Michael Williams

Serotonin-releasing effects of substituted piperazines in vitro

The effects of various piperazine-containing compounds on the release of endogenous serotonin (5-HT) from rat hypothalamic slices were evaluated. Incubation of hypothalamic slices with m-chlorophenylpiperazine ( mCPP ) or m- trifluoromethylphenylpiperazine ( mTFMPP ) evoked a potent, dose-dependent release of endogenous 5-HT that was similar in magnitude to that seen with tryptamine, p-chloroamphetamine, or fenfluramine. In the presence of the 5-HT uptake blockers fluoxetine or chlorimipramine, this release was reduced dramatically. Furthermore, removal of calcium from the incubation medium had little effect on the drug-induced release, suggesting that the release mechanism involved displacement of 5-HT stores and not depolarization-induced exocytosis. Trazodone, MK-212, and quipazine had only small effects on release. These studies show that several piperazine-containing compounds can evoke a potent release of endogenous stores of hypothalamic 5-HT in vitro, actions which should be considered together with their direct agonist activity when interpreting the CNS effects in vivo.

Pharmacological profiles of the putative dopamine autoreceptor agonists 3-PPP and TL-99

The putative dopamine (DA) autoreceptor agonists, N-n-propyl-3-(3-hydroxyphenyl)-piperidine (3-PPP) and 6, 7-dihydroxy-2-dimethylaminotetralin (TL-99) were compared with apomorphine in a series of tests indicative of DA receptor activation. All three agents displaced [3H] apomorphine and [3H] spiroperidol from DA recognition sites in rat brain and caused contralateral turning in the 6-hydroxydopamine lesioned rat. Apomorphine and TL-99 were generally more potent than 3-PPP. All three agents were also active at the DA autoreceptor that controls the synthesis of dopamine as indicated in vivo using the gamma-butyrolactone (GBL) procedure and in vitro using a synaptosomal preparation. In addition, all agents produced emesis in beagles. clear differences in the drugs actions were observed in other test procedures. In the rat, apomorphine was the only compound which caused stereotypy or rotation following a reversible KCI-induced lesion of the striatum. Conversely, TL-99 and 3-PPP lacked activity in these procedures. Presumably, activity in these two tests indicates postsynaptic DA receptor activation. Each of the putative autoreceptor agonists produced a monotonic dose-related decrease in the mouse locomotor activity as opposed to the biphasic effect exerted by apomorphine. This action on the mouse locomotor activity, coupled with the results for the GBL test, provides an index of autoreceptor activation. In contrast to 3-PPP, both apomorphine and TL-99 increased locomotor activity in animals pretreated with reserpine and alpha-methyl-p-tyrosine and caused rotation in unilaterally caudectomized mice. In these test procedures thought to reflect activity at the postsynaptic DA receptor, TL-99 differed in its action from 3-PPP in a manner which suggests 3-PPP may be a more selective DA autoreceptor agonist.

Molecular aspects of the action of benzodiazepine and nonbenzodiazepine anxiolytics: A hypothetical allosteric model of the benzodiazepine receptor complex

The availability of radiolabeled benzodiazepines has resulted in the identification of high affinity receptors in the central nervous system for this class of psychotherapeutic agent which are linked to recognition sites for the inhibitory neurotransmitter, GABA. Evaluation of new, synthetic compounds in the benzodiazepine radioligand binding assay has resulted in the identification of nine classes of non-benzodiazepine putative anxiolytic agents, some of which may be more anxioselective than the benzodiazepines. At least three and possibly five subclasses of benzodiazepine receptor have been identified in mammalian tissues using radioligand binding assays. The possibility exists that one of these receptor subclasses may mediate the anxiolytic effects of the benzodiazepines while the remainder may be involved in the mediation of the sedative, ataxic and anticonvulsant properties associated with benzodiazepine-like agents. Several endogenous ligands for the benzodiazepine receptor(s) have been postulated. These include various proteins and peptides, purines and the beta-carbolines. This latter group, which competitively antagonizes the pharmacological and biochemical effects of the benzodiazepines, has the highest affinity for the benzodiazepine receptor of all compounds thus far examined; however, none of these compounds has been conclusively identified as the endogenous ligand akin to the enkephalins and endorphins at the opiate receptor. The majority of available evidence would indicate that the endogenous ligand for the benzodiazepine receptor(s) is an antagonist of the benzodiazepines and other putative anxiolytic agents.

Interaction of the putative dopamine autoreceptor agonists, 3-PPP and TL-99, with the dopamine-sensitive adenylate cyclase of carp retina

The putative dopamine autoreceptor agonists, 3-PPP and TL-99 were examined for their ability to stimulate postsynaptic dopamine receptors associated with adenylate cyclase (D1-receptors) in the carp retina. In intact pieces of retina, 3-PPP had no significant effect on cyclic AMP production at concentrations up to 100 microM, whereas the aminotetralin, TL-99, caused a concentration-dependent increase in cyclic AMP levels with an approximate EC50 of 3.6 microM. Dopamine and ADTN had EC50 values of 3.5 and 3.1 microM respectively. Furthermore, in homogenates of the retina, 100 microM ADTN and 100 microM TL-99 stimulated adenylate cyclase activity 92 and 79% respectively as compared to the stimulation evoked by 100 microM DA. In contrast, 100 microM 3-PPP was essentially inactive at stimulating adenylate cyclase in carp retinal homogenates. These findings suggest that TL-99 can interact with postsynaptic D1-receptors and is not as selective a dopamine autoreceptor agonist as 3-PPP, which has no apparent activity at the D1-receptor.

Ivermectin Interactions with Benzodiazepine Receptors in Rat Cortex and Cerebellum In Vitro

Abstract: The anthelmintic macrolide, ivermectin, enhances the binding of benzodiazepine agonist ([3H]‐diazepam) and antagonist ([3H]β‐carboline ethyl ester) ligands to rat cortical and cerebellar membrane preparations. Enhancement of benzodiazepine agonist binding is partially additive with that of γ‐aminobutyric acid (GABA) and is inhibited by etazolate, bicuculline, and the steroid GABA antagonist R5135. Ivermectin‐stimulated benzodiazepine antagonist binding is enhanced by bicuculline and inhibited by GABA and etazolate. The modulatory effects of bicuculline are chloride‐dependent. The stimulatory effects of ivermectin, while quantitatively different in cortex and cerebellum, are qualitatively similar in both brain regions and are reduced in the presence of chloride. Ivermectin effects on benzodiazepine ligand binding to the benzodiazepine receptor complex and the differences in the effects of GABA, bicuculline, and R5135 on ivermectin‐stimulated agonist and antagonist binding may provide evidence for distinct differences in the recognition sites for the two classes of benzodiazepine receptor ligand and their interactions with other components of the receptor complex.

Discovery of orally bioavailable imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors.

We report a series of potent imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors. Optimization of the solvent accessible 8-position led to improvements in both oral bioavailability and off-target kinase inhibition. Compound 25 demonstrates anti-tumor activity in an A2780 ovarian tumor xenograft model.

Selectivity of cyproheptadine as assessed by radioligand binding

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Interaction of 2-phenylamimoadenosine (CV 1808) with adenosine systems in rat tissues

2-Chloroadenosine (2-CADO) and 2-phenylaminoadenosine (CV 1808) were compared in a CNS purinergic receptor binding assay and the inhibition of neurogenic contractions of the vas deferens. Both 2-CADO and CV 1808 are more potent than adenosine in both preparations. CV 1808 was 10 times more active than dipyridamole in enhancing the response of the vas deferens to exogenous adenosine. Thus, CV 1808 may owe its potent coronary vasodilator activity to both a direct action on adenosine receptors and the ability to augment adenosine responses.

Interaction of avermectins with [3H]β-carboline-3-carboxylate ethyl ester and [3H]Diazepam binding sites in rat brain cortical membranes

The binding of [3H] beta-carboline-3-carboxylate ethyl ester ([3H] beta-CCE), a ligand for the benzodiazepine receptor in the mammalian CNS, to rat cortical membranes, is enhanced by avermectin B1a and its therapeutic formulation, Ivermectin. In contrast to the effects of the avermectins on [3H]diazepam binding, which involve changes in both receptor affinity and number, increases in beta-CCE binding, which are much less than those observed for the benzodiazepine ligand, involve only alterations in receptor number. This Bmax increase is bicuculline insensitive whereas Ivermectin effects on benzodiazepine binding are partially antagonized by GABA antagonist. The data suggest a differential interaction by the avermectins on benzodiazepine and beta-CCE binding sites in rat cortical membranes and indicate that these macrolide anthelmintics may be a useful tool for characterizing benzodiazepine/anxiolytic receptor subtypes.

Adenosine receptors in the mammalian central nervous system

Adenosine by interaction with discrete extracellular recognition sites can modulate cyclic AMP formation and cell firing in the mammalian CNS. The effects of adenosine on cyclic AMP formation are mediated through two extracellular recognition sites: a high affinity (Kd = 10(-9) M) site designated A-1, activation of which results in an inhibition of adenylate cyclase activity and a lower affinity site (Kd = 10(-6) M) designated A-2, activation of which stimulates adenylate cyclase activity. Stable radiolabeled analogs of adenosine have been used to label A-1 receptors in mammalian brain. Adenosine and its stable analogs are potent inhibitors of neurotransmitter release. In addition to being phosphodiesterase inhibitors, the alkylxanthines are also adenosine antagonists, stimulating neurotransmitter release and increasing cell firing by antagonism of the effects of endogenous adenosine. These effects have been attributed to the presence of an inhibitory purinergic tone. Adenosine and related purines have been implicated in the mode of action of several centrally active drugs including anxiolytics, antidepressants and analgesics. Future progress in understanding the potential physiological role of adenosine in the mammalian CNS will depend on the availability of more potent and specific adenosine antagonists, ligands specific for the A-2 receptor, and a better understanding of the factors that regulate adenosine availability.