Apomorphine Treatment Research Articles

Locomotor activity in relation to dopamine and noradrenaline in the nucleus accumbens, septal and frontal areas: a 6-hydroxydopamine study.

Locomotor activity was automatically recorded in a circular corridor in rats treated with 6-hydroxydopamine in the ventral tegmental area (VTA), septum and frontal cortex. Control and experimental groups showed similar hyperlocomotor responses in the novel apparatus lasting 3 h. Circadian changes are described. VTA lesions resulted in increased dark activity and a large response to apomorphine compared to other lesion and control groups. Septal lesions did not affect locomotion. The frontal group showed a small increase of locomotion after apomorphine treatment that might reflect increased receptor sensitivity in cortical or subcortical areas. Together with correlations between motor activity and cortical levels of dopamine and noradrenaline these results are interpreted to support a role for dopamine, noradrenaline and the frontal cortex in modulating locomotion which is primarily mediated by VTA-accumbens-dopamine activity.

The effect of dopamine receptor agonist treatment of haloperidol-induced supersensitivity in mice

Mice were pretreated with haloperidol (HP) (3–4 mg/kg/day in drinking water) or vehicle for 21 days. On the 25th day, HP-pretreated mice were supersensitive to the locomotor stimulant effects of apomorphine (after acute premedication with reserpine and alpha-methyl-p-tyrosine). This behavioural supersensitivity was accompanied by a 25–39% increase in the number of [ 3H]-spiperone binding sites in the striata of HP-pretreated mice. Short-term repeated administration of the dopamine (DA) agonist drugs d-amphetamine and L-DOPA during the HP withdrawal phase (days 22, 23 and 24) had no effect on either measure of DA receptor supersensitivity. In contrast, the administration of apomorphine on days 22, 23 and 24 enhanced the HP-induced behavioural supersensitivity but decreased the HP-induced elevation of the number of [ 3H]-spiperone binding sites. Apomorphine treatment alone did not alter either measure. The results do not support the hypothesis that supersensitive DA receptors can be down-regulated by short-term treatment with DA agonist drugs and, moreover, indicate that important discrepancies may exist between behavioural and biochemical measures of DA receptor supersensitivity.

Simultaneous catalepsy and apomorphine-induced stereotypic behavior in mice

Intraventricular administration of haloperidol or chlorpromazine produces catalepsy and blocks apomorphine-induced stereotypic behavior. Low intraventricular doses of domperidone, sulpiride and spiperone, equally cataleptogenic as haloperidol or chlorpromazine, augment rather than diminish stereotypic behavior produced by subsequent apomorphine treatment. The resultant stereotypic behavior continues even while the animal is in a rigid cataleptic posture and is marked by persistent gnawing and licking. Prior to the induction of catalepsy and after recovery from it, mice display the entire range of typical apomorphine-induced behavior including sniffing, climbing, gnawing, and licking. This animal model may be related to the clinical observation of the coexistence of tardive dyskinesia and drug-induced Parkinsonism in individual patients.

Increased or decreased locomotor response in rats following repeated administration of apomorphine depends on dosage interval.

Administration of drugs that reduce the influence of dopamine at its receptor site can lead to postsynaptic supersensitivity, whereas treatment with dopamine (DA) agonists can cause postsynaptic subsensitivity. Both unaltered and enhanced postsynaptic responses to DA have been shown after pretreatment with DA agonists. In the present manuscript pretreatment with apomorphine, a dopaminergic agonist, is shown to induce either increased or reduced locomotor activity. When a drug-free period between successive injections was allowed, apomorphine induced an enhanced locomotor response, whereas a reduced response occurred when each dose was injected before the previous apomorphine dose had been completely metabolized. Pretreatment with both high (1 and 3 mg/kg) and low (0.05 mg/kg) apomorphine doses enhanced the response. Apomorphine treatment that caused enhanced locomotor responses did not modify the stereotypy response to the drug. Similar enhanced or reduced response were found in rats with partial lesions of the nigrostriatal system. These altered responses to DA agonists may have important clinical consequences. The present data also suggest the existence of a different DA systems for locomotor and stereotypy actions of dopaminergic agonists.

Differential biochemical and behavioral effects of single and chronic administration of amphetamine and apomorphine

1. 1. The single and repeated effects of apomorphine (AP) and amphetamine (AM) administrations were compared on rearing behaviour in an open field (RF) and on rearing stereotyped behaviour (RSB). 2. 2. Single AP treatment did not modify RSB while decreased the ability of low doses of AP to inhibit RF. Opposite data were observed after AM single administration. Repeated treatment with both drugs reduced the inhibitory effects of AP low doses on open field behaviour. 3. 3. The AP repeated administration enhanced the dihydroxyphenilacetic (DOPAC) and homovanilic acid (HVA) striatal levels while the same AM treatment was unable to affect the dopamine (DA) metabolites levels. 4. 4. Taken together, our results support the view that behavioural changes observed after AP single and repeated treatment are a result of DA autoreceptors subsensitivity. 5. 5. Nevertheless, the behavioural changes detected after AM treatments are probably related to mechanisms other than the development of DA autoreceptors subsensitivity.

Behavioral and biochemical evidence of apomorphine-induced supersensitivity of the striatal dopamine receptors

The effect of repeated administration of apomorphine was studied behaviorally and biochemically in rats bearing either a unilateral lesion of the the substantia nigra with 6-OHDA or an electrolytic lesion of the entopeduncular nucleus. Rats with the nigral lesion displayed a progressive increase in contralateral circling rate. In animals with the entopeduncular lesion, the ipsiversive circling response was unchanged after the eight injection of apomorphine. [ 3h] Spiroperidol binding to striatal membranes did not appear modified by the apomorphine treatment on the intact side. It was however increased on the side of the 6-OHDA lesion. We propose that a denervated striatum responds to repeated stimulation by dopamine agonists with a paradoxical increase in sensitivity. This may explain in part the appearance of dyskinesia in treated parkinsonian patients.

Administration of small doses of apomorphine attenuates feeding in non-deprived pigeons

The dopamine agonist apomorphine was administered peripherally at small doses of 25, 50 or 100 μg to non-deprived pigeons, either in the morning or in the afternoon. The food and water consumption of the birds was then measured at 4 times (30, 60, 90 and 120 min) after the injection. In the control condition (injection of saline), the pigeons ate less in the morning than in the afternoon, whereas a reverse situation was observed for drinking. Administration of apomorphine attenuated the food consumption in a dose-related fashion, at both times of the day, and for no longer than 90 min post-injection; the reduction of feeding was relatively larger when the drug was given in the morning than in the afternoon, and it was not accompanied by consistent changes of the water consumption. These results show that in pigeons, the feeding-like responses to apomorphine treatment (pecking, swallowing, mandibulating) which have been described previously are not associated with an actual enhancement of the food intake. Possible mechanisms and loci of action of dopamine agonists on these 2 types of behaviors are discussed.

Effects of apomorphine administration on rearing activity of control and experimental rats withdrawn from long-term haloperidol treatment

Rats were administered increasing doses of haloperidol or control solution for 25 days. 72 hr after drug withdawal they were observed for rearing activity in an open field with or without apomorphine treatment. 2. Rearing frequency was higher in haloperidol withdrawn rats. 3. In control rats rearing frequency decreased 15 min after apomorphine administration in a dose-dependent way. 4. In haloperidol withdrawn animals the apomorphine effects were dual, first an increase in rearing frequency induced by the smaller apomorphine doses (0.025-0.1 mg/kg) was observed and secondly a progressive and dose-dependent decrease was scored. 5. Apomorphine also induced different motor effects not necessarily similar in control and experimental rats. 6. Supersensitivity of dopaminergic receptors induced by the long-term neuroleptic administration was considered to be involved with the difference observed.

Automated analysis of stereotypic behavior induced by psychomotor stimulants

A newly developed rotation sensing device has been applied to the continuous monitoring of animal movement. Animals treated with morphine, amphetamine or apomorphine display different stereotypic movements which can be distinguished by the apparatus. Initial studies have indicated that the apparatus is able not only to identify but also to quantitate some measures of stereotypic behavior. For example, the number and direction of rotations (a measure of motor asymmetry), frequency of changes in movement direction (a measure of stereotypic movement) and periods of cessation of movement are affected differentially with acute morphine, apomorphine or amphetamine treatment. Moreover, using this apparatus, morphine was shown to increase the degree of rotational asymmetry of normal animals and of animals with unilateral lesions of the nigrostriatal pathway.

Effects of dopaminergic stimulation on functional brain metabolism in rats with unilateral substantia nigra lesions

We have studied regional cerebral glucose utilization (RCGU) in awake, unrestrained rats 21 days after unilateral substantia nigra lesions following treatment with either apomorphine (0.5 mg/kg s.c.) or d-amphetamine (2.5 mg/kg s.c.). In ‘control’ rats with a unilateral SN lesion, there was a 30–40% increase in RCGU in the ipsilateral globus pallidus (GP) and a 15–25% increase in the ipsilateral lateral habenular nucleus (LH). Apomorphine treatment produced contralateral while d-amphetamine elicited ipsilateral turning in the lesioned rats. Apomorphine administration led to an increase in RCGU in the ipsilateral striatum, entopeduncularis (EP), and substantia nigra pars reticulata (SNPR); while d-amphetamine elicited similar changes in the same structures contralateral to the lesion. Both apomorphine and d-amphetamine treatment led to bilateral increases in RCGU in the subthalamic nuclei. The increased RCGU found in the ipsilateral GP in ‘lesioned controls’ was reduced to control levels by apomorphine administration, while amphetamine treatment increased RCGU in the contralateral GP without affecting glucose utilization in the ipsilateral GP. Furthermore, apomorphine treatment markedly reduced RCGU in the LHN bilaterally while amphetamine reduced RCGU only in the contralateral LHN. The effects of apomorphine were dose-dependent. Haloperidol (1 mg/kg s.c.) pretreatment completely blocked the development of asymmetric changes in RCGU in nigral lesioned rats after apomorphine administration. These results suggest that apomorphine, a direct dopamine agonist, selectively activated basal ganglia pathways ipsilateral to substantia nigra lesion by interacting with supersensitive dopamine receptors in the ipsilateral striatum. In contrast, d-amphetamine, an indirect dopamine agonist, selectively activated pathways in the contralateral basal ganglia by releasing endogenous dopamine from the intact nigrostriatal pathway. Furthermore, the data suggest that striatal efferents to the GP are not controlled in the same manner as efferents to the EP and SNPR. Finally, these asymmetric changes in RCGU in basal ganglia structures produced by apomorphine or d-amphetamine do not appear to be a consequence of the turning behavior, but rather appear to be proximate effects of the drugs administered.

Repeated apomorphine treatment causes behavioural supersensitivity and dopamine D2 receptor hyposensitivity

This study reports the changes in the behavioural responsiveness of rats in the ‘Ungerstedt Model’ following repeated injections of apomorphine. The changes in striatal [ 3H]haloperidol binding coincident with the behavioural responses are also estimated. Following unilateral lesions of the substantia nigra, the number of [ 3H]haloperidol binding sites in the ipsilateral striatum increase, and this effect correlates with the behavioural effect following a single apomorphine injection. Repeated apomorphine treatment, however, results in a decrease of neuroleptic binding sites in the ipsilateral and contralateral striatum accompanied by increased behavioural responses. Thus repeated apomorphine treatment discriminates the receptor mechanisms involved in the behavioural response from those receptors labelled by neuroleptics.

Effects of apomorphine administration on locomotor activity of control and experimental rats withdrawn from long-term haloperidol treatment

1. 1. Rats were administered increasing doses of haloperidol or control solution for 25 days, 72 hr after drug withdrawal they were observed for locomotor activity in an open field with and without apomorphine treatment. 2. 2. Locomotion frequency was higher in haloperidol withdrawn rats. 3. 3. In both groups locomotion frequency decreased 15 min after apomorphine administration, in a dose-dependent way. 4. 4. Apomorphine induced, also, different motor effects not necessarily similar in control and experimental rats. 5. 5. Supersensitivity of dopaminergic receptors induced by the long-term neuroleptic administration was considered to be involved with the differences observed.

Differential subsensitivity of dopaminergic and neostriatal neurons to apomorphine with long-term treatment

The apomorphine-induced inhibition of dopaminergic neurons in the substantia nigra of the rat was significantly attenuated following 2 daily injections of 0.05, 0.5 or 2.0 mg/kg apomorphine for 5 consecutive days. In fact, many of these neurons responded with an increase in firing rate whiich was never observed in control animals. Neostriatal neurons, on the other hand, decreased their sensitivity to apomorphine only after long-term treatment with 0.5 or 2.0 mg/kg. Multiple injections of the low dose actually potentiated the apomorphine-induced inhibition in the neostriatum. These results, which are consistent with the differential sensitivity of dopaminergic and neostriatal neurons to acute apormorphine, suggest that the subsensitivity of pre- and postsynaptic dopamine receptors produced by long-term apomorphine treatment is dose-dependent.

Dopamine turnover estimated by simultaneous LCEC assay of dopamine and dopamine metabolites

The estimation of changes in tissue levels of dopamine (DA) and its metabolites has been employed to approximate the turnover rate or release of DA. We have developed an assay using high pressure liquid chromatography with electrochemical detection to quantify DA, dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), and homovanillic acid (HVA) simultaneously in brain homogenates. The assay is simple, inexpensive, rapid and accurate; the sensitivity of the assay for DA and DOPAC was 10 pg, for HVA 50 pg, and 200 pg for 3-MT. Apomorphine treatment resulted in a reduction in tissue levels of DOPAC and HVA, while haloperidol administration increased tissue levels of DOPAC and HVA. Neither drug treatment caused changes in DA levels. Administration of damphetamine 2.5 mg/kg S.C. resulted 1 hour later in increases in the striatal concentration of DA (57%) and 3-MT (44%) and decreases in DOPAC (40%) and HVA (39%). These data are consistent with the agonistic effect of apomorphine and antagonistic effect of haloperidol on DA autoreceptors and post-synaptic receptors. In the case of amphetamine, the increases in the levels of DA and 3-MT probably reflect the ability of d-amphetamine to induce DA release and block re-uptake. The reduction of DOPAC and HVA levels are consistent with the ability of d-amphetamine to competitively inhibit monoamine oxidase activity as well as the neuronal reuptake of DA. The simultaneous estimation of DA, DOPAC, 3-MT, and HVA should facilitate the understanding of dopaminergic drugs with complicated mechanisms of action.

Behavioral and neurochemical effects of apomorphine in the cat

Administration of apomorphine (2–10 mg/kg i.p.) elicited a number of behaviors, such as limb flicking, abortive grooming, investigatory and hallucinatory-like responses, head and body shakes, and excessive grooming, which we have previously proposed as an animal model for studying the actions of LSD and related hallucinogens. Repeated administration of apomorphine resulted in a significant tolerance, which occurred within 2h of the initial injection, and completely dissipated within 24 h. A pronounced LSD-apomorphine cross tolerance was observed; however there was no significant apomorphine-LSD cross tolerance. Apomorphine-induced behavioral changes were blocked by prior treatment with haloperidol, but were unchanged by pretreatment with L-DOPA. Administration of L-DOPA, in combination with a peripheral decarboxylase inhibitor, did not elicit these characteristic behavioral changes. Increasing synaptic serotonin levels by monoamine oxidase inhibition, precursor administration, or reuptake blockade in general did not alter the behavioral response to apomorphine. Similarly, pretreatment with serotonin receptor blockers produced no large changes in apomorphine-induced behaviors. Prior serotonin depletion with chronic p-chlorophenylalanine administration, however, potentiated certain apomorphine-induced behaviors. Neurochemical studies revealed that apomorphine administration increased striatal dopamine, and decreased dopamine metabolites. Norepinephrine levels were generally decreased throughout the CNS by apomorphine treatment. Administration of apomorphine increased CNS serotonin and 5-hydroxyindoleactic acid levels, while tryptophan levels were unchanged. The biological bases of the limb flick model is discussed in the context of these pharmacological and neurochemical studies.

Persistent behavioural effect in apomorphine in 6-hydroxydopamine-lesioned rats.

The rotational (circling) behaviour of rodents with unilateral nigrostriatal damage has been used extensively to investigate nigrostriatal function and the action of dopaminergic compounds1. Rats lesioned by unilateral microinjection of the catecholaminergic neurotoxin, 6-hydroxydopamine (6-OHDA), spontaneously exhibit slight ipsilateral (towards the lesioned side) rotation. Systemic challenge with the dopamine receptor agonist apomorphine induces active contralateral rotation, apparently as a result of supersensitivity in the lesioned hemisphere2,3. We report here that apomorphine treatment also results in an extraordinarily persistent change in spontaneous (undrugged) rotation. After one treatment with 50 µg per kg apomorphine, exposure to the rotation environment resulted in a brief, intense burst of contralateral rotation. This behaviour, apparent for months after drug treatment, did not fully develop until 2 weeks after treatment and was never observed in lesioned, but otherwise drug-naive rats. The latent apomorphine effect, unlike the acute effect, was inversely related to dose over the range tested. The behaviour was relatively specific for the environment in which drug treatment had occurred, suggesting a role for learning, but it is difficult to reconcile the inverse dose–response function, lack of recency effect and inability to induce an analogous phenomenon using (+)amphetamine with this explanation.

Effects of apomorphine on behavioural activity and brain catecholamine synthesis in normal and L-triiodothyronine-treated rats.

The effect of chronic apomorphine treatment on behavioural activity as well as brain dopamine metabolism was studied in normal and neonatally L-triiodothyronine-treated rats. Neonatal hyperthyroidism was accompanied by an increase in spontaneous locomotor activity as well as by enhanced synthesis and release of dopamine as evidenced by increased catecholamine synthesis in crude synaptosomal preparation (P2 pellet), elevated tyrosine hydroxylase activity and higher concentrations of homovanillic acid and 3, 4-dihydroxyphenylacetic acid in striatum of rats. Repeated apomorphine treatment (1 mg/kg/day s.c) for 15 days, beginning from the 15th day of age, produced hypermobility and stereotyped behavior (consisting of sniffing, gnawing, rearing) which appeared to be more pronounced in neonatally hyperthyroid rats than in normal controls. In addition, apomorphine-treated hyperthyroid animals marched in a row with straub tail, and displayed increased aggressiveness and bizarre social behavior consisting of "mock fighting" when left in pairs. In contrast to normal rats, apomorphine-treated hyperthyroid animals displayed marked hyperactivity which was evident even at 24 hours after the last injection of apomorphine. Administration of apomorphine resulted in significant decreases in striatal tyrosine hydroxylase, catecholamine synthesis in crude synaptosomal preparation (P2 pellet) as well as dopamine metabolite levels in brains of both normal and hyperthyroid animals. Our present data showing that apomorphine potentiates behavioural activity in hyperthyroid rats suggest that L-triiodothyronine and apomorphine probably share certain features common to activating dopaminergic neurons in the brain.

Effects of drugs on the formation of 3-methoxytyramine, a dopamine metabolite, in the substantia nigra, striatum, nucleus accumbens and tuberculum olfactorium of the rat.

Abstract 3-Methoxytyramine (3-MT) was assayed with a sensitive and rapid liquid chromatographic separation on a Sephadex G 10 column in combination with a fluorimetric detection in a continuous flow system. The method made it possible to measure pargyline-induced 3-MT concentrations in various regions of a single rat brain. After haloperidol, morphine or sulpiride treatment, pargyline-induced 3-MT concentrations in the striatum, nucleus accumbens, tuberculum olfactorium and substantia nigra of the rat were comparable with reported changes of homovanillic acid concentrations. Dose-response curves for 3-MT increase in various brain regions after (+)-amphetamine pretreatment were studied. The effect of (+)-amphetamine on 3-MT formation was much more pronounced in nerve terminal areas, especially in the mesolimbic structures. The influence of apomorphine, γ-hydroxybutyric acid, haloperidol, reserpine or combined treatment of haloperidol and (+)-amphetamine revealed pronounced differences on regional 3-MT concentrations, indicating important differences between the regulation of dopamine metabolism in the substantia nigra and nerve terminal areas.

Further studies on the sequence of dopamine metabolism in the rat brain

The time—response curve of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations in the striatum of the rat were measured during apomorphine, haloperidol, morphine, oxotremorine or reserpine treatment as well as after a brain lesion. The results showed that changes in DOPAC concentrations consistently preceded changes in HVA concentrations. It was concluded that HVA must be considered as a “second metabolite” rather than as a marker of extra-neuronal metabolism. The turnover of HVA calculated after tropolone treatment revealed that this compound can be considered as a reliable COMT inhibitor. The turnover of 3-methoxytyramine (3-MT) calculated after tropolone treatment (during MAO inhibition) appeared to be 1.9 nmol/g/h. From this relatively low value it was concluded that 3-MT cannot be considered as an alternative metabolite for DA degradation during MAO inhibition. 3-MT concentrations measured after apomorphine or γ-hydroxybutyric acid treatment also suggest that 3-MT leaves the brain to only a minor extent during MAO inhibition. The effects of reserpine on pargyline-induced 3-MT concentrations indicate that there is hardly any COMT-activity in dopaminergic terminals. Evidence was provided that, at least during reserpine or pargyline treatment, dopamine leaves the brain unmetabolized or via unknown metabolic pathways.

Presynaptic subsensitivity as a possible basis for sensitization by long-tern dopamine mimetics

A possible cellular basis for dopaminergic sensitization by long-term dopamine mimetics was examined in rat brain striatum. Long-term apomorphine or amphetamine administration (10 mg/kg/day for 14 days) resulted in a decrease in the specific binding of 3H-apomorphine, but no change in 3H-haloperidol binding. Long-term apomorphine treatment also enhanced the cataleptogenic action of haloperidol, wtih many rats being spontaneously cataleptic after apomorphine withdrawal. It is suggested that the reduced 3H-apomorphine binding signifies less presynaptic receptors. This permits less autoregulation and enhanced dopamined agonist action, possibly accounting for the dopaminergic sensitization by long-term agonists.