Pharmacological characteristics and regulation of 5-HT receptor-stimulated phosphoinositide hydrolysis in the rat spinal cord.

In slices from immature rat spinal cord, both 5-hydroxytryptamine (5-HT) and the 5-HT2A/C receptor agonists (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and alpha-methyl-5-HT (alpha-Me-5-HT) stimulate phosphoinositide (PI) hydrolysis. PI breakdown is also increased by the 5-HT3 receptor agonist 2-Me-5-HT but not by phenylbiguanide. The effect of either 5-HT or DOI is blocked by selective 5-HT2A receptor antagonists such as spiperone and ketanserin and more markedly by mixed 5-HT2 receptor antagonists, such as ritanserin, methysergide and mesulergine, with higher affinity at the 2C subtype. The effect of 2-Me-5-HT is blocked by 5-HT2 and not by 5-HT3 receptor antagonists, indicating that 5-HT3 receptors do not directly or indirectly take part in PI hydrolysis in the spinal cord. Moreover, lesion with neonatal capsaicin of thin primary afferents to the dorsal spinal cord enhances inositol phosphate formation stimulated by 5-HT or DOI but not by 2-Me-5-HT. This lesion also increases 5-HT2A and 5-HT2C receptor density. After neonatal injection of 5,7-dihydroxytryptamine, which results in a marked loss of 5-HT content in the cord, 5-HT and 5-HT2 receptor agonists also enhance PI breakdown without a concomitant change in receptor number. The results suggest that the 5-HT-stimulated PI response in the rat spinal cord is associated only with the 5-HT2 receptor class, in particular with the 5-HT2C subtype.

Synthesis of thiophene carboxamide derivatives as serotonin 5-HT4 receptor agonists.

New thiophene carboxamide derivatives 3 (a-j) were synthesized as serotonin 5-HT4 receptor agonists. Preliminary results showed that the compounds 3a, 3d, 3e and 3f caused concentration dependent relaxation of carbachol-induced contraction in tunica muscularis mucosae in rat oesophagus.

Synthesis and 5-HT3 affinity of new 3-substituted indoles at central nervous system.

A series of 3-imino and 3-aminomethyl-N-methylindoles, in which the amine substituents were 3-quinuclidyl and 1-adamantyl groups, were synthesized and their in vitro affinity towards 5-HT3 central receptors evaluated. Of the nine compounds tested, three caused displacement of 3H-BRL 43694 binding to 5-HT3. 2-Chloro-3-(3-quinuclidylimino)-1-methylindole, 4, was the most potent compound with an IC50 = 5.15 10(-8) M. Moreover, the monoamine oxidase inhibition activity was tested and three compounds were shown to be MAO inhibitors, their IC50 was in the range of that of (-)-Deprenyl. Again, 4 was the most potent compound. Structure-activity relationships within the series are briefly discussed.

Neurotoxicity induced by prenatal exposure to MPTP on the monoaminergic and peptidergic systems of the marmoset brain.

The neurotoxicity induced by incidental prenatal exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was studied in three marmosets. The baby marmosets exposed in utero to MPTP looked normal in the first few weeks of life but around 8 to 10 weeks of life they started to behave abnormally and were sacrificed when they were 20 weeks old. A marked reduction in DA levels was found in the baby marmosets prenatally exposed to MPTP as compared to the corresponding age-matched controls and this was highly significant in the caudate nucleus, putamen, and nucleus accumbens. Serotonin content was normal in the caudate and putamen and was only significantly reduced in the nucleus accumbens, hypothalamus, and cingulate cortex. Met-enkephalin levels were reduced in the caudate nucleus, putamen, and globus pallidus. Substance P content tended to be lower in all regions examined; however, the decrease was only statistically significant in the substantia nigra. These results indicate that prenatal exposure to MPTP induces a marked and long-lasting alteration in monoaminergic and peptidergic systems of the primate brain. This observation may provide a new insight into the role of toxins in the etiology of Parkinson's disease.

MPTP-induced parkinsonism in primates: pattern of striatal dopamine loss following acute and chronic administration.

We analyzed the effect of two different schedules of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment on dopaminergic systems in the striatum of cynomolgus monkeys. Acute MPTP treatment produced a marked dopamine (DA) depletion, more severe in the caudate nucleus than in the putamen. Chronic MPTP induced a more pronounced reduction in DA levels, the putamen being slightly more affected than the caudate nucleus, in accord with immunohistochemical findings that showed a higher loss of tyrosine-hydroxylase positive neurons in ventral subpopulations of the substantia nigra pars compacta. A striking increment in the quotient DOPAC+HVA/DA was also observed in chronically but not in acutely treated monkeys, especially in the putamen. In chronically treated animals there was a nearly complete loss of DA in all subdivisions of the putamen. In the caudate nucleus, a rostrocaudal gradient of DA depletion was found, with a greater decrease in DA concentration in the rostral parts, especially in the dorsolateral portions. The pattern of striatal DA loss characteristic of Parkinson's disease can be reproduced to a certain extent in MPTP-intoxicated primates.

GM-1 ganglioside promotes the recovery of surviving midbrain dopaminergic neurons in MPTP-treated monkeys.

We have examined the influence of chronic GM-1 treatment (20 mg/kg i.m. for 16 consecutive days) on the extent of dopaminergic damage induced by acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in cynomolgus monkeys using immunohistochemical and neurochemical analysis. The total number of tyrosine hydroxylase-immunoreactive neurons was reduced in different catecholaminergic mesencephalic regions of MPTP-treated monkeys such as substantia nigra pars compacta, mainly in the ventral portion of the nucleus (39% reduction), substantia nigra pars lateralis (31%), peri- and retrorubral catecholaminergic cell group and ventral tegmental area (A8 and A10 respectively, 20% reduction). A similar degree of neuronal loss was observed in the MPTP+GM-1-treated animals, suggesting that GM-1 ganglioside does not exert a protective effect against MPTP-induced dopaminergic cell loss. Moreover, no neurochemical recovery from the striatal dopaminergic depletion induced by MPTP was found after GM-1 treatment. However, the optical density of tyrosine hydroxylase fibers and the cellular tyrosine hydroxylase content were increased in the substantia nigra pars compacta and ventral tegmental area of the MPTP-treated monkeys which received GM-1 ganglioside, compared with animals treated only with the neurotoxin. These results indicate that GM-1 does not protect against cell death but exerts a neurotrophic effect on surviving dopaminergic neurons in the midbrain of MPTP-lesioned monkeys, suggesting that GM-1 ganglioside may be potentially useful for the treatment of neurodegenerative disorders such as Parkinson's disease.

Neurotoxic effect of prenatal exposure to MPTP on the dopaminergic systems of the marmoset brain.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was incidentally administered to pregnant marmosets during the whole gestational period, except for the last 15 days before term. The infant monkeys were killed 5 months after birth, and dopamine and its metabolites were measured in the striatum and the nucleus accumbens. Prenatal exposure to MPTP produced a marked dopamine depletion in these brain regions of the offspring, showing that MPTP is able to cross the placental barrier in primates.

Extensive loss of brain dopamine and serotonin induced by chronic administration of MPTP in the marmoset.

Common marmosets were given a subcutaneous injection of MPTP (1.25-2.5 mg/kg twice a week) for 5 or 10 consecutive months and were sacrificed after a survival time of 6 months or 15 days, respectively. The parkinsonian symptoms were not very marked at the time of sacrifice but there was a strong decrease of dopamine and, to a lesser extent, of its metabolites in the striatum and in some extrastriatal regions. There was also a profound loss of serotonin in the striatum and in all of the extrastriatal regions analyzed, which was still highly significant 6 months after discontinuation of MPTP treatment. The results suggest that the selected dosage schedule produces a widespread and lasting neuronal degeneration closely resembling the neurochemical pathology of Parkinson's disease.