Effects of dopamine partial-agonist aminoergolines on dopamine metabolism in limbic and extrapyramidal regions of rat brain
ABSTRACT The aminoergolines SDZ-208-911, -208-912, and -212-327, weak partial D2 agonists with agonist/antagonist properties, are proposed as potential atypical antipsychotic agents with limited risk of extrapyramidal effects or hyperprolactinemia. The in vivo effects on dopamine (DA) metabolism in limbic (accumbens) and extrapyramidal (striatum) regions of rat brain were evaluated by measuring the accumulation of L-dihydroxyphenylalanine (DOPA) after inhibiting decarboxylation alone ("open-loop" model) or with added gamma-butyrolactone (GBL, autoreceptor model). All three aminoergolines markedly increased DOPA in both regions, dose-dependently, with only minor decreases when GBL was included, and so evidently lack appreciable agonist activity at D2-like autoreceptors and resemble typical neuroleptics in stimulating DA synthesis, without regional selectivity.
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- "Saline and HBC vehicle had similar effects on DOPA accumulation, therefore data from the two vehicle groups were combined for each experiment . For presentation purposes, DOPA accumulation data were converted to percent of vehicle controls (see also Clark et al. 1991; Baldessarini et al. 1994). For the receptor ligand experiments, DA binding sites (B max ) and affinity (K D ) were determined using nonlinear regression with Prism (GraphPad Software, San Diego, CA, USA). "
ABSTRACT: The purpose of the present study was to determine whether repeated treatment with the D2 partial agonist aripiprazole or the D2 antagonist haloperidol alters dopamine (DA) synthesis characteristics in the dorsal striatum of young rats. To this end, rats received a daily pretreatment regimen of aripiprazole or haloperidol on postnatal days (PD) 10-20 and were tested 24 or 72 h later after an acute injection of vehicle, aripiprazole, haloperidol, or quinpirole (a D2 agonist). For comparison purposes, adult rats were pretreated with an 11-day regimen of saline or haloperidol on PD 70-80 and DA synthesis was measured after acute drug treatment on PD 83. Dorsal striatal DA synthesis was determined by measuring L-dihydroxyphenylalanine accumulation after NSD-1015 treatment. In a separate experiment, the ability of repeated drug treatment to up-regulate dorsal striatal D2 receptors was assessed in young and adult rats 72 h after drug discontinuation. The major findings of this study were that: (a) acute treatment with haloperidol and aripiprazole increased DA synthesis while quinpirole reduced it; (b) pretreatment with haloperidol and aripiprazole blunted the synthesis-modulating effects of acutely administered dopaminergic drugs; and (c) DA synthesis of young and adult rats was affected in a qualitatively similar manner by DA agonist, antagonist, and partial agonist drugs. In conclusion, results from the present study suggest that synthesis-modulating autoreceptors in the dorsal striatum are functionally mature by the end of the preweanling period and DA synthesis declines to near basal levels during the course of repeated aripiprazole treatment.Journal of Neural Transmission 04/2010; 117(5):573-83. DOI:10.1007/s00702-010-0396-5 · 2.87 Impact Factor
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- "In the GBL experiment , DOPA accumulation data were analyzed using a one-way randomized block ANOVA, with litter serving as the blocking factor (Hughes 1979). For presentation purposes, DOPA accumulation data were converted to percent of vehicle controls (see also Baldessarini et al. 1994; Clark et al. 1991). Saline and HBC vehicle had similar effects on DOPA accumulation, therefore data from the two vehicle groups were combined for each experiment. "
ABSTRACT: The purpose of this study was to determine whether aripiprazole, a D2-like partial agonist increasingly prescribed to children, alters DA synthesis via actions at autoreceptors in the dorsal striatum and medial prefrontal cortex (mPFC) of preweanling rats. The ability of dopaminergic agents to alter DOPA accumulation in the striatum and mPFC was measured after NSD-1015 on postnatal day (PD) 20. Dopaminergic tone was manipulated by administering reserpine, gamma-butyrolactone (GBL), or through amphetamine withdrawal. Results showed that the partial agonists aripiprazole and terguride increased striatal DOPA accumulation under normosensitive conditions, but decreased DOPA accumulation in states of low dopaminergic tone. A different pattern of results was observed in the mPFC, because terguride and haloperidol, but not aripiprazole, increased DOPA accumulation under normosensitive conditions. In conclusion, the present data show that aripiprazole affects striatal synthesis modulating autoreceptors in an adult-typical manner during the late preweanling period. Unlike in adult rats, however, the mPFC of preweanling rats appears to contain transitory synthesis modulating autoreceptors that are sensitive to drug manipulation.Journal of Neural Transmission 02/2008; 115(1):97-106. DOI:10.1007/s00702-007-0820-7 · 2.87 Impact Factor
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ABSTRACT: There is evidence that partial D2-like dopamine agonists (e.g., terguride) may not affect D2-like postsynaptic receptors in an adult-typical manner during the preweanling period. To determine whether synthesis modulating dopamine autoreceptors are also affected in an adult atypical manner by partial D2-like agonists, preweanling rats were treated either acutely or repeatedly with reserpine (low dopaminergic tone) or vehicle (high dopaminergic tone). The ability of terguride, quinpirole (a full D2-like agonist), or haloperidol (a D2-like antagonist) to alter striatal DOPA accumulation was assessed after NSD-1015 treatment on postnatal day (PD) 21. In a separate set of experiments, terguride's ability to modulate dopamine synthesis was assessed in rats treated with the nerve impulse flow inhibitor gamma-butyrolactone (GBL). Results showed that both terguride and quinpirole reduced striatal DOPA accumulation during a state of low dopaminergic tone (i.e., after reserpine pretreatment). During a state of high dopaminergic tone (i.e., after vehicle pretreatment), terguride had similar effects as haloperidol and increased DOPA accumulation. Terguride, like quinpirole, partially inhibited the GBL-induced increase in striatal DOPA accumulation. When considered together, these results indicate that synthesis modulating D2-like autoreceptors are functional during the late preweanling period, and they respond in an adult-typical manner to a partial D2-like agonist.Brain Research 03/2006; 1073-1074(1):269-75. DOI:10.1016/j.brainres.2005.12.054 · 2.83 Impact Factor