Effects of ergot drugs on serotonergic function: behavior and neurochemistry

Effects of serotoninergic drugs on tremor induced by physostigmine in rats

We investigated the effects of various serotoninergic drugs and serotonin (5-HT) depletion on physostigmine-induced visible tremor in rats. Physostigmine (0.25-1.5 mg/kg) caused dose-dependent tremor, initiated at 3-5 min (latency decreases as dose increases) and lasted for 30-35 min. Serotonin agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (2.5 mg/kg) and buspirone (5 mg/kg) augmented the tremor response caused by physostigmine. The 5-HT(1)/5-HT(2) receptor antagonist, metergoline (1 mg/kg), and 5-HT(2) blocker, cyproheptadine (10 mg/kg) significantly decreased the duration (40%) as well as intensity (45-50%) of physostigmine-tremor. The 5-HT(2a)/5-HT(2c) antagonist ritanserin (5 mg/kg) significantly reduced the duration (60%) without affecting the intensity of the tremor. In 5-HT depleted rats (p-chlorophenylalanine; 300 mg/kg, for 3 days), physostigmine failed to produce tremor. Interestingly, in these animals, administration of a non-specific 5-HT agonist, 5-methoxy-N,N-dimethyl tryptamine, caused high intensity tremor. These results suggest that presence of 5-HT at the pre-synaptic terminals is needed for the tremor response by physostigmine and the response is greatly mediated via post-synaptic 5-HT receptors. The overall data indicated a direct involvement of central 5-HT system in the cholinergic tremor induced by physostigmine.

Lisuride in de novo parkinsonian patients: a four-year follow-up

Lisuride at a mean daily dose of 3.2 mg was given to 15 untreated idiopathic Parkinson's disease patients. There were 10 dropouts, due mainly to inefficacy in the first months of therapy. The parkinsonian pattern in the patients who remained in the study for the full 4 years showed distinct improvement, which was maintained for less than 2 years. The patients did not develop "on-off" phenomena or abnormal involuntary movements during follow-up.

Chronic treatment with bromocriptine induces behavioral supersensitivity in rats

Chronic treatment of rotating rats with equipotent doses of the dopamine (DA) agonists apomorphine (APO), 3-(3,4-dihydroxyphenyl)-1-n-propylpyrrolidine hydrobromide (DPPP) and bromocriptine (BRO) for four weeks resulted in marked differences in rotational activity following acute administration of these agonists. Whereas chronic treatment with APO and DPPP failed to produce any significant changes in agonist-induced rotational behavior, chronic BRO treatment induced a progressive increase in rotational activity up to a mean 200% increase over controls at four weeks. These findings may, in part, explain the long-term clinical efficacy of bromocriptine in patients with Parkinson's disease.

Effect of dihydroergosine (DHESN) on the serotoninergic system and behaviour: is DHESN a new antidepressive agent?

Acute (50.0 mg/kg) and repeated (0.1-10.0 mg/kg) administration of dihydroergosine (DHESN) to rats over 5 days lowered the concentration of 5-HIAA in the brain. DHESN given acutely increased the brain 5-HT in p-CPA-treated animals and diminished the probenecid-induced increase in brain 5-HIAA. In pargyline-treated rats DHESN enhanced the 5-HT/5-HIAA ratio. DHESN administered to rats repeatedly over 5 days decreased the level of 5-HT in blood platelets, and in vitro at concentrations of 10(-4) M and 10(-3) M inhibited the uptake of [14C]-5-HT in platelets. DHESN (10.0-100.0 mg/kg) potentiated the 5-HT syndrome produced in rats by pargyline and 5-HTP. This potentiation was blocked with cyproheptadine but not with haloperidol. DHESN (1.0 and 10.0 mg/kg) lowered the locomotor activity of rats and 10.0 mg/kg DHESN also reduced the duration of immobility in rats forced to swim in a restricted space. The results indicate that DHESN, like antidepressants, decreases the turnover of serotonin in the brain and potentiates the 5-HT-mediated behaviour. This might suggest that the drug should be further investigated for its potential antidepressive properties.

Differential effects of 5-hydroxytryptaminergic antagonists upon apomorphine- and lergotrile-induced hypothermia and stereotyped behaviour in rats

The dopaminergic stimulants apomorphine and lergotrile both evoked hypothermia and stereotyped behaviour in rats. These drug effects were sensitive to antagonism by haloperidol, a dopaminergic receptor blocker. In rats pretreated with 5-hydroxytryptaminergic receptor blockers, cinanserin reduced apomorphine-induced hypothermia but cyproheptadine did not. Both cinanserin and cyproheptadine significantly potentiated lergotrile-induced hypothermia. Similarly, the stereotypic effects of apomorphine were partly reduced by cyproheptadine, although higher doses of cyproheptadine did potentiate lergotrile-induced stereotyped behaviour. These findings of different influences of 5-HT antagonists upon the effects of apomorphine and lergotrile indicate that these two dopaminergic stimulants may not work in identical manner to produce outwardly similar drug effects.

Comparative study of central dopaminergic properties of RU 29717 (N-propyl-9-oxaergoline) and pergolide

RU 29717, a 9-oxaergoline derivative, has been compared with pergolide in a variety of biochemical and behavioural tests indicative of dopaminergic (DAergic) activity. RU 29717 and pergolide have a similar affinity for DA receptors labelled by [3H]spiroperidol or [3H]dihydroergocryptine ( [3H]DHEC) by using striatal or anterior pituitary membranes respectively. Both compounds stimulate the striatal DA-sensitive adenylate cyclase and inhibit the activity of this enzyme in dispersed cells from the neurointermediate lobe of the pituitary gland. In anterior pituitary cells in primary culture, they decrease prolactin release with the same efficacy. In vivo, they exert a long-lasting inhibition of the reserpine-induced hyperprolactinemia. They equally retard the alpha-MPT-induced disappearance of striatal DA and increase striatal acetylcholine levels. In behavioural models, the similarity between RU 29717 and pergolide is also evident: they induce contralateral circling in animals lesioned unilaterally with 6-OHDA, produce stereotyped behaviour and have emetic activity within the same dose range. Therefore, RU 29717, like pergolide, is a potent direct acting DAergic agonist. In experimental models used to investigate this activity at the striatal or the anterior pituitary levels the compounds present a similar profile of action.

Inhibition of neurotransmitter receptor binding by ergot derivatives

Bromocriptine, lergotrile, lisuride, metergoline, and the Sandoz ergot derivatives 25-397, 29-712, and 29-717 have been tested for their ability to inhibit the synaptic receptor binding of spiroperidol, 5-hydroxytryptamine (5-HT), d-lysergic acid diethylamide (LSD), quinuclidinyl benzilate (QNB), WB.4101, and gamma-aminobutyric acid (GABA). Only GABA binding was not affected, and QNB binding was decreased only by lergotrile and metergoline at high concentrations. The most potent inhibitors of the other ligands were bromocriptine and lisuride for spiroperidol (1-2 nMM), metergoline for 5-HT (29 nM), lisuride for LSD (15 nM), and lergotrile for WB.4101 (17 nM). The direct receptor effects of the ergot derivatives in vitro may contribute to understanding their in vivo effects on behavior and in predicting their therapeutic potential in neurological and neuroendocrine disorders.