Impaired performance of rats in the Morris swim-maize test late in abstinence following long-term sodium barbital treatment

Rats were tested for place learning in the Morris swim maze on days 110-114 of abstinence following 48 weeks of treatment with sodium barbital. A retarded acquisition of the swim-maze task, that could not be ascribed to motor impairments, was found in the barbital-treated rats. There was a significant difference in brain weight, but there were no significant differences between the control and barbital-treated rats in the frontal cortical concentrations of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), nor in the intra- and extrasynaptosomal activities of cerebral cortical monoamine oxidase towards NA and 5-HT. Postsynaptically, neither the cerebral cortical inositol phospholipid breakdown responses to carbachol and NA (mediated by muscarinic and alpha 1-adrenergic receptors, respectively), nor the striatal and cortical densities of muscarinic receptors labelled by [3H]quinuclidinyl benzilate [( 3H]QNB) were found significantly to be altered in the barbital-treated rats. A strong correlation between the density of striatal and cortical [3H]QNB binding sites was seen for the barbital-treated (r = 0.91) but not for the control (r = -0.05) rats. It is suggested that the deficit in performance of the barbital-treated rats in the Morris maze may be related to a cholinergic dysfunction.     

Chiral resolution and binding study of 1,3,4,14b-tetrahydro-2,10-dimethyl-2H,10H-pyrazino[2,1-d]pyrrolo[1,2-b] [1,2,5]benzotriazepine (10-methyl-10-azaaptazepine) and 2-methyl-1,3,4,14b-tetrahydro-2H-pyrazino[2,1-d]pyrrolo[1,2-b] [1,2,5]benzothiadiazepine 10,10-dioxide (tiaaptazepine)

The affinities of the enantiomers of 1,3,4,14b-tetrahydro-2,10-dimethyl-2H,10H-pyrazino[2,1-d]pyrrolo[1,2-b] [1,2,5]benzotriazepine (10-methyl-10-azaaptazepine, 5) and 2-methyl-1,3,4,14b-tetrahydro-2H-pyrazino[2,1-d]pyrrolo[1,2-b] [1,2,5]benzothiadiazepine 10,10-dioxide (tiaaptazepine, 6) were evaluated in receptor binding assays. Compound (+)-(S)-5, the most significant tested enantiomer, showed good affinities for 5-HT1A, 5-HT2A 5-HT2C and alpha2NA receptors, moderate affinities for DA1, DA3r and 5-HT3 receptors and it was devoid of affinity for DA2, alpha(1NA) and muscarinic receptors. Compound (+)-(S)-5 showed an interesting pharmacological profile different from those of the reference compounds mirtazepine, mianserin and 6-methoxymianserin.     

Extracellular protons differentially potentiate the responses of native AMPA receptor subtypes regulating neurotransmitter release

1. The effects of pH changes on the basal and evoked release of [(3)H]noradrenaline ([(3)H]NA) and [(3)H]5-hydrohytryptamine ([(3)H]5-HT) from hippocampal synaptosomes and of [(3)H]dopamine ([(3)H]DA) and [(3)H]acetylcholine ([(3)H]ACh) from striatal and cortical synaptosomes were investigated in rat brain. 2. Changing pH between 6.4 and 8.0 did not affect the spontaneous release of the four [(3)H]neurotransmitters; alkalinization to pH 8.8 significantly enhanced release. Acidification to pH 6.4 augmented the AMPA-evoked overflows of [(3)H]NA, [(3)H]5-HT and [(3)H]DA, but not that of [(3)H]ACh. In contrast, lowering pH to 6.4 decreased the K(+)-evoked overflows of [(3)H]NA, [(3)H]5-HT, [(3)H]DA and [(3)H]ACh. 3. AMPA released transmitters in a Ca(2+)-dependent, exocytotic manner since its effects, at pH 7.4 or 6.4, were abolished by omitting external Ca(2+) or by depleting vesicular transmitter stores with bafilomycin A1. AMPA did not evoke carrier-mediated release because the uptake blockers nisoxetine, 6-nitroquipazine, GBR12909 and hemicholinium-3 could not inhibit the AMPA-induced release of [(3)H]NA, [(3)H]5-HT, [(3)H]DA and [(3)H]ACh. 4. Extraterminal acidification to pH 6.4 prevented the potentiating effect of cyclothiazide on the AMPA-evoked release of [(3)H]NA, [(3)H]DA and [(3)H]5-HT, whereas the proton-insensitive AMPA-evoked release of [(3)H]ACh, previously found to be cyclothiazide-insensitive at pH 7.4 was cyclothiazide-resistant also at pH 6.4. 5. To conclude, the cyclothiazide-sensitive AMPA receptors mediating release of NA, 5-HT and DA, but not the cyclothiazide-insensitive AMPA receptors mediating the release of ACh, become more responsive when external pH is lowered to pathophysiologically relevant values. The results with cyclothiazide suggest that H(+) ions may prevent desensitization of some AMPA receptor subtypes.     

Influence of supidimide on brain neurotransmitter systems of rats and mice

The influence of 2-(2-oxo-3-piperidyl)-1,2-benzisothiazoline-3-one-1, 1-dioxide (supidimide), a representative of a new class of sedative drugs, on the noradrenergic, dopaminergic, serotoninergic and gamma-aminobutyric acid (GABA)ergic neuronal systems of rodent brains was investigated. In each case the brain transmitter levels after administration of supidimide were determined. Utilisation of noradrenaline (norepinephrine, NE), dopamine (DA), and 5-hydroxytryptamine (5-HT) was also investigated ex vivo. The study was complemented with in vitro investigations of biosynthesis, synaptosomal uptake, degradation, and receptor binding of the transmitters. Based on a preliminary study of the distribution of [35S]-supidimide in rat brain, in vitro effects observed at greater than 10(-4) mol/l were considered irrelevant. Similarly, in vivo effects requiring dosages higher than 300 mg/kg i.p. were not regarded adequate to explain the sedative and antiaggressive efficacy of supidimide. With the above restrictions, the following parameters can be rated as not influenced by supidimide: levels of tryptophan in rat brain and serum (free and total); 5-HT biosynthesis in vivo (rat brain; 5-HT accumulation after monoamine oxidase (MAO) blockade); activity of MAO-A and MAO-B (rat brain mitochondria); uptake of 5-HT, NE and DA (rat synaptosomes); 5-HT receptor binding ( [3H]-LSD binding assay in rat cortical membranes); tyrosine hydroxylase activity (rat adrenal glands); catechol-O-methyl transferase (COMT) (rat liver); NE binding to central alpha 1- and alpha 2-receptors (rat brain; radioligand assay with [3H]-dihydroergocryptine, [3H]-prazosin and [3H]-WB 4101 (2',6'-dimethoxy-(G-3H]-phenoxy]-ethylaminomethylbenzo-1,4-dioxane ); DA levels (whole rat brain and striata); dihydroxyphenylacetic acid (DOPAC) levels (whole rat brain without cerebellum and striata); elevated DOPAC levels after pretreatment with haloperidol; DA-dependent adenylate cyclase in vitro (rat striatum); D2 receptor binding ( [3H]-spiperone binding assay, rat striatum); GABA levels (mouse brain); GABA transaminase activity (mouse brain stem); sodium-independent [3H]-GABA receptor binding (rat brain) and benzodiazepine binding (rat cortical membranes, [3H]-diazepam binding assay). Two effects on the GABAergic system were induced by supidimide. Starting at 300 mg/kg i.p., supidimide slowed down the GABA accumulation in brains of aminooxyacetate-treated mice. At 10(-4) mol/l supidimide caused a significant inhibition of GABA uptake (rat synaptosomes).(ABSTRACT TRUNCATED AT 400 WORDS)     

Indirect modulation by alpha7 nicotinic acetylcholine receptors of noradrenaline release in rat hippocampal slices: interaction with glutamate and GABA systems and effect of nicotine withdrawal

Nicotinic acetylcholine receptors (nAChRs) can modulate transmitter release. Striatal [(3)H]dopamine ([(3)H]DA) release is regulated by presynaptic nAChR on dopaminergic terminals and alpha7 nAChR on neighboring glutamatergic afferents. Here, we explored the role of alpha7 nAChR in the modulation of [(3)H]noradrenaline ([(3)H]NA) release from rat hippocampal slices. The nicotinic agonist anatoxin-a (AnTx) evoked monophasic [(3)H]NA release (EC(50) = 1.2 microM) that was unaffected by alpha-conotoxin-MII or dihydro-beta-erythroidine, antagonists of alpha3/alpha6beta2* and beta2* nAChR, respectively. In contrast AnTx-evoked striatal [(3)H]DA release was biphasic (EC(50) = 138.9 nM; 7.1 microM) and blocked by these antagonists. At a high AnTx concentration (25 microM), alpha7 nAChR antagonists (methyllycaconitine, alpha-conotoxin-ImI) and glutamate receptor (GluR) antagonists [kynurenic acid, 6,7-dinitroquinoxaline-2,3-dione (DNQX)] partially inhibited [(3)H]NA release. The alpha7 nAChR-selective agonist choline evoked [(3)H]NA release (E(max) = 33% of that of AnTx) that was blocked by GluR antagonists, supporting a model in which alpha7 nAChRs trigger glutamate release that subsequently stimulates [(3)H]NA release. A GABAergic component was also revealed: choline-evoked [(3)H]NA release was partially blocked by the GABA(A) receptor antagonist bicuculline, and coapplication of bicuculline and DNQX fully abolished this response. These findings support alpha7 nAChR on GABAergic neurons that can promote GABA release which, in turn, leads to [(3)H]NA release, probably by disinhibition. To investigate the impact of long-term nicotine exposure on this model, rats were exposed for 14 days to nicotine (4 mg/kg/day) with or without 3 or 7 days of withdrawal. alpha7 nAChR responses were selectively and transiently up-regulated after 3 days of withdrawal. This functional up-regulation could contribute to the withdrawal effects of nicotine.     

Effects of botulinum A toxin on presynaptic modulation of evoked transmitter release

A possible influence of botulinum A toxin on the modulation of evoked neurotransmitter release was investigated in hippocampus tissue. Rabbit hippocampal slices prelabelled with [3H]noradrenaline ([3H]NA), [3H]5-hydroxytryptamine ([3H]5-HT) or [3H]choline were superfused with physiological medium and were stimulated electrically during superfusion. The evoked release of [3H]NA, [3H]5-HT and [3H]acetylcholine [( 3H]ACh) was inhibited by botulinum A toxin in a concentration- and time-dependent manner. Neither the inhibition of release of [3H]NA and [3H]5-HT by the alpha 2-adrenoceptor agonist clonidine nor facilitation of release in the presence of alpha 2-antagonists were influenced by pretreatment of the tissue with botulinum toxin. The toxin caused no [32P]ADP ribosylation of synaptosomal proteins of hippocampus. The facilitation of the stimulation-induced [3H]NA and [3H]5-HT release by the specific protein kinase C (PKC) activator 4 beta-phorbol-12,13-dibutyrate (PDB) was significantly diminished by botulinum A toxin. These results show that the evoked transmitter release is inhibited by botulinum A toxin by a mechanism which does not involve ADP ribosylation or an interaction with the alpha 2-adrenoceptor mechanism.     

Role of brain neurotransmitters on neurotensin-induced gastric cytoprotection

We have reported previously that intracisternal (IC) administration of neurotensin (NT) prevents stress-induced gastric ulcers in rats. This effect of NT appears to be mediated by the central nervous system because peripheral (IV) NT is totally ineffective. The present study sought to clarify the central mechanism of the cytoprotective effect of NT by utilizing pharmacological treatments which alter the function of brain neurotransmitter systems. Pretreatment with intracerebroventricular (ICV) administration of agonists and antagonists of acetylcholine (ACh), gamma-aminobutyric acid (GABA), and serotonin (5-HT) receptors or with an anti-opiate (naloxone) agent did not significantly alter NT-induced cytoprotection. However, pretreatment with ICV haloperidol, a dopamine (DA) receptor antagonist, totally blocked NT's cytoprotective effect. In addition, pretreatment with methylphenidate, a DA receptor agonist, produced cytoprotection similar to IC NT. These data indicate that NT-induced cytoprotection is not mediated by 5-HT, GABA, ACh (muscarinic) receptors, or endogenous opiate systems, but suggest interactions between brain DA systems and NT.     

Recovery of alpha 2-adrenoceptor binding and function after irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)

Treatment of rats with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) resulted in a pronounced loss of alpha 2-adrenoceptor binding ( [3H]RX-781094) and a marked reduction in the ability of the alpha 2-agonist UK-14,304 to inhibit K+-stimulated release of both [3H]NA and [3H]5-HT in cerebral cortex. Repopulation of alpha 2-adrenoceptors was monoexponential with a t1/2 of 4.1 days; functional recovery was also monoexponential, with t1/2 values of 2.4 and 4.6 days for restoration of alpha 2-mediated inhibition of [3H]NA and [3H]5-HT release, respectively. Other studies suggest the difference in functional recovery rate may reflect the presence of a large receptor reserve for autoreceptors relative to heteroreceptors.     

Alterations in central monoaminergic neurotransmission induced by polycyclic aromatic hydrocarbons in rats.

Benzo[alpha]pyrene (B[a]P) is a product derived from incomplete combustion of organic material and is considered responsible for chemically-induced cancer in humans. In the present study, the levels of noradrenaline (NA), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the brains of female Wistar rats 6, 12, 24 and 96 h after a single dose of B[alpha]P (50 mg kg(-1) b.w., i.p.), and also after repeated administration of B[alpha]P (50 mg kg(-1) b.w., i.p., 2 x wk, 1 mo). The brain regions studied were the striatum, hypothalamus, midbrain and cortex. Catecholamines were measured using high performance liquid chromatography (HPLC) and electrochemical detection. Significant changes were observed in the striatum where NA, DA, DOPAC were decreased after 24 h and HVA was decreased after 6 h. In contrast, no major alterations occurred in 5-HT and 5- HIAA. In the hypothalamus, a significant decrease in NA was observed after 96 h. In the midbrain, the most important change observed was the decrease in NA after 24 h. A trend toward an increase in 5-HIAA was observed in the cortex after 6 h. The results demonstrate that B[alpha]P induces alterations in the dopaminergic and serotoninergic systems throughout the brain. These alterations may lead to behavioural and hormonal disturbances.     

Augmented potentiation of renal vasoconstrictor responses by thromboxane A2 receptor stimulation in the alloxan-diabetic rat

Dose-response curves were obtained to bolus injections of noradrenaline (NA) and 5-hydroxytryptamine (5-HT) in blood and Krebs-perfused kidneys of male Wistar rats. Vasoconstrictor responses to both NA and 5-HT were significantly attenuated in blood-perfused kidneys of alloxan-treated 14 day diabetic rats compared with non-diabetic animals. Responses to low doses of NA were also significantly attenuated in Krebs-perfused kidneys from diabetic rats but responses to 5-HT were augmented. Dose-dependent potentiation of vasoconstrictor responses to NA and 5-HT in Krebs-perfused kidneys of both non-diabetic and diabetic rats occurred during infusion of the thromboxane A2 (TxA2)-mimetic U46619 [15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano) prosta-5Z, 13E-dienoic acid). The potentiation by U46619 (11 ng mL-1) was inhibited in both groups during infusion of the thromboxane receptor antagonist AH23848 [( 1 alpha(Z), 2 beta, 5 alpha]-(+/-)-7-[5[[(1,1'-biphenyl)-4-yl]methoxyl]-2-(4- morpholinyl)-3-oxocyclopentyl]-4-heptenoic acid). Infusion of 5-HT in Krebs-perfused kidneys of non-diabetic rats, causing a rise in perfusion pressure of similar magnitude to that produced by infusion of 111ng mL-1 U46619, did not significantly affect responses to bolus injections of NA. Potentiation of vasoconstrictor responses to low concentrations of 5-HT by U46619 was significantly greater in Krebs-perfused kidneys of diabetic rats than kidneys from non-diabetic animals. Activation of vascular TxA2 receptors augments the vasoconstrictor effects of 5-HT in Krebs-perfused diabetic rat kidneys to a greater extent than in non-diabetic kidneys.     

Release of [3H]-noradrenaline from rat hippocampal synaptosomes by nicotine: mediation by different nicotinic receptor subtypes from striatal [3H]-dopamine release.

1. The aim of the present experiment was to characterize nicotine-evoked [3H]-noradrenaline ([3H]-NA) release from rat superfused hippocampal synaptosomes, using striatal [3H]-dopamine release for comparison. 2. (-)-Nicotine, cytisine, DMPP and acetylcholine (ACh) (with esterase inhibitor and muscarinic receptor blocker) increased NA release in a concentration-dependent manner (EC50 6.5 microM, 8.2 microM, 9.3 microM, and 27 microM, respectively) with similar efficacy. 3. Nicotine released striatal dopamine more potently than hippocampal NA (EC50 0.16 microM vs. 6.5 microM). (+)-Anatoxin-a also increased dopamine more potently than NA (EC50 0.05 microM vs. 0.39 microM), and maximal effects were similar to those of nicotine. Isoarecolone (10-320 microM) released dopamine more effectively than NA but a maximal effect was not reached. (-)-Lobeline (10-320 microM) evoked dopamine release, but the effect was large and delayed with respect to nicotine; NA release was not increased but rather depressed at high concentrations of lobeline. High K+ (10 mM) released and NA to similar extents. 4. Addition of the 5-hydroxytryptamine (5-HT) reuptake blocker, citalopram (1 microM) to hippocampal synaptosomes affected neither basal NA release nor nicotine-evoked release. 5. The nicotinic antagonist, mecamylamine (10 microM), virtually abolished NA and dopamine release evoked by high concentrations of nicotine, ACh, cytisine, isoarecolone, and anatoxin-a. Although NA release evoked by DMPP (100 microM) was entirely mecamylamine-sensitive, DMPP-evoked dopamine release was only partially blocked. Dopamine release evoked by lobeline (320 microM) was completely mecamylamine-insensitive. 6. The nicotinic antagonists dihydro-beta-erythroidine and methyllycaconitine inhibited nicotine-evoked dopamine release approximately 30 fold more potently than NA release. In contrast, the antagonist chlorisondamine, displayed a reverse sensitivity, whereas trimetaphan and mecamylamine did not preferentially block either response. None of these antagonists, given at a high concentration, significantly altered release evoked by high K+. 7. Blockade of nicotine-evoked transmitter release by methyllycaconitine and dihydro-beta-erythroidine was surmounted by a high concentration of nicotine (100 microM), but blockade by mecamylamine, chlorisondamine, and trimetaphan was insurmountable. 8. Nicotine-evoked NA release was unaffected by tetrodotoxin, whereas veratridine-evoked NA release was virtually abolished. 9. We conclude that presynaptic nicotinic receptors associated with striatal dopamine and hippocampal NA terminals differ pharmacologically. In situ hybridization studies suggest that nigrostriatal dopaminergic neurones express mainly alpha 4, alpha 5, and beta 2 nicotinic cholinoceptor subunits, whereas hippocampal-projecting noradrenaline (NA) neurones express alpha 3, beta 2 and beta 4 subunits. Pharmacological comparisons of recombinant receptors suggest that release of hippocampal NA may be modulated by receptors containing alpha 3 and beta 4 subunits.     

Facilitation of [3H]acetylcholine and [3H]5-hydroxytryptamine release from rat cerebral cortex synaptosomes by a factor extracted from the skin of the Australian frog Pseudophryne coriacea

A partly purified extract of the skin of the Australian frog Pseudophryne coriacea (PsC) evoked the release of [3H]acetylcholine [( 3H]ACh) and of [3H]5-hydroxytryptamine [( 3H]5-HT) from superfused rat cerebral cortex synaptosomes prelabeled with [3H]choline or [3H]5-HT, respectively. The PsC-evoked release of both transmitters was sensitive to tetrodotoxin and was strictly Ca2+-dependent. The release of [3H]5-HT caused by PsC was unaffected by the 5-HT uptake inhibitor citalopram. Activation of muscarinic autoreceptors by ACh or of serotonin autoreceptors by 5-HT depressed the PsC-evoked release of [3H]ACh or of [3H]5-HT, respectively. It is concluded that PsC elicits a Ca2+-dependent exocytotic-like transmitter release, possibly by opening Na+ channels in the presynaptic membrane.     

Differential effects of triethyllead on synaptosomal [3H]dopamine vs. [3H]acetylcholine and [3H]gamma-aminobutyric acid release.

In vitro exposure to tetraethyllead (Et4Pb, 10 microM) did not alter the release of [3H] dopamine (DA), [3H]acetylcholine (ACh), or [3H]gamma-aminobutyric acid (GABA) from superfused synaptosomes isolated from rat brain striatum, hippocampus, and cortex, respectively. On the other hand, a concentration-dependent increase in the spontaneous release of these transmitters was observed following exposure to triethyllead (Et3Pb, 0.1-10 microM). The magnitude of 1 microM Et3Pb-induced [3H]DA release was 5-fold greater than that observed for [3H]ACh or [3H]GABA release. Removal of [Ca2+]e did not alter the Et3Pb-induced increase in the release of these three transmitter substances, nor did Et3Pb alter synaptosomal 45Ca efflux. EtePb-induced [3H]ACh and [3H]GABA release, but not [3H]DA release, was blocked by lowering [Na+]e from 140 to 50 mM. Similarly, the release of [3H]ACh and [3H]GABA, but not [3H]DA, induced by either Na,K-ATPase inhibition or veratridine (a Na(+)-ionophore), was attenuated by lowering [Na+]e from 140 to 50 mM. However, Et3Pb did not inhibit isolated synaptic membrane Na,K-ATPase, nor did the magnitude or temporal patterns of Et3Pb-induced transmitter release resemble transmitter release induced by Na,K-ATPase inhibition. Et3Pb and veratridine, but not Na,K-ATPase inhibition, produced an increase in synaptosomal [3H] deoxyglucose phosphate (dGluP) efflux, suggesting that both compounds increase membrane permeability. A Et3Pb-induced increase in membrane permeability is further supported by electrophysiological studies using the frog neuromuscular junction in which Et3Pb was found to reduce both the input resistance and membrane potential of muscle cells. As with [3H]ACh and [3H]GABA release, the Et3Pb-induced increase in synaptosomal [3H]dGluP efflux was attenuated by lowering [Na+]e.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-term effect of antidepressant drugs and electroconvulsive shock on brain alpha 1-adrenoceptors following destruction of noradrenergic or serotonergic nerve terminals

Antidepressant drugs and electroconvulsive shock (ECS) given repeatedly increase the density of brain alpha 1-adrenoceptors. However, the mechanism involved in this effect is unknown. To study the role of presynaptic noradrenaline (NA) and 5-hydroxytryptamine (5-HT) nerve terminals in the above phenomenon we examined the density of [3H]prazosin binding sites in the rat cerebral cortex following a prolonged treatment with imipramine and citalopram (10 mg/kg po, twice daily for 14 days) or ECS (once daily for 8 days) in animals pretreated with DSP-4 (62.5 mg/kg ip) and p-chloroamphetamine (PCA, 2 x 10 mg/kg ip). In normal rats imipramine, citalopram and ECS increased the density (Bmax) of [3H]prazosin binding sites by 30, 25 and 19%, respectively. DSP-4 pretreatment abolished the effect of imipramine and citalopram but not that of ECS. Pretreatment with PCA influenced the effect of neither antidepressant drugs nor ECS. Our results indicate that the "up-regulation" of alpha 1-adrenoceptors induced by imipramine and citalopram, but not by ECS, depends on intact NA nerve terminals. They also show that the 5-HT system is not involved in the above phenomenon.     

AHR-16303B, a novel antagonist of 5-HT2 receptors and voltage-sensitive calcium channels.

In vivo and in vitro methods were used to characterize AHR-16303B, a novel compound with antagonistic action at 5-HT2 receptors and voltage-sensitive calcium channels. The 5-HT2 receptor-antagonistic properties of AHR-16303B were demonstrated by inhibition of (a) [3H]ketanserin binding to rat cerebral cortical membranes (IC50 = 165 nM); (b) 5-hydroxytryptamine (5-HT)-induced foot edema in rats (minimum effective dose, (MED) = 0.32 mg/kg orally, p.o.); (c) 5-HT-induced vasopressor responses in spontaneously hypertensive rats (SHR) (ID50 = 0.18 mg/kg intravenously (i.v.), 1.8 mg/kg p.o.), (d) 5-HT-induced antidiuresis in rats (MED = 1 mg/kg p.o.), and (e) platelet aggregation induced by 5-HT + ADP (IC50 = 1.5 mM). The calcium antagonist properties of AHR-16303B were demonstrated by inhibition of (a) [3H]nimodipine binding to voltage-sensitive calcium channels on rabbit skeletal muscle membranes (IC50 = 15 nM), (b) KCl-stimulated calcium flux into cultured PC12 cells (IC50 = 81 nM), and (c) CaCl2-induced contractions of rabbit thoracic aortic strips (pA2 = 8.84). AHR-16303B had little or no effect on binding of radioligands to dopamine2 (DA2) alpha 1, alpha 2, H1, 5-HT1 alpha, beta 2, muscarinic M1, or sigma opioid receptors; had no effect on 5-HT3 receptor-mediated vagal bradycardia; and had only minor negative inotropic, chronotropic, and dromotropic effects on isolated guinea pig atria. In conscious SHR, 30 mg/kg p.o. AHR-16303B completely prevented the vasopressor responses to i.v. 5-HT, and decreased blood pressure (BP) by 24% 3 h after dosing.     

Effects of acetaminophen on monoaminergic systems in the rat central nervous system

Although acetaminophen is a well established analgesic, its mechanism of action is still unknown. We investigated whether this drug could affect central monoaminergic neurotransmission in rats. Significant increases in serotonin (5-HT) levels were found in the posterior cortex, hypothalamus, striatum, hippocampus and brain stem, but not spinal cord, 45 min after per os administration of 200-400 mg/kg of acetaminophen. However, this treatment altered neither the levels of 5-hydroxyindoleacetic acid nor the accumulation of 5-hydroxytryptophan after blockade of aromatic L-amino acid decarboxylase. On the other hand, a decrease in both the levels of the dopamine (DA) metabolite, dihydroxyphenylacetic acid, and the accumulation of dihydroxyphenylalanine were noted in the striatum of acetaminophen-treated rats. Finally, acetaminophen administration significantly increased noradrenaline (NA) levels in the posterior cortex. In vitro studies showed that acetaminophen (1 mM) enhanced K+-evoked overflow of [3H]5-HT, but not [3H]DA and [3H]NA, previously taken up in brain slices, and exerted no direct effect on monoamine oxidase A, tyrosine hydroxylase and catechol-O-methyl-transferase activities. These results indicate that acetaminophen affects central monoaminergic neurotransmission, thereby suggesting that monoamines (especially 5-HT) might participate in its analgesic action.     

Studies on the mechanism of wet dog shakes produced by carbachol in rats

In an attempt to elucidate the mechanism of wet dog shakes (WDS) produced by carbachol administered into the rat lateral brain ventricle, the effects of blockade of muscarinic and nicotinic receptors on shaking response and the effects of carbachol on central catecholaminergic, serotonergic (5-HT) and GABAergic functions were studied in rats. The muscarinic receptor antagonists, atropine and scopolamine attenuated WDS produced by carbachol, whilst a peripherally active muscarinic receptor antagonist, scopolamine methyl nitrate, failed to influence WDS. The nicotine antagonist, mecamylamine, did not affect WDS caused by carbachol either. Carbachol dose dependently decreased brain concentration of noradrenaline (NA) but failed to affect the concentration of dopamine (DA). While the brain concentration of 5-HT was unchanged, the concentration of 5-hydroxyindoleacetic acid (5-HIAA) was increased in a dose-related manner. The catecholamine turnover times were unaffected whereas 5-HT turnover time was significantly prolonged. Atropine, but not mecamylamine, prevented the decrease in brain NA induced by carbachol. Consequently, the carbachol-induced enhancement in the level of 5-HIAA was completely blocked by atropine and only slightly influenced by mecamylamine. Neither brain GABA concentration nor glutamic acid decarboxylase activity were affected by carbachol. Behavioral and biochemical data suggest that WDS produced by carbachol may be mediated through the stimulation of central muscarinic receptors. The anatomical localization and exact mechanism of carbachol-induced WDS remain to be elucidated.     

Heterogeneity of muscarinic autoreceptors and heteroreceptors in the rat brain: effects of a novel M1 agonist, AF102B

The effects of oxotremorine and AF102B (cis-2-methylspiro-(1,3-oxathiolane-5,3')-quinuclidine), a novel M1-selective muscarinic agonist, on acetylcholine (ACh) and dopamine (DA) release from superfused rat hippocampal and striatal synaptosomes were investigated. Synaptosomes that had been prelabeled with [3H]choline or [3H]DA were depolarized by high K+. Oxotremorine and AF102B decreased the K+-evoked [3H]ACh release from hippocampal synaptosomes and increased the K+-evoked [3H]DA release from striatal synaptosomes. The dose-response curves showed that AF102B was far less potent than oxotremorine at the hippocampal presynaptic muscarinic receptors (autoreceptors). On the other hand, AF102B was more potent than oxotremorine at the muscarinic receptors on the striatal dopaminergic terminals (heteroreceptors). Pirenzepine, a selective M1 antagonist, counteracted the effects of oxotremorine on [3H]DA release more potently than it did the effects of oxotremorine on [3H]ACh release. Our results suggest that AF102B and pirenzepine discriminate pharmacologically between muscarinic autoreceptors and heteroreceptors.     

Ventral pallidal extracellular fluid levels of dopamine, serotonin, gamma amino butyric acid, and glutamate during cocaine self-administration in rats

RATIONALE: Dopamine innervation of the nucleus accumbens is thought to have a major role in the biological processes underlying cocaine self-administration. Recent data suggest that dopamine innervation of the ventral pallidum (VP) may also play an important role. OBJECTIVES: This experiment was initiated to assess extracellular fluid levels of dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and glutamate (Glu) in the VP of rats self-administering cocaine using in vivo microdialysis. METHODS: Rats were implanted with intravenous jugular catheters and a microdialysis probe guide cannula into the VP and trained to self-administer (SA) three different doses of cocaine during each daily session. Other rats (yoked rats) were surgically prepared in identical fashion and received vehicle infusions during microdialysis sessions when the SA rat to whom they were yoked produced cocaine infusions. When stable baselines of self-administration were obtained, microdialysates were collected during two consecutive daily self-administration sessions. Neurotransmitter levels were measured using HPLC with electrochemical (DA and 5-HT) or fluorescence detection (GABA and Glu). RESULTS: In SA rats, extracellular fluid levels of DA [DA]e and 5-HT [5-HT]e were elevated throughout the session and levels of Glu [Glu]e showed small increases at a few isolated time points during the session. The increases in [DA]e and 15-HT]e were dose-dependent. Extracellular fluid levels of GABA [GABA]e were unchanged, as were levels of all four neurotransmitters in the yoked rats. CONCLUSIONS: These data support a potential role for DA and 5-HT innervations of the VP in intravenous cocaine self-administration.     

Asenapine: a novel psychopharmacologic agent with a unique human receptor signature

Asenapine is a novel psychopharmacologic agent under development for the treatment of schizophrenia and bipolar disorder. We determined and compared the human receptor binding affinities and functional characteristics of asenapine and several antipsychotic drugs. Compounds were tested under comparable assay conditions using cloned human receptors. In comparison with the antipsychotics, asenapine showed high affinity and a different rank order of binding affinities (pKi) for serotonin receptors (5-HT1A [8.6], 5-HT1B [8.4], 5-HT2A [10.2], 5-HT2B [9.8], 5-HT2C [10.5], 5-HT5 [8.8], 5-HT6 [9.6] and 5-HT7 [9.9]), adrenoceptors (alpha1 [8.9], alpha2A [8.9], alpha2B [9.5] and alpha2C [8.9]), dopamine receptors (D1 [8.9], D2 [8.9], D3 [9.4] and D4 [9.0]) and histamine receptors (H1 [9.0] and H2 [8.2]). It had much lower affinity (pKi相似文献