A paradigm shift in brain research.

As late as the 1950s, it was assumed that communication between nerve cells in the brain occurred predominantly, if not entirely, by electrical impulses. A decade later, the theory of chemical transmission, which until then had been thought to occur only in the peripheral nervous system, had gained strong entrance for the central nervous system. This paradigm shift opened up an enormous new perspective in brain research, not least by facilitating the study of brain function by means of chemical tools, which in different ways could modify the chemical signaling between nerve cells. Moreover, such tools sometimes turned out to be useful as therapeutic agents. Thus for the first time, a variety of disorders in the central nervous system could be treated effectively.

Daidzin and daidzein suppress free-choice ethanol intake by Syrian golden hamsters.

Syrian Golden hamsters prefer and consume large and remarkably constant amounts of ethanol in a simple two-bottle free-choice regimen. Ethanol intake is significantly suppressed by zimelidine, bromocriptine, buspirone, and lithium carbonate, pharmacological agents that have been shown to be beneficial in controlling ethanol intake in alcohol-dependent humans. These results suggest that this ethanol-drinking animal model has high "predictive validity" and can be used effectively in the search for and identification of new agents for the treatment of alcohol abuse. The model has enabled us to confirm the putative antidipsotropic effect of Radix puerariae (RP), an herb long used in traditional Chinese medicine for the treatment of patients who abuse alcohol. A crude extract of RP at a dose of 1.5 g.kg-1 x day-1 significantly suppresses (> 50%) the free-choice ethanol intake of Golden hamsters. Moreover, two major constituents of RP, daidzein (4',7-dihydroxyisoflavone) and daidzin (the 7-glucoside of daidzein), were also shown to suppress free-choice ethanol intake. Daidzin and daidzein, at doses of 150 and 230 mg.kg-1 x day-1, respectively, suppress ethanol intake by > 50%. RP, daidzein, and daidzin treatment do not significantly affect the body weight and water or food intake of the hamsters. These findings identify a class of compounds that offer promise as safe and effective therapeutic agents for alcohol abuse.

Quantification of presynaptic alpha 2-adrenoceptors in rat brain after short-term DSP-4 lesioning.

The relative numbers of pre- and postsynaptic alpha 2-adrenoceptors were determined in various rat brain regions after short-term DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) lesioning. For these studies, rats pretreated with zimeldine (10 mg/kg i.p.) were injected with DSP-4 (100 mg/kg i.p.) and were killed either 3 or 15 days later. At the 3 day time-point, DSP-4 treatment produced marked reductions in the noradrenaline content of the cortex (93%), hippocampus (89%), hypothalamus (83%) and cerebellum (92%) with no change in the levels of dopamine or 5-HT. This treatment also decreased the number of alpha 2-adrenoceptors labelled with [3H]idazoxan in the cortex (20%), hippocampus (18%), cerebellum (24%) and hypothalamus (39%). Fifteen days after DSP-4 lesioning, the marked reductions of noradrenaline were sustained in the cortex, hippocampus and cerebellum, but there was a considerable reversal of the effect of DSP-4 in the hypothalamus. At this time-point, the decrease in alpha 2-adrenoceptors was attenuated in cortex (4%) and cerebellum (0%) and their number was increased in hippocampus (8%) and hypothalamus (7%). Together, the data argue that presynaptic alpha 2-adrenoceptors comprise approximately 20% of the total alpha 2-adrenoceptor population in the cortex, hippocampus and cerebellum, but about 40% of it in the hypothalamus. Furthermore, they also demonstrate that although the number of presynaptic alpha 2-adrenoceptors in rat brain can be determined by the reduction of radioligand-receptor binding shortly after DSP-4 lesioning, this effect is rapidly masked by receptor proliferation in response to noradrenergic denervation.

Correlations between catecholamine levels and sexual behavior in male zebra finches.

In zebra finches, the combined actions of estrogens and androgens activate male courtship, including singing, and also strongly modulate norepinephrine (NE) levels and turnover in brain areas known to be involved in controlling courtship behavior. To determine whether changes in NE levels mediate changes in courtship, we administered DSP-4 to males and measured its effects on monoamine levels and reproductive behavior. DSP-4 treatment did not affect serotonin (5-HT), had small, variable effects on dopamine (DA), and caused moderate, nonsignificant reductions in NE. However, in DSP-4-treated males, NE levels in specific vocal-control nuclei showed high positive correlations with courtship singing. There were no significant correlations between NE levels in hypothalamic nuclei and any behavior or DA or 5-HT levels in any nuclei and any behavior. DSP-4-treated males took longer to begin singing and performed fewer song bouts and courtship displays, but their songs could not be differentiated from those of control males. This suggests that their behavioral deficits resulted from deficits in attention rather than an inability to sing.

Evidence for feeding elicited through antihistaminergic effects of tricyclic antidepressants in the rat hypothalamus.

We studied central mechanisms of antidepressants that affect feeding behavior in rats. The tricyclic compounds amitriptyline, doxepin and imipramine significantly induced feeding after their infusion into the third cerebral ventricle in the light phase, but the tricyclic, desipramine, and the dicyclic zimelidine, did not. Drinking was not affected by any compound tested. The relative order of potency in eliciting feeding was: amitriptyline and doxepin greater than imipramine greater than desipramine and zimelidine. To clarify the involvement of neuronal histamine in antidepressant-induced feeding, alpha-fluoromethylhistidine (FMH), a "suicide" inhibitor of histidine decarboxylase, was intraperitoneally administered before infusion of amitriptyline. FMH attenuated the amitriptyline's effect. Bilateral microinfusion of amitriptyline into the ventromedial hypothalamus or the paraventricular nucleus verfied that these are loci for the modulation of feeding by amitriptyline. In the lateral hypothalamus, amitriptyline was less effective. These findings indicate that tricyclic antidepressants directly facilitate feeding, which is, at least in part, mediated by histamine in the hypothalamus.

In vivo labeling of serotonin uptake sites with [3H]paroxetine.

Previous work has shown that [3H]paroxetine is a potent and selective in vitro label for serotonin uptake sites in the mammalian brain. In the present study, [3H]paroxetine was tested in mice as an in vivo label for serotonin uptake sites. Maximum tritium concentration in the whole brain (1.4% of the intravenous dose) was reached 1 h after injection into a tail vein. Distribution of the tracer at 3 h after injection followed the distribution of serotonin uptake sites known from previous in vitro binding studies (r = 0.85). The areas of highest [3H]paroxetine concentration, in decreasing order, were: hypothalamus greater than frontal cortex greater than olfactory tubercles greater than thalamus greater than upper colliculi greater than brainstem greater than hippocampus greater than striatum greater than cerebellum. Preinjection of carrier paroxetine (1 mg/kg) significantly decreased [3H]paroxetine concentration in all areas except in the cerebellum, which is known to contain a relatively low number of specific binding sites. Kinetic studies showed highest specific [3H]paroxetine binding (tissue minus cerebellum) at 2 h after injection and slow clearance of activity thereafter (half-time of dissociation from the hypothalamus, 215 min). The specificity of in vivo [3H]paroxetine binding was studied by preinjecting monoamine uptake blockers or receptor antagonists 5 min before administration of [3H]paroxetine. Serotonergic or muscarinic cholinergic receptor antagonists and dopamine or norepinephrine uptake blockers did not reduce the in vivo binding of [3H]paroxetine. In contrast, there was an excellent correlation (r = 0.99) between the in vivo inhibitory potencies of serotonin uptake blockers in this study and previously published in vitro data on inhibition of [3H] serotonin uptake in brain synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of monoamine oxidase within monoaminergic neurons in the rat brain by (E)-beta-fluoromethylene-m-tyrosine (MDL 72394).

The irreversible inhibition of the monoamine oxidase (MAO) activity within monoaminergic neurons in the rat brain 24 h after single or repeated administration of (E)-beta-fluoromethylene-m-tyrosine (FMMT, MDL 72394) was examined. The enzyme activity was determined by incubating synaptosome-rich homogenates of hypothalamus or striatum with low concentrations of 5-[14C]hydroxytryptamine (5-HT), [14C]noradrenaline (NA), or [14C]dopamine (DA) in the absence and presence of the selective amine uptake inhibitors citalopram (5-HT), maprotiline (NA), and GBR 12909 (DA). After a single subcutaneous injection of FMMT, the inhibition of MAO within the noradrenergic and dopaminergic neurons was significant but only slightly greater than that outside these neurons. The opposite relationship was observed for the serotonergic neurons. After 7 days' treatment of rats with carbidopa, 20 mg/kg p.o., + FMMT once daily, the preference for the inhibition of MAO within the noradrenergic and dopaminergic neurons was accentuated further. The inhibition outside the serotonergic neurons was still greater than within these neurons. The NA uptake inhibitor CPP 199 antagonized the selective inhibition of MAO within the noradrenergic neurons, which indicates that this preference is due to the accumulation of the active metabolite (E)-beta-fluoromethylene-m-tyramine by the NA transporter.

Cortical beta- and alpha 2- adrenoceptor binding, hypothalamic noradrenaline and pineal melatonin concentrations measured at different times of the day after repeated treatment of rats with imipramine, zimeldine, alaproclate and amiflamine.

The effect of repeated treatment of rats for 21 days with the monoamine reuptake inhibitors imipramine, zimeldine, alaproclate (in each case 10 mumol/kg b.i.d.) and the reversible monoamine oxidase-A inhibitor amiflamine (3 mumol/kg b.i.d.) on brain noradrenergic mechanisms measured at different times of the day and night was investigated. Imipramine treatment produced a down-regulation of the Bmax for 3H-dihydroalprenolol binding to cortical beta-adrenoceptors that was not dependent upon the time of day the animals were killed. Zimeldine, on the other hand, reduced both Bmax and Kd of binding for day-time, but not night-time samples. Alaproclate and amiflamine were without effect on the binding. Twenty-four hour mean values for 1 nM 3H-p-aminoclonidine binding to alpha 2-adrenoceptors were lower for the zimeldine-treated rats than for the saline-treated rats. Pineal melatonin concentrations, which are regulated by beta-adrenoceptors, showed a pronounced diurnal rhythm, with the highest concentrations being found at 02:00. At this time point, a lower pineal melatonin content was found after amiflamine treatment, whereas imipramine, zimeldine and alaproclate were without significant effect. The importance of the use of more than one time point and the use of more than one biochemical test for the determination of the effects of repeated antidepressant treatment on central noradrenergic systems measured ex vivo is discussed.

[Effect of antidepressants on the balance of biogenic amines and their metabolites in the rat brain]. / Vliianie antidepressantov na balans biogennykh aminov i ikh metabolitov v mozge krysy.

A study was made of changes in the balance of neuromediator monoamines and metabolistes in rat brain, induced by a single administration of pyrazidol, imipramine and norzimelidine. It was revealed that pyrazidal in a dose of 50 mg/kg increased the level of noradrenaline (NA) and serotonin (5-HT), particularly in the hypothalamus and raphe-nucleus of rat brain. In the same brain regions, imipramine (30 mg/kg) raised the NA content and lowered the concentration of 5-HT and dopamine (DA) metabolites. Norzimelidine (60 mg/kg) elevated the levels of NA and DA in the hypothalamus and reduced the 5-HT content in the raphe nucleus of rat brain. It is suggested that the topography of changes in the balance of biogenic amines in the brain induced by different antidepressants reflects the pharmacological features of their action.

Effects of 5-hydroxytryptamine uptake blockers on the concentration in brain of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in male rats, pro-oestrous rats and ovariectomized rats treated with oestrogen and progesterone.

The aim of this study was to determine the effect of 5-hydroxytryptamine (5-HT) uptake blockade on 5-HT turnover by measuring the concentrations of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in brain with the aid of high performance liquid chromatography and electrochemical detection. The indoleamines were measured in the anterior hypothalamus (AH), posterior hypothalamus (PH) and raphe nuclei 30 min after the i.v. injection of either alaproclate (30 mg/kg) or zimelidine (20 mg/kg). The effect of alaproclate was studied in male rats, pro-oestrous female rats, rats ovariectomized and injected s.c. with 20 micrograms oestradiol benzoate (OB) on dioestrus and at 12.00 h of the next day (presumptive pro-oestrus) with 2 mg progesterone (model 1) and rats ovariectomized 3-4 weeks before an s.c. injection of 20 micrograms OB followed 72 h later by an s.c. injection of 2 mg progesterone (model 2). Alaproclate caused a significant decrease in the 5-HIAA/5-HT ratio in the AH and PH of the brain of male rats, in the PH and raphe nuclei in pro-oestrous rats and model 1, and in the raphe nuclei alone in model 2. Zimelidine had no effect on the 5-HIAA/5-HT ratio in any area in model 2. In male rats the injection of parachlorophenylalanine produced a marked reduction in the brain concentrations of 5-HT and 5-HIAA, but the 5-HIAA/5-HT ratio was unchanged by a subsequent injection of alaproclate. None of the pharmacological agents affected significantly the brain concentrations of noradrenaline, dopamine or dihydroxyphenylacetic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral screen for antidepressants: the effects of drugs and electroconvulsive shock on performance under a differential-reinforcement-of-low-rate schedule.

Those antidepressant drugs that are in wide clinical use decrease response rate and increase reinforcement rate when administered to rats performing on a differential-reinforcement-of-low-rate 72-s (DRL 72-s) schedule. Drugs that are not antidepressants do not have this effect. In this experiment, the following were examined for their effects on a DRL 72-s schedule: trazodone, zimelidine, fluoxetine, and bupropion (atypical antidepressants); electroconvulsive shock (ECS, which is an effective treatment for depression); and haloperidol and clozapine (antipsychotic drugs). Trazodone (3.12-25.00 mg/kg), fluoxetine (10-20 mg/kg), and ECS decreased response rate and increased reinforcement rate. Zimelidine (20 mg/kg) increased reinforcement rate and nonsignificantly decreased response rate. At doses between 2.5 and 40 mg/kg, bupropion had no effect on reinforcement rate or response rate, but at 60 mg/kg response rate was increased and reinforcement rate was nonsignificantly decreased. At the higher dose, the effects of bupropion resemble those of a psychomotor stimulant. Haloperidol (0.04 mg/kg) and clozapine (2.5-10.0 mg/kg) decreased response rate and reinforcement rate. These results suggest that the DRL 72-s schedule may be useful for testing the antidepressant potential of new drugs.

Reduced metabolism and turnover rates of rat brain dopamine, norepinephrine and serotonin by chronic desipramine and zimelidine treatments.

As part of of an ongoing effort to compare changes in whole body turnover of catecholamines and serotonin in man with those induced by antidepressants in the rat brain, we have evaluated the chronic effects of desipramine (DMI) and zimelidine (ZMI) on brain catecholamines and serotonin in the rat. The amines and metabolites measured include norepinephrine (NE), dopamine (DA) and their metabolites, 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Three brain areas were analysed; the hypothalamus, caudate nucleus and frontal cortex. Chronic DMI and ZMI reduced hypothalamic MHPG and caudate nucleus DA metabolites, in particular HVA. Both drugs reduced NE and DA turnover rates (estimated after alpha-methyl-p-tyrosine injection) and the rate of MHPG formation in the hypothalamus (estimated after pargyline treatment). They did not change NE turnover rate, but reduced DA turnover rate and rate of HVA formation in the caudate nucleus. Chronic DMI but not ZMI reduced DOPAC rate of formation in the caudate nucleus. Apparently changes in DA turnover and metabolism produced by these antidepressants are better related to changes in HVA than DOPAC concentrations. Similar to their influence on hypothalamic and caudate nucleus catecholamines, both chronic DMI and ZMI produced changes in serotonin concentration in the caudate nucleus and frontal cortex serotonin that suggest a reduction in its turnover rate and metabolism. The reduction in NE turnover in hypothalamus is consistent with the effects of chronic DMI and ZMI on whole body NE turnover observed in man.(ABSTRACT TRUNCATED AT 250 WORDS)

The research and development of a 5-HT selective reuptake blocker. Preclinical aspects.

The preclinical development of zimeldine according to the 5-HT (serotonin) hypothesis is briefly reviewed. Zimeldine is a selective 5-HT reuptake inhibitor based on the "chemical lead" of brompheniramine--an antihistamine with some 5-HT reuptake inhibitory properties. By chemical manipulation of the position of the pyridine ring in brompheniramine and the stereochemistry of the side chain, a selective 5-HT reuptake inhibitor has been developed.