Pharmacological characteristics of dopamine receptors involved in the dual effect of dopamine agonists on yawning behaviour in rats

On the Emergence of Tremor in Prodromal Parkinson's Disease

Clinical, neuropathological and neuroimaging research suggests that pathological changes in Parkinson's disease (PD) start many years before the emergence of motor signs. Since disease-modifying treatments are likely to be most effective when initiated early in the disease process, there has been significant interest in characterizing prodromal PD. Some people with PD describe autonomic symptoms at the time of diagnosis suggesting that autonomic dysfunction is a common feature of prodromal PD. Furthermore, subtle motor signs may be present and emerge prior to the time of diagnosis. We present a series of patients who, in the prodromal phase of PD, experienced the emergence of tremor initially only while yawning or straining at stool and discuss how early involvement of autonomic brainstem nuclei could lead to these previously unreported phenomena. The hypothalamic paraventricular nucleus (PVN) plays a central role in autonomic control including bowel/bladder function, cardiovascular homeostasis and yawning and innervates multiple brainstem nuclei involved in autonomic functions (including brainstem reticular formation, locus ceruleus, dorsal raphe nucleus and motor nucleus of the vagus). The PVN is affected in PD and evidence from related phenomena suggest that the PVN could increase tremor either by increasing downstream cholinergic activity on brainstem nuclei such as the reticular formation or by stimulating the locus ceruleus to activate the cerebellothalamocortical network via the ventrolateral nucleus of the thalamus. Aberrant cholinergic/noradrenergic transmission between these brainstem nuclei early in PD couldlead to tremor before the emergence of other parkinsonian signs, representing an early clinical clue to prodromal PD.

Behavioral and neurochemical profiles of discriminant benzamide derivatives

Discriminant benzamide derivatives (DBD), the prototype of which is DO 710 i.e. N- [(1-propyl 2-pyrrolidinyl) methyl] 5-methyl sulfamoyl 2-methoxy benzamide, were compared to classical neuroleptics such as haloperidol in various behavioral and biochemical tests. Whereas the ID50(or ED50) of haloperidol for antagonising various apomorphine-induced behavioral responses and producing catalepsy in rats were all around 0.1 mg/kg. DO 710 clearly distinguished catalepsy, HVA increase and apomorphine-induced licking and sniffing in rats (for which the ED50(or ID50) were 13-54 mg/kg) from apomorphine-induced climbing, yawning and hypothermia (for which the ID50were 1-2 mg/kg) (fig. 1, 2 and 4). Moreover, DO 710 and other DBD potentiated stereotypies in mice, whereas haloperidol and other classical neuroleptics did not (fig. 3). These features do not seem to be attributable to a heterogenous distribution of DBD in brain, since their ED50for HVA increase and for inhibiting3H-N-propylnorapomorphine binding in vivo did not differ in striatum and in limbic regions.

In in vitro binding experiments, DO 710 and other DBD discriminated two classes of3H-domperidone binding sites in striatum, whereas only one component with a relatively low affinity for DBD could be detected in pituitary (fig.5-6, Table 3).3H-DO 710 allowed charaterization of a D-2 site with a low affinity for DBD, which was fully sensitive to GTP regulation and present in pituitary and brain, and of a “D-4” site, preferred by DBD, which was little or not sensitive to GTP, present in brain and particularly enriched in olfactory bulb but absent in pituitary (fig. 7).3H -azidosulpride (i.e. N-[(1-3H- propyl 2-pyrrolidinyl) methyl] 2-methoxy 4-azido 5-methylsulfamoyl benzamide), a photoactivable analog of3H-DO 710, was used for irreversible labelling of dopamine recognition sites. When subjected to SDS-PAGE, receptor from striatum, pituitary and olfactory bulb co-migrated as a single band of 85 kDa (fig. 8).

These results may suggest the existence of two subclasses of dopamine D-2 receptor as targets for neuroleptic actions, one being preferred by DBD. The recognition subunits of these receptors have similar apparent molecular size.

Pain and u-shaped dose responses: occurrence, mechanisms, and clinical implications

This article assesses pain within the context of the dose response. A substantial number of studies indicate that the dose response for pain-related endpoints is commonly biphasic, being independent of the type of biological model employed, endpoint measured, or agent tested. The quantitative features of the dose response are also remarkably consistent regardless of the receptor pathway that mediates the nociceptive response, indicating a likely downstream message convergence. These findings have important implications for drug discovery, development, and clinical evaluation.

Dopamine inhibits trigeminovascular transmission in the rat

OBJECTIVE

Clinical evidence, such as premonitory or postdromal symptoms, indicate involvement of dopamine in the pathophysiology of migraine.

METHODS

To study the influence of dopamine on nociceptive trigeminovascular neurotransmission, we first determined using immunohistofluorescence that dopamine receptors were present in the rat trigeminocervical complex; then using extracellular recording techniques, we examined whether dopamine modulates cell firing in the trigeminocervical complex.

RESULTS

We identified a discrete population of D1 receptors (median, 11; interquartile range, 7-30 neurons/hemisection) predominantly located in the deep laminae and a more abundant population of D2 receptors (median,75; interquartile range, 30-99 neurons/hemisection) that were evenly distributed in the trigeminocervical complex. Intravenous dopamine had no effect on trigeminovascular neurons, whereas when dopamine was applied microiontophoretically, a potent reversible inhibition of L-glutamate-evoked firing was observed. The effect of microiontophoretically applied dopamine was dose dependent. Dopamine also strongly inhibited activation of trigeminocervical neurons in response to middle meningeal artery stimulation in vivo with a maximum effect obtained within 10 minutes after the application and return to baseline within 30 minutes.

INTERPRETATION

We conclude that central dopamine-containing neurons may play a role in modulating trigeminovascular nociception; these neurons offer an important target that will expand our understanding of migraine and may offer new directions for therapy.

Dopamine agonist-induced yawning in rats: a dopamine D3 receptor-mediated behavior

A specific role for the dopamine D3 receptor in behavior has yet to be elucidated. We now report that dopamine D2/D3 agonists elicit dose-dependent yawning behavior in rats, resulting in an inverted U-shaped dose-response curve. A series of experiments was directed toward the hypothesis that the induction of yawning is a D3 receptor-mediated effect, whereas the inhibition of the yawning observed at higher doses is due to competing D2 receptor activity. We compared several dopaminergic agonists with a range of in vitro D3 selectivity, including PD-128,907 [(S)-(+)-(4aR, 10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol HCl], PD-128,908 [(R)-(-)-(4aS,10bS)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol HCl], quinelorane [(5aR-trans)-5,5a,6,7,8, 9,9a,10-octahydro-6-propylpyrido[2,3-g]quinazolin-2-amine dihydrochloride], pramipexole (N'-propyl-4,5,6,7-tetrahydrobenzothiazole-2,6-diamine), 7-OH-DPAT [(+/-)-7-hydroxy-2-dipropylaminotetralin HBr], quinpirole [trans-(-)-(4aR)-4,4a,5,6,7,8, 8a,9-octahydro-5-propyl-1H-pyrazolo[3,4-g]quinoline HCl], bromocriptine [(+)-2-bromo-12'-hydroxy-2'-(1-methylethyl)-5'-(2-methylpropyl) ergotaman-3',6'-18-trione methanesulfonate], and apomorphine [(R)-(-)-5,6,6a,7-tetrahydro-6-methyl-4H-dibenzo-[de,g]quinoline-10,11-diol HCl] with respect to their ability to induce yawning in rats. A series of D2/D3 antagonists differing in selectivity for D3 over D2 receptors were evaluated for their ability to alter the effects of the dopamine agonists. The antagonists L-741,626 (3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole), haloperidol (4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4-fluorophenyl)-1-butanone HCl), nafadotride (N-[(1-butyl-2-pyrrolidinyl)methyl]-4-cyano-1-methoxy-2-naphtha-lenecarboxamide), U99194 (2,3-dihydro-5,6-dimethoxy-N,N-dipropyl-1H-inden-2-amine maleate), SB-277011A (trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarboxamide), and PG01037 (N-{4-[4-(2,3-dichlorophenyl)-piperazin-1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide HCl) were used to determine effects on dose-response curves for D2/D3 agonist-induced yawning. In addition, the potential contribution of cholinergic and/or serotonergic mechanisms to the yawning response was investigated using a series of pharmacological tools including scopolamine [(a,S)-a-(hydroxymethyl)benzeneacetic acid (1a,2b,4b,5a,7b)-9-methyl-3-oxa-9-azatricyclo[3.3.1.02,4]-non7-yl ester hydrobromide], mianserin (1,2,3,4,10,14b-hexahydro-2-methyldibenzo[c,f]pyrazino[1,2-a]azepine HCl), and the D3-preferring antagonists nafadotride, U99194, SB-277011A, and PG01037 to differentially modulate yawning induced by PD-128,907, physostigmine [(3aS)-cis-1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethylpyrrolo[2,3-b]indol-5-ol methylcarbamate hemisulfate], and N-[3-(trifluoromethyl)phenyl]piperazine HCl. The results of these experiments provide convergent evidence that dopamine D2/D3 agonist-induced yawning is a D3 agonist-mediated behavior, with subsequent inhibition of yawning being driven by competing D2 agonist activity. Thus, dopamine agonist-induced yawning may represent an in vivo method for selectively identifying D3 and D2 receptor-mediated activities.

Interleukin-2-induced increases in climbing behavior: inhibition by dopamine D-1 and D-2 receptor antagonists

Interleukin (IL)-2 is a potent modulator of dopamine activity in the mesocorticolimbic and mesostriatal systems. It is also associated with behavioral changes (increased motor activity) and psychopathological outcomes (schizophrenia, Parkinson's Disease, cognitive deficits) that at least partly reflect aberrations in central dopaminergic transmission. Nonetheless, there is no evidence that a functional link exists between IL-2, dopaminergic processes, and related behavioral changes. We thus determined if IL-2 treatment increases the expression of climbing behavior, a behavior that is linked with dopamine D-1 and/or D-2 receptors and one used to test the efficacy of neuroleptics. IL-2 treatment (5-daily i.p. injections; 0.4 microg/BALB/c mouse) induced a marked 2-fold increase in climbing scores; a single injection had no effect. IL-2-induced increases in climbing behavior were completely blocked by a selective dopamine D-1 receptor antagonist (SCH 23390; 0.05 or 0.2 mg/kg; i.p.), or by a relatively high dose of a D-2 antagonist (sulpiride; 80 mg/kg; i.p.). In contrast, MK-801, a noncompetitive NMDA receptor antagonist, had no effect. This is the first demonstration of a functional link between IL-2, dopaminergic receptors, and behavior. These findings could shed light on the mechanisms by which IL-2 increases vulnerability to psychiatric abnormalities associated with aberrations in central dopaminergic processes.

Biochemical and behavioral effects of boldine and glaucine on dopamine systems

The aporphine alkaloids boldine and glaucine have been reported to show "neuroleptic-like" actions in mice, suggesting that they may act as dopamine antagonists. We have found that in vitro boldine displaces specific striatal [3H]-SCH 23390 binding with IC50 = 0.4 microM and [3H]-raclopride binding with IC50 = 0.5 microM, while the affinities of glaucine at the same sites are an order of magnitude lower. In vivo, however, 40 mg/kg boldine (i.p.) did not modify specific striatal [3H]-raclopride binding and only decreased [3H]-SCH 23390 binding by 25%. On the other hand, 40 mg/kg glaucine (i.p.) displaced both radioligands by about 50%. Behaviors (climbing, sniffing, grooming) elicited in mice by apomorphine (0.75 mg/kg s.c.) were not modified by boldine at doses up to 40 mg/kg (i.p.) but were almost completely abolished by 40 mg/kg glaucine (i.p.). In the apomorphine-induced (0.1 mg/kg s.c.) rat yawning and penile erection model, boldine and glaucine appeared to be similarly effective, inhibiting both behaviors by more than 50% at 40 mg/kg (i.p.). Boldine and glaucine, injected i.p. at doses up to 40 mg/kg, were poor modifiers of dopamine metabolism in mouse and rat striatum. These data suggest that boldine does not display effective central dopaminergic antagonist activities in vivo in spite of its good binding affinity at D1- and D2-like receptors, and that glaucine, although less effective in vitro, does appear to exhibit some antidopaminergic properties in vivo.

Influence of different adrenoceptor agonists and antagonists on physostigmine-induced yawning in rats

In the present study, effects of adrenoceptor agonists and antagonists on physostigmine-induced yawning was investigated. Intraperitoneal (i.p.) injection of different doses of physostigmine (0.03, 0.05, 0.1, and 0.2 mg/kg) induced yawning in rats. The maximum response was obtained by 0.2 mg/kg of the drug. The alpha1-adrenoceptor agonist, phenylephrine, and the alpha2-adrenoceptor agonist, clonidine, decreased yawning induced by physostigmine. Prazosin and higher doses of phenoxybenzamine reduced the inhibitory effect of phenylephrine. Higher doses of yohimbine also reduced the clonidine response. The adrenoceptor antagonists, prazosin, phenoxybenzamine, and propranolol, did not significantly alter the physostigmine response. However, yohimbine, or lower doses of prazosin, decreased the physostigmine response. It may be concluded that alpha1- and alpha2-adrenoceptor stimulation decreases the physostigmine-induced yawning behavior in rats.

The octadecaneuropeptide ODN inhibits apomorphine-induced yawning in rats

High concentrations of diazepam-binding inhibitor (DBI) have been detected in brain areas containing dopaminergic cell bodies and nerve terminals. In the present study, we have investigated the effect of a proteolytic fragment of DBI, the octadecaneuropeptide ODN, on apomorphine-induced yawning in Sprague-Dawley rats. Injection of graded doses of ODN (12.5 to 100 ng i.c.v.) caused a dose-dependent inhibition of apomorphine-induced yawning and penile erections. At a dose of 100 ng, intracerebroventricularly administered ODN was able to inhibit, during more than 3 h, the apomorphine-evoked yawning. ODN also inhibited pilocarpine-induced yawning. Apomorphine induces a bell-shaped dose-dependent effect on yawning with a maximum response at the dose of 100 microg/kg and a much lower effect at a dose of 200 microg/kg. Injection (i.c.v.) of 100 ng ODN markedly attenuated the number of yawns induced by 100 microg/kg apomorphine but partially restored the yawning behavior in rats treated with a 200 microg/kg dose of apomorphine. At doses of 0.5 or 5 mg/kg s.c., diazepam did not modify the inhibitory effect of ODN on the apomorphine-induced yawning. Taken together, the present data suggest that ODN inhibits yawning downstream dopaminergic as well as cholinergic synapses involved in yawning. In addition, the effect of ODN cannot be ascribed to an inverse agonistic activity on central-type benzodiazepine receptors.

Effects of lead exposure on licking and yawning behaviour in rats

In the present study, effects of lead exposure on licking and yawning behaviour have been studied. The dopaminergic receptor agonist, apomorphine (0.15, 0.25 and 0.5 mg/kg), induced dose-dependent licking in rats. The maximum response was obtained with 0.5 mg/kg of the apomorphine. Lead acetate (0.05%) exposure significantly increased apomorphine-induced licking. Yawning induced by the D2 dopaminergic agonist, bromocriptine (2, 3, 4, 8 mg/kg), and the cholinergic drug, physostigmine (0.1 or 0.3 mg/kg), was significantly decreased by lead acetate (0.05%) exposure. It may be concluded that the behaviour induced by dopaminergic or cholinergic agents can be affected by lead subchronic exposure.

The neuropharmacology of yawning

Yawning is a phylogenetically old, stereotyped event that occurs alone or associated with stretching and/or penile erection in humans and in animals from reptiles to birds and mammals under different conditions. Although its physiological function is still unknown, yawning is under the control of several neurotransmitters and neuropeptides at the central level as this short overview of the literature on the neurochemistry of yawning shows. Among these substances, the best known are dopamine, excitatory amino acids, acetylcholine, serotonin, nitric oxide, adrenocorticotropic hormone-related peptides and oxytocin, that facilitate yawning and opioid peptides that inhibit this behavioral response. Some of the above compounds interact in the paraventricular nucleus of the hypothalamus to control yawning. This hypothalamic nucleus contains the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas that play a key role in the expression of this behavioral event. When activated by dopamine, excitatory amino acids and oxytocin itself, these neurons facilitate yawning by releasing oxytocin at sites distant form the paraventricular nucleus, i.e. the hippocampus, the pons and/or the medulla oblongata. Conversely, activation of these neurons by dopamine, oxytocin or excitatory amino acids, is antagonized by opioid peptides, that, in turn, prevent the yawning response. The activation and inhibition, respectively of these oxytocinergic neurons is related to a concomitant increase and decrease, respectively, of paraventricular nitric oxide synthase activity. However, other neuronal systems in addition to the central paraventricular oxytocinergic neurons are involved in the control of yawning, since they do not seem to be involved in the expression of yawning induced by the stimulation of acetylcholine or serotoninergic receptors, nor by adrenocorticotropic hormone (ACTH) and related peptides. Nitric oxide is also involved in the induction of yawning by the latter compounds and neuronal links, for instance between dopamine and acetylcholine and dopamine and serotonin, seem to be involved in the yawning response. Finally, other neurotransmitters, i.e. gamma-aminobutyric acid (GABA) and noradrenaline, and neuropeptides, i.e. neurotensin and luteinizing hormone-releasing hormone (LH-RH), influence this behavioral response. In conclusion, in spite of some recent progress, little is known of, and more has to be done to identify, the neurochemical mechanisms underlying yawning at the central level.

Behavioural and neurochemical sensitization of morphine-withdrawn rats to quinpirole

The sensitivity of dopamine D2-like receptors in morphine-withdrawn rats was studied using the selective agonist quinpirole. Morphine was administered twice daily increasing the daily dose from 20 to 50 mg/kg during 7 days. Twenty-four hours after the last morphine administration the rats were given quinpirole (0.01-1 mg/kg) and their behavior was assessed. Withdrawal from repeated morphine treatment enhanced yawning behavior and penile erections induced by small doses (0.01-0.1 mg/kg) as well as the intensity of stereotypy induced by a large dose (1.0 mg/kg) of quinpirole. In the morphine-withdrawn rats the dose of 1 mg/kg of quinpirole caused less yawning than in the control rats, whereas the number of erections induced by this dose was enhanced as compared with the control animals. In the control rats, the striatal and limbic concentrations of dopamine metabolites, 3,4-dihydroxphenylacetic acid (DOPAC), and homovanillic acid (HVA), were not clearly affected by the smallest dose of quinpirole. However, the small dose of quinpirole (0.01 mg/kg) significantly reduced the levels of DOPAC and HVA in the striatum and limbic forebrain of the rats withdrawn from morphine either for 24 or 48 h. These findings indicate that withdrawal from repeated morphine treatment enhances the sensitivity of dopamine D2-like receptors.

Effects of picotesla flux electromagnetic fields on dopaminergic transmission in Tourette's syndrome

Tourette's syndrome (TS), a chronic familial neuropsychiatric disorder of unknown etiology, is characterized clinically by the presence of motor and vocal tics that wax and wane in severity over the time and by the occurrence of a variety of neurobehavioral disorders. It is believed that the tics of TS result from increased dopamine (DA) activity caused by postsynaptic DA receptor supersensitivity. The synthesis and release of DA is regulated presynaptically by a specific class of DA D2 receptors, termed autoreceptors activation of which causes inhibition of DA synthesis and release. In experimental animals and humans administration of small doses of apomorphine, a DA D2 autoreceptor agonist, produces yawning. Recurrent episodes of yawning followed by increased motor tic activity was observed in two patients with TS during exposure to brief, extracranial applications of picotesla flux electromagnetic fields (EMFs). On the basis of these observations it is suggested that recurrent episodes of yawning in response to application of EMFs was induced by activation of presynaptic DA D2 autoreceptors while further exposure to these EMFs caused excessive stimulation of postsynaptic DA D2 receptors resulting in exacerbation of the tics. Thus, the dual effects of picotesla flux EMFs on the DA D2 autoreceptor and the postsynaptic receptor resemble the biphasic pharmacological and behavioral properties of apomorphine, a DA agonist which activates the autoreceptors in low doses while in higher doses causes stimulation of the postsynaptic receptors producing exacerbation of symptoms of TS. These findings demonstrate that picotesla flux EMFs applied extracerebrally may influence nigrostriatal DA transmission at pre- and postsynaptic DA D2 receptor sites.

Effects of adenosine agents on apomorphine-induced yawning in rats

In the present work, adenosine agonists and antagonists on apomorphine-induced yawning in rats was investigated. Subcutaneous (SC) injection of apomorphine (0.02, 0.05 and 0.1 mg/kg) induced dose-dependent yawning behaviour in rats. Intracerebroventricular (ICV) administration of different doses of the drug (1, 3, 5 micrograms/rat) also caused a dose-related yawning. ICV administration of the adenosine receptor agonists 5-N-ethylcarboxamidoadenosine (NECA) and N6-cyclohexyladenosine (CHA) decreased apomorphine-induced yawning. The response induced by the adenosine agonists was reduced by 8-phenyladenosine (8-PT) pretreatment. The yawning induced by SC and ICV administration of apomorphine was decreased by ICV or IP injection of theophylline, respectively. It is concluded that at least A1 adenosine receptors may exert negative influence on the apomorphine-induced yawning. However, the exact mechanism(s) of adenosine receptors in this behaviour remain to be established.

Apomorphine produced more yawning in Sprague-Dawley rats than in F344 rats: a pharmacological study

Apomorphine induced yawning in both Sprague-Dawley and F344 rats in the same dose range, but F344 rats emitted only about 1/4 as many yawns as did Sprague-Dawley rats. At higher doses, rats of both strains exhibited stereotypic behavior with a comparable intensity. Pretreatment with either SCH 23390 [R(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-o l] or pindolol increased apomorphine-induced yawning further in Sprague-Dawley rats, but had little effect on the low yawning score produced by apomorphine in F344 rats. The low yawning response to apomorphine in F344 rats is, therefore, not due to a high baseline dopaminergic or adrenergic activity. Apomorphine-induced yawning in F344 rats was increased after an acute injection of physostigmine, or 24 h after an injection of reserpine. It is postulated that a low baseline cholinergic activity in F344 rats may be responsible, in part, for their lower yawning response to dopaminergic receptor stimulation.

Post-synaptic 5-HT1A receptor involvement in yawning and penile erections induced by apomorphine, physostigmine and mCPP in rats

Apomorphine and mCPP induced yawning associated with penile erections in rats, whereas physostigmine induced only yawns. Apomorphine-induced yawning and penile erections were antagonized by low doses of raclopride, whereas physostigmine-induced yawning and mCPP-induced effects were only partly inhibited at high doses of raclopride. Scopolamine as well as clozapine antagonized yawning and penile erections induced by apomorphine, mCPP and physostigmine. Similarly, the 5-HT1A agonists 8-OH-DPAT and S 14506 inhibited yawning and penile erections induced by apomorphine, mCPP and physostigmine, and at similar doses induced lower lip retraction and hyperreactivity to handling. The beta/5-HT1A antagonist tertatolol reversed the inhibitory effects of 8-OH-DPAT and S 14506 on drug-induced yawning and penile erections and increased apomorphine- and physostigmine-induced yawn frequency but not penile erection frequency. Like tertatolol, propranolol increased apomorphine- and physostigmine-induced yawn frequency, whereas ICI 118551 increased only physostigmine-induced yawning. 8-OH-DPAT- and S 14506-induced lower lip retraction and hyperreactivity to handling were also significantly antagonized by tertatolol. Finally, p-chlorophenylalanine pretreatment produced about 95% depletion in 5-HT in hypothalamus, hippocampus, striatum and frontal cortex and modified neither the responses of the inducing drugs nor the inhibitory effects of 8-OH-DPAT and S 14506 on drug-induced yawning and penile erections.(ABSTRACT TRUNCATED AT 250 WORDS)

Atypical neuroleptic-like behavioral effects of neurotensin

To better characterize the neuroleptic-like properties of neurotensin, the dose-related effects of the peptide on the following behavioral phenomena were examined: a) the yawning-penile erection syndrome induced by small doses of the dopamine agonists apomorphine and N-propylnorapomorphine (NPA); b) yawning produced by the anticholinesterase physostigmine, and c) stereotyped climbing and sniffing produced by a larger dose of apomorphine. Several doses of the peptide were injected intraventricularly 30 min prior to drug administration. Results indicate that neurotensin markedly decreased yawning and penile erections produced by both apomorphine and NPA. These effects were seen with relatively small doses (0.9-3.75 micrograms). Neurotensin also potently decreased physostigmine-induced yawning with the initial inhibitory effect seen with 50 ng of the peptide. Apomorphine-induced climbing was significantly attenuated with 30.0 and 60.0 micrograms neurotensin, whereas stereotyped sniffing was unaffected, even by doses as large as 120.0 micrograms. These findings suggest that neurotensin might antagonize dopamine autoreceptors and indicate that the peptide possess central anticholinergic activity. Furthermore, these results lend support to the hypothesis that neurotensin's profile of central actions resemble that of atypical neuroleptics.

Beginning-of-dose motor deterioration following the acute administration of levodopa and apomorphine in Parkinson's disease

Six Parkinsonian patients on long term levodopa therapy complained of short-lived deterioration of Parkinsonian symptoms immediately after levodopa intake. After withdrawal of the drug overnight, and following an oral challenge with levodopa/carbidopa (250/25) in all six cases, and with subcutaneous apomorphine (3 mg) in two, deterioration below base line levels of disability were observed which would not be explained by loss of sleep benefit. This occurred 10-20 minutes after levodopa challenge and lasted for 10-20 minutes. The latency and duration of this phenomenon were shorter with apomorphine but the characteristics were similar. This phenomenon may be due to an inhibitory effect of levodopa acting via presynaptic dopamine receptors.

Influences of dopamine receptors on chewing behaviour in rats

1. Intraperitoneal (i.p.) injection of different doses of pilocarpine induced purposeless chewing in rats. Physostigmine (i.p.), but not neostigmine (i.p.) also induced chewing behaviour. 2. Subcutaneous (s.c.) pretreatment of animals with the D-1 receptor blocker SCH 23390 decreased the number of chews induced by pilocarpine. 3. The D-2 dopamine antagonist sulpiride (i.p.) and anticholinergic atropine (i.p.) pretreatment also decreased the frequency of chews induced by the drug. 4. The response induced by pilocarpine (1 mg/kg i.p.) also was dose-dependently decreased in animals pretreated with apomorphine (0.25-1 mg/kg s.c.). 5. Administration of low doses of apomorphine (s.c.) also induced chewing, which was decreased with increasing the doses of the drug. 6. Chewing-induced by apomorphine was decreased by sulpiride or atropine and increased by SCH 23390 pretreatment. 7. Single administration of D-2 dopamine agonist bromocriptine also showed a slight but significant purposeless chewing, which was decreased by sulpiride pretreatment. 8. Single administration of D-2 agonist quinpirole, D-1 agonist SKF 38393 or D-1 antagonist SCH 23390, but not sulpiride caused a slight chewing. 9. It may be concluded that D-1 or D-2 activation exert opposite influences on chewing behaviour in rats, although to prove this effect more elucidation is needed.

Characterization of dopamine receptors involved in apomorphine-induced pecking in pigeons

1. The possible involvement of subtypes of dopamine-receptors in apomorphine induced pecking was studied in pigeons. Different doses of apomorphine induced pecking in pigeons which was dose-dependent. 2. The response was decreased by SCH 23390 (D-1 antagonist) or high doses of sulpiride (D-2 antagonist) pretreatment, but increased by lower doses of sulpiride. 3. Combination of SCH 23390 with sulpiride completely antagonized the apomorphine effect. 4. Single dose administration of SKF 38393 (D-1 agonist) or bromocriptine (D-2 agonist) and combination of these drugs did not induce pecking, although either SK 23390 or bromocriptine increased the apomorphine-induced pecking which was decreased by SCH 23390 or sulpiride pretreatment. 5. It may be concluded that pecking, induced by apomorphine in pigeons, is elicited through activation of both D-1 and D-2 dopamine-receptors.

Inhibitory effect of morphine on yawning induced by cholinoceptor and dopamine D2 receptor activation in rats

1. Bromocriptine (2, 4 and 8 mg kg-1, i.p.), physostigmine (0.05, 0.1 and 0.2 mg kg-1, i.p.) and pilocarpine (1, 3 and 5 mg kg-1, i.p.) induced dose-dependent yawning in rats. 2. These responses were reduced in a dose-dependent manner by pretreatment with morphine. 3. The inhibitory effect of morphine was reversed by naloxone. 4. Naloxone alone induced slight but significant yawning. 5. The present results suggest that morphine inhibits yawning in rats at an opiate receptor downstream from the sites at which cholinoceptor and dopamine D2 activation induce yawning. The anatomical location of these sites remains to be established.

Do autoreceptors mediate dopamine agonist--induced yawning and suppression of exploration? A critical review

The hypothesis that stimulation of dopamine autoreceptors is the mechanism by which dopamine agonists induce yawning and suppression of exploration is critically examined. It is shown that the relation between reduced extracellular dopamine levels, assessed by microdialysis, and behavioural effects of dopamine agonists, a dopamine synthesis inhibitor and a granule storage blocker is highly inconsistent. The time-course and duration of the behavioural effects of dopamine agonists differ from the reduction of extracellular dopamine. Amphetamine cotreatment is shown to increase dopamine levels, while yawning and suppression of exploration can still be induced. The data strongly indicate that autoreceptors are not the mediators of these behavioural effects. It is proposed that postsynaptic receptors mediate dopamine agonist induced yawning and suppression of exploration. Evidence is also presented showing that yawning and suppression of exploration are not functionally equivalent.

5-HT1A receptor agonists prevent in rats the yawning and penile erections induced by direct dopamine agonists

The new compound (+) S-20499, an amino chromane derivative (8[-4[N-(5-methoxychromane-3yl)N-propyl]aminobutyl] azaspiro[4-5] décane-7,9 dione), is a high affinity full 5-HT1A agonist. We have investigated its effects on dopaminergic transmission. (+) S-20499 displayed a 10(-8) M affinity for D2 dopamine (DA) receptors, 100 fold lower than for 5-HT1A receptors. The hypothermic effect of the drug was reversed by haloperidol in mice, suggesting that it behaves as a direct dopamine agonist. However, increasing doses of (+) S-20499 induced neither yawning nor penile erections, which constitute characteristic responses of direct DA agonists administered at low doses. In addition, (+) S-20499 prevented the apomorphine (100 micrograms/kg SC) induced yawning and penile erections. This inhibition appears to result from the stimulation of 5-HT1A receptors since it is an effect shared by both buspirone (from 5 mg/kg) and 8-OH-DPAT (from 0.10 mg/kg). In addition, when rats are treated with the 5-HT1A receptor antagonist tertatolol (2-5 mg/kg; SC), increasing doses of (+) S-20499 elicit the expected yawns and penile erections. It is concluded that the 5-HT1A agonist property opposes to that of D2 dopamine receptor stimulation with regard to yawning and penile erections.

Effects of [D-Ala2, D-Leu5]enkephalin and [D-Pen2, L-Pen5]enkephalin on apomorphine-induced motor activity in the mouse

The effects of intracerebroventricular injections of opioid peptides such as DADL [( D-Ala2, D-Leu5]enkephalin) and DPLPE [( D-Pen2, L-Pen5]enkephalin) with different degrees of selectivity for delta- over mu-receptor on apomorphine (0.1, 0.3, 1.0 and/or 3.0 mg/kg)-induced motor activity were investigated in the mouse using multi-dimensional behavioral analyses. Lower doses (0.1 and 0.3 mg/kg) of apomorphine failed to affect significantly motor activity, whilst higher doses (1.0 and 3.0 mg/kg) of the drug produced a marked increase in linear locomotion, circling, rearing, and/or grooming behaviors. DADL (0.03, 0.1 or 0.3 microgram) by itself did not influence behaviors, while the peptide (0.1 and 0.3 microgram) produced a marked inhibition on apomorphine (1.0 but not 3.0 mg/kg)-induced increase in rearing behaviors. Furthermore, the inhibitory effect of DADL (0.3 micrograms) on the apomorphine (1.0 mg/kg)-induced increase in rearing was reversed by treatment with the alkylating agent beta-FNA (beta-funaltrexamine) (5.0 micrograms). In contrast to the effects of DADL, the much more delta-selective opioid agonist DPLPE (0.3, 1.0 or 1.75 micrograms) had no marked effects on apomorphine (1.0 mg/kg)-induced behaviors. These results suggest that delta opioid receptors do not play a principal role in the apomorphine-induced increase in circling, rearing or grooming behaviors.

DAGO ([D-Ala2,N-Me-Phe4,Gly-ol]enkephalin) specifically reverses apomorphine-induced increase in rearing and grooming behaviors in the mouse

The effects of intracerebroventricular injections (10 microliters) of the mu-selective opioid peptide DAGO on apomorphine (0.1, 0.56, 1.0 and/or 3.0 mg/kg)-induced motor activity were investigated in the mouse using multi-dimensional behavioral analyses. A lower dose (0.1 mg/kg) of apomorphine failed to significantly affect motor activity, whilst higher doses (0.56, 1.0 and 3.0 mg/kg) of the drug produced a marked increase in linear locomotion, circling, rearing and/or grooming behaviors. DAGO (0.003 and 0.01 micrograms) did not significantly affect different behaviors. DAGO (0.01 micrograms) antagonized the apomorphine (1.0 mg/kg)-induced increase in behaviors such as rearing and grooming. However, DAGO (0.003 or 0.01 micrograms) did not affect behaviors induced by a 3.0 mg/kg dose of apomorphine. Furthermore, the effects of DAG]O on apomorphine-induced behaviors were fully reversed by treatment with the mu-selective alkylating agent beta-FNA (beta-funaltrexamine) (5.0 micrograms). These results suggest that mu opioid receptors play a principal role in the apomorphine-induced increase in rearing and grooming behaviors.

Inhibition of apomorphine-induced yawning and penile erection by neurotensin

The yawns and penile erection elicited in rats by apomorphine (100 micrograms/kg SC) are dose-dependently suppressed by the enkephalinase-resistant analog of NT, [D-Trp11]NT, intracerebroventricularly (ICV) injected (10-120 ng per rat). This antagonistic effect was shared by NT (0.75-3 micrograms per rat) administered ICV. The yawns induced by pilocarpine (2 mg/kg IP) were similarly antagonized by [D-Trp11]NT (30-120 ng per rat). The enkephalinase inhibitor acetorphan (5 mg/kg IV) reduced in a naloxone (2 mg/kg, SC)-resistant manner the apomorphine-induced penile erection or yawning.

Use of amfonelic acid to discriminate between classical and atypical neuroleptics and neurotensin: an in vivo voltammetric study

Previous ex vivo studies have shown that the non-amphetamine stimulant amfonelic acid potentiates the increase in DOPAC induced by classical but not by atypical neuroleptics. In the present study, we have demonstrated that this neurochemical model can be used to discriminate typical from atypical neuroleptics in vivo using differential pulse voltammetry with carbon fibre electrodes. The study also compared the effect of intracerebroventricular (i.c.v.) administration of neurotensin, on extracellular striatal DOPAC following amfonelic acid, with the effects of both classical and atypical neuroleptics. Saline or amfonelic acid (2.5 mg/kg s.c.) were administered; followed 5 min later by the classical neuroleptics haloperidol, perphenazine, or the atypical neuroleptics clozapine, thioridazine, or by neurotensin. After drug administration extracellular striatal DOPAC was recorded every 5 min for 90 min. Amfonelic acid did not alter basal striatal DOPAC but potentiated the increase in DOPAC induced by haloperidol (1.0 and 0.05 mg/kg s.c.) and perphenazine (10 mg/kg s.c.). Both clozapine (30 mg/kg i.p.) and thioridazine (20 mg/kg s.c.) increased extracellular DOPAC, but pretreatment with amfonelic acid prevented the increase in DOPAC produced by both drugs. Neurotensin (10 micrograms, i.c.v.), in a similar manner to the atypical neuroleptics, increased extracellular DOPAC in the striatum and the effect was prevented by amfonelic acid. The present study demonstrates that pretreatment with amfonelic acid is a valuable tool to discriminate between classical and atypical neuroleptics in vivo. The results also indicate that neurotensin in the presence of amfonelic acid has a profile similar to the atypical neuroleptics.

Dissociation of autoreceptor activation and behavioral consequences of low-dose apomorphine treatment

1. Low dose dopaminergic agonist effects have been used as a behavioral screen for identifying compounds with selective autoreceptor activity. 2. However, results from several recent investigations suggest that these behaviors may not be generated from an autoreceptor substrate but rather from a subpopulation of postsynaptic dopamine receptors with a high affinity for the agonist. 3. In support of this hypothesis, the present investigation reports that both hypomotility and yawning, induced in the rat with 0.07 mg/kg apomorphine, were not paralleled by autoreceptor-induced reductions in transmitter metabolism from either mesolimbic or neostriatal dopamine regions.

Apomorphine-induced blinking and yawning in healthy volunteers

Yawning and spontaneous blink rate (SBR) are two physiological reflexes which have been incompletely examined but one neurobiological step of these two behaviours seems, at least in part, dopamine-dependent. The reference dopaminergic agonist, apomorphine hydrochloride (0.5, 1, and 2 micrograms kg-1 s.c.), was compared with a placebo in a double-blind latin-square design, and was shown to induce yawning and increase SBR in a population of eight healthy volunteers. These two behavioral effects were not dose-related. The individual SBR differences were correlated with the individual number of yawns for all the four treatments at the 10-30 min interval. Thus, parallel yawning and SBR behaviour suggests a similar pharmacological mechanism. Apomorphine-induced yawning and blinking may be therefore of use in the evaluation of central dopaminergic pathways in man.

Genotypic dependency of spontaneous yawning frequency in the rat

By inbreeding we have obtained two sublines of Sprague-Dawley rats which differ significantly in spontaneous mean yawning frequency (MYF). In generation F21 of the high-yawning (HY) subline MYF was 21.5 yawns/h (y/h) in males and 1.95 y/h in females, at the age of 2 months. In the low-yawning (LY) subline, in generation F16 the MYF was 0.9 y/h in males and only 0.5 y/h in females. During the first 15 days there are no differences in yawning frequency between HY and LY rats. Thereafter yawning increases with age, more steeply in the HY subline. The results of reciprocal crosses between both sublines indicate that the LY character is partially dominant over the HY one.

Pharmacological characterization of the behavioural syndrome induced by the NK-3 tachykinin agonist senktide in rodents: evidence for mediation by endogenous 5-HT

The effects of various manipulations of brain 5-HT mechanisms on the behavioural responses induced by the selective NK-3 tachykinin agonist senktide in rodents were assessed. Senktide elicited wet dog shakes in the rat which were attenuated by the 5-HT1C/2 antagonist mianserin and the selective 5-HT2 antagonist altanserin. Senktide-induced forepaw treading was stereospecifically attenuated by the 5-HT1A + B antagonist (-)-alprenolol. Senktide also elicited chewing mouth movements and yawning, which were unaffected by mianserin, altanserin, (+)- or (-)-alprenolol, or the selective 5-HT3 antagonist ICS 205-930, but attenuated by the muscarinic antagonist scopolamine. Penile grooming elicited by senktide was attenuated by mianserin, but was unaffected by the other antagonists. Senktide-induced wet dog shakes were enhanced by the 5-HT reuptake inhibitors citalopram and fluoxetine, suppressed by the monoamine oxidase (MAO)-B inhibitor pargyline, but unaffected by the MAO-A inhibitor clorgyline. Forepaw treading was potentiated by citalopram and clorgyline, but not significantly altered by fluoxetine or pargyline. Depletion of 5-HT by p-chlorophenylalanine (PCPA) in the rat attenuated senktide-induced wet dog shakes and forepaw treading. Neither PCPA nor 5,7-dihydroxytryptamine affected senktide-induced behaviours in the mouse, but the degree of brain 5-HT depletion caused by these treatments in mice was relatively small. These findings indicate that stimulation of NK-3 tachykinin receptors by senktide results in a complex behavioural syndrome which is mediated by multiple 5-HT receptors, and dependent upon intact stores of endogenous 5-HT. Independent stimulation of brain cholinergic mechanisms by senktide is also confirmed.

Bromocriptine induces climbing behaviour: possible D-1 or D-2 dopamine receptor involvement

The ability of bromocriptine (BRC), a dopamine D-2 receptor agonist, to induce climbing behaviour was studied in mice. BRC (2-32 mg/kg IP) evoked climbing behaviour. The maximum effect was obtained with 8 mg/kg, while higher doses of BRC (16 and 32 mg/kg) were less effective. Climbing began about 2 h after injection and was most marked 5 h after bromocriptine administration. Pretreatment of animals with the dopamine antagonist pimozide (0.5 mg/kg IP) decreased BRC-induced climbing. Sulpiride (0.25-1.25 mg/kg IP), a potent D-2 antagonist and/or SCH 23390 (0.025 and 0.05 mg/kg SC), a D-1 receptor antagonist, also decreased the response. Furthermore, the climbing behaviour induced by BRC was abolished by pretreatment with reserpine plus alpha-methyl-p-tyrosine (AMPT). Concomitant administration of apomorphine (APO) and BRC potentiated the effect of APO on climbing. Concomitant injection of BRC and SKF 38393 (SKF, D-1 agonist) reduced the effect of SKF on climbing, while administration of BRC 4 h before SKF potentiated the effect of both drugs. It is suggested that BRC induces climbing through D-1 and/or D-2 dopamine receptors.

Yawning and suppression of exploration induced by dopamine agonists: no relation to extracellular striatal levels of dopamine

The present study was aimed at testing the hypothesis that yawning and suppression of exploration induced by low doses of dopamine agonists in the rat are caused by a reduction of synaptic dopamine levels. The decrease in extracellular levels of dopamine in the corpus striatum induced by alpha-methyl-p-tyrosine (alpha MPT, 50-200 mg/kg IP), reserpine (2-5 mg/kg SC) and apomorphine (APO, 0.05 mg/kg SC) was measured in microdialysis experiments. Reserpine and alpha MPT reduced the dopamine levels to the same extent as APO. Exploratory behaviour was suppressed by APO, but not by alpha MPT (50 and 100 mg/kg) when tested in a separate experiment. Reserpine (2 mg/kg) suppressed exploration after 4 hr, but not after 3 hr. Changes in extracellular levels of dopamine were tested simultaneously with changes in yawning in another group of rats implanted with guide cannulae for microdialysis probes. There was a discrepancy in the time-course for the induction of yawning as compared to the changes in extracellular dopamine levels after APO (0.05 mg/kg) as well as after pergolide (0.02 mg/kg SC). Yawning appeared before and lasted shorter than the decrease in dopamine. The time-courses for APO-induced suppression of exploration and yawning were similar. The dose-response curve for APO-induced yawning was not changed by alpha MPT (200 mg/kg), while the suppression of exploration induced by APO, but not by pergolide, was enhanced by pretreatment with alpha MPT. The results show that yawning and suppression of exploration induced by dopamine agonists are not related to changes in extracellular levels of dopamine. It is proposed that these behaviours may be mediated by postsynaptic receptors.

Yawning behavior in male rats is associated with decreases in in vivo DOPAC efflux from the caudate nucleus

Young adult male rats were implanted with a push-pull cannula aimed at the dorsal and rostral areas of the caudate nucleus. Perfusate samples were collected at two-minute intervals for approximately one hour and assayed for DOPAC concentrations. Simultaneously, yawning, penile erections and grooming behavior were recorded. Yawns were induced by systemic prolactin or apomorphine injections. While mean DOPAC efflux was elevated following prolactin (PRL) and apomorphine decreased mean DOPAC efflux as expected, yawns and penile erections induced by both compounds were associated with rapid momentary decreases in DOPAC efflux in these living animals. Although yawning was associated with significant decreases in DOPAC output, not every momentary DOPAC decrease was associated with a yawn, suggesting that the 'yawning generator' most likely requires additional inputs for the expression of a yawn.

Effects of single and repeated treatment with antidepressants on apomorphine-induced yawning in the rat: the implication of alpha-1 adrenergic mechanisms in the D-2 receptor function

Acute (10 or 20 mg/kg IP) and subchronic (2 x 5 or 10 mg/kg IP daily for 7 days) effects of desipramine, imipramine, maprotiline, (+)- and (-)-oxaprotiline enantiomers as well as selective 5-HT-uptake inhibitors citalopram and ifoxetine on yawning, induced by low doses of apomorphine, were investigated in the rat. In addition, the effects of alpha-1 receptor agonist adrafinil and antagonist prazosin were also tested. After acute treatment, desipramine, the stereoselective NA-uptake inhibiting (+)-enantiomer of oxaprotiline, and the alpha-1 agonist adrafinil, markedly and significantly suppressed yawning. Prazosin, in contrast, clearly potentiated it. This potentiating effect was abolished by the pretreatment with (+)-oxaprotiline and adrafinil. Other drugs were inactive. After subchronic administration, yawning was antagonized by NA-uptake-inhibiting antidepressants, including imipramine and maprotiline. By comparison to the acute treatment, the inhibitory effects of desipramine and (+)-oxaprotiline were considerably enhanced. Neither selective 5-HT-uptake inhibitors nor (-)-oxaprotiline (levoprotiline) were active. Antidepressants therefore modulate the functional activity of D-2 receptors, activated by low doses of apomorphine, predominantly by the virtue of their noradrenergic enhancing properties. This modulatory effect appears to be mediated by alpha-1 adrenergic receptors.

The effects of dihydropyridine compounds in behavioural tests of dopaminergic activity

1. The effects of the dihydropyridine calcium channel blocker nifedipine and the activator Bay K 8644 were investigated in different behavioural tests involving dopaminergic systems. These were the discriminative stimulus induced by amphetamine, rotational behaviour in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions and apomorphine-induced yawning in rats. 2. The yawning induced by apomorphine (40 micrograms kg-1 s.c.) was significantly potentiated by nifedipine (5-10 mgkg-1 i.p.). Bay K 8644 (0.05-0.5 mgkg-1 i.p.) dose-dependently inhibited yawning induced by apomorphine (80 micrograms kg-1 s.c.) and, at 0.4 mgkg-1, inhibited the nifedipine potentiation of apomorphine-induced yawning. In contrast to their effects on apomorphine-induced yawning, nifedipine and Bay K 8644 had no effect on apomorphine-induced penile erection. 3. Bay K 8644 (0.06-0.5 mgkg-1 i.p.) and nifedipine (5-20 mgkg-1 i.p.) had no dose-related effect on the discrimination performance of rats trained to discriminate amphetamine from saline. However, nifedipine dose-dependently reduced the response rate of amphetamine-treated rats. Bay K 8644 had no effect on this measure except at high doses that also caused disruption. 4. Neither nifedipine (5-10 mgkg-1 i.p.) nor Bay K 8644 (0.06-0.5 mgkg-1 i.p.) affected the turning behaviour induced by amphetamine (1 mgkg-1 i.p.) in rats with unilateral 6-OHDA lesion of the medial forebrain bundle, and did not induce turning themselves. 5. As the dihydropyridine compounds affected apomorphine-induced yawning but not penile erection, and did not affect amphetamine-induced rotation or drug discrimination, it seems unlikely that they are affecting dopamine release in vivo.

Effects of repeated administration of low doses of apomorphine in three behavioural models in the rat

A low dose of the dopamine (DA) receptor agonist apomorphine (APO 0.05 mg/kg) was given repetitively and the effects were tested in three different behavioural models: reduction of spontaneous locomotion, induction of yawning and decrease in water intake in water-deprived animals. The APO-induced suppression of exploration and decrease in water intake were not affected by a previous injection of APO given 1 or 3 hours before the test dose of APO. There was a small, but significant, decrease in the induction of yawning by a previous dose of APO given 1 hour or 30 min before the test dose. However, pretreatment with APO 3 hours before the test dose did not diminish the yawning response. It is suggested that the dopaminergic mechanisms mediating APO induced yawning are different from those mediating decrease in water intake and suppression of exploration. The results are also discussed in relation to the proposed efficiency of low doses of DA agonists in the treatment of various neurological and psychiatric disorders.

Effects of ageing on the behavioural responses to dopamine agonists: decreased yawning and locomotion, but increased stereotypy

Sensorimotor function and the behavioural responses to a range of doses of subcutaneous apomorphine were assessed in mature (6-8 months) and old (23-26 months) Sprague-Dawley rats of comparable weight. In addition, the locomotor activity response of 12-month-old and 24-month-old rats to continuous infusions (14 days by osmotic minipump) of a selective dopamine D2 agonist. (+)-4-propyl-9-hydroxynaphthoxazine (PHNO, 10 micrograms/h) was investigated. Measures of spontaneous locomotor activity and motor coordination revealed impairments in the aged animals. Low doses of apomorphine (10-50 micrograms/kg), which preferentially activate dopamine autoreceptors, induced yawning, chewing mouth movements and penile grooming. The frequency of yawning and duration of penile grooming were significantly decreased in the old animals. In contrast, 200 micrograms/kg of apomorphine induced stereotyped sniffing and licking or gnawing, and these responses were significantly increased in the aged animals. There was a 25% decrease in striatal dopamine levels in the aged animals in this experiment. PHNO increased the amplitude of the circadian rhythms in locomotor activity exhibited by mature rats, and daytime tolerance to the stimulant effects of PHNO was reversed by stress in these animals. Both of these effects were attenuated in the aged rats. These findings suggest that (1) the dopamine receptors mediating yawning and stereotypy have different anatomical locations (2) ageing is associated with decreased responsiveness to stimulation of dopamine autoreceptors, consequent upon the loss of dopaminergic nerve terminals, and (3) while the functional response to selective stimulation of postsynaptic D2 receptors decreases with age, the postsynaptic response to a mixed D1/D2 agonist increases.

Dopamine D-2 antagonists reverse apomorphine-induced decreased water intake in the rat: prediction of antipsychotic drugs with few extrapyramidal side-effects?

Water intake in water deprived rats was decreased by administration of a low dose of apomorphine (0.1 mg/kg s.c.). This dose is too low to induce hyperactivity and stereotypies. Four different dopamine (DA) D-2 antagonists were used to counteract this effect of apomorphine; haloperidol [an antipsychotic inducing extrapyramidal side-effects (EPS)], sulpiride (an antipsychotic inducing less EPS than haloperidol), metoclopramide (not used as an antipsychotic but inducing EPS) and domperidone (not passing through the blood brain barrier). Domperidone did not counteract the apomorphine effect, indicating a central mechanism of action for apomorphine. Metoclopramide did not counteract the apomorphine effect and, in higher doses, water intake was even further reduced. Sulpiride completely counteracted the apomorphine effect but, in higher doses, did not by itself reduce water intake. Haloperidol counteracted the apomorphine effect in a small dose-range and caused a further reduction in the water intake when given in high doses. The results can be explained by the existence of two subpopulations of D-2 receptors related to different functions. The model described may be used in screening experiments aimed at finding new antipsychotic drugs with a low incidence of EPS.

Interactions of drugs acting on central dopamine receptors and cholinoceptors on yawning responses in the rat induced by apomorphine, bromocriptine or physostigmine

1. Yawning was induced by subcutaneous (s.c.) injection of low doses of apomorphine to rats. This effect decreased with increasing doses of the drug. 2. Intraperitoneal (i.p.) pretreatment of animals with sulpiride (D2-receptor blocker) reduced the frequency of the yawns induced by apomorphine, while SCH 23390 (D1-receptor blocker, s.c.) pretreatment increased the small number of yawns which was induced by higher doses of apomorphine. Administration of SCH 23390 alone to rats also produced a low degree of yawning. 3. Apomorphine-induced yawning was decreased in animals treated with SK&F 38393 (D1-agonist, i.p.), atropine (i.p.) or theophylline (i.p.). 4. Intraperitoneal injection of bromocriptine (D2-agonist) in rats also induced dose-dependent yawning. The effect was decreased in animals pretreated with sulpiride, while SCH 23390 pretreatment did not change bromocriptine-induced yawning significantly. Pretreatment of animals with SK&F 38393, atropine or theophylline reduced the number of yawns induced by bromocriptine. 5. Physostigmine (i.p.) but not neostigmine (i.p.) also induced yawning. The effect was antagonized by atropine or theophylline but not by sulpiride. Administration of SK&F 38393 decreased yawning induced by physostigmine. This inhibitory influence of SK&F 38393 was reduced by SCH 23390 in pretreated animals. Treatment of animals with SCH 23390 or bromocriptine increased the frequency of yawns induced by physostigmine. 6. It is concluded that D2-receptor activation elicits yawning through influence on cholinergic mechanisms, whereas D1-receptor stimulation decreases yawning behaviour by a negative influence on the cholinergic system.

Effect of the D1 receptor agonist SKF 38393 on some behavioural effects of apomorphine in rats

The dopamine receptor agonist apomorphine in experiments on rats in low doses (0.025-0.2 mg/kg, s.c.) induced yawning which reflected a selective activation of presynaptic dopamine receptors. In high doses (0.25-1.0 mg/kg) apomorphine induced stereotyped sniffing and yawning in consequence of postsynaptic D2 receptor activation. Dopamine D1 receptor agonist SKF 38393 inhibited yawning induced by low doses of apomorphine. The inhibitory effect of SKF 38393 on apomorphine-induced yawning was attenuated by pretreatment with specific D1 receptor antagonist SCH 23390 [2-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol). On the other hand however, SKF 38393 potentiated sniffing induced by the high doses of apomorphine without affecting gnawing. These data indicate that D1 receptor activation modulates both pre- and postsynaptic effects of apomorphine in opposite directions.

Inhibition of drinking by naltrexone in the rat: interaction with the dopamine D-1 antagonist SCH 23390 and the D-2 antagonist sulpiride

The involvement of dopamine receptors in water intake was investigated in the rat deprived of water for 24 hr. A 0.03 mg/kg dose of SCH 23390 markedly enhanced naltrexone (0.1 and 10.0 mg/kg)-induced hypodipsia, whilst the drug alone significantly decreased water intake at doses of 0.01 to 3.0 mg/kg, accompanied by marked motor dysfunction. Sulpiride (20.0 and 40.0 mg/kg) did not markedly affect water intake and naltrexone-induced hypodipsia. Consistent with previous results, apomorphine (0.3 mg/kg) alone was without marked effects, while it produced a marked potentiation of naltrexone (1.0 and 10.0 mg/kg)-induced hypodipsia. SCH 23390 (0.003 mg/kg) and sulpiride (40.0 mg/kg) completely antagonized the enhancing effects of apomorphine on naltrexone-induced hypodipsia. Similar effects were also seen in the latency to begin drinking. In contrast to the effects on naltrexone-induced hypodipsia, it appears that both dopamine D-1 and D-2 receptors play a key role in the effects of apomorphine on naltrexone-induced hypodipsia in the rat.

Potentiation by serotonergic inhibition of yawning induced by dopamine receptor agonists in rats

Low doses of the dopamine D2-receptor agonist, B-HT 920 (25 micrograms/kg, SC), and the dopamine D1/D2-receptor agonists, apomorphine (50 micrograms/kg, SC) and piribedil (1 mg/kg, SC), evoked yawning. However, the dopamine D1-receptor agonist, SK&F 38393 (2 mg/kg, SC), failed to induce yawning. The yawning responses induced by B-HT 920, apomorphine or piribedil were markedly increased without eliciting stereotypy by pretreatment with reserpine (5 mg/kg, IP, 24 hr). These yawning responses were also enhanced by p-chlorophenylalanine (PCPA) (300 mg/kg, IP, 72 hr), but not by alpha-methyl-p-tyrosine (300 mg/kg, IP, 6 hr). The yawning induced by B-HT 920 given alone and in combination with reserpine or PCPA was inhibited by spiperone (0.5 mg/kg, IP) or scopolamine (0.5 mg/kg, IP), but not by SCH 23390 (0.5 mg/kg, IP). The present results suggest that yawning is evoked by stimulation of dopamine D2-receptors having a high affinity and consequent muscarinic activation, and that the yawning induced by dopamine receptor agonists is potentiated by decreases in serotonergic neuron activity.

SKF 38393 potentiates yawning induced by LY 171555: further evidence against the autoreceptor hypothesis of yawning

The effect of concurrent D-1 receptor stimulation by SKF 38393 on the expression of yawning elicited by D-2 receptor stimulation with LY 171555 was studied in the rat. A low dose of SKF 38393 (2.5 mg/kg SC), while failed to elicit yawning, potentiated the effectiveness of LY 171555 in eliciting yawning at all the doses tested (12.5, 25 and 50 micrograms/kg SC) and this effect was abolished by SCH 23390 (0.012 mg/kg SC). The results indicate that in analogy with typical post-synaptic dopaminergic effects (hypermotility-stereotypy), yawning elicited by a D-2 agonist is facilitated by concurrent stimulation of D-1 receptors and therefore is consistent with previous evidence that yawning in response to a D-2 agonist is not mediated by autoreceptors.

Yawning and suppression of exploration in amphetamine-treated rats, incompatibility with the autoreceptor hypothesis

The hypothesis that yawning and suppression of exploration, induced by low doses of dopamine agonists, are mediated by stimulation of dopamine autoreceptors was tested by studying the influence of amphetamine on these behavioural models and on extracellular levels of dopamine sampled by microdialysis. Behaviour was measured in a holeboard apparatus. A low dose of amphetamine (0.2 mg/kg) caused slight activation of habituated rats. The same dose of amphetamine completely counteracted the decrease in extracellular dopamine levels caused by pergolide (0.02 mg/kg) and, instead, elevated the dopamine levels to 300% above baseline. The same or higher doses of amphetamine (0.5-1.0 mg/kg) did not completely antagonise suppression of exploration or yawning induced by apomorphine (0.05 mg/kg) or pergolide (0.02 mg/kg). The results suggest that both yawning and suppression of exploration induced by low doses of dopamine agonists are not mediated by dopamine autoreceptors, since these behaviours could be elicited when the extracellular levels of dopamine were elevated above baseline. The alternative hypothesis that these behaviours are mediated by sensitive post-synaptic receptors is suggested. It was also found that combined treatment with SCH 23390 (0.05 mg/kg) and amphetamine (2 mg/kg) induced yawning, which further supports the new hypothesis.

LHRH antagonizes yawning and genital grooming induced by apomorphine in rats

The effects of the pretreatment with LHRH on the behavioral effects induced by low doses of apomorphine were studied in male rats. Three doses of apomorphine (31.25, 62.50 and 125 micrograms/kg) were subcutaneously administered two hours after LHRH 100 micrograms/kg or solvent SC treatment. Apomorphine induced repeated episodes of yawning and genital grooming. Pretreatment with LHRH abolished or reduced yawning and genital grooming induced by the three doses of apomorphine, suggesting that the peptide could induce subsensitivity of DA receptors responsible for yawning and genital grooming.

Climbing and stereotyped behaviours in mice require the stimulation of D-1 dopamine receptors

Apomorphine-induced climbing and sniffing behaviours in mice were antagonize by low doses of SCH 23390 and metoclopramide. The selective D-2 dopamine receptor agonists, LY 171555 and RU 24926, and some other dopamine agonists (piribedil, lergotrile, bromocriptine) exerted only inhibitory effects on spontaneous behaviours. The selective D-1 dopamine receptor agonist, SK&F 38393, did not modify the climbing score but increased the sniffing and decreased the gnawing scores compared to the scores of control mice. Typical climbing and stereotyped behaviours were produced by the combination of SK&F 39383 with LY 171555, RU 24926 or with the other dopamine agonists tested. These data suggest that the stimulation of D-1 dopamine receptors is required for the induction of climbing and stereotyped behaviours in mice.