DA-sensitive Adenylate Cyclase Activity Research Articles

Blockade of D-1 dopamine receptors in the medial prefrontal cortex produces delayed effects on pre- and postsynaptic indices of dopamine function in the nucleus accumbens.

The present experiments assessed the acute and delayed effects of D-1 dopamine (DA) receptor blockade in the medial prefrontal cortex (mPFC) on pre- and postsynaptic indices of DA neurotransmission in the nucleus accumbens (N.Acc). Different groups of rats received intra-mPFC injections of saline (control animals) or the D-1 DA receptor antagonist SCH-23390 (0.25 microgram/side). Acutely, intra-mPFC injections of this antagonist did not affect spontaneous locomotion but significantly increased the locomotion induced by intra-N.Acc. amphetamine (1.5 micrograms/side), in agreement with our earlier findings [Vezina et al. (1991) Eur. J. Neurosci., 3:1001-1007]. When tested two days post-injection, however, mPFC-SCH-23390 preexposed animals showed lower levels of locomotor activity than Control animals in response to intra-N.Acc. injections of amphetamine. This effect was not observed in other animals preexposed two days earlier to mPFC injections of amphetamine (2.5 micrograms/side) or the D-2 DA receptor antagonist sulpiride (1.0 microgram/side). Animals preexposed two days earlier to mPFC SCH-23390 also showed higher levels of locomotor activity (+98%) when tested with intra-N.Acc. injections of the D-1 DA receptor agonist SKF-38393 (1.0 microgram/side) and a 36% increase in maximal DA-sensitive adenylate cyclase activity in comparison to Control animals. These effects were no longer observed in animals tested seven days following the mPFC SCH-23390 injections. These results demonstrate delayed actions resulting from cortical D-1 DA receptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo partial inactivation of dopamine D1 receptors induces hypersensitivity of cortical dopamine-sensitive adenylate cyclase: permissive role of alpha 1-adrenergic receptors.

As shown by autoradiography, peripheral injections of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) induced a dose-dependent decrease of [3H]SCH 23390 and [3H]prazosin high-affinity binding sites in the rat prefrontal cortex. EEDQ showed similar efficacy in inactivating cortical and striatal dopamine (DA) D1 receptors, whereas prazosin-sensitive alpha 1-adrenergic receptors were more sensitive to the action of the alkylating agent, as for all doses of EEDQ tested (from 0.8 to 3 mg/kg, i.p.), the decrease in cortical [3H]SCH 23390 binding was less pronounced than that of [3H]prazosin. The effects of EEDQ on [3H]SCH 23390 binding and DA-sensitive adenylate cyclase activity were then simultaneously compared in individual rats. In the striatum, whatever the dose of EEDQ used, the decrease of DA-sensitive adenylate cyclase activity was always lower than that of D1 binding sites, suggesting the occurrence of a large proportion of spare D1 receptors. In the prefrontal cortex, a significant increase in DA-sensitive adenylate cyclase activity was observed in rats treated with a low dose of EEDQ (0.8 mg/kg), this effect being associated with a slight reduction in [3H]SCH 23390 binding sites (-20%). Parallel decreases in the enzyme activity and D1 binding sites were observed with higher doses. The EEDQ-induced supersensitivity of DA-sensitive adenylate cyclase did not occur in rats in which the decrease in [3H]prazosin binding sites was higher than 35%.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of dark adaptation to upregulate D-1 dopamine receptors in retina of senescent rats

The effect of aging on the binding parameters of 3H-SCH 23390, the most selective ligand of D-1 DA receptors, was studied in membrane preparations from the rat retina. DA-stimulated adenylate cyclase activity was also measured in order to better characterize the changes in retinal D-1 DA receptors induced by aging. The binding studies revealed that the density of 3H-SCH 23390 was increased (34 and 73%) in the retina of 14- and 26-month-old rats, when compared to young adult animals, respectively. In contrast, aging failed to alter the sensitivity of the adenylate cyclase to the action of DA. In fact, DA (10 −6 M to 10 −4 M) elicited a similar enhancement in cyclic AMP formation in retinal homogenates of both adult and senescent rats. Since dark adaptation increases the density of D-1 DA receptors in the retina of adult rats we studied the effect of light deprivation on 3H-SCH 23390 binding and DA-sensitive adenylate cyclase activity in the retina of senescent rats. As previously shown (25) light deprivation increased 3H-SCH 23390 binding and enhanced DA-sensitive adenylate cyclase activity in the retina of young adult rats. On the contrary, dark adaptation failed to increase 3H-SCH 23390 binding and to enhance DA-sensitive adenylate cyclase activity in the retina of senescent rats. Taken together these results indicate that D-1 DA receptors in the retina of aged rats have biochemical and functional properties different from those found in the retina of adult animals; these changes may result in an altered response to the physiological stimuli elicited by environmental lighting.

Nondopaminergic prefrontocortical efferent fibers modulate D1 receptor denervation supersensitivity in specific regions of the rat striatum

A unilateral injection of 6-OHDA (6 microgram/1.5 microliter) was made into the fields of Forel in order to estimate the effects of the destruction of ascending dopaminergic (DA) pathways on the denervation supersensitivity of DA D1 receptors in the rat striatum. DA-sensitive adenylate cyclase activity was markedly enhanced in the anteromedian part of the striatum 3 weeks after the lesion (+68%) and remained elevated for several weeks thereafter (+36%). A different response occurred in the laterodorsal striatum, where the increase in DA-sensitive adenylate cyclase activity was less pronounced after 3 weeks (+40%) and no longer present after 7 weeks. Estimations of catecholamine levels indicated that the lesion made destroyed not only nigrostriatal DA neurons but other ascending catecholaminergic fibers projecting into the cerebral cortex as well. In addition, retrograde transport experiments made with wheat germ agglutinin coupled to horseradish peroxidase indicated that the anteromedian part of the striatum, but not the laterodorsal one, receives both an ipsi- and contralateral cortical projection originating in the prefrontocortical DA field. When the destruction by 6-OHDA of this contralateral DA innervation was combined to the unilateral lesion of the fields of Forel, the increase in DA-sensitive adenylate cyclase activity in each striatal area 3 or 7 weeks postlesion was prevented. This effect was due to DA denervation of the prefrontal cortex since striatal D1 denervation supersensitivity was still observed when contralateral ascending noradrenergic fibers were selectively destroyed by a 6-OHDA lesion made laterally to the pedunculus cerebellaris superior. These results suggest that, by controlling the activity of corticostriatal neurons, the mesocorticoprefrontal DA neurons exert a permissive role on the development of D1-receptor denervation supersensitivity in specific areas of the striatum.

Differential Modulation of D1 and D2 Dopamine‐Sensitive Adenylate Cyclases by 17β‐Estradiol in Cultured Striatal Neurons and Anterior Pituitary Cells

Primary cultures of anterior pituitary cells from female rats and of mouse embryonic striatal neurons were used to study the effects of 17 beta-estradiol on D1- and D2-dopamine (DA)-sensitive adenylate cyclase. 17 beta-Estradiol pretreatment (10(-9) M, 72 h) suppressed the D2-DA-induced inhibition of adenylate cyclase activity in anterior pituitary cells. The steroid (10(-9) M, 24 h) also blocked the D2-DA-evoked response in striatal neurons whereas it enhanced by twofold the D1-DA-induced stimulation of the enzyme activity in these neurons. All these effects of the steroid were dose dependent and specific, as neither 17 alpha-estradiol, dexamethasone, nor progesterone used at the same concentration (10(-9) M) was effective. Furthermore, the modulation of DA-sensitive adenylate cyclases by the steroid required long-term exposure of living cells to 17 beta-estradiol since neither 17 beta-estradiol pretreatment for 4 h nor its addition to broken cells directly into the adenylate cyclase assay induced any alteration in the DA-sensitive adenylate cyclase activity. These results are in agreement with a genomic effect of the steroid. Using both anterior pituitary cells and striatal neurons in culture, 17 beta-estradiol affected neither the total number of DA (D1 and D2) receptors nor the estimated number of adenylate cyclase catalytic units. Therefore, it is suggested that the steroid modifies the coupling process by a mechanism that still has to be elucidated. These results demonstrate an effect of 17 beta-estradiol on DA target cells in both systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of dopamine-dependent adenylate cyclase activity in human renal cortex

The effects of dopamine (DA) and of two selective DA DA1 agonists (SKF 38393 and SKF 82526) on adenylate cyclase activity were studied with human kidney cortex membrane preparations. DA elicited a dose-related stimulation of adenylate cyclase activity with an EC 50 of 60 μM. The selective DA DA1 antagonist SCH 23390 behaved as a competitive antagonist, shifting the dose-response curce to the right. The non-selective β-adrenoceptor antagonist (−)-propranolol did not affect the EC 50 of the dose-response curve to DA but attenuated the maximal stimulatory effect of DA at concentrations higher than 100 μM. (+)-Sulpiride inhibited DA-induced adenlylate cyclase stimulation in a dose-dependent manner with an IC 50 of 4.6 × 10 −8 M but (−)-sulpiride was without effect. Both SKF 38393 and SKF 82526 stimulated the adenylate cyclase activity of human kidney cortex; this effect was completely antagonized by SCH 23390. Our results, demonstrating the presence of DA-sensitive adenylate cyclase activity, strongly suggest the presence of a DA receptor of the DA1 subtype in human kidney cortex.

Sulfated cholecystokinin octapeptide (CCK 8) failed to modulate basal or dopamine-stimulated adenylate cyclase activity in the rat striatum

Morency, Michel A., Gregory M. Ross, Jason S. Kajiura and Ram K. Mishra: Sulfated cholecystokinin octapeptide (CCK 8) failed to modulate basal or dopamine-stimulated adenylate cyclase activity in the rat striatum. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1988, 12 :331–336 1. 1. In view of previously demonstrated modulatory effects of CCK 8 on DA-sensitive adenylate cyclase activity in the nucleus accumbens, we examined the effects of this neuropeptide in the striatum. 2. 2. Adenylate cyclase activity was measured by conversion of α-[ 32P]ATP into [ 32P]cAMP. 3. 3. CCK 8, when added to the adenylate cyclase assay in concentrations up to 100 μM, failed to significantly alter, either positively or negatively, basal or DA-stimulated (30 or 100 μM) adenylate cyclase activity. Similar results were obtained in the presence of various peptidase inhibitors. 4. 4. Under the assay conditions employed in these experiments, it would appear that there is no effect of CCK 8 on DA-sensitive adenylate cyclase in the striatum.

D 1 dopamine receptors in the rat retina: effect of dark adaptation and chronic blockade by SCH 23390

Chronic administration of SCH 23390 (0.03 mg/kg s.c., three times daily), a selective D 1 dopamine (DA) receptor blocker, markedly increased the [ 3H]SCH 23390 binding in the rat retina. As revealed by the Scatcard plot analysis of saturation data from retinal homogenates, chronic SCH 23390 increased the total number of binding sites by 34% when compared to tissue from solvent-treated rats but failed to change the apparent affinity of [ 3H]SCH 23390 for its binding sites. The up-regulation of [ 3H]SCH 23390 binding sites was paralleled by an increase in the sensitivity of retina DA-sensitive adenylate cyclase. In fact, DA (5 × 10 −6 M to 10 −4 M) produced a higher accumulation of cyclic AMP (from 58 to 128%) in the retina of SCH 23390-treated rats as compared to the accumulation (from 35 to 80%) found in tissue from solvent-treted rats. Since dark adaptation decreases dopaminergic function in the rat retina, the influence of environmental lighting on [ 3H]SCH 23390 binding and DA-sensitive adenylate cyclase activity was studied. After 4 h of dark adaptation the density of [ 3H]SCH 23390 binding sites was higher (32%) than that from light-adapted rats. On the other hand, dark adaptation failed to change the apparent affinity of [ 3H]SCH 23390 for its binding sites. Moreover, DA elicited a greater stimulation of adenylate cyclase activity in homogenates of retina from dark-adapted rats. Thus, the maximum adenylate cyclase response to DA resulted higher in the retina of dark-adapted rats (152%) than that found in the retina of light-adapted animals (97%). Taken together, these results indicate that retinal D 1 DA receptors are sensitive to the decrease in dopaminergic function elicited either by light deprivation or by their chronic blockade with SCH 23390 and that retinal D 1 DA receptors receive a tonic innervation by DA.

Dopamine D-1 receptor agonists combined with the selective D-2 agonist quinpirole facilitate the expression of oral stereotyped behaviour in rats

The behaviour of rats was studied after combined treatment with the selective DA D-2 agonist quinpirole and three selective D-1 agonists (SK & F 38393, SK & F 75670 and Lu 24-040). The effects on behaviour were compared with those on receptor binding and adenylate cyclase (AC). While the D-1 agonists alone did not induce stereotyped behaviour, quinpirole induced dose-dependent hyperactivity (locomotion, sniffing, head movements and rearing), whereas licking/biting was absent or seen only occasionally. Combined treatment with quinpirole and a D-1 agonist was followed by dose-dependent licking and occasional biting behaviour. The D-1 agonists had similar efficacies, but SK & F 75670 and Lu 24-040 were more potent than SK & F 38393. The maximal effects of SK & F 38393 plus quinpirole were effectively blocked by either a D-1 antagonist (SCH 23390) or a D-2 antagonist (YM 09151-2) confirming the close relation between D-1 and D-2 receptor sites in the brain. Good correspondence was found between affinities to D-1 receptors ([ 3H]SCH 23390 binding) in vitro and the EC 50 values for stimulation of AC activity. However, the maximal effects on DA-sensitive AC activity were less for SK & F 75670 and Lu 24-040 than for SK & F 38393. Thus, the results indicate that efficacies in the adenylate cyclase assay are dissociated from those on behaviour. Furthermore, the data indicate that in normal rats D-1 receptors are functionally relevant since D-1 agonists facilitate the expression of oral stereotyped behaviour after combination with a D-2 agonist.

Non-DA prefronto-cortical efferents modulate D 1 receptors in the nucleus accumbens

Bilateral injections of 6-OHDA in the ventral mesencephalic tegmentum (VMT) destroy the DA afferents of the nucleus accumbens but do not induce any denervation supersensitivity of the D1 receptors in the nucleus accumbens. Because other non-DA afferent fibers might also regulate D1 receptors in that structure, bilateral ablations of the prefrontal cortex were performed. This lesion induced a 55% decrease of [3H]glutamic acid high-affinity uptake activity in the nucleus accumbens. When the prefronto-cortical ablation was performed simultaneously with the bilateral injection of 6-OHDA in the VMT, a marked hypersensitivity of DA-sensitive adenylate cyclase activity was observed in the nucleus accumbens (+52% increase of Vmax and a two-fold decrease of the Kapp for DA) while the ablation of the prefrontal cortex alone induced only a +14% (P less than 0.01) increase of D1 receptors in that structure. These results indicate that the regulation of D1 receptors in the nucleus accumbens is not solely dependent on the presynaptic DA innervation and that other non-DA fibers, such as those of the cortico-nucleus accumbens pathway, might contribute to it.

ChemInform Abstract: APORPHINES. 36. DOPAMINE RECEPTOR INTERACTIONS OF TRIHYDROXYAPORPHINES. SYNTHESIS, RADIORECEPTOR BINDING, AND STRIATAL ADENYLATE CYCLASE STIMULATION OF 2,10,11‐TRIHYDROXYAPORPHINES IN COMPARISON WITH OTHER HYDROXYLATED APORPHINES

The presence of the A ring of aporphines and the addition of substituents to it and to other portions of the aporphine ring systems can extend explorations of the dimensions and other characteristics of the dopamine receptors. Accordingly, the synthesis and some physical and pharmacological properties of a series of (-)-2,10,11-trihydroxyaporphines (3a-g) are described. Structure-activity relationships among mono-, di-, and trihydroxyaporphines were evaluated against the high-affinity (nanomolar) binding of [3H]apomorphine (APO) and [3H]spiroperidol (SPR) with a subcellular fraction (P4) of caudate nucleus from bovine brain. In addition, DA-sensitive adenylate cyclase activity was evaluated in homogenates of rat brain striatal tissue. The rank order of displacement of [3H]APO by potent aporphines (IC50 less than or equal to 30 nM) correlated approximately with their ability to stimulate cyclic AMP synthesis. Potency orders against two ligands were dissimilar; for example, increasing the size of N6-alkyl substituents increased potency vs. [3H]SPR but not vs. [3H]APO binding. Moreover, [3H]SPR binding correlated poorly with cyclase activity or [3H]APO binding, suggesting a closer relationship of [3H]APO binding to dopamine-sensitive adenylate cyclase activity.

Non-dopaminergic fibres may regulate dopamine-sensitive adenylate cyclase in the prefrontal cortex and nucleus accumbens.

The dopaminergic (DA) innervation of the prefrontal cortex in rat originates from neurones distributed in the anterior medial part of the ventral tegmental area (VTA)1. Biochemical2,3 and electrophysiological4 studies have demonstrated that these mesocortico-prefrontal neurones are distinct from others located in the VTA which project to subcortical structures such as the nucleus accumbens. DA receptors coupled to an adenylate cyclase (D-1 receptors) are present in the prefrontal cortex and their topographical distribution closely resembles that of DA nerve terminals5–7. We have now further analysed the properties of the cortical D-1 receptors and compared them with those of a subcortical limbic structure examining, in the rat, the effects on DA-sensitive adenylate cyclase activity in the prefrontal cortex and the nucleus accumbens of (1) bilateral 6-hydroxydopamine (6-OHDA) microinjections in the VTA and (2) bilateral electrolytic lesions of the VTA. The results suggest that regulation of D-1 receptors is not solely dependent on the presynaptic DA innervation and that other non-DA fibres may contribute to it.

Role of calmodulin in states of altered catecholamine sensitivity.

Calmodulin, an endogenous calcium-binding protein, can modulate the intracellular concentration of adenosine 3',5'-cyclic monophosphate (cyclic AMP] by stimulating membrane-bound adenylate cyclase activity and soluble phosphodiesterase (PDE) activity.' There is increasing evidence that calmodulin can modulate the effects of calcium at both preand postsynaptic sites in some areas of brain. Calmodulin is enriched in rat brain synaptic membranes2 and has been located in postsynaptic densities in mouse basal ganglia3 and canine cerebral ~ o r t e x . ~ Previous studies have suggested that calmodulin is involved with dopamine IDA)-sensitive adenylate cyclase activity in rat striaturn. Gnegy et aL5 found that depletion of calmodulin t'rom striatal membranes results in a decreased ability of DA to stimulate adenylate cyclase activity. Furthermore, the calmodulin content in the striaturn was increased under conditions of dopamine supersensitivity.6 Rats treated chronically with cataleptogenic antipsychotic drugs and then withdrawn from the drugs hail increased calmodulin content in their striatal membranes. These animals exhibited behavioral supersensitivity to apomorphine and their striatal adenylate cyclase had an increased affinity for dopamine as demonstrated by a 3to 4-foid increase in dopamine sensitivity. The increase in calmodulin could positively affect DA-sensitive adenylate cyclase activity and thus contribute to dopaminergic: supersensitivity. The increased calmodulin in the striatal membranes of the supersensitive rats seems to be more tightly bound to its membrane binding protein^.^ In the brain, calmodulin can be hound to membrane proteins in a calcium-dependent and calcium-independent manner.' Calmodulin has been shown to hind to Caz+dependent PDE' and Caz+-sensitive adenylate cyclase'o as well as other proteins. Vandermeers et (11. have demonstrated a correlation between increased ['ZSI]calmodulin binding and activation of adenylate cyclase activity in guinea pig membranes. In this work we investigate more directly whether calmodulin can affect DA-sensitive activity in rat striatal membranes. We found that calmodulin could affect both the maximal velocity of the reaction and the sensitivity to DA. We studied the binding of calmodulin to striatal membranes in order to further investigate the relationship between calmodulin interaction with adenylate cyclase activity. We showed specific binding of ['251]calmodulin to striatal membranes that was competitively inhibited by trifluoperazine, an antipsychotic drug that binds to calmodulin and inhibits its action. We have also shown that the ability of the calmodulin content to increase could be specific for dopaminergic supersensitivity in the striatum.

Dopamine metabolism, spiperone binding and adenylate cyclase activity in the adult rat hippocampus after ingrowth of dopaminergic neurones from embryonic implants

The growth of dopamine (DA) neurones of rat embryonic mesencephalic brain tissue implanted close to the anterior part of the hippocampus of adult rats was studied by measuring the levels of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) in the host hippocampus. The hippocampal levels of DA and DOPAC reached maximal values 6 months after transplantation. The neuroleptic drug haloperidol evoked an increase in the levels of DOPAC. No evidence was found for the induction of DA-sensitive adenylate cyclase activity or of binding sites of [3H]spiperone. These results indicate that there is a substantial ingrowth of transplanted DA neurones into the host hippocampus, but no evidence was found for the development of functional contacts between the embryonic DA neurons and the host tissue.

Topographical distribution of dopaminergic innervation and dopaminergic receptors of the anterior cerebral cortex of the rat

The quantitative topographical distribution of the dopaminergic innervation and the DA-sensitive adenylate cyclase were estimated in the anterior cerebral cortex of the rat. The high affinity uptake of [ 3H]DA and endogenous levels of DA were used as markers of the dopaminergic innervation. [ 3H]DA uptake, DA levels and DA-sensitive adenylate cyclase were estimated in microdiscs of tissues punched out from frozen serial frontal slices. The uptake of [ 3H]DA was measured on sucrose homogenates prepared from such microdiscs. The ventral part of the frontal cortex contained the highest DA concentration and DA-sensitive adenylate cyclase activity; the other structures rich in DA and in DA receptors were the cingular (close to the corpus callosum) and the rhinal cortices. All of these cortical areas were rich in [ 3H]DA uptake sites. However, curiously, the dorsal part of the frontal cortex, which contained only moderate amounts of DA and of DA-sensitive adenylate cyclase, presented the highest number of [ 3H]DA uptake sites. Nevertheless, the uptake of [ 3H]DA in this region decreased by 60% after bilateral electrolytical lesions of the ventral tegmental area (A10 group). The parietal cortex was practically devoid of dopaminergic innervation and of DA-sensitive adenylate cyclase. The activity of the DA-sensitive adenylate cyclase in the frontal, cingular and rhinal cortices was 10-fold higher than that found in the striatum when compared to their respective DA levels.

Regional effects of neuroleptics of dopamine metabolism and dopamine-sensitive adenylate cyclase activity

The effect of haloperidol, chlorpromazine, thioridazine and sulpiride on the levels of DOPAC and HVA, as an index of DA turnover, and on the activity of DA-stimulated adenylate cyclase was investigated in the striatum, the nucleus accumbens and the tuberculum olfactorium of the rat brain. Haloperidol, chlorpromazine and thioridazine caused a more marked increase in DA turnover in the striatum than in the mesolimbic areas, while the reverse was true for sulpiride. In contrast, although the relative potency of these compounds varied greatly, the K i of each drug for the DA-sensitive adenylate cyclase was similar in these three stuctures of rat brain. The results indicate that in the three brain structures investigated there was no correlation between the differential effects of neuroleptics on dopamine turnover in vivo and the blockade by these drugs of the DA-sensitive adenylate cyclase activity in vitro.