New drugs selective for histamine H3-receptors can be used to establish that these receptors are involved in the feedback control of histamine synthesis and release, and to demonstrate their distribution in the brain and peripheral tissues. These drugs provide new tools for affecting physiological and possibly pathological conditions in which histamine is involved.

The first medical cure of Acanthamoeba keratitis was obtained by use of propamidine isethionate. Since then, it has been the basic drug recommended for use in treatment. Because some Acanthamoeba strains have been reported to be resistant to propamidine and propamidine was found to be only weakly cysticidal, superior homologs such as butamidine, pentamidine, hexamidine, heptamidine, octamidine, and nonamidine were tested for their amoebicidal effects on two Acanthamoeba strains isolated from patients with keratitis. Trophozoicidal and cysticidal efficiencies were found to be increased from propamidine to nonamidine; i.e., when the alkyl chain connecting the two benzene rings in their molecular structures was elongated, in comparison with propamidine, hexamidine and octamidine were the most amoebicidal molecules. As a result of these data, a kinetic study carried out on propamidine, hexamidine, and octamidine demonstrated that the amoebicidal effects resulted from two events: the diffusion of molecules through the plasma membrane or the double wall of trophozoites or cysts, respectively, and the lethal effects of molecules on amoebic protoplasm. The diffusion kinetics were increased when the alkyl chain was elongated, i.e., with an increase in the lipophilic properties of molecules. In contrast, the lethal effect kinetics were found to be unchanged by this elongation, indicating that they originated from the cationic surface-active properties induced by the protonated amidine groups attached to each benzene ring, which themselves remained unchanged from one molecule to the other. These results strongly advocate the immediate replacement of propamidine by hexamidine in the medical treatment of Acanthamoeba keratitis; in France, 0.1% hexamidine eyedrops are available (Desomedine). The results also advocate clinical investigations on the efficiency and toxicity of octamidine, which appears to be the most amoebicidal diamidine in vitro.Acanthamoeba keratitis is a serious and potentially devastating corneal infection generally seen in soft contact lens wearers. The responsible amoeba has been detected in the human cornea in two forms: as fragile trophozoites and as resistant dormant cysts. The medical treatment of this ocular infection remains very difficult because of the lack of antiamoebic drugs effective against cysts, which are responsible for frequent and serious recurrences.Since the first medical cure reported in 1985 (16), propamidine isethionate, an antimicrobial agent belonging to the diamidine family, has been the basic drug recommended for use in treatment, which includes the use of topical neomycin sulfate and various imidazoles (2,5,7,8,15). Unfortunately, propamidine is poorly cysticidal and the resistance of some Acanthamoeba strains has been reported (6, 10). In the present study, superior homologs of propamidine were tested for their amoebicidal effects both on trophozoites and cysts with the intent of finding whether some of them are more amoebicidal and, especially, cysticidal than propamidine. At...

In continuation of our previous work on piperazinopyrrolothienopyrazine derivatives, three series of piperazinopyridopyrrolopyrazines, piperazinopyrroloquinoxalines, and piperazinopyridopyrroloquinoxalines were prepared and evaluated as 5-HT3 receptor ligands. The chemical modifications performed within these new series led to structure-activity relationships regarding both high affinity and selectivity for the 5-HT3 receptors that are in agreement with those established previously for the pyrrolothienopyrazine series. The best compound (8a) obtained in these new series is in the picomolar range of affinity for 5-HT3 receptors with a selectivity higher than 10(6). Four of the high-affinity 5-HT3 ligands (8a, 15a,b, and 16d) were selected in both the pyridopyrrolopyrazine and the pyrroloquinoxaline series and were characterized in vitro and in vivo as agonists or partial agonists. Compound 8a was also evaluated in the light/dark test where it showed potential anxiolytic-like activity at very low doses per os.