Independent effects of morphine and apomorphine on stereotyped gnawing in the hamster

Eight experiments were conducted to investigate the effects of apomorphine, a dopaminergic agonist, and of morphine, an opiate, on stereotyped behavior in the hamster. Animals were observed at two minute intervals for one hour and incidents of stereotyped gnawing, licking and sniffing were recorded using a time-sampling method. Both morphine and apomorphine produced dose-related increases in stereotyped gnawing. A low dose of the opiate antagonist, naloxone (0.4 mg/kg), blocked morphine-induced gnawing but neither that dose nor higher doses of naloxone (1, 4 and 10 mg/kg) blocked apomorphine-induced gnawing. A low dose of the dopaminergic antagonist, haloperidol (0.05 mg/kg), blocked apomorphine-induced gnawing but did not block morphine-induced gnawing. Further experiments indicated that morphine administration did not sensitize, or influence in any way, subsequent apomorphine-induced stereotyped behavior.     

Systematic comparison of apomorphine-induced behavioral changes in two mouse strains with inherited differences in brain dopamine receptors

Dosage and time dependencies of apomorphine-induced changes in stereotyped behaviors (climbing, gnawing and sniffing), locomotor activity and rearing activity were compared in young adult male mice of two inbred strains, DBA/2 and C57BL/6. These two strains are known to differ in their genetically specified brain dopamine receptor number. Apomorphine administered intraperitoneally at dosages of 0.5-20 mg/kg failed to induced stereotyped climbing in DBA/2 at any of the doses tested but markedly increased climbing in C57BL/6 at higher dosages. Apomorphine-induced stereotyped gnawing occurred in both strains at higher dosages although the latency was shorter and maximal effect greater in C57BL/6. Stereotyped sniffing was induced in both strains to a comparable degree at doses greater than or equal to 2.0 mg/kg, and the duration of this stereotypy was indistinguishable between strains. Locomotor activity was inhibited maximally in DBA/2 at an apomorphine dosage of 2 mg/kg and was inhibited to a greater extent than was C57BL/6. Rearing was inhibited in both strains by doses of apomorphine greater than or equal to 0.5 mg/kg; however the duration of the effect was considerably greater in DBA/2 than in C57BL/6. These data suggest that genetically determined differences in central dopamine receptors may have profound and selective effects on behaviors mediated by dopamine pathways; that complex behavioral patterns, e.g., apomorphine-induced stereotypy, may be dissected in to individual components by identifying neuropharmaco genetic differences between strains; that marked strain-specific, inherited differences in dopamine agonist-induced behavioral changes do occur among inbred, non-mutant mouse strains and that their occurrence in other mammalian species including man should be considered.     

An observational method for quantifying the behavioural effects of dopamine agonists: Contrasting effects of d-Amphetamine and apomorphine

A novel means of measuring and analysing behavioural effects of dopamine agonists is described and illustrated by a comparison of the effects of d-amphetamine and apomorphine in the rat. d-Amphetamine (0–15 mg/kg IP) produced significant dose- and time-dependent changes in responses such as locomotion, rearing and sniffing, but not in licking or gnawing. In contrast, apomorphine (0–5 mg/kg SC) produced significant increases in licking and gnawing, as well as in locomotion and sniffing, but no changes in rearing. The results are discussed in comparison with those obtained by other methods, such as photocell beam interruptions or stereotypy rating scales, and may be of importance in elucidating the functions of the forebrain dopamine projections.     

Ontogeny of GABA-ergic and dopaminergic mediation of gnawing behavior in the mouse

The ontogenetic course of dopaminergically mediated gnawing and the potentiation of this behavior by muscimol (a GABA receptor agonist) was explored in developing and young adult mice using a time-sampling (in 5-, 8-, 11-, and 14-day-old pups), or a corrugated paper procedure (in 14-, 17-, 20-, 23-, 26-, 35-, and 53-day-old animals). In experiment 1, the older mice group (14–53 days), displayed a dose-dependent gnawing behavior after methylphenidate, a dopamine indirect agonist (20, 30, 50 mg/kg). Similarly, in 5-, 8-, 11-, and 14-day-old pups, methylphenidate (10, 20, 50 mg/kg) evoked stereotyped gnawing (or indissociable gnawing-licking in 5-day-old pups), with maximal effects after the two lower doses at 8–11 days of age (experiment 2). Muscimol pretreatment (dosages ranging from 0.025 to 1.3 mg/kg) induced a clear-cut potentiation of gnawing elicited by methylphenidate (10 or 20 mg/kg) as early as 8 days of age (experiments 3 and 4). However, muscimol did not potentiate gnawing in 5-day-old pups treated with 10 or 2.5 mg/kg methylphenidate. The effectiveness of methylphenidate in inducing gnawing-licking among 5-day-old pups confirms the early maturation of central dopamine receptors reported in the literature. It is speculated that the absence of potentiating action of muscimol on methylphenidate-induced gnawing-licking at this age may be due to a functional immaturity of the GABAergic striato-nigro-tectal system, which is thought to transmit dopaminergic striatal stereotyped response at the output stations (recent review by Scheel-Krüger 1986). It is also pointed out that the lack of behavioral response in muscimol-methylphenidate treated neonates may indicate that their motor repertoire has not yet sufficiently differentiated.     

Behavioral effects of apomorphine isomers in the rat: Selective locomotor-inhibitory effects of S(+)N-n-propylnorapomorphine

The optical isomers of apomorphine (APO) and N-n-propylnorapomorphine (NPA) were evaluated behaviorally in the rat. Both R(-) isomers induced motor-excitatory effects and strong stereotyped sniffing, licking, and gnawing, as has been reported previously. The S(+) isomers selectively inhibited locomotor activity and did not induce stereotypy or catalepsy. These actions of the S(+) aporphines were selective against locomotor activity stimulated by low doses of R(-) isomers. (+)NPA (ID₅₀=0.2 mg/kg) was 20 times more potent than (+)APO (ID₅₀=4 mg/kg) in antagonizing the locomotor arousal-inducing effects of (-)APO (at ED₅₀=0.3 mg/kg). (+)NPA also inhibited spontaneous locomotor activity much more potently (ID₅₀=3.0 mg/kg) than did (+)APO (ID₅₀>50 mg/kg). Neither S(+) aporphine had a significant effect against stereotypy induced by the R(-) isomers, even at high doses (up to 30 mg/kg). Inhibition of the effects of (-)APO by (+)NPA appeared not to be due to altered uptake of (-)APO into brain. These results suggest that S(+)NPA or its congeners and analogs may have selective antidopaminergic actions in limbic rather than striatal areas of mammalian brain.     

The effects of some atypical neuroleptics on apomorphine-induced behaviors as a measure of their relative potencies in blocking presynaptic versus postsynaptic dopamine receptors

The effects of the atypical neuroleptics clozapine, thioridazine and sulpiride on behaviors induced by apomorphine were recorded, using a time-sampling observational paradigm. A low dose of apomorphine (0.1 mg/kg, SC) produced hypomotility. Of the neuroleptics tested, only sulpiride antagonized this hypomotility. Apomorphine in higher doses (0.2-1.0 mg/kg, SC) produced stereotyped behaviors (sniffing down and licking or gnawing). All three atypical neuroleptics antagonized stereotypy. The effects of sulpiride on apomorphine-induced hypomotility and stereotypy are consistent with the notion that this drug has strong presynaptic and weak postsynaptic blocking effects at dopamine receptors. The mechanisms of action of clozapine and thioridazine may be different from that of sulpiride. Perhaps the anticholinergic activities of these drugs mediate some of their behavioral effects. The effects of these atypical neuroleptics on apomorphine-induced stereotypy are opposite in direction to their effects on amphetamine-induced stereotypy, suggesting that these two behavioral patterns are not measures of the same neural process.     

Functional reactivity of the dopaminergic system following acute and chronic ketamine treatments

This study examined the effects of acute (15 mg/kg, i.p.) and chronic subanesthetic (15 mg/kg, i.p., t.i.d, for 6 days) doses of ketamine [a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist] on amphetamine (presynaptic dopamine releasing agent; 10 mg/kg, i.p.) and apomorphine (a D₂ receptor agonist; 1 mg/kg, i.p.)-induced stereotyped behaviors. The effect of acute and chronic ketamine on haloperidol (a D₂ receptor antagonist; 1.6 mg/kg, i.p.)-induced catalepsy was also examined. Acute ketamine and chronic ketamine pretreatment increased amphetamine-induced stereotyped sniffing and locomotion compared with control groups. Acute ketamine significantly increased apomorphine-induced stereotyped sniffing. However, chronic ketamine had no significant effect on apomorphine-induced stereotyped sniffing. Acute, but not chronic ketamine treatment abolished haloperidol-induced catalepsy. The increase in amphetamine-induced stereotyped behaviors and the reversal of haloperidol-induced catalepsy by acute ketamine suggest that blockade of NMDA receptors by ketamine facilitates dopaminergic transmission. The absence of significant effect of chronic ketamine on apomorphine-induced stereotyped sniffing and haloperidol-induced catalepsy suggests that chronic ketamine does not modulate postsynaptic dopaminergic D₂ receptors. It is suggested that chronic ketamine increased amphetamine-induced behaviors by causing hypersensitivity of presynaptic dopamine releasing mechanisms on dopaminergic terminals.     

An assessment of the spontaneous activity of rats administered morphine,phencyclidine, or nicotine using automated and observational methods

The effects of morphine, phencyclidine, and nicotine on motor activity in rats were characterized using both observational and automated methods. Activity was scored observationally using a time-sampling method that tabulates discrete response categories (still, locomotion, rearing, sniffing, licking, gnawing, head down, swaying, grooming, falling). Behavior was assessed automatically using an activity monitor that records both the time and activity counts spent in large and small (less than 3 cm) movements, rearing, and resting. The following results using male Sprague-Dawley rats represent significant differences from saline-treated controls. Morphine (1–4 mg/kg SC) increased the incidence of locomotion, sniffing, swaying, and grooming depending on the time after drug injection. These changes corresponded to an increase in large and small movement counts and time as measured by the activity monitor. Phencyclidine (1.25–5 mg/kg SC) caused dose-related increases in the incidence of locomotion, sniffing, swaying, and falling, and induced greater large and small activity movement counts and time especially after the 5 mg/kg dose. Nicotine (0.033–0.33 mg/kg SC) decreased the incidence of rearing and increased the frequency of sniffing and grooming. These changes corresponded to a decrease of rearing activity and to a slight increase in small activity. The present data indicate that morphine, phencyclidine, and nicotine exert dose-related and time-related appearances of various categories of behavior in the rat, and that the data from the automated method complement the findings of the direct observational method.     

Influence of phenoxybenzamine on the stereotyped behaviour induced by fencamfamine in rats: evidence for a qualitative alteration

The interactions between norepinephrine (NE) and dopamine (DA) systems in mediating stereotyped behaviour induced by different doses of fencamfamine (1-30 mg/kg) were studied in male rats. Pretreatment with phenoxybenzamine (5.0 mg/kg) resulted in a significant leftward shift of the control curve for stereotypy. The qualitative analysis of the stereotyped behaviour parameters when compared to controls showed: higher rearing frequency at a dose of 3.0 mg/kg; lower locomotor activity at a dose of 6.0 mg/kg; higher licking and gnawing frequencies at a dose of 10.0 mg/kg. These findings indicate that the role of DA systems on the stereotyped behaviour induced by fencamfamine is dependent on the degree of NE transmission in the CNS.     

Evidence for postsynaptic dopamine agonist effects of B-HT 920 in the presence of the dopamine D-1 agonist SKF 38393

The ability of B-HT 920, a selective dopamine (DA) D-2 agonist, to stimulate postsynaptic DA receptors in brain was evaluated by assessing its ability to induce stereotypy and to increase locomotor activity in rats. When administered alone, B-HT 920 (0.03–3.0 mg/kg) did not induce stereotypy and produced only inhibition of locomotor activity, suggesting a lack of postsynaptic DA agonist actions. However, a different pattern of effects emerged when B-HT 920 was administered in combination with the selective DA D-1 agonist SKF 38393 (10 mg/kg): stereotypies (sniffing, licking, and gnawing) were induced and there was an inverted U-shaped function for locomotor activity. These data are consistent with the hypothesis that B-HT 920 has postsynaptic DA D-2 receptor agonist effects in normal rats that are revealed when D-1 receptor stimulation is also increased. Offprint requests to: L.T. Meltzer     

Selective antagonism by clonidine of the stereotyped and non-stereotyped motor activity elicited by atropine

The effects of clonidine, an indirectly-acting cholinergic antagonist, on 5 behaviors elicited by atropine (locomotion, rearing, sniffing, grooming and gnawing) were studied in rats. Clonidine did not alter the prevalence or magnitude of atropine-elicited locomotion and rearing. In contrast, clonidine suppressed the occurrence and degree of 3 stereotyped behaviors, namely, sniffing, grooming and gnawing. This selectivity of clonidine suggests differences in the neural pathways subserving the various stereotyped motor activities.     

Effects of AMPA receptor antagonists on dopamine-mediated behaviors in mice

 Current data indicate that dopaminergic and glutamatergic neurotransmitter systems interact. The role of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) glutamate receptor subtypes in modulating dopamine neurotransmission, however, remains unclear. The noncompetitive AMPA antagonists, GYKI 52466 (5–40 mg/kg) and LY300164 (1–6 mg/ kg), and the competitive AMPA antagonists, LY326325 (5–80 mg/kg) and NBQX (10–80 mg/kg), were compared to the dopamine antagonist, haloperidol (0.03– 1.0 mg/kg), for their ability to inhibit dopamine-mediated behaviors after IP administration in mice. The behavioral paradigms included amphetamine- or dizocilpine-induced hyperactivity, amphetamine-induced stereotyped sniffing, and apomorphine-induced climbing and stereotyped sniffing. All four AMPA antagonists and haloperidol attenuated amphetamine- and dizocilpine-induced hyperactivity and decreased spontaneous locomotion. Haloperidol and GYKI 52466 were more potent against amphetamine than against dizocilpine. In contrast, LY326325 was more potent against dizocilpine than against amphetamine. The hyperactivity decreases by LY300164 and NBQX were most likely due to non-specific effects on motor behavior. The AMPA antagonists and haloperidol also attenuated amphetamine- induced stereotypy. Unlike haloperidol, however, GYKI 52466, LY300164, and NBQX failed to attenuate apomorphine-induced climbing and stereotyped sniffing. LY326325, on the other hand, attenuated apomorphine-induced stereotypy, but not climbing. These results indicate that AMPA receptor antagonists can attenuate the behavioral effects of drugs, such as amphetamine and dizocilpine, that increase dopamine neurotransmission. However, the behavioral effects of the direct dopamine agonist apomorphine are not consistently attenuated by AMPA antagonists. The competitive AMPA receptor antagonist LY326325 appears to have a profile distinct from both haloperidol and the other AMPA antagonists tested. Received: 23 December 1996/Final version: 8 September 1997     

Scopolamine produces locomotor stereotypy in an open field but apomorphine does not

Both dopaminergic and nondopaminergic drugs produce hyperlocomotion in rats. Dopaminergic drugs also produce focused stereotypy (absence of locomotion and intense sniffing or licking/biting of a restricted area of the environment). Some drugs produce repetitive routes of locomotion; this phenomenon might represent a combination of hyperlocomotion and stereotypy. Scopolamine (an acetylcholine antagonist) and apomorphine (a dopamine agonist) both produce hyperlocomotion in rats; apomorphine also produces focused stereotypy but scopolamine does not. This research determines whether these drugs also produce locomotor stereotypy as measured by gamma. Scopolamine (0.5 and 2.0 mg/kg) produced locomotor stereotypy at both doses. Apomorphine (1.0, 2.0, and 3.0 mg/kg) failed to reliably produce locomotor stereotypy. Thus, there is not necessarily a relationship between the ability of a drug to produce focused stereotypy and the ability of the drug to produce locomotor stereotypy.     

Measurement of acute and chronic behavioural effects of methamphetamine in the mouse

A simple and reliable method was developed for rating the dose-related behavioural effects of methamphetamine in male Swiss Albino mice for acute or chronic drug treatment. This procedure was based on a frequency count of certain behaviours made at 15-min intervals over a 90-min period following drug administration. The Fisher Randomization procedure was adapted to analyze behavioural data for the chronic studies. Clear-cut, dose-related behavioural responses occurred following acute (+)-methamphetamine administration and ranged from decreased quiescence (0.64 mg/kg) through increased locomotor activity (2.5 mg/kg), a mixture of stereotyped behaviour and increased locomotor activity (5.0 and 7.5 mg/kg), to primarily stereotyped gnawing, licking or sniffing (10 mg/kg). In studies involving chronic administration of (+)-methamphetamine at 0.64, 2.5 and 10 mg/kg conducted over six and seven weeks, behavioural responses were more exaggerated than in acute studies. All behaviours returned to normal levels in the recovery week except for locomotor activity at the 10 mg/kg dosage. In some animals, chronic treatment with 10 mg/kg (+)-methamphetamine led to protracted self-tearing that replaced the gnawing, licking, sniffing stereotype.     

Changes in drug-induced stereotyped behavior after 6-OHDA lesions in noradrenaline neurons

Drug-induced stereotyped behaviors are often assessed by rating scales where the eventual appearance of sniffing, licking, and biting are rated as increasing intensity of dopaminergic stimulation. A 6-OHDA induced bilateral lesion (4×3-8 g/4 l 6-OHDA) in the ascending noradrenaline neurons, lateral to the medial raphe nucleus, of 180 g Wistar rats, affecting selectively noradrenaline and not dopamine or 5-hydroxytryptamine neurons, caused a change in the d-amphetamine sulphate (5–3 mg/kg s.c.) and phenethylamine hydrochloride (40 mg/kg) induced stereotyped sniffing behavior to the performance of discontinuous or continuous licking behavior; biting/gnawing was rarely induced. The site of the lesion and the partial antagonism of 6-OHDA by the uptake inhibitor protriptyline indicate a noradrenergic influence on the behavioral expression of the dopaminergically mediated stereotyped behavior.     

Acute and long-term effects of thyrotropin releasing hormone on behavior mediated by dopaminergic and cholinergic activities in mice

Acute and long-term (3 weeks) effects of thyrotropin releasing hormone (TRH) on behavior were investigated in mice. A single injection of TRH produced Straub tail, tremor and salivation, as well as stereotyped responses, such as head bobbing, jaw movement, digging and sniffing. Dose- and time-dependency for the effects of TRH were different depending on each response. A single injection of TRH at a low dose of 2.5 mg/kg SC did not produce stereotypy but this behavior was induced when this dose of TRH was administered in combination with atropine (3 mg/kg IP). In addition, a single low dose of TRH elicited tremor and salivation which were potentiated by physostigmine (0.1 mg/kg IP). A single high dose (20 mg/kg IP) produced marked tremor and salivation which were conversely blocked by atropine. Following daily administration of TRH at a low dose of 2.5 mg/kg SC for 21 days, stereotyped behavior was progressively increased whereas tremor and salivation were decreased. This increase in stereotyped behavior was inhibited by haloperidol (1 mg/kg IP) or physostigmine (0.1 mg/kg IP). When saline was administered instead of TRH for 3 days after long-term administration of TRH, stereotyped behavior was maintained for 2 days but thereafter decreased to some extent. When TRH (1.25 mg/kg SC) was again administered at this stage, there was a marked increase in stereotyped response. These results suggest that TRH induces dopaminergic activation, accompanied by both cholinergic inhibition and cholinergic activation, and that the former is potentiated while the latter is reduced after daily administration of TRH.     

Role of the laterodorsal tegmental nucleus in scopolamine- and amphetamine-induced locomotion and stereotypy

Scopolamine (1.5 mg/kg; i.p.) or amphetamine (3 mg/kg; i.p.) increases locomotion and stereotyped behavior patterns in rats. Previous studies suggest that scopolamine acts via muscarinic receptors near the midbrain-pons border. In this study, unilateral microinjections in N-methyl-scopolamine (2.5-10 microg) into the laterodorsal tegmental nucleus (LDT) increased locomotion. Bilateral ibotenate lesions of the LDT attenuated scopolamine-induced locomotion by 68% 7 days postlesion, and by 35% 28 days postlesion. LDT lesions reduced scopolamine-induced stereotypy less than locomotion. The sensitization to amphetamine observed on repeated tests was attenuated by LDT lesions for stereotypy, but not for locomotion. These findings suggest that scopolamine induces locomotion largely, but not exclusively, by blocking muscarinic receptors in LDT.     

Individual and morphological differences in the behavioural response to apomorphine in rats

The topography of stereotyped behaviour produced by apomorphine in rats was studied by using either a scoring system, based on observation in a wire cage, or by quantification of horizontal and vertical activities, and of the total distances run in an open field, using an automatic recording system. The latter design was combined with a classification of the type of stereotyped behaviour observed during recording. In addition, the reproducibility of the nature of the stereotyped behaviour and its dose-dependence in individual animals was evaluated. In rats observed in a wire cage, apomorphine at lower doses (0.25 or 0.50 mg/kg SC) produced stereotyped sniffing. Increasing the doses led to stereotyped licking and the largest dose (5.00 mg/kg SC) produced predominantly stereotyped gnawing, as was demonstrated graphically. The type of behaviour produced by 2 mg/kg apomorphine in the open field was reproduced well in individuals after a second administration 4 days later. The shift from sniffing to gnawing was observed in most, but not all of the individually classified animals after administration of the largest dose (5 mg/kg). The locomotor part of motility was highest in sniffing animals and lower when gnawing occurred. The non-locomotor part of motility was low in sniffing rats and increased when licking and gnawing occurred. In some of the animals a characteristic climbing behaviour was observed in addition after the larger doses, which did not interfere with sniffing, licking or gnawing.A combination of classification by observation and automatic recording seems the most appropriate way to study the topography of stereotyped behaviour produced by apomorphine.     

Lack of effect of anticonvulsant topiramate on methamphetamine-induced stereotypy and rewarding property in mice

The effects of topiramate, a structurally novel anticonvulsant, on the methamphetamine (METH)-induced expression of stereotypy and conditioned place preference (CPP) in male ICR mice were investigated. After a single administration of METH (10 mg/kg, i.p.), mice showed stereotyped behaviors with a plateau level 25 min after drug challenge. Pretreatment with topiramate (1, 10, and 100 mg/kg, i.p.) 30 min prior to METH challenge had no effect on the expression frequency of stereotypy, compared with saline challenge. No differential effects of topiramate on METH-induced stereotyped behavior (that is, head-bobbing, circling, continuous sniffing, nail and/or wood-chip biting, and vigorous and compulsive grooming) were observed. In saline-challenged groups, the doses of topiramate examined did not induce any stereotyped behaviors. Although mice showed a significant CPP for METH (0.5 mg/kg, i.p.), pretreatment with subchronic topiramate did not affect the magnitude of CPP. Locomotor activity was not affected by the doses of topiramate tested. Conditioned rewarding or aversive effects of topiramate were not observed as indexed by the place preference procedure. These results suggested the lack of effect of topiramate on METH-induced stereotypy and rewarding property in mice.     

p-Chlorophenylalanine and p-chloroamphetamine pretreatment of apomorphine-challenged rats: effects on solitary and social behavior

Following an initial rise in locomotor activity, apomorphine in large doses causes a concurrent rise in brain serotonin levels, locomotor akinesia, and stereotypic gnawing. However, reports to date have failed to observe any effect of pretreatment with serotonin depletors parachlorophenylalanine (pCPA) or parachloroamphetamine (pCA) on apomorphine-induced stereotypy. In the present study the effects of pCPA (250 or 400 mg/kg i.p., 3 days) and pCA (6.4 or 10.4 mg/kg i.p., 3 days) pretreatment on apomorphine-induced (5.0 mg/kg s.c., 5 min) behavior of male rats in the open-field were compared. For half of the trials in the 78 min session, the rats were alone and for half of the trials they were paired with an untreated male rat. pCA pretreatment increased the frequency of line-crossing and of jumping, whereas pCPA pretreatment increased the duration of bouts of locomotion and gnawing. These behavioral differences may be related to the interaction of pCA and pCPA with dopaminergic subsystems in the brain.