Pituitary and brain D2 receptor density measured in vitro and in vivo in EEDQ treated male rats

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A 15-mer, all-phosphorothioate-modified antisense oligodeoxynucleotide (ASO) targeted against rat dopamine D3 receptor mRNA (4 microM, 5 days) significantly reduced (28%) the amount of binding sites labelled with [3H]spiperone in monolayer cultured Chinese hamster ovary (CHO) cells transfected with the complementary desoxyribonucleic acid (cDNA) for the rat D3 receptor. In contrast, D3-ASO treatment did not reduce the amount of bound [3H]spiperone in CHO cells transfected with D2 receptor cDNA. Intracerebroventricular infusion of D3-ASO (osmotic minipump, 10 microg/microl/h, 7 days) influenced dopamine receptor density in the limbic forebrain such that the upper part of the dopamine/[3H]spiperone displacement curve--tentatively representing the D3 receptor--was altered significantly. Spontaneous locomotor activity of non-habituated rats was increased significantly in D3-ASO-treated animals; in addition, in vivo microdialysis revealed a moderate increase in dopamine release in the nucleus accumbens in these animals. In all experiments, an oligodeoxynucleotide comprising the same nucleotides as the antisense sequence, but in random order, was used as control. It is concluded that the antisense strategy is useful for investigating the functional role of dopamine D3 receptors and that the dopamine D3 receptor is involved in rat locomotor behaviour.

Section: Methodsmentioning

confidence: 99%

Central administration of dopamine D3 receptor antisense to rat: effects on locomotion, dopamine release and [3H]spiperone binding

Ekman

Nissbrandt

Heilig

et al. 1998

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Effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline on the prolactin suppression induced by a series of full and partial dopamine D2 receptor agonists in male rats

Ekman

Eriksson

1992

The effect of pretreatment with a high dose of the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) (20 mg/kg, 24 h) on the intrinsic activity displayed by a series of full and partial dopamine D2 receptor agonists on prolactin regulating pituitary D2 receptors in male rats was studied. To increase baseline prolactin levels, gamma-butyrolactone in a dose inhibiting brain dopamine neurotransmission was given to all animals. In controls, i.e. rats not given EEDQ, supramaximal doses of all full and partial D2 receptor agonists tested decreased serum prolactin levels with greater than 80%. While the intrinsic activities of the dopamine precursor 1-DOPA and of the full agonists (+)-3-PPP, 5-OH-DPAT, B-HT 920 (talipexole), apomorphine, and NPA (R-(-)-N-n-propylnorapomorphine) were not affected by pretreatment with EEDQ, the effects of supramaximal doses of the partial agonists (-)-HW-165, TDHL (terguride), SDZ208-911, (-)-3-PP) (preclamol), and SDZ 208-912 were reduced to 66%, 74%, 59%, 100%, and 100%, respectively. The effect of EEDQ on the intrinsic activity displayed by the various agonists corresponds inversely to the intrinsic efficacy displayed by the drugs in other models of D2 receptor function with one exception only; thus, the prolactin suppressive effect of (-)-3-PPP was more effectively antagonized by EEDQ than would have been predicted from the intrinsic efficacy usually attributed to the drug. Since the dose of EEDQ used in the present study has previously been shown not to decrease D2 receptor density in the pituitary as measured using in vivo radioligand binding, it is suggested that alkylation of D2 receptors may change the conformation of the individual receptor complexes in a way that decreases the responsiveness to partial but not full agonists.

Effects of ?2-adrenoceptor agonists on locus coeruleus firing rate and brain noradrenaline turnover in N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)-treated rats

Engberg

Eriksson

1991

Previous studies have shown that a low dose of the alkylating compound N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) reduces the density of alpha 2-adrenoceptors in rat cerebral cortex and antagonizes the effects of an alpha 2-adrenoceptor agonist on noradrenaline release in rat cortical slices. In the present study, a corresponding dose of EEDQ (1 mg/kg, s.c., 24 h) was shown to reduce the effect of the alpha 2-adrenoceptor agonists clonidine and guanfacine on noradrenaline turnover in rat brain while not affecting the inhibitory effect of clonidine on locus coeruleus (LC) cell firing. When considerably higher doses of EEDQ were administered (10 and 20 mg/kg, s.c., 24 h) not only the biochemical but also the electrophysiological effects of clonidine were markedly reduced (or even reversed). The data support the notion the EEDQ decreases the responsiveness of brain alpha 2-adrenergic receptors; moreover, they indicate that alpha 2-adrenoceptors regulating LC activity are characterized by a larger receptor reserve or are less sensitive to the influence of alkylation than are the population of alpha 2-adrenoceptors regulating noradrenaline utilization.