Effects of nitrendipine and nisoldipine on biogenic amines in discrete areas of rat brain

Actions of nimodipine on the serotonergic systems of rat brain

1. The effects of the serotonin (5-HT) precursor, L-5-hydroxytryptophan (L-5-HTP), or the selective 5-HT1A receptor agonist, 8-OHDPAT, on behavior or brain 5-HT metabolism or both were evaluated in rats IP pretreated with nimodipine at doses ranging from 0.31 to 40 mg/kg. 2. Nimodipine, in a wide dose range (0.6-20.0 mg/kg) potentiated the head-twitch response to L-5-HTP. 3. The effects of nimodipine on the 5-HT metabolism of rats treated with L-5-HTP did not comply with the increase in the behavioral response to this 5-HT precursor. 4. Nimodipine antagonized the effects on 5-HT metabolism induced by 8-hydroxy-2-(di-N-propyl-amino)-tetralin through stimulation of 5-HT1A autoreceptors. 5. It was concluded that the effects of nimodipine on brain 5-HT metabolism appeared to be linked to activation of serotonergic neurotransmission likely due to inhibition of the back-regulation mechanism mediated by presynaptic 5-HT1A receptors.

Effects of isradipine and darodipine on serotonergic system of the rat brain

Isradipine and darodipine are dihydropyridine calcium antagonists that easily pass into the brain, showing high affinity for cerebral L-type voltage-sensitive calcium channel (VSCC). These drugs were IP administered to rats to study their effects on serotonergic systems of discrete brain areas. Isradipine (0.05-5.0 mg/kg) and darodipine (0.3-20 mg/kg) increased the 5-HIAA/5-HT ratio, mostly enhancing the metabolite (5-HIAA) content in various brain areas, suggesting that serotonin (5-HT) turnover was increased. This increase appeared to depend on facilitation of serotonergic neurotransmission, because low doses of isradipine (< 0.075 mg/kg) or darodipine (< 0.6 mg/kg) enhanced the number of head twitches induced by L-5-hydroxytryptophan (L-5-HTP). However, higher doses of isradipine (1.5 mg/kg) or darodipine (5 mg/kg) also appeared to stimulate a negative feedback mechanism, which predominated over the facilitation when the serotonergic neurotransmission was strongly activated. Thus, higher drug doses decreased both the serotonin turnover and the number of head twitches on rats treated with L-5-HTP. It was speculated that the observed effects were due to brain VSCC blockade, although the studied compounds showed a peculiar profile of properties when compared to other previously studied calcium antagonists. Moreover, it was concluded that darodipine appeared to be more effective and selective than isradipine regarding the effects on brain serotonergic systems.

Interaction between dihydropyridine calcium antagonists and morphine on the brain biogenic amines

1. Nifedipine, nimodipine or nisoldipine, were i.p. administered to normal, morphine treated or morphine abstinent rats in order to study their effects on brain biogenic amines and metabolites. 2. On various brain areas, the compounds studied decreased DOPAC and/or HVA levels, but increased 5-HIAA levels, leaving unchanged DA and 5-HT contents. 3. This suggested that DA turnover was decreased, whereas 5-HT turnover was increased, by inhibition of neuronal calcium influx. 4. Calcium antagonists: (a) further enhanced the effect of morphine on 5-HT turnover, which may involve an indirect inhibition of voltage sensitive calcium channels; (b) antagonized the effects of morphine on DA turnover, which are believed to be mediated by disinhibition of dopaminergic pathways. 5. The dihydropyridine calcium antagonists showed some differences in regional specificity and in profile of effects.

Comparison among the effects of nifedipine, nimodipine and nisoldipine on the brain biogenic amines of normal or haloperidol treated rats

1. Previous studies have shown that dihydropyridine calcium antagonists affected the metabolism of the brain biogenic amines more extensively than the non-dihydropyridine ones. The effects of three dihydropyridines (nifedipine, nimodipine or nisoldipine, 0.05-0.10 mmol/kg i.p.) on brain monoamines and metabolites have been evaluated on both normal and haloperidol treated rats. 2. The small changes induced by the drugs on normal rats were markedly increased in the haloperidol treated rats, clearly showing an inhibition of dopaminergic systems. 3. These effects were selective for the striatum and cerebral cortex, with nisoldipine being more effective than nimodipine or nifedipine. 4. The effects of the three drugs on serotonergic systems were similar or more marked on haloperidol treated rats than on normal rats. These effects, showing activation of serotonergic systems, displayed some regional specificity and different potency of the three compounds. Nisoldipine also appeared to be the most effective drug on serotonergic systems. 5. In conclusion nisoldipine, as well as other calcium antagonists, may have a place in the treatment of some mood disorders.