Apomorphine enhances harmaline-induced tremor in rats.
BACKGROUND
Harmaline-induced tremor is a well-known model of essential tremor in humans. The aim of the present study was to examine the influence of apomorphine, a non-selective dopamine receptor agonist, on the tremor induced by harmaline in rats. Propranolol (a first-line drug in essential tremor) was used as a reference compound.


METHODS
Tremor, locomotor activity and focused stereotypy were measured objectively using force plate actimeters. Tremor was analyzed using a Fourier transform to generate power spectra for rhythmic behavior.


RESULTS
The tremor induced by harmaline administered at a dose of 15 mg/kg ip was associated with an increase in power in the 9-15 Hz band (AP2) and in the tremor index, calculated as a difference between AP2 and power in the 0-8 Hz band (AP1). Propranolol injected at a dose of 20mg/kg ip reversed both of these effects of harmaline. Apomorphine administered at the doses of 0.5 and 1mg/kg sc further enhanced AP2 and at the lower dose also the tremor index elevated by harmaline. This increase in AP2 was stronger than enhancement of locomotor activity induced by apomorphine in the harmaline-treated animals.


CONCLUSIONS
The present study suggests that the dopamine agonist apomorphine enhances the tremor induced by harmaline, and this effect is at least partly independent of hyperactivity.
Department of Neuro-Psychopharmacology, Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland. Electronic address: ossowska@if-pan.krakow.pl.
Krystyna
K
Ossowska
Department of Neuro-Psychopharmacology, Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland.
Urszula
U
Głowacka
Department of Neuro-Psychopharmacology, Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland.
Barbara
B
Kosmowska
Department of Neuro-Psychopharmacology, Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland.
Jadwiga
J
Wardas
D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000633:toxicity*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000633:toxicity; D018491:Dopamine Agonists / Q000008:administration & dosage / Q000633:toxicity*; D004357:Drug Synergism; D006246:Harmaline / Q000008:administration & dosage / Q000633:toxicity*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014202:Tremor / Q000139:chemically induced* / Q000473:pathology*
D000697:Central Nervous System Stimulants; D018491:Dopamine Agonists; D006246:Harmaline; D001058:Apomorphine
Apomorphine; Harmaline; Propranolol; Rat; Tremor