Diazepam increases membrane fluidity of rat hippocampus synaptosomes

Diazepam in vitro produced a concentration-dependent increase of membrane fluidity in crude synaptic membranes from rat hippocampus, but not cerebellum. Similar effects were obtained with higher concentrations of Ro 15-1788 and PK 11195, while zopiclone was completely inactive. In vivo acute treatment with diazepam and Ro 15-1788 gave results similar to those in vitro. The specific benzodiazepine antagonist also significantly increased membrane fluidity and was not able to reverse diazepam's effect. The data are discussed in terms of a possible role of protein kinase inhibition by the drugs not mediated by the 'central' or 'peripheral' type of benzodiazepine receptors.

In vitro interaction of premazepam with benzodiazepine receptors in rat brain regions

Premazepam (PRZ) in vitro competitively displaced 3H-diazepam (DIA), 3H-flunitrazepam (FLU) and 3H-RO 15-1788 from their binding sites on rat brain synaptosomes, with a potency intermediate to other benzodiazepines (BDZs), and Hill coefficients near 1 in different brain regions. Incubation at 37 degrees C reduced premazepam's affinity for BDZ receptors to a lower extent than other benzodiazepines and had no effect on the Hill coefficient. The IC50 of PRZ on 3H-RO 15-1788 and 3H-FLU binding was markedly reduced by GABA in rat cortex, like those of reference classical BDZs, but was GABA-independent in the cerebellum. The IC50 of the BDZ antagonist, RO 15-1788 was unaffected by GABA in both brain areas. The possibility that PRZ behaves as a partial agonist in the cortex and as an antagonist in the cerebellum is discussed.

Modifications in recognition sites for neurotransmitters in rat hippocampus by kainic acid lesion

The specific binding of the tritiated radioligands of dexetimide, serotonin, clonidine, prazosin, WB-4101 and dihydroalprenolol to hippocampal membranes was determined two weeks after producing a virtual complete degeneration of perikarya by the local application of 0.5 micrograms of kainic acid in the dorsal and ventral parts of the hippocampus. Afferent terminals were unaffected by the neurotoxin since the contents of noradrenaline, serotonin and acetylcholine, as well as the activity of choline acetyltransferase, were not modified. Scatchard analysis revealed that the kainic acid lesion produced a 60% decrease in the density of both cholinergic muscarinic binding sites and serotonin binding sites. A significant portion of alpha 1- and alpha 2-adrenoceptor binding sites are also associated with intrinsic neurons of the hippocampus, as shown by the approximately 30% reduction in the densities of tritiated WB-4101, prazosin and clonidine produced by the action of kainic acid. By contrast, the affinity and density of beta-adrenoceptor binding sites were unaffected by the lesion. It is suggested that the recognition sites of the different receptor populations surviving the lesion most likely reside on homologous and/or heterologous nerve terminals.

The affinity of metergoline for 3H-serotonin (5HT) binding sites is regulated by guanine nucleotide

100 microM guanine nucleotide Gpp (NH)p reduces the affinity of the serotonergic antagonist metergoline for 3H-5HT binding sites in rat cerebral cortex. This effect is present both in inhibition binding and in saturation experiments. The hypothesis that the interaction of some serotonergic antagonists with 3H-5HT binding sites is regulated by guanine nucleotides is discussed.

Differences between d-fenfluramine and d-norfenfluramine in serotonin presynaptic mechanisms

The abilities of d-fenfluramine (d-F) and that of d-norfenfluramine (d-NF) to inhibit [3H]serotonin ([3H]5-HT) accumulation in normal and reserpinized synaptosomes were compared to establish to what extent the serotonin-releasing activity of the two drugs might contribute to reduced accumulation of [3H]5-HT. The results indicate that the inhibitory action of (d-NF) on [3H]5-HT accumulation is due principally to its ability to release [3H]5-HT. In contrast, the interference of release in accumulation studies does not seem to play an important role for d-F, suggesting that release from the granular pool and true uptake inhibition are two different mechanisms by which d-F affects serotonin neurons in vitro.

Notes on buspirone's mechanisms of action

Buspirone is a novel psychotropic drug with clear anxiolytic activity in man. There are a number of neurochemical differences between buspirone and both neuroleptics and benzodiazepines. Moreover, buspirone is extensively metabolized, and several metabolites are present in the brain together with the parent compound. One of these, 1-PP, is present in the brain at higher concentrations than the parent drug, particularly when the drug is given orally. On the basis of the reported experimental data, it can be postulated that buspirone's anticonflict activity in rats may be mediated, at least partially, through 1-PP, without involving any effect on the dopaminergic system. The possibility that buspirone and 1-PP may mimic the action of benzodiazepine on some sites in the complex benzodiazepine-GABA receptors is discussed.

d-Amphetamine-induced anorexia and motor behavior after chronic treatment in rats: relationship with changes in the number of catecholamine receptor sites in the brain

No tolerance to the anorectic activity of d-amphetamine was found in rats given two daily injections of 1.25 mg/kg for 28 days. Such rats also presented no changes in the number of binding sites for serotonin and catecholamines in various brain areas. A 28-day treatment with 10 mg/kg d-amphetamine twice daily caused a significant reduction in the number of binding sites for 3H-dihydroalprenolol (beta adrenergic receptor ligand) in hippocampus, and 3H-spiroperidol (dopamine receptor ligand) in striatum and nucleus accumbens. This treatment did not modify the anorectic effect of 1.25 mg/kg of amphetamine but it markedly reduced the motor hyperactivity induced by this treatment and completely blocked the stereotyped licking and biting induced by apomorphine. Amphetamine stereotypy was not significantly reduced but disappeared faster in chronically treated rats. The possible reasons for the different results (tolerance or sensitization) reported by various authors on changes in amphetamine's effects on motor behaviour during chronic treatment are discussed.

Brain levels of tofizopam in the rat and relationship with benzodiazepine receptors

The effect of tofizopam on 3H-flunitrazepam binding was studied in rat hippocampus and cerebellum. Tofizopam (at a concentration of 10(-7) M) increased 3H-Flu binding through a 30% rise in the Bmax with no modification of Kd in either brain area. Similar results were obtained when the binding was measured in tofizopam (50 mg/kg p.o.) pretreated rats. Even though tofizopam has no anticonvulsive action against pentetrazol-induced convulsions, it significantly potentiated the action of diazepam but with no modification of brain diazepam levels and metabolism. The brain levels of tofizopam are reported and compared to plasma levels after oral administration of 5 and 50 mg/kg to rats.

Selective changes of receptor binding in brain regions of aged rats

Binding to several receptors was compared in brain regions of 3 and 21-23 month-old rats. In crude membrane preparations of aged rats the number of dopamine antagonist receptors in striatum was much reduced (-53%). beta-Noradrenergic receptors (cortex) and benzodiazepine receptors (hippocampus and cerebellum) were less but significantly reduced and serotonergic receptors, alpha 1 noradrenergic receptors (both in cortex) and dopamine agonist receptors (striatum) were unchanged. For each receptor binding the KD values were the same in young and old animals. GABA receptor binding (hippocampus and cerebellum) evaluated at only one 3H-GABA concentration (8 nM) was similar in both groups when expressed per protein content but significantly reduced in aged rats when expressed per tissue wet weight because of the partial purification of the synaptic membranes used for 3H-GABA binding. In our experimental conditions age-related changes of specific binding sites in the central nervous system were selective for some receptors studied and did not seem to be due to general non-specific modification of brain tissue composition.

Selective reduction of one class of dopamine receptor binding sites in the corpus striatum of aged rats

In aged rats (21-23 vs 3 month) the neuroleptic receptor number was reduced in the striatum (--53%), in the limbic area (--36%), and not changed in the cortex. The in vitro pharmacological profile of the remaining [3H]spiroperidol receptors in each area was not modified in aged animals. The binding of [3H]ADTN (2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronapthalene) in the striatum and of [3H]serotonin ([3H]-5 HT) in the cortex was also the same in both age groups.

Hyper- and hyposensitivity of central serotonin receptors:[3H]serotonin binding and functional studies in the rat

The effect of repeated treatment with D-fenfluramine, a serotonin releaser, or methergoline, a serotonin antagonist, on [3H]5-HT binding was studied in various rat brain areas. In animals with the same pretreatments, the anorectic activity of m-chlorophenylpiperazine, a serotonin agonist, was investigated. A 14-day treatment with D-fenfluramine caused a significant decrease in the number of [3H]5-HT binding sites (Bmax) in the diencephalon. A reduction of binding sites was found in the cortex too when D-fenfluramine was administered for 28 days. Methergoline caused no changes of [3H)5-HT binding in any brain area examined when given for 14 days but 28-day treatment led to a significant increase in the striatum, hippocampus and cortex. D-Fenfluramine and methergoline caused, respectively, a decrease and increase in the effect of m-chlorophenylpiperazine on food intake. The data show that central 5-HT receptor numbers and sensitivity may change after repeated treatments with drugs acting on brain serotonin.

Repeated treatment with d-fenfluramine or metergoline alters cortex binding of 3H-serotonin and serotenergic sensitivity in rats

28-day treatment with d-fenfluramine, a serotonin (5HT) releaser and uptake inhibitor, caused significant reduction (23%) of 3H-5HT binding sites (Bmax) in the rat cortex. These sites were significantly increased (31%) in cortical membranes of rats which had received metergoline, a potent serotonin antagonist, for 28 days. Parallel changes were found in the anorectic activity of metachlorophenylpiperazine (m-CPP), a potent central 5HT agonist: chronic treatment with d-fenfluramine or metergoline caused respectively a decrease and in the effect of m-CPP on food intake. The data show that changes in 5HT central receptor number and sensitivity may occur after chronic treatment with drugs acting on brain serotonin.

Further studies on the mechanism of serotonin-dependent anorexia in rats

4-(3-Indolyl-2-ethyl) piperidine (LM 5008), 2-(1-piperazinyl) quinoline (quipazine), and metachlorophenylpiperazine (mCPP) were studied for their ability to affect serotonergic mechanisms in vitro. Their relative potency in inhibiting serotonin (5-HT) uptake in vivo and reducing food intake in rats was also examined. mCPP was very potent in displacing 3H-5-HT bound to brain membranes (IC50, 6.2 X 10(-7) M), followed by quipazine, which showed an IC50 of 3.8 X 10(-6) M. LM 5008 was the least effective with an IC50 of 3.6 X 10(-5) M. mCPP and quipazine were less potent than d-fenfluramine in releasing 14C-5-HT from brain synaptosomes, while LM 5008 caused no significant effects at a concentration of 10(-5) M. Conversely, both in vitro and in vivo studies on 5-HT uptake showed that LM 5008 was the most potent compound in inhibiting 5-HT uptake and mCPP the least potent. Since a 50% reduction of food intake was not reached even with a dose of LM 5008 27-times higher than the ED50 for inhibiting 5-HT uptake in vivo, it is suggested that even marked inhibition of 5-HT uptake at central synapses is not sufficient per se to trigger serotonin-dependent anorexia in the rat. Increased release and/or direct stimulation of post-synaptic receptors may be necessary to obtain this effect. This could be of interest for developing new agents which can cause anorexia by interacting with brain serotonin.

Chlorophenylpiperazine: a central serotonin agonist causing powerful anorexia in rats

Meta-chlorophenylpiperazine inhibited serotonin and noradrenaline uptake by synaptosomes to the same extent with IC50 of 1.3 x 10(-6) M and 5.8 x 10(-6) M respectively. Dopamine uptake was less affected by meta-chlorophenylpiperazine (IC50 of 2.2 x 10(-5) M). Unlike d-amphetamine and d-fenfluramine, the drug did not significantly increase monoamine release in synaptosomal preparations. On the other hand, metachlorophenylpiperazine showed an IC50 of 620 nM in displacing 3H-5HT binding to brain membranes. Meta-chlorophenylpiperazine produced a dose-dependent reduction of food intake and this effect was prevented by a pretreatment with methergoline, a serotonin antagonist. The effect of metachlorophenylpiperazine was not modified by an intraventricular injection of 6-hydroxydopamine, electrolytic lesions of nucleus medianus raphe or ventral noradrenergic bundle, nor by a pretreatment with penfluridol, propranolol or phentolamine. The data suggest that the decrease of food intake induced by metachlorophenylpiperazine depends on its ability to act as a serotonin agonist is the brain. The specificity of the effects on serotonin suggests that this compound could prove an important tool for studies aimed at elucidating the functional role of serotonin in the central nervous system.

Effects of narcotic analgesics on the uptake and release of 5-hydroxytryptamine in rat synaptosomal preparations

1 The effects of various narcotic analgesics on the uptake and release of labelled 5-hydroxytryptamine (5-HT) in brain and spinal cord synaptosomes were investigated.2 Methadone was most active in inhibiting 5-HT uptake (IC(50) 2.5 x 10(-7) M). Levorphanol also inhibited 5-HT uptake to a large extent (IC(50) 8.8 x 10(-7) M) while dextrophan, pethidine and pentazocine showed much less activity. Etorphine and morphine had virtually no such activity, with IC(50)S higher than 10(-4) and 10(-3) M respectively.3 The same order of potency as ;5-HT releasers' was found when radioactivity was measured in [(3)H]-5-HT preloaded synaptosomal pellets incubated for 20 min with the various narcotics. Methadone, like chlorimipramine, showed a significant effect at a concentration of 10(-7) M while morphine, at a concentration of 10(-4) M, had no effect.4 When 5-HT release was studied by a perfusion technique, which largely prevents reuptake of the released amine, only fenfluramine, an anorectic agent proposed as a 5-HT releaser, significantly increased spontaneous 5-HT release. These data suggest that the apparent 5-HT release induced by various narcotics in traditional incubation techniques may largely depend on their ability to interfere with neurotransmitter reuptake mechanisms.5 The effects of the various narcotics on 5-HT uptake have no relationship to their relative potency as analgesics in the rat. In the light of their poor effectiveness as 5-HT releasers, it can be concluded that mechanisms other than 5-HT uptake inhibition and release are probably involved in the analgesic effects of these compounds in intact animals.

Subcellular distribution of etorphine in rat brain and evidence for in vitro stereospecific binding

1 Control experiments were carried out by homogenizing rat brain at 0 degrees C with sucrose containing various concentrations of [3H]-etorphine. Subcellular fractionation of this homogenate showed that the distribution of the labelled drug amongst the primary fractions was dependent on the concentration of etorphine in the homogenate. 2 Rats were injected intravenously with 0.2 and 20 microgram/kg of [3H]-etorphine. The brains were homogenized and fractionated in sucrose containing 4.2 x 10(-5) M unlabelled etorphine in order to control redistribution artifacts. Different distribution profiles in the subcellular fractions were observed at these two dose levels. 3 Concurrent administration of either cyprenorphine or naloxone with intravenous etorphine, caused a shift of the labelled drug from the P3 fraction to the supernatant fraction. 4 The subcellular distribution of intravenously administered [3H]-etorphine was also studied by homogenizing brains in etorphine-free sucrose, and sucrose containing either levorphanol or dextrorphan. From these experiments it was concluded that the P3 microsomal fraction is a major site to which in vivo etorphine is stereospecifically bound in the rat brain.

Excretion of 35S-Tobias acid (2-naphthylamino, 1-sulphonic acid) by the rat after oral and intravenous administration

Urinary and faecal excretion of radioactivity after either an intravenous or oral (1 mg/kg) dose of 35S-labelled Tobias acid (2-naphthylamino, 1-sulphonic acid), a dyestuff intermediate structurally similar to the powerful carcinogen 2-naphthylamine, was studied in rats. The Tobias acid was eliminated from the body within 24 hours of administration, almost exclusively through the urine. TLC-chromatography of faecal extracts and urine did not disclose the presence of excreted products other than unchanged Tobias acid and the search for inorganic 35SO4 in the urine by BaCl2 precipitation was negative. There was significant absorption from the gastrointestinal tract, but neither cleavage of the sulphonic group nor other biotransformation by the intestinal flora was apparent under the test condition. There was no evidence that the sulphonic group of Tobias acid is cleaved in the body to a significant extent to give 2-naphthylamine. This information should help in the evaluation of the occupational hazard potential of Tobias acid.

Prevention by calcium administration of reserpine action on rat brain noradrenaline stores: a reappraisal

The conditions under which pretreatment with a calcium salt may prevent the action of reserpine on brain noradrenaline stores in the rat were investigated. The results show that only after subcutaneous administration of reserpine in the same site as a previous CaCl2 injection, was the action of reserpine prevented and reduced levels of this drug were found in the brain. Conversely, the depletion of encephalic noradrenaline following reserpine, as well as the reserpine brain concentration, were not affected by subcutaneously administered calcium chloride, when reserpine was administered either intravenously, or subcutaneously in a site different from that selected for pretreatment with the calcium salt. In essence calcium chloride, a well known irritant, acts accordingly at the site of subcutaneous administration, thus limiting by a non specific mechanism the absorption of reserpine. Under similar conditions, in fact, the absorption of a different drug, i.e. harmaline, was likewise altered. In view of these findings the significance of some studies on calcium-reserpine interaction appearing in the literature requires a reappraisal.