Synthesis and 5-hydroxytryptamine (5-HT) activity of 2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5-(6H)ones and 2,3,4,4a,5,6-hexahydro-1H-pyrazino[1,2-a]quinoxalines

A series of 2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5-(6H)ones and 2,3,4,4a,5,6-hexahydro-1H-pyrazino[1,2-a]quinoxalines was shown to exhibit 5-HT2C agonist binding and functional activity. Compound 21R inhibited food intake over 2 h in fasted, male Sprague Dawley rats with ED50 values of 2 mg/kg (i.p.) and 10 mg/kg (p.o.).

The synthesis and vasopressin (AVP) antagonist activity of a novel series of N-aroyl-2,4,5,6-tetrahydropyrazolo[3,4-d]thieno[3,2-b]azepines

Synthesis and SAR of N-[4-[(4,5-dihydropyrazolo[3,4-d]thieno[3,2-b]azepin-6(2H)-y l)carbonyl]phenyl]benzamides as arginine vasopressin (AVP) receptor antagonists are discussed. Potent orally active AVP receptor antagonists are produced when the benzamide moiety contains a phenyl group at the 2-position. Similar analogues of 4,6,7,8-tetrahydro-5H-thieno[3,2-b]azepine and VPA-985 are reported.

New generation dopaminergic agents. 7. Heterocyclic bioisosteres that exploit the 3-OH-phenoxyethylamine D2 template

The synthesis of several bioisosteric analogs based on the 3-OH-phenoxyethylamine dopamine D2 agonist template (i.e., 3) is described. The benzimidazol-2-ones and benzthioimidazol-2-ones (7-10) and 2-trifluoromethyl-benzimidazole (13) were observed to have excellent affinity for the D2 receptor.

5-fluoro-2-methyl-N-[5-(5H-pyrrolo[2,1-c][1,4]benzodiazepine-10(11H)-yl carbonyl)-2-pyridinyl]benzamide (CL-385004) and analogs as orally active arginine vasopressin receptor antagonists

Synthesis and structure-activity relationships (SAR) of orally active arginine vasopressin (AVP) receptor antagonists are discussed. Potent and orally active AVP receptor antagonists are produced when ring A of VPA-985 (1) is replaced with a 3-pyridinyl unit (2b).

4,10-dihydro-5H-thieno[3,2-c][1]benzazepine derivatives and 9,10-dihydro-4H-thieno[2,3-c][1]benzazepine derivatives as orally active arginine vasopressin receptor antagonists

Synthesis and structure-activity relationships (SAR) of arginine vasopressin receptor (AVP) antagonists are described. Potent and orally active compounds are prepared when tricyclic 10,11-dihydro-5H-pyrrolo[2,1-c][1,4]benzodiazepine moiety in VPA-985 1 is replaced with a compound 7 or 12.

New generation dopaminergic agents. 5. Heterocyclic bioisosteres that exploit the 3-OH-N1-phenylpiperazine dopaminergic template

The synthesis of several bioisosteric analogs based on the 3-OH-N1-phenylpiperazine dopamine D2 agonist template (i.e., 4) is described. The indolone (5) and 2-CF3-benzimidazole (13) were observed to have excellent affinity for the D2 receptor. Several D4 selective compounds were also identified. Molecular modeling studies and a putative bioactive conformation are discussed.

New generation dopaminergic agents. 2. Discovery of 3-OH-phenoxyethylamine and 3-OH-N1-phenylpiperazine dopaminergic templates

Described in this report is a systematic study which led to the identification of two new dopamine D2 partial agonists (5 and 17). Phenols 5 and 17 represent prototypes of two new classes of D2 partial agonists as well as templates for the future design of novel dopaminergic agents.

New generation dopaminergic agents. 1. Discovery of a novel scaffold which embraces the D2 agonist pharmacophore. Structure-activity relationships of a series of 2-(aminomethyl)chromans

A series of 2-(aminomethyl)chromans (2-AMCs) was synthesized and evaluated for their affinity and selectivity for both the high- and low-affinity agonist states (D2High and D2Low, respectively) of the dopamine (DA) D2 receptor. The 7-hydroxy-2-(aminomethyl)chroman moiety was observed to be the primary D2 agonist pharmacophore. The 2-methylchroman moiety was discovered to be an entirely novel scaffold which could be used to access the D2 agonist pharmacophore. Attaching various simple alkyl and arylalkyl side chains to the 7-hydroxy 2-AMC nucleus had significant effects on selectivity for the D2High receptor vs the 5HT1A and alpha 1 receptors. A novel DA partial agonist, (R)-(-)-2-(benzylamino)methyl)chroman-7-ol [R-(-)-35c], was identified as having the highest affinity and best selectivity for the D2High receptor vs the alpha 1 and 5HT1A receptors. Several regions of the 2-AMC nucleus were modified and recognized as potential sites to modulate the level of intrinsic activity. The global minimum conformer of the 7-hydroxy-2-AMC moiety was identified as fulfilling the McDermed model D2 agonist pharmacophoric criteria and was proposed as the D2 receptor-bound conformation. Structure-activity relationships gained from these studies have aided in the synthesis of D2 partial agonists of varying intrinsic activity levels. These agents should be of therapeutic value in treating disorders resulting from hypo- and hyperdopaminergic activity, without the side effects associated with complete D2 agonism or antagonism.

Coronary artery stenosis in rats affects beta-adrenergic receptor signaling in myocytes

OBJECTIVE

The purpose of this study was to determine whether the early chronic ischemic cardiomyopathy produced by non-occlusive coronary artery constriction was characterized by alterations in the regulation of beta-adrenoreceptor (beta-AR) signaling.

METHODS

Coronary artery narrowing was surgically induced in rats and the animals sacrificed at 7 and 14 days. The changes in the biochemical properties of the multiple components of the beta-AR pathway were examined in enzymatically dissociated myocytes.

RESULTS

Coronary stenosis, involving an average 55% reduction in luminal diameter, was associated with left ventricular failure and right ventricular dysfunction at both time intervals. A decrease in the quantity of beta-AR was detected at 7 days and preceded the loss of high-affinity binding sites. This regulatory modification was characterized by a reduction in beta 1 and beta 2 receptors and a shift in the isoproterenol dose response curve indicating a functional correlation between the decrease in beta-AR and attenuated inotropic support of the myocardium. The percentage of beta-AR binding agonist with high affinity decreased significantly at 14 days along with a further reduction in the density of beta 1 and beta 2 receptors. Reconstitution studies with cyc S49 lymphoma cells did not detect an impairment of Gs alpha functional activity, but the quantity of Gi alpha was increased at both intervals. Finally, activation of the catalytic unit of adenylyl cyclase by forskolin and GTP was not altered by coronary stenosis, however, basal cyclic AMP in myocytes was depressed at 14 days.

CONCLUSIONS

Coronary stenosis induces distinct and progressive modifications in the beta-AR signaling cascade which may contribute to the impaired ventricular performance in this model of myocardial ischemia.

Coronary artery constriction in rats affects the activation of alpha 1 adrenergic receptors in cardiac myocytes

OBJECTIVE

To determine whether alpha 1 adrenergic receptor mediated myocyte contractility and growth are depressed acutely after non-occlusive coronary artery narrowing, the left coronary artery was constricted in rats and mechanical behaviour, cytosolic calcium, and regulation of alpha 1 adrenergic receptors were examined in myocytes seven days later.

METHODS

Coronary artery stenosis was surgically induced in rats and following the estimation of global cardiac performance myocytes were enzymatically dissociated and radioligand binding studies were performed. In addition, the isotonic contractile performance, cytosolic calcium transients and noradrenaline stimulated inositol phosphate generation in myocytes were measured in the presence of WB 4101 or after chlorethylclonidine treatment.

RESULTS

Estimations of cell mechanics in vitro established that peak shortening was decreased by 36% and 18% in left and right ventricular myocytes of coronary stenosed rats. Time to peak shortening was prolonged by 29% in left and 20% in right myocytes, whereas velocity of shortening was decreased by 27% in left myocytes. These alterations were associated with increases in cell length and width, indicative of myocyte hypertrophy. In addition, coronary stenosis was accompanied by reductions in the expression of alpha 1a and alpha 1b receptor subtypes in myocytes. alpha 1 Adrenergic receptor density and noradrenaline stimulated phosphoinositol turnover were decreased by 30% and 34% in left myocytes. alpha 1a Adrenergic receptor subtype mediated cytosolic calcium concentration and myocyte mechanical performance were also impaired in left myocytes only. The alpha 1a adrenergic receptor subtype antagonist WB 4101 abolished noradrenaline stimulated inositol phosphate generation in myocytes, whereas chlorethylclonidine at large doses only partially inhibited this response.

CONCLUSIONS

In conclusion, coronary narrowing leads to defects in the regulation of alpha 1 adrenergic receptors on myocytes which are coupled with attenuation in the transmission of signals, possibly affecting myocyte cell function and ongoing reactive cellular hypertrophy.

Regulation of angiotensin II receptors on ventricular myocytes after myocardial infarction in rats

To determine the effects of acute myocardial infarction on the regulation of angiotensin II (Ang II) receptors and contractile performance of left and right ventricular myocytes, coronary artery ligation was surgically induced in rats, and Ang II receptor density and affinity and the mechanical properties of surviving muscle cells were examined 1 week later. Physiological determinations of cardiac pump function revealed the presence of ventricular failure, which was associated at the cellular level with a depression in the velocity of myocyte shortening and relengthening, a prolongation of time to peak shortening, and a reduction in the extent of cell shortening. These abnormalities in single-cell function were more prominent in left than in right ventricular myocytes. Cellular hypertrophy was documented by increases in cell length and width, which were also greater in the spared myocytes of the infarcted left ventricle. Reactive hypertrophy was accompanied by a 1.84- and 1.85-fold increase in the density of Ang II receptors on left and right myocytes, respectively. On the other hand, the affinity of Ang II receptors for the radiolabeled antagonist was not altered. However, Ang II-stimulated phosphoinositol turnover was enhanced by 3.7- and 2.5-fold in left and right myocytes, respectively, after infarction. Ventricular myocytes were found to possess the AT1 receptor subtype exclusively. In conclusion, myocardial infarction leads to impairment in the contractile behavior of the remaining cells and to the activation of Ang II receptors and effector pathway associated with these receptors, which may be involved in the reactive growth adaptation of the viable myocytes.

Neuropeptide Y stimulates inositol phospholipid hydrolysis in rat brain miniprisms

Neuropeptide Y (NPY) stimulates the hydrolysis of inositol phospholipid in rat brain miniprisms. The stimulation was two-fold in the frontal cortex and in the hippocampus, and 1.5-fold in the striatum. NPY produced no significant effects on basal inositol monophosphate levels in hypothalamic miniprisms. However, those basal levels were much higher than in the other brain regions.

Striatally-mediated response of some structurally rigid analogues of dopamine

The potency of structurally rigid analogues of dopamine (DA) at striatal dopamine receptors was evaluated in rats using three types of assessments: (a) effectiveness in producing rotational and sniffing behaviors by intrastriatal injections (b) inhibition of [3H]-spiroperidol binding and (c) stimulation of adenylate cyclase activity. The compounds included apomorphine (APO) and its analogues, (R)-2,10,11-trihydroxyaporphine (R-THA) and (R)-2-hydroxy-10,11-methylenedioxyaporphine (MDO-APO), 2-amino-6,7-dihydroxyaminotetraline (ADTN) and its analogue, exo-2-amino-6,7-dihydroxybenzonorbornene (exo-amine). (R)-THA produced no stereotypy yet it was a potent inhibitor of [3H]-spiroperidol binding and adenylate cyclase activity. MDO-APO was quite active in inducing stereotypy and stimulating cyclase activity, but it showed low potency in displacing [3H]-spiroperidol. The exo-amine and ADTN were equally potent in enhancing rotation and sniffing intensity, however, the former was completely inactive in biochemical assessments. Except for (R)-THA, all DA analogues studied elicited dopaminomimetic behavioral activities of circling and sniffing. Relationships between the actions of these drugs in the behavioral and biochemical assessments are discussed.

Interaction of amoxapine with muscarinic cholinergic receptors: an in vitro assessment

Amoxapine, an antidepressant with a rapid onset of therapeutic efficacy and great utility in psychotic depression, has been reported to produce anticholinergic side effects in man similar to those observed with imipramine and amitriptyline. To establish its cholinergic disposition, amoxapine and its metabolites 7-hydroxyamoxapine and 8-hydroxyamoxapine, have been evaluated by determining their effects on quinuclidinyl benzilate (QNB) binding to membrane fractions of rat and human brain, on the carbamoylcholine-stimulated accumulation of inositol phosphates in rat cerebral cortex and on the acetylcholine-induced contraction of the guinea pig ileum. In all three preparations, amoxapine was found to be a considerably weaker antagonist of muscarinic cholinergic receptors than either imipramine (4-27 fold) or amitriptyline (51-300 fold). These results indicate that for amoxapine, no correlation exists between the magnitude of muscarinic receptor inhibition and the extent of 'anticholinergic' side effects found in the clinic. Neither the metabolites of amoxapine nor species differences could account for this discrepancy.

Assay of brain calmodulin levels using high-performance liquid chromatography

A simple, sensitive, and efficient HPLC method for the determination of calmodulin levels in brain tissue extracts is described. The assay is linear with respect to both calmodulin and protein concentrations. The specificity and validity of this assay for calmodulin is demonstrated by parallel radioimmunoassay determinations which give equivalent results. Determination of calmodulin levels in various brain regions revealed a high concentration of this protein in the hypothalamus, by comparison to other areas examined.

Hippocampal muscarinic receptor loss following trimethyl tin administration

The effects of trimethyl tin on passive and active avoidance behavior, hippocampal muscarinic receptors and hippocampal cell destruction were examined in male rats. The animals were intubated with 18 mumoles/kg (3.5 mg/kg) of TMT hydrochloride or vehicle. When tested two weeks later treated animals exhibited marked deficits in retention of passive avoidance and extinction of active avoidance tasks. Receptor binding analysis, using 3H-QNB, revealed a significant decrease (21%) in muscarinic receptor density in the hippocampus. Histological examination of the hippocampus revealed a concomitant loss in pyramidal cells in these animals. These results suggest that muscarinic receptors reside on the hippocampal pyramidal cells and that these cells and receptors may be involved in retention of passive avoidance behavior.

The effect of microwave irradiation on vasopressin in plasma and hypothalamo-neurohypophyseal system

Radioimmunoreactive vasopressin was measured in plasma, neurohypophysis and hypothalamus of the rats after different procedures of killing: a) microwave irradiation; b) decapitation; c) decapitation following a stress induced by immobilization in a restrainer. Vasopressin content in the neurohypophysis and hypothalamus was much lower in microwave irradiated than in both decapitated and stressed decapitated rats. In addition, the data from microwave technique were inconsistent with a large scatter. Plasma vasopressin concentration was elevated in both the microwave irradiated and stressed decapitated rats, demonstrating that restraining of the animals induced an excessive stress. Microwave irradiation technique including the necessary manipulation of the animal proved to be less suitable than decapitation technique for the measurement of vasopressin. It is likely that vasopressin in the hypothalamus and neurohypophysis is relatively resistant against post-mortem proteolysis.

The separation of 3H-benzodiazepine binding sites in brain and of benzodiazepine pharmacological properties

In addition to anxiolytic and anticonvulsant properties, benzodiazepines (BDZ) produce sedation, ataxia, and muscular relaxation. In general, it was difficult to separate these properties within this chemical class during the search for clinically useful anxiolytics; and when BDZ's were used to characterize 3H-BDZ binding sites they indicated only a single homogenous class of receptors. A new chemical series was discovered, triazolopyridazines (TPZ, prototype CL 218,872), which showed anticonflict activity in rats and monkeys without sedation or ataxia and inhibited 3H-BDZ binding in brain membranes with kinetic characteristics suggesting the presence of multiple BDZ receptors. High affinity and low affinity sites for the TPZ were demonstrated, the former designated at Type 1 and the latter as Type 2. Anatomical and in vivo studies have supported different distributions of each receptor in brain. Lately, the physical separation of discrete proteins which bind 3H-BDZ has been reported. The multiple receptors and the variety of endogenous substances which have been proposed as modulators and ligands of the receptors might explain variability as well as selectivity in pharmacological properties in these drugs.

Human brain receptor alterations in suicide victims

A comparison was made of human postmortem muscarinic-cholinergic, beta-adrenergic and serotonergic (presynaptic) recognition sites in cortical tissues derived from suicide and homicide (control) victims. An elevation of 47% and 35% in the suicide group compared to controls was observed in receptor ligand binding for 3H-quinuclidinyl benzilate (QNB, muscarinic antagonist) and 3H-imipramine (IMI, a presynaptic serotonin marker), respectively. In contrast, no appreciable differences in 3H-dihydroalprenolol (DHA, beta-adrenergic antagonist) binding were observed between the two groups. Additionally, tissues from both groups of subjects were analyzed for tricyclic antidepressive agent (TAD) content. High performance liquid chromatographic (HPLC) tissue analysis revealed no detectable levels of tricyclic agents with an assay sensitivity of 50 picograms/mg tissue. The results presented herein demonstrate neurotransmitter-receptor alterations in suicide subjects compared to homicide (control) victims. The attendant roles of serotonergic and muscarinic-cholinergic processes in the psychobiology of suicide and depression are addressed.

The effects of acute administration of diazepam on the binding of [3H]-diazepam and [3H]-gaba to rat cortical membranes

Specific [3H]-diazepam binding and [3H]-GABA binding were measured in cortical membranes of untreated rats and rats which had been administered unlabeled diazepam (5.0 mg/kg, IP) thirty minutes prior to sacrifice. Washed and unwashed membranes from control animals showed identical levels of [3H]-diazepam binding. Unwashed membranes of diazepam-treated animals showed consistently and significantly lower binding of [3H]-diazepam than membranes derived from control animals and treated similarly. [3H]-GABA was almost non-existent in unwashed membranes of either group of animals. The binding capability of membranes of treated animals for [3H]-diazepam returned to control levels upon washing with buffer prior to the binding assay. The specific binding of [3H]-GABA in membranes derived from either group of animals also improved after the buffer washes. However, no difference could be detected in [3H]-GABA binding between control and diazepam-treated animals. The failure of diazepam to modulate [3H]-GABA binding in unwashed membranes and the participation of an endogenous inhibitory material repressing [3H]-GABA binding are discussed.

Brain histamine H1- and H2-receptors and histamine-sensitive adenylate cyclase: effects of antipsychotics and antidepressants

Several classes of psychoactive compounds have been investigated for their effects on histamine-sensitive adenylate cyclase in cell free preparations from the guinea-pig cerebral cortex. Their inhibitory actions on this enzyme system have been compared with their abilities to displace [3H]pyrilamine and [3H]cimetidine from histamine H1- and H2-receptor sites, respectively. The results of these studies show that compounds which inhibited the histamine-sensitive cyclase were also displacers of either ([3H]pyrilamine or [3H]cimetidine or both 3H]ligands from their binding sites. In spite of the lack of a correlation between binding and cyclase antagonism, it was observed that compounds that displace both ligands showed greater inhibition of the cyclase than those that have affinities for sites labeled by one or the other ligand. It was concluded that antihistamines, the antipsychotics and the antidepressants share a common property through their antagonism of H1-receptors and that may be responsible for their sedative side effect.

Is dopamine antagonism a requisite of neuroleptic activity?

Neuroleptic activity in laboratory animals is characterized by a decrease in locomotor activity, ptosis, catalepsy, antagonism of certain amphetamine-induced responses, and inhibition of a conditioned avoidance response. Neuroleptics have also been shown to be potent antagonists of dopamine (DA), cis-5,6-Dimethoxy-2-methyl-3-[2-(4-phenyl-1-piperazinyl)-ethyl]indoline (DHO) has been shown to possess the above described pharmacological profile. However, in contrast to known neuroleptics, DHO has no effect on DA levels, DA turnover rate or DA-stimulated cyclase; nor did it have an effect on tyrosine hydroxylase activity. In addition, DHO did not antagonize apomorphine-induced gnawing or amphetamine-induced stereotyped behavior, both of which have been reported to be DA-dependent. However, the agent decreased the level of norepinephrine in the forebrain. An attempt is made to demonstrate that the "DA-hypothesis" of schizophrenia may not be valid in all cases, and that the biochemistry of the disease state is very complex.

A synthetic non-benzodiazepine ligand for benzodiazepine receptors: a probe for investigating neuronal substrates of anxiety

CL 218,872 is the first non-benzodiazepine to selectively displace brain specific 3H-diazepam binding with a potency comparable to that of the benzodiazepines. Like the benzodiazepines, CL 218,872 increased punished responding in a conflict situation and protected against the convulsions induced by pentylenetetrazole. These three pharmacological properties are highly predictive of anxiolytic activity. Unlike the benzodiazepines, however, CL 218,872 was relatively inactive in tests designed to measure effects on neuronal systems which utilize GABA, glycine and serotonin as transmitters. Furthmore, CL 218,872 was relatively free of the ataxic and depressant side effects commonly associated with the benzodiazepines. Because of this high degree of selectivity, CL 218,872 may represent a new probe for investigating neuronal substrates of anxiety.

Some properties of brain specific benzodiazepine receptors: new evidence for multiple receptors

Several new lines of evidence suggest the existence of two or more distinct types of benzodiazepine receptors, in contrast to earlier results suggesting the presence of only one class of receptors. Appropriate thermoinactivation experiments indicate two receptors with different thermostabilities. Several triazolopyridazines, with some of the pharmacological properties of anxiolytics have recently been shown to displace 3H-diazepam and 3H-flunitrazepam with Ki values in the 6 to 100 nanomolar range. These new substances are active in conflict tests in rats and monkeys and prevent metrazol induced seizures in vivo, but strikingly lack the ataxia and sedative properties of the benzodiazepines. Hill analyses of dose-response curves for some of these substances yields Hill coefficients in the range of 0.4--0.6, suggesting that these compounds may be able to discriminate between several types of benzodiazepine receptors.

Benzodiazepine receptors: cellular and behavioral characteristics

Brain specific benzodiazepine receptors appear to mediate the pharmacological properties of benzodiazepines. A neuronal localization for these receptors is suggested by the parallel decrease in the number of benzodiazepine receptors and cerebellar Purkinje cells in "nervous" mutant mice. Electrophysiological results are compatible with an action of benzodiazepines on neuronally localized, physiological receptors. Biochemical, electrophysiological and behavioral experiments highlight the possible importance of frontal cortex in mediating the anxiolytic properties of the benzodiazepines. Triazolenetetrazoles act upon benzodiazepine receptors, increase punished responding and protect against penetylenetetrazole-induced convulsions, but do not produce the side effects associated with benzodiazepines or affect classical neurotransmitter systems. The structural similarities between triazolopyridazines, purines and the indole portion of certain peptides may provide insights into the nature of the endogenous ligand.

3H-Spiroperidol binding to dopamine receptors in rat striatal membranes: influence of loxapine and its hydroxylated metabolites

The effects of loxapine and its hydroxylated metabolites 7-hydroxyloxapine and 8-hydroxyloxapine on 3H-spiroperidol binding to rat striatal membranes were investigated. Whereas 7-hydroxyloxapine and loxapine displayed strong affinities for 3H-spiroperidol binding sites, 8-hydroxyloxapine was essentially inactive. The potency of 7-hydroxyloxapine to displace 3H-spiroperidol is 1.5 times and 8 times those of haloperidol and chlorpromazine, respectively. These results suggest that the combined effects of loxapine and 7-hydroxyloxapine on the postsynaptic dopamine receptors in the brain may explain the clinical efficacy of loxapine in the treatment of schizophrenia.