A series of potent 5-hydroxytryptamine 7 (5-HT 7) ligands has been synthesized that contain a 1,3-dihydro-2 H-indol-2-one (oxindole) skeleton. The binding of these compounds to the 5-HT 7 and 5-HT 1A receptors was measured. Despite the structural similarity of these two serotonin receptor subtypes, several derivatives exhibited a high selectivity to the 5-HT 7 receptor. According to the structure-activity relationship observations, compounds unsubstituted at the oxindole nitrogen atom and containing a tetramethylene spacer between the oxindole skeleton and the basic nitrogen atom are the most potent ligands. Concerning the basic group, besides the moieties of the 4-phenylpiperazine type, halophenyl-1,2,3,6-tetrahydropyridines also proved to be 5-HT 7 receptor-ligands. Because of halogen substitution on the aromatic rings, good metabolic stability could be achieved. A representative of the family, 3-{4-[4-(4-chlorophenyl)-piperazin-1-yl]-butyl}-3-ethyl-6-fluoro-1,3-dihydro-2 H-indol-2-one ( 9e') exhibited selective 5-HT 7 antagonist activity ( K i = 0.79 nM). The in vivo pharmacological potencies of these 5-HT 7 receptor-ligands were estimated by the conflict drinking (Vogel) and the light-dark anxiolytic tests.

Distribution, chemical-neuroanatomy, concentration, and uptake-release properties of histamine (HA)-containing neurons and the possible physiological effects of HA in the central and peripheral nervous system of the pulmonate snails, Helix pomatia and Lymnaea stagnalis, are described. In the CNS of both species, the distribution pattern of HA-immunoreactive (HA-IR) neurons was similar. In both species the majority were located in the buccal, cerebral, and pedal ganglia. In Helix, approximately 400 HA-IR neurons were seen, whereas in Lymnaea approximately 130 labeled cells were visualized. The neuropils, connectives, commissures, several peripheral nerves, and a part of the peripheral tissues (lip and foot of both species and the upper tentacles of Helix) were innervated by HA-IR elements. Numerous sensory cells were found in the tentacles, lip, and statocysts. The HA concentration values assayed by HPLC ranged from 4.8 to 47.4 pmol/mg in the different central ganglia of Helix, and from 4.3 to 18.6 pmol/mg in Lymnaea CNS, whereas the peripheral tissues contained 0.33-1 pmol/mg HA in Helix and 0.26-0.46 pmol/mg in Lymnaea. In the Lymnaea CNS, a high-affinity (37.6 microM), single component 3H-HA uptake system was demonstrated. 3H-HA release evoked by either electrical stimulation or 100 mM K+ could be prevented in Ca2+-free physiological solution. Voltage-clamp experiments indicated specific changes caused by HA in the membrane conductance of identified central neurons of Helix and Lymnaea. Exogenously applied 10(-5) M HA resulted in the acceleration of locomotion (gliding by foot cilia) of Lymnaea. The findings suggest an important signaling role of HA, described here for the first time, in the nervous system of higher-order, pulmonate, gastropods, involving efferent, integrative, and sensory functions. The data can also be applied as a background for further specification of HA in the regulation of different behaviors in these species.

Embryogenesis of the histaminergic system in the pond snail, Lymnaea stagnalis, was investigated by means of immunocytochemistry and HPLC assay. From the earliest onset of the of histamine-immunoreactive (HA-IR) elements, the labelled neurons were confined to the pedal, cerebral and buccal ganglia, whereas no IR cells within the pleural, parietal and visceral ganglia were detectable during the embryogenesis. Peripheral projections of the embryonic HA-IR neurons were missing. No transient HA-IR neurons could be found either inside or outside the CNS. The first HA-IR elements appeared at about E55% of embryonic development, at the beginning of metamorphosis, and were represented by three pairs of neurons located in the cerebral ganglia. Following metamorphosis, four pairs of HA-IR neurons were added; two of them occurred in the pedal (E65% stage of development) and two in the buccal (E90% stage of development) ganglia. During embryogenesis, HA-IR fibers were present in the cerebro-pedal connectives and in the cerebral, pedal and buccal commissures, whereas only little arborization could be observed in the neuropil of the ganglia. HPLC measurements revealed a gradual increase of HA content in the embryos during development, corresponding well to the course of the appearance of immunolabeled elements. It is suggested that the developing HAergic system plays a specific role in the process of gangliogenesis and CNS plasticity of embryonic Lymnaea.