Spiroperidol Binding Research Articles

Prenatal exposure of rats to antidepressants enhances agonist affinity of brain dopamine receptors and dopamine-mediated behaviour

The effects of acute treatment or prenatal exposure of rats to antidepressants on locomotor activity and [ 3H]spiroperidol binding to striatal membranes were studied in 25 day old rats. Prenatal exposure or acute treatment with the antidepressants chlorimipramine, iprindole or mianserin reduced locomotor activity on postnatal day 25. On the contrary, prenatal exposure to nomifensine induced locomotor hyperactivity. It was also found that chlorimipramine, iprindole or nomifensine enhanced the locomotor response to apomorphine. Acute treatment with mianserin, markedly decreased locomotion but in utero mianserin did not modify the apomorphine-induced hyperactivity. Scatchard analysis showed no change in the characteristics of binding of [ 3H]spiroperidol to striatal dopamine receptors after antidepressant treatment. However, the ability of dopamine to compete for these sites was significantly enhanced after prenatal exposure to all the antidepressants. This increase in agonist affinity for dopamine receptors may explain the long-lasting behavioural supersensitivity of dopamine receptors observed after chronic treatment with typical or atypical antidepressants.

D2 Dopamine Receptors in Calf Globus Pallidus: Agonist High‐ and Low‐Affinity Sites Not Regulated by Guanine Nucleotide

By use of the radioligand [3H]spiroperidol, D2 3,4-dihydroxyphenylethylamine (dopamine) receptor binding characteristics were studied in calf globus pallidus and compared with those of neostriatum. Antagonist competition curves were monophasic and revealed similar affinities for neostriatum and globus pallidus, suggesting a uniform receptor population with one affinity state for antagonists. In both regions, competition curves with the agonist dopamine were biphasic, distinguishing a high- and low-agonist-affinity state. In neostriatum and globus pallidus, respectively, 45% and 19% of [3H]spiroperidol binding was displaced with high affinity and the remainder with low affinity. In neostriatum, the addition of 0.4 mM GTP resulted in a partial conversion from high- to low-affinity state with a remaining high-affinity component of 15%. In globus pallidus, dopamine binding was not altered by GTP. The capability of GTP to modulate agonist binding to D2 receptors appears to be dependent on their neuroanatomical localization.

Antagonism of the lsd cue by putative serotonin antagonists: Relationship to inhibition of in vivo [ 3H]spiroperidol binding

In two groups of rats trained to discriminate 0.08 or 0.16 mg/kg of lysergic acid diethylamide (LSD) from saline, pirenperone and ketanserin completely blocked the stimulus effect of LSD. Pizotifen (BC-105) blocked the LSD cue when the training dose was 0.08 mg/kg, but had variable effects in the 0.16 mg/kg of LSD-trained group. The antagonism of the 0.08 mg/kg cue occurred at doses of the antagonists which blocked [ 3H]spiroperidol labeled 5-HT 2 receptors in the frontal cortex in vivo; binding in the striatum was unaffected by the LSD antagonists. However, in doses which produce the LSD cue, neither LSD nor the 5-HT agonist, 5-methoxy-N,N-dimethyltryptamine, which substitutes for LSD, inhibited the binding in either the cortex or the striatum. The results are discussed in relation to the possible neuropharmacological basis for the LSD cue.

Dopamine D-2 receptors in rat caudate-putamen: the lateral to medial gradient does not correspond to dopaminergic innervation

The topography of dopamine D-2 receptors within the rat caudate-putamen (CPU) was characterized by measuring [ 3H]spiroperidol binding to membranes from dissected regions of the CPU and to thin sections of rat forebrain using quantitative autoradiography. Specific binding, defined using 1 μM (+)-butaclamol, was considerably higher in the lateral CPU than the medial CPU, without any obvious gradient in the dorsoventral axis. The difference in B max between the lateral and medial CPU was similar whether determined by digital subtraction autoradiography of coronal forebrain sections or by [ 3H]spiroperidol binding to membrane homogenates derived from CPU subregions. No regional differences were observed in the affinity of [ 3H]spiroperidol for D-2 sites. There were no lateral-to-medial differences in the dopaminergic innervation of the CPU, as determined by the measurement of the levels of dopamine, homovanillic acid and dihydroxyphenylacetic acid in subregions of the CPU using high pressure liquid chromatography. Thus, regional variations in the density of D-2 receptors within the CPU do not correspond to the degree of dopaminergic innervation. The functional importance of the organization of this dopamine receptor system is discussed in relation to the lateral-to-medial organization of the CPU.

A comparison between centrifugation and filtration as a means to separate bound and unbound ligand during 3[H]-spiroperidol binding

A centrifugation method for the separation of bound and unbound ligand during 3[H]-spiroperidol binding in rat brain was compared with the more widely used filtration method. The centrifugation method yielded significantly greater total and specific binding, and lower nonspecific binding, than filtration. Assay reproducibility was also found to be superior when the centrifugation method was used as compared to the filtration binding method. Scatchard plots produced by both methods yielded comparable K d and B max values that were consistent with those previously reported.

Synthesis and neuroleptic activity of 3-(1-substituted-4-piperidinyl)-1,2-benzisoxazoles.

The synthesis of a series of 3-(1-substituted-4-piperidinyl)-1,2-benzisoxazoles is described. The neuroleptic activity of the series was evaluated by utilizing the climbing mice assay and inhibition of [3H]spiroperidol binding. Structure-activity relationships were studied by variation of the substituent on the benzisoxazole ring with concomitant variation of four different 1-piperidinyl substituents. Maximum neuroleptic activity was realized when there was a 6-fluoro substituent on the benzisoxazole ring. The 1-piperidinyl substituent appeared less significant, although in most cases, the (1,3-dihydro-2-oxo-2H-benzimidazol-1-yl)propyl group imparted maximum potency. The most potent compound in both assays was 6-fluoro-3-[1-[3-(1,3-dihydro-2-oxo-2H-benzimidazol-1-yl) propyl]-4-piperidinyl]-1,2-benzisoxazole (11b).

Cis- and trans-4-n-Propyl-1,2,3,4,4a,5,6, 10b-octahydrobenzo(f)quinolines

cis- and trans-4-n-Propyloctahydrobenzo(f)quinolines 4a,b were prepared for further assessment of dopaminergic effects of non-oxygenated dopamine congeners. The trans isomer 4b exhibited marked dopamine-like effects in the cat cardioaccelerator nerve assay and in a rat rotation model. Compound 4b produced dose-related lowering of blood pressure in the cat. The cis isomer 4a was inactive in these assays. Both compounds were inactive in a dopamine binding assay, but both appeared active in a spiroperidol binding assay. Both compounds are active α1- and α2-adrenoceptor antagonists. Compound 4b provides evidence that α2-adrenoceptors and dopamine receptors are different entities, since this compound is an α2 antagonist and a dopamine receptor agonist at presynaptic sites.

Reactive capacity: A sensitive behavioral marker of movement initiation and nigrostriatal dopamine function

Thirty-two Long Evans male rats with sham operations or unilateral 6-OHDA-induced damage to meso-telencephalic dopaminergic neurons were evaluated on a reactive capacity task that demanded high speed movement initiation. The task required lever manipulation to avoid signalled shock. The interval between the warning and the shock was incrementally reduced. A one-sleeved vest provided the opportunity to measure movement initiation of each limb independently. Extent of lesion was assessed by [ 3H]DA uptake, [ 3H]spiroperidol binding, or DA levels. Movement initiation latencies for each forelimb were found to be linearly related to interhemispheric striatal DA asymmetry induced by microinjections of 6-OHDA. Even those lesions resulting in small to moderate decreases in DA function, including deficits causing no chronic posture or sensory asymmetries, resulted in reactive capacity deficits and greatly slowed reaction time in the paw contralateral to the lesion. Following severe lesions, small yet substantial deficits were also seen in ipsilateral paw performance, which may be related to DA depletions found in the non-lesioned striatum. Thus, a reactive capacity task which requires the animal to react with maximal speed appears to be a potentially good index of nigrostriatal dopamine integrity even when the depletion is not severe.

Effects of pertussis toxin on D 2-dopamine receptor in rat striatum: Evidence for coupling of Ni regulatory protein with D 2-receptor

It is well established that a pertussis toxin, islet activating protein (IAP), interacts directly with the Ni regulatory protein involved in the receptor-adenylate cyclase system. In this study we investigated the effect of the toxin on the dopaminergic function of the central nervous system in conjunction with the adenylate cyclase system. Direct bilateral microinjection of the toxin into rat striatum reduced the stereotyped behavior induced by apomorphine. This inhibitory effect was observed even 40 h after administration of the toxin, whereas the inhibition by haloperidol disappeared within 15 h. Toxin administration did not influence either the Bmax or affinity of specific binding of [3H]spiroperidol to the striatal membrane. However, it increased the IC50 value of apomorphine for the specific binding of [3H]spiroperidol. GTP (10(-4) M) had little effect on the apparent affinity of apomorphine to the [3H]spiroperidol binding sites in IAP-treated membrane, though an effect was clearly observed in untreated membrane. [3H]Spiroperidol binding sites were increased 34 +/- 8% (n = 4) on chronic treatment of haloperidol for 2 weeks. On the contrary, on long-term administration of IAP the ligand binding sites were decreased by 25 +/- 10% (n = 4). These results indicate that pertussis toxin can interact with the Ni protein coupled with striatal D2-dopamine receptor. Inhibition of the coupling between Ni protein and the D2-dopamine receptor attenuated the manifestation of rat stereotyped behavior. Furthermore, chronic administration of dopamine antagonist resulted in the up-regulation of the D2-dopamine receptor, while long-term inhibition of coupling between the D2-dopamine receptor and Ni regulatory protein reduced the amount of receptors.

Pharmacological changes in dopaminergic systems induced by long-term administration of amantadine

The pharmacological effects of 6 weeks administration of amantadine was evaluated in the mouse. Motor stimulation induced by amphetamine or the amantadine analog memantine was reduced while that of apomorphine was enhanced by the long-term amantadine treatment. This was accompanied by an increase in the binding of spiroperidol to putative striatal dopamine receptors, without a change in amantadine-induced inhibition of dopamine uptake in the striatum. The possible significance of changes in pre- and postsynaptic dopamine mechanisms is discussed in relation to the anti-parkinson activity of the drug.

Denervation accelerates the reappearance of neostriatal D-2 receptors after irreversible receptor blockade

The effect of denervation on the turnover of striatal dopaminergic D-2 receptors was examined by determining the rate of receptor reappearance in vivo after administration of the irreversible receptor antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) to rats that received prior unilateral intracerebral injection of 6-hydroxydopamine (6-OHDA). Initial experiments confirmed that EEDQ (10 mg/kg i.p.) induces a severe, prolonged blockade of D-2 receptors. Recovery of [ 3H]spiroperidol binding occurred at a rate of approximately 9% of control binding per day. 6-OHDA injection into the ascending dopaminergic projection 3 or 5 days prior to EEDQ administration revealed that denervation had no effect on the rate of D-2 receptor recovery during the first post-operative week. By 4–5 weeks postoperatively, however, denervation enhanced the rate of recovery of [ 3H]spiroperidol binding. These results are consistent with our finding that, when homogenized tissue preparations are used, steady-state receptor density does not change within the first postoperative week but increases by 3–4 weeks after the injury. Saturation analysis determined that both EEDQ and denervation altered the density of binding sites, whereas neither treatment significantly affected the affinity of the receptor for [ 3H]spiroperidol. By 4–5 weeks postoperatively, the receptor degradation rate constant in the denervated striatum (0.0054/h) was equal to that in the intact striatum (0.0052/h). Thus, only the receptor reappearance rate was elevated in the denervated striatum (3.8 fmol/mg protein/h) relative to the intact striatum (2.8 fmol/mg protein/h).

Stimulation of [3H]spiroperidol binding after prolonged neuroleptic therapy by the cholecystokinin octapeptide analog cerulein

Evidence has recently been obtained that cholecystokinin and its analog cerulein have marked antipsychotic action on patients with schizophrenia who are resistant to neuroleptics; this is the basis for interest in this study of the effect of cerulein, a high-affinity analog of the octapeptide cholecystokinin, on binding of tritium-spiroperidol in vivo. Considering the apormorphine-like action of cerulein, this biochemical analysis was undertaken in the form of a comparative study with N-propyl-norapomorphine, a high-affinity analogy of apomorphine.

Inhibition of neuroleptic binding by human brain extracts — an effect of endogenous dopamine?

Extracts of autopsied human brain tissue exhibited a specific inhibition of [ 3H]spiroperidol binding, in support of previous reports. The extent of binding inhibition varied depending upon the brain region from which the tissue was taken. We observed two peaks of inhibition binding from extracts of caudate or putamen placed on a Sephadex G 10 column. Results of experiments to characterize the extract in the second peak indicate a correlation between inhibition of spiroperidol binding and dopamine content of the tissue. The content of the first peak could not be definitively identified but indirect evidence indicates that it may be a high molecular weight conjugate of dopamine that is formed at low concentrations. No evidence was obtained to suggest the existence of previously undetected neuroleptic-like material in human brain.

Effects of chronic bromocriptine treatment of an estrone-induced, prolactin-secreting rat pituitary adenoma.

Bromocriptine (BROM), a dopamine (DA) agonist, is commonly and successfully used for long-term treatment of human prolactinomas. We have studied the effects of chronic BROM administration to female 344 Fisher/Lis rats bearing an estrone-induced, prolactin (PRL)-secreting pituitary tumor recently characterized as a model for human prolactinoma. The animals were injected twice daily with BROM (2.5 mg/kg) or with diluent. After 1 month of treatment, the animals were sacrificed, and plasma collected and stored at -20 degrees C for PRL radioimmunoassay. The pituitary tumors were removed and tumoral mammotrophs dispersed enzymatically for studies of DA receptor binding and PRL release in vitro. BROM treatment significantly reduced tumor weight, cell size, rough endoplasmic reticulum, Golgi complexes and plasma PRL levels. [3H]-spiroperidol binding to tumoral mammotrophs was also evaluated. BROM induced a significant decrease in the number of DA binding sites without any changes in affinity. These results indicate that chronic BROM treatment of an animal model of prolactinoma induces tumor involution, reduction of PRL release and probably synthesis, and down regulation of dopaminergic binding sites.

Vasoconstrictor and norepinephrine potentiating action of 5-hydroxykynuramine in the isolated perfused rat kidney: involvement of serotonin receptors and alpha1-adrenoceptors

Kynuramines are endogenously occurring diamines derived from tryptophan. In the present study, we have compared the pharmacological actions of 5-hydroxykynuramine (5-OH-K) with kynuramine and 5-hydroxytryptamine (5-HT) on vascular resistance changes and responsiveness to adrenergic stimuli in the isolated perfused rat kidney. 5-OH-K was found to mimic the actions of 5-HT in that it produced vasoconstriction, potentiation of alpha 1-adrenoceptor-mediated responses to norepinephrine (NE) and periarterial nerve stimulation, and displaced specific [3H]spiroperidol binding from rat cortical membranes. With regard to all parameters measured, 5-OH-K was about 15-times less active than 5-HT. Vascular responses to 5-OH-K and 5-HT were inhibited noncompetitively by ketanserin and cyproheptadine. Unlike 5-OH-K, kynuramine, failed to evoke vasoconstriction and inhibited vascular responses to NE via alpha 1-adrenoceptors. Thus, kynuramine lacks serotonin receptor agonist activity but possesses alpha 1-adrenoceptor blocking properties. In contrast, 5-OH-K potentiates NE and acts as a serotonin agonist. The present results raise the possibility that kynuramine and 5-OH-K might act as endogenous modulators of serotonergic and adrenergic mechanisms in the renal vascular bed.

Effect of neurotensin, substance P and TRH on the regulation of dopamine receptors in rat brain

Rats were exposed for one week to either neurotensin (4 μg/h), substance P (3.3 μg/h), thyrotropin-releasing hormone (5 μg/h), or saline administered intracerebroventricularly via mini osmotic-pumps and either haloperidol (2.5 mg/kg i.p., 2 × daily) or vehicle control. The peptide treatments by themselves did not alter [ 3H]spiroperidol binding in either the nucleus accumbens or the striatum. Neurotensin, however, augmented the increase in [ 3H]spiroperidol binding caused by the haloperidol treatment in both the nucleus accumbens and striatum.

Formula omitted] binding of spiroperidol and bromosphiroperidol at low drug loadings

The binding of spiroperidol and bromospiroperidol, in vivo , was studied over a wide range of drug dosages. It was found that while spiroperidol and bromospiroperidol bind selectively in vivo to tissues known to be high in dopamine receptor binding sites, this specificity of binding does not persist at very low doses. Such anomalous binding behavior can have implications for the non-invasive imaging of these drugs.

Changes of [ 3H]spiroperidol binding in the renal artery of aged rabbits

Using mature (12 months), old (70 months) rabbits and 3H-labeled spiroperidol, the characteristics of renal artery dopamine receptors were studied. In old age the dissociation constant of [ 3H]spiroperidol was unchanged, while maximum specific binding was reduced more than 45%. The present data seem to indicate an impairment of peripheral dopaminergic function in ageing.

Behavioral and biochemical evidence of apomorphine-induced supersensitivity of the striatal dopamine receptors

The effect of repeated administration of apomorphine was studied behaviorally and biochemically in rats bearing either a unilateral lesion of the the substantia nigra with 6-OHDA or an electrolytic lesion of the entopeduncular nucleus. Rats with the nigral lesion displayed a progressive increase in contralateral circling rate. In animals with the entopeduncular lesion, the ipsiversive circling response was unchanged after the eight injection of apomorphine. [ 3h] Spiroperidol binding to striatal membranes did not appear modified by the apomorphine treatment on the intact side. It was however increased on the side of the 6-OHDA lesion. We propose that a denervated striatum responds to repeated stimulation by dopamine agonists with a paradoxical increase in sensitivity. This may explain in part the appearance of dyskinesia in treated parkinsonian patients.

Dopaminergic and cholinergic muscarinic receptor effects of L-alphacetylmethadol (LAAM) and its metabolites.

In isolated rat hearts L-alphacetylmethadol (LAAM) produced a concentration-dependent decrease in the spontaneous beating rate. This effect was completely prevented by 1.0 microM atropine. Chronic treatment of rats with LAAM increased the number of striatal dopamine receptors measured by [3H]spiroperidol binding. The affinity of these binding sites for [3H]spiroperidol was unchanged by LAAM treatment. There were no significant changes in the number or affinity of binding sites for the labeled muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB) with chronic LAAM treatment. The ability of LAAM, nor-LAAM, or dinor-LAAM to antagonize the binding of [3H]spiroperidol (40 pM) or [3H]QNB (125 pM) to striatal membrane fragments was tested. The measured affinity constants for LAAM and metabolites were 100-3000 times higher than the affinity constants of unlabeled spiroperidol at [3H]spiroperidol binding sites. The affinity constants of LAAM and metabolites at muscarinic binding sites were 10-20 times higher than pilocarpine and 5000-8000 times higher than atropine. These results suggest that LAAM can produce some of its effects by acting as a weak agonist at muscarinic receptor sites.