Prolactin response as an index of dopaminergic receptor function in Parkinson's disease. Correlation with clinical findings and therapeutic response

CuATSM effectively ameliorates ALS patient astrocyte-mediated motor neuron toxicity in human in vitro models of amyotrophic lateral sclerosis

Patient diversity and unknown disease cause are major challenges for drug development and clinical trial design for amyotrophic lateral sclerosis (ALS). Transgenic animal models do not adequately reflect the heterogeneity of ALS. Direct reprogramming of patient fibroblasts to neuronal progenitor cells and subsequent differentiation into patient astrocytes allows rapid generation of disease relevant cell types. Thus, this methodology can facilitate compound testing in a diverse genetic background resulting in a more representative population for therapeutic evaluation. Here, we used established co-culture assays with motor neurons and reprogrammed patient skin-derived astrocytes (iAs) to evaluate the effects of (SP-4-2)-[[2,2'-(1,2-dimethyl-1,2-ethanediylidene)bis[N-methylhydrazinecarbothioamidato-κN² ,κS]](2-)]-copper (CuATSM), currently in clinical trial for ALS in Australia. Pretreatment of iAs with CuATSM had a differential effect on neuronal survival following co-culture with healthy motor neurons. Using this assay, we identified responding and non-responding cell lines for both sporadic and familial ALS (mutant SOD1 and C9ORF72). Importantly, elevated mitochondrial respiration was the common denominator in all CuATSM-responders, a metabolic phenotype not observed in non-responders. Pre-treatment of iAs with CuATSM restored mitochondrial activity to levels comparable to healthy controls. Hence, this metabolic parameter might allow selection of patient subpopulations best suited for CuATSM treatment. Moreover, CuATSM might have additional therapeutic value for mitochondrial disorders. Enhanced understanding of patient-specific cellular and molecular profiles could help improve clinical trial design in the future.

Association between Serum Prolactin Levels and Neurodegenerative Diseases: Systematic Review and Meta-Analysis

INTRODUCTION

Prolactin (PRL) exerts inflammatory and anti-inflammatory properties and is also thought to play an important role in the pathogenesis of neurodegenerative diseases (NDs). However, serum PRL levels in patients with NDs were inconsistent in the research literature.

OBJECTIVE

We aimed to assess the serum PRL levels in patients with NDs.

METHODS

Electronic databases, including MEDLINE, Embase, Cochrane Library database, clinicaltrials.gov, Web of Science, and Google Scholar, and reference lists of articles were searched up to December 31, 2020. Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated by fixed-effect or random-effect model analysis.

RESULTS

A total of 36 comparisons out of 29 studies (3 RCTs and 26 case controls) focusing on NDs (including Parkinson's disease, Alzheimer's disease, Huntington's disease [HD], multiple sclerosis [MS], and epilepsy) were reported. The meta-analysis showed that there was no statistically significant difference in serum PRL levels between patients with NDs and healthy controls (SMD = 0.40, 95% CI: -0.16 to 0.96, p = 0.16). Subgroup analysis showed that serum PRL levels in patients with HD and MS were higher than those of healthy controls. Furthermore, patients with NDs aged <45 years had higher serum PRL levels (SMD = 0.97, 95% CI: 0.16-1.78, p = 0.018) than healthy controls. High serum PRL levels were found in subgroups such as the microenzymatic method, Asia, and the Americas.

CONCLUSIONS

Our meta-analysis showed serum PRL levels in patients with HD and MS were significantly higher than those in healthy controls. Serum PRL levels were associated with age, region, and detection method. Other larger sample studies using more uniform detection methods are necessary to confirm our results.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

Non-invasive diagnostic tool for Parkinson's disease by sebum RNA profile with machine learning

Parkinson's disease (PD) is a progressive neurodegenerative disease presenting with motor and non-motor symptoms, including skin disorders (seborrheic dermatitis, bullous pemphigoid, and rosacea), skin pathological changes (decreased nerve endings and alpha-synuclein deposition), and metabolic changes of sebum. Recently, a transcriptome method using RNA in skin surface lipids (SSL-RNAs) which can be obtained non-invasively with an oil-blotting film was reported as a novel analytic method of sebum. Here we report transcriptome analyses using SSL-RNAs and the potential of these expression profiles with machine learning as diagnostic biomarkers for PD in double cohorts (PD [n = 15, 50], controls [n = 15, 50]). Differential expression analysis between the patients with PD and healthy controls identified more than 100 differentially expressed genes in the two cohorts. In each cohort, several genes related to oxidative phosphorylation were upregulated, and gene ontology analysis using differentially expressed genes revealed functional processes associated with PD. Furthermore, machine learning using the expression information obtained from the SSL-RNAs was able to efficiently discriminate patients with PD from healthy controls, with an area under the receiver operating characteristic curve of 0.806. This non-invasive gene expression profile of SSL-RNAs may contribute to early PD diagnosis based on the neurodegeneration background.

Neuroendocrinology and neurobiology of sebaceous glands

The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro-regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α-melanocyte-stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro-autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin-mediated or facial paresis-associated reduction of human sebum secretion suggests that cutaneous nerve-derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin.

Prolactin and sex hormones levels in males with Parkinson's disease

BACKGROUND

The role that oestradiol and testosterone play in Parkinson's disease and their potential to influence the course of the disease has been covered in medical literature. The aim of this work was to compare oestradiol, testosterone, sex hormone-binding protein and prolactin blood levels in males affected with Parkinson's disease and in an age-matched control group, and to show possible dependence between concentrations of plasma hormones and the progression of symptoms of Parkinson's disease.

METHODS

The plasma levels of oestradiol, testosterone, prolactin and sex hormone-binding protein were examined in 36 patients affected with Parkinson's disease and in 69 age-matched control subjects, using chemiluminescent reactions. Patients with Parkinson's disease were examined using scales assessing their clinical state.

RESULTS

The level of prolactin was higher in the affected group. Concentrations of oestradiol and testosterone in the control group exceeded those found in patients. The level of sex hormones was positively correlated with better mood and quality of life in patients affected with Parkinson's disease; prolactin levels correlated negatively with sex steroid concentrations.

CONCLUSIONS

Lower blood levels of sex steroids and higher concentrations of prolactin and its antigonadotrophic activity in males affected with Parkinson's disease may result in a bigger susceptibility to the disease in men. The level of hormones may influence patients' cognition, mood and quality of life.

Monoamine reuptake inhibitors in Parkinson's disease

The motor manifestations of Parkinson's disease (PD) are secondary to a dopamine deficiency in the striatum. However, the degenerative process in PD is not limited to the dopaminergic system and also affects serotonergic and noradrenergic neurons. Because they can increase monoamine levels throughout the brain, monoamine reuptake inhibitors (MAUIs) represent potential therapeutic agents in PD. However, they are seldom used in clinical practice other than as antidepressants and wake-promoting agents. This review article summarises all of the available literature on use of 50 MAUIs in PD. The compounds are divided according to their relative potency for each of the monoamine transporters. Despite wide discrepancy in the methodology of the studies reviewed, the following conclusions can be drawn: (1) selective serotonin transporter (SERT), selective noradrenaline transporter (NET), and dual SERT/NET inhibitors are effective against PD depression; (2) selective dopamine transporter (DAT) and dual DAT/NET inhibitors exert an anti-Parkinsonian effect when administered as monotherapy but do not enhance the anti-Parkinsonian actions of L-3,4-dihydroxyphenylalanine (L-DOPA); (3) dual DAT/SERT inhibitors might enhance the anti-Parkinsonian actions of L-DOPA without worsening dyskinesia; (4) triple DAT/NET/SERT inhibitors might exert an anti-Parkinsonian action as monotherapy and might enhance the anti-Parkinsonian effects of L-DOPA, though at the expense of worsening dyskinesia.

An antibody microarray analysis of serum cytokines in neurodegenerative Parkinsonian syndromes

BACKGROUND

Microarray technology may offer a new opportunity to gain insight into disease-specific global protein expression profiles. The present study was performed to apply a serum antibody microarray to screen for differentially regulated cytokines in Parkinson's disease (PD), multiple system atrophy (MSA), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS).

RESULTS

Serum samples were obtained from patients with clinical diagnoses of PD (n = 117), MSA (n = 31) and PSP/CBS (n = 38) and 99 controls. Cytokine profiles of sera from patients and controls were analyzed with a semiquantitative human antibody array for 174 cytokines and the expression of 12 cytokines was found to be significantly altered. In a next step, results from the microarray experiment were individually validated by different immunoassays. Immunoassay validation confirmed a significant increase of median PDGF-BB levels in patients with PSP/CBS, MSA and PD and a decrease of median prolactin levels in PD. However, neither PDGF-BB nor prolactin were specific biomarkers to discriminate PSP/CBS, MSA, PD and controls.

CONCLUSIONS

In our unbiased cytokine array based screening approach and validation by a different immunoassay only two of 174 cytokines were significantly altered between patients and controls.

Diurnal secretion profiles of growth hormone, thyrotrophin and prolactin in Parkinson's disease

Recently, a massive loss of both hypocretin and melanin-concentrating hormone (MCH) neurones was found in the hypothalamus of Parkinson's disease (PD) patients. Because both hypocretin and MCH play a key role in the regulation of sleep, energy homeostasis and autonomic function, partly by modulation of the somatotrophic, thyrotrophic and lactotrophic axes, neuroendocrine dysregulation may contribute to some of the non-motor features of PD. In eight de novo, medication-free PD patients and eight age-, sex- and body mass index-matched controls, we measured serum levels of growth hormone (GH), thyroid-stimulating hormone (TSH) and prolactin every 10 min for 24 h. Auto-deconvolution, cosinor and approximate entropy analysis were applied to quantify GH, TSH and prolactin secretion rates, diurnal rhythmicity, as well as regularity of hormone release. Sleep was polygraphically-recorded throughout the night. Total 24-h secretion of GH (191 ± 31 versus 130 ± 39 mU/l/24 h), TSH (38 ± 9 versus 36 ± 2 mU/l/24 h) and prolactin (102 ± 14 versus 116 ± 17 μg/l/24 h), as well as their diurnal rhythmicity and regularity of release, were not significantly different between PD patients and controls (all P ≥ 0.12). Fasting levels of insulin-like growth factor-1 were also unaltered in PD patients. However, free thyroxine (T(4) ) levels were significantly higher in PD patients compared to controls (16.19 ± 0.80 versus 13.88 ± 0.40 pmol/l; P = 0.031). In PD patients, prolactin levels were related to disease duration (r = 0.76, P = 0.028), whereas both GH (r = -0.91, P = 0.002) and free T(4) (r = -0.71, P = 0.050) levels correlated inversely with body fat content. Apart from a mild increase in free T(4) levels, we found no indications for altered somatotrophic, thyrotrophic and lactotrophic axes activity in early-stage PD patients.

Medical causes and consequences of hyperprolactinaemia. A context for psychiatrists

Hyperprolactinaemia is the commonest endocrine disorder of the hypothalamic-pituitary axis and can lead to both short-term sexual dysfunction and galactorrhoea, and long-term loss of bone mineral density. Prolactin is secreted from the anterior pituitary gland under the influence of dopamine, which exerts a tonic inhibitory effect on prolactin secretion. Physiological regulators of prolactin secretion include many different types of 'stress' and sleep. Disruption of the normal control of prolactin secretion results in hyperprolactinaemia from pathological and pharmacological causes. The administration of antipsychotic medication is responsible for the high prevalence of hyperprolactinaemia in people with severe mental illness. Physiological hyperprolactinaemia, such as pregnancy and lactation, should be distinguished from pathological causes to prevent unnecessary investigation and treatment. The causes, consequences and management of hyperprolactinaemia are discussed in this article.

Biologic rhythms and Parkinson's disease: a chronopharmacologic approach to considering fluctuations in function

The existence of circadian rhythms and their implication in many pathologic processes have been underlined in several diseases but have not been evaluated in Parkinson's disease. The aim of this paper is to review diurnal variations of clinical, biologic, or experimental factors described with Parkinson's disease. Clinical data often report daily fluctuations of motor activity pattern, but the effect of the stage of the disease and the respective roles of drugs are difficult to evaluate. Sleep disturbances in Parkinson's disease patients also reveal alterations of circadian rhythms. Autonomic dysfunction, described in Parkinson's disease, reveals numerous alterations in circadian regulations including loss of circadian rhythm of blood pressure, increased diurnal blood pressure variability, and postprandial hypotension. Many biologic indices such as cortisol, catecholamines, and melatonin are also altered. Circadian rhythms in dopaminergic systems as well as possible daily fluctuations in kinetics of drug treatments are likely involved in such variations. Few clinical studies have been devoted to circadian patterns of drug response. As for other diseases where biologic rhythms are concerned Parkinson's disease therapy may be influenced by further understanding of circadian influence.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Effect of treatment with L-deprenyl on age-dependent microanatomical changes in the rat kidney

The influence of aging and of treatment with L-deprenyl on the structure of the kidney was investigated in 24-month-cld male Sprague Dawley rats by microanatomical techniques associated with image analysis. L-Deprenyl was administrated orally for 5 months at a dose not inhibiting monoamine oxidase (MAO) B activity (1.25/mg/kg/day) and at a dose inhibiting MAO B activity (5 mg/kg/day). In 24 month-old-rats the number and the volume of glomeruli was reduced in comparison with 12-month-old rats used as reference adult animals. Vascular changes characterised by increased thickness of the tunica media, decreased size of arterial lumen and increased wall-to-lumen ratio were also noticeable in 24-month-old rats. Moreover, an increased MAO B reactivity was noticeable within glomerular tufts and renal tubules. Treatment with the low dose of L deprenyl did not cause changes in MAO B reactivity, or in the number of glomeruli, but increased glomerular volume and reduced the wall-to-lumen ratio in medium-sized renal artery branches. The dose of 5 mg/kg/day of L-deprenyl significantly decreased MAO B reactivity within both glomerular tufts and tubules, increased the number and the volume of glomeruli and countered-age-related vascular changes. The above results suggest that treatment with L-deprenyl counters to some extent microanatomical changes occurring in the kidney of aged rats. The observation that the dose of the compound inactive on MAO B activity reduces in part age dependent renal microanatomical changes, indicates that the renal protective effect of L-deprenyl is only in part related to MAO B inhibition.

A review of the effects of dopaminergic agents on humans, animals, and drug-seeking behavior, and its implications for medication development. Focus on GBR 12909

Medication development for cocaine abuse has focused on potential mechanisms of action related to the abuse of cocaine. The hypothesis that mesolimbic dopamine (DA) is the key neurochemical mediator of cocaine's addictive and reinforcing effects is well supported by a wide variety of data from animal studies. On the other hand, medications that increase DA or block its action in humans can produce effects that appear incompatible with this hypothesis. This article reviews these incompatibilities between animal and human data with a focus on the DAergic actions of drugs, including DA reuptake inhibitors, direct DA agonists, DA increasers, and DA antagonists. Possible reasons for these discrepancies are discussed, and the potential role of high-affinity DA uptake inhibitors, such as GBR12909, for pharmacotherapies for treating cocaine addiction in humans is likely to come from understanding its mechanisms of action, it is clear that further research on the effects of cocaine in humans and animals will be critical to the medication development effort.

Cortisol, ACTH, and beta-endorphin after dexamethasone administration in Parkinson's dementia

The dexamethasone suppression test (DST) has been suggested as an effective tool for differentiating between depression and dementia. After administering 1 mg dexamethasone, we measured cortisol, ACTH, and beta-endorphin levels in 32 nondepressed patients with idiopathic Parkinson's disease (PD) (14 also with dementia) and 20 healthy, age-matched controls. Four of the 20 controls, 9 of the 18 with PD alone, and 8 of the 14 with PD and dementia were dexamethasone nonsuppressors (cortisol value greater than or equal to 5 micrograms/100 ml). PD patients without dementia (nonsuppressors) showed higher basal plasma values of cortisol (22.06 +/- 5.30 micrograms/100 ml) compared with the suppressors (13.38 +/- 3.30 micrograms/100 ml). Plasma ACTH and beta-endorphin responded in a coupled way to dexamethasone challenge. Higher basal levels of both peptides were found among PD patients (demented and nondemented), nonresponders to DST. Thus, the DST does not appear to be effective in differentiating between depression and dementia in PD. In addition, PD nonsuppressors showed higher basal values of plasma ACTH, beta-endorphin, and cortisol (similar to patients with major depression). This suggests that although the depression is clinically undetectable, both disorders may share some pathophysiological features at the hypothalamic hypophyseal adrenal level.

Growth hormone responses to growth hormone releasing factor in primary degenerative dementia

The growth hormone (GH), thyroid-stimulating hormone (TSH), and prolactin (PRL) responses to growth hormone releasing factor (GRF) were investigated in 18 patients suffering from primary degenerative dementia (PDD) and in 20 age- and sex-matched normal elderly controls. There was no significant difference in the growth hormone response to GRF stimulation between patients and controls, and in neither subject group was there a demonstrable TSH or prolactin response to GRF. These findings indicate that the pathophysiology underlying the blunted growth hormone response to pharmacological challenge in PDD must lie at a suprapituitary level.

The circadian rhythms of thyrotrophin and prolactin secretion

As with other anterior pituitary hormones, the secretion of both thyrotrophin (TSH) and prolactin (PRL) displays a circadian variation with different patterns for each hormone. In recent years there has been a substantial increase in the understanding of the neuroregulation of TSH and PRL. However the primary events involved in the generation of their circadian rhythms remains unclear. Regulatory pathways comprise two major groups: central factors, where the control is exerted by the central nervous system via the hypothalamus and peripheral factors, which include all extra CNS mechanisms. The first group is represented mainly by neuropeptides and neurotransmitters controlling TSH and PRL release, whereas the second one comprises both physical phenomena such as variations in plasma volume or postural changes and hormonal influences arising from target glands such as the adrenal, the thyroid and the gonads.

Effect of hypoglycaemia, TRH and levodopa on plasma growth hormone, prolactin, thyrotropin and cortisol in Parkinson's disease before and during therapy

Thirteen drug-free and not severely affected patients with idiopathic Parkinson's disease underwent an insulin-hypoglycaemia test, a TRH test and a levodopa test. The responses of growth hormone, prolactin, cortisol and thyrotropin were measured, and retested under stable therapy with levodopa and benserazide. Mean basal and stimulated hormonal concentrations were in the normal range before and during therapy. Minor abnormalities were observed in individual cases, but did not indicate a hypothalamic dopamine deficit.

Dexamethasone suppression test and serum prolactin in dementia disorders

The dexamethasone suppression test (DST) was performed on 21 patients with dementia of the Alzheimer type (DAT), 11 patients with multi-infarct dementia (MI) and 14 healthy controls. Twelve of the DAT patients and eight of the MI patients showed abnormal lack of suppression, compared with just one member of the control group. Abnormal DST was related to dementia as such and not to age or depression, or to levels of CSF monoamine metabolites. Basal serum prolactin concentrations were not increased.

Serum prolactin response to chlorpromazine and psychopathology in schizophrenics: implications for the dopamine hypothesis

The prolactin (PRL) response to 12.5 and 25 mg of chlorpromazine (CPZ) was studied in unmedicated schizophrenic patients and normal control subjects. Both doses produced significant increases in serum PRL levels compared to saline, but the response to 25 mg CPZ was significantly greater than that to 12.5 mg. The PRL response to the 12.5 mg dose only was significantly correlated with baseline PRL levels for both males and females, suggesting that endogenous dopamine release from tuberoinfundibular neurons has a much greater effect upon the PRL response to the 12.5 mg dose of CPZ than to the 25 mg dose. Both doses of CPZ tended to show lower PRL responses in the schizophrenic females. The PRL response to the 25 mg dose was negatively correlated with ratings of severity of delusions at the time of study. The PRL response to 25 mg correlated highly with the morning serum PRL levels following treatment with CPZ 100 mg and 200 mg orally b.i.d. for 1 week at each dose. The PRL response to both doses did not predict clinical response at the end of 2 weeks of treatment with fixed dosages of CPZ. Serum PRL levels during treatment with CPZ 200 mg b.i.d. were significantly negatively correlated with ratings of hallucinations. The negative correlations between severity of delusions and hallucinations and various PRL measures suggest that increased dopaminergic activity in the tuberoinfundibular hypothalamic-pituitary axis may be associated with increased activity of subcortical and cortical dopaminergic systems.