Mechanisms by which quipazine, a putative serotonin receptor agonist, alters brain 5-hydroxyindole metabolism

Psychedelic-like Properties of Quipazine and Its Structural Analogues in Mice

Known classic psychedelic serotonin 2A receptor (5-HT2AR) agonists retain a tryptamine or phenethylamine at their structural core. However, activation of the 5-HT2AR can be elicited by drugs lacking these fundamental scaffolds. Such is the case of the N-substituted piperazine quipazine. Here, we show that quipazine bound to and activated 5-HT2AR as measured by [3H]ketanserin binding displacement, Ca2+ mobilization, and accumulation of the canonical Gq/11 signaling pathway mediator inositol monophosphate (IP1) in vitro and in vivo. Additionally, quipazine induced via 5-HT2AR an expression pattern of immediate early genes (IEG) in the mouse somatosensory cortex consistent with that of classic psychedelics. In the mouse head-twitch response (HTR) model of psychedelic-like action, quipazine produced a lasting effect with high maximal responses during the peak effect that were successfully blocked by the 5-HT2AR antagonist M100907 and absent in 5-HT2AR knockout (KO) mice. The acute effect of quipazine on HTR appeared to be unaffected by serotonin depletion and was independent from 5-HT3R activation. Interestingly, some of these features were shared by its deaza bioisostere 2-NP, but not by other closely related piperazine congeners, suggesting that quipazine might represent a distinct cluster within the family of psychoactive piperazines. Together, our results add to the mounting evidence that quipazine's profile matches that of classic psychedelic 5-HT2AR agonists at cellular signaling and behavioral pharmacology levels.

Evidence for a possible functional interaction between serotonergic and cholinergic mechanisms in memory retrieval

A total of three experiments were conducted. In Experiment 1, the dose-dependent effects of the pretest administration of the serotonergic agonist alaproclate and the selective muscarinic cholinergic agonist oxotremorine, alone and in combination, were assessed in a one-trial inhibitory avoidance task. A clear dose-dependent enhancement of performance was demonstrated as a result of all three treatment conditions, which could not be explained in terms of nonspecific effects of the drugs on behavior in general. In addition, the facilitation of retrieval performance produced by the combined treatment of alaproclate and oxotremorine was observed at dose levels well below those observed following administration of either compound alone. In Experiment 2 attempts were made to block the enhancements of retention resulting from the different treatment conditions (alaproclate, oxotremorine, or the combination of alaproclate and oxotremorine) by pretreating the mice with either scopolamine (a muscarinic cholinergic antagonist) or quipazine (a serotonergic agonist). The results of these experiments indicate that (a) quipazine completely blocked the enhancement of retrieval resulting from alaproclate but not that following oxotremorine or oxotremorine in combination with alaproclate, while (b) scopolamine blocked the enhancement of retrieval resulting from oxotremorine alone as well as that resulting from alaproclate plus oxotremorine but failed to block the memory enhancement resulting from alaproclate. The present results lend further support to the view that both serotonin and acetylcholine play important roles in memory retrieval. More importantly, the results of the present series of experiments provide additional support for a functional interaction between the serotonergic and cholinergic nervous systems in the mediation of behavior.

Evaluation of the direct actions of drugs with a serotonergic link in spinal analgesia on the release of [3H]serotonin from spinal cord synaptosomes

Morphine, ketamine, ethylketocyclazocine and quipazine, drugs with an apparent local spinal serotonergic action, which contributes to their analgesic effects, were tested for their ability to alter the release of [3H]serotonin ([3H]5-HT) from a synaptosomal preparation from the spinal cord of the rat. Related compounds including [D-Ala2, D-Leu5]enkephalin (DADLE), n-allylnormetazocine and phencyclidine were also examined. None of the drugs was found to be capable of inducing a direct release of [3H]5-HT or of facilitating potassium-induced release of 5-HT. However, quipazine inhibited the depressant action of exogenous 5-HT on overflow of 3H (mediated through the 5-HT autoreceptor), an action that should facilitate serotonergic neurotransmission. In contrast to the other drugs, DADLE was found to depress K+ stimulated release of 5-HT. The results suggests that the serotonergic mechanism involved in the antinociceptive action of some of these drugs (i.e. ketamine, morphine and ethyl-ketocyclazocine) is not related to direct presynaptic interactions to promote release of 5-HT. On the other hand, a small population of serotonergic nerves critical for analgesia may be involved and are not detected using tissue from the whole spinal cord, However, it seems equally plausible that these drugs may produce their antinociceptive action through interactions with other neurotransmitter systems that in turn interface with the serotonergic nerves, perhaps through interneurons or collateral connections.

Local cerebral glucose utilisation following indoleamine- and piperazine-containing 5-hydroxytryptamine agonists

Substances with varying structural components have been shown to have 5-hydroxytryptamine (5-HT)-like properties in the CNS. In this study, putative 5-HT agonists with indoleamine moeities--lysergic acid diethylamide (LSD) and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)--and with piperazine moieties--quipazine (Quip) and 6-chloro-2-(1-piperazinyl)pyrazine (6-CPP) were administered to rats. Local cerebral glucose utilisation was measured using the [14C]2-deoxyglucose autoradiographic technique. It was found that in most cerebral structures, these substances produced dose-dependent reductions in glucose utilisation. However, Quip and 6-CPP increased glucose utilisation in specific areas of the diencephalon (e.g., nucleus reuniens) and produced a biphasic effect in some but not all extrapyramidal structures (e.g., ventromedial caudate nucleus). No such increases in local cerebral glucose utilisation were measured following LSD or 5-MeODMT administration. These results indicate that although similarities exist between the effects of indoleamine- and piperazine-containing 5-HT agonists on local cerebral glucose utilisation there are also significant differences in the overall patterns of response produced.

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.

Drug-induced activation of the inferior olivary nucleus in young rabbits. Differential effects of harmaline and quipazine

Ontogenic evolution of behavioural and electrophysiological responses to the serotonergic agents, quipazine and harmaline, was studied in the maturing rabbit in normal and pretreated conditions. As regards behavioural effects, tremor induced by quipazine was present from the first postnatal day and was antagonized by methysergide, but not by p-chlorophenylalanine (PCPA) or pretreatment with 5,7-dihydroxytryptamine (5,7-DHT). In contrast, tremor induced by harmaline could not be elicited before the second postnatal week and was partially antagonized by methysergide and 5,7-DHT, but not by PCPA. Electrophysiological studies of cell activity in the inferior olivary nucleus revealed a similar dependency on age since rhythmic activation of the inferior olivary nucleus could be registered from the first postnatal day with quipazine and only from the 8th postnatal day with harmaline; drug interactions with methysergide, PCPA and 5,7-DHT were the same as for the behavioural observations. It is suggested that quipazine directly activates serotonin receptors which are already present at birth, whereas harmaline requires the presence of serotonergic fibres for such activation.

Functional change in the rat spinal cord by chronic spinal transection and possible roles of monoamine neurons

Two types of spinal reflex responses, extensor reflex and ventral root potential, were compared physiologically and pharmacologically in acute and chronic spinal cord transected rats. The recovery curve of the extensor reflex, recorded as evoked electromyogram, in chronic spinal rats was strikingly different from that in acute spinal rats. Namely, shortening of the reflex amplitude suppression period (stimulus interval: 20 msec) and appearance of the supernormal period (30-60 msec) were observed in chronic spinal rats. The recovery curves of ventral root potential (monosynaptic reflex) and M wave were almost the same in both preparations. In the frequency depression curve, the amplitude of the extensor reflex in chronic spinal rats was higher at high frequency stimulation than that in acute spinal rats. 5-Hydroxytryptophan, 5-methoxy-N,N-dimethyltryptamine and quipazine enhanced the extensor reflex in chronic spinal rats with a potency of 200-400, 8 and 4 times stronger than that in acute spinal rats, respectively. These drugs did not show consistent effects on the monosynaptic reflex of ventral root potential in chronic spinal rats. These results strongly suggest that the spinal interneurons where descending serotonergic fibers terminate become supersensitive and functionally modified in chronic spinal rats. It is speculated that the supersensitivity of these interneurons may play an important role in spasticity.

The influence of pharmacological manipulation of serotonin on serum growth hormone and luteinizing hormone levels in young turkeys (Meleagris gallopavo)

Serum growth hormone (GH) and luteinizing hormone (LH) levels were determined by homologous radioimmunoassay in 8 to 10-week-old domestic white turkeys treated by intraperitoneal injection of agents that alter serotonergic activity. The serotonin, 5-hydroxytryptamine (5-HT) precursor, 5-hydroxytryptophan (5-HTP), at doses of 80 and 150 mg/kg, produced a dose-related elevation in serum GH (P = .09) and no change in serum LH (P = .30). Administration of fluoxetine (10 mg/kg), a 5-HT reuptake blocker, produced no change in serum GH or LH. When fluoxetine injection preceded the administration of a nonstimulatory dose of 5-HTP, an elevation in GH was observed, but again no change in LH level was evident. Stimulation of postsynaptic 5-HT receptors with quipazine (.5 to 10.0 mg/kg) resulted in a similar elevation in GH; persistence of the effect was dose dependent. Quipazine administration had no influence on serum LH levels. Administration of methysergide (10 or 25 mg/kg), a 5-HT antagonist, induced no change in either serum GH or LH levels. Serotonergic input appears to stimulate GH release and has no apparent influence on LH release in young turkeys.

Acrylamide neurotoxicity: altered spinal monosynaptic responses to quipazine, a serotonin agonist, in cats

The effects of the serotonin agonist quipazine on the spinal monosynaptic reflex (MSR) were investigated in acrylamide-treated cats. Cats were administered 30 mg/kg acrylamide (ACR) for 10 days, and the MSR and spontaneous ventral root discharge (VRD) were recorded on the tenth day (ACR 10) or 10 days subsequent to the last injection (ACR 20). Cumulative doses of quipazine were administered to increase the MSR and VRD. It was found that the MSR in ACR 10 cats was significantly depressed by ACR while the ACR 20 cats showed increased MSRs with double peaks. Dose-response relationships between quipazine and the area-under-the-MSR showed a significant shift to the right in the ACR 10 from control and no significant change in the ACR 20 from control. Dose-response curves of quipazine vs VRD showed no significant difference in either group from control. These data suggest that the alpha-motoneuron in ACR-treated cats was responding normally to quipazine while the primary afferent terminal was not.

Evidence for selective serotonergic receptor involvement in p-chloroamphetamine-induced antinociception

Administration of the serotonin (5-HT) releasing compound p-chloroamphetamine (PCA; 2.5 mg/kg) induced potent analgesia in rats tested with the hot plate method. The analgesia was prevented by pretreatment with either of the 5-HT uptake inhibitors alaproclate (20 mg/kg) or fluoxetine (10 mg/kg). Taking into account that the noradrenergic uptake inhibitor desipramine in previous experiments failed to interfere with the effect of PCA, these results demonstrate that PCA selectively acts on 5-HT terminals. The analgesia was attenuated by administration of the 5-HT antagonists methiothepin (0.125-0.5 mg/kg) and danitracen (0.25-2.5 mg/kg) but not by a series of other 5-HT receptor antagonists or antagonists acting on noradrenergic, dopaminergic, GABAergic, histaminergic or muscarinic receptors. It is concluded that the analgesic effect of PCA is mediated via stimulation of a type of 5-HT receptors possibly belonging to the 5-HT-1 class. Further studies are, however, needed in order to firmly establish the relationship to any particular sub-type of 5-HT receptor as characterized in in vitro binding studies.

Involvement of the serotonergic system in the prolongation of pentobarbital sleeping time produced by prostaglandin D2

In the present study, the depressant and sedative actions of prostaglandin D2 (PGD2) were investigated. Intravenous (IV) administration of PGD2 produced a significant decrease in the spontaneous locomotor activity of mice from 1 to 15 minutes following injection. Prostaglandin D2 was also able to potentiate pentobarbital sleeping time at doses of 0.4 and 4.0 mg/kg when administered intravenously. Distribution studies with 3H-PGD2 (6 microCi, 4 mg/kg) showed that only 0.04% of the tritium administered could be found in brain at 5 min after the injection, and that only 50% of this was parent 3H-PGD2. The role of the serotonergic neurotransmitter system in the depressant action of PGD2 was investigated with drugs which modulate this system. The ability of PGD2 to potentiate pentobarbital sleeping time was diminished by pretreatment with agents that reduce brain level or synthesis rate of serotonin. Such agents include para-chlorophenylalanine (PCPA), a tryptophan hydroxylase inhibitor, 5,7-dihydroxytryptamine (5,7-DHT), a neurotoxin with selectivity for serotonergic neurons, and quipazine, a serotonergic autoreceptor stimulant. On the other hand, pretreatment with 5-hydroxytryptophan (5-HTP), the precursor of serotonin, further enhanced the potentiation of pentobarbital sleeping time by PGD2. These data suggest that the depressant actions of PGD2 are linked to the serotonergic neurotransmitter system.

Brain serotonergic neurons: their role in a form of dominance-subordination behavior in rats

The present study evaluated the possible role of brain serotonergic neurons in dominant-subordinate (D-S) behavior in Wistar male rats competing for water. Treatment of D rat with drugs that stimulate serotonergic neurons of receptors (tryptophan, 5-hydroxytryptophan, quipazine, femoxetine) resulted in D-S reversal. A similar effect was observed when the S animal was treated with drugs that blocked serotonin synthesis (p-chlorophenylalanine) or receptors (metergoline). The D-S relationship was unchanged when serotonergic drugs were given to the S subject (tryptophan or quipazine) or when D animal received p-chlorophenylalanine. None of the drugs tested influence the water intake and the general activity of rats. Rats with lesioned midbrain raphe nuclei were always dominant when paired with sham lesioned counterparts. Our results indicate that one form of dominance behavior can be inversely related to the activity of brain 5-HT system.

Evidence that the medial and dorsal raphe nuclei mediate serotonergically-induced increases in prolactin release from the pituitary

Electrolytic lesions of the medial (MR) or dorsal (DR) raphe nucleus significantly antagonized serum prolactin elevations produced by 5-hydroxytryptophan (5-HTP) in rats pretreated with fluoxetine or citalopram, (serotonin (5-HT) uptake blockers). Lesioned animals in which total blockade of serum prolactin elevations was observed also had total blockade of 5-HT accumulation in the median eminence. However, the increase in serum prolactin levels produced by 5-HTP plus 5-HT reuptake blockade in lesioned rats was not significantly different from sham-operated rats if as little as 15-20% of control median eminence accumulation was present. Serum prolactin elevations produced by quipazine, a direct acting 5-HT agonist, were not significantly affected by MR lesions. On the basis of these results, we suggest that: (1) serum prolactin elevations following 5-HT reuptake blockade plus 5-HTP are correlated with 5-HT concentration in the median eminence; (2) lesion-induced antagonism of 5-HTP-induced prolactin elevation is critically dependent upon complete blockade of median eminence 5-HT accumulation; and (3) 5-HT neurons arising from cell bodies located in the MR and DR are necessary for endogenous serotonergically mediated effects on prolactin secretion in the rat.

Serotonin-releasing effects of substituted piperazines in vitro

The effects of various piperazine-containing compounds on the release of endogenous serotonin (5-HT) from rat hypothalamic slices were evaluated. Incubation of hypothalamic slices with m-chlorophenylpiperazine ( mCPP ) or m- trifluoromethylphenylpiperazine ( mTFMPP ) evoked a potent, dose-dependent release of endogenous 5-HT that was similar in magnitude to that seen with tryptamine, p-chloroamphetamine, or fenfluramine. In the presence of the 5-HT uptake blockers fluoxetine or chlorimipramine, this release was reduced dramatically. Furthermore, removal of calcium from the incubation medium had little effect on the drug-induced release, suggesting that the release mechanism involved displacement of 5-HT stores and not depolarization-induced exocytosis. Trazodone, MK-212, and quipazine had only small effects on release. These studies show that several piperazine-containing compounds can evoke a potent release of endogenous stores of hypothalamic 5-HT in vitro, actions which should be considered together with their direct agonist activity when interpreting the CNS effects in vivo.

Behavioral effects of serotonergic and dopaminergic drugs in cats following chronic amphetamine administration

Chronic administration of amphetamine to cats (twice daily, in doses increasing from 5 to 15 mg/kg over a 10-day period) elicited a number of behaviors e.g., limb flicking, abortive grooming, and excessive head shaking, which were originally proposed as an animal behavioral model for studying the actions of hallucinogens that depress central serotonergic neurotransmission. This drug treatment produced large decreases (approximately 50%) in central nervous system serotonin (5HT) and its major metabolite, 5-hydroxyindoleacetic acid, and even larger decreases (approximately 90%) in the levels of dopamine (DA) and norepinephrine. Administration of the 5HT precursors L-tryptophan (25 mg/kg i.p.) or L-5-hydroxytryptophan (12.5 mg/kg i.p.), a direct-acting 5HT agonist (quipazine, 1 mg/kg i.p.) or a monoamine oxidase inhibitor (tranylcypromine, 4 mg/kg i.p.) produced no significant changes in these behaviors in cats treated chronically with amphetamine. Administration of a 5HT reuptake blocker (fluoxetine, 5 mg/kg i.p.) produced a small, but significant, decrease in the frequency of occurrence of these behaviors in amphetamine-treated cats. L-Dihydroxyphenylalanine (L-DOPA, 20 mg/kg i.p.) greatly potentiated these behaviors in cats chronically treated with amphetamine, but L-DOPA was totally ineffective in eliciting these behaviors in naive animals. The behavioral effects of apomorphine (2 mg/kg i.p.) were also significantly potentiated by chronic amphetamine pretreatment. The amino acid precursor of DA, L-tyrosine (25 mg/kg i.p.), and a DA reuptake blocker, bupropion (5 mg/kg i.p.) were without significant effect on these behaviors in amphetamine-treated cats. The data suggest that these cat behaviors are elicited by an action at central DA receptors and that these receptors become supersensitive following chronic amphetamine administration. Furthermore, there may be a qualitative change in DA receptors, since L-DOPA is very effective in potentiating these behaviors in cats treated chronically with amphetamine, but is totally ineffective in naive cats.

Role of serotonin in memory: facilitation by alaproclate and zimeldine

The effects of alaproclate and zimeldine on memory retrieval were examined in male Swiss-Webster mice using a one-trial inhibitory avoidance task. All drugs were administered IP prior to the retention test 24 h after training. Both drugs were found to facilitate memory retrieval significantly in a dose- and time-dependent fashion that could not be explained in terms of non-specific effects of the drug (illness, lack of motility, etc.) at the time of the test. The temporal effects of alaproclate and zimeldine on memory closely followed their course of concentration of the drug within the blood stream. The facilitation of retrieval induced by alaproclate and zimeldine was blocked by the putative serotonergic receptor agonist quipazine but not blocked by the antagonist cyproheptadine. Pretreatment with quipazine alone in a group of animals trained to a shock level which normally results in high levels of suppression was not sufficient to produce memory impairment, suggesting that quipazine was probably antagonizing the facilitative effects of alaproclate and zimeldine directly, rather than overriding the facilitation through an indirect action on retrieval in general. The present results lend further support to the suggestion that serotonin plays a significant role in memory.

Serotonergic stimulation of prolactin release in the young turkey (Meleagris gallopavo)

Serum prolactin (PRL) levels were determined by homologous radioimmunoassay in 6- to 10-week-old domestic white turkeys treated by intraperitoneal injection of agents that alter serotonergic activity. Quipazine (0.1-10.0 mg/kg), a serotonin (5-hydroxytryptamine; 5-HT) agonist, induced a dose-dependent rise in serum PRL level 1 hr after injection. The 5-HT precursor, 5-hydroxytryptophan (5-HTP), at doses of 80 and 150 mg/kg produced over a twofold elevation in PRL level 1 hr after administration, though the 50 mg/kg dose failed to produce any change. Administration of fluoxetine (10 mg/kg), a 5-HT reuptake blocker, induced an elevation in PRL level persisting 3 hr. When fluoxetine injection preceded administration of a weakly stimulatory dose of 5-HTP, a prolonged elevation in PRL level was observed. methysergide (MES), a 5-HT antagonist, administered in a 10 mg/kg dose produced no change in PRL level, while the 25 mg/kg dose initially produced a spike in PRL level which subsequently dropped slightly below the control level. Prior injection of 20 mg/kg MES completely blocked the serum PRL rises induced by quipazine and 5-HTP. These results suggest that serotonergic mechanisms are involved in the regulation of pituitary PRL release beyond basal levels in young domestic turkeys.

Synergistic effect of propranolol and quipazine on desipramine enhanced shock-elicited fighting in rats

Changes in shock-elicited fighting (SEF) were measured following single or repeated injections (IP) of dl-propranolol (5 mg/kg, 20 mg/kg) or quipazine (1.25 mg/kg, 2.5 mg/kg) given either alone or in combination to saline or desipramine (DMI) (10 mg/kg) treated rats. DMI + propranolol (20 mg/kg) caused a greater increase in fighting than DMI + saline 18 hours after last dose. Propranolol (20 mg/kg) produced an equal inhibition in both of these groups at 15 min. Propranolol (5 mg/kg) had no effect. Quipazine (2.5 mg/kg) failed to alter DMI induced increase in SEF. The combination of propranolol (5 mg/kg) + quipazine (1.25 mg/kg) blocked the enhanced SEF significantly in DMI treated rats in comparison to DMI + saline treated group. This combination of propranolol + quipazine produced no significant change in SEF in saline treated group in comparison to the pretest level. These results suggested that propranolol + quipazine act synergistically at low doses to inhibit the increased SEF seen in DMI treated rats and might have therapeutic implications for the management of irritable aggression or mania.

Effects of quipazine on pre- and postsynaptic serotonin receptors: single cell studies in the rat CNS

Many behavioural and biochemical studies have pointed to an agonistic activity of quipazine on serotonin (5-HT) receptors. In the present electrophysiological study, the effect of quipazine on pre- and postsynaptic 5-HT receptors in the rat was studied. Quipazine, administered intravenously, depressed the firing rate of 5-HT-containing dorsal raphe neurones (ED50 = 0.82 mg/kg). Microiontophoretic applications of quipazine on 5-HT-containing neurones in the dorsal raphe and on neurones of two forebrain regions receiving a 5-HT input (the ventral lateral geniculate nucleus and the dorsal hippocampus) consistently depressed neuronal firing rate as did 5-HT and D-lysergic acid diethylamide (LSD). Quipazine was more potent on 5-HT neurones than on the ventral lateral geniculate nucleus and hippocampal neurones: the post/presynaptic efficacy ratio for quipazine was similar to that of LSD. Following a selective denervation of 5-HT neurones with intraventricular injection of 5,7-di-hydroxy-tryptamine in desipramine-pretreated rats, the responsiveness of neurones in the ventral lateral geniculate nucleus to quipazine, applied microiontophoretically, was increased as was that to 5-HT and to LSD. These results provide direct evidence for the agonistic activity of quipazine on both pre- and postsynaptic 5-HT receptors.

Participation of spinal monoaminergic and cholinergic systems in the regulation of adrenal tyrosine hydroxylase

The role of spinal pathways in the regulation of tyrosine hydroxylase activity (ATHA) in the adrenal medulla was characterized in adult rats with surgical transection of the upper thoracic cord. The animals received injections of centrally active agonists, which could then act on the sympathoadrenal preganglionic neurons isolated from their supraspinal afferents. All agonists tested produced distinct increases of tyrosine hydroxylase activity in rats with a surgical sham operation. The injection of quipazine or oxotremorine into spinalized rats led to decreased tyrosine hydroxylase activity. Clonidine and several dopamine agonists did not affect tyrosine hydroxylase activity. Considering the mechanism of the observed changes in tyrosine hydroxylase activity it is concluded that the changes are mediated by neural pathways and that variations in the secretion of adrenocorticotrophic hormone (ACTH) do not play a role. The results suggest (a) that there are serotonergic and cholinergic (muscarinic) receptors in the lower thoracic cord generating a net inhibitory action on tyrosine hydroxylase activity; and (b) that increases of tyrosine hydroxylase activity mediated by dopaminergic drugs probably originate from areas rostral to the thoracic cord. It is possible that an alpha-adrenergic system participates in the regulation of tyrosine hydroxylase activity in the adrenal medulla.

Possible dopamine agonist properties of quipazine maleate

Though quipazine is widely regarded as a relatively pure serotonergic (5-HT) agonist and has been reported to have no dopamine (DA) agonist properties, it has produced stereotyped behavior (SB) associated with DA agonist arousal of striatal DA mechanisms. Since we observed a dose-related inhibition of quipazine induced stereotypy (QISB) by a centrally acting DA antagonist (haloperidol) that could not be mimicked by a central 5-HT receptor blocking agent (methysergide), it appeared likely that QISB is mediated by striatal DA mechanisms. This was further supported by our observing that QISB could be potentiated by a subthreshold dose of the central DA agonist apomorphine. In light of this, and the presence of abnormal movements seen concomitantly with QISB that are typically produced by intrastriatal injections of 5-HT agonists, it appears that QISB is a complex phenomenon. While QISB seems to be primarily due to the stimulation of DA mechanisms, the effect of quipazine on behavior appears to be a combined result of its effects on both DA and 5-HT mechanisms. Specifically, central striatal DA receptors appear to mediate QISB per se, while serotonergic mechanisms stimulated by quipazine inhibit its further development and produce extrapyramidal-like abnormal movements.

Serotonin-like actions of quipazine and CPP on spinal motoneurones

The actions of iontophoretically applied quipazine (QPZ) and 6-chloro-2-[1-piperazinyl]-pyrazine (CPP) were compared with those of serotonin (5-HT) on rat spinal motoneurones. QPZ and CPP qualitatively resembled 5-HT in that both facilitated single unit activity evoked by glutamate. Like 5-HT, the facilitation they produced could be antagonized by metergoline or methysergide. These observations are compatible with the suggestion that the actions of QPZ and CPP are mediated by 5-HT receptors. In rats pretreated with the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), QPZ and CPP remained effective in facilitating the glutamate evoked activity, whereas p-chloroamphetamine (PCA), a known releaser of 5-HT, was without effect. In contrast, PCA produced a long lasting facilitation in untreated rats. These data, taken together, suggest that QPZ and CPP are direct agonists at 5-HT receptors, but do not preclude the possibility that they might also act indirectly.

Behavioral effects of quipazine in the cat

Administration of quipazine to cats elicits a number of behaviors, such as limb flicking abortive grooming, investigatory behavior and hallucinatory-like behavior, which we have previously proposed as an animal behavioral model for studying the actions of LSD and related hallucinogens. While recent studies have indicated that these model behaviors may not be totally specific for hallucinogenic drugs, the model can still be useful for studying drug action. Quipazine (0.5-5.0 mg/kg i.p.) produced significant increases in limb flicking, abortive grooming, investigatory behavior, hallucinatory-like behavior grooming, head and body shakes, staring and yawning. These behavioral changes persisted for 1-6 h, depending on the dose of quipazine employed. Administration of quipazine (5.0 mg/kg per day) for 5 consecutive days produced no significant tolerance effect on any of these model behaviors. These quipazine induced behavioral changes were potentiated by pretreatment with apomorphine, and partially blocked by pretreatment with haloperidol. Quipazine-induced behavioral changes were potentiated by prior serotonin depletion with p-chlorophenylalanine, and completely blocked by pretreatment with a monoamine oxidase inhibitor or the serotonin precursor, L-5-hydroxytryptophan. These quipazine-induced behavioral changes were also blocked by pretreatment with the serotonin receptor blockers, cinnanserin, methysergide or cyproheptadine. The mechanism of action of quipazine, as well as the neuropharmacology of the limb flick model, is discussed in the content of these studies with serotonergic and dopaminergic drugs.

Differences in the effects of d-fenfluramine and morphine on various responses of rats to painful stimuli

The effects of d-fenfluramine and morphine on various nociceptive responses of rats were investigated. Unlike morphine, which inhibited all the responses examined, d-fenfluramine inhibited jumping and paw licking of rats on a hot plate, but did not increase the latency of tail withdrawal from hot water. The effects of d-fenfluramine on both responses on the hot plate were prevented by pretreatment with metergoline, a serotonin antagonist, whereas this pretreatment only reduced the effect of morphine on paw licking. The inhibition of tail withdrawal by morphine was also significantly reduced by metergoline treatment. The results confirm previous findings suggesting a role of serotonin in the mechanism by which morphine inhibits some nociceptive responses in rats. They also show that d-fenfluramine, a selective releaser and uptake inhibitor of serotonin at nerve endings, does not completely reproduce the antinociceptive effects of morphine in this species.

Role of 5HT in the morbidity of cerebral infarction-a study in the gerbil stroke model

Cerebral infarction was produced by unilateral carotid ligation in the gerbil, and 5HT levels in the cerebral hemispheres were assayed 3.5 hours later. A bilateral fall as confirmed, with the greatest change occurring on the side of carotid ligation in animals showing the clinical sequelae of infarction. Neither absolute levels nor right left differences in 5HT content related directly to the nature or prevalence of neurological morbidity. Neither putative 5HT receptor antagonists nor agents causing increasing brain 5HT levels produced consistent changes in the prevalence of neurological morbidity. It is argued that the fall in 5HT in a cerebral infarct is more likely to be due to reduced synthesis and turnover than to release of the amine into the synaptic cleft. These findings cast doubt on the hypothesis that a significant part of the morbidity and mortality of cerebral infarction is due to the sequelae of 5HT release.

Tonic immobility in domestic fowl: anticataleptic effects of quipazine

Quipazine, a putative serotonergic agonist, produced marked decreases in tonic immobility (TI) duration in doses of 5--25 mg/kg. Quipazine-treated animals required more elicitation attempts before displaying TI. Quipazine also blocked the haloperidol enhancement of tonic immobility. In a third experiment, quipazine produced stereotyped responses in chickens which yielded increases in activity on a stabilimeter platform. The results are discussed in terms of catalepsy and serotonerigic and dopaminergic mechanisms.

Effects of 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-THbetaC) on audiogenic seizures in DBA/2J mice

It was found previously that 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-THbetaC) increased brain concentration of the neurotransmitter serotonin (5-HT) and decreased the concentration of its metabolite 5-hydroxyindole acetic acid (5-HIAA) at the same time the compound attenuated audiogenic seizures (AGS) in DBA/2J mice. In the present study we determined the time-course and dose-response effects of 6-MeO-THbetaC for blockade of AGS. Drugs sharing common effects with 6-MeO-THbetaC were also tested. At a dose of 100 mg/kg, 6-MeO-THbetaC blocked AGS between 10 min and 12 hr after injection, with maximal inhibition at 1 hr at which time a dose-related decrease in AGS was also demonstrated. All of the drugs tested which blocked AGS, including 6-MeO-THbetaC, THbetaC, 5-Hydroxytryptophan, chlorimipramine and pargyline, have biochemical similarities suggesting that facilitating serotonin function may be responsible for seizure-attenuating effects.

Evidence for the role of noradrenaline in some effects of quipazine

In mice, quipazine has shown several behavioral effects: It antagonizes hypothermia induced by a high dose of apomorphine without altering climbing or stereotyped behavior; it antagonizes oxotremorine-induced hypothermia without altering tremors or peripheral signs; and it increases the toxicity of yohimbine. These three responses are considered to be predictive of an antidepressive action; in these three tests the effects of quipazine are inhibited by D,L-propranolol but not by D-propranolol or methysergide. Quipazine, in mice pretreated with pargyline, induced head twitches which were inhibited by methysergide but not by D,L-propranolol. Quipazine, in addition to its well-known serotonergic effects, seems to have beta-adrenergic properties which should be kept in mind when this drug is used as a pharmacological tool and which suggest that the beta-adrenergic system is implied in depression.

Immobility induced by forced swimming in rats: effects of agents which modify central catecholamine and serotonin activity

Rats were forced to swim in a restricted space will rapidly cease apparent attempts to escape and adopt a characteristic posture which we have termed "immobility". We show in previous experiments that immobility was reduced by a variety of antidepressant agents and thus suggested that the method could serve as a screening model for antidepressants. The present experiments showed that immobility was reduced by drugs which increase central dopaminergic and alpha-adrenergic activity but was less affected by drugs which act mainly on central serotonin. Conversely, immobility could be increased by drugs which diminish central catecholamine activity but not by drugs which inhibit central serotonin. It was concluded that immobility depended primarily on the activity of central catecholamines but that caution was required before ascribing immobility exclusively to activity within a single system.

Effect of quipazine on brain stem monoamine neurons histofluorescence studies

Using two fluorescence histochemical methods, formaldehyde-induced fluorescence and sucrose-potassiumphosphate-glyoxylic acid fluorescence (SPG), we studied the effect of 5-hydroxytryptamine receptor stimulation by quipazine (2-[-piperazinyl]quinoline maleate) on monoamine fluorescence in the brain stem of rats. It was found that quipazine in a dose of 5 mg/kg i.p., after 60 min, decreased noradrenaline fluorescence intensity in noradrenergic neurons of the subcoeruleus area and diminished th density of catecholamine terminals visualized in the central part of the dorsal raphé nucleus. In the principal locus coeruleus, the intensity of fluorescence in nerve cells was not changed using either method, but with the SPG procedure, diffuse fluorescence outside cell bodies was observed after quipazine. In dorsal raphé neurons, a slight increase in 5-hydroxytryptamine fluorescence intensity was observed. The results obtained indicate that quipazine, apart from its effect on 5-hydroxytryptamine neurons, may also affect certain noradrenergic neurons.

Shape change of blood platelets--a model for cerebral 5-hydroxytryptamine receptors?

1. In blood platelets of rabbits isolated by a stractan gradient and incubated in a protein-poor medium, tryptamine, 5-hydroxytryptamine (5-HT) and derivatives, quipazine and mescaline caused a shape change. This shape change was inhibited by low concentrations of methysergide. 2. The most potent antagonists of the 5-HT-induced shape change included ergoline derivatives and neuroleptic drugs, which showed high stereoselectivity. 3. (+)-Lysergic acid diethylamide ((+)-LSD), psilocine and some N',N'-dimethylated tryptamines acted as mixed agonist-antagonists. 4. The compounds found to be agonists or mixed agonist-antagonists on platelets have previously been shown to act also as 5-HT agonists in the central nervous system (CNS). 5. With regard to 5-HT antagonists, the 5-HT receptors of platelets reacted differently from those described earlier in brain areas with dense 5-hydroxytryptaminergic innervation, but showed similarities to 5-HT receptors investigated previously in spinal cord, cerebral cortex and possibly reticular formation. 6. It is concluded that platelets may be considered with caution as models for some, but not for all, 5-HT receptors in the CNS.

Effect of 1-(m-trifluoromethylphenyl)-piperazine on 3H-serotonin binding to membranes from rat brain in vitro and on serotonin turnover in rat brain in vivo

1-(m-Trifluoromethylphenyl)-piperazine inhibited the specific binding of tritiated serotonin to membranes from rat brain in vitro at lower concentrations than did quipazine or MK-212 (6-chloro-2-[1-piperazinyl]-pyrazine). In rats 1-(m-trifluoromethylphenyl)-piperazine decreased the concentration of 5-hydroxyindoleacetic acid (5-HIAA) without altering the concentration of serotonin in whole brain. The decrease in 5-HIAA was apparently due to a decrease in serotonin turnover, since 1-(m-trifluoromethylphenyl)-piperazine caused a slower decline in serotonin concentration after synthesis inhibition by alpha-propyldopacetamide and a slower accumulation of 5-HIAA after probenecid injection to block its efflux from brain. The decrease in serotonin turnover is an expected result of stimulating serotonin receptors in brain and has earlier been reported to occur with quipazine. Thus all of the results are compatible with the idea that 1-(m-trifluoromethylphenyl)-piperazine acts as a serotonin receptor agonist in rat brain.

Gabaminergic and serotonergic modulation of the antidyskinetic effects of tiapride and oxiperomide in the model using 2-(N,N-dipropyl)animo-5,6-dihydroxytetralin

The activities of oxiperomide and tiapride were compared with those of control "neuroleptic" agents in the dyskinesia model using 2-(N,N-dipropyl)amino-5,6-dihydroxytetralin to induce peri-oral movements, in order to determine whether the differential activities (oxiperomide and tiapride being comparatively more effective as antagonists) may involve striatal gabaminergic and serotonergic mechanisms. The peri-oral movements induced by the 2-aminotetralin compound (0.05 mg/kg s.c.) were antagonised by intrastriatal GABA (2.5--10 microgram bilateral) and serotonin (25--100 microgram bilateral). Sodium valproate (i.p.) had little effect but 1.25 mg/kg s.c. quipazine abolished the peri-oral dyskinesia. Subthreshold doses (i.p.) of oxiperomide and tiapride synergised with subthreshold intrastriatal doses of both GABA and serotonin, and with s.c. quipazine, to antagonise the peri-oral movements induced by the 2-aminotetralin compound. Subthreshold doses of haloperidol, sultopride, metoclopramide and pimozide failed to consistently antagonise peri-oral movements when similarly combined with GABA, serotonin or quipazine. It is suggested that, in addition to their known action on cerebral dopamine mechanisms, oxiperomide and tiapride may modify abnormal peri-oral movements by modulation of striatal gabaminergic and serotonergic mechanisms.

Lysergic acid diethylamide antagonizes shaking induced in rats by five chemically different compounds

Thyrotropin-releasing hormone (TRH), sodium valproate, AF-3-5 (1-[2-hydroxyphenyl]-4-[3-nitrophenyl]-1,2,3,6-tetrahydropyrimidine-2-one), RX336-M (7,8-dihydro-5',6'-dimethylcyclohex-5'-eno-1',2',8',14 codeinone), and Sgd 8473 (alpha-[4-chlorobenzylideneamino)-oxy]-isobutyric acid) each induced repetitive shaking of the body of rats after intraperitoneal injection. This action of the five diverse chemicals appears to be subserved by a common pharmacological component, because pretreatment with d-lysergic acid diethylamide (0.03--1.0 mg kg-1, s.c.) attenuated the shaking behavior in a dose-related manner, and cross tolerance was found between RX336-M and TRH, sodium valproate, and AG-3-5.

Suckling behavior of the infant rat: modulation by a developing neurotransmitter system

Drugs which alter serotonin receptor activity modified the suckling behavior of 20-day-old rat pups. Suckling could be reinstated in nondeprived pups, which normally do not suckle, by blockade of serotonin receptors with methysergide. Stimulation of serotonin receptors with quipazine inhibited suckling in deprived pups, and this effect was prevented by methysergide pretreatment. This evidence suggests that suckling in weaning age pups is controlled by a serotonergic inhibitory mechanism.

Regional differences in the sensitivity of cholinergic neurons to dopaminergic drugs and quipazine in the rat striatum

Marked differences were found in the activity of choline acetylase (ChAc) in various discrete areas of the rat striatum. The richest cholinergic innervation was observed in the centrolateral part of the structure. A similar distribution was obtained by measuring acetycholine (ACh) levels in punches taken from frozen frontal serial slices. As revealed by the analysis of the topographical distributions of ChAc activity, ACh, 5-HT and DA, the regional cholinergic innervation differed markedly from that of aminergic terminals. Changes in ACh levels induced by drugs could be estimated in microdiscs of tissues punched from frozen slices. Apomorphine and haloperidol, which increased and decreased ACh levels respectively, induced similar effects in the various striatal areas examined. By contrast quipazine, a drug acting on 5-HT uptake and release and on serotoninergic receptors, selectively increased ACh levels in some areas of the striatum but not in others. The regional changes in ACh levels induced by quipazine were satisfactorily correlated with the regional distribution of 5-HT but not with that of DA. These results suggest that a limited population of striatal cholinergic neurons is under the inhibitory control of serotoninergic neurons. They also indicate that some striatal cholinergic neurons influenced by dopaminergic neurons are not controlled by serotoninergic neurons.