoge- nates of the caudate, dopamine stimulated adenylate cyclase with a about threefold greater than norepinephrine, DOPA Decarboxylase whereas at the known α- and β-receptors for norepinephrine, dopamine is much weaker. Moreover, the β- is most potently activated by isoproterenol, which failed to stimulate Dopamine adenylate cyclase in the caudate, even at high concentrations. , D1 Receptor D2 Receptor known to mimic dopamine pharmacologi- cally, was even more potent than dopa- (Stimulates Dopamine (Inhibits adenylate mine in stimulating the cyclase. adenylate cyclase) cyclase; blockade by In this study, Kebabian et al. (6) noted β-hydroxylase antipsychotic drugs that two antipsychotic drugs, chlorproma- underlies therapeutic zine and , blocked dopamine’s ) effects. These drugs, first introduced into psychiatry in 1952, had revolutionized the Norepinephrine treatment of schizophrenia, and therefore, understanding their was of great importance. The first insights into how they acted came from the studies of Carlsson and Lindqvist (12) just a Fig. 2. Biosynthesis and receptor actions of dopamine. few years after they identified dopamine as a putative neurotransmitter/neuro- patients with Parkinson’s disease, whereas The protein kinase was at least two steps modulator. Carlsson and Lindqvist (12) i.v. administration of L-dihydroxyphenyl- removed from the neurotransmitter. noted that the pharmacology of these , the precursor of dopa- Hence, to link cAMP to neurotransmitters drugs resembled , an antipsy- mine, dramatically and rapidly alleviated would require monitoring cAMP levels, chotic drug that acts by depleting the brain Parkinsonian symptoms. which was a tedious procedure in small of dopamine, serotonin, and norepineph- The path of Kebabian and Greengard ganglia at that time. Because of his back- rine. and haloperidol (5) and Kebabian et al. (6) to character- ground as a neurophysiologist, Greengard failed to influence levels of dopamine or izing synaptic actions of dopamine began focused on the hyperpolarizing influences norepinephrine but increased metabolic in a peripheral system, the superior cervi- of presumed interneurons in the superior products of dopamine fairly selectively. cal ganglion, in which the presynaptic cervical ganglion. First, he showed that Carlsson and Lindqvist (12) speculated neuron uses acetylcholine as its trans- preganglionic stimulation increases cAMP that the were causing mitter, whereas the postsynaptic neuron levels several fold. At this point, he had no a functional dopamine depletion by employs norepinephrine. Besides rapid reason to favor dopamine over norepi- blocking receptors, leading to a feedback nephrine as the transmitter, because gan- excitatory transmission from presynaptic augmentation of dopamine turnover. The glionic levels of the two are increased turnover of dopamine was con- to postsynaptic neuron in this ganglion, about the same. In slices of the ganglion, firmed by numerous investigators, but no neurophysiologists had identified a slow dopamine increased cAMP levels with one had examined a receptor-linked hyperpolarizing inhibitory component that substantially greater potency than norepi- event directly. seemed to involve an interneuron. Histo- nephrine. In homogenates, dopamine and In a subsequent study, Clement-Cormier chemical studies revealed dopamine in norepinephrine increased adenylate cy- et al. (13) explored potencies of a series of these interneurons, suggesting that it clase activity to a similar extent. In the antipsychotics of the phenothiazine and might have a transmitter function. The ganglion, norepinephrine was well-estab- butyrophenone class and found substantial interest of Kebabian and Greengard (5) lished as the principal in the potency in inhibiting the dopamine-sensi- and Kebabian et al. (6) in cAMP followed postganglionic cells, but histochemical tive adenylate cyclase. Among the pheno- the discovery that the cAMP-dependent studies had revealed that dopamine, rather thiazines, clinical potency paralleled protein kinase, discovered by Krebs (10) than norepinephrine, predominated in the inhibition of the . Thus, the very and associated as a mediator of interneurons. Based on these findings, potent antipsychotic fluphenazine in- effects (10), also was prominent in the Kebabian and Greengard (5) cautiously hibited the enzyme about 10 times more brain (11). concluded that “the physiologic effects of potently than chlorpromazine.

18870 | www.pnas.org/cgi/doi/10.1073/pnas.1114346108 Snyder Downloaded by guest on September 26, 2021 , a phenothiazine antihista- activates adenylate cyclase, whereas at D2 cation by Kebabian et al. (6) that is the mine that is not antipsychotic, was about receptors, the transmitter inhibits the en- subject of this essay, “Dopamine-sensitive 25-fold weaker than chlorpromazine. This zyme (Fig. 2). Antipsychotic drug poten- adenylate cyclase in caudate nucleus of rat finding suggested that these drugs act by cies are predicted by blockade of D2 brain, and its similarity to the ‘dopamine blocking dopamine receptors associated receptors at which haloperidol and pimo- receptor,’” was itself a hedge. Throughout with the adenylate cyclase. However, there zide are much more potent than chlor- the paper, Kebabian et al. (6) always ad- were exceptions to the rule. Thus, halo- . The dopamine-sensitive umbrated the term in quotation marks. peridol and , which clinically, are adenylate cyclase characterized by With the use of ligand binding techniques one to two orders of magnitude more po- Kebabian et al. (6) corresponds to D1 just a few years after the publication by tent then chlorpromazine, were, re- receptors. Kebabian et al. (6), it became easy to char- spectively, 3 and 20 times weaker The studies of dopamine by Greengard, acterize neurotransmitter receptors in depth than chlorpromazine. coupled with his epic contributions to and investigate the linkage between the The resolution to this knotty problem neural regulation of protein kinases, have receptor, defined as the recognition site came a few years later when it was possible been landmarks in the biochemical eluci- for the neurotransmitter, and coupling to to identify dopamine receptors by ligand dation of synaptic transmission in the G proteins followed by influences on binding (4). Two classes of dopamine re- brain, which was acknowledged by his 3 adenylate cyclase and related molecules ceptors could be labeled with [ H]halo- coreceiving of the Nobel Prize in Physiol- (4). Greengard’s efforts lie at the base of peridol and [3H]dopamine (14) cor- ogy or Medicine in 2000. In regards to the this edifice. responding, respectively, to dopamine-D2 question raised at the outset of this essay and dopamine-D1 receptors, which were (how does one pinpoint a neurotransmitter ACKNOWLEDGMENTS. This work was supported subsequently enunciated by Kebabian and receptor at a biochemical level), Green- by US Public Health Service Grants MH18501 Calne (15). At D1 receptors, dopamine gard was cautious. The title of the publi- and DA000266.

1. Chang MM, Leeman SE (1970) Isolation of a sialogogic brain, and its similarity to the “dopamine receptor.” 12. Carlsson A, Lindqvist M (1963) Effect of chlorpromazine peptide from bovine hypothalamic tissue and its Proc Natl Acad Sci USA 69:2145–2149. or haloperidol on formation of 3methoxytyramine and characterization as substance P. J Biol Chem 245: 7. Sutherland EW, Rall TW (1958) Fractionation and in mouse brain. Acta Pharmacol – 4784 4790. characterization of a cyclic adenine ribonucleotide Toxicol (Copenh) 20:140–144. 2. Hökfelt T, Johansson O, Goldstein M (1984) Chemical formed by tissue particles. J Biol Chem 232:1077–1091. 13. Clement-Cormier YC, Kebabian JW, Petzold GL, anatomy of the brain. Science 225:1326–1334. 8. Carlsson A, Lindqvist M, Magnusson T, Waldeck B Greengard P (1974) Dopamine-sensitive adenylate 3. Cohen JB, Changeux JP (1975) The receptor (1958) On the presence of 3-hydroxytyramine in brain. cyclase in mammalian brain: A possible site of action protein in its membrane environment. Annu Rev Science 127:471. Pharmacol 15:83–103. of antipsychotic drugs. Proc Natl Acad Sci USA 71: 9. Hornykiewicz O (2010) A brief history of levodopa. J 4. Snyder SH (1984) Drug and neurotransmitter receptors 1113–1117. – in the brain. Science 224:22–31. Neurol 257 (Suppl 2):S249 S252. 14. Snyder SH (1981) Dopamine receptors, neuroleptics, 5. Kebabian JW, Greengard P (1971) Dopamine-sensitive 10. Krebs EG (1972) Protein kinases. Curr Top Cell Regul 5: and schizophrenia. Am J Psychiatry 138:460–464. – adenyl cyclase: Possible role in synaptic transmission. 99 133. 15. Kebabian JW, Calne DB (1979) Multiple receptors for Science 174:1346–1349. 11. Miyamoto E, Kuo JF, Greengard P (1969) Adenosine dopamine. Nature 277:93–96. 6. Kebabian JW, Petzold GL, Greengard P (1972) Dopamine- 3′,5′-monophosphate-dependent protein kinase from sensitive adenylate cyclase in caudate nucleus of rat brain. Science 165:63–65.

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