Behavioral and neurochemical effects of apomorphine in the cat

The development of behavioral sensitization induced by a single morphine exposure in adult zebrafish (Danio rerio)

BACKGROUND

Accumulating evidence suggest that behavioral sensitization is involved in the process of drug addiction. Zebrafish are sensitive to a variety of addictive drugs and are thus suitable for the study of behavioral sensitization. However, in contrast to mature rodent models of behavioral sensitization, how this phenomenon manifests in aquatic organisms, especially zebrafish, is largely unknown. In this study, we developed a morphine-induced behavioral sensitization adult zebrafish model and performed a preliminary investigation of the underlying mechanisms.

METHODS

Behavioral sensitization was established in zebrafish by observing their behavior after treatment and challenge with morphine. The effect of morphine was evaluated by a behavioral locomotor test. Different doses of morphine and withdrawal times were used to evaluate the establishment of the behavioral sensitization model.

RESULTS

Hyperlocomotion was induced after administration of morphine in adult zebrafish. After withdrawing the drug for a period, challenge with low-dose morphine evoked behavioral sensitization in zebrafish acutely pre-treated with morphine. Low-dose morphine failed to induce behavioral sensitization in zebrafish if the withdrawal time was less than 5 days or more than 7 days. Morphine induced behavioral sensitization in zebrafish may involve dopaminergic, glutamatergic and opioid systems.

CONCLUSION

A single low-dose of morphine could induce behavioral sensitization in zebrafish acutely pre-treated with morphine, and this phenomenon was highly correlated with drug dose and withdrawal time. These findings suggest that zebrafish is a suitable model for the study of behavioral sensitization.

Apomorphine in patients with Parkinson's disease

We present a review of the recent literature and personal experience with apomorphine in patients with Parkinson's disease. Apomorphine is a potent D1 and D2 dopaminergic agonist. It has a rapid and short duration effect after subcutaneous administration at doses ranging from 15 to 180 micrograms/kg. Plasma maximal concentration is reached in 8-16 minutes, with a plasma half life of 34-70 minutes. Bioavailability is close to 100%. Repeated injections in patients show post-stimulative hyposensitivity. Apomorphine test appears very useful for the differential diagnosis between idiopathic Parkinson's disease and other Parkinson plus syndromes, and as a predictive test for dopaminergic responsiveness. Appropriate doses are able to alleviate akinesia, rigidity and tremor. Recent therapeutic trials have demonstrated the high interest of intermittent multiple subcutaneous apomorphine injections to cut the "off" motor phases in fluctuating parkinsonian patients under chronic levodopa treatment. In some cases, continuous apomorphine subcutaneous infusion with a portable pump may be required, particularly when levodopa treatment is temporarily interrupted, as after abdominal surgery. During long-term treatment, the apomorphine dose able to relieve akinesia remains stable. Peripheral side effects such as nausea and hypotension may be prevented by the co-administration of domperidone, a peripheral dopaminergic antagonist. Cutaneous fibrous nodules and psychiatric symptoms may occur, but usually at high dosages with continuous infusion. Local allergic effects have limited the use of other routes of administration, such as intranasal, sublingual, and rectal routes. Apomorphine is also used as a pharmacological tool for clinical research with the aim of a better understanding of the pathophysiology of Parkinson's disease.

The role of pulsatile versus continuous dopamine receptor stimulation for functional recovery in Parkinson's disease

More effective measures to control and replace the dopaminergic deficit of Parkinson's disease are being actively sought. One basic problem is how the striatal dopamine loss should be replaced in order to mimic most accurately the physiological state. Animal electrophysiology indicates that the dopaminergic nigrostriatal pathway has a dual tonic and phasic action. Intermittent dopaminergic stimulation is associated with behavioural hyposensitivity both in animal models and in patients with Parkinson's disease. Continuous dopaminergic stimulation provides a tonic background and improves some clinical problems but is also associated with tolerance. None of the available pharmacological approaches can restore the dopamine deficiency of Parkinson's disease to physiological levels. Continuous dopaminergic stimulation for < 24 h, associated with small doses of levodopa or a short-acting dopamine agonist, appears to be the best, albeit imperfect, therapeutic approach until other, more efficacious remedies are developed.

Behavioral tolerance to repeated apomorphine administration in parkinsonian monkeys

Four consecutive injections (s.c.) of apomorphine (Apo) were given to 5 parkinsonian monkeys after i.v. MPTP administration. The minimal effective dose (MED) of Apo was defined as that capable of reducing motor disability by 50% or more for a minimum period of 30 min. Repeated apomorphine injections were given with an interval of 30 min after the motor effect of the previous injection had worn off or with a separation of 3 h between injections. The doses used in different experiments were the MED (2.4 micrograms/kg), 4 MED and 8 MED. In every experiment the duration of motor benefit was longest with the first Apo injection. There was a decay in the duration of the response elicited by consecutive Apo injections when given 30 min after the previous effect had waned. This was significant for the MED and 4 MED (ANOVA, P < 0.01). When Apo boluses were given with an interval of 3 h there was a significant reduction in the duration of the response elicited by the MED, 4 MED and 8 MED of apomorphine. For the MED the reduction in the duration of the motor response was significantly greater for injections given with a 30-min interval than 3-h interval. These findings indicate that behavioral hyposensitivity to repeated Apo administration in parkinsonian monkeys occurs preferentially when near threshold doses are given with short intervals.

Diurnal differences in response to oral levodopa

Diurnal differences in duration and quality of motor response to levodopa are frequently described by patients. The quality and duration of motor responses were objectively assessed to morning and afternoon oral levodopa doses in five patients with Parkinsonian motor fluctuations who complained of diurnal variation in response to their normal levodopa medication. Results suggest that under controlled conditions which eliminated the effects of diet and overlapping levodopa effects the response to levodopa remained unchanged throughout the day, and that the duration of response could be predicted by plasma levodopa levels.

The role of D1 and D2 receptors in dopamine agonist-induced modulation of affective defense behavior in the cat

The role of D1 and D2 dopamine (DA) receptor subtypes in mediating DAergic modulation of affective defense behavior in the cat has been investigated in the present study. Feline affective defense, characterized mainly by autonomic arousal, ear retraction, hissing and paw striking, was elicited by electrical stimulation of the ventromedial hypothalamus. Following the establishment of a stable threshold current for eliciting the hissing response of the behavior, the effect of systemic (IP) administration of various DAergic agonists and antagonists on the hissing threshold was determined. The injection of the nonselective DA agonist apomorphine (1.0, 0.3 and 0.1 mg/kg) facilitated hissing in a dose-related manner. This effect was mimicked by the D-2 selective agonist LY 171555 (0.1, 0.03 and 0.01 mg/kg) but not by the D1-selective agonist SKF 38393 (1.0, 5.0 and 10.0 mg/kg), and was blocked by the nonselective and the D2-selective antagonists haloperidol (0.1 and 0.5 mg/kg) and spiperone (0.2 mg/kg), respectively. The D1-selective antagonist SCH 23390 blocked apomorphine-induced facilitation only at a high dose (0.5 mg/kg). In addition, the injection of haloperidol (1.0 mg/kg), spiperone (0.2 mg/kg) or SCH 23390 (0.1 mg/kg) alone inhibited the behavior. It was therefore concluded that DAergic facilitation of affective defense behavior is mainly mediated by the D2 receptors, but that activation of the D1 receptors may play a "permissive" role. The interaction between the D1 and D2 receptors in mediating this facilitation and the behavioral specificity of the effect are discussed.

Comparative study of the behavioral changes evoked by d-amphetamine and apomorphine in adult cats. Dose-response relationship

The behavioral effects of d-amphetamine and apomorphine administration were studied in 17 adult cats. The doses of amphetamine administered were 0.1, 0.5, 1.0 and 5.0 mg/kg; those of apomorphine, 0.1, 0.5, 1.0 and 2.0 mg/kg. These two drugs evoked in the same animal marked differences in behavioral responses. Amphetamine induced a dose-dependent hypomotility, which was marked with the higher doses. In addition, rhythmic, bilateral slow movements of the head as a mode of stereotypy, indifference to the environment and dose-dependent increase in respiratory rate. Apomorphine elicited limb flicking, dose-dependent hypermotility and increase in olfactory behavior, the last two reactions with stereotypy characteristics. The animals appeared as if being scared, hyperreacting to sudden stimuli and showing total indifference to the surrounding environment. There were marked differences in behavioral responses evoked by these two agonists of the catecholaminergic system. These data do not conform with the behavioral reactions reported in the rat by other investigators. The disagreement with other communications is probably due to differences in reactivity of the species employed. The processes involved in the diversity of the behavioral responses of the cat to the administration of amphetamine and apomorphine have not been delucidated.

Tyrosine hydroxylase immunochemistry and quantitative light microscopic studies of the mesolimbic dopamine system in rat brain: effects of chronic methamphetamine administration

Long-term treatment of rats with methamphetamine (20 mg/kg, IP, every 12 hours for 10 days) resulted in a large decrease in tyrosine hydroxylase staining axons and terminal boutons in the nucleus accumbens and frontal cortex, as well as the ventral tegmental area of the midbrain, when examined 60 days following termination of the drug treatment regimen. Quantitative analysis showed a 71 and 78% decrease in tyrosine hydroxylase staining processes in the nucleus accumbens and frontal cortex, respectively, and a 90% decrease in tyrosine hydroxylase positive material in the ventral tegmental area. Thus, tyrosine hydroxylase enzyme in both the cell bodies of the midbrain ventral tegmental area as well as in the nerve terminals in post-synaptic target regions of the forebrain is depleted by chronic methamphetamine administration.

Comparison of motor depressant effects of caerulein and N-propylnorapomorphine in mice

The motor depressant effects of caerulein and N-propylnorapomorphine (NPA) were compared in male mice. Caerulein (1-50 micrograms/kg SC) in a dose dependent manner depressed the exploratory activity, whereas NPA in lower doses (0.5-10 micrograms/kg SC) decreased the motor activity, but in higher doses (over 50 micrograms/kg) had stimulating effect on the exploratory behavior. In mice selected according to their motor response after administration of 100 micrograms/kg NPA to weak and strong responders, the low dose of NPA (1 microgram/kg) similarly suppressed motor activity in both selected groups, while the effect of caerulein (2 micrograms/kg) was apparently higher in weak responders. Destruction of catecholaminergic terminals by 6-hydroxydopamine (60 micrograms ICV) reversed completely the motor depressant effect of NPA, whereas degeneration of serotoninergic terminals (5,7-dihydroxytryptamine 60 micrograms ICV or p-chloroamphetamine 2 X 15 mg/kg IP) enhanced the sedative effect of NPA. The motor depressant effect of caerulein remained unchanged after lesions of monoaminergic terminals in forebrain. Subchronic haloperidol (0.25 mg/kg IP, twice daily during 14 days) treatment, reducing significantly the density of high-affinity dopamine2- and serotonin2-receptors, decreased the motor depressant action of caerulein. It is possible that motor depressant effect of caerulein, differently from the action of NPA, is mediated through the high-affinity dopamine2-receptors and in lesser extent through the high-affinity serotonin2-receptors.

Dissociations between the effects of hallucinogens on behavior and raphe unit activity in behaving cats

The hypothesis that hallucinogenic drugs exert their behavioral effects by an action at pre- or postsynaptic serotonin receptors was evaluated by co-administering various drugs that possess either serotonin agonist or antagonist properties, while concurrently monitoring behavior and the electrophysiological activity of serotonin-containing dorsal and median raphe neurons in freely moving cats. Co-administration of the serotonin receptor blockers, metergoline or mianserin, with lysergic acid diethylamide (LSD) produced no change in the inhibitory effects of LSD on raphe neurons, but produced a dose-dependent blockade of the behavioral effects of LSD in the cat. The latter data suggest that perhaps LSD exerts its behavioral effects by an action at postsynaptic serotonin receptors. Co-administration of drugs that increase synaptic serotonin, L-5-hydroxytryptophan, tranylcypromine, fluoxetine or p-chloramphetamine with LSD greatly potentiated the inhibitory effect of LSD on raphe unit activity, but also produced dose-dependent decreases in these behavioral effects of LSD in the cat. Thus, both enhancing the activity at postsynaptic serotonin receptors and receptor antagonism blocked the behavioral effects of LSD. Co-administration of dopamine receptor blockers, haloperidol or chlorpromazine, produced no significant change in the response of raphe neurons to LSD, but these drugs also produced a dose-dependent blockade of the behavioral effects of LSD in the cat. Co-administration of the dopamine agonists, apomorphine or d-amphetamine, however, potentiated the behavioral effects of LSD, while producing a partial reversal of the inhibitory effects of LSD on raphe unit activity. The results are discussed in the context of using animal models to study the possible actions of hallucinogens in humans.

Simultaneous recording of dorsal raphe unit activity and serotonin release in the striatum using voltammetry in awake, behaving cats

Simultaneous recordings of unit activity in the dorsal raphe nucleus (RD) and serotonin (5HT) release in the striatum were made in the cat. Unit recordings were made using Formvar-coated 32 microns diameter nichrome wires. 5HT release was measured using linear sweep voltammetry with semi-differentiation using electrodes prepared from Teflon-coated 32-gauge stainless steel wire filled with carbon paste and Ag/AgCl electrodes and 27-gauge stainless steel needles as reference and auxiliary electrodes, respectively. The working electrodes were scanned at a rate of 10 mV/s over the range of -0.1 to +0.5 V every 5 minutes using a BAS CV37 voltammograph. During REM sleep RD unit activity was decreased 94% from quiet waking (QW) baseline, while the voltammetric response was decreased by only 57%. Chloral hydrate anesthesia decreased RD unit activity by 18% from QW while the voltammetric response was decreased by 39%. LSD decreased RD unit activity by 50% from QW, but the voltammetric response was decreased by 88%. P-chlorophenylalanine produced no significant change in RD unit activity but decreased the voltammetric response by 82%. These data suggest that RD unit activity and 5HT release often differed dramatically.

Ascorbic acid antagonizes the behavioural effects of LSD in cats

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

Biphasic modulation of spontaneous activities of entopeduncular neurons by systemic application of apomorphine in anesthetized cats

The responses of entopeduncular neurons to apomorphine were investigated with extracellular recording methods in anesthetized cats. Apomorphine was applied intravenously in increasing doses, which cumulatively doubled with each addition (5-640 micrograms/kg). The spontaneous firing rates of entopeduncular neurons, which were inhibited by electrical stimulation of the caudate nucleus, increased when lower doses of apomorphine (5-20 micrograms/kg) were applied. However, higher doses (40-640 micrograms/kg) produced a dose-dependent decrease in the firing rate. The results suggest that there are direct and indirect effects of systemically administered apomorphine on entopeduncular neurons which may contribute to biphasic responses in the spontaneous discharge rate.

Chronic administration of D-amphetamine increases [3H]spiroperidol binding in cat brain

Administration of D-amphetamine sulfate twice daily for 10 consecutive days, in doses increasing from 10 mg/kg per day (i.p.) to 30 mg/kg per day resulted in significant increases in the Bmax for [3H]spiroperidol receptor binding in the striatum (+44.7%) and limbic forebrain (+40.3%) in cats. There were no significant changes in the KD value for either brain region. A single dose of amphetamine (15 mg/kg i.p.) produced no significant changes in [3H]spiroperidol binding in either brain region. These data are in contrast with previous studies which reported a significant decrease in dopamine receptor binding following chronic amphetamine treatment in rats.

Activity of dopamine-containing substantia nigra neurons in freely moving cats

The present series of studies examined the activity of presumed dopamine-containing neurons in the substantia nigra of freely moving cats. These neurons were found to have a slow (1-9 spikes/sec) discharge rate, unusually long duration action potentials (2-4 msec) and frequently fired in bursts with progressive decreases in the amplitude of the action potential within the burst. These neurons showed no significant change in their activity across the sleep-waking cycle, and showed no changes in activity with phasic movement. Most units were unresponsive to olfactory, noxious, tactile, auditory and visual stimulation, when unit activity was integrated over several seconds following stimulus presentation. However, phasic auditory and visual stimuli produced a period of excitation lasting approximately 120 msec after a delay of about 80 msec. The period of excitation was followed by a period of inhibition lasting approximately 60 msec. Presumed dopamine-containing substantia nigra units showed no significant circadian changes in activity. The firing rates of these units were inhibited by dopamine agonists, including the direct-acting agonist, apomorphine, the dopamine precursor, L-dihydroxyphenylalanine, a dopamine releasing agent, d-amphetamine, and a dopamine reuptake blocker, bupropion, and were excited by a dopamine receptor blocker, haloperidol. Thus, these neurons show many similarities to dopamine units recorded in anesthetized rats; however, they showed several notable differences as well. Recording the activity of these units in behaving animals allows one to examine behavioral correlates of unit activity. Furthermore, the data (sensory stimulation, pharmacological, etc.) obtained in the unanesthetized preparation are far more relevant to the physiological and pharmacological effects that may occur in humans.

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.

Ontogeny of the behavioral effects of lysergic acid diethylamide in cats

The ontogeny of the behavioral effects of lysergic acid diethylamide (LSD) was examined in cats between the ages of 4 and 112 days postpartum. The kittens showed little LSD-induced behavioral change prior to 14 days of age. By the age of 21 days, however, the kittens exhibited many of the behavioral signs characteristic of LSD-induced behaviors in adult cats. These behaviors include limb-flicking, abortive grooming, head-shakes, grooming, and investigatory responses. In general, these behaviors began at a low frequency of occurrence, then increased rapidly with advancing age, reaching adult values by approximately 35-40 days of age, and remained relatively constant through 112 days postpartum. The time course for the behavioral effects following an acute injection of LSD showed the adult pattern, i.e., persisting for approximately 8 hr post-injection, from their earliest appearance during ontogeny. Young kittens (21-42 days of age) were resistant to the development of tolerance following repeated administration of the drug. LSD was capable of eliciting certain behaviors, such as head-shakes and grooming, well in advance of the age at which they normally appear spontaneously. This indicates that the neuronal and musculature substrata are developed for the performance of these behaviors long before the kitten naturally employs them.

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.

Amphetamine and LSD as discriminative stimuli: alterations following neonatal monoamine reductions

Male adult Sprague-Dawley rats (70 days of age), neonatally depleted of either 5-hydroxytryptamine (5HT) via 5,7-dihydroxytryptamine (5,7-DHT; ICS) + desmethylimipramine (DMI; IP) at 3 days of age or dopamine (DA) via 6-hydroxydopamine (6-OHDA; ICS) + DMI at 14 days of age, were trained to discriminate either d-LSD-tartrate (80 micrograms/kg; IP) or d-amphetamine (d-AMPH) sulfate (0.90 mg/kg; IP) from saline utilizing a two lever drug discrimination paradigm. A neurochemical analysis at the termination of these studies revealed the following in terms of %DA or %5HT (presented in that order) depleted with respect to the appropriate vehicle control group: telencephalon; 96 and 96%, diencephalon; 51 and 31%, and brain stem; 76 and 80%. Rats learned to discriminate either d-AMPH or LSD regardless of amine depleted. In addition, the depletion of 5HT had little effects on dose or drug generalizations, or the ability of known antagonists to antagonize the discrimination stimulus (DS) effects of either LSD or d-AMPH. The effect of DA depletion, on the other hand, was to increase the sensitivity of the LSD DS at low doses, while decreasing the sensitivity of the d-amphetamine DS. DA depletion also had the effect of reducing the effectiveness of the LSD-antagonists, pizotifen maleate (BC105), while the opposite was observed for the d-AMPH antagonist, trifluoperazine HCI. These data suggest that: (1) LSD and d-amphetamine discrimination stimuli are not mediated and/or influenced via the compromised aspects of the 5HT systems (other central mechanisms may have compromised for these 5HT deficits); (2) the LSD DS is mediated or influenced both by serotonergic and dopaminergic mechanisms; and (3) the d-amphetamine DS is mediated by certain aspects of the dopaminergic system with little evidence for the involvement of 5HT systems.

Lack of synergism and cross tolerance between tactile stimulus- and LSD-induced limb flicking in the cat

The hypotheses that LSD-induced limb flicking, as well as tolerance to this behavioral effect following repeated drug administration, are due to alterations in somatosensory thresholds were tested by examining the rate of limb flicking to LSD alone, saline plus water on the limbs, or LSD plus water on the limbs, and by comparing the limb flick rate with water on the limbs in drug tolerant versus non-tolerant conditions. Cats exhibited the same rate of limb flicking in response to water on the limbs regardless of whether they were pretreated with saline of LSD. Furthermore, there was no significant difference in the tactile stimulus-induced rate of limb flicking in the tolerant versus non-tolerant states. These data suggest that LSD-induced limb flicking is not simply a function of drug-induced altered somatosensory thresholds, but is apparently reflective of more complex neural processes.