A. Theodorou

Changes in rat striatal dopamine turnover and receptor activity during one years neuroleptic

Administration of trifluoperazine (2.5--3.5 mg/kg/day p.o.) or thioridazine (30--40 mg/kg/day) for up to 1 year initially increased homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations in striatum. However, by 1 month and thereafter metabolite levels returned almost to control values. Dopamine concentrations were elevated after 3 months administration of both drugs and also after 12 months administration of trifluoperazine. Trifluoperazine administration for 1 month produced a marked increase in the dissociation constant (KD) for striatal 3H-spiperone binding but a reduction in receptor numbers. Thereafter receptor numbers increased at 6 and 12 months in both trifluoperazine and thioridazine treated animals compared to control values. The KD for both drug treated groups returned to normal at 6 months; however, by 12 months drug treated animals again demonstrated high KD values. Dopamine stimulation of striatal adenylate cyclase was inhibited after administration of trifluoperazine or thioridazine for 1 week or 1 month. However, by 6 and 12 months this effect was replaced by an enhanced stimulation. Administration of lower doses of trifluoperazine (0.7--0.9 mg/kg/day p.o.) or thioridazine (6--9 mg/kg/day p.o.) for up to 1 year produced similar although generally less marked changes in these biochemical indices of dopamine function. This study provides evidence of biochemical changes which parallel the behavioural findings of enhanced dopamine receptor activity that occur during continuous long-term neuroleptic administration to rodents.

Cerebral dopamine function in rats following withdrawal from one year of continuous neuroleptic administration

Continuous administration of trifluoperazine (2.5--3.5 mg/kg/day) or thioridazine (30--40 mg/kg/day) to rats for 12 months enhanced the stereotyped response to apomorphine (0.5 mg/kg s.c.), increased dopamine 1--150 muM) stimulation of striatal adenylate cyclase, increased KD and Bmax for dopamine (10(-4) M) specific 3H-spiperone striatal binding and produced spontaneous mouthing movements. On drug withdrawal, spontaneous locomotor activity was enhanced after 2 weeks and the enhanced stereotyped response was maintained for up to 1 month. Spontaneous mouthing had disappeared 2 weeks after drug withdrawal. The increase in Bmax for 3H-spiperone binding was maintained for up to 3 months after drug removal, but KD reverted to control levels by 2 weeks. In contrast, the dopamine stimulation of striatal adenylate cyclase remained enhanced for the 6 month withdrawal period. Administration of trifluoperazine (0.7--0.9 mg/kg/day) or thioridazine (6--8 mg/kg/day) for 12 months produced a less marked effect than administration of the higher dose. No enhancement of effect was observed on drug withdrawal and the initial changes disappeared rapidly on removal of drug. Supersensitivity of striatal dopamine mechanisms produced by continuous long-term neuroleptic administration differs from that produced by shorter treatment periods since no enhancement of effect occurs on drug withdrawal. The behavioural and biochemical components of the supersensitivity show variable time courses and in particular the enhanced stimulation of striatal adenylate cyclase persists for at least 6 months. Such effects may be of relevance to tardive dyskinesias in man.

Specific binding of [3H]sulpiride to rat striatal preparations

Chang, T. M. S. (1972) Artificial Cells. Charles C. Thomas, Springfield, 111. Chang, T: M. S. ,(1977) in: Chang,. T. M. S. (ed.) Biomedical Applications of Immobilized Enzymes and Proteins, Vol. 1. Plenum Press, pp. 69-90 Coover, H. W., Jr., Joyner, F. B., Shearer, N. H., Wicker, T. H. (1959) SOC. Plast. Eng. J. 15: 413417 Couvreur, P., Kante, B., Roland, M. (1978) Pharm. Acta Helv. 53: 341-347 Florence, A. T., Haq, M. E., Johnson, J. R. (1976) J. Pharm. Pharmacol. 28: 539-543 Leonard, F. (1970) ic: Manly, R. S. (ed.) Adhesion in Biological Systems. Academic Press; New York, pp.

A behavioural and biochemical comparison of dopamine receptor blockade produced by haloperidol with that produced by substituted benzamide drugs.

Haloperidol inhibited dopamine (DA) mediated behaviours and induced pronounced catalepsy in rodents. Metoclopramide, sulpiride, sultopride, tiapride and clebopride, in general, also inhibited these behaviours but only clebopride induced marked catalepsy. Haloperidol displaced 3H-haloperidol and 3H-spiperone from striatal binding sites and inhibited DA stimulated cyclase from striatal and mesolimbic regions. In general, substituted benzamide drugs displaced labelled ligands, but did not inhibit adenylate cyclase. Elevations of striatal HVA produced by haloperidol and sulpiride, but not other benzamide drugs, were partially reversed by atropine. Hypophysectomy did not prevent the elevation of forebrain HVA produced by sulpiride and metoclopramide. Substituted benzamide drugs appear to act on cerebral DA receptors that are independent of DA-sensitive adenylate cyclase and are not balance by a cholinergic input.

Kainic acid lesions of striatum and decortication reduce specific [3H]sulpiride binding in rats, so D‐2 receptors exist post‐synaptically on corticostriate afferents and striatal neurons

Unilateral kainic acid lesions of rat striatum reduced specific striatal [3H]spiperone and [3H]sulpiride binding sites (Bmax) by 52 and 67% respectively compared with the intact side. The dissociation constant (KD) for [3H]spiperone binding was unchanged but that for [3H]]sulpiride binding was reduced. Specific striatal [3H]spiperone and [3H]sulpiride binding was reduced by 22 and 37% respectively in unilateral decorticate animals, but there was no change in KD. Unilateral 6‐hydroxydopamine lesions of the medial forebrain bundle caused no change in striatal [3H]spiperone binding sites or KD value, but produced a 27% increase in [3H]sulpiride binding sites with no change in KD. These data support the hypothesis of D‐2 receptors located on cortico‐striate glutamate fibres, but also indicate the presence of both D‐1 and D‐2 receptors on the cell bodies of striatal neurons.

Stereoselective actions of substituted benzamide drugs on cerebral dopamine mechanisms

Apomorphine‐induced locomotor activity in reserpine‐pretreated mice was antagonized by pretreatment with (‐)‐sulpiride and (‐)‐sultopride. The (+)‐enantiomers were inactive. Apomorphine‐ and amphetamine‐induced stereotyped behaviour in rats were antagonized by (‐)‐sultopride but not by the (+)‐enantiomer. Neither enantiomer of sulpiride prevented the onset of the stereotyped response. Both (‐)‐sulpiride and (‐)‐sultopride induced increases in striatal and mesolimbic HVA and DOPAC concentrations; (+)‐sultopride elevated striatal and mesolimbic DOPAC concentrations but not HVA, while (+)‐sulpiride had no effect on HVA or DOPAC in either area. Dopamine concentrations were reduced by the enantiomers of sultopride but not by sulpiride. Low concentrations (10−9 −10−66 M) of the (‐)‐enantiomers of both drugs displaced [3 H]spiperone from its specific binding site in rat striatal preparations, but the (+)‐enantiomers were 40 and 100 times less active. However, neither enantiomer of either drug anatagonized the dopamine‐induced stimulation of adenylate cyclase in rat striatal preparations. The data suggest that the central pharmacological activity of sulpiride and sultopride resides in the (‐)‐enantiomers and that this activity occurs at cerebral dopamine receptors not dependent on adenylate cyclase for functional activity.

A comparison of striatal and mesolimbic dopamine function in the rat during 6-month trifluoperazine administration

Previous work has shown that 6–12 months continuous trifluoperazine (TFP) administration to rats causes striatal dopamine receptor supersensitivity. We have now replicated our original findings in the striatum and report concurrent changes in mesolimbic dopamine function during chronic TFP (2.8–4.0 mg/kg/day) administration for 6 months. Initial inhibition of apomorphine-induced stereotyped behaviour, which lasted for 2 weeks after the beginning of drug administration, was replaced by an exaggerated response to apomorphine (0.5 mg/kg SC) after 6 months drug intake. Striatal dopamine sensitive adenylate cyclase activity was inhibited at 1 and 3 months, but by 6 months was enhanced compared to control values. Mesolimbic adenylate cyclase activity was inhibited after 2 weeks and thereafter returned to control levels. Dopamine-identified 3H-spiperone binding sites (Bmax) in the striatum were increased by 2 weeks, reduced at 1 month and increased again at 6 months. In mesolimbic areas Bmax was increased at 2 weeks and 1 month but thereafter returned to control levels. The dissociation constant (kD) of specific 3H-spiperone binding was increased in the striatum and mesolimbic areas at 1 month and 2 weeks respectively. The results show differential changes in dopamine function in striatal and mesolimbic brain areas during 6 months continuous TFP administration to rats.

Repeated administration of sulpiride for three weeks produces behavioural and biochemical evidence for cerebral dopamine receptor supersensitivity.

Administration of sulpiride (2 X 100 mg/kg i.p.) or haloperidol (5 mg/kg i.p.) to rats for 3 weeks with subsequent withdrawal for 3 or 4 days induced cerebral dopamine receptor supersensitivity. Apomorphine-induced stereotyped behaviour after drug withdrawal was enhanced by pretreatment with either haloperidol or sulpiride both of which increased the number of specific striatal binding sites (Bmax) for [3H]spiperone, [3H]N,n-propylnorapomorphine and [3H]sulpiride. Neither drug altered the dissociation constant (KD) for the ligand binding assays. Striatal dopamine sensitive adenylate cyclase activity was unaltered by such a pretreatment with either haloperidol or sulpiride. The data show that sulpiride, like haloperidol, is capable of inducing behavioural and biochemical supersensitivity of cerebral dopamine receptors.

Persistent increase in striatal dopamine stimulated adenylate cyclase activity persists for more than 6 months but disappears after 1 year following withdrawal from 18 months cis-flupenthixol intake

Administration of cis-flupenthixol to rats for 18 months enhanced apomorphine-induced stereotyped behaviour, increased the number of specific [3H]spiperone binding sites in striatum and potentiated striatal dopamine stimulated cyclic AMP formation, but did not alter specific [3H]piflutixol binding. Following withdrawal of cis-flupenthixol intake, apomorphine-induced stereotypy returned to control values after 1 month and Bmax for [3H]spiperone binding returned to normal after 3 months. In contrast, the increased dopamine stimulated adenylate cyclase activity remained elevated 6 months after drug removal, but was normal 1 year after drug withdrawal.

Cation specificity of 3H-sulpiride binding involves alteration in the number of striatal binding sites

Specific 3H-sulpiride binding to rat striatal membranes shows an absolute requirement for the presence of sodium ions in the incubation buffer. Potassium, rubidium and caesium ions were unable to initiate specific 3H-sulpiride binding in a sodium free buffer, and lithium ions could only partially replace sodium ions. Specific 3H-spiperone binding was unaffected by variation of the cation content of the incubation buffer. The alteration in 3H-sulpiride binding caused by sodium and lithium ions was due predominantly to an increase in the number of available binding sites, rather than to altered receptor affinity. Sodium ions may be essential for the accessability of 3H-sulpiride to a single site labelled also by 3H-spiperone. However, the Ki value for sulpiride displacement of 3H-spiperone in the presence of sodium ions was 20 times greater than the KD value for 3H-sulpiride binding. So, 3H-sulpiride may interact with a highly sodium dependent binding site distinct from that labelled by 3H-spiperone.