Multiple receptors for brain dopamine

Decreased taste sensitivity to sucrose in dopamine D3 receptor mutant mice

Dopamine plays a key role in food rewards and sweet-taste stimulation. We examined the basis for behavioral responses to sweet taste in dopamine D3 receptor-deficient (D3-/-) mice by determining whether the absence of D3 receptors affects the sensitivity to dilute sucrose solutions. In experiment 1, we measured the intensity generalization threshold of conditioned taste aversion (CTA) to a 0.2 M sucrose solution. Results showed that the generalization thresholds were 0.025-0.05 M in D3-/- mice and 0.0025-0.005 M in wild-type (WT) mice. In experiment 2, we found that D3-/- and WT mice had similar capabilities to form and extinguish CTAs. Since the intensity generalization threshold is mainly due to a combination of sweet-taste sensitivity and the robust nature of CTA formation, the results showed that taste sensitivity to sucrose in D3-/- mice was lower than that in WT mice. In experiment 3, to test whether the peripheral sensory signaling may also be affected by the disruption of the dopamine D3 receptors, the mRNA expression levels of sweet-taste-related proteins in taste buds of D3-/- mice were determined. The T1R1 and BDNF mRNA expression levels in D3-/- mice were higher than the controls, whereas T1R2, T1R3, α-gustducin, and TRPM5 mRNA were similar. These findings suggest that disruption of dopamine D3 receptor-mediated signaling decreases the sweet-taste sensitivity and alters the mRNA expression levels of some taste-related molecules.

Effects of nicotine on DARPP-32 and CaMKII signaling relevant to addiction

Paul Greengard brought to neuroscience the idea of, and evidence for, the role of second messenger systems in neuronal signaling. The fundamental nature of his contributions is evident in the far reach of his work, relevant to various subfields and topics in neuroscience. In this review, we discuss some of Greengard's work from the perspective of nicotinic acetylcholine receptors and their relevance to nicotine addiction. Specifically, we review the roles of dopamine- and cAMP-regulated phospho-protein of 32kDa (DARPP-32) and Ca2+/calmodulin-dependent kinase II (CaMKII) in nicotine-dependent behaviors. For each protein, we discuss the historical context of their discovery and initial characterization, focusing on the extensive biochemical and immunohistochemical work conducted by Greengard and colleagues. We then briefly summarize contemporary understanding of each protein in key intracellular signaling cascades and evidence for the role of each protein with respect to systems and behaviors relevant to nicotine addiction.

Heterodimeric D1-D2 dopamine receptors: a review

This review summarizes modern data on the structure and functions ofheteromersformed by D1 and D2 dopamine receptors focusing on their role in the mechanisms of drug dependence. This article discusses potential functional significance of heterodimeric D1-D2 dopamine receptorsdue to their localization in the brain as well as unique pharmacological propertiesversus constituent monomers. It is shown that heteromerization results in dramatic changes in activated signaling pathways compare to the corresponding monomers. These studies update our current knowledge of ligand-receptor interactions and provide better understanding of dopamine receptors pharmacology. Furthermore elucidation of significance of heterodimeric D1-D2 dopamine receptors as drug targets is important for the development of new effective drug addiction treatment.

Twenty years of dopamine research: individual differences in the response of accumbal dopamine to environmental and pharmacological challenges

Individual differences in the dopaminergic system of the nucleus accumbens of rats have extensively been reported. These individual differences have frequently been used to explain individual differences in response to environmental and pharmacological challenges. Remarkably, only little attention is paid to the factors that underlie these individual differences. This review gives an overview of the studies that have been performed in our institute during the last 20 years to investigate individual differences in accumbal dopamine release. Data are summarised demonstrating that individual differences in accumbal dopamine release are due to individual differences in: the functional reactivity of the noradrenergic system, the accumbal concentration of vesicular monoamine transporters and tyrosine hydroxylase as well as in the quantal size of the presynaptic pools of dopamine. Our data are embedded in the available literature to create a model that illustrates the putative hardware giving rise to the individual-specific release of accumbal dopamine. An important role is contributed to individual differences in the reactivity of the: hypothalamic-pituitary-adrenal axes, the reactivity of second messenger systems as well in the aminergic reactivity of the accumbens shell and core. The consequences of the individual-specific make-up and reactivity of the nucleus accumbens on the regulation of behaviour and the response to drugs of abuse will also be discussed. Apart from agents that interact with dopaminergic receptors, re-uptake or breakdown, noradrenergic agents as well as agents that interact with vesicular monoamine transporters or tyrosine hydroxylase are suggested to have therapeutic effects in subjects that are suffering from diseases in which the dopaminergic system is disturbed.

Monoclonal antibodies against the S2-serotonin receptor from rat brain that cross-react with dopamine and opiate receptors

Balb/c mice were immunized with rat striatal integral membrane proteins. After hybridization of splenocytes with myeloma cells, hybridoma lines secreting antibodies against serotonin, dopamine and opiate receptors were detected by inhibition of ligand binding to brain membrane preparations. Antibodies from two positive lines, Mab/a9 and Mab/a18, were able to inhibit ligand binding to the S2-serotonin (Kd range: 10-100 nM), the mu-opiate (Kd range: 0.4-3 microM) and the delta-opiate receptors (Kd range: 0.7-1.1 microM), while Mab/a9 was also found to inhibit ligand binding to the D2/D4-dopamine receptor (Kd approximately 50 nM). An apparent molecular mass of 60 kDa could be ascribed to the delta-opiate receptor and apparent molecular masses of 29 and 36 kDa to the mu-opiate receptor by ligand elution from immuno-precipitates.

Biogenic amines stimulate regeneration of cilia in Tetrahymena thermophila

Serotonin and catecholamines affect the regeneration of cilia in Tetrahymena thermophila in a dose-dependent manner: micromolar concentrations are stimulatory, whereas millimolar concentrations have little or no effect. This conclusion is based on motility measurements in regenerating cells and on ciliary counts in scanning electron micrographs. In addition, the recognition mechanism for each hormone appears to be specific and independent. Our results suggest an evolutionary link with hormonal mechanisms in multicellular eukaryotes.

Effect of biogenic amines on phagocytosis in Tetrahymena thermophila

Stimulation of phagocytosis by serotonin and catecholamines in Tetrahymena grown in proteose-peptone medium proved to be concentration dependent, the optimal concentrations being approximately 0.1 to 1.0 microM. The serotonergic antagonists, spiperone, and metergoline, also stimulated the process, whereas the beta- and alpha-adrenergic antagonists, propranolol, alprenolol, and ergocryptine, had no effect or inhibited phagocytosis. A wide variety of derivatives of the biogenic amines had no effect on phagocytosis, demonstrating the specificity of recognition mechanism for neurohormones in Tetrahymena. Such hormones act by at least two independent mechanisms, one for adrenergic agonists, another for dopamine. Presumably, recognition mechanisms for hormones in protozoa resemble in some respects those in multicellular organisms, therefore bespeaking a common origin.

A case of hypophyseal prolactinoma with treatable delusions of dermatozoiasis

The case of an autopsied patient with hypophyseal prolactinoma and dermatozoic delusions is reported, and the mechanism of onset of this special form of delusion is discussed from the neuroendocrinological view point, including response to medications, and neuropathological and pituitary hormonal studies. The subject (69-year-old female) with dermatozoic delusions suffered hypophyseal prolactinoma with high serum prolactin level. Major tranquilizers, minor tranquilizers, or drugs enhancing cerebral blood flow and/or cerebral metabolism did not expell the delusion. Bromocriptine (dopamine agonist) was administered for prolactinoma treatment. After bromocriptine treatment, small doses of haloperidol successfully expelled the delusion. The neuropathological study indicates that the genesis of this delusion is not based on any organic change, but is induced by functional changes related to the prolactin and dopamine systems.

Multiple dopamine receptors in brain and the pharmacological action of substituted benzamide drugs

Neuroleptic drugs are believed to control schizophrenia by blocking brain dopamine receptors, although most act also on a number of other neuronal systems in brain. Substituted benzamide drugs in general, are more specific for the dopamine system. Brain dopamine receptors, however, are not a single entity. They can be divided on the basis of their linkage to adenylate cyclase. Substituted benzamide drugs are selective antagonists of the adenylate cyclase independent dopamine receptor population. They may be selective antagonists of one sub-population of these adenylate cyclase independent receptors, for unlike typical neuroleptics the receptor interaction of substituted benzamide drugs with brain dopamine receptors depends upon the presence of sodium ions. The specificity of substituted benzamide drugs for brain dopamine receptors is reflected in their behavioural profile. Typical substituted benzamide drugs do not cause catalepsy and, in general, only weakly inhibit motor phenomena. This inability to act in vivo cannot be entirely explained by the poor penetration of these drugs into brain. The unique properties of the substituted benzamide drugs might explain their clinical value in the treatment of schizophrenia and in the treatment of dyskinesias.

A brain synaptic dopamine-binding protein: isolation and partial characterization

A dopamine-binding protein (DABP) has been purified from the rat brain cortex to homogeneity. Solubilization of the DABP from the synaptosomal membranes (P2M) by cholic acid, subsequent agarose gel filtration of the cholic acid extract to separate phospholipids from the DABP, and lastly DA affinity chromatography successfully resulted in a purified DABP with approximately 0.006% yield in protein concentration and 0.03% yield in specific [3H]-DA binding. The specific [3H]-DA binding of the purified DABP was 117 fmol/mg protein/10 min with a 4.6-fold purification compared with the whole homogenate. The purified DABP had an Rf value of 0.67 on native disk polyacrylamide gel and it gave one single polypeptide subunit on the SDS gel with an Rf value of 0.63. The apparent molecular weight of this single subunit was estimated to be 34.5 kilodaltons. The elution patterns from either DA- or ADTN-affinity (2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene-affinity) columns indicated that this DABP had higher affinity for DA agonists than for DA antagonists. Photoaffinity labeling of [3H]-DA to this DABP in the P2M fraction and the specific [3H]-DA to the purified DABP demonstrated a nanomolar range affinity corresponding to either D2 or D3 receptors. These data suggested that the purified DABP could be related to either D2 or D3 receptors in the brain.

Aminergic receptors in Drosophila melanogaster: properties of [3H]dihydroergocryptine binding sites

[3H]Dihydroergocryptine ([3H]DHE) binds to a particulate preparation from Drosophila melanogaster heads at a level of 2.4 +/- 0.4 pmol/mg protein, with an apparent dissociation constant of 2.0 +/- 0.5 nM. The binding sites are inactivated by heat, pronase treatment, and sulfhydryl and disulfide reagents. [3H]DHE binding is inhibited by low concentrations of serotonergic and alpha-adrenergic ligands. The specificity of the binding sites, as revealed by displacement studies, differs from that of [3H]DHE binding sites in various vertebrate tissues. The [3H]DHE binding sites may correspond to serotonergic receptors, and possibly, to additional classes of receptors for putative neurotransmitters in Drosophila.

Kainic acid lesions of striatum and decortication reduce specific [3H]sulpiride binding in rats, so D-2 receptors exist post-synaptically on corticostriate afferents and striatal neurons

Unilateral kainic acid lesions of rat striatum reduced specific striatal [3H]spiperone and [3H]sulpiride binding sites (Bmax) by 52 and 67% respectively compared with the intact side. The dissociation constant (KD) for [3H]spiperone binding was unchanged but that for [3H]sulpiride binding was reduced. Specific striatal [3H]spiperone and [3H]sulpiride binding was reduced by 22 and 37% respectively in unilateral decorticate animals, but there was no change in KD. Unilateral 6-hydroxydopamine lesions of the medial forebrain bundle caused no change in striatal [3H]spiperone binding sites or KD value, but produced a 27% increase in [3H]sulpiride binding sites with no change in KD. These data support the hypothesis of D-2 receptors located on cortico-striate glutamate fibres, but also indicate the presence of both D-1 and D-2 receptors on the cell bodies of striatal neurons.

Binding of 3H-ADTN, a dopamine agonist, to membranes of the bovine retina

The binding of 3H-ADTN, a potent dopamine receptor agonist, to crude membrane preparations of bovine retina was studied, using a filtration method to isolate membrane-bound ligand. Specific binding was found to be saturable and occurred at a single binding site with an affinity constant of 7.3 nM. Binding was sodium-independent, slightly enhanced by Triton X-100 treatment, but drastically reduced by both trypsin and sodium laurylsulphate. The binding sites demonstrated a high degree of pharmacological specificity, with dopamine, apomorphine, and epinine being potent displacers of 3H-ADTN. A higher degree of 3H-ADTN binding was associated with subcellular fractions enriched with conventional synaptosomes rather than fractions enriched with photoreceptor synaptosomes.

Dopaminergic mechanisms in the teleost retina. I. Dopamine-sensitive adenylate cyclase in homogenates of carp retina; effects of agonists, antagonists, and ergots

A specific dopamine-sensitive adenylate cyclase has been identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 microM-dopamine resulted in a 5--10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 microM. l-Noradrenaline and l-adrenaline were some 10 times less potent than dopamine whilst the alpha- and beta-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity whilst various ergot alkaloids produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, alpha-flupenthixol and alpha-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with the alpha- and beta-adrenoreceptor blocking agents, phentolamine and propranolol respectively were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. These data suggest the presence of a highly specific dopamine-sensitive adenylate cyclase in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the mammalian central nervous system.

Optimal conditions for [3H]apomorphine binding and anomalous equilibrium binding of [3H]apomorphine and [3H]spiperone to rat striatal membranes: involvement of surface phenomena versus multiple binding sites

I. Binding of [3H] apomorphine to dopaminergic receptors in rat striatum was most reproducible and clearly detectable when incubations were run at 25 degrees C in Tris-HCl buffer, pH 7.5, containing 1 mM-EDTA and 0.01% ascorbic acid, using a washed total-membrane fraction. The receptor binding was stereospecifically inhibited by (+)-butaclamol, and dopamine agonists and antagonists showed high binding affinity for these sites. Unlabelled apomorphine inhibited an additional nonstereospecific binding site, which was unrelated to dopamine receptors. EDTA in the incubation mixture considerably lowered nonstereospecific [3H]apomorphine binding, apparently by preventing the complexation of the catechol moiety with metal ions which were demonstrated in membrane preparations. Stereospecific [3H]apomorphine binding was not detectable in the frontal cortex, whereas in the absence of EDTA much saturable nonstereospecific binding occurred. II. Kinetic patterns of stereospecific [3H]spiperone and [3H]apomorphine binding to rat striatal membranes and the inhibition patterns of a dopamine antagonist and an agonist were evaluated at different temperatures in high-ionic-strength Tris buffer with salts added and low-ionic-strength Tris buffer with EDTA. Apparent KD values of spiperone decreased with decreasing tissue concentrations. KD values of both spiperone and apomorphine were little influenced by temperature changes. Scatchard plots of the stereospecific binding changed from linear to curved; the amount of nonstereospecific binding of the 3H ligands varied considerably, but in opposite directions for spiperone and apomorphine in the different buffers. In various assay conditions, interactions between agonists, and between antagonists, appeared fully competitive, but agonist-antagonist interactions were of mixed type. The anomalous binding patterns are interpreted in terms of surface phenomena occurring upon reactions of a ligand with complex physicochemical properties and nonsolubilized sites on membranes suspended in a buffered aqueous solution. It is concluded that anomalous binding patterns are not necessarily an indication of binding to multiple sites or involvement of distinct receptors for high-affinity agonist and antagonist binding.

[Relation between dopamine and serotonin motor effects on isolated rat duodenum. Possible participation of an excitatory dopaminergic receptor]

The experimental facts presented here allow us to establish a relationship between DA motor effects on isolated rat duodenum, studied in a previous work, (excito-motor between 10(-9) M and 10(-5) M and inhibitor beyond 10(-5) M) and the functional aptitude of this duodenum to answer to 5-HT : 5-HT excito-motor effects are amplified by DA at concentrations less than or equal to 2.6 X 10(-6) M and on the contrary antagonized by DA at concentrations above 5 X 10(-6) M. On the other hand, DA excito-motor effects do not appear on 5-HT-desensitized duodenums. The study of 5-HT dose-response curves in the presence of different concentrations of DA suggests that the amplification of serotonergic effects observed with small DA concentrations can be possibly related to the additional effects of 5-HT on its own receptors and of DA on another receptor. The receptor involved in DA excito-motor action seems to be closely related to the 5-HT receptor since its effects are blocked by the same molecules (methylsergide, cyproheptadine) and since DA excito-motor action is no more evident on 5-HT-desensitized duodenums, but several arguments support the specificity of this receptor for DA (though it is not blocked by haloperidol). Some of its effects are in line with those of DA receptors made conspicuous in other territories and not blocked by haloperidol : central and human colon receptors. On the contrary, DA used at high concentrations (greater than or equal to 5 X 10(-6) M) seems to be able to occupy serotonergic sites, preventing 5-HT access to its receptors until its concentration is high enough to displace DA. From a functional point of view, this antagonistic effect of DA at high concentrations against 5-HT excito-motor effects could facilitate alpha- and beta-mediated inhibitory effects.

Dopaminergic stimulation of prolactin release

Prolactin (PRL) secretion from anterior pituitary is believed to be under tonic inhibitory control of dopamine (DA) released from the tubero-infundibular dopaminergic neurones into the hypophysial portal blood. Inhibition of PRL release by DA seems to be mediated by sereospecific DA receptors located in PRL cells. Apomorphine and various ergot alkaloids such as bromocryptine mimic the inhibitory effect of DA both in vivo and in vitro, presumably by a direct agonist action on these 'inhibitory' receptors. We now report that PRL secretion in primary cultures of rat pituitary cells can be stimulated by DA when concentrations a thousand times lower than those required for inhibition are used. Secretion rates above basal release can also be induced by apomorphine and bromocryptine when the 'inhibitory' receptors are blocked with certain DA receptor antagonists.

Hypothermic effects of apomorphine homologues in mice

A single intraperitoneal (i.p.) injection in mice of apomorphine (I) and its analogues norapomorphine (II), N-ethylnorapomorphine (III), N-n-propylnorapomorphine (IV) and apocodeine (V), caused dose-related decreases in deep-core body temperature. The neuroleptic agent haloperidol blocked the hypothermia produced by these apomorphines but alpha-methyl-p-tyrosine failed to do so. This indicated a direct post-synaptic stimulation of dopamine receptors. Methysergide potentiated the hypothermic effect of the apomorphine analogues. Taking the amount of apomorphine to produce a 3 degree C fall in temperature at 30 min as unity, the approximate relative potencies were: I 1.00, II 0.06, III 47.50, IV 85.00, V 0.340. The doses of the apomorphines needed to produce hypothermia were much less than those needed to cause stereotypy. The ratios of the minimal doses required to produce hypothermia, to those producing stereotypy were: I 8.82, II 4.00, III 125.00, IV 28.50, V 1.43.

Antiparkinsonian drug doses and neuroleptic receptors

The clinical potency of 3 drugs, apomorphine, N-propylnorapomorphine, and bromocryptine, have been found to be closely correlated to their potencies in competing for 3H-haloperidol and 3H-spiroperidol both of which label the dopamine receptor. This correlation indicates that the direct binding assay may be used to predict clinical potencies of anti-parkinsonian drugs, and indicates that agonists as well as antagonists compete potently for 3H-neuroleptic binding.

Dopamine and schizophrenia. A therapy revisited and revised

Evidence is presented for a modulatory role for dopamine in the C.N.S. and for an indirect rather than a direct involvement of dopaminergic systems in the production of schizophrenic symptoms. The fine structure of dopaminergic fibres indicates that a majority of presynaptic boutons are not in close juxtaposition with postsynaptic neuronal membranes. This points to a wider distribution of receptors than localisation to dense postsynaptic membrane. Preliminary studies of receptor localisation support this conclusion, providing indirect evidence for autoreceptors and evidence for localisation, in the glia, of a substantial number of receptors.