Turning behaviour in animals

Prostaglandin inhibition of amphetamine-induced circling in mice

The effect of prostaglandins (PG) on amphetamine(AMPH)-induced circling was examined in mice unilaterally lesioned with 6-hydroxy-dopamine. At doses of 0.03-1.0 nmol/g, intraventricularly injected PGD2, PGE2, and PGF2 alpha all inhibited AMP-induced circling, while thromboxane-B2 (TxB2) was inactive at 1.0 nmol/g. The inhibition of circling was not due to alterations in body temperature as measured by rectal temperature changes. When injected intrastriatally, the same major PG inhibited AMP-induced circling at the lower doses of 0.01-0.1 nmol/g, while the PGE2 metabolite 13, 14-dihydro-15-keto-PGE2 was inactive at 0.1 nmol/g. PG administered alone did not procude circling. For both routes of administration, the order of potency was PGE2 greater than PGD2 greater than PGF2 alpha. These results suggest that PG can alter motor function governed by central dopaminergic pathways.

Possible mechanism of 5-methoxy-N,N-dimethyltryptamine-induced turning behaviour in DRN lesioned rats

5-Methoxy-N,N-dimethyltryptamine (5-MeODMT) (7.5 mg/kg SC) caused a contralateral turning in rats with a unilateral lesion of the dorsal raphe nucleus (DRN). This turning behaviour was blocked by pretreatment with putative 5-HT antagonists, methysergide, cyproheptadine and cinanserin. The peripheral 5-HT antagonist, xylamidine, also prevented the response to 5-MeODMT. Of the other neurotransmitter antagonists, only haloperidol was active, hyoscine, picrotoxin, naloxone and strychnine were ineffective. Pretreatment with alpha-methyl-p-tyrosine (alpha-MT) also significantly reduced the turning response to 5-MeODMT. These results indicate that a central dopaminergic system is involved in 5-MeODMT-induced turning behaviour. This suggestion is supported by the finding that an ipsilateral turning in response to 5-MeODMT was observed in the rats with additional 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle (MFB). The possible mechanisms by which 5-MeODMT induced turning in DRN lesioned rats are discussed.

Involvement of a central dopaminergic system in 5-methoxy-N,N-dimethyltryptamine-induced turning behaviour in rats with lesions of the dorsal raphé nuclei

The turning behaviour induced by 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) has been investigated in rats with lesions of the dorsal raphé nucleus (DRN). 5-MeODMT caused a dose-related contralateral turning in rats with 5,7-dihydroxytryptamine (5,7-DHT) lesions of the substantia nigra and a similar effect was observed in DRN-lesioned rats. In contrast, a dose-related ipsilateral turning was observed when 5-MeODMT was injected into rats with 5,7-DHT lesions of the striatum. These results suggest that the effects of 5-MeODMT in DRN-Lesioned rats are mediated via the substantia nigra. The contralateral turning induced by 5-MeODMT in rats with a 5,7-DHT lesion of the DRN was significantly reduced when a second 5-hydroxydopamine lesion was placed in the striatum, but not when it was placed in the nucleus accumbens. Thus the nigrostriatal dopaminergic system seems to be involved in 5-MeODMT-induced turning. The release of tritium from slices of substantia nigra previously labelled with [3H]-dopamine was inhibited by 5-MeODMT (10(-7) to 10(-5) M) and this effect was blocked by methysergide in a concentration-related manner. Tetrodotoxin (10(-7) M) failed to antagonise 5-MeODMT. These results suggest that 5-MeODMT can inhibit dopamine release from nigral dendrites, which could in turn enhance nigrostriatal activity by reducing the auto-inhibitory actions of dopamine, thereby causing contralateral turning in DRN-lesioned rats.

Motor effects following application of putative excitatory amino acid antagonists to the region of the mesencephalic dopamine cell bodies in the rat

The excitatory amino acid antagonists 2-amino-5-phosphonovalerate and gamma-D-glutamylglycine have been applied focally to the ventral tegmental area and both the pars compacta and pars reticulata of the substantia nigra of the rat. The injections were performed under halothane anaesthesia so that behavioural effects could be observed 5 min afterwards. Bilateral application of either antagonist to the ventral tegmental area and the pars compacta of the substantia nigra induced enhanced locomotor activity in an open field. This effect was blocked by pretreatment of the animals with a low dose of the dopamine receptor antagonist fluphenazine. Bilateral application of either antagonist to the pars reticulata of the substantia nigra produced sedation and a reduction in locomotor activity. Unilateral injection of either of the excitatory amino acid antagonists into the pars reticulata or pars compacta of the substantia nigra both resulted in contraversive circling behaviour. The effect of intranigral (both pars compacta and reticulata) 2-APV and gamma-DGG was accompanied by a significant increase in concentrations of both 3,4-dihydroxyphenylacetic acid (to 158-160% of control following injection into pars compacta, and 134-146% of control injected into pars reticulata) and homovanillic acid (to 161-166% of control following injection into pars compacta, and 186-210% of control injected into pars reticulata) in the ipsilateral striatum. Pretreatment of these animals with fluphenazine (0.3 mg/kg) antagonized this circling behaviour. These results indicate that antagonism of excitatory amino acid receptors in the region of the midbrain of the rat leads to specific behavioural effects which may in part be mediated through the ascending dopaminergic projections.

Anatomical demonstration of the involvement of the substantia nigra in contraversive circling elicited by electrical stimulation of the medial forebrain bundle in the cat: a retrograde transport study using horseradish peroxidase subsequent to an electrolytic lesion

A method is described for the anatomical identification of groups of neurones likely involved in the elaboration of component acts of a centrally elicited behaviour, when involvement of fibres of passage is suspected. The contraversive circling which accompanied the predatory attack of a cat upon a rat elicited electrical stimulation within the hypothalamic and ventral midbrain trajectory of the medial forebrain bundle (MFB) was used as a model because of the established role played by the nigrostriatal dopamine system in the production of the circling. Following horseradish peroxidase (HRP) injections, made after electrolytic lesion at such MFB sites, substantial numbers of labelled cells were found in the substantia nigra, pars compacta (SNC). In contrast, many fewer SNC neurones were labelled following:(1) HRP injections made after electrolytic lesion at MFB sites at which the elicited predatory behaviour was not accompanied by contraversive circling; and (2) HRP injections made without a prior lesion at MFB sites at which the elicited predatory behaviour was accompanied by contraversive circling.

The nucleus tegmenti pedunculopontinus and circling behaviour in the rat

Lesioning the rat's substantia nigra (SN) with kainic acid (0.8 microgram) or by electrocoagulation (1 mA for 6 sec) significantly lowered GABA and glutamate decarboxylase levels at the treatment site, but not in the nucleus tegmenti pedunculopontinus (PPN), suggesting nigro-PPN fibres do not synthesize or store GABA. Stereotaxic injection of one PPN with muscimol (40 ng), picrotoxin (40 ng) or tetanus toxin (30 mouse LD50 doses) had little or no effect on the animals' behaviour; kainate caused ipsilateral body flexion, sporadic ipsiversive circling and contraversive barrel-rolling. These behavioural abnormalities disappeared after 7 days when histology confirmed virtually complete loss of PPN perikarya, intense gliosis and some demyelination of passing axons. Impairing PPN transmission with kainate (chronically) or muscimol (acutely) caused weak apomorphine-induced contraversive rotation, but did not modify the robust nigral muscimol-evoked contraversive asymmetry. While we do not exclude a role of PPN in motor control, these data suggest that nigro-PPN neurones are neither GABAergic nor mediators of central dopaminergic function.

The effects of muscimol and picrotoxin injections into the cat substantia nigra

The behaviour of cats after unilateral injections of muscimol, picrotoxin and bicuculline into the posterior and lateral parts of the substantia nigra was observed. The antagonism between muscimol and picrotoxin was limited to some effects of the drugs: (1) muscimol-induced sniffing, licking and enhanced locomotor activity was attenuated by picrotoxin in contrast to the muscimol-induced contralateral turning which was even enhanced by picrotoxin; (2) picrotoxin-induced balance disorders as well as characteristic motor disturbances in the hind legs remained unaffected following an additional treatment with muscimol. Furthermore, subcutaneously given apomorphine did not affect the picrotoxin-induced balance and hind leg disorders, although the apomorphine-induced stereotyped behaviour itself was enhanced and suppressed by intranigral administration of muscimol and picrotoxin respectively. The conclusion is reached that there are at least two distinct populations of GABA receptors within the substantia nigra: one group controlling or being controlled by dopaminergic neurons and one group operating fully independently of the former neurons. The similarities to experiments on rats are stressed. The mechanism underlying the muscimol-resistant picrotoxin-induced effects (balance disorders and motor disturbance of the hind legs) is discussed.

The influence of striatal stimulation and putative neurotransmitters on identified neurones in the rat substantia nigra

The response of two populations of neurones in the substantia nigra (nigro-striatal compacta neurones and reticulata neurones) to microelectrophoretically administered putative neurotransmitters and stimulation of the ipsilateral striatum has been investigated in anaesthetized rats. There were marked differences between compacta and reticulata neurones in respect to their action potential configurations, spontaneous firing rates and their responses to striatal stimulation. However, both compacta and reticulata neurones were excited and/or inhibited by striatal stimulation, although inhibition was usually the predominant response in both neuronal populations. Compacta neurones were strongly inhibited by noradrenaline (NA) and dopamine (DA) but were unaffected by acetylcholine (ACh) and 5-hydroxytryptamine (5-HT). Reticulata neurones were excited by ACh and showed mixed responses to 5-HT, DA and NA. Excitant amino acids overdepolarized compacta neurones preventing them from firing rapidly, but induced large increases in reticulata neurone firing rate; effects that were readily antagonized by D-alpha-aminoadipate. Compacta neurones were less sensitive than reticulata neurones to GABA and glycine. The action of these inhibitory amino acids were selectively and reversibly antagonized by bicuculline methochloride and strychnine, respectively. The striatal-evoked inhibition of both compacta and reticulata neurones was reversibly reduced by bicuculline methochloride and irreversibly reduced by tetanus toxin, but was unaffected by strychnine. These results demonstrate that nigrostriatal-compacta neurones and reticulata neurones are physiologically and pharmacologically distinct neuronal populations and both receive inhibitory GABAergic and excitatory striatal inputs.

Evidence for a crossed nigrostriatal pathway in rats

In order to characterize further the origin of striatal afferents, adult rats underwent a unilateral intrastriatal infusion of 30% Evans Blue solution (0.2 - 0.5 mul). Labeled neurons were observed in ipsilateral substantia nigra, thalamus, cortex, ventromedial mesencephalic tegmentum and dorsal raphe. Several labeled neuronal somata, albeit considerably fewer than seen ipsilaterally, were found also in the contralateral substantia nigra and ventral tegmental area, a result contrary to previously reported findings in the rat. Control injections restricted to cortex overlying striatal target site did not result in similar labeling, and corpus callosum transection prior to intrastriatal injection did not prevent labeling of contralateral substantia nigra. These findings indicate that rats, like cats, have a sparse crossed nigrostriatal pathway.

Amphetamine-induced rotation in normal cats

Amphetamine elicited dose-related rotation (circling behavior) in 9 naive cats; all cats also rotated, at lower rates, during non-drug sessions. The direction of rotation was consistent for each cat, with 6 cats rotating to the right and 3 to the left. The results extend the generality of previous findings involving rodents and suggest that an endogenous asymmetry in striatal dopamine activity may be a common characteristic of many animal species.

Involvement of dopamine in circling responses to muscimol depends on intranigral site of injection

The intensity, direction and dopamine dependence of circling behaviour were determined following stereotaxic injections of 40 ng muscimol (in 0.2 microliter over 3 min) into different regions of the rat's substantia nigra (SN). Weak, haloperidol-sensitive ipsilateral postural or locomotor asymmetries were invariably obtained from the rostral SN zona compacta (SNC), whilst robust contraversive rotational behaviour was always initiated from the SN zona reticulata (SNR) and caudal SNC. This was most rapid from the central SNR and was markedly attenuated by i.p. pretreatment with haloperidol (0.1 mg/kg) or pimozide (0.25 mg/kg), or by week-old 6-OHDA lesions of the nigrostriatal dopamine (DA) tract. Turning was significantly weaker from the lateral and ventral areas of the SNR, where it was not susceptible to DAergic blockade. Lower circling rates were also obtained if the SNR injections were made rapidly (in 30 sec), in a large volume (0.5 microliter) or at a supramaximal dose level (400 ng), possibly due to increased spread of the drug to remote neurones having an opposite effect on directional behaviour, or to exaggerated stereotypy. The variable action of muscimol at multiple sites in the SN is suggested to account for the earlier conflicting data in the literature.

Effect of nicotinic and muscarinic drugs on amphetamine- and apomorphine-induced circling behaviour in rats

The effect of drugs modulating the activity of nicotinic or muscarinic cholinergic receptors on the circling behaviour induced by amphetamine and apomorphine in rats with unilateral 6-hydroxydopamine lesion of nigrostriatal dopaminergic pathway was studied. Nicotine (0.2 mg/kg subcutaneously) significantly increased amphetamine-induced circling behaviour and tended to inhibit apomorphine-induced circling behaviour. Mecamylamine and pempidine (both 2 mg/kg intraperitoneally) slightly but significantly depressed the intensity of circling behaviour induced by amphetamine, but failed to modify the induced by apomorphine. Pilocarpine (10 mg/kg intraperitoneally) clearly inhibited both amphetamine- and apomorphine-induced circling behaviour. Unlike pilocarpine, atropine (10 mg/kg intraperitoneally significantly increases the intensity of the circling behaviour induced by amphetamine and also to some extent that induced by apomorphine. Neither hexamethonium (5 mg/kg intraperitoneally) nor methylatropine (1 mg/kg subcutaneously) modified the circling behaviour induced by either amphetamine or apomorphine. The results show that stimulation of central nicotinic and muscarinic receptors may have some opposite effects on the dopamine dependent circling behaviour. The presynaptic nicotinic cholinergic receptors on the terminals of the nigrostriatal dopaminergic neurones, stimulation of which may increase the release of dopamine, might be involved in the action of nicotinic drugs. The muscarinic cholinergic receptors in the striatum and/or in the substantia nigra might be involved in the action of muscarinic drugs.

Effect of L-prolyl-L-leucyl-glycinamide (MIF-I) on some neutrotransmitter-receptor interactions

Some neurotransmitter-receptor interactions have been studied in an attempt to determine how L-prolyl-L-leucyl-glycinamide (MIF-I) exerts its antiparkinson effect. MIF-I affected neither the contractile responses of isolated mouse vas deferens and guinea pig ileum to noradrenaline, acetylcholine, substance P and histamine, nor the inhibitory effects of dopamine and GABA on the rat vas deferens and guinea pig ileum. MIF-I, as well as L-leucine and Pro-Leu, antagonized the contractile response of the ileum to 5-hydroxytryptamine (5-HT). Behavioural tests were used to examine the action of MIF-I on CNS transmitter-receptor interactions. MIF-I did not modify the circling produced by either dopamine agonists in nigro-striatal lesioned rats of 5-HT agonists in rats with a lesion of the medial raphe nucleus. MIF-I affected neither 5-hydroxytryptophan-induced head twitches in mice, which is a measure of 5-HT receptor stimulation, nor striatally-evoked head turning in the rat, which is a model for brain GABA function. It is concluded that MIF-I, at the doses used, does not directly modify the function of any of the CNS transmitter examined. Other possibilities to explain its antiparkinson action are discussed.

Contralateral circling behaviour induced by intranigral injection of morphine and enkephalin analogue FK 33-824 in rats

Contralateral circling behaviour induced by intranigral injection of morphine or an enkephalin analogue, FK 33-824, was studied in rats. Both morphine (0.625-10.0 micrograms) and FK 33-824 (1.25-40.0 ng) evoked the same kind of contralateral circling behaviour when injected into the substantia nigra. FK 33-824 was about 1000 times more potent than morphine and its effect lasted a little longer. Pretreatment with naloxone (5 mg/kg subcutaneously or 1 microgram intranigrally) almost completely blocked the circling induced by intranigral morphine or FK 33-824. The lesion of the ipsilateral nigrostriatal dopaminergic pathway with 6-hydroxydopamine significantly antagonized both morphine- and FK 33-824-induced circling. Pretreatment with d-amphetamine (1 mg/kg intraperitoneally) significantly increased the intensity of the circling induced by morphine or FK 33-824, and pretreatment with haloperidol (0.5 mg/kg subcutaneously) attenuated this intensity. Pretreatment with pilocarpine (10 mg/kg intraperitoneally) or mecamylamine (2 mg/kg intraperitoneally) inhibited the circling, whereas pretreatment with atropine (10 mg/kg intraperitoneally) or nicotine (0.2 mg/kg subcutaneously) increased morphine- and FK 33-824-induced circling. Pretreatment with muscimol (0.5 mg/kg subcutaneously) did not significantly increase morphine-induced circling but tended to increase FK 33-824-induced circling. Pretreatment with bicuculline (3 mg/kg intraperitoneally) slightly but significantly inhibited both morphine- and FK 33-824-induced circling. Pretreatment with strychnine (0.25 mg/kg intraperitoneally) did not modify the circling induced by morphine or FK 33-824. The results show that the contralateral circling behaviour induced by intranigral injection of morphine and FK 33-824 seems to be mediated by the activation of the dopaminergic nigrostriatal system.

Activation and lateralization of sensorimotor field for perioral biting reflex by intranigral GABA agonist and by systemic apomorphine in the rat

In Experiment 1 unilateral injection of the GABA agonist, muscimol (20 ng in 0.1 microliter saline) into the substantia nigra (SN) of rats elicited contraversive turning and a correlated transient asymmetry in responsiveness to tactile stimulation of the mouth area. On the side of the face contralateral to the injected SN they responded stronger than on the ipsilateral side, and, furthermore, they responded to tactile stimulation with a withdrawal of the lip, followed by a vigorous biting of the probe. In Experiment 2, systemic injection of apomorphine also sensitized the perioral biting response to tactile stimulation. Unilateral injection into the SN of 8 micrograms 6-OHDA blocked this response to stimulation of the side of the face ipsilateral to the lesion. The experiments demonstrate: (1) pharmacological control of sensory-motor neglect, the asymmetry being determined by the direction of turning; and (2) a possible neuropharmacological basis of the perioral biting reflex, which may be related to certain types of aggressive behaviors.