The importance of the ascending dopaminergic systems to the extrapyramidal and mesolimbic brain areas for the cataleptic action of the neuroleptic and cholinergic agents

A functional role for complex gangliosides: motor deficits in GM2/GD2 synthase knockout mice

Although gangliosides are abundant molecular determinants on all vertebrate nerve cells (comprising approximately 1.5% of brain dry weight) their functions have remained obscure. We report that mice engineered to lack a key enzyme in complex ganglioside biosynthesis (GM2/GD2 synthase), and which express only the simple ganglioside molecular species GM3 and GD3, develop significant and progressive behavioral neuropathies, including deficits in reflexes, strength, coordination, and balance. Quantitative indices of motor abilities, applied at 8 and 12 months of age, also revealed progressive gait disorders in complex ganglioside knockout mice compared to controls, including reduced stride length, stride width, and increased hindpaw print length as well as a marked reduction in rearing. Compared to controls, null mutant mice tended to walk in small labored movements. Twelve-month-old complex ganglioside knockout mice also displayed significant incidence of tremor and catalepsy. These comprehensive neurobehavioral studies establish an essential role for complex gangliosides in the maintenance of normal neural physiology in mice, consistent with a role in maintaining axons and myelin (Sheikh, K. A. , J. Sun, Y. Liu, H. Kawai, T. O. Crawford, R. L. Proia, J. W. Griffin, and R. L. Schnaar. 1999. Mice lacking complex gangliosides develop Wallerian degeneration and myelination defects. Proc. Natl. Acad. Sci. USA 96: 7532-7537), and may provide insights into the mechanisms underlying certain neural degenerative diseases.

7-[3-(1-piperidinyl)propoxy]chromenones as potential atypical antipsychotics. 2. Pharmacological profile of 7-[3-[4-(6-fluoro-1, 2-benzisoxazol-3-yl)-piperidin-1-yl]propoxy]-3-(hydroxymeth yl)chromen -4-one (abaperidone, FI-8602)

A series of novel 7-[3-(1-piperidinyl)propoxy]chromenones was synthesized and tested as potential antipsychotics in several in vitro and in vivo assays. The compounds possessed good affinity for D2 receptors, together with a greater affinity for 5-HT2 receptors, a profile which has been proposed as a model for atypical antipsychotics. Several agents also displayed a high potency in the climbing mice assay on oral administration, suggesting a potent antipsychotic effect as compared to reference standards. Compound 23 was selected for further pharmacological evaluation. Induction of catalepsy and inhibition of stereotypies weaker than standards, along with a lower increase in serum prolactin levels, were indicative of a potential atypical profile for this compound. From these results, 7-[3-[4-(6-fluoro-1, 2-benzisoxazol-3-yl)piperidin-1-yl]propoxy]-3-(hydroxymethyl )chromen- 4-one (23, abaperidone) has been proposed for clinical evaluation in humans as a potential atypical antipsychotic.

7-[3-(1-piperidinyl)propoxy]chromenones as potential atypical antipsychotics

Compound 1 (1-benzyl-3-methyl-4-[4-(4-fluorophenyl)-4-oxobutyl]piperazine), a synthetic intermediate identified as a potential atypical antipsychotic, was selected as the starting point for pharmacological improvement. From 1, sequential structural variations were conducted in order to improve its potency and oral bioavailability. These variations included a series of piperazine, ethanediamine, and piperidine derivatives. The piperidine series afforded some orally potent compounds in the inhibition of apomorphine-induced climbing and hyperactivity in mice, which are regarded as behavioral models predictive of antipsychotic efficacy. Further optimization of these structures led to the highly potent 7-[3-(1-piperidinyl)propoxy]chromenones. Inhibition of stereotypies and induction of catalepsy in rats at doses substantially higher than required for inhibition of climbing suggest an atypical antipsychotic profile, which is assumed to predict a reduced induction of extrapyramidal side effects in humans.

Catalepsy induced by carbachol microinjected into the pontine reticular formation of rats

Rats were implanted stereotaxically with permanent guide tubes aimed at the pontine reticular formation. Carbachol was microinjected in the awake, freely moving rats. Catalepsy was evaluated with the horizontal bar test. Intense and long-lasting, dose-dependent catalepsy was observed following microinjections of 2-8 micrograms of carbachol. Pretreatment with intraperitoneally administered scopolamine significantly reduced the cataleptogenic effect of carbachol. These results show that the pontine reticular formation is part of the neuroanatomical substrate of catalepsy induced by cholinergic drugs.

Dopamine receptor blocking action of a dibenzothiepin derivative isofloxythepin in rats

1. Subcutaneous injection of isofloxythepin or haloperidol inhibited exploratory behaviour, methamphetamine (3 mg/kg)-induced hyperactivity and bromocriptine (15 mg/kg)-induced yawning, and also elicited catalepsy. 2. Isofloxythepin and haloperidol increased concentrations of dihydroxyphenylacetic acid in the striatum and elevated serum prolactin levels. 3. The results suggest that isofloxythepin, as well as haloperidol, blocks the action of the dopamine D2-receptors in the striatum, nucleus accumbens and pituitary.

Hypothyroidism leads to increased dopamine receptor sensitivity and concentration

Rats treated with iodine-131 were confirmed to be hypothyroid by their reduced baseline core body temperatures, reduced serum thyroxine concentrations and elevated serum thyroid stimulating hormone concentrations. When hypothyroid rats were compared to euthyroid controls they were more sensitive to the effects of apomorphine (1.0 mumol/kg) on stereotypy, operant responding and body temperature and showed a smaller reduction in locomotor activity after injection of haloperidol (0.25 mumol/kg). Receptor binding studies on striatal homogenates indicated that hypothyroid rats had increased concentrations of D2 dopamine receptors but there was no change in the affinity. It is concluded that hypothyroidism increases dopamine receptor sensitivity by increasing receptor concentration.

Modification of the behavioural effects of haloperidol and of dopamine receptor regulation by altered thyroid status

Rats made hypothyroid by the chronic oral administration of 200 mg/kg propylthiouracil were less sensitive to the cataleptic effects of haloperidol (0.1 mg/kg) treatment than were euthyroid rats chronically treated with isotonic saline. However, rats made hyperthyroid by the chronic injection of 200 micrograms/kg thyroxine were not more sensitive to the cataleptic suppressant effects of haloperidol (0.1 mg/kg). Higher doses of haloperidol (1 and 5 mg/kg) produced significantly greater catalepsy in the hyperthyroid rats and significantly reduced catalepsy in the hypothyroid rats. Receptor binding studies carried out on the striata from rats sacrificed 48 h after a 6-day course of chronic haloperidol (0.1 mg/kg once daily) treatment revealed a significant upregulation (increase) of dopamine receptors in the hypothyroid rats only. These findings are consistent with the hypothesis that altered thyroid status can modify the sensitivity of dopamine receptors.

Diazepam potentiates the effect of neuroleptics on behavioural activity as well as dopamine and norepinephrine turnover: Do benzodiazepines have antipsychotic potency?

A single injection of diazepam (10 mg/kg, s.c.), haloperidol (2 mg/kg, i.p.) or chlorpromazine (10 mg/kg, i.p.) decreased the ambulatory as well as sniffing behaviour of rats. These behavioural responses were further decreased when diazepam was administered concurrently with the neuroleptic. Acute haloperidol or chlorpromazine treatment increased striatal dopamine as well as cerebro-cortical norepinephrine turnover. In contrast, diazepam diminished the release of both of these catecholamines. When diazepam was administered together with haloperidol or chlorpromazine, a further decrease particularly in dopamine release was seen in striatum. This effect of diazepam on norepinephrine and dopamine turnover persisted even after 21 days of daily treatment, Similarly, the sedative effect of diazepam elicited in the form of depressed locomotor activity was also apparent after long-term administration of this benzodiazepine. However, chronic administration of neuroleptics enhanced the spontaneous locomotor activity and sniffing behaviour by about 25%. Furthermore, repeated neuroleptic treatment decreased the synthesis and turnover of dopamine and norepinephrine. This was reflected in decreased tyrosine hydroxylase and homovanillic acid level in striatum as well as by low concentration of 3-methoxy-4-hydroxyphenylethylene glycol in the cerebral cortex. When diazepam was administered together with haloperidol or chlorpromazine for 21 days, behavioural activity remained elevated and was comparable to groups of rats receiving neuroleptics alone. The cocomitant injection of diazepam and neuroleptics for 21 days elicited a synergistic effect on decreased synthesis and release of dopamine as well as norepinephrine. These data provide neurochemical evidence for potentiation of the neuroleptic effects by a benzodiazepine.

The action of DL-2,4-diaminobutyric acid on the cataleptogenic effects of pilocarpine and alpha-flupenthixol in rats

The existence of a strionigral GABA-ergic pathway having an inhibitory effect on the nigrostriatal dopaminergic system has been proposed. The work reported in this paper was undertaken to investigate whether modification of the GABA-eric system by the GABA neuronal uptake inhibitor DL-2,4-diaminobutyric acid (DABA) would affect cholinergic (pilocarpine) and/or neuroleptic alpha-flupenthixol (alpha-FPT) induced catalepsy. DABA pretreatment was shown to enhance significantly both alpha-FPT and pilocarpine induced catalepsy. DABA alone had no cataleptic activity. The results are interpreted as supporting the existence of an inhibitory strionigral GABA-ergic pathway.

Altered response to apomorphine and haloperidol after nine days of cocaine injections

Sprague Dawley rats, pretreated with nine daily injections of 20 mg/Kg cocaine or saline, were evaluated for aspects of their behavioral response to apomorphine, haloperidol, or cocaine, twenty-four hours after their last pretreatment injection. Data obtained from saline and cocaine pretreated animals indicated that: cocaine pretreated rats were more sensitive to haloperidol-induced catalepsy, less responsive to some of the stereotypic effects of apomorphine and similar in their responses to the anticataleptic properties of cocaine.

Antagonism of morphine-induced catalepsy by L-prolyl-L-leucyl-glycinamide

In view of the recently demonstrated extra-endocrine central actions of hypothalamic releasing hormones, we have investigated the effects of prolyl-leucyl-glycinamide (PLG) and thyrotropin releasing hormone (TRH) on morphine-induced catalepsy. Although acute administration of PLG (10 mg kg-1 s.c.) slightly attenuated the cataleptic response, chronic PLG treatment (10 mg kg-1 s.c. for 10 days) virtually abolished morphine-induced catalepsy. TRH, administered subcutaneously, exhibited little or no anti-cataleptic activity. These results are discussed in relation to the possible central site of narcotic-induced catalepsy and the therapeutic potential of PLG in Parkinson's disease.

A study of the sites of interaction between dopamine and 5-hydroxytryptamine for the production of fluphenazine-induced catalepsy

The effect of reducing 5-hydroxytryptamine (5-HT) concentration within various areas of the central dopamine (DA) system on catalepsy has been investigated. The neurotoxin 5,7-dihydroxytryptamine was used to selectively deplete 5-HT in the striatum, nucleus accumbens septi, tuberculum olfactorium or substantia nigra. Localised depletion of 5-HT within the nucleus accumbens septi and substantia nigra reduced the cataleptic effects of the neuroleptic agent fluphenazine, while lesions of the striatum or tuberculum olfactorium were without effect. Each injection of neurotoxin resulted in a 38--47% depletion of 5-HT in the target site: DA levels were not significantly altered. The results suggest that varied dopamine/5-hydroxytryptamine interactions within the nucleus accumbens may contribute to the action of the neuroleptic. The reduction of fluphenazine-induced catalepsy produced by 5-HT depletion within the substantia nigra supports the concept of a controlling influence of 5-HT on nigro-striatal DA function.

Reconsideration of a test for dopaminergic stimulation: inability of apomorphine to induce mouse jumping

Apomorphine was administered parenterally to mice in an unsuccessful attempt to induce amphetamine and L-3,4-dihydroxyphenylalanine-like elicited jumping. The efficacy of jumping behavior as an indicator of dopaminergic overstimulation is criticized in light of the results.

Computer analysis of interacting dopaminergic and cholinergic control mechanisms in the extrapyramidal system

The experimental results of many authors suggest that the output activity of the extrapyramidal motor control system depends on a balance between the levels present of the chemical transmitters dopamine and acetylcholine. In this paper it is proposed that these results are best explained by two feedback regulatory systems interconnected with positive interaction--in the sense of the relative gain array (Bristol, 1966). Using the computer-aided design procedure CAIAD, a simple two-input two-output model is simulated so as to give responses similar to those observed when dopaminergic or cholinergic drugs are applied. The effect of reducing the gain in one control loop corresponds to the effect of lesioning part of the extrapyramidal system in the brain. In addition, the effect of an anti-schizophrenic drug such as haloperidol is interpreted as a disturbance input on one of the interacting paths.

The effect of baclofen on alpha-flupenthixol-induced catalepsy in the rat

1 alpha-Flupenthixol (alpha-FPT; 0.2 mg/kg i.p.) when administered to rats produced catalepsy. 2 Baclofen (10 mg/kg i.p.) given 30 min after alpha-FPT had a biphasic effect on the catalepsy. Initially there was a potentiation of the effect, followed by a significant attenuation of the degree of catalepsy. 3 Possible mechanisms of action are discussed.

Noradrenergic involvement in dopamine-dependent stereotyped and cataleptic responses in the rat

Two animal models were used to investigate the effect of lowered central noradrenaline levels on two dopamine-dependent behavioural parameters in the rat. Newborn rats were injected with 6-hydroxydopamine or adult animals had bilateral electro-lesions placed in the region of the locus coeruleus in the brain stem. The effect of these two lesions on amphetamine- and apomorphine-induced stereotyped behaviour and on haloperidol-induced catalepsy was studied. 1. Both 6-hydroxydopamine treatment at birth and bilateral locus coeruleus lesions specifically harmed the ascending dorsal noradrenergic pathway, causing significant decreases in cortical and limbic forebrain noradrenaline concentrations. 2. Both types of lesion had no apparent effect on stereotyped behaviour induced by either amphetamine and apomorphine. 3. Both types of lesions significantly enhanced the cataleptic response induced by varying doses of the neuroleptic agent haloperidol. 4. The results indicate that noradrenergic function may partly influence some dopaminergic mechanisms, and its possible site of action in terms of neostriatal and limbic populations of dopamine receptors is discussed.

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 degrees) 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 hold-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.

Interaction of benzodiazepines with neuroleptics at central dopamine neurons

Several benzodiazepines (chlordiazepoxide, clonazepam, diazepam and flunitrazepam) markedly counteracted the elevation of the homovanillic acid (HVA) content of the rat brain induced by neuroleptics (haloperidol, pimozide, chlorpromazine, and clozapine). A similar effect was obtained with the inhibitor of GABA transaminase, aminooxyacetic acid (AOAA). The interaction of benzodiazepines with the neuroleptic-induced HVA increase was similar in the striatum and in the limbic forebrain and was antagonized by the GABA receptor-blocking agent, picrotoxin. Both the benzodiazepines used and AOAA potentiated the cataleptic effect of the four neuroleptics. It is concluded that benzodiazepines, by intensifying GABA-ergic transmission, enhance the ongoing inhibition of mesencephalic dopamine neurons exerted by the striatonigral GABA system. As a consequence, the feedback activation of dopamine neurons induced by the neuroleptic blockade of dopamine receptors in the striatum and the limbic system is attenuated. This results in a reduction of the neuroleptic-induced increase of HVA and in the potentiation of the cataleptic effect of neuroleptics.

Neuropharmacological studies on D145 (1,3-dimethyl-5-aminoadamantan)

The effects of D145 (1,3-dimethyl-5-aminoadamantan) and amantadine on dopaminergic mechanisms in the rat were investigated by use of pharmacological agents known to disrupt dopamine function, by placing electrolytic lesions in the dopamine-containing areas of the extrapyrimidal and mesolimbic systems and by the direct application to dopamine sensitive areas. Stereotypy and circling behaviour were used as behavioural indices of dopaminergic stimulation and apomorphine and d-amphetamine were used as standard dopaminergic agonists. In addition, the possible importance of 5-hydroxytryptamine to the dopamine effects was investigated using electrolytic lesions of the midbrain raphé nuclei. Both D145 and amantadine caused a stereotyped behaviour characterized by periodic sniffing, repetitive limb movements and biting, but the effect of amantadine was far more periodic. In addition D145, but not amantadine, caused marked hyperactivity. These behavioural effects were resistant to pretreatment with alpha-methylparatyrosine but not to combined alpha-methylparatyrosine/reserpine or low doses of haloperidol. Also, the prior administration of D145 or amantadine inhibited the development of the biting components of apomorphine and d-amphetamine stereotypy. Both D145 and amantadine caused circling behaviour in animals with asymmetric lesions of the medial raphé nucleus or unilateral lesions of the substantia nigra but the action of D145 was more intense. Bilateral electrolytic lesions placed in the extrapyrimidal (caudate-putamen, globus pallidus, substantia nigra), mesolimbic (nucleus accumbens septi, tuberculum olfactorium, nucleus interstitialis stria terminalis, nucleus amygdaloideus centralis) nuclei or the neuronal pathways supplying them showed D145 and amantadine to act in both areas although their action on the extrapyrimidal system was most marked. However, of particular note was the significantly greater involvement of the substantia nigra with the D145 effect, and the greater involvement of the D145 effect with mesolimbic function. Lesions placed in the medial and/or dorsal raphé nucleus indicated some involvement of 5-hydroxytryptamine with the actions of both D145 and amantadine. The bilateral intrastriatal application of D145 or amantadine in nialamide pretreated animals failed to induce stereotyped or hyperactive behaviour although contralateral asymmetries, which were abolished by lesions of the substantia nigra, were recorded following the unilateral intrastriatal application of D145 or amantadine in haloperidol pretreated animals.

Progress in understanding Huntington's chorea

The present paper analyses the new data accumulated since 1972 concerning the etiology and pathogenesis of Huntington's chorea. Particular attention is paid to the respective roles of the dopaminergic and GABA-ergic systems.

The behavioural effects of dopamine applied intracerebrally to areas of the mesolimbic system

The intracerebral injection technique was used to apply dopamine directly into dopamine-containing areas of the mesolimbic system, the nucleus accumbens septi, tuberculum olfactorium and nucleus amygdaloideus centralis. 200 mug dopamine injected bilaterally into the nucleus accumbens septi caused a stereotyped sniffing behaviour and hyperactivity but only a periodic hyperactivity developed after similar injections into the tuberculum olfactorium and no change in behaviour was observed following injections into the nucleus amygdaloideus centralis. After pretreatment with nialamide, the effects of intracerebral dopamine were enhanced, doses of 1-50 mug dopamine causing consistent stereotyped sniffing and a dose-dependent hyperactivity on injection into the nucleus accumbens septi or tuberculum olfactorium. The effects initiated from the nucleus accumbens septi were most marked. In addition, 50-100 mug dopamine injected into the tuberculum olfactorium caused a periodic biting behaviour. Biting was not observed after injections into the nucleus accumbens septi and, even in the presence of nialamide, injections of dopamine into the nucleus amygdaloideus centralis failed to cause any change in motor behaviour.

On a prime role for newly synthesized dopamine in striatal function

Rats were given either the tyrosine hydroxylase inhibitor, alpha-methyltyrosine (alphaMT), in doses of 10 or 250 mg/kg or the neuroleptic, haloperidol (0.25 mg/kg). Other rats received both drugs (haloperidol 30 min after alphaMT). This dose of haloperidol alone caused only a slight, gradually developing catalepsy, while alphaMT alone caused none. The combination quickly caused a strong catalepsy. Striatal dopamine (DA) stores were only minimally depleted at the time of catalepsy potentiation. Th e marked elevation of striatal homovanilluc acid concentration seen after haloperidol administration was greatly inhibited by alphaMT pretreatment. It is concluded that the marked potentiation of haloperidol-induced catalepsy by alpha MT is related to the absence of newly synthesized DA rather than to an exhausted main DA pool and that newly synthesized DA has a greater role in striatal function than does DA of the main striatal storage pool.