Preneural transmitters as regulators of embryogenesis. Current state of problem

Our knowledge about the preneural neurotransmitter systems and their functions were based on the old pharmacological and biochemical data that have recently been confirmed and substantially supplemented. Specific components of the preneural serotoninergic and endocannabinoid systems were identified in developing echinoderm embryos using immunocytochemistry, Western immunoelectroblotting, and HPLC-mass spectroscopy. These data were corroborated by the results of pharmacological experiments: it was found that some ligands of serotonin receptors, as well as the agonist of cannabinoid receptors anandamide induced the appearance of abnormal embryonic phenotypes, whose expression depended on the ligand-teratogen concentration. Their appearance was prevented, correspondingly, by serotonin and its lipophilic (or hydrophilic) analogs and antagonists of cannabinoid (CB₁CB₂)-receptors.     

Pharmacological characterization of a serotonin receptor involved in an early embryonic behavior of Helisoma trivolvis

In contrast to the abundance of information on the many physiological and developmental actions of serotonin in molluscan nervous systems, comparatively little is known about the serotonin receptors involved in these responses. Embryos of the pulmonate gastropod, Helisoma trivolvis, display a cilia-driven rotational behavior that is regulated by endogenous serotonin. In the present study, two functional assays were used to determine some of the pharmacological properties of the receptors that mediate the cilio-excitatory action of serotonin. Timelaspe video microscopy was used to measure whole embryo rotation rat and cilia beat frequency in isolated cells. In dose-response experiments, serotonin was approximately 10 times more potent in stimulating cilia beat frequency over embryo rotation. In rotation experiments, 5-carboxyamidotryptamine and methysergide had effective agonist activity in dose ranges similar to that of serotonin (1 to 100 μM). In contrast, 8-hydroxydiproylaminotetralin HBr (8-OH-DPAT) displayed agonist activity of lower potency and effectiveness. Several compounds displayed antagonist activity in the 1 to 100 μM dose range, including mianserin, spiperone, ritanserin, 1-(1-naphthyl) piperazine, and Propranolol. α-Methylserotonin had mixed agonist–antagonist activity, and metoclopramide, MDL-72222, and ketanserin were inactive. Experiments on isolated cells suggested that the extremely effective antagonism displayed by mianserin in the embryo rotation assay was due to its specific activity at ciliary serotonin receptors. These results implicate the presence of a novel serotonin receptor on embryonic ciliated cells that is pharmacologically distinct from those previously characterized in vertebrate or invertebrate systems. 1994 John Wiley & Sons, Inc.     

Serotonin and Central Mechanisms Underlying Motor Control

The review considers in a historical aspect the published data on the role of serotonin in brain activity, as well as on the structure and organization of neuronal projections of serotonergic nuclei. In addition, information on the facilitatory and inhibitory effects of serotonin on neurons of various brain regions under both in vivo and in vitro conditions is presented. General characteristics of the main types of central serotonin receptors are also given. It is emphasized that such receptors form a heterogeneous group, and this is the reason for the diversity of the effects when agonists and antagonists are applied. Regularities characteristic of changes in the activity of serotonergic system over the sleep-wakefulness cycle are also analyzed in this review; data on the involvement of serotonin in motor control are cited. Possible reasons for the complexity and multiplicity of the effects evoked by serotonin at different levels of the CNS and within various neuronal structures in the course of motor behavior are discussed.     

The amphiphilic peptide adenoregulin enhances agonist binding to A1-adenosine receptors and [35S]GTPγS to brain membranes

Summary 1. Adenoregulin is an amphilic peptide isolated from skin mucus of the tree frog,Phyllomedusa bicolor. Synthetic adenoregulin enhanced the binding of agonists to several G-protein-coupled receptors in rat brain membranes.2. The maximal enhancement of agonist binding, and in parentheses, the concentration of adenoregulin affording maximal enhancement were as follows: 60% (20 µM) for A₁-adenosine receptors, 30% (100 µM) for A_2a-adenosine receptors, 20% (2 µM) for ₂-adrenergic receptors, and 30% (100 µM) for 5HT_1A receptors. High affinity agonist binding for A_1-, _2-, and 5HT_1A-receptors was virtually abolished by GTPS in the presence of adenoregulin, but was only partially abolished in its absence. Magnesium ions increased the binding of agonists to receptors and reduced the enhancement elicited by adenoregulin.3. The effect of adenoregulin on binding of N⁶-cyclohexyladenosine ([³H]CHA) to A₁-receptors was relatively slow and was irreversible. Adenoregulin increased the B_max value for [³H]CHA binding sites, and the proportion of high affinity states, and slowed the rate of [³H]CHA dissociation. Binding of the A₁-selective antagonist, [³H]DPCPX, was maximally enhanced by only 13% at 2 µM adenoregulin. Basal and A₁-adenosine receptor-stimulated binding of [³⁵S]GTPS were maximally enhanced 45% and 23%, respectively, by 50 µM adenoregulin. In CHAPS-solubilized membranes from rat cortex, the binding of both [³H]CHA and [³H]DPCPX were enhanced by adenoregulin. Binding of [³H]CHA to membranes from DDT₁ MF-2 cells was maximally enhanced 17% at 20 µM adenoregulin. In intact DDT₁ MF-2 cells, 20 µM adenoregulin did not potentiate the inhibition of cyclic AMP accumulation mediatedvia the adenosine A₁ receptor.4. It is proposed that adenoregulin enhances agonist binding through a mechanism involving enhancement of guanyl nucleotide exchange at G-proteins, resulting in a conversion of receptors into a high affinity state complexed with guanyl nucleotide-free G-protein.     

Psychedelic-inspired drug discovery using an engineered biosensor

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Differences among three macaque species in responsiveness to an observer

Behavioral responses of experimentally naive captive-born juvenile females of three macaque species (Macaca mulatta, M. radiata, M. fascicularis)to a passive human observer were compared across three periods, beginning approximately 6 weeks after animals were transferred from multianimal groups housed outdoors to individual cages in colony rooms and ending approximately 6 months later. Responsiveness was assessed using eight relatively stereotyped behavior patterns characteristic of this genus. Although overall responsiveness declined across periods in all groups, this measure was consistently highest for M. fascicularis.Patterns were also analyzed as indicative of “fear” or “hostility.” Responses of M. fasciculariswere frequent in both categories, although fear scores exceeded those for hostility. M. mulattascored more frequently as hostile than as fearful. Both fear and hostility scores for M. radiatawere extremely low. The only response shown with more than minimal frequency was lip-smacking, a pattern that is usually construed as an appeasing, submissive, or affiliative display. Differences among species in their responses to the observer are generally consistent with other behavioral and psychophysiological data on the same subjects and with patterns of social interaction between conspecifics.     

Gene duplication and recombination in the evolution of mammalian Fc receptors

The immunoglobulin-related chains of cell-surface receptors for the Fc region of immunoglobulins (FCERIα, FcγRI, FcγRII, and FcγRIIIα) are encoded by members of a gene family. Phylogenetic analysis of representative members of this family from mammals revealed that FcγRIIIα genes of human, mouse, and rat are not orthologous to one another in the region of the gene encoding the Immunoglobulin C2-set domains. In phylogenetic trees of this region, FcγRIIIα and FcγRII clustered together. However, in trees based on both coding and noncoding regions 5′ and 3′ to the C2 domains, FcγRIIIα genes of human, mouse, and rat clustered together. This pattern of relationship is most easily explained as a result of two independent recombinational events occurring in the mouse and rat after these two species diverged, in each of which the exons encoding the C2 domains were donated to an FcγRIIIα gene by an FcγRII gene.     

Enantiomers of 11-hydroxy-10-methylaporphine having opposing pharmacological effects at 5-HT1A receptors

The two enantiomers of the title compound have been prepared by different synthetic routes. Both bind strongly to 5-HT1A receptors from rat forebrain membrane tissue. However, in a guinea pig ileum preparation, the (R)-enantiomer exhibits properties consistent with its being an agonist, whereas the (S)-enantiomer shows no agonist effect, but it blocks the actions of the (R)-enantiomer and of 8-hydroxy-2-di-n-propylaminotetralin (8-OH-DPAT), a 5-HT1A agonist. These data are presented as a rare example of enantiomers which demonstrate opposite pharmacological effects at the same receptor.     

The resolution, isolation, and pharmacological characterization of the enantiomers of a benzamide containing a chiral sulfoxide.

Rac-ML-1035 (MDL 201,035: 4-amino-5-chloro-2-[2-(methylsulfinyl)ethoxy]-N-[2-(diethylamino)ethyl] benzamide hydrochloride) is a racemic gastroprokinetic with serotonergic (5-hydroxytryptamine, 5-HT) activity and a novel chiral sulfoxide substituent. Chromatographic and chemical methods have been developed to resolve the enantiomers of rac-ML-1035, and the absolute configuration of the (R)-enantiomer has been determined. We also report pharmacological characterization of rac-ML-1035 and its respective isomers. Radioligand binding to rat cortical membranes revealed that (R)-ML-1035 (MDL 201,226) and (S)-ML-1035 (MDL 201,227) had equivalent activity at the 5-HT3 receptor. However, in isolated tissue studies including field-stimulated guinea pig ileum, field-stimulated rat fundic strip, and nonstimulated guinea pig ileum, (S)-ML-1035 was equally potent yet had greater maximal activity than (R)-ML-1035 in eliciting or facilitating cholinergic contractions. Thus, enantiomers of rac-ML-1035 can be resolved, and the relative configuration of these isomers influences their pharmacological activity.     

Inhibitory actions of muscarinic cholinergic receptor agonists on serotonin N-acetyltransferase in bovine pineal explants in culture

We have previously identified muscarinic cholinergic receptors in the bovine pineal gland with a K_D value of 0.423±0.01 nM and a B_max value of 69.75±20.91 fmol/mg protein. Similarly, we have shown that the bovine pineal gland possesses a specific choline acetyltransferase with an activity of 0.034±0.004 nmol/mg protein/min. In order to delineate the function of these cholinergic receptor sites, we have studied the effects of muscarinic cholinergic receptor agonists on the activity of serotonin N-acetyltransferase, the melatonin synthesizing enzyme. Cholinergic receptor agonists such as methacholine (10 M), carbachol (10 M), and oxotremorine (10 M) inhibited the activity of serotonin N-acetyltransferase in the bovine pineal explants in culture, from a control value of 5.02±0.45 to 1.25±0.25, 1.30±0.15, and 1.22±0.20 pmol/mg protein/min, respectively. These inhibitory effects were blocked by muscarinic cholinergic receptor antagonists such as atropine (20 M) or QNB (20 M). The presence of high affinity muscarinic cholinergic binding sites, of a specific choline acetyltransferase, along with an inhibitory action of cholinomimetic agents on the activity of serotonin N-acetyltransferase, are interpreted to suggest that muscarinic cholinergic fibers may modulate the synthesis and actions of pineal melatonin.     

Effect of local microapplication of serotonergic drugs on membrane currents of <Emphasis Type="Italic">Paracentrotus lividus</Emphasis> early embryos

It was shown that local application of agonists of the 3rd type receptors 5-HTQ and quipazine into the interblastomere cleft of Paracentrotus lividus embryos evoked specific membrane currents. At the same time, ligands of 5-HT₃-receptors specifically affected the cleavage patterns of half-embryos, i.e., imitated or avoided the interblastomere signal. In the view of the data obtained, we discuss a more precise concept of protosynapse, where the distribution of membrane serotonin receptors is restricted to the period of blastomere formation during cleavage and localized in the area of interblastomere contact.