Pimozide attentuates d-amphetamine-induced sleep changes in man.

Pretreatment with pimozide (mean dose = 13 mg/day) blocked the effect of d-amphetamine (20 mg base, administered by intravenous bolus infusion at 0815) on all-night EEG sleep patterns in seven hospitalized psychiatric patients. Each patient was studied for five nights (2 nights baseline, 1 night on the day of the infusion, and 2 nights recovery) with and without pretreatment with pimozide. Without treatment with pimozide, d-amphetamine significantly reduced duration of total sleep, REM and nonREM sleep, Stage I, and Stage II. With coadministration of pimozide, d-amphetamine had no effect on sleep. These results suggest that the d-amphetamine induced changes in sleep are mediated by dopaminergic neurons.     

d-Amphetamine raises serum prolactin in man: evaluations after chronic placebo, lithium and pimozide treatment.

One of the major biochemical effects of d-amphetamine is the release and uptake inhibition of dopamine (DA). We measured the effect of d-amphetamine upon prolactin release which is inhibited by DA and stimulated by serotonin. d-Amphetamine (20 mg i.v.) significantly raised the serum prolactin levels of drug-free schizophrenic patients over preinfusion levels and levels following a paired placebo lactose infusion. Amphetamine infusions were repeated after both chronic DA blockade with pimozide and after chronic lithium treatment that has been reported to attenuate amphetamine effects. These chronic pretreatments did not prevent significant increases in prolactin following d-amphetamine infusions. Pimozide raised preinfusion prolactin levels but lithium had no effect. Further studies are needed to clarify the d-amphetamine-induced rise in prolactin.     

D-amphetamine-induced hypothermia and hypermotility in rats: Changes after systemic administration of beta-endorphin

Systemically administered beta-endorphin was tested in rats for its ability to modify the hypothermia and hypermotility induced by d-amphetamine. Colonic temperature and motor activity were measured in a cold (4°C) ambient temperature in animals given IP injections of beta-endorphin (0.1, 1.0, or 3.0 mg/kg), naloxone (10 mg/kg), or morphine (30 mg/kg). The same measurements were taken in animals given beta-endorphin (1.0 mg/kg) in combination with naloxone or saline pretreatment and d-amphetamine (15 mg/kg) or saline post-treatment. Morphine alone had a biphasic effect on thermoregulation, but did not affect d-amphetamine-induced hypothermia. Activity scores were decreased by morphine, in both d-amphetamine and saline treated animals. The thermal response of rats to beta-endorphin alone was variable, depending on dosage, but all 3 dosages partially blocked the hypothermic effect of d-amphetamine. Naloxone blocked the thermal effects of both beta-endorphin and d-amphetamine. Motor activity tended to be decreased by naloxone, regardless of amphetamine treatment, but beta-endorphin tended to increase activity in amphetamine-treated animals and reduce it in saline-treated controls. In their actions on both thermoregulation and activity, naloxone and beta-endorphin appeared to interact independently with d-amphetamine, often producing effects in the same direction, but in combination, they tended to be mutually inhibitory.     

Ibogaine reduces amphetamine-induced locomotor stimulation in C57BL/6By mice, but stimulates locomotor activity in rats.

The effect of ibogaine hydrochloride on locomotor stimulation induced by d-amphetamine sulfate was tested in male C57BL/6By mice and in female Sprague-Dawley rats. In mice, locomotor stimulation induced by d-amphetamine at 1 or 5 mg/kg s.c. was reduced by prior administration of one or two injections of ibogaine (40 mg/kg), given 2 or 18 hours earlier. This reduction in locomotor activity persisted for two days. Locomotor stimulation induced by a higher dose (10 mg/kg) of d-amphetamine was not reduced by such prior administration of ibogaine. A lower dose of ibogaine (20 mg/kg) did not reduce the subsequent locomotor activity induced by d-amphetamine. Ibogaine decreased striatal dopamine levels, while d-amphetamine increased them. Ibogaine treatment (2 x 40 mg/kg, 18 hours apart) induced a decrease by 30% in the level of striatal dopamine and its metabolites measured in tissue extracts 3 hours after the second ibogaine injection. One hour after d-amphetamine (5 mg/kg) administration, the level of striatal dopamine increased by 26%. Although the level of striatal dopamine was initially lower in the ibogaine-pretreated mice, d-amphetamine (5 mg/kg) administration induced an increase in striatal dopamine and its metabolites. The effect of ibogaine seems to be species specific, since in rats pretreated with ibogaine 18 hours before d-amphetamine, locomotor stimulation induced by d-amphetamine was further increased. In addition, the in vitro electrical-evoked release of [3H]dopamine from striatal tissue was either unchanged or inhibited in the presence of d-amphetamine, and after ibogaine pretreatment in vivo, the release of tritium in the presence of d-amphetamine was inhibited or stimulated in mice and rats, respectively.     

Potentiation by naltrexone of d-amphetamine-induced behavioral suppression and its reversal by clonidine

Rats were trained to perform a fixed ratio-15 operant for food reinforcement during a 30 minute daily session. Naltrexone, in doses up to 45 mg/kg administered 15 min before the behavioral session, failed to disrupt responding. However, 0.3 and 1.0 mg naltrexone/kg produced a dose related potentiation of the operant behavioral suppression induced by 1.0 mg d-amphetamine/kg injected immediately before the session. The naltrexone/d-amphetamine combination also produced excessive salivation and postural abnormalities not seen when either drug was administered alone. [A subsequent study indicated that the salivation induced by naltrexone in combination with d-amphetamine may require previous exposure to naltrexone and/or d-amphetamine.] Blockade of dopamine receptors with pimozide did not modify the interaction. Functional noradrenergic blockade with a low dose of clonidine significantly reversed the potentiated suppression, of operant behavior, as well as the excessive salivation and abnormal posture. These data suggest that there is an important noradrenergic component to the interaction of naltrexone with d-amphetamine. The impressive interaction of behaviorally inactive doses of naltrexone with a moderate dose of d-amphetamine reported here for rats may have clinical implications for detoxified opiate addicts maintained on naltrexone in antagonist therapy programs.     

Development of tolerance in rats to the hypothermic effects of D-amphetamine and apomorphine

Rats given d-amphetamine (15 mg/kg i.p.) or apomorphine (10 mg/kg i.p.) and placed in a cold environment (4°C) developed marked hypothermia. After daily injections of either drug for seven weeks, the maximal hypothermic responses to d-amphetamine or apomorphine were reduced to 72% and 19% of those obtained initially. Subsequent injection of ET-495, a central dopamine receptor stimulant, caused rectal temperature to decrease only 72% and 49% as much as in control animals. The hypothermic response to apomorphine was also depressed in d-amphetamine-treated animals. These observations suggest that the tolerance to the hypothermic effects of both d-amphetamine and apomorphine that develops is due at least in part to alterations in the sensitivity of dopamine receptors.     

Interaction of MIF-I or alpha-MSH with D-amphetamine or chlorpromazine on thermoregulation and motor activity of rats maintained at different ambient temperatures

Administration of several doses of MIF-I or alpha-MSH did not modify colonic temperature or the level of motor activity of rats in ambient temperatures of 4 degree or 20 degrees C. However, the thermoregulatory but not motor effects of the interaction between MIF-I or alpha-MSH with d-amphetamine were dependent upon ambient temperature. At 4 degree C, 1.0 mg/kg of both peptides enhanced the d-amphetamine-induced hypothermia, but at 20 degrees C both peptides blocked the hyperthermic effects of d-amphetamine. The hypothermic effect of chlorpromazine (CPZ) at 4 degree C and 20 degrees C was blocked by 1.0 mg/kg MIF-I but not by 1.0 mg/kg alpha-MSH. No linear dose response relationships between various doses of MIF-I or alpha-MSH and thermal responses were found. Administration of melanin or the use of hypophysectomized rats did not alter the significant interactions observed after peripheral injections.     

Tolerance to d-amphetamine: behavioral specificity.

In a Y-maze exploratory task mice tend to enter that compartment which was least recently visited (spontaneous alternation). Low doses of d-amphetamine (1.0 mg/kg) reduce alternation to chance levels, while high doses (10.0 mg/kg) result in animals successively visiting only two compartments of the Y-maze (perseveration). Following daily d-amphetamine injection (1.0 or 10.0 mg/kg) over a 30 day period tolerance to the d-amphetamine induced perseveration was observed; however, chronic amphetamine treatment did not modify the locomotor stimulating effects of d-amphetamine or the reduction of alternation to chance levels produced by low doses of the drug. It was hypothesized that tolerance to d-amphetamine occurs exclusively to behaviors mediated by norepinephrine.     

Potentiation of apomorphine and d-amphetamine effects by naloxone

The effects of naloxone, an opiate antagonist, on the stereotypic behavior and locomotor activity induced by apomorphine and d-amphetamine were studied. Groups of adult male Sprague-Dawley rats were first tested for stereotypy and locomotor activity after apomorphine (0.0 – 2.0 mg/kg) or d-amphetamine (0.0 – 10.0 mg/kg). Groups were subsequently tested with saline or naloxone (1.0 – 4.0 mg/kg) plus the previously used dosage of apomorphine or d-amphetamine. Naloxone alone did not produce stereotypy, but did significantly reduce locomotor activity. Naloxone potentiated apomorphine and d-amphetamine induced stereotypy. Apomorphine-induced activity was increased by naloxone, but d-amphetamine-induced activity at 2.5 mg/kg was reduced. The results are compatible with the suggestion that naloxone may potentiate both apomorphine and d-amphetamine by inhibiting an opiate receptor mechanism which normally interacts with catecholamine neuronal action.     

Biphasic effects of pimozide on sleep-wakefulness in dogs

Sleep-wakefulness patterns in dogs were studied using computerized on-line power spectral analysis and off-line automatic stage-classification during control recordings and after oral treatment with three doses of the specific dopamine blocker pimozide. A biphasic effect on sleep-wakefulness patterns was found. At 0.016 mg/kg (the ED₅₀-value for the antagonism of apomorphine-induced vomiting in dogs), pimozide significantly increased the time spent awake, and significantly decreased slow wave sleep and REM sleep. No significant effects were obtained with a four times higher dose of pimozide. At 0.16 mg/kg, pimozide significantly decreased the time spent awake and significantly increased slow wave sleep and REM sleep. The effects appear the opposite of those described for apomorphine and suggest that dopamine plays a role in the physiology of sleep-wakefulness regulation.     

Demonstration of reduced levels of zinc in rat brain after treatment with d-amphetamine, but not after treatment with reserpine

Histochemical and atomic absorption spectrophotometric methods were used to study the effects of reserpine and d-amphetamine on the neuronal trace metal distribution in various regions of the central nervous system (hippocampus, parietal cortex, cerebellum). Six hours after single d-amphetamine treatment (15 mg/kg i.p.), the neuronal zinc level was significantly decreased in the hippocampus and in the parietal cortex. The intensity of sulphide silver staining was similarly greatly decreased in all layers of the hippocampus and the parietal cortex. Such a change was not observed when d-amphetamine was administered in a lower dose (5 or 10 mg/kg i.p.). Twenty hours after single reserpine treatment (10 mg/kg i.p.), there were no changes in the tissue levels and distribution of zinc, copper, iron and manganese. In animals treated with reserpine on five consecutive days, in a dose of 10 mg/kg/day i.p., the trace metal distribution twenty hours following the final treatment was essentially the same as in the control. The results strongly suggest that zinc does not play a direct role in vivo in the storage and mobilization processes of the catecholamines. A high dose of d-amphetamine, however, has a non-specific, toxic effect that is not interrelated with the catecholaminergic neuronal function; this effect is manifested in a diminished intensity of sulphide silver staining and in a reduction of the tissue zinc level.     

Pimozide blocks establishment but not expression of cocaine-produced environment-specific conditioning

Two experiments were conducted to examine the effects of pimozide on cocaine-produced conditioning to a specific environmental context. On 8 treatment days, 12 rats were injected with cocaine (10 mg/kg i.p.) and 12 with saline prior to placement for 60 min into a test chamber outfitted with infrared emitters and detectors. Following each treatment session the saline group received cocaine in their home-cages and the cocaine group received saline. Cocaine produced a significant increase in vertical activity on treatment days. On test days all rats received saline. Significantly greater vertical activity was observed in the group previously receiving cocaine in the test environment. All rats then received 8 more treatment sessions. On saline test days, pimozide (0.4 mg/kg i.p.) pretreatment failed to antagonize expression of the conditioned effect. In experiment 2, pimozide was given prior to treatment and no evidence of conditioning was seen on saline test days. Thus, pimozide blocked the establishment but not the expression of cocaine-produced environment-specific conditioning. These results suggest that during conditioning, the effects of cocaine on dopaminergic neurons may have produced a change that subsequently influenced behaviour even when dopaminergic systems were blocked.     

The effects of MIF-I, beta-endorphin and alpha-MSH on d-amphetamine induced paradoxical behavioral thermoregulation: possible involvement of the dopaminergic system

The neuropharmacological basis for d-amphetamine induced paradoxical behavioral thermoregulation remains unclear. This study examined thermoregulatory behavior of rats in a runway device that housed a heat source at one end and in which locomotion along the length of the runway could be observed. Sprague Dawley rats were pretreated with IP injections of saline, beta-endorphin, MIF-1, or alpha-MSH, with a repeat injection after 30 min. In a second experiment, d-amphetamine was administered as the repeat drug for all Ss. The results showed clear differences for heat-source-on vs. heat-source off. All peptides induced hypermotility, although no differentiated effects for the peptides on d-amphetamine induced paradoxical behavioral thermoregulation were found. These findings are discussed in light of the theoretical possibilities that: (a) a ceiling effect exists; (b) there are separate control systems for maintaining body temperature and another for behavioral thermoregulatory responses, and (c) other neurotransmitters may be involved in such induced paradoxical behavioral thermoregulation.     

Involvement of nitric oxide in the head regeneration of Hydra vulgaris

Recent data have shown that a functional NO-cGMP signalling system plays an important role during development and seems to be operative early during the differentiation of embryonic stem cells. The intriguing possibility exists that this role can be evolutionarily conserved between vertebrates and invertebrates. In this paper, we have analyzed the effect of NO-cGMP pathway on the regeneration process in Hydra vulgaris, the most primitive invertebrate possessing a nervous system. Our results indicate that NO production increased during Hydra regeneration. The NOS inhibitor L-NAME reduced the regenerative process and the same effect was obtained by treatment with either the specific guanylate cyclase inhibitor ODQ or the protein kinase G (PKG) inhibitor KT-5823. In contrast, the regeneration process was increased by treating decapitated Hydra with the NO donor NOC-18. Furthermore, we found that cell proliferation was also increased by treating decapitated Hydra with the NO donor NOC-18 and reduced by treatment with the NOS inhibitor L-NAME. Our results strongly suggest that the NO-cGMP-PKG pathway is involved in the control of the proliferative-differentiative patterns of developing and regenerating structures in cnidarians as well as bilaterians.     

Effects of pimozide on the ultrastructure of the pars intermedia in the rat

Summary The effects of pimozide, a dopamine receptor-blocking agent, were studied in the pars intermedia of the rat. The animals received 100 g/100 g pimozide daily for 2, 5, 10, 15, and 20 days. Pimozide induces ultrastructural changes after 5 days of treatment. About 50% of the MSH-cells display characteristics of stimulation. Their cytoplasm is partially or totally depleted of secretory granules. The rough endoplasmic reticulum displays a network of interconnecting cisternae and ribbon-like structures. The well-developed Golgi complexes exhibit numerous dilatations of their cisternae, which contain electron-dense material. The nerve endings are not altered. Twenty days after treatment, the above-described changes have not decreased in magnitude. The present findings suggest that pimozide stimulates the mechanism of synthesis and release in some MSH-cells, most probably the elements underlying an inhibitory dopaminergic control.Supported by CONICET and CIUNC of ArgentinaMember of the Research Career of CONICET, ArgentinaFellow of CONICET, Argentina     

Evidence that pimozide is not a partial agonist of dopamine receptors.

The dopamine receptor antagonist pimozide, at concentrations up to 10 nM, competitively antagonized the inhibitory action of a pomorphine on prolactin (PRL) secretion by cultured rat pituitary cells. At higher concentrations pimozide as well as the analogues clopimozide and penfluridol suppressed PRL secretion. The latter effect could not be reversed by dopamine antagonists devoid of intrinsic effects on PRL release. Suppression of PRL release was also observed with compounds which were devoid of dopamine receptor agonistic or antagonistic properties such as R 6694 and R 5052, structurally related to pimozide, and also with loperamide. The inhibitory action of pimozide on PRL release resembled that of the calcium antagonist flunarizine. Concentration effect curves showed parallel slopes and the effect of both compounds could be reversed by increasing the concentration of calcium ions (Ca²⁺). Both flunarizine and pimozide were also capable of inhibiting releasing factor-stimulated luteinizing hormone secretion, an effect not shared by apomorphine. Pimozide and the various structurally related compounds used, also antagonized Ca²⁺-induced smooth muscle contractions of the isolated caudal artery of the rat.The present findings indicate that pimozide is a competitive antagonist without partial agonistic activity on apomorphine-sensitive dopamine receptors in the pituitary and that its inhibitory effect on PRL release as well as on vascular smooth muscle contractions is due to interference with a Ca²⁺-dependent mechanism of the stimulus-effect coupling process.     

Effect of pimozide on the cytology of the eel pituitary

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 to 9 days in freshwater (FW) eels or eels acclimated to sea water (SW), for 10 to 30 days. The daily dose was 100 or 200 microgram/100 g. In FW, pimozide induces a nuclear hypertrophy in the prolactin (PRL) cells of eels; these elongated cells increase in height. The amount of erythrosinophilic granules in the cytoplasm, initially reduced, increases. Plasma electrolyte values are not modified: only the plasma sodium level slightly rises with the higher dose. In SW, PRL cells appear less active. After 10 days, this hypoactivity is not yet fully evident; pimozide stimulates PRL cells without affecting electrolyte values. After 1 month in SW, PRL cells are stimulated with pimozide and a slight regranulation may occasionally occur. The response in SW is never as marked as it is in FW; a high dose is not more effective than a low one. The higher dose significantly raises Na+, Ca2+ and Cl- plasma levels. These data suggest that prolactin synthesis and release increase with pimozide. They corroborate the hypothesis of a hypothalamic inhibitory control on PRL secretion mediated through dopaminergic fibers in the eel, but other factors may also be involved in this regulation in addition to the effect of salinity.     

Influence of pimozide on a TRH induced TSH secretion in the rat during food deprivation.

Adult Wistar rats food deprived for 3 days had lower basal levels of TSH compared to normal fed animals. An increase of these lower levels to normal values was obtained following a prolonged (injections during 3 consecutive days) or acute treatment (single injection) with pimozide (1 mg/injection). Blood samples obtained after the last or an only injection of pimozide contained profound increased prolactin levels. Prolactin increase was more than 100-fold in fed and more than 30-fold in starved rats following prolonged pimozide treatment and more than 25-fold and 10-fold following a single injection of pimozide. An injection of 250 ng of TRH increased plasma concentrations of TSH in all groups, but this increase was more pronounced in fasted rats injected with pimozide during 3 consecutive days. It is concluded that fasting results in a dopaminergic inhibition of the sensitivity of the thyrotrophs to a TRH challenge.     

Effect of adrenergic blocking drugs on secretion of luteinizing hormone in the ovariectomized ewe.

The effects of the adrenergic blocking drugs phenoxybenzamine, phentolamine, and pimozide on basal luteinizing hormone (LH) levels and on estrogen-induced LH release were tested in ovariectomized ewes. Phentolamine was given at a dose of 10 mg/kg; phenoxybenzamine was given at a dose of 8 mg/kg; and pimozide was given at a dose of 800 mcg/kg. Estradiol benzoate (EB) was given at a dose of 50 mcg/animal. Sera were assayed for LH levels by double-antibody radioimmunoassay. Phenoxybenzamine given as a single dose significantly reduced basal LH levels. Given at extremenly high doses, phenoxybenzamine was unable to consistently block estrogen-induced LH release. Pimozide significantly reduced basal LH levels in the ewes and blocked or greatly reduced estrogen-induced LH release in 9 of 10 treated animals. Reduced basal LH levels were seen with phentolamine injection but were of short duration of action. It is concluded that normal function of noradrenergic neurons is required for maintenance of normal basal LH release but unnecessary for estrogen-induced LH release. Dopaminergic neurons appear to facilitate basal and estrogen-induced LH release.     

Evidence for dopaminergic regulation of prolactin and a luteotropic complex in the ferret

The role of dopaminergic agents in prolactin (Prl) release and the luteotrophic role of Prl and luteinizing hormone (LH) were investigated in pseudopregnant female ferrets. A single injection of the dopamine antagonist pimozide (0.63 mg/kg) resulted in a tenfold elevation of plasma Prl in anestrous females. Subcutaneous injection of pimozide on alternate days from Day 2 through Day 16 of pseudopregnancy elevated both Prl and progesterone levels. Daily treatment with the dopamine agonist 2 alpha-bromoergocryptine (bromocriptine, 4 mg/kg), from Day 2 through Day 16 of pseudopregnancy lowered levels of both plasma Prl and progesterone. Neither pimozide nor bromocriptine had a direct effect on progesterone secretion by luteal cells in vitro. Daily intraperitoneal administration of a monoclonal antibody against gonadotropin-releasing hormone from Day 2 through Day 10 of pseudopregnancy lowered both plasma LH and progesterone, but had no effect on plasma Prl concentrations. Daily administration of equine antisera against bovine LH or 100 IU of human chorionic gonadotrophin to pseudopregnant ferrets lowered progesterone levels. It is concluded that Prl release is influenced by dopaminergic compounds, and both Prl and LH are required for luteal maintenance in the ferret.