BACKGROUND AND AIMS: Harmaline-induced tremor is a model of essential tremor (ET). Tremor induced by harmaline has been suggested to result from activation of the olivo-cerebellar projection. Recent studies have indicated that cerebellum functions may be modulated by dopamine. METHODS: We examined the effects of preferential agonists of dopamine D3 receptors: pramipexole and 7-OH-DPAT on the harmaline-induced tremor in rats. In order to study receptor mechanisms of these drugs rats were pretreated with dopamine D3 receptor antagonists [SB-277011-A (10 mg/kg ip) and SR-21502 (15 mg/ kg ip)], an antagonist of presynaptic D2/D3 receptors [amisulpride (1 mg/kg ip)], or a non-selective antagonist of postsynaptic dopamine receptors [haloperidol (0.5 mg/kg ip)]. RESULTS: The tremor was measured using fully automated Force Plate Actimeters. The following parameters were calculated: power within 0–8 Hz band (AP1) and 9–15 Hz band (AP2), and tremor index (a difference in power between AP2 and AP1). Harmalinetriggered (15 mg/kg ip) tremor was manifested by an increase in AP2 and tremor index. Pramipexole at a low (0.1 mg/kg sc), but not higher doses (0.3 and 1 mg/kg sc) lowered the harmaline-increased AP2. 7-OH-DPAT (0.1 mg/kg sc) reduced AP2 in the harmalinetreated rats. None of the examined dopamine antagonists influenced the above effect of dopamine agonists. In contrast, SB-277011-A administered alone lowered the harmaline-increased AP2. CONCLUSIONS: The present study indicates that pramipexole reduces the harmaline-induced tremor. However, mechanisms underlying its action are still unclear and require further examination. Financial support: Statutory Funds of the Department of NeuroPsychopharmacology, Institute of Pharmacology, PAS; National Science Center (grant OPUS 6, 2013/11/B/NZ4/04565); Southern Research Institute, Birmingham, AL, USA (S. Ananthan) - SR21502 donation. Barbara Kosmowska is a holder of scholarship from the KNOW sponsored by Ministry of Science and Higher Education, Poland.
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