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PubMed1988

Experimental evidence that tryptamine alkaloids do not cause Phalaris aquatica sudden death syndrome in sheep.

The acute toxicity for sheep of 3 alkaloids that occur in Phalaris acquatica was examined by intravenous and oral administration. The lowest tested dose rates that produced clinically observed signs were, for 5-methoxy dimethyltryptamine, 0.1 mg/kg body weight intravenously and 40 mg/kg orally; for gramine, 10 mg/kg intravenously and 500 mg/kg orally; and for hordenine, 20 mg/kg intravenously and 800 mg/kg orally. All induced the clinical signs observed in the nervous form of phalaris toxicity, but none induced the cardiac, sudden death, syndrome.

Alkaloids↗
PubMed1990

The pathogenesis of the nervous syndrome of Phalaris aquatica toxicity in sheep.

The clinical signs displayed by 96 sheep affected by the nervous syndrome of Phalaris aquatica toxicity and 10 normal sheep injected intravenously with the phalaris alkaloid, 5-methoxy dimethyltryptamine (dose range 0.01 to 5.0 mg/kg), were observed. The distributions of phalaris indole-like cytoplasmic pigments in nuclei of the brains and spinal cords of 9 naturally affected sheep were determined microscopically. Based on the relationship between clinical signs and the central nervous system nuclei involved in their production, the distribution of phalaris indole-like pigments, and the pharmacology of dimethylated tryptamines, it is suggested that the nervous syndrome induced by Phalaris aquatica results from a direct action of phalaris alkaloids upon serotonergic receptors in specific brain and spinal cord nuclei.

Alkaloids↗
PubMed1985

Ascorbic acid antagonizes the behavioural effects of LSD in cats.

Pretreatment with ascorbic acid (500 mg kg-1 i.p.) antagonized the behavioural effects of lysergic acid diethylamide (LSD) and apomorphine, but not 5-methoxy-N,N-dimethyltryptamine, in cats. The data support the hypothesis that these behavioural effects in cats are due to drug action at both 5-HT and dopamine receptors, and that the action of LSD at dopamine receptors is modulated by ascorbic acid.

Animals↗
PubMed1985

Antagonism of 5-methoxy-N,N-dimethyltryptamine-induced changes in postdecapitation convulsions in rats by repeated treatment with drugs enhancing 5-hydroxytryptamine neurotransmission.

Repeated administration of drugs that increase tryptaminergic neurotransmission antagonized the increase in latency to onset and the duration of postdecapitation convulsions (PDCs) induced by an acute 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) injection; Zimelidine (2 X 5 mg kg-1), fluoxetine (2 X 5 mg kg-1), amiflamine (2 X 2.5 mg kg-1) and alpha-ethyltryptamine (2 X 2.5 mg kg-1) administered orally over 10 days caused a substantial blockade of the increase in latency to onset and duration of PDCs following 5-MeODMT, whereas alaproclate (2 X 5 mg kg-1), clorgyline (1 X 1 mg kg-1) and pargyline (2 X 2.5 mg kg-1) caused a lesser blockade. Repeated 5-MeODMT (3 X 2 mg kg-1) administration blocked the acute effects of 5-MeODMT (2 and 4 mg kg-1) upon PDCs completely. These findings indicate down-regulation of the 5-hydroxytryptamine receptors which mediate the action of 5-MeODMT on the PDCs and offer a simple model system for studying 5-HT receptor sensitivity changes at the spinal level.

Animals↗
PubMed1990

Increased dopamine turnover in the ventral striatum by 8-OH-DPAT administration in the rat.

The administration of the 5-HT1A agonist 8-OH-DPAT (0.8 mumols kg-1 s.c.-40 min) produced an increase in dopamine (DA) turnover, estimated by the quotient (DOPAC + HVA) DA-1, in the ventral striatum of the rat. No statistically significant effects were obtained in the dorsal striatum. The accumulation of 3-MT in pargyline-treated animals (375 mumols kg-1 s.c.-60 min) was not affected by 8-OH-DPAT treatment (0.15-2.4 mumols kg-1 s.c.-30 min). These findings indicate that 8-OH-DPAT has weak antagonist properties at striatal DA receptors in normal rats. Both the 5-HT1A agonist flesinoxan (0.06-17.8 mumos kg-1 s.c. -50 min) and the mixed 5-HT1 and 5-HT2 agonist 5-MeODMT (1.6-26.0 mumols kg-1 s.c.-50 min) produced a decrease in forebrain 5-HTP accumulation (striatum and neocortex), following decarboxylase inhibition by means of NSD-1015 in reserpine treated rats, indicating stimulation of central 5-HT receptors by these two compounds. At the same time, the DOPA accumulation by the ventral striatum was decreased by flesinoxan and increased by 5-MeODMT treatment. These observations show that, under these conditions, the decrease in DA synthesis is not directly coupled to the decreased 5-HT synthesis produced by flesinoxan, as previously demonstrated for 8-OH-DPAT. Taken together with previous observations, the present results suggest that 8-OH-DPAT, depending on the experimental conditions, is an agonist or antagonist at striatal DA receptors, in all probability due to partial DA receptor agonist properties of the compound.

5-Hydroxytryptophan↗
PubMed1984

Indoleamine-mediated reciprocal modulation of on-centre and off-centre ganglion cell activity in the retina of the cat.

The effects of applying the indoleamines serotonin (5-hydroxytryptamine) and 5-methoxy-N,N-dimethyltryptamine (MDT) ionophoretically onto cat retinal ganglion cells were studied in the optically intact eye of the cat. Serotonin suppressed both the spontaneous activity and light-evoked discharge of on-centre ganglion cells, regardless of the visual stimulus used; on the other hand, it enhanced the activity of off-centre ganglion cells. MDT produced the opposite effects, i.e. it enhanced the activity of on-centre ganglion cells but suppressed that of off-centre ganglion cells. Much of the effect of serotonin on light-evoked discharge can be attributed to an alteration of maintained discharge. There was no major difference in the way brisk-sustained (X) and brisk-transient (Y) cells responded to the application of serotonin and MDT, although the effects of the indoleamines on brisk-transient (Y) cells were generally weaker than on brisk-sustained (X) cells. In view of the fact that the action of serotonin is similar to the action of a gain control system, a possible contribution of indoleamine-accumulating neurones to gain control in the cat retina is discussed.

Action Potentials↗
PubMed2005

Lecozotan (SRA-333): a selective serotonin 1A receptor antagonist that enhances the stimulated release of glutamate and acetylcholine in the hippocampus and possesses cognitive-enhancing properties.

Recent data has suggested that the 5-hydroxytryptamine (5-HT)(1A) receptor is involved in cognitive processing. A novel 5-HT(1A) receptor antagonist, 4-cyano-N-{2R-[4-(2,3-dihydrobenzo[1,4]-dioxin-5-yl)-piperazin-1-yl]-propyl}-N-pyridin-2-yl-benzamide HCl (lecozotan), which has been characterized in multiple in vitro and in vivo pharmacological assays as a drug to treat cognitive dysfunction, is reported. In vitro binding and intrinsic activity determinations demonstrated that lecozotan is a potent and selective 5-HT(1A) receptor antagonist. Using in vivo microdialysis, lecozotan (0.3 mg/kg s.c.) antagonized the decrease in hippocampal extracellular 5-HT induced by a challenge dose (0.3 mg/kg s.c.) of 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT) and had no effects alone at doses 10-fold higher. Lecozotan significantly potentiated the potassium chloride-stimulated release of glutamate and acetylcholine in the dentate gyrus of the hippocampus. Chronic administration of lecozotan did not induce 5-HT(1A) receptor tolerance or desensitization in a behavioral model indicative of 5-HT(1A) receptor function. In drug discrimination studies, lecozotan (0.01-1 mg/kg i.m.) did not substitute for 8-OH-DPAT and produced a dose-related blockade of the 5-HT(1A) agonist discriminative stimulus cue. In aged rhesus monkeys, lecozotan produced a significant improvement in task performance efficiency at an optimal dose (1 mg/kg p.o.). Learning deficits induced by the glutamatergic antagonist MK-801 [(-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate] (assessed by perceptually complex and visual spatial discrimination) and by specific cholinergic lesions of the hippocampus (assessed by visual spatial discrimination) were reversed by lecozotan (2 mg/kg i.m.) in marmosets. The heterosynaptic nature of the effects of lecozotan imbues this compound with a novel mechanism of action directed at the biochemical pathologies underlying cognitive loss in Alzheimer's disease.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

Single-unit responses of serotonergic neurons to vasoactive drug administration in behaving cats.

Single-unit activity of serotonergic neurons in the dorsal raphe nucleus (DRN), heart rate (HR), and arterial blood pressure were recorded in freely moving cats during spontaneous behavior and in response to systemic administration of vasoactive drugs. The activity of serotonergic neurons varied in association with behavioral arousal but was unrelated to spontaneous fluctuations in HR and blood pressure. Bolus administration of phenylephrine hydrochloride and sodium nitroprusside (15-20 micrograms/kg iv) produced a rapid transient increase (35 mmHg) and decrease (49 mmHg), respectively, in mean arterial pressure (MAP). Infusion of phenylephrine and sodium nitroprusside (100 micrograms/ml) produced sustained hypertension (avg MAP 166 mmHg) and hypotension (avg MAP 49 mmHg), respectively. The activity of serotonergic neurons was not significantly altered in response to phenylephrine or sodium nitroprusside administration. Furthermore, no significant changes in unit activity were observed after hydralazine administration (1 mg/kg iv) despite prolonged reflex activation of sympathetic outflow. Thus the activity of DRN serotonergic neurons was unrelated to transient alterations in blood pressure and baroreceptor activity. These results suggest that changes in the activity of serotonergic DRN neurons are not involved in physiological mechanisms underlying reflex alterations in sympathetic (and parasympathetic) outflow invoked by hypertension and hypotension.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1986

Evidence for multiple serotonergic influences on LH release in ovariectomized rats and for modulation of their relative effectiveness by estrogen.

Both opiates and serotonin (5HT) are known to inhibit LH release in ovariectomized rats, and estrogen has been shown to reverse certain serotonergic effects. Therefore studies were undertaken to compare the effects of morphine and the serotonin agonist 5-methoxy-N,N-dimethyltryptamine (5MEODMT) on LH release in ovariectomized rats with and without estrogen priming. Serial blood samples were collected via jugular cannulae before and 5, 15, 30 and 60 min after intravenous administration of morphine, 5MEODMT or both to rats receiving no pretreatment, or a serotonin receptor antagonist (methysergide, METH; or ketanserin, KET) 60 min earlier. In the absence of estrogen, morphine inhibited LH release, and the response was delayed by METH or abolished by KET, suggesting mediation by serotonin2 (5HT2) receptors. 5MEODMT alone failed to alter the release of LH significantly, but apparently activated both stimulatory and inhibitory serotonergic systems. Blockade of 5HT2 receptors with KET enabled an inhibitory system to prevail. No significant changes in LH concentrations were observed following combined administration of morphine and 5MEODMT. Similarly, in estrogen-primed rats morphine appeared to activate both inhibitory (5HT2) and stimulatory (5HT1) systems, resulting in no net change unless the inhibitory system had been antagonized by KET. Administration of 5MEODMT alone or in combination with morphine resulted in a strong stimulatory effect which appeared to be mediated by 5HT1 receptors. These results suggest the existence of a multiplicity of serotonergic influences on the release of LH in the rat, not only in terms of particular species of 5HT receptors, but also in neuronal connectivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Hypotensive spinal serotonergic effect. Are S1 or S2 receptors involved?

Since previous data obtained in anesthetized rats supported the idea that the activation of spinal serotonergic receptors induced a hypotensive effect, it was decided to characterize more closely the serotonergic spinal involvement and to elucidate the serotonergic receptor type involved in this effect. After female Wistar rats were anesthetized, the femoral artery (for blood pressure measurement) and vein (for parenteral injection of drugs) were cannulated. An intrathecal catheter was positioned with the tip at the T6-L3 intervertebral space. The results showed that the dose-dependent decrease in mean blood pressure induced by serotonin administered at the T6-L3 level was prevented by giving the serotonergic S2 antagonist ritanserin intravenously. The intravenous administration of 5-methoxy-N,N-dimethyltryptamine, a direct serotonergic agonist, induced a dose-dependent hypotension previously shown to originate at spinal cord level. This effect was prevented by intrathecal administration of ketanserin, an S2-receptor antagonist. The selective agonist of the S1-type receptors, 8-hydroxy-dipropylaminotetralin, given at the same level of the spinal cord, failed to induce any effect on mean blood pressure. The results suggest that the hypotensive effect obtained after the spinal serotonergic activation involves serotonin receptors of the S2 type.

Animals↗
PubMed2004

Mechanism of action of aripiprazole predicts clinical efficacy and a favourable side-effect profile.

The antipsychotic efficacy of aripiprazole is not generally associated with extrapyramidal symptoms, cardiovascular effects, sedation or elevations in serum prolactin that characterize typical or atypical antipsychotics. The aim of this study was to clarify the mechanism of action of aripiprazole that underlies its favourable clinical profiles. The preclinical efficacy and side-effect profiles of aripiprazole were evaluated using several pharmaco-behavioural test systems in mice and rats, both in vivo and ex vivo, and compared with those of other conventional and atypical antipsychotics. Each of the antipsychotics induced catalepsy and inhibited apomorphine-induced stereotypy. The catalepsy liability ratios for these drugs were 6.5 for aripiprazole, 4.7 for both olanzapine and risperidone. The ptosis liability ratios for aripiprazole, olanzapine and risperidone were 14, 7.2 and 3.3, respectively. Aripiprazole slightly increased DOPA accumulation in the forebrain of reserpinised mice, reduced 5-HTP accumulation at the highest dose and exhibited a weaker inhibition of 5-methoxy-N,N-dimethyl-tryptamine-induced head twitches. Aripiprazole did not inhibit physostigmine- or norepinephrine-induced lethality in rats. In conclusion, aripiprazole shows a favourable preclinical efficacy and side-effect profile compared to a typical antipsychotics. This profile may result from its high affinity partial agonist activity at D2 and 5-HT1A receptors and its antagonism of 5-HT2A receptors.

Animals↗
PubMed1987

Two kinds of modification by 5-methoxy-N,N-dimethyltryptamine of contractile responses to electrical stimulation of isolated guinea-pig vas deferens.

Two kinds of electrical stimulation, low frequency stimulation (5 Hz, 1 msec, 5 pulses, every 20 sec) and high frequency stimulation (30 Hz, 0.1 msec, 20 pulses, every 20 sec), produced contractions in isolated guinea-pig vas deferens. These responses were blocked by alpha, beta-methylene-ATP, but not prazosin. Phentolamine potentiated the contractions produced by low frequency stimulation, while it had little or no effect on the contractions produced by high frequency stimulation. The effect of 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), a potent short acting hallucinogen, on the contractile response to two kinds of electrical stimulation was examined. On the contraction produced by low frequency stimulation, 5-MeODMT showed a biphasic action. 5-MeODMT at concentrations of 3 X 10(-8)-10(-6) M reduced the contractile response. 5-MeODMT at concentrations of 3 X 10(-6)-2 X 10(-5) M potentiated the contractile response, and this potentiation was reversed by prazosin and ketanserin. Clonidine caused an inhibition of the contractile response to low frequency stimulation. This action of clonidine was reversed by 5-MeODMT. The reverse action of 5-MeODMT was greatly inhibited in the presence of prazosin and ketanserin. The results suggest that 5-MeODMT exerts two different kinds of modification on the contractile response to low frequency stimulation of isolated guinea-pig vas deferens: in one type of modification, 5-MeODMT at concentrations higher than 3 x 10(-8) M exerts an action similar to that of 5-hydroxytryptamine on postganglionic sympathetic nerve terminals and reduces the release of transmitter presynaptically, and in the other type, 5-MeODMT at concentrations higher than 3 x 10(-6) M causes the release of noradrenaline from postganglionic sympathetic nerve terminals.

Adenosine Triphosphate↗
PubMed1987

Thyrotrophin releasing hormone--5-hydroxytryptamine interactions in the brain studied using chronic immunization and chemical lesioning techniques.

This study investigates the effects of chemically lesioning 5-hydroxytryptamine (5HT) neurones and chronic passive immunization of central thyrotrophin releasing hormone (TRH) on 5HT and TRH mediated behavioural responses. 5HT lesions produced by 5,7-dihydroxytryptamine (5,7-DHT) enhanced the behavioural response produced by the 5HT receptor agonist 5-methoxy-N,N-dimethyltryptamine (5-MEODMT) while decreasing the locomotor hyperactivity observed following administration of the TRH analogue CG 3509 but having no effect on the reversal of pentobarbitone sleep-time produced by CG 3509. Chronic intracerebroventricular infusion of the purified TRH antibody markedly increased the length of pentobarbitone-induced sleep-time while enhancing the effects of CG 3509 both on locomotor activity and pentobarbitone-induced sleep. TRH antibody infusion also increased the response produced by 5-MEODMT. The results indicate that chronic passive immunization of central TRH induces changes in TRH receptor responsiveness and that there is a functional interaction between TRH and 5HT neuronal systems.

Animals↗
PubMed1999

Are there non-monoaminergic paradoxical sleep-off neurons in the brainstem?

Using extracellular single unit recording in the medulla of freely moving cats, we have found a population of PS-off ("Type II") neurons that are distinct from the classically described monoaminergic PS-off ("Type I") neurons. The presumed non-monoaminergic Type II PS-off neurons (n=22) showed a relatively high rate of tonic discharge during both quiet waking and slow-wave sleep (10.4+/-4.1 and 9.3+/-3.1 spikes/sec, mean +/- S.D., respectively) and a marked overall decrease in discharge rate during PS (0.3+/-0.4 spikes/sec). In contrast to the presumed monoaminergic PS-off neurons (n=62), Type II PS-off neurons showed short-lasting phasic discharges during PS, often in association with rapid eye movement and PGO wave bursts. These Type II neurons were all characterized by a short action potential which was significantly different from that of the monoaminergic PS-off neurons described so far. Five out of 22 neurons were identified antidromically by stimulation of the ventrolateral reticulospinal tract (vlRST) at the caudal medulla, while 2 of the 22 were identified antidromically by stimulation of the peri-locus coeruleus alpha of the mediodorsal pontine tegmentum. Their mean conduction velocity (7.2+/-1.9 m/sec) was significantly higher than that (0.9+/-0.3 m/sec) of the presumed monoaminergic PS-off neurons which were identified exclusively by stimulation of the vlRST. In addition, when examined during the sleep-waking cycle, the antidromic responses of Type II PS-off neurons were either completely blocked or reduced, with a prolongation of antidromic latency during PS. Most of these neurons were located in medullary structures containing no, or virtually no, monoaminergic neurons, and none responded by inhibition to systemic administration of serotonergic or adrenergic autoreceptor agonists. These findings indicate the existence, in the medulla, of non-monoaminergic PS-off neurons that would play an important role in PS generation.

Action Potentials↗
PubMedDate not supplied

Modulation of the 5-HT1C receptor-mediated behavior by 5-HT2, but not 5-HT1A, receptor activation.

The effects of 5-HT1A-receptor agonists 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) and gepirone, a 5-HT1A/5-HT2-receptor agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) and a 5-HT2-receptor agonist (+-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ((+/)DOI) on the 5-HT1C-receptor-mediated exploratory hypoactivity in rats, induced by m-trifluoromethylphenylpiperazine (TFMPP) or m-chlorophenylpiperazine (m-CPP), were studied in the open field test. (+/-)DOI attenuated the effects of TFMPP and abolished those of m-CPP (not dose-dependently). 5-MeODMT showed a weak antagonistic action only at one, intermediate dose. The effects of TFMPP or m-CPP were not changed by 8-OH-DPAT or gepirone. At the same time, 8-OH-DPAT, gepirone, 5-MeODMT and (+/-)DOI themselves practically did not change the exploratory activity of rats. The obtained results permit an assumption that a functional interaction exists between 5-HT1C- and 5-HT2-receptors, but not between 5-HT1C- and 5-HT1A-ones.

8-Hydroxy-2-(di-n-propylamino)tetralin↗