DA Activity Research Articles

Protein kinase C and dopamine transport—2. Effects of amphetamine in vitro

Synaptoneurosomes, incubated with amphetamine, showed a biphasic dose-response change in activity of PKC and release of DA. Activity of particulate PKC activity and release of DA were decreased at 0.01–10.00 nM, while activity of both was increased at 1–10 μM. The effects of 0.1 nM amphetamine were attenuated by pretreatment with N-ethoxy-carbony1-2-ethoxy-1,2-dihydroquinoline (EEDQ), a peptide-coupling agent which inactivated DA receptors. They persisted if the autoreceptors were protected with sulpiride or apomorphine (0.05 mg/kg), prior to the treatment with EEDQ. In these protected rats, the amphetamine-induced change in activity of PKC was attenuated by sulpiride. In contrast, the effects of the larger doses of amphetamine on the activity of PKC were not affected by pretreatment with EEDQ. Subcellular fractionation of tissues, incubated with 1 μM amphetamine, showed an increase in activity of particulate PKC, only in the synaptic plasma membrane fraction, while tissues incubated with reserpine showed a decrease in activity of particulate PKC, only in the vesicular fraction. Similar results were seen when synaptic plasma membrane or synaptic vesicles were incubated directly with amphetamine or reserpine. These findings suggest the presence of multiple metabolic pools of PKC: a reserpine-sensitive pool, present in synaptic vesicles and an amphetamine-sensitive pool, present in the synaptic plasma membrane. That the latter pool of PKC may be involved in the transport of DA was indicated by the good correlation between the ability of drugs to inhibit the activity of PKC and their ability to inhibit the amphetamine-induced release of DA.

Norepinephrine, dopamine, and 5-HT release from perfused hypothalamus of the rat during feeding induced by neuropeptide Y.

In the unrestrained rat, the hyperphagic-like ingestion of food evoked by the sustained elevation of neuropeptide-Y (NPY) in the hypothalamus was correlated with the release and turnover of monoaminergic transmitters in this structure. A single guide tube was implanted stereotaxically in the perifornical region of the hypothalamus for localized push-pull perfusion of an artificial CSF vehicle or NPY1-36 in a concentration of 10, 50, or 100 ng/1.0 microliters. After the rat was fully satiated, a site reactive to NPY was perfused repeatedly at a rate of 20 microliters/min for 6.0 min with an interval of 6.0-12 min elapsing between each perfusion. Samples of perfusate were analyzed by HPLC with coulometric detection for DA, HVA, DOPAC, NE, MHPG, 5-HT, and 5-HIAA. Although control perfusions were without effect on feeding or monoamine activity, NPY evoked mean cumulative intakes of food of 14 +/- 2.4, 25.6 +/- 3.0 and 26.5 +/- 3.2 g in response to 10, 50, or 100 ng/microliter concentrations of NPY, respectively, over the 4.0-5.0 hr test interval. HPLC analyses showed that during feeding the release of both NE and DA was enhanced significantly. The turnover of both catecholamines likewise increased significantly as reflected by the elevated levels of MHPG, DOPAC and HVA. However, neither the basal efflux of 5-HT nor its turnover, as reflected by the output of 5-HIAA, was affected during feeding induced by NPY perfused in the hypothalamus. These results suggest that a sustained elevation of NPY in the hypothalamus causes a perturbation in the basal activity of NE and DA which are both implicated in the neuronal mechanism regulating normal eating behavior. Thus, these catecholamine neurotransmitters are envisaged to comprise an intermediary step in the functional role played by NPY in the hypothalamus in integrating the control of energy metabolism and caloric intake.

Facilitation and inhibition of feeding by a single dose of amphetamine: relationship to baseline intake and accumbens cholecystokinin

Amphetamine (AMP) administered in high doses suppresses feeding. However, in low doses AMP has been shown to both suppress and facilitate feeding. Further, there is some indication of individual differences in the feeding response to low doses of AMP. Evidence indicates that AMP's effects on feeding are dopamine-mediated and that the nucleus accumbens (Acb) may be an important site of action. Of interest here is the fact that CCK terminals exist within the Acb and CCK modulates DA activity. Experiment 1 investigated the effects of intra-Acb CCK administration as a function of individual differences in the feeding response to a low dose of systemic AMP. Results indicate that response to AMP was baseline dependent. AMP stimulated feeding in low baseline feeders and suppressed feeding in high baseline feeders. Intra-Acb CCK blocked the AMP-induced increase in feeding but not the AMP-induced anorexia. In experiment 2, the effects of intra-Acb CCK administration on baseline feeding were assessed. Intra-Acb CCK suppressed baseline feeding, but only when there was a high level of intake. It is speculated that Acb-DAergic activity may play a role in the observed feeding effects of both AMP and CCK.

Stressor-induced alterations of natural killer cell activity and central catecholamines in mice

Natural killer (NK) cell cytotoxicity was determined at various intervals (0.5, 24 or 48 h) following exposure to uncontrollable footshock in 3 strains of mice. Stressor application provoked reductions of NK activity, but the time course of the NK changes varied across strains. Whereas NK cytotoxicity was markedly reduced in C57BL/6J mice 0.5–48 h following stressor exposure, this effect was delayed in C3H/HeJ mice, being evident 24–48 h following stressor application. In BALB/cByJ mice, NK activity was significantly reduced 24 h after footshock, but in contrast to the other strains returned to control levels within 48 h of stressor exposure. Central NE and DA concentrations and activity were influenced by the stressor treatment in a strain-dependent fashion. However, the relationship between the central amine variations and the alterations of NK cytotoxicity associated with the stressor was limited.

Muscarinic cholinergic hyperactivity in schizophrenia: relationship to positive and negative symptoms

Based on the implication of increased muscarinic ACh activity in the production of negative symptoms, the association of decreasing cholinergic activity with positive symptoms, and the covariance of positive and negative symptoms in the psychotic phase of schizophrenia, a model of (DA) dopaminergic/(ACh) cholinergic interactions in schizophrenia was recently formulated. It suggests that DA/ACh balance is of central importance in schizophrenic pathophysiology and that muscarinic ACh activity increases in an attempt to maintain this balance in the face of increasing DA activity that occurs in the psychotic phase of the illness. The model further suggests that the muscarinic system exerts a damping influence on the emergence of positive symptoms associated with DA hyperactivity, but that this compensatory increase in muscarinic activity is accompanied by an intensification of negative symptoms. In the present study, we tested two important postulates of this model. We tested the prediction that muscarinic activity is increased in schizophrenia by comparing the effect of biperiden, an antimuscarinic M-1 agent, on REM latency in 12 drug-free schizophrenic inpatients and matched normal controls. We found that biperiden caused a smaller increase in REM latency in schizophrenic patients, suggesting that muscarinic activity is increased in schizophrenia. We tested the prediction that an anticholinergic agent would increase positive symptoms and decrease negative symptoms by studying the effect of 8 mg of biperiden/day for 2 days on positive and negative symptoms (assessed by the BPRS) in 30 medication-free schizophrenic inpatients. Biperiden produced a significant increase in positive symptoms ( t = 6.36, df = 29, P < 0.001) and reduction in negative symptoms ( t = −2.05, df = 29, P < 0.05). These findings suggest that central muscarinic activity is increased in the psychotic phase of schizophrenia and is relevant to the expression of positive and negative symptoms.

GM1 gangliosides alter acute MPTP-induced behavioral and neurochemical toxicity in mice

We investigated the effect of GM1 gangliosides on a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson disease. Five groups of mice (saline, GM1 (30 mg/kg), MPTP, MPTP + GM1 (15 mg/kg), MPTP + GM1 (30 mg/kg)) were compared. GM1 was given daily via intraperitoneal injection before and during 13 daily doses of MPTP (30 mg/kg). Mice were tested for locomotion (1) within 2 h of an MPTP dose (to measure reduced motor activity), and (2) within 24 h of an MPTP dose (after animals had recovered and exhibited hyperactivity). We found that mice given GM1 gangliosides exhibited significantly less MPTP-induced behavior. This effect was most evident with the 15 mg/kg GM1 dose. GM1 also appeared to attenuate MPTP-induced neurochemical changes. GM1 effects indicating enhancement of DA turnover and preservation of DA, DOPAC and HVA concentrations in the striatum were found after the 8th MPTP dose. These latter neurochemical changes, however, were transient and not present after the 13th MPTP dose. Our data would suggest that gangliosides may reduce acute MPTP-induced neurotoxicity in mice either through an increase in DA neuron survival and/or the augmentation of striatal DA activity.

The Signal Transducer for the Dopamine-1 Regulated Sodium Transport in Renal Cortical Brush Border Membrane Vesicles

We have reported the presence of dopamine-1 (DA-1) and dopamine-2 (DA-2) receptors in renal brush border and basolateral membranes. DA-1 agonists stimulate adenylate cyclase (AC) and phospholipase C (PLC) activity in both membranes. Moreover, the ability of a DA-1 agonist (fenoldopam) to stimulate PLC activity is independent of AC activity. A DA-2 agonist (LY171555) by itself was without effect and did not enhance the ability of the DA-1 agonist to stimulate PLC activity. The DA-1 but not DA-2 agonists inhibit Na+/H+ exchange activity in brush border membrane vesicles (BBMV) and Na+/K(+)-ATPase activity in basolateral membranes. However, cAMP inhibits, while protein kinase C (presumably via PLC activity) stimulates, Na+/H+ exchange activity. We therefore determined the effect of DA-1 agonists on Na+/H+ exchange activity when PLC or AC activity was blocked using neomycin or dideoxyadenosine, respectively. The drugs were incubated with minced renal cortex prior to preparation of BBMV by differential centrifugation and MnCl2 precipitation. Enrichment of BBMV was not affected by drug treatment. The Na+/H+ exchange activity was assessed by measuring amiloride (1 mmol/L) sensitive 22Na+ uptake in BBMV (pHi = 5.5, pHo = 7.5, Nai+ = O, Nao+ = 1 mmol/L). Neomycin inhibited DA and DA-1-stimulated PLC activity in BBMV in a concentration dependent manner (10(-6) to 10(-4) mol/L). Neomycin (10(-4) mol/L) completely blocked the ability of DA and DA-1 agonist to stimulate PLC activity but had no consistent effect on DA-1 inhibited Na+/H+ exchange activity. Dideoxyadenosine inhibited DA and DA-1 simulated AC activity without affecting DA-1 stimulated PLC activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine effects on the developing central nervous system: behavioral, psychopharmacological, and neurochemical studies.

IMPLICATIONS and FUTURE DIRECTIONS. The data we have collected thus far support the following conclusions: 1. Subcutaneous administration of cocaine results in dose-dependent increases in brain and plasma cocaine in both dams and fetuses, and maternal plasma levels in the range of or above those observed in human cocaine users. Fetal levels are lower than those of the dam, suggesting that the placenta may partially restrict cocaine entry into the fetus. Concentrations of the active cocaine metabolite benzoylecgonine, however, are greater in fetal than in maternal brain; this may have important implications for brain development given the calcium-binding properties of this metabolite. 2. Chronic subcutaneous administration of 10, 20 or 40 mg/kg cocaine from E8-E20 does not alter litter size, body weights at birth or weaning, or development of reflexes or physical landmarks in the offspring. 3. Offspring exposed gestationally to cocaine exhibit learning and/or retention deficits in some but not all conditioning situations. 4. Behaviorally and psychopharmacologically, there is evidence for a potential attenuation in DA activity in preweanling pups exposed gestationally to cocaine. There is, however, no sign of any alteration in DA turnover in treated offspring sacrificed at weaning, although preliminary data suggest that DA levels may be increased in exposed pups during the neonatal period. Possible alterations in DA receptor function are currently being assessed. We are still at the initial stages of our work, and the data we have collected thus far have raised as many questions as they have answered. We plan to assess further the cognitive deficits observed in cocaine-exposed offspring. Under what contingencies are these learning and/or retention deficits observed, and are they permanent deficits or does recovery eventually occur? Is there actually an attenuation in DA activity in treated offspring? If so, is this attenuation related to compensations at the presynaptic and/or postsynaptic level, and what is the time course for this effect on the DA system? What are the critical periods for the production of these alterations; is cocaine exposure during the second or third trimester alone sufficient? How do our results compare with those of other laboratories that are using other methods for administering cocaine during gestation? At some point in the future we also hope to examine potential therapeutic approaches to reduce the cognitive deficits observed in exposed offspring.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationships between mesolimbic dopamine function and eating behavior.

These experiments are the first to correlate a specific stimulus of eating--the orosensory stimulation by sucrose--to mesolimbic dopaminergic activity. The pharmacological results and the increase in hypothalamic DOPAC/DA are convergent evidence for this relationship. The meaning of the relationship is not clear. The possibility that the decreased intake after dopaminergic receptor antagonist treatment and the increase in hypothalamic DOPAC/DA is related to the ingestive movements necessary for sham feeding seems unlikely for the following reasons: first, at least one dose of the antagonist had a preferential inhibition on sucrose intake compared to water intake; second, the D1 and D2 selective receptor antagonists decreased the initial rate of sucrose intake, but did not affect the rate of decay of sucrose intake over a 30-min test; third, in the second neurochemical experiment (Table 1), the volume ingested during 9 min of sham feeding 10% sucrose was not significantly different from the volume ingested from sham feeding 40% sucrose, but there was a significantly larger increase in the hypothalamic DOPAC/DA after 40% sucrose. Of course, a finer measurement of movements, such as lick rate, may reveal a significant difference that would correlate with the metabolic change. Fourth, striatal DOPAC/DA did not change during sham feeding of sucrose. Fifth, Bailey et al. demonstrated that a response-frequency summation analysis of the inhibitory effect of pimozide on sucrose intake did not reveal a motoric deficit. Thus, we interpret the increase of hypothalamic DOPAC/DA during the sham feeding of sucrose as evidence that activation of mesolimbic dopaminergic terminals in the hypothalamus is necessary for the normal processing of the central sensory and/or positive-reinforcing information produced by oral sucrose stimulation. Experiments are in progress to test this hypothesis and to attempt to distinguish between the sensory and positive-reinforcing effects of sucrose during sham feeding. In addition to generating this specific hypothesis concerning sucrose and hypothalamic DA activity, the results of these experiments suggest that the sham feeding preparation will be useful for the analysis of the important problem of the natural reinforcing properties of sweet taste. And finally, since sham feeding of sucrose is a form of oral self-stimulation, it provides a new experimental tool for comparing the role of central DA mechanisms in the positive-reinforcing effects of food, psychostimulant self-administration, and intracranial electrical self-stimulation.

Lesion of dopaminergic terminals in the amygdala produces enhanced locomotor response to d-amphetamine and opposite changes in dopaminergic activity in prefrontal cortex and nucleus accumbens

In a previous study using differential pulse voltammetry we demonstrated an interaction between dopaminergic activity in the amygdala and the nucleus accumbens. In the present study, by post-mortem biochemical measurements, we showed that bilateral 6-OHDA lesions of DA innervation of the amygdala leads to an increase in DA activity in the nucleus accumbens (DOPAC/DA ratio +24%) and a reduction (DOPAC/DA ratio-40%) in the prefrontal cortex. In addition, after these lesions in the amygdala, there was an increased behavioral sensitivity to d-amphetamine, demonstrated by enhanced locomotor activity. Increased understanding of the interregulations between dopaminergic activity in forebrain structures may help explain forebrain functions and/or dysfunction.

Effects of tiaspirone (BMY-13859) and a chemical congener (BMY-13980) on A9 and A10 dopamine neurons in the rat

Two new potential antipsychotic drugs, BMY-13980 and BMY-13859 were compared for the ability to influence the electrophysiological activity of dopaminergic neurons in the substantia nigra zona compacta (A9 DA cells) and ventral tegmental area (A10 DA cells) in the brain of the rat. Both drugs reversed the rate-suppressant effects of the DA agonist apomorphine on DA cells in A10 to a greater extent than DA cells in A9; BMY-13980 was particularly selective in this regard. These results indicate that both drugs may exert DA antagonist effects which are suggestive of antipsychotic potential. In other experiments, the effects of chronic (28 days) treatment with BMY-13980 and BMY-13859 on the neuronal activity of DA were evaluated. Both compounds caused a significant decrease in the number of spontaneously active DA neurons in A10 recorded per electrode track, an effect previously demonstrated to be associated with antipsychotic efficacy. The drug BMY-13859, but not BMY-13980, also significantly decreased the number of spontaneously active DA cells/track in A9, an effect which may predict the liability of potential antipsychotic drugs for causing extrapyramidal motor dysfunction, including tardive dyskinesia. Thus, these experiments indicate that both BMY-13980 and BMY-13859 exert effects which may predict potential antipsychotic efficacy in clinical trials and that BMY-13980 may be less likely to cause extrapyramidal side effects.

Repeated stress increases locomotor response to amphetamine.

Adult male rats submitted to mild, 20 min electric foot shock sessions for 10 days displayed an enhanced locomotor response to 0.75 mg/kg (+)amphetamine 24 h after the last shock session, when compared to non-stressed controls. This effect was still present in rats specifically deprived of their forebrain noradrenergic innervation, suggesting the involvement of a dopaminergic mechanism. Cortical and limbic dopamine turnover which increased immediately after acute and repeated foot shocks returned to normal 24 h later, at the time of the pharmacological testing. This fact indicates that a permanent modification of the basal DA activity is not responsible for the above effect of stress. Locomotor hyperactivity produced by 0.6 mg/kg apomorphine was enhanced in experimental animals, while hypoactivity resulting from the injection of 0.05 mg/kg apomorphine was similar in control and shocked rats. This latter result suggests the existence of an increased postsynaptic DA sensitivity as a result of repeated stress.

Dopamine-norepinephrine interaction in hyperactive boys treated with D-amphetamine

We studied the relationship between the excretion of 3-methoxy-4-hydroxyphenylglycol, the main metabolite of central nervous system norepinephrine, and homovanillic acid, the main metabolite of dopamine, in 16 hyperactive boys and ten controls who were admitted to a clinical research center. We further examined the effect of d-amphetamine (0.5 mg/kg body weight daily for two weeks) on that relationship. The correlation coefficients r between MHPG and HVA excretion were significantly negative in hyperactive boys and significantly positive in controls when the relational effects of age, body surface, and 24-hour urinary creatinine with MHPG and HVA excretion were removed. Furthermore, the correlation coefficient r in hyperactive boys and in responders at baseline differed significantly from the correlation coefficients in post-treatment and in controls. The post-treatment correlation coefficient in hyperactive boys and responders did not differ from that in controls. We suggest an altered relationship between DA and NE activity in hyperactive children. Meaningful interpretation of the data should await the availability of more information on the amount of contribution of central NE and DA metabolism to urinary MHPG and HVA in both hyperactive and normal children.

Multiple receptors for brain dopamine in behavior regulation: Concept of dopamine-e and dopamine-i receptors

From current knowledge, it is possible to substantiate the original concept of DAe and DAi receptors including the predicted correlation with the anatomical, histochemical, biochemical and functional features of the distinct neuronal structures, in which they occur; labelling them as neostriatal DAe receptors and mesolimbic DAi receptors appears to be justified. Available data warrant a revision of currently employed behavior and pharmacological tests. When revised in terms of the DAe-DAi concept, assessment of such tests reveals that agents such as (-)NPA, 6, 7ADTN and certain ergot alkaloids like lergotrile, lisuride and, to a less degree, CB-154 are weak DAe agonists and strong DAi antagonists (Table I). The discovery that mesolimbic α-like NE receptors which regulate the DA activity at the level of the mesolimbic DAi, but not neostriatal DAe, receptors show adaptational changes following priming or subacute treatments with apomorphine or haloperidol, opens new perspectives for understanding phenomena such as the development of hypersensitivity to apomorphine etc. Presynaptic DA receptors located within the DA synaps and DA receptors located at DA cell-bodies resemble closely the DAe receptors, although absence of linkage to the enzyme adenylyl cyclase hints at some distinction. It is possible that the distinct classes of DA receptors identified by behavior and pharmacological studies in mice correspond with the DAe and DAi receptors in snails, rats and cats. There is no evidence to suggest that DAe and DAi receptors are directly related to a) so-called DA1 and DA2 receptors which are coupled and uncoupled respectively to the enzyme adenylyl cyclase, or to b) any of the DA-specific binding sites identified with radiolabelled DA agonists or antagonists. Nonetheless, it cannot be excluded that DAe receptors may correspond with DA-specific binding sites identified with tritiated DA and/or haloperidol, and DAi receptors with a particular subclass of DA-specific binding sites identified within certain mesolimbic structures with radiolabelled spiperone. Thus, future work is still required to relate DAe and DAi receptors to particular, molecular entities within the brain.

Relevance of GABA in the nigrostriatal system.

In conclusion, even though the mutual integration of intrastriatal circuits remains an open question, the electrophysiological and neurochemical approaches seem to provide valid support toward understanding the complexity of these systems. Recent findings seem to indicate that, besides a dopaminergic and cholinergic link, interactions between DA and GABA neurons may be operative within the striatum. An understanding of these functional interplays may facilitate future attempts aimed at clarifying the electrophysiological discrepancies concerning the inhibitory or excitatory action of DA on the target cells in this brain structure. Studies on the functional roles of pathways projecting from striatum to substantia nigra have indicated that these may be implicated in the regulation of nigral efferents to other brain nuclei and that they do control striatal DA activity through feedback mechanisms.

Norepinephrine-dopamine interactions and behavior.

The proposed hypothesis is directed toward explaining a number of disparate findings in terms of a stress-related interaction between the NE- and DA-containing systems in the brain. The deleterious behavioral effects of decreased DA activity, for example, may be counterbalanced by a similar decrease occurring in NE activity, such compensation being most likely to occur under conditions of stress. This hypothesis may have application to the understanding of neurological and mental disorders such as Parkinson's disease and schizophrenia.

Dopamine and noradrenaline releasing action of amantadine in the central and peripheral nervous system: A possible mode of action in Parkinson's disease

Histochemical, biochemical and functional analyses of the effects of amantadine on the monoamine neurons in the peripheral and central nervous system of rat after various pretreatments have shown that amantadine, both in vivo and in vitro, is capable of releasing DA and NA from extragranular stores in central DA and NA neurons and in peripheral NA neurons. The functional findings on rotational behaviour, reflex activity and locomotor behaviour show that the increased release of DA and NA induced by amantadine in the brain also results in increased DA and NA receptor activity. Thus, both from a chemical and functional viewpoint amantadine has an amphetamine-like action. The potency of amantadine, however, is weak compared to that of amphetamine. A direct action on DA receptors can be excluded, since presynaptic stores of CA are required for amantadine to increase CA receptor activity.

Cholinergic and dopaminergic mechanisms in Huntington's chorea

Physostigmine 40 μg/kg intravenously has been shown to depress involuntary movements in Huntington's chorea. The increase in CSF - HVA obtained after probenecid administration indicates no decrease of DA activity in the disorder. Based on these findings, it is suggested that a cholinergic hypofunction in a mechanism regulating striatal motor activity may exist in Huntington's chorea.

Substrate specificity of ribosomal peptidyl transferase. II. 2′(3′)- O-Aminoacyl nucleosides as acceptors of the peptide chain in the fragment reaction

Transfer of the acetyl- l-leucine (AcLeu) residue from AcLeu-pentanucleotide to synthetic substrates under conditions of the fragment reaction was used to study the specificity of the acceptor site of ribosomal peptidyl transferase. 2′(3′)- O-Aminoacyl nucleosides are the simplest acceptor substrates. Their acceptor activity is dependent on the nature of the nucleoside to which the amino acid residue is bound. The acceptor activity decreased in the sequence 2′(3′)-O- l-phenylalanyladenosine (A-(Phe)) > I-(Phe) > C-(Phe); U-(Phe) was inactive. The presence of a free 2′-hydroxyl group in the ribose moiety of the aminoacyl adenosines was important for the acceptor activity, as shown by the low activity of dA-(Phe) in comparison with A-(Phe). Acceptor activity was influenced by the nature of the side chain of the amino acid residue bound to adenosine: A-(Phe) was a more active acceptor than puromycin, while the acceptor activity of 2′(3′)- O-glycyladenosine A-(Gly) was very low. Free phenylalanine, phenylalanine methyl ester, and adenosine did not act as acceptors. As terminal products of the reactions of AcLeu-pentanucleotide with puromycin, A-(Phe), I-(Phe) and C-(Phe), we isolated AcLeu-puromycin, 2′(3′)-O- acetyl- l-leucyl- l-phenylalanyladenosine (A-(AcLeu-Phe)), I-(AcLeu-Phe) and C-(AcLeu-Phe), respectively.