David H. Fortune

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.

Neuroleptic antagonism of the motor inhibitory effects of apomorphine within the nucleus accumbens: drug interaction at presynaptic receptors?

Abstract Intra-accumbens d-amphetamine caused a dose-dependent hyperactivity which was shown to involve the release of newly synthesized dopamine. The amphetamine response was antagonised by apomorphine in a narrow dose range. This antagonistic effect of apomorphine was specifically inhibited by the neuroleptic agents pimozide and haloperidol in doses too low to inhibit the amphetamine response per se. Also, apomorphine exerted its antagonistic effect only when administered directly into the nucleus accumbens, not when injected into the caudateputamen or tuberculum olfactorium. Further, doses of intra-accumbens apomorphine which antagonised the amphetamine response reduced the homovanillic acid content of the nucleus accumbens but not that of the caudateputamen or tuberculum olfactorium. The apomorphine induced change in accumbens homovanillic acid was antagonised by haloperidol at doses effective in the behavioural experiments. Finally, the ability of apomorphine to antagonise amphetamine hyperactivity was abolished following the intra-accumbens injection of 6-OHDA (the amphetamine response being maintained after lesion) which specifically destroyed dopamine nerve terminals in the nucleus accumbens. This data is forwarded to support a general conclusion that intra-accumbens apomorphine antagonises the hyperactivity induced by intra-accumbens amphetamine by an action at neuroleptic sensitive sites within the nucleus accumbens and which may be located on nerve terminals, i.e. presynaptic receptors. The ability of neuroleptic agents to antagonise at postsynaptic dopamine receptors (antagonise the amphetamine response per se) was compared with an ability to reverse the apomorphine antagonism of the amphetamine response at a hypothesised ‘presynaptic receptor’. A differential dose could not be determined for clozapine of thioridazine. For pimozide and haloperidol the ratio of pre- to postsynaptic activity was small, whilst (−)-sulpiride was 5 fold more effective to inhibit pre- than postsynaptic receptors. This data provides support for the hypothesis that there may exist more than one neuroleptic mechanism in the nucleus accumbens which contribute to an overall control of motor function via the mesolimbic system.

The induction of catalepsy and hyperactivity by morphine administered directly into the nucleus accumbens of rats

The injection of morphine (1–100 μg) into the nucleus accumbens of the rat caused dose-dependent changes in motor function. An initial cataleptic phase was followed by hyperactivity which was associated with a weak and periodic biting behaviour. Injection of morphine (1–50 μg) into associated brain areas (anterior and posterior regions of the olfactory tubercle, anterior caudate putamen, area preoptica, globus pallidus and ventricular system) failed to induce catalepsy or induce a catalepsy of comparable intensity to that observed after intra-accumbens morphine. The catalepsy induced by 12.5 or 50 μg intra-accumbens morphine was antagonised by nalorphine when administered s.c. (2.5–10 mg/kg) and by nalorphine (2.5–10 μg)_and naloxone (0.25–1.0 μg) when injected into the nucleus accumbens, by low doses of cyproheptadine (1.25–5 mg/kg i.p.) and by large and probably non-specific doses of atropine (10 mg/kg i.p.) and piperoxan (20 mg/kg i.p.). In relatively large doses haloperidol (0.25–1.0 mg/kg i.p.) potentiated morphine (3.125 μg) catalepsy whereas α-methylparatyrosine reduced or failed to modify the morphine (1–50 μg) response. It is considered that the catalepsy induced by intra-accumbens morphine is due to a significant action within that nucleus which directly or indirectly involves an enhanced serotonergic activity. The subsequent hyperactivity phase induced by intra-accumbens morphine was markedly reduced by α-methyl-p-tyrosine pretreatment (250 mg/kg i.p.) and the biting component was abolished. The hyperactivity was more sensitive to the antagonistic action of α-adrenoceptor blocking agents piperoxan (10–40 mg/kg i.p.), aceperone (1.25–20 mg/kg i.p.), piperoxan (6.25–25 μg intra-accumbens) and phentolamine (1.25– 10 μg intra-accumbens) than fluphenazine (1.25–2.5 mg/kg i.p.), whilst the biting was inhibited by both the α-adrenoceptor blocking agents and fluphenazine. These data suggest that whereas the hyperactivity induced by intra-accumbens morphine primarily involves an enhanced noradrenergic action, the biting effect involves both noradrenaline and dopamine. However, it is uncertain as to whether mechanisms within the nucleus accumbens or associated areas are primarily or jointly involved as substrates for this effect, for whilst injections of morphine (1–50 μg)_into the anterior alfactory tubercle failed to induce hyperactivity, injections into the anterior caudata putamen and globus pallidus evoked a weak response, and injections into the posterior olfactory tubercle and area preoptica induced marked hyperactivity associated with weak biting. An assessment of the diffusion of (N-methyl-14C)-morphine on intra-accumbens injection, and particularly at the time when the hyperactivity phase was apparent indicated an ability to reach and more speculatively influence other than brain areas. This would emphasise that an extra-accumbens site of action for the mediation of the hyperactivity/biting effects cannot be excluded. The results indicate a differential involvement of forebrain structures with the biphasic motor behaviour induced by intracerebral injections of morphine and a usefulness of this agent to investigate the mechanisms involved in motor control.

Involvement of mesolimbic and extrapyramidal nuclei in the motor depressant action of narcotic drugs

The ability of narcotic drugs to induce motor depression from the mesolimbic nucleus accumbens (ACB) and extrapyramidal caudate‐putamen (CP) was investigated using the bilateral intracerebral injection technique. Fluphenazine and procaine were used as control agents. Firstly, drugs were injected alone into the ACB or CP and catalepsy was assessed. Fentanyl (2·5–10μg), sufentanil (0·25–1 μg) and carfentanil (0·05–0·5μg) were shown to be potent cataleptogens when injected into both the ACB and CP, the responses being dose‐dependent and achieving maximum intensity. Morphine (1–50 μg) also induced a marked dose‐dependent catalepsy, but only after injection into the ACB. In contrast, pethidine and methadone, in doses up to 160 μg, caused only weak and inconsistent responses from the ACB and CP. Similar injections of procaine (50–200 μg) were ineffective, but fluphenazine (25–200 μg) induced a moderate dose‐dependent response from both the ACB and CP, although onset of action was more rapid and the duration markedly longer for the latter injections. Secondly, drugs were injected peripherally and intracerebrally to determine their ability to antagonize the marked hyperactivity induced by intra‐ACB dopamine in the presence of nialamide. Two agents shown to induce catalepsy from the ACB, fluphenazine and morphine, antagonized dopamine hyperactivity when they were administered peripherally or directly into the ACB (0·1–0·2 mg kg−1, i.p. or 3·1–25 μg fluphenazine and 1–5 mg−1 kg, s.c. or 1–5 μg morphine), but only a weak antagonism occurred at much larger doses after intra‐CP injections (100 μg fluphenazine and 50 μg morphine). Larger doses of intra‐ACB pethidine (160 μg) and procaine (100–200 μg) also antagonized the dopamine response, but methadone was inactive. Again, the most potent and effective drugs in this test were fentanyl (1–5 μg), sufentanil (0·25–0·5μg) and carfentanil (0·05–0·1 μg). It is suggested that the ACB, and not the CP, is the site at which morphine acts to cause motor depression, whilst other narcotic drugs are able to act in both areas (although there is some indication of a further unspecified site of action for methadone). In contrast, the neuroleptic fluphenazine appears to differentially affect motor function via the ACB and CP, antagonizing a dopamine hyperactivity in the former and primarily inducing catalepsy from the latter nucleus.

A study of drug action on normal and denervated striatal mechanisms

Abstract Apomorphine, N-n-propylnorapomorphine, N,N-di-n-propyldopamine, 1-aza-7,8-dihydroxy-1-a-1,2,3,4,4a,9, 10,10a-octahydrophenanthrene (CS-224) and 2-di-n-propylamino-5,6-dihydroxytetralin each caused ipsilateral circling (with respect to the side of electrolesion) in mice with electrolesions of the striatum or electrolesions combined with 6-hydroxydopamine (6-OHDA) lesions of the contralateral straitum. All agents were more potent (2–4 fold) in the latter model: the shift of the dose response curves to the left was approximately parallel (indicating increased dopamine receptor sensitivity on the side of 6-OHDA injection) except where stereotypy development interfered with circling. In contrast to these dopamine agonists, 1-aza-7,8-dihydroxy-1-1-propyl-1,2, 3,4,4a,9,10,10a-octahydrophenanthrene (TL-140-III) was more potent in the single electrolesion model: the action of this agent was abolished by α-methyl-p-tyrosine similarly to d-amphetamine but unlike the directly acting dopamine agonists. Haloperidol, fluphenazine, sulpiride, thioridazine, clozapine and metoclopramide each reduced/abolished the circling induced by apomorphine in mice with electrolesions or combined 6-OHDA/ electrolesions of the striatum. Doses required appeared the same for both models, or the neuroleptic was a maximum of 2× more active in the combined lesioned model. In contrast, tiapride and oxiperomide were 8× and 4× more active in mice with combined 6-OHDA/electrolesion than in animals with a single electrolesion. The α- and β-adrenergic blocking agents, aceperone and propranolol, were inactive in both circling models. Biochemical determinations showed that 6-OHDA depleted striatal dopamine content by 85% whilst failing to cause any significant depletions in mesolimbic (nucleus accumbens and tuberculum olfactorium) dopamine or noradrenaline. The possibility that tiapride may be more effective as an antagonist at denervated dopamine mechanisms is discussed in terms of its known spectrum of activity as a dopamine antagonist both experimentally and clinically.

Differential activities of some benzamide derivatives on peripheral and intracerebral administration.

The benzamide group of drugs has been classified with the neuroleptic agents, and there is evidence to suggest that agents from the series are able to inhibit dopamine function. Indeed, a common characteristic of the benzamides is their ability to affect dopamine systems outside the blood-brain barrier, for example, in the pituitary gland, area postrema or in the stomach (Fang, Zirno & Byyny, 1977; Horowsky & Graf, 1976; Jenner, Elliott & others, 1978; Prieto, Moragues & others, 1977; Valenzuela, 1976). However, the central activity spectra of the benzamides differ markedly when the agents are administered by a peripheral route (Jenner & others, 1978), and this may reflect differing abilities to penetrate cerebral tissue. The present studies were, therefore, designed to compare against an amphetamine-induced hyperactivity, the antagonistic effects of metoclopramide, sultopride, clebopride, tiapride and sulpiride when administered peripherally (i.p.) or intracerebrally. Fluphenazine was used as the control neuroleptic and the site of intracerebral administration was established by determining its antiamphetamine effects after injection into several brain regions. Male Sprague-Dawley rats (250-300 g) which were prepared for intracerebral injection by stereotaxically implanting guide cannulae (0.64 mm diameter stainless steel tubing) for bilateral administration into the nucleus accumbens, Ant. 9.4, Vert. +2-5 (2-5 mm), Lat. f l . 6 , the tuberculum olfactorium, Ant. 9.0, Vert. f4.0 (6.7 mm), Lat. k-23, the amygdala, Ant. 5.6, Vert. +2.0 (3.7 mm), Lat. rt4.5, the caudateputamen, Ant. 8.0, Vert. +3.0 (1.5 mm), Lat. &3,0, the cerebral cortex, Ant. 8.0, Vert. +5.5 (l.Omm), Lat. 3.5, and into the midbrain, Ant. 1.0, Vert. +0.5 (3.0 mrn), Lat. f1.5, or unilateral injection into the lateral ventricles, Ant. 8.0, Vert. +4.0 (2.0 mm), Lat.1.5 (De Groot, 1959). Animals were used once, 14 days after surgery when stainless steel stylets (0.3 mm diameter), which kept the guides patent, were replaced by injection units made of the same tubing and extending below the guides by a distance indicated in parentheses with the vertical coordinates above. Drug was delivered from micrometer syringes in a volume of 1 pI over 60 s, the animals being manually restrained. The locations of the guide cannulae were confirmed histologically. Hyperactivity was induced by amphetamine 1.5 mg kg-I, i.p. (preliminary studies show this dose produces a maximal hyperactivity in the absence of a stereo-

On the ability of N-chloroethyl aporphine derivatives to cause irreversible inhibition of dopamine receptor mechanisms

The potential dopamine inhibitory properties of (‐)N‐(2‐chloroethyl)‐norapomorphine [(‐)NCA], (‐)N‐(hydroxyethyl)norapomorphine [(‐)NHA], (‐)N‐(2‐chloroethyl)‐norapocodeine[(‐)NCC] and 6‐[2‐bis‐(2‐chIoroethyl)‐amino]acetyl‐11‐acetoxy‐2‐hydroxy‐10‐methoxynoraporphine (I) were assessed in behavioural (ability to antagonize apomorphine climbing, stereotypy and circling after unilateral electrolesions of the striatum in the mouse, ability to initiate circling/asymmetry alone or after challenge with apomorphine when injected unilaterally into the striatum of rat) and biochemical (ability to inhibit the binding of [3H] (‐)N‐n‐propylnorapomorphine, 3H‐NPA, to rat striatal homogenates) tests. (‐) NCA, 10–20 mg kg−1 s.c., antagonized apomorphine climbing for a period of 5 days, the response recovering to control values by the 7th day. 10 mg kg−1 s.c. (‐)NHA, (‐)NCC or I failed to modify apomorphine climbing. Similarly, 2–4 mg kg−1 s.c. (‐)NCA caused a long‐lasting inhibition of apomorphine circling in the mouse (up to 5 days) whilst (‐)NHA, (‐)NCC and I were inactive. (‐)NCA (10–40 μg) (but not (‐)NHA, (‐)NCC or I) also caused ipsilateral circling/asymmetry when injected unilaterally into the striatum of rat: this effect was enhanced by apomorphine. However, all agents, including (‐)NCA, failed to consistently modify apomorphine stereotypy in the mouse. Non‐labelled (‐)NPA, (‐)NCA and (‐)NHA were shown to inhibit the ‘specific’ binding of 3H‐NPA to rat striatal homogenates; (‐)NCC and I were ineffective. A single washing removed the (‐)NHA inhibition whilst repeated washing caused only a modest reversal of the inhibition afforded by (‐)NCA. It is concluded that N‐chloroethylation in the aporphine series can abolish dopamine agonist action and confer a long‐lasting dopamine antagonist potential.

Behavioural actions of neuroleptics are not reduced by hypophysectomy

mediated indirectly via the release o f cyclo-oxygenase products unlike some other SRS-A induced response\ (Piper et al 1981). Responses of both preparations to SRS-A were blocked by FPL 557 12, however. our results demonstrate two differences in the effects of FPL 55712 on these preparations. Firstly, FPL 55712 is a less potent antagonist on the fundus than on the ileum and secondly. whereas a contact time of 10 min was sufficient to achieve equilibrium on the ileum, 60 min was necessary on the fundus. One possible explanation for the potency difference is that the receptors in the ileum are different from those in the fundus. However, there are many factors unrelated to receptor differences which can influence the potency of antagonists, for example the presence of inactivation processes for the agonist (Furchgott 1972), and further quantitative studies with synthetic leukotrienes will be necessary to resolve this question. The finding that FPL 55712 equilibrates more rapidly on the ileum than on the fundus has implications for the use of this compound as a pharmacological tool. FPL 55712 has been shown to be a potent antagonist of the actions of SRS-A on guinea-pig ileum using contact times as short as 15 s (Augstein et al 1973). Our data show that not only does the potency of FPL 55712 vary between tissues but the equilibration time also varies. Therefore when this compound is used as a tool to investigate the involvement of leukotrienes in anaphylactic reactions (Chand 1979) it will be necessary to establish both the potency and contact time for the tissue under study before valid conclusions can be drawn