C. Pycock

Stereotyped behaviour patterns and hyperactivity induced by amphetamine and apomorphine after discrete 6-hydroxydopamine lesions of extrapyramidal and mesolimbic nuclei

Changes in stereotyped sniffing, biting and hyperactivity induced by apomorphine and D-amphetamine in the rat were determined after bilateral 6-hydroxy-dopamine (6-OHDA) lesions (8-16 micron/4micron6) of the extrapyramidal caudate-putamen (CP) (anterior and centre), globus pallidus (GP) and substantia nigra (SN), the mesolimbic nucleus (ACB), tuberculum olfactorium (TUO) and central amygdaloid nucleus (ACE). Lesions were also induced in the medial forebrain bundle in the lateral hypothalamus (LH). The 6-OHDA lesions of the CP reduced amphetamine biting but not sniffing or hyperactivity. Centrally placed 6-OHDA failed to modify any response to apomorphine but anterior locations reduced apomorphine biting. Both lesion locations led to a 45-65% reduction in striatal dopamine (DA) content, but the anterior location also involved depletions of mesolimbic DA. 6-OHDA lesions of the GP reduced striatal DA by 62% but initially potentiated before reducing both apomorphine and amphetamine biting. These lesions also potentiated amphetamine hyperactivity but other parameters were unmodified. The LH and SN lesions reduced striatal and mesolimbic DA by 75-80% and potentiated apomorphine biting. The LH lesions reduced amphetamine biting and hyperactivity but the SN lesions initially potentiated these responses. 6-OHDA lesions of the ACB reduced the DA content of this nucleus by 72% but had little effect on the TUO: these lesions reduced the duration of amphetamine hyperactivity and potentiated apomorphine biting. In contrast, equally selective lesions of the TUO (80% DA depletion) enhanced the locomotor activity response to both apomorphine and amphetamine; apomorphine biting was also increased but other parameters were unmodified. Lesions of the ACE depleted amygdaloid DA by at least 80% and reduced or abolished apomorphine and amphetamine biting in the chronic stage. The results indicate that the sites for mediation of sterotyped sniffing, biting or hyperactivity are not the same for apomorphine and amphetamine, and that each behavioural state involves the functioning of more than one DA-containing area.

The rotating rodent: a two component system?

The hypothesis that the rotating rat requires both nigro-striatal and mesolimbic dopaminergic components for activity has been tested. 6-Hydroxydopamine lesions were induced unilaterally in either or both the ascending nigrostriatal and mesolimbic dopamine pathway. In one group of rats the nucleus accumbens was destroyed bilaterally with electrolesions. Circling behaviour was only recorded when there was both an imbalance in striatal dopamine concentrations concomitant with stimulation of the limbic dopamine regions. Lesions of the mesolimbic dopamine pathway resulted in changes in drug-induced motor activity but postural asymmetry or circling behaviour was not observed. The results support the hypothesis that the rotating rodent requires two functional dopamine components: striatal dopamine imbalance causing a postural asymmetry and stimulation of mesolimbic dopamine systems providing a locomotor component. The relevance of these components in this animal model is discussed with reference to dopaminergic agonist and antagonist drugs.

Serotoninergic modulation of the dopamine response from the nucleus accumbens

The depletion of brain 5-hydroxytryptamine (5-HT) by electrolytic lesions of the midbrain raphC nuclei, or by synthesis inhibition, results in marked hyperactivity in the rat (Kostowski, Giacolone & others, 1968; Jacobs, Trimbach & others, 1975). This would suggest that 5-HT may normally participate in motor control by exerting a powerful inhibitory effect. The nature of the system or systems subjected to such a control is not known but catecholaminergic mechanisms have been shown to be essentially involved in the regulation of motor activities and some workers have suggested a possible relation between these controlling mechanisms and 5-HT function (Neil], Grant & Grossman, 1972; Costall & Naylor, 1974). A site for such an interaction is suggested by recent studies showing that a marked hyperactivity results from an increased dopaminergic activity within the nucleus accumbens (Pijnenburg, Honig & van Rossum, 1975; Costall & Naylor, 1975), and this nucleus is known to be innervated by serotoninergic as well as by dopaminergic neurons (Fuxe, 1965; Conrad, Leonard & Pfaff, 1974). Therefore, we investigated the possible role of the nucleus accumbens in the hypothesized dopaminergic/serotoninergic control of motor function. Bilateral stainless-steel guide cannulae (0.65 mm diameter) were chronically implanted, using stereo: taxic techniques, to allow the direct injection into the nucleus accumbens of male, Sprague-Dawley rats (250-300 g). Chloral hydrate (300 mg kg-l, i.p.) was used as anaesthetic. 0.3 mm diameter stainless-steel stylets terminated 0-5 mm below the guide tips and kept the guides patent. Animals were subjected to intracerebral injections 10-14 days after surgery when they were manually restrained as the stylets were replaced by stainless-steel injection units which terminated 2.5 mm below the guides at the centre of the nucleus accumbens (Ant. 9.0, Vert. 0, Lat. d~l .6) (De Groot, 1959). Injection units were coupled to Agla micrometer syringes and 2 pl drug or solvent solution was delivered bilaterally over 5 s with a further 55 s allowed for deposition of drug. Rats were used on two occasions with an intervening 7-10 day recovery period, and were then killed for histological and biochemical examination. In some experiments, lesions were made in the medial raphk nucleus on the same occasion as implantation of the guides. These lesions were induced electrolytically using a stainless-steel electrode, 0.64 mm diameter, which was insulated excepting at the tip. The electrode

Serotonergic involvement with neuroleptic catalepsy

Abstract The electrolytic brain lesion technique was used to interrupt the ascending serotonergic pathways at the level of the midbrain raphe nuclei in order to determine the role of 5-hydroxytryptamine in the mediation of neuroleptic catalepsy. Lesions of either the medial or dorsal raphe nuclei were shown to reduce the 5-hydroxytryptamine content of the cerebral cortex, striatum and limbic forebrain but had no significant effect on limbic and striatal dopamine levels or on cortical and limbic noradrenaline levels. A differential innervation from the raphe nuclei could not be demonstrated. Lesions of the medial or dorsal raphe nuclei were shown to significantly reduce the cataleptic actions of the neuroleptic agents haloperidol, fluphenazine, oxiperomide and spiroxatrine but had no consistent effect on the cataleptic actions of the dibenzazepine neuroleptics, loxapine and clothiapine. The weak cataleptic action of thioridazine tended to be reduced similarly to that of the classical neuroleptics. The weak effect of clozapine was significantly potentiated by lesions of the dorsal raphe nucleus. The cataleptic effect of the non-neuroleptic agent metoclopramide could not be differentiated from either group of neuroleptics: its actions were reduced by the medial raphe lesions (similarly to the classical neuroleptics), but were not reduced by the dorsal lesions (similarly to the dibenzazepines). The results indicate that 5-hydroxytryptamine function may be important, but not necessarily essential, for the cataleptic action of some neuroleptic agents.

The relationship between striatal and mesolimbic dopamine dysfunction and the nature of circling responses following 6-hydroxydopamine and electrolytic lesions of the ascending dopamine systems of rat brain.

The importance of extrapyramidal and mesolimbic function for circling behaviour was investigated by placing 6-hydroxydopamine (6-OHDA) and electrolesions in the cell bodies, axons and terminals of each system. Circling behaviour was weak when 6-OHDA was placed at the centre of the substantia nigra (SN), but the characteristic contralateral/ipsilateral turning to apomorphine/amphetamine were recorded. Circling was more marked when 6-OHDA was placed anterior to the SN but was generally absent following injections posterior to the SN. However, 6-OHDA placed in the medial forebrain bundle in the lateral hypothalamus resulted in intense contralateral/ipsilateral turning to apomorphine/amphetamine. Generally, the intensity of circling responses was related to the degree of striatal dopamine (DA) depletion but the more effective lesions also caused reductions in mesolimbic DA content. However, circling was not observed following any 6-OHDA injection into the mesolimbic DA system and it is concluded that mesolimbic DA function is not essential for the initiation of circling. In contrast to the 6-OHDA lesions, rats circled ipsilateral to both apomorphine and amphetamine when the SN was damaged by electrocoagulation to cause marked depletion of striatal dopamine. Lesser depletions of striatal dopamine after electrocoagulation in different regions of the medial forebrain bundle were associated with a lower intensity of ipsilateral circling to both drugs. In general, the differences between 6-OHDA and electrolesions could not be explained by additional damage to ascending noradrenaline or 5-hydroxytryptamine pathways. Lower doses of apomorphine were effective in the 6-OHDA circling rats, and the ipsilateral striatum of such rats was more sensitive to directly applied DA. Higher doses of apomorphine were required to produce circling after chronic electrolesions which rendered the ipsilateral striatum insensitive to DA. The contralateral circling to apomorphine after 6-OHDA lesions was abolished by chronic but not by acute electrolesion of the SN. It is suggested that electrolesions of the SN cause different effects to 6-OHDA because they destroy neuronal pathways in addition to the dopaminergic nigrostriatal tract. These appear to be required for the expression of circling behaviour caused by stimulation of the denervated striatum. Whereas 6-OHDA lesions result in super-sensitivity of the denervated strital DA receptors, electrolesions may cause a hypo-sensitivity of the same receptor sites.

Circling behaviour produced by unilateral lesions in the region of the locus coeruleus in rats

Rats with unilateral lesions in the region of the locus coeruleus circled tightly to the opposite side when given apomorphine or amphetamine. This turning behaviour was transient and disappeared within some 30 days after surgery. It was seen most obviously in animals with severe unilateral destruction of the locus coeruleus, which caused on average a 55% reduction in the level of noradrenaline in the ipsilateral cerebral cortex. It was not marked in animals with partial unilateral lesions of the locus coeruleus, which caused only an average fall in cortical noradrenaline of 22%. It was not seen in sham operated animals or animals in which lesions were placed into adjacent structures such as the cerebellum above, superior cerebellar peduncle laterally, and brain stem ventrally. A clue to the mechanism of this phenomenon may lie in the observation that dopamine in the ipsilateral striatum was increased 5 days after operation, when circling occurred, but had returned to normal by 30 days when circling had ceased. It is suggested that the lesion causes a reduction in impulse traffic in the ipsilateral nigrostriatal pathway, and that circling is due to preferential stimulation of the ipsilateral striatal dopamine receptors by both drugs; apomorphine directly, amphetamine by release of endogenous dopamine.

Rotational behavior induced in rats by intranigral picrotoxin.

There is considerable anatomic, biochemical, and physiologic evidence for a descending pathway in mammalian brain between the caudate nucleus-putamen (neostriatum) and substantia nigra (SN) which is mediated by y-aminobutyric acid (GABA) and exerts an inhibitory effect on neurons of the substantia nigra. GABA and its synthesizing enzyme, glutamic acid decarboxytase (GAD) are both found in high concentration in the SN 7,11 and mechanisms of uptake and release have been demonstrated for GABA in brain slice preparations of SN 13,25, Striatal ablation or transection of striatonigral pathways both produce a reduction in the concentration of GABA and GAD in the SN of several animal species 13,1a,20,2a, together with degeneration of a specific group of nigral terminal boutons 1~ which, on the basis of autoradiographic evidence, are believed to be GABA terminals 5. Intracellular recordings of SN neurons following electrical stimulation of the caudate nucleus in ether-anesthetized cats have disclosed short latency EPSPs followed by IPSPs 14. Electrical stimulation of the caudate nucleus in barbiturateanesthetized cats, however, has produced longer latency IPSPs in nigral neurons which are believed to be mediated by monosynaptic transmission3L This inhibition of SN neurons is mimicked by microiontophoretic application of GABA onto nigral neurons 10,12 and blocked by intravenous 27 or microiontophoretic 1° picrotoxin, a drug believed to block the postsynaptic inhibitory action of GABA in the mammalian central nervous systemlS,24, 27. Since the SN gives rise to an ascending dopaminergic projection to the neostriatum 30, this GABA-mediated inhibitory striatonigral projection would be expected to influence activity in the nigrostriatal dopaminergic system. Recent biochemical studies indicate that GABA, in fact, does mediate an inhibitory effect on dopamine synthesis in the nigrostriatal tract 1,3,17. This study provides behavioral evidence for GABA-mediated inhibition of the dopaminergic nigrostriatal system. In rodents, a relative increase in activity of one nigrostriatal system is known to produce rotational behavior towards the contra-

The roles of noradrenaline and dopamine in contraversive circling behaviour seen after unilateral electrolytic lesions of the locus coeruleus

Unilateral electrolytic lesions of the locus coeruleus in rats result in spontaneous ipsiversive rotation, which is then replaced by contraversive rotation. One week after lesioning, when spontaneous turning ceases, apomorphine and d-amphetamine elicit contraversive circling behaviour, which was not affected by noradrenergic receptor blockade but was abolished by dopamine receptor blockade. The drug-induced contraversive circling response was also reproduced by piribedil but not clonidine. Combined unilateral electrolytic locus coeruleus and substantia nigra lesions on the same side resulted in apomorphine- and d-amphetamine-induced ipsilateral rotational behaviour which was indistinguishable from that seen with substantia nigra lesions alone. In rats with unilateral locus coeruleus lesions, the dose of intrastriatally injected apomorphine required to produce circling was less on the lesioned than the non-lesioned side. Direct injection of noradrenaline into one substantia nigra caused contraversive circling. Direct injection of phenoxybenzamine into one substantia nigra followed by apomorphine caused ipsiversive circling. The results suggest that the circling behaviour seen after unilateral locus coeruleus lesions depends on an asymmetry of striatal dopamine receptor activity and are consistent with a proposed coeruleus-nigral noradrenergic pathway, which enhances impulse flow in the dopaminergic nigrostriatal system.

Pharmacological evidence for cerebral dopamine receptor blockade by metoclopramide in rodents

Metoclopramide antagonises apomorphine-in-duced stereotypy in rats (ED50 1.5 mg/kg), apomorphine reversal of reserpine-induced locomotor suppression in mice (50% inhibition produced by 17 mg/kg), and apomorphineor amphetamine-induced turning behaviour in mice with unilateral lesions of the striatal dopaminergic nerve terminals (ED50 5.0 and 4.0 mg/kg respectively). Metoclopramide resembles pimozide in all these respects and appears to be a relatively potent antagonist of striatal dopamine receptors. Yet metoclopramide, in anti-emetic doses, has no effect on disability in Parkinsons disease or on the therapeutic benefit of l-Dopa and l-Dopa dyskinesias.

Possible GABA-mediated control of dopamine-dependent behavioural effects from the nucleus accumbens of the rat.

The effect of elevating GABA levels in the region of the nucleus accumbens on various dopamine-dependent behaviours in the rat has been studied. The GABA-transaminase inhibitor, ethanolamine O-sulphate (EOS) was injected bilaterally (through a needle angled at 45°) into the nucleus accumbens. This resulted in a 4–5-fold increase in the GABA concentrations in the mesolimbic areas on day 1, a 2-fold increase on day 3, and a return to normal by day 7. Moderate increases in striatal and cortical GABA levels were also seen on days 1 and 3. At all times animals exhibited normal spontaneous activity and exploratory behaviour in a hole-board apparatus. However, on day 1, when mesolimbic GABA levels were maximal, a low dose of systematically administered amphetamine (0.5 mg/kg) did not induce the increased locomotor activity seen in a control group of animals. Similarly on day 1, the direct injection of dopamine into the nucleus accumbens of rats previously injected with EOS did not evoke the usual hyperactivity response. This response returned to normal on day 7. Apomorphine-induced stereotyped behaviour patterns observed on days 1 and 2 did not significantly differ in those rats previously injected with EOS with animals of a control group. A possible GABA-mediated control of dopaminergic mechanisms in the nucleus accumbens is suggested, and the possible site of interaction discussed.