Identification and characterization of the 5-HT4 receptor in the intestinal tract and striatum of the guinea pig

Receptors for 5-hydroxytryptamine (5-HT) of the 5-HT4 type were investigated in the intestinal tract and the striatum in guinea-pig, in binding studies using the 5-HT4 radioligand, [3H]GR113808. In the intestinal tract, specific binding was observed in preparations of the longitudinal muscle with the myenteric plexus (LMMPs) but not in the whole tissue. Saturable binding of [3H]GR113808 was demonstrated (striatum: Kd = 0.054 +/- 0.002 nM, Bmax = 90.25 +/- 10.44 fmol/mg protein, LMMPs of ileum: Kd = 0.077 +/- 0.016 nM, Bmax = 11.95 +/- 3.24 fmol/mg protein). Selective 5-HT4 receptor agonists and antagonists inhibited binding of [3H]GR113808 with high affinities in LMMPs of the ilcum and which correlated well with their actions on the striatum (r = 0.98), as indicated by the rank order of displacement potencies: SDZ205-557 > LY297524 > cisapride = BIMU8 > 5-HT > mosapride > renzapride > 5-hydroxy-N-methyltryptamine(5-HMT) > (+/-) zacopride > alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT) > 5-methyltryptamine(5-MT) > 5-carboxamidotryptamine (5-CT). The number of binding sites of [3H]GR113808 in the intestine was significantly smaller than that in the brain. In the intestine, a larger number of binding sites was noted in the upper part of the intestine, the rank order being duodenum > jcjunum > ilcum > > colon > rectum. Such data are relevant regarding the potential use of the 5-HT4 receptor ligand to modify motility and secretion in the intestine.

VA-045, a novel apovincamic acid derivative attenuates neuronal injury induced by hypoxia or by excitatory amino acids in cultures of rat cortices

Effects of VA-045, a novel apovincaminic acid derivative, on neuronal damage induced by hypoxia or by excitatory amino acids (glutamate (Glu), N-methyl-D-aspartate and kainate) were examined in cultures of the rat cortices. The extent of cell injury was quantified by measuring lactic dehydrogenase activity released from the damaged cells into the culture medium. VA-045 at concentrations between 1 microM and 30 microM significantly attenuated this neuronal damage and exceeded those of vinpocetine. VA-045 had no significant binding affinity to Glu receptor subtypes. The cytoprotection of VA-045 does not seem to be the result of antagonism at Glu receptors. VA-045 inhibited lipid peroxide production in brain homogenates. Vitamin E also had this antioxidant effect, but did not attenuate the hypoxia-induced neuronal damage. A cAMP analogue and a phosphodiesterase (PDE) inhibitor also attenuated the hypoxia-induced neuronal damage. As VA-045 inhibits the activity of PDE, the effect of VA-045 may possibly relate to cAMP cascade. VA-045 may prove to be efficacious for the treatment of disorders related to cerebral neuronal injury.

Prostacyclin analogue TTC-909 reduces memory impairment in rats with cerebral embolism

The effects of the stable prostacyclin analogue TTC-909 on memory impairment in the water maze task and on neuronal damage were studied in rats with cerebral embolism induced by injecting polyvinyl acetate (PVA) into the right internal carotid artery and the ensuing embolism extending out into the right middle cerebral artery. Areas supplied by the lenticulostriate artery were most markedly damaged. In the water maze test, the PVA-embolized rats took longer to reach the platform than did the nontreated control rats. To some extent, repeated administrations of TTC-909 (200 ng/kg, IV) overcame this impairment in water maze learning in the rats. We assume that the vasodilating effects of TTC-909 maintain this blood supply to the ischemic area and that TTC-909 prevents the development of thrombosis around the PVA particles in the arterial capillaries, as a result of antiplatelet aggregative effects. These two mechanisms are likely to be involved in memory improvement. TTC-909 may prove effective for treating subjects with stroke and other cerebrovascular disorders.

Depolarization and hypoxia-induced cell damage in serum-free cultures of the rat cortex, and related extracellular glutamate changes

Experiments were carried out to clarify the influence of K+-induced chronic membrane depolarization on cytotoxicity and changes in extracellular glutamate, as induced by hypoxia in serum-free cortical cultures. Excitotoxic cell death was examined by measuring lactic dehydrogenase (LDH) activity released into the culture medium. In culture grown in the presence of 25 mM K+, morphological injury occurred during a 4 h exposure to hypoxia, together with a substantial efflux of LDH. In hypoxic cultures, extracellular glutamate concentrations were elevated and these responses were absent in cultures grown in physiological medium (K+ = 5.4 mM), even with 16 h of hypoxia. In cultures at 25 mM K+, the cytotoxicity induced by hypoxia was attenuated by NMDA receptor antagonists, in a concentration dependent manner. We also examined the effects of excitatory amino acids, agonists of the main glutamate receptor classes (glutamate, NMDA, kainate, and AMPA). In both 5.4 nM and 25 mM K+ cultures, a dose dependent release of LDH was induced by a long exposure to glutamate receptor agonists, although the release of LDH in the 5.4 mM K+ was less than that in the 25 mM K+ cultures. Despite of the expression of the glutamate receptor in the 5.4 mM K+ cultures, hypoxic neuronal damage did not occur. These results suggest that when cultures grown in a chronically depolarizing environment are exposed to hypoxia, they are damaged by an excitotoxic mechanism in which the main cause seems to be the glutamate released into the medium at high extracellular levels.

Changes in the extracellular concentrations of amino acids in the rat striatum during transient focal cerebral ischemia

Although considerable evidence supports a role for amino acids in transient global cerebral ischemia and permanent focal cerebral ischemia, effects of transient focal cerebral ischemia on the extracellular concentrations of amino acids have not been reported. Accordingly, our study was undertaken to examine the patterns of changes of extracellular glutamate, aspartate, GABA, taurine, glutamine, alanine, and phosphoethanolamine in the striatum of transient focal cerebral ischemia, as evidence to support their pathogenic roles. Focal ischemia was induced using the middle cerebral artery occlusion model, with no need for craniotomy. Microdialysis was used to sample the brain's extracellular space before, during, and after the ischemic period. One hour of middle cerebral artery occlusion followed by recirculation caused neuronal damage that was common in the frontoparietal cortex and the lateral segment of the caudate nucleus. During 1 h of ischemia, the largest increase occurred for GABA and moderate increases were observed for taurine, glutamate, and aspartate. Alanine, which is a nonneuroactive amino acid, increased little. After recirculation, the levels of glutamate and aspartate reverted to normal baseline values right after reperfusion. Despite these rapid normalizations, neuronal damage occurred. Therefore, uptake of excitatory amino acids can still be restored after 1 h of middle cerebral artery occlusion, and tissue damage occurs even though high extracellular levels of glutamate are not maintained.

Effect of minaprine on changes in monoamine contents in Mongolian gerbils with 5-min occlusion of common carotid arteries

Effects of minaprine, a psychotropic drug, on changes in monoamines and their metabolites were examined in Mongolian gerbils with 5-min occlusion of the common carotid arteries. Noradrenaline (NA), dopamine, serotonin (5-HT), 5-hydroxyindol acetic acid, homovanillic acid and 3,4-dihydroxyphenyl acetic acid contents in the cortex, hippocampus and striatum remained unaltered during a 5-min occlusion. NA levels in the cortex, hippocampus and striatum and 5-HT levels in the hippocampus and striatum significantly decreased 30 min-2 hr after re-circulation. Particularly, minaprine significantly inhibited the decrease of 5-HT in the hippocampus. These observations suggest that the effect of this drug on delayed neuronal death in the CA1 neurons in the hippocampus in Mongolian gerbils with occluded common carotid arteries may be related to the serotonergic system.

Changes in monoamine contents in the brains of Mongolian gerbils following a 5-min occlusion of the bilateral carotid arteries

Changes in cerebral monoamine metabolism were investigated in gerbils following a 5-min ischemia. During ischemia, monoamines were not changed, and 3-methoxy tyramine increased remarkably. After re-circulation, noradrenaline and serotonin decreased, and 5-hydroxyindole-3-acetic acid increased. Dopamine was not significantly changed, but its metabolites were elevated. At 1, 3 and 7 days after the ischemia, monoamine metabolism did not change. We discussed the possibility that these monoamine metabolism changes in the early period of reflow might be related to the delayed neuronal damage.