Dopaminergic D2 Receptors Research Articles

Consequence of dopamine D2 receptor blockade on the hyperphagic effect induced by cannabinoid CB1 and CB2 receptors in layers

ABSTRACT1. Endocannabinoids (ECBs) and their receptors play a regulatory function on several physiological processes such as feed-intake behaviour, mainly in the brain. This study was carried out in order to investigate the effects of the dopaminergic D1 and D2 receptors on CB1/CB2 ECB receptor-induced hyperphagia in 3-h feed-deprived neonatal layer chickens.2. A total of 8 experiments were designed to explore the interplay of these two modulatory systems on feed intake in neonatal chickens. In Experiment 1, chickens were intracerebroventricular (ICV) injected with control solution, l-DOPA (levo-dihydroxyphenylalanine as precursor of dopamine; 125 nmol), 2-AG (2-arachidonoylglycerol as CB1 receptor agonist; 2 µg) and co-administration of l-DOPA (125 nmol) plus 2-AG (2 µg). Experiments 2–4 were similar to Experiment 1 except birds were injected with either 6-OHDA (6-hydroxydopamine as dopamine synthesis inhibitor; 150 nmol), SCH23390 (D1 receptor antagonist; 5 nmol) and AMI-193 (D2 receptor antagonist; 5 nmol) instead of l-DOPA, respectively. Additionally, Experiments 5–8 followed the previous ones using the same dose of l-DOPA, 6-OHDA and dopamine antagonists except that birds were injected with CB65 (CB2 receptor agonist; 5 µg) instead of 2-AG. Coadministrations were at the same dose for each experiment. Cumulative feed intakes were measured until 120 min after each injection.3. ICV administration of 6-OHDA and AMI-193 significantly attenuated 2-AG-induced hyperphagia. Interestingly, the hyperphagic effect of CB65 was significantly attenuated by administration of l-DOPA, whereas the administration of 6-OHDA and AMI-193 together amplified the hyperphagic effect of CB65.4. It was concluded that cannabinoid-induced feeding behaviour is probably modulated by dopamine receptors in neonatal layer-type chickens. It seems that their interaction may be mediated by the D2-dopamine receptor.

The role of dopamine D2 receptors in the nucleus accumbens during taste-aversive learning and memory extinction after long-term sugar consumption

The nucleus accumbens (NAcc) is a forebrain region that may significantly contribute to the integration of taste and visceral signals during food consumption. Changes in dopamine release in the NAcc have been observed during consumption of a sweet taste and during compulsive consumption of dietary sugars, suggesting that NAcc dopaminergic transmission is strongly correlated with taste familiarity and the hedonic value content. NAcc core and shell nuclei are differentially involved during and after sugar exposure and, particularly, previous evidence suggests that dopamine D2 receptors could be related with the strength of the latent inhibition (LI) of conditioned taste aversion (CTA), which depends on the length of the taste stimulus pre-exposure. Thus, the objective of this work was to evaluate, after long-term exposure to sugar, the function of dopaminergic D2 receptors in the NAcc core during taste memory retrieval preference test, and during CTA. Adult rats were exposed during 14days to 10% sugar solution as a single liquid ad libitum. NAcc core bilateral injections of D2 dopamine receptor antagonist, haloperidol (1μg/μL), were made before third preference test and CTA acquisition. We found that sugar was similarly preferred after 3 acute presentations or 14days of continued sugar consumption and that haloperidol did not disrupt this appetitive memory retrieval. Nevertheless, D2 receptors antagonism differentially affects aversive memory formation after acute or long-term sugar consumption. These results demonstrate that NAcc dopamine D2 receptors have a differential function during CTA depending on the degree of sugar familiarity.

The wake-promoting drug Modafinil prevents motor impairment in sickness behavior induced by LPS in mice: Role for dopaminergic D1 receptor

The wake-promoting drug Modafinil has been used for many years for treatment of Narcolepsy and Excessive Daytime Sleepiness, due to a dopamine-related psychostimulant action. Recent studies have indicated that Modafinil prevents neuroinflammation in animal models. Thus, the aim of the present study was to evaluate the effect of Modafinil pretreatment in the Lipopolysaccharide (LPS)-induced sickness and depressive-like behaviors. Adult male C57BL/6J mice were pretreated with Vehicle or Modafinil (90mg/Kg) and, 30min later, received a single saline or LPS (2mg/Kg) administration, and were submitted to the open field and elevated plus maze test 2h later. After 24h, mice were subjected to tail suspension test, followed by either flow cytometry with whole brain for CD11b+CD45+ cells or qPCR in brain areas for cytokine gene expression. Modafinil treatment prevented the LPS-induced motor impairment, anxiety-like and depressive-like behaviors, as well as the increase in brain CD11b+CD45high cells induced by LPS. Our results indicate that Modafinil pretreatment also decreased the IL-1β gene upregulation caused by LPS in brain areas, which is possibly correlated with the preventive behavioral effects. The pharmacological blockage of the dopaminergic D1R by the drug SCH-23390 counteracted the effect of Modafinil on locomotion and anxiety-like behavior, but not on depressive-like behavior and brain immune cells. The dopaminergic D1 receptor signaling is essential to the Modafinil effects on LPS-induced alterations in locomotion and anxiety, but not on depression and brain macrophages. This evidence suggests that Modafinil treatment might be useful to prevent inflammation-related behavioral alterations, possibly due to a neuroimmune mechanism.

Antisecretory Effects of Chimeric Somatostatin/Dopamine Receptor Ligands on Gastroenteropancreatic Neuroendocrine Tumors.

The recent finding that gastroenteropancreatic neuroendocrine tumors expressed the dopaminergic D2 receptor in addition to somatostatin (sst) receptors suggested that multiple targeting approaches might decrease hormone hypersecretion more effectively than sst agonists alone. To test this hypothesis, (i) we measured the expression of sst receptor type 2 (sst2 receptor) and D2 receptor in 11 gastroenteropancreatic neuroendocrine tumors and (ii) we compared the ability of lanreotide, cabergoline, their combination, and sst/D2 chimeric ligands to decrease chromogranin A (CgA), gastrin, or serotonin release in primary cultures derived from these tumors. Moderate to high positivity was observed for sst2 receptor and D2 receptor, the latter being more expressed in pancreatic tumors. Lanreotide decreased CgA secretion in all cultures, but only 3 tumors responded to cabergoline. No additivity was observed in lanreotide. BIM 23A781 decreased CgA release to the same extent as lanreotide, whereas the other chimeric ligands were less efficient. However, BIM 23A781 was 50 times less potent than lanreotide. Similar patterns were found for gastrin or serotonin. No improvement was brought by the sst/D2 combination or chimeric ligands. Factors that underlie these tissue-specific differences remain to be elucidated.

Activation of angiotensin II type 1 receptors increases D4 dopamine receptor expression in rat renal proximal tubule cells.

Both the dopaminergic and renin-angiotensin systems play important roles in the regulation of blood pressure. Our previous study showed that the stimulation of dopaminergic D4 receptors reduced angiotensin II type 1 (AT1) receptor expression in renal proximal tubule (RPT) cells. In this study, we tested whether AT1 receptors, in return, would regulate D4 receptor expression and function in RPT cells. Expression of the D4 receptor from Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHRs) RPT cells and renal cortex tissues were determined by western blot, and Na+-K+ ATPase activity was determined using an enzyme assay. Urine volume and urine sodium of WKY rats and SHRs treated with or without D4 receptor stimulation were measured. Thus, activation of AT1 receptors with angiotensin II (Ang II) increased D4 receptor protein expression in RPT cells, and this increase was blocked by nicardipine, a calcium influx blocker. The D4 receptor agonist PD168077 inhibited Na+-K+ ATPase activity in WKY RPT cells but not in SHR RPT cells. Ang II pre-treatment promoted D4 receptor-mediated inhibition of Na+-K+ ATPase in RPT cells in WKY rats but not in SHRs. Meanwhile, Ang II pre-treatment augmented the natriuretic effect of PD168077 in WKY rats but not in SHRs. In conclusion, AT1 stimulation can regulate the expression and natriuretic function of dopaminergic D4 receptors in RPT cells and might be involved in the pathogenesis of essential hypertension.

Visualizing the Competition between Gs and Gi Signaling at the Membrane

At the cell membrane, G-protein coupled receptors couple to a variety of signaling pathways. The Gs and Gi pathways compete to stimulate, or inhibit, adenyl cyclases at the membrane, regulating the levels of cAMP within the cell. Our goal was to create a genetically encoded, fluorescent biosensor to detect, in real time, this competition. We created a new generation of the cADDis cAMP biosensor which is remarkably bright and can be used to detect Gs signaling kinetics in fluorescence microscopes and fluorescence plate readers with a Z’ statistic of 0.9 or greater. The next step was to determine if cADDis could be used to detect Gi signaling. A variety of Gi-coupled receptors were expressed in HEK293 cells, but known agonists produced no detectable change in cADDis fluorescence. Reasoning that this was due to low basal adenylyl cyclase activity, we increased Gs signaling using the controlled co-expression of a constitutively active Gs mutant. In this context, the cADDis sensor showed large changes in fluorescence, reported EC50 values consistent with literature, and yielded high Z’ values in a standard automated fluorescence plate reader.To test whether cADDis can detect the competition between Gs and Gi, we first stimulated a Gs pathway and then followed with Gi-coupled receptor activation. The cADDis sensor reports the Gi mediated inhibition of the Gs response. The opposite experiment works as well. While the competition between Gs and Gi is easily measured, the competition between Forskolin and the Gi pathway produces inconsistent results with different kinetics. This was particularly true for the Adenosine 1 and D2-dopaminergic receptors, which produced robust Gi responses in HEK293 cells when cAMP was elevated with the Gs mutant or isoproterenol, but failed to produce a response in the presence of forskolin.

The role of central and peripheral D2R receptors in the mechanism of colonic vascular permeability during experimental colitis in rats

We investigated the involvement of central and peripheral D2 dopaminergic receptors in the mechanism of vascular permeability in rat's colon during experimental ulcerative colitis. Ulcerative colitis was induced in male white inbred rats by 6 % iodoacetamide enema. For the investigation of central and peripheral D2R, separate and joint injections of D2R antagonist domperidone (2 mg/100 g, per os) and D2R agonist quinpirole (1 mg/100 g, per os) were applied. Central D2R were destroyed by neurotoxin injection – 6OHDA. Colonic vascular permeability was measured by colonic extravasation of 1,5 % Evans blue. It was observed that blockade of peripheral D2R decreased colonic vascular permeability, while simultaneous activation of central D2R and inhibition of peripheral D2R have additive positive effect in prevention of increased colonic vascular permeability during experimental colitis.

Coupling of D2R Short but not D2R Long receptor isoform to the Rho/ROCK signaling pathway renders striatal neurons vulnerable to mutant huntingtin

Huntington's disease, an inherited neurodegenerative disorder, results from abnormal polyglutamine extension in the N-terminal region of the huntingtin protein. This mutation causes preferential degeneration of striatal projection neurons. We previously demonstrated, invitro, that dopaminergic D2 receptor stimulation acted in synergy with expanded huntingtin to increase aggregates formation and striatal death through activation of the Rho/ROCK signaling pathway. In vivo, in a lentiviral-mediated model of expanded huntingtin expression in the rat striatum, we found that the D2 antagonist haloperidol protects striatal neurons against expanded huntingtin-mediated toxicity. Two variant transcripts are generated by alternative splicing of the of D2 receptor gene, the D2R-Long and the D2R-Short, which are thought to play different functional roles. We show herein that overexpression of D2R-Short, but not D2R-Long in cell lines is associated with activation of the RhoA/ROCK signaling pathway. In striatal neurons in culture, the selective D2 agonist Quinpirole triggers phosphorylation of cofilin, a downstream effector of ROCK, which is abrogated by siRNAs that knockdown both D2R-Long and D2R-Short, but not by siRNAs targeting D2R-Long alone. Aggregate formation and neuronal death induced by expanded huntingtin, were potentiated by Quinpirole. This D2 agonist-mediated effect was selectively inhibited by the siRNA targeting both D2R-Long and D2R-Short but not D2R-Long alone. Our data provide evidence for a specific coupling of D2R-Short to the RhoA/ROCK/cofilin pathway, and its involvement in striatal vulnerability to expanded huntingtin. A new route for targeting Rho-ROCK signaling in Huntington's disease is unraveled with our findings.

Frontline Science: D1 dopaminergic receptor signaling activates the AMPK-bioenergetic pathway in macrophages and alveolar epithelial cells and reduces endotoxin-induced ALI.

Catecholamines, including β-adrenergic and dopaminergic neurotransmitters, have an essential role in regulating the "fight or flight" reflex and also affects immune cell proinflammatory action. However, little is known about whether catecholamines prevent dysfunction of metabolic pathways associated with inflammatory organ injury, including development of acute lung injury (ALI). We hypothesize that selected catecholamines may reduce metabolic alterations in LPS-stimulated macrophages and in the lungs of mice subjected to endotoxin-induced ALI, a situation characterized by diminished activity of AMP-activated protein kinase (AMPK). We found that activation of the dopamine 1 receptor (D1R) with fenoldopam, but not stimulation of adrenergic receptors with norepinephrine, resulted in a robust activation of AMPK in peritoneal macrophages, human monocytes, or alveolar epithelial cells (AECs). Such AMPK activation was mediated by a phospholipase C (PLC)-dependent mechanism. Unlike norepinephrine, D1R activation also prevented Thr172-AMPK dephosphorylation and kinase inactivation in LPS-treated macrophages. Furthermore, we show that a culture of AECs with either fenoldopam or the AMPK activator metformin effectively diminished IL-1β-induced release of adverse paracrine signaling, which promotes the macrophage proinflammatory response. In vivo, fenoldopam reduced the severity of LPS-induced ALI, including development of pulmonary edema, lung permeability, and production of inflammatory cytokines TNF-α, MIP-2, or KC and HMGB1. Fenoldopam also prevented AMPK dephosphorylation in the lungs of LPS-treated mice and prevented loss of mitochondrial complexes NDUFB8 (complex I) and ATP synthase (complex V). Collectively, these results suggest that dopamine is coupled to AMPK activation, which provides a substantial anti-inflammatory and bioenergetic advantage and reduces the severity of endotoxin-induced ALI.

P.1.g.044 - New molecular insights into the mechanism of lithium action at the dopaminergic D2 receptor

P.1.g.044 - New molecular insights into the mechanism of lithium action at the dopaminergic D2 receptor

Evidence of sexual dimorphism in D1 and D2 dopaminergic receptors expression in frontal cortex and striatum of young rats

D1 and D2 receptors are key mediators of dopaminergic signaling in the brain, and since the manifestations of pathologies related to dopamine are different in female and male patients, it is important to analyze if there are sex-related differences in dopaminergic markers. To contribute to the knowledge in this regard, the objective of this report was to characterize the particular expression level of D1 and D2 dopamine receptors in young male and female rats. Striatum (STR) and frontal cortex (CTX) were obtained from intact 30-days old animals, and the D1 and D2 expression level was analyzed by Western blot. The results show a greater expression of D1, but less of D2, in female CTX compared with males, whereas in STR, both D1 and D2 receptors shows predominance in females. These results support the evidence of dimorphic expression in dopaminergic markers, outside of the sex-related brain nuclei, and suggests an early effect of hormones in establishing long life characteristics in dopaminergic circuits.

Abstract # 1864 Modafinil prevents sickness behavior induced by LPS in mice: Role for dopaminergic D1 receptor

Modafinil is a psychostimulant drug that is used to treat Narcolepsy and Excessive Daytime Sleepiness, due to a dopamine-related action. Recent studies indicated that Modafinil prevents inflammation in animal models of neurodegeneration. However, the effect of Modafinil on the behavioral changes induced by systemic inflammation is still unknown. Thus, the aim of the present study was to evaluate the effect of Modafinil pretreatment in the Lipopolysaccharide (LPS)-induced sickness behavior, and determine the role of dopaminergic D1 receptor in this phenomenon. Adult male C57BL/6J mice were pretreated with Vehicle or Modafinil and, 30 min later, received a single saline or LPS administration, followed by open field and elevated plus maze test 2 h later. Modafinil treatment prevented the LPS-induced increases in immobility and anxiety-like behavior. The pharmacological blockage of the dopaminergic D1R by the drug SCH-23390 counteracted the preventive effect of Modafinil on locomotion and anxiety-like behavior. Our results indicate that Modafinil pretreatment prevented the behavioral inhibition of an acute LPS challenge. The dopaminergic D1 receptor signaling is essential to the Modafinil effects on locomotion and anxiety. This evidence suggests that Modafinil treatment may be useful to prevent inflammation-related behavioral inhibition, possibly due to a neuroimmune mechanism.

Changes in [3H]-ouabain and [3H]-neurotensin binding to rat cerebral cortex membranes after administration of antipsychotic drugs haloperidol and clozapine

Evidences indicate the relationship between neurotensinergic and dopaminergic systems. Neurotensin inhibits synaptosomal membrane Na+, K+-ATPase activity, an effect blocked by SR 48692, antagonist for high affinity neurotensin receptor (NTS1) type. Assays of high affinity [3H]-ouabain binding (to analyze K+ site of Na+, K+-ATPase) show that in vitro addition of neurotensin decreases binding. Herein potential interaction between NTS1 receptor, dopaminergic D2 receptor and Na+, K+-ATPase was studied. To test the involvement of dopaminergic D2 receptors in [3H]-ouabain binding inhibition by neurotensin, Wistar rats were administered i.p.with antipsychotic drugs haloperidol (2mg/kg) and clozapine (3, 10 and 30mg/kg). Animals were sacrificed 18h later, cerebral cortices harvested, membrane fractions prepared and high affinity [3H]-ouabain binding assayed in the absence or presence of neurotensin at a 10 micromolar concentration. No differences versus controls for basal binding or for binding inhibition by neurotensin were recorded, except after 10mg/kg clozapine. Rats were administered with neurotensin (3, 10y 30μg, i.c.v.) and 60min later, animals were sacrificed, cerebral cortices harvested and processed to obtain membrane fractions for high affinity [3H]-ouabain binding assays. Results showed a slight but statistically significant decrease in binding with the 30μg neurotensin dose. To analyze the interaction between dopaminergic D2 and NTS1 receptors, [3H]-neurotensin binding to cortical membranes from rats injected with haloperidol (2mg/kg, i.p.) or clozapine (10mg/kg) was assayed. Saturation curves and Scatchard transformation showed that the only statistically significant change occurred in Bmax after haloperidol administration. Hill number was close to the unit in all cases. Results indicated that typical and atypical antipsychotic drugs differentially modulate the interaction between neurotensin and Na+, K+-ATPase. At the same time, support the notion of an interaction among dopaminergic and neurotensinergic systems and Na+, K+-ATPase at central synapses.

Nicotinic receptor subtypes differentially modulate glutamate release in the dorsal medial striatum

The dorsal medial striatum is a crucial part of the neural network that subserves dynamic, goal-directed behaviors. Functional output of this nucleus is shaped, in part, by the influence of glutamatergic inputs. Striatal cholinergic systems have the capacity to modulate these excitatory inputs through presynaptic nicotinic acetylcholine receptors (nAChRs); however, the individual contribution of the two major nicotinic receptor subtypes, α4β2 and α7, to such modulation is not well characterized. In the present experiments, glutamate biosensors were used to monitor nAChR-dependent glutamate release with high temporal precision in the dorsal medial striatum of rats. Both α4β2 and α7 nAChRs were found to potently modulate glutamate release; however the two receptor subtypes do so in strikingly different ways. α7 nAChRs appear to enhance release from glutamatergic terminals. In contrast, α4β2 nAChRs act as a brake on glutamate release via an interaction with local dopaminergic inputs and D2 receptors. Combined, the present data reveal the capacity of local striatal cholinergic signaling to dynamically modulate excitatory inputs through nAChRs.

Cognition and Dopamine D2 Receptor Availability in the Striatum in Older Patients with Schizophrenia

To assess the impact of reducing the dose of antipsychotics on cognition and dopaminergic D2 receptor availability in the whole striatum, and identify their relationship in patients with schizophrenia aged 50 years or older. Open-label prospective PET [11C]-raclopride study. A tertiary care center outpatient setting. Thirty-seven clinically stable participants with schizophrenia or schizoaffective disorder, aged 50 years or greater, and having been treated with olanzapine or risperidone monotherapy at the same dose for at least 6 months. Gradual reduction in their olanzapine or risperidone daily dose of up to 40%. Clinical and cognitive assessments, and [11C]-raclopride PET to determine D2 receptor availability at baseline and after the dose reduction. Main outcome measures were overall cognition and D2 receptor availability in whole striatum. Reducing the antipsychotic dose resulted in an increase in D2 receptor availability in the whole striatum and an association between D2 receptor availability and overall cognition despite lack of change in the latter. There was also an association between change in D2 receptor availability and change in overall cognition. Our findings suggest that optimizing D2 receptor availability by reducing antipsychotic dose allows this system to contribute more significantly to cognitive function in patients with schizophrenia. This uncovered association could be harnessed by cognitive-enhancing interventions.

The Role of Spinal Dopaminergic Transmission in the Analgesic Effect of Nefopam on Rat Inflammatory Pain.

BackgroundNefopam has been known as an inhibitor of the reuptake of monoamines, and the noradrenergic and/or serotonergic system has been focused on as a mechanism of its analgesic action. Here we investigated the role of the spinal dopaminergic neurotransmission in the antinociceptive effect of nefopam administered intravenously or intrathecally.MethodsThe effects of intravenously and intrathecally administered nefopam were examined using the rat formalin test. Then we performed a microdialysis study to confirm the change of extracellular dopamine concentration in the spinal dorsal horn by nefopam. To determine whether the changes of dopamine level are associated with the nefopam analgesia, its mechanism was investigated pharmacologically via pretreatment with sulpiride, a dopaminergic D2 receptor antagonist.ResultsWhen nefopam was administered intravenously the flinching responses in phase I of the formalin test were decreased, but not those in phase II of the formalin test were decreased. Intrathecally injected nefopam reduced the flinching responses in both phases of the formalin test in a dose dependent manner. Microdialysis study revealed a significant increase of the level of dopamine in the spinal cord by intrathecally administered nefopam (about 3.8 fold the baseline value) but not by that administered intravenously. The analgesic effects of intrathecally injected nefopam were not affected by pretreatment with sulpiride, and neither were those of the intravenous nefopam.ConclusionsBoth the intravenously and intrathecally administered nefopam effectively relieved inflammatory pain in rats. Nefopam may act as an inhibitor of dopamine reuptake when delivered into the spinal cord. However, the analgesic mechanism of nefopam may not involve the dopaminergic transmission at the spinal level.

Using iPSC-derived human DA neurons from opioid-dependent subjects to study dopamine dynamics.

IntroductionThe dopaminergic (DA) system plays important roles in addiction. However, human DA neurons from drug‐dependent subjects were not available for study until recent development in inducible pluripotent stem cells (iPSCs) technology.MethodsIn this study, we produced DA neurons differentiated using iPSCs derived from opioid‐dependent and control subjects carrying different 3′ VNTR (variable number tandem repeat) polymorphism in the human dopamine transporter (DAT or SLC6A3). In addition, the effects of valproic acid (VPA) exposures on iPSC‐derived human DA neurons are also examined.ResultsWe present the first evidence suggesting that the 3′ VNTR polymorphism in the hDAT gene affects DAT expression level in iPSC‐derived human DA neurons. In human DA neurons, which provide an appropriate cellular milieu, VPA treatment alters the expression of several genes important for dopaminergic neuron function including DAT, Nurr1, and TH; this might partly explain its action in regulating addictive behaviors. VPA treatment also significantly increased DA D2 receptor (Drd2) expression, especially in the opioid‐dependent iPSC cell lines.ConclusionsOur data suggest that human iPSC‐derived DA neurons may be useful in in vitro experimental model to examine the effects of genetic variation in gene regulation, to examine the underlying mechanisms in neurological disorders including drug addiction, and to serve as a platform for therapeutic development.

Effects of Stimulation and Blockade of D2 Dopamine Receptors on the Behavior of Gonadectomized Male Rats

The present study aims to perform the comparative assessment of stimulation and blockade for D2-dopaminergic receptors in depression-like behavior in male rats with deficiency of androgen hormones. Two weeks after surgery, GDX rats began 14 days of treatment with vehicle, a low dose of testosterone propionate (0.5 mg/kg, s.c.), quinpirole (0.1 mg/kg, i.p.), sulpiride (10.0 mg/kg, i.p.), quinpirole plus testosterone propionate or sulpiride plus testosterone propionate. The animals were then tested in forced swimming test (FST) and the open field test (OFT). Quinpirole administered alone or in a combination with a low dose of testosterone propionate resulted in antidepressant-like effect in GDX rats in the FST. Repeated treatment of quinpirole and testosterone propionate profoundly increased antidepressant-like effect of the single substances they exert per se. Application of neither quinpirole nor quinpirole plus testosterone propionate led to any changes of behavioral reactions in GDX rats in the OFT, except increased grooming behavior. On the contrary, sulpiride treatment failed to alter depression-like behavior in GDX rats in the FST. In addition, sulpiride blocked the antidepressant-like effect of testosterone propionate in GDX rats and its combination with a low dose of testosterone propionate induced prodepressant-like effect in GDX rats. Co-administration of sulpiride with testosterone propionate or its single application increased frequency of rearing and grooming in GDX rats in the OFT. In summary, the results of the present study suggest that stimulation of D2-dopaminergic receptors results in antidepressant-like effect at androgen deficiency in male rats, while blockade of D2-dopaminergic receptors resulted in prodepressant-like effect.

HBK-7 — A new xanthone derivative and a 5-HT1A receptor antagonist with antidepressant-like properties

Xanthone derivatives possess many biological properties, including neuroprotective, antioxidant or antidepressant-like. In this study we aimed to investigate antidepressant- and anxiolytic-like properties of a new xanthone derivative – 6-methoxy-4-[4-(2-methoxyphenyl)piperazin-1-yl]-9H-xanthen-9-one (HBK-7), as well as its possible mechanism of action, and the influence on cognitive and motor function. HBK-7 in our earlier studies showed high affinity for serotonergic 5-HT1A receptor. We determined the affinity of HBK-7 for CNS receptors and transporters using radioligand assays and examined its intrinsic activity towards 5-HT1A receptor. We evaluated antidepressant- and anxiolytic-like activity of HBK-7 in the mouse forced swim test, and four-plate test, respectively. We examined the influence on locomotor activity in mice to determine if the effect observed in the forced swim test was specific. We used step-through passive avoidance and rotarod tests to evaluate the influence of HBK-7 on cognitive and motor function, respectively. HBK-7 showed moderate affinity for dopaminergic D2 receptor and very low for serotonergic 5-HT2A, adrenergic α2 receptors, as well as serotonin transporter. Functional studies revealed that HBK-7 was a 5-HT1A receptor antagonist. HBK-7 (10mg/kg) decreased immobility time in the forced swim test. Combined treatment with sub-effective doses of HBK-7 and fluoxetine reduced immobility of mice in the forced swim test. Pretreatment with p-chlorophenylalanine and WAY-100,635 antagonized the antidepressant-like effect of HBK-7. Neither of the treatments influenced locomotor activity of mice. HBK-7 at antidepressant-like dose did not impair memory or motor coordination in mice. We demonstrated that HBK-7 was a 5-HT1A receptor antagonist with potent, comparable to mianserin, antidepressant-like activity. HBK-7 mediated its effect through serotonergic system and its antidepressant-like action required the activation of 5-HT1A receptors. At active dose it did not influence cognitive and motor function. Since 5-HT1A receptor antagonists may accelerate the occurrence of antidepressant effect, our findings highlight their potential as future antidepressants.

Unraveling a new circuitry for sleep regulation in Parkinson's disease

Sleep disturbances are among the most disabling non-motor symptoms in Parkinson's disease. The pedunculopontine tegmental nucleus and basal ganglia are likely involved in these dysfunctions, as they are affected by neurodegeneration in Parkinson's disease and have a role in sleep regulation. To investigate this, we promoted a lesion in the pedunculopontine tegmental nucleus or substantia nigra pars compacta of male rats, followed by 24 h of REM sleep deprivation. Then, we administrated a dopaminergic D2 receptor agonist, antagonist or vehicle directly in the striatum. After a period of 24 h of sleep-wake recording, we observed that the ibotenic acid infusion in the pedunculopontine tegmental nucleus blocked the so-called sleep rebound effect mediated by REM sleep deprivation, which was reversed by striatal D2 receptors activation. Rotenone infusion in the substantia nigra pars compacta also blocked the sleep rebound, however, striatal D2 receptors activation did not reverse it. In addition, rotenone administration decreased the time spent in NREM sleep, which was corroborated by positive correlations between dopamine levels in both substantia nigra pars compacta and striatum and the time spent in NREM sleep. These findings suggest a new circuitry for sleep regulation in Parkinson's disease, involving the triad composed by pedunculopontine nucleus, substantia nigra pars compacta and striatum, evidencing a potential therapeutic target for the sleep disturbances associated to this pathology.