Dopaminergic activity of quipazine

Time- and dose-dependent effects of the serotonergic agent quipazine on regional cerebral metabolism in rats

The time course and the relation to dose of regional cerebral metabolic rates for glucose (rCMRglc) were measured in awake male adult Fischer-344 rats after administration of quipazine, a serotonin 5-HT2-3 receptor agonist. rCMRglc was determined, using the quantitative autoradiographic [14C]deoxyglucose technique, in 92 brain regions at 30, 60, 90 and 120 min after quipazine 20 mg/kg i.p. and at 60 min after quipazine 5 mg/kg i.p. Peak metabolic effects were observed 60 min after quipazine 20 mg/kg i.p. when rCMRglc was significantly elevated in 27 (29%) brain regions (mean rise 17%). Quipazine increased rCMRglc in brain regions with high densities of 5-HT3 receptors (area postrema, olfactory tubercle, amygdala), in dopaminergic nuclei (substantia nigra pars compacta and pars reticulata) and terminal fields of their projections (zona incerta, subthalamic nucleus, preoptic magnocellular area, nucleus of facial nerve). The topographic distribution and direction of rCMRglc changes induced by quipazine are different from those produced by the 5-HT2 agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and, consistent with the pharmacological and binding properties of quipazine, suggest a preferential activation of 5-HT3 receptors.

Further evidence that prolactin secretion in adult female rats is differently modified after neonatal estrogenization or androgenization: responses to methysergide, quipazine, and pizotifen

The role of the serotoninergic system in the control of prolactin secretion was investigated in adult female rats treated on the first day of life with estradiol benzoate (EB) (100 micrograms), testosterone propionate (TP) (25 or 100 micrograms), or olive oil. Blood of rats was obtained through a chronic intraatrial cannula at 0, 30, 60, 90, and 120 min after the IP administration of the serotoninergic blockers methysergide (0.75, 2.5, and 7.5 mg/kg) or pizotifen (2 mg/kg), the agonist quipazine (3 or 30 mg/kg), or saline. We have found that 1) the anovulatory syndrome induced by EB or 100 micrograms injection of TP was associated with hyperprolactinaemia, whereas normal prolactin concentrations in plasma were observed in females injected with 25 micrograms of TP; 2) methysergide administration increased plasma prolactin concentrations in control and androgenized females but not in the estrogenized ones. This different response may be related to the antidopaminergic action of methysergide, because both estrogenized and androgenized females responded similarly after pizotifen injection; 3) after quipazine injection, an initial stimulation was observed in females injected with estradiol or 100 micrograms of TP, but not in other groups, whereas a delayed inhibition occurred in androgenized females. These results suggest that the effects of estrogenization and androgenization on both the dopaminergic and serotoninergic control of prolactin secretion are qualitatively different.

Possible serotonergic and dopaminergic mediation of the N-ethyl-3,4-methylenedioxyamphetamine discriminative stimulus

Eight male rats previously trained to discriminate 2.0 mg/kg N-ethyl-3,4-methylenedioxyamphetamine (MDE) from its vehicle in a two-lever, food motivated task were utilized to characterize the stimulus properties of MDE. The 5-HT receptor agonists 1-(m-trifluoromethylphenyl)piperazine (TFMPP), quipazine and 6-methoxy-1,2,3,4 tetrahydro-beta-carboline were able to generalize to the stimulus produced by MDE. However, the 5-HT receptor agonists m-chlorophenylpiperazine (mCPP), buspirone and norfenfluramine, the dopamine receptor agonist amphetamine, as well as the acetylcholine receptor agonist arecoline did not completely generalize. In addition, the simultaneous administration of norfenfluramine and amphetamine generalized to MDE. Pretreatment with the serotonin receptor antagonists cinanserin and metergoline or the dopamine receptor antagonist haloperidol failed to completely inhibit the discriminative stimulus produced by MDE. Multiple p-chlorophenylalanine (PCPA) pretreatments significantly reduced MDE discrimination, whereas vehicle discrimination was unaffected. Five days following cessation of PCPA pretreatment, MDE discrimination returned to criterion levels and remained at that level. These results suggest that the stimulus produced by MDE involve a complex interaction of various neurotransmitters, with both serotonergic and dopaminergic components.

Serotonin, dopamine, noradrenaline and their metabolites: levels in the brain of the house cricket (Acheta domesticus L.) during a 24-hour period and after administration of quipazine--a 5-HT2 receptor agonist

1. The levels of 5-HT, DA, NA and DA metabolites (NADA, DOPAC) measured by HPLC (with electrochemical detection) in the brain of the house cricket did not change over a 24-hr period. The level of 5-HIAA, a 5-HT metabolite, was below the limit of detection. 2. The 5-HT and DOPAC levels decreased and NADA increased after quipazine injection but DA and NA levels did not change after it. 3. [3H]Ketanserin was used to identify serotonin receptors bound to sites in the house cricket brain with a KD of 5 nM and a concentration of Bmax 180 fmol/mg protein.

Enhanced sensitivity to quipazine in the genetically dystonic rat (dt)

Both normal and genetically dystonic (dt) rats show a high-frequency forepaw tremor in response to systemic administration of the serotonin (5-HT) agonist quipazine at 8 days of age. The response declines with age in normal, but not dystonic, rats. By 16 days of age and after the development of a generalized movement disorder, the dystonic rat exhibits enhanced sensitivity to the tremorogenic effects of the drug in comparison with normal rats. Tremor was blocked by pretreatment with ketanserin, suggesting that it is mediated by 5-HT2 receptors. The dystonic rat has previously been shown to be insensitive to the tremorogenic effects of harmaline, a drug presumed to act indirectly through serotonergic neurons. This finding, coupled with the increased sensitivity to quipazine, suggests the presence of an abnormality in serotonergic systems in the mutants. Since there is evidence of abnormality in the olivo-cerebellar system in the dystonic rat, the alternative hypothesis that a nonserotonergic defect in the olivo-cerebellar system accounts for both the failure of behavioral response to harmaline and the persistent expression of a response to quipazine is also discussed.

Three-choice discrimination among (+)-amphetamine, fenfluramine and saline in pigeons

Five pigeons were trained to discriminate among (+)-amphetamine (AMPH; 1.7 or 3.0 mg/kg), fenfluramine (FEN; 5.6 or 10 mg/kg), and saline using a three-choice drug discrimination procedure. The results of the study demonstrated that a reliable discrimination between AMPH and FEN could be obtained and the discriminative stimulus (DS) effects of these two drugs did not overlap, i.e., were mutually exclusive. Phenmetrazine produced a dose-related increase in AMPH-appropriate responding with no responding occurring on the FEN-appropriate key. Two serotonin agonists, quipazine (5-HT2) and MK 212 (5-HT1), produced FEN-appropriate responding in two of three pigeons, while a third pigeon responded predominantly on the AMPH-appropriate key following their administration. In contrast, phencyclidine produced predominantly (greater than 50%) saline-appropriate responding, indicating that the DS effect of phencyclidine was unlike either AMPH or FEN. Finally, compounds known to have multiple DS properties such as MDA and MDMA were tested. The results with these compounds confirmed that these drugs have complex DS effects both within and across individual pigeons.

5HT-2 mediation of acute behavioral effects of hallucinogens in rats

In rats tested during their first exposure to a Behavioral Pattern Monitor chamber, acute injections of the 5HT-2 agonists mescaline, quipazine, 2,5-dimethoxy-4-iodoamphetamine (DOI), 2,5-dimethoxy-4-methylamphetamine (DOM), or 2,5-dimethoxy-4-ethylamphetamine (DOET) produced an inhibition of locomotor and investigatory behavior during the first 30 min of the test session. This suppression of exploratory behavior was attenuated when rats were familiarized with the testing chamber prior to the administration of DOI. Hence, as previously observed with both LSD and DOM, 5HT-2 agonists appear to potentiate the normal neophobic reaction to a novel environment. The mixed 5HT-1 and 5HT-2 agonist 5-methoxy-N,N-dimethyltryptamine (5MeODMT) also produced a decrease in activity when animals were tested in the novel environment. However, as previously found with 5HT-1A agonists, this effect was unchanged when animals were tested in the familiar environment and may therefore reflect a generalized sedation. The receptor specificity of these differential effects of 5HT-1 and 5HT-2 agonists in this paradigm was tested by assessing the ability of selective 5HT-2 antagonists to block the effects of the agonists. A dose of the 5HT-2 antagonist ketanserin which had no effect by itself significantly reduced the behavioral effects of mescaline, DOM, and quipazine. Similarly, the selective 5HT-2 antagonist ritanserin blocked the effect of quipazine. In contrast, ketanserin had no significant effect on the suppression of activity produced by the 5HT-1A agonist 8-hydroxy-2(di-n-propylamino)tetralin (8OHDPAT).(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonergic-dopaminergic mediation of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")

A series of three experiments were conducted to investigate the possible serotonergic and dopaminergic mediation of the discriminative stimulus properties of the "designer" drug MDMA. In Experiment 1, rats trained to discriminate 1.5 mg/kg (+/-)-MDMA from its vehicle at 20 min postadministration were shown to generalize to another drug of abuse, N-ethyl-3,4-methylenedioxyamphetamine (MDE) and to the serotonergically-active agents norfenfluramine and TFMPP. In contrast, testing of various dopaminergically-active agonists did not result in MDMA-like responding. In Experiment 2, dopaminergic and serotonergic antagonist were employed to observe their effect upon MDMA discrimination at 20 min postinjection. The serotonin antagonist pirenperone significantly decreased MDMA discrimination, whereas the dopamine decreasing drugs CGS 10746B and haloperidol had no effect. In Experiment 3, another group of rats were trained to discriminate MDMA at 105 min postadministration to investigate if, at this (later) time, the dopaminergic properties of MDMA may be more salient. Indeed, the dopaminergically-active drugs had a heightened effect upon MDMA at this later time, although the serotonergic component of the MDMA discriminative stimulus was predominant. The results suggest that the effects of MDMA at 20 min postadministration are solely serotonergic in nature. At 105 min postinjection there appears to be the presence of a weak dopaminergic component. This biphasic serotonergic-then-dopaminergic action of MDMA may explain the reported human experience with the drug, as well as the often controversial results in the literature.

Neuroleptic-induced reduction of quipazine-elicited head-twitches in rats: possible involvement of striatal dopaminergic supersensitivity

Rats were treated with a single large dose of various neuroleptic compounds and, 5-7 days after, they were assayed for either behavioral sensitivity to apomorphine (hypermotility and stereotyped behavior) or head-twitch response to the mixed serotonin-dopamine agonist quipazine. The animals withdrawn from chlorpromazine, fluphenazine, haloperidol, metoclopramide and the D1 selective blocker SCH 23390, showed enhanced hypermotility and/or stereotyped responses to apomorphine and reduced head-twitch response to quipazine. The rats withdrawn from thioridazine, (-)-sulpiride and sultopride responded to apomorphine only with enhanced hypermotility while their response to quipazine was either unchanged or even increased. The results are discussed in terms of dopaminergic brain areas and/or receptor subtypes involved in the modulation of the head-twitch response to quipazine. We concluded that an enhancement of dopaminergic tone at the striatal level could be related to the reduced head-twitch response to quipazine.

Reduced head-twitch response to quipazine of rats previously treated with methiothepin: possible involvement of dopaminergic system

Methiothepin has been reported to induce an increase of specific binding sites for 3H-5TH 2-3 days following a single administration of a large dose. The present study was intended to ascertain whether methiothepin pretreatment would induce behavioral serotonergic supersensitivity, as assayed by evaluating head-twitch response to quipazine and L-5-hydroxytryptophan (L-5HTP). Methiothepin-pretreated rats exhibited a significantly reduced response after quipazine but not a significant change after L-5HTP. Such findings could be explained by considering that quipazine stimulates both serotonin and dopamine receptors and by hypothesizing that methiothepin also induced dopaminergic supersensitivity which hampered head-twitch behavior. Such an explanation was supported by the following findings. Rats tested 5 days after a large dose of haloperidol exhibited reduced head-twitch response to quipazine. Moreover, rats which had received a single administration of either haloperidol or methiothepin showed (1) more sustained spontaneous locomotor activity, and (2) enhanced stereotyped response to apomorphine.

Effects of selective dopamine receptor agonists in rats trained to discriminate apomorphine from saline

Rats (N = 12) were trained to discriminate apomorphine (0.25 mg/kg, IP) from saline in a two-lever, food-reinforced (FR 30) drug discrimination paradigm. When the discrimination was acquired, various doses of apomorphine as well as several other dopamine receptor agonists were injected before test sessions. Apomorphine (0.03-0.25 mg/kg, IP) produced a dose-related increase in the percent of responses that occurred on the drug lever during test sessions. The selective DA2 receptor agonist piribedil (0.25-8.0 mg/kg, IP) produced a dose-related increase in drug lever responding that was similar to that seen with apomorphine. On the other hand, administration of the selective DA1 receptor agonist SKF 38393 (1.0-32 mg/kg, IP) resulted in principally saline lever responding, even at doses that substantially reduced the rate of responding. Administration of dopamine (1.0-8.0 mg/kg, IP), which does not readily cross the blood-brain barrier, also resulted in principally saline lever responding. These results suggest that the discriminative stimulus properties of apomorphine are based on its action at a receptor that is similar to the DA2 receptor that has been characterized in the periphery and that this receptor is centrally located.

The effects of quipazine and fluoxetine on extinction of a previously-reinforced operant response in rats

Previous studies have shown that treatments that reduce serotonergic neurotransmission lead to enhanced responding during extinction. To evaluate the generality of this effect, the present study examined the effects of the serotonin agonists, quipazine and fluoxetine on responding in extinction. In Experiment 1, 72 rats were trained to lever press on a continuous reinforcement schedule for 5 30-min sessions. Four sessions of extinction followed; 30-min prior to each, 3 groups (n = 16) received quipazine (0, 1.0, 5.0 mg/kg) and 3 groups (n = 8) received fluoxetine (0, 1.0, 5.0 mg/kg). The 5.0 mg/kg dose of quipazine resulted in a significant reduction in responding on day 1; the lower dose of quipazine and both doses of fluoxetine were without significant effect. In Experiment 2, 3 similarly trained groups (n = 8) received either saline or quipazine (5.0 mg/kg) prior to each extinction session; additionally, one quipazine group was injected twice with the 5.0 mg/kg dose in its home cage several days before the beginning of extinction. The results of the drug-naive quipazine group replicated those of that group from Experiment 1 whereas the drug-experienced group showed no significant effect of quipazine in extinction. The results suggested that prior drug experience could modify the effects of quipazine on behaviour. Apart from this drug novelty effect the lack of significant effect of either quipazine or fluoxetine suggested that the effects of manipulations believed to increase and decrease serotonin functioning on responding in extinction may not be symmetrical. These results may be understood with reference to the hypothesis that serotonin plays a role in tuning out or reducing responsiveness to nonreinforced or irrelevant stimuli.

Evidence for a direct dopaminergic effect of lisuride

The discriminative stimulus properties of the clinically important ergot derivative lisuride hydrogen maleate were studied by training 2 groups of rats to discriminate 0.04 mg/kg lisuride from saline and 0.16 mg/kg apomorphine from saline. Dose-response and substitution tests between these groups showed that lisuride and apomorphine are discriminated similarly by both groups and that lisuride is 5 to 9 times more potent. The dopaminergic agonists d-amphetamine, quipazine, bromocriptine, cocaine and cathinone did not substitute for lisuride. In antagonism studies, only the dopamine receptor blocker haloperidol attenuated the lisuride cue; the serotonin receptor blockers pirenperone and BC-105 were ineffective. These data indicate that the primary central action mediating the discriminative stimulus effects of lisuride was direct activation of dopamine receptors.

Effects of metergoline and quipazine on locomotor activity of rats in novel and familiar environments

Many studies have investigated the effects on locomotor activity of various manipulations of the brain's serotonin (5-hydroxytryptamine, 5-HT) systems but the results have not been consistent. However, besides employing different techniques for manipulating brain 5-HT, previous studies have differed in size of apparatus, amount of apparatus pre-exposure and length of session. To test the possibility that apparatus familiarity interacts with the effects of 5-HT manipulations on locomotor activity, this variable was manipulated in groups of rats treated with the 5-HT receptor blocker, metergoline or the agonist, quipazine. Within each drug treatment group, 18 rats had prior experience with the activity monitoring photocell chambers (pre-exposed condition) and 18 were not previously exposed (novel condition); each condition was further subdivided into 3 dose subgroups (n = 6). Testing consisted of 3 30-min sessions with subgroups receiving metergoline (0, 2.5, 5.0 mg/kg) or quipazine (0, 2.5, 5.0 mg/kg) 30 min before. Results with metergoline treatment revealed no significant drug effect in the pre-exposed groups but a decrease in activity in the novel condition. Quipazine, on the other hand, had no significant effect in the novel condition but produced a time-dependent effect on activity in the pre-exposed condition. These results suggest that the effects on locomotor activity of compounds affecting 5-HT neurotransmission may interact with the familiarity of the test apparatus and with the duration of testing. Interexperiment differences in these variables may account for some of the inconsistencies previously reported.