Differences in pre- and post-synaptic sensitivity to apomorphine between saline and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated C57BL/6 mice as reflected in climbing activity.
The climbing behaviour after low doses (0.05, 0.1 and 0.2 mg/kg) or a high dose (1.5 mg/kg) of apomorphine was studied in saline or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57BL/6 mice. Following a 3-week recovery from two injections of saline or MPTP (50 mg/kg inter-injection period: 72 h), mice were randomly selected for determinations of contents of neurotransmitters and metabolites (dopamine, homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-hydroxytryptamine, 5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA)) or the apomorphine-induced climbing paradigm. For the climbing experiment, the animals were habituated for 60 min to metal climbing cylinders after which they received a subcutaneous injection of apomorphine or its solvent. Subsequently, the animals were placed back in the cylinders and their climbing scores were recorded every 5 min for 60 min. The biochemical data indicated that striatal levels of dopamine, DOPAC and HVA were significantly reduced following MPTP-treatment whereas striatal 5-HT and 5-HIAA levels were unaffected. In the climbing paradigm saline and MPTP-treated C57BL/6 mice responded diametrically opposite to low doses of apomorphine: 0.1 and 0.2 mg/kg apomorphine reduced the climbing score in saline-treated mice as compared to saline injections whereas 0.2 mg/kg apomorphine increased the climbing score in MPTP-treated mice. A relatively high dose of apomorphine (1.5 mg/kg) increased the climbing score in both saline- and MPTP-treated mice. However, the climbing score was significantly higher in MPTP-treated mice than in saline-treated mice. These data suggest that MPTP-treated mice lack pre-synaptic dopamine receptors and have an increased post-synaptic sensitivity for apomorphine which is in agreement with the fact that MPTP selectively affects the dopaminergic nigro-striatal pathway which then results in an up-regulation of post-synaptic receptors.
Spooren
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Novartis Pharma AG, Nervous System, Basel, Switzerland. willibrordus.spooren@pharma.novartis.com
Vassout
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A
Waldmeier
P
P
Gentsch
C
C
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D015259:Dopamine Agents / Q000633:toxicity*; D018491:Dopamine Agonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006185:Habituation, Psychophysiologic; D020267:MPTP Poisoning; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D017661:Receptors, Presynaptic / Q000819:agonists; D012965:Sodium Chloride / Q000494:pharmacology*; D013569:Synapses / Q000187:drug effects* / Q000502:physiology
D015259:Dopamine Agents; D018491:Dopamine Agonists; D017661:Receptors, Presynaptic; D012965:Sodium Chloride; D001058:Apomorphine