Apomorphine enhances harmaline-induced tremor in rats

Abstract

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.

Tremorolytic effect of 5′‐chloro‐5′‐deoxy‐(±)‐ENBA, a potent and selective adenosine A1 receptor agonist, evaluated in the harmaline‐induced model in rats

“…Harmaline altered additionally locomotor activity of rats, measured by the total distance traveled. In agreement with our previous study, this drug reduced exploratory activity during the first 30 minutes after its injection but later (30‐60 minutes) it increased motility of rats (Figures and ). This hyperactivity was characterized by episodic slow locomotor movements, general agitation, and sniffing and was accompanied by ataxia, balance disturbances, and tremor.…”

“…As reported previously, harmaline induced generalized tremor of the whole body which started as early as a few minutes after its administration and was manifested by an increase in power within the frequency band of 9‐15 HZ (AP2), and in the tremor index (Figures , and 4). Moreover, a decrease in the power within the frequency band of 0‐8 Hz (AP1) was noted within the first 30 minutes of measurement (Figures , and 4).…”

“…Harmaline hydrochloride dihydrate (Sigma‐Aldrich, St Louis, MO, USA) was dissolved in redistilled water and administered as previously described at a dose of 15 mg/kg ip, immediately before tremor measurements, which lasted 60 minutes. 5′‐Chloro‐5′‐deoxy‐N 6 ‐(±)‐( endo ‐norborn‐2‐yl)adenosine (5′Cl5′d‐(±)‐ENBA, Tocris Cookson Ltd., Bristol, UK) was dissolved in 0.5% DMSO in physiological saline and administered at doses of 0.01‐0.5 mg/kg ip 30 minutes before harmaline.…”

“…Besides phenomenological similarities between ET and the harmaline‐induced tremor, their pharmacological treatments are also analogical . Moreover, a recent study has shown that, similar to its beneficial effect in ET, high‐frequency stimulation of the ventrolateral thalamic nucleus in mice (a region receiving glutamatergic projections from deep cerebellar nuclei) reduced the harmaline‐induced tremor .…”

Modification of 5-methoxy-N,N-dimethyltryptamine-induced hyperactivity by monoamine oxidase A inhibitor harmaline in mice and the underlying serotonergic mechanisms

“…However, different from a partial attenuation of the late-phase hyperactivity by Lu AF21934, a positive allosteric modulator of metabotropic glutamate receptor 4 (mGlu4) [41], the present study showed a complete attenuation of the early-phase hypoactivity by 5-HT 1A receptor antagonist WAY-100635 (Figure 4). While harmaline interacts with various receptors [41–43], the contribution of 5-HT 1A receptor to mouse home-cage activity may be explained by the facts that harmaline acts as a 5-HT 1A receptor agonist [28, 42, 44], and harmaline-mediated inhibition of MAO-A leads to a remarkable increase of 5-HT level in central nervous system where 5-HT itself exhibits a higher affinity to 5-HT 1A receptor than other 5-HT receptors [25, 45, 46]. In addition, the critical role of 5-HT 1A receptor in hypoactivity, different from the transient hyperactivity caused by handling and injection stresses (Figure 1), is in agreement with previous findings on the importance of 5-HT 1A receptor in the control of locomotor activities in rats [47].…”