Thérèse Di Paolo

17β-estradiol at a physiological dose acutely increases dopamine turnover in rat brain

Ovariectomized rats injected with 17 beta-estradiol (30 ng, s.c.) showed an increase of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) with no change of dopamine concentrations in the striatum and nucleus accumbens. This increase was observed 30 min after the steroid injection and coincided with peak plasma 17 beta-estradiol concentrations. Plasma prolactin concentrations were not significantly elevated after 30 ng of 17 beta-estradiol. In ovariectomized rats with a unilateral lesion of the entopeduncular nucleus, the same dose of 17 beta-estradiol induced a postural deviation to the lesioned side with a maximum at 30 min. Thus, very small doses of estradiol were able to increase dopamine turnover. This effect was seen within minutes and was relatively short. It is probably non-genomic, presynaptic and similar to the effect of a small dose of a dopamine releasing agent.

Levodopa-induced motor complications are associated with alterations of glutamate receptors in Parkinson's disease.

Glutamate receptors were studied in the brains of controls and Parkinsons disease (PD) patients, of which 10 of 14 developed motor complications (dyskinesias and/or wearing-off) following levodopa therapy. (125)I-RTI binding to the dopamine transporter and dopamine concentrations show comparable nigrostriatal denervation between the subgroups of PD patients. (3)H-Ro 25-6981 binding to the NR1/NR2B NMDA receptor was increased in the putamen of PD patients experiencing motor complications compared to those who did not (+53%) and compared to controls (+18%) whereas binding remained unchanged in the caudate nucleus. (3)H-AMPA binding was increased in the lateral putamen (+23%) of PD patients with motor complications compared to those without whereas it was decreased in the caudate nucleus of the PD patients (-16%) compared to controls. Caudate and putamen (3)H-CGP39653 binding to NR1/NR2A NMDA receptor and NR1 subunit mRNA levels measured by in situ hybridization were unchanged in subgroups of PD patients compared to controls. These findings suggest that glutamate receptor supersensitivity in the putamen plays a role in the development of motor complications (both wearing-Off and dyskinesias) following long-term levodopa therapy in PD.

Neuroprotective actions of sex steroids in Parkinson's disease

The sex difference in Parkinsons disease, with a higher susceptibility in men, suggests a modulatory effect of sex steroids in the brain. Numerous studies highlight that sex steroids have neuroprotective properties against various brain injuries. This paper reviews the protective effects of sex hormones, particularly estradiol, progesterone and androgens, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinsons disease as compared to methamphetamine toxicity. The molecular mechanisms underlying beneficial actions of sex steroids on the brain have been investigated showing steroid, dose, timing and duration specificities and presently focus is on the dopamine signaling pathways, the next frontier. Both genomic and non-genomic actions of estrogen converge to promote survival factors and show sex differences. Neuroprotection by estrogen involves activation of signaling molecules such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. Interaction with growth factors, such as insulin-like growth factor 1, also contributes to protective actions of estrogen.

Control of ACTH Secretion by the Central Nucleus of the Amygdala: Implication of the Serotoninergic System and Its Relevance to the Glucocorticoid Delayed Negative Feedback Mechanism

The possible implication of the amygdaloid central nucleus (ACE) of the rat in the control of ACTH secretion in response to immobilization stress was assessed. The ACTH secretion, in response to stress and/or bilateral lesions of the ACE, was correlated with the serotoninergic activity in specific hypothalamic and amygdaloid nuclei. Bilateral lesions of the ACE produced a striking decrease of plasma ACTH levels in response to stress. However, basal plasma ACTH levels measured between 7 and 11 a.m. were identical in both control and lesioned groups. Stress, applied to intact animals, did not modify the serotoninergic activity in any of the following areas: hypothalamic paraventricular (PVH), ventromedial (VMH) and dorsomedial (DMH) nuclei; the anterior hypothalamic area (AHA); the lateral part of the basal amygdaloid nucleus (ABL), the amygdaloid medial (AME) and cortical (ACO) nuclei. However, lesion of the ACE increased the serotoninergic activity in all these structures except for the VMH. Immobilization stress applied to lesioned animals decreased the serotoninergic activity to control levels in the PVH, AHA and DMH and decreased the activity to below control levels in the VMH. The serotoninergic activity remained at an increased level in the glucocorticoid receptor-rich areas of the amygdala, namely the AME, ACO and ABL nuclei. These results provide evidence for a stimulatory role of the central nucleus of the amygdala in the control of ACTH secretion. Moreover, they substantiate an implication of the amygdaloid complex in the control of the delayed negative feedback of glucocorticoids on ACTH secretion via interaction with the serotoninergic system.

AFQ056 treatment of levodopa‐induced dyskinesias: Results of 2 randomized controlled trials

Study objectives were to assess the efficacy, safety, and tolerability of AFQ056 in Parkinsons disease patients with levodopa‐induced dyskinesia. Two randomized, double‐blind, placebo‐controlled, parallel‐group, in‐patient studies for Parkinsons disease patients with moderate to severe levodopa‐induced dyskinesia (study 1) and severe levodopa‐induced dyskinesia (study 2) on stable dopaminergic therapy were performed. Patients received 25–150 mg AFQ056 or placebo twice daily for 16 days (both studies). Study 2 included a 4‐day down‐titration. Primary outcomes were the Lang‐Fahn Activities of Daily Living Dyskinesia Scale (study 1), the modified Abnormal Involuntary Movement Scale (study 2), and the Unified Parkinsons Disease Rating Scale–part III (both studies). Secondary outcomes included the Unified Parkinsons Disease Rating Scale–part IV items 32–33. The primary analysis was change from baseline to day 16 on all outcomes. Treatment differences were assessed. Fifteen patients were randomized to AFQ056 and 16 to placebo in study 1; 14 patients were randomized to each group in study 2. AFQ056‐treated patients showed significant improvements in dyskinesias on day 16 versus placebo (eg, Lang‐Fahn Activities of Daily Living Dyskinesia Scale, P = .021 [study 1]; modified Abnormal Involuntary Movement Scale, P = .032 [study 2]). No significant changes were seen from baseline on day 16 on the Unified Parkinsons Disease Rating Scale‐part III in either study. Adverse events were reported in both studies, including dizziness. Serious adverse events (most commonly worsening of dyskinesias, apparently associated with stopping treatment) were reported by 4 AFQ056‐treated patients in study 1, and 3 patients (2 AFQ056‐treated patient and 1 in the placebo group) in study 2. AFQ056 showed a clinically relevant and significant antidyskinetic effect without changing the antiparkinsonian effects of dopaminergic therapy.

Ovarian steroids and selective estrogen receptor modulators activity on rat brain NMDA and AMPA receptors

Glutamate and glutamate receptors are well known to play a major excitatory role in the brain. Recent findings on ovarian steroids and selective estrogen receptor modulators (SERMs) activity on rat brain AMPA and NMDA receptors are reviewed. Ovarian steroid withdrawal by ovariectomy is without effect on NMDA and AMPA receptors in most brain regions, except in hippocampus, where it decreases NMDA receptor specific binding, compared to intact rat values. Estradiol treatment increases hippocampal NMDA receptor specific binding of ovariectomized rats while it decreases this binding in frontal cortex and striatum. Estradiol treatment has no effect on AMPA receptor specific binding in hippocampus, but decreases binding in frontal cortex, striatum and nucleus accumbens. Progesterone and estradiol+progesterone treatments decrease NMDA, but not AMPA receptors specific binding in frontal cortex compared to ovariectomized rats. No effect was observed in other brain regions. Tamoxifen and raloxifene are SERMs with varying effects on estrogen responses in mammary, bone and uterine tissues. Tamoxifen and raloxifene have estrogenic activity upon modulation of brain NMDA and AMPA receptors. Using specific ligands for binding autoradiography of NMDA receptor subunits and specific probes for subunits measured by in situ hybridization, it was shown that estradiol and SERMs modulate NR1 and NR2B subunits whereas the NR1/2A subunit remains unchanged. In summary, regional agonist estrogenic activity on brain AMPA and NMDA receptors of tamoxifen and raloxifene, like that of estradiol, is observed, whereas progesterone has limited effects or opposes the estradiol effect.

Rapid conversion of high into low striatal D2-dopamine receptor agonist binding states after an acute physiological dose of 17β-estradiol

Ovariectomized female rats injected with 17 beta-estradiol (100 ng, s.c.) showed, as previously observed, an increase of the dopamine (DA) metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) with no change of DA concentrations in the striatum. This increase was observed as soon as 15 min following the injection while plasma estradiol reached a peak of 78 pg/ml after 5 min and was significantly elevated until 45 min to ultimately return to control values at 60 min. We observed no significant change of the inhibition constants of high- and low-affinity D2 DA agonist binding sites and of the sum of high + low agonist DAergic agonist binding densities as detected by apomorphine competition of [3H]spiperone binding. By contrast, a significant conversion of high into low agonist affinity binding states was seen at 15 min (38.6% of conversion, P less than 0.05) and 30 min (40.0% of conversion, P less than 0.01) after the acute physiological steroid injection. Thus, very small doses of estradiol were able to rapidly increase DA turnover and modulate the striatal agonist affinity states of the D2 DA receptor. This effect of estradiol is probably non-genomic, presynaptic and may involve a membrane effect at the DA autoreceptor level.

Preproenkephalin mRNA expression in the caudate-putamen of MPTP monkeys after chronic treatment with the D2 agonist U91356A in continuous or intermittent mode of administration: comparison with L-DOPA therapy.

The effect of chronic treatment with the D2 dopamine agonist U91356A or L-DOPA therapy on the regulation of preproenkephalin (PPE) mRNA was investigated in the caudate-putamen of previously drug-naive cynomolgus monkeys Macaca fascicularis rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In MPTP monkeys, pulsatile treatment with either L-DOPA or U91356A relieved parkinsonian symptoms but caused progressive sensitization to treatment and, as expected, induced choreic dyskinesias. In contrast, U91356A given in a continuous mode led to partial behavioral tolerance without appearance of dyskinesias. Using in situ hybridization histochemistry, lesioning was shown to produce elevation of PPE mRNA levels in the lateral and medial parts of the putamen and in the lateral part of the caudate nucleus compared to control animals at the three rostrocaudal regions analyzed. In general, no change of PPE mRNA levels were observed in the medial caudate after MPTP lesioning with or without L-DOPA or U91356A treatments in the three rostrocaudal regions measured except for an increase in the caudal part of L-DOPA-treated MPTP monkeys. In the putamen and lateral caudate nucleus, elevated PPE mRNA expression by MPTP generally was not corrected (or only partially corrected) by chronic L-DOPA treatment except for the rostral medial putamen where correction to control values was observed. In general, pulsatile administration of U91356A partially corrected the lesion-induced elevation of PPE mRNA levels in the putamen and lateral caudate nucleus whereas the correction was more pronounced and widespread when MPTP monkeys received the continuous administration of this drug. These results indicate that the mode of administration of a D2 dopamine receptor agonist, such as U91356A, although at a roughly equivalent dosage influences the extent of inhibition of the expression of PPE in the denervated striatum of monkeys. In addition, the general lack of correction of the MPTP-induced increase of PPE mRNA in the striatum of L-DOPA-treated monkeys compared to the decreases observed with the D2 agonist treatments suggest that the D1 agonist component of L-DOPA therapy opposes the D2 agonist activity. Hence, D1 receptor agonist activity would stimulate PPE mRNA expression whereas D2 receptor agonists inhibit the expression of this peptide. Increases in PPE expression in the striatum may be implicated in the induction of dyskinesias since both groups of treated MPTP monkeys displaying dyskinesias had elevated striatal PPE mRNA levels whereas the MPTP monkeys with the lowest striatal PPE mRNA levels developed tolerance without dyskinesias.

Brain dopamine transporter : gender differences and effect of chronic haloperidol

Gender differences and the effect of chronic haloperidol on the rat brain dopamine transporter is reported. The density of striatal dopamine transporter sites labelled with [3H]GBR 12935, and of substantia nigra dopamine transporter mRNA measured by in situ hybridization were higher in female compared to male rats whereas striatal D2 specific binding labelled with [3H]spiperone was not significantly higher. Daily haloperidol treatment (1 mg/kg, i.p.) for 21 days increased striatal [3H]spiperone specific binding but left unchanged striatal [3H]GBR 12935 binding density and affinity as well as substantia nigra dopamine transporter mRNA levels. A reduce clearance rate of dopamine in the striatum after acute and chronic haloperidol was previously reported; the present results indicate that this may occur without changes in the sites of dopamine transport or in gene expression of this transporter.

Stereospecific prevention by 17?-estradiol of MPTP-induced dopamine depletion in mice

Neuroprotective activity of estrogens is reported in Alzheimer disease and recently has also been suggested for Parkinson disease, a disease affecting more men than women. To characterize this estrogenic activity, we studied the effects of 17β‐ and 17α‐estradiol treatment (1 μg twice daily 5 days before, during the day of four MPTP (15 mg/kg) injections, and for the following 5 days) on dopamine striatal toxicity induced by the neurotoxin MPTP in retired breeder male C57BL/6 mice. Striatal dopamine concentrations and its metabolites dihydroxyphenylacetic acid and homovanillic acid measured by HPLC in MPTP mice that received 17β‐estradiol were comparable to control animals, whereas MPTP mice treated with saline or 17α‐estradiol showed important decreases of dopamine and its metabolites. Striatal serotonin and its metabolite 5‐hydroxyindoleacetic acid concentrations remained unchanged after MPTP and treatments with steroids. Striatal [3H]GBR 12935 binding autoradiography to the dopamine transporter was as extensively decreased and correlated with dopamine depletion in MPTP mice, whereas this transporter mRNA decrease in the substantia nigra pars compacta was less pronounced. Treatment with steroids did not significantly change [3H]GBR 12935 binding, whereas dopamine transporter mRNA levels were not significantly different from controls. Under the present paradigm in retired breeder male mice, our results show dopaminergic and stereospecificity of estradiol to augment dopamine levels in MPTP‐lesioned mice without protecting against the extensive loss of dopamine terminals and moderate cell body loss. Synapse 37:245–251, 2000.