Dopamine receptor D1 agonist inhibits glioblastoma via calpain­mediated ER stress and mitochondrial dysfunction.

Recent studies have reported the important roles of dopamine receptors in the early development and progression of glioblastoma (GBM). The present research aimed to explore the antineoplastic effect and intrinsic pathways of action of dopamine receptor D1 agonist SKF83959 on GBM cells. Flow cytometric analysis revealed a significant level of apoptotic cell death under SKF83959 treatment. SKF83959 administration increased intracellular calcium levels and oxidative stress through the phospholipase C/inositol trisphosphate pathway. The downstream calpains were activated and dysregulated by the increased calcium levels. The mitochondrial membrane potential­dependent staining assay revealed decreased mitochondrial transmembrane potential in GBM cells under SKF83959 treatment. The mitochondrial/cytosolic fraction and western blotting further demonstrated mitochondrial dysfunction and endoplasmic reticulum stress, followed by apoptosis. The calpain inhibitor, calpastatin, significantly reversed the increase in mitochondrial injury and endoplasmic reticulum stress and eventually ameliorated GBM cell apoptosis during SKF83959 treatment. Finally, the in vivo inhibitory efficacy of SKF83959 was verified in GBM xenograft models. In addition, immunohistochemistry and western blotting both revealed increased expression of calpains in xenograft GBM tissues. These results suggested a potential therapeutic target for human GBM treatment regarding calpain expression and activity regulation.

Dopaminergic mechanisms in the lateral hypothalamus regulate feeding behavior in association with neuropeptides.

This study investigated dopaminergic function in the lateral hypothalamus (LH) in the regulation of feeding behavior. Refeeding increased dopamine levels in the LH. Glucose injection also increased dopamine levels in the LH. When the retrograde tracer Fluoro-Gold (FG) was injected into the LH, FG-positive cells were found in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNC), which were mostly tyrosine hydroxylase-positive. Injection of the dopamine D1 receptor agonist SKF 38393, but not the antagonist SCH 23390, into the LH increased food intake. Similarly, injection of the dopamine D2 receptor agonist quinpirole, but not the antagonist l-sulpiride, into the LH increased food intake. The effect of each agonist was blocked by its respective antagonist. Furthermore, injection of quinpirole, but not SKF 38393, decreased the mRNA level of preproorexin. In addition, injection of SKF 38393 decreased the mRNA levels of neuropeptide Y and agouti-related peptide, whereas the injection of quinpirole increased the mRNA level of proopiomelanocortin. These results indicate that food intake activates dopamine neurons projecting from the VTA/SNC to the LH through an increase in blood glucose levels, which terminates food intake by stimulation of dopamine D1 and D2 receptors. It is also possible that stimulation of dopamine D1 and D2 receptors in the LH inhibits feeding behavior through different neuropeptides.

Dopamine D1 and D2 receptors mediate analgesic and hypnotic effects of l-tetrahydropalmatine in a mouse neuropathic pain model.

RATIONALE: Levo-tetrahydropalmatine (l-THP), an active ingredient of Corydalis yanhusuo, has been reported to be a partial agonist for dopamine D1 receptors (D1R) and an antagonist for D2R. Although it has been safely used clinically in China for decades as an analgesic with sedative/hypnotic properties, there are few studies that address the mechanisms by which l-THP exerts its beneficial effects in chronic pain-induced sleep disturbance. OBJECTIVES: To investigate the effects and mechanisms of l-THP on sleep disturbance in a neuropathic pain-like condition. METHODS: A mouse model of chronic neuropathic pain induced by partial sciatic nerve ligation (PSNL) was employed. The antinociceptive and hypnotic effects of l-THP were evaluated by measurement of mechanical allodynia, thermal hyperalgesia, and electroencephalogram (EEG) recordings in PSNL mice. Pharmacological approaches and c-Fos expression were used to clarify the mechanisms of l-THP. RESULTS: Intraperitoneal injection of l-THP at 5 and 10 mg/kg not only significantly increased the mechanical threshold by 134.4% and 174.8%, and prolonged the thermal latency by 49.4% and 69.2%, but also increased non-rapid eye movement sleep by 17.5% and 29.6%, and decreased sleep fragmentation in PSNL mice, compared with the vehicle control. Moreover, the antinociceptive effect of l-THP was prevented by D1R antagonist SCH23390 or D2R agonist quinpirole; meanwhile, the hypnotic effect of l-THP was blocked by quinpirole rather than by SCH23390. Immunohistochemistry demonstrated that l-THP inhibited c-Fos overexpression induced by PSNL in the cingulate cortex and the periaqueductal gray. CONCLUSIONS: These findings indicated that l-THP exerted analgesic effects by agonism D1R and antagonism D2R, and the antagonism of D2R mediated the hypnotic effect of l-THP in PSNL mice.

Dopamine D1-Like Receptor Agonist and D2-Like Receptor Antagonist (-)-Stepholidine Reduces Reinstatement of Drug-Seeking Behavior for 3,4-Methylenedioxypyrovalerone (MDPV) in Rats.

Psychostimulant reinforcement is mediated by stimulation of both dopamine (DA) D1-like and D2-like receptors, suggesting that pharmacotherapy agents with a dual DA receptor mechanism may be useful for managing psychostimulant abuse. (-)-Stepholidine (L-SPD) is a Chinese herbal extract that functions as a D1-like receptor agonist and D2-like receptor antagonist. L-SPD has been shown to attenuate the reinforcing effects of heroin; however, its effects on the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) have not been examined. The current study determined the effects of L-SPD on reinstatement of MDPV-seeking behavior in the drug intravenous self-administration (IVSA) and conditioned place preference (CPP) paradigms. To determine whether the effects of L-SPD were specific to psychostimulant reinforcement, we also examined its effects on sucrose-seeking behavior. Using a locomotor activity assay, we tested the locomotor effects of L-SPD, as well as its effects on MDPV-induced hyperactivity. The results of a battery of in vitro binding and functional assays confirmed that L-SPD functioned as a D1-like receptor agonist and D2-like receptor antagonist. In behavioral experiments, L-SPD dose-dependently attenuated cue plus MDPV-primed reinstatement of MDPV-seeking behavior in the IVSA model. The highest dose of L-SPD also attenuated MDPV-primed reinstatement of MDPV CPP, as well as cue-induced reinstatement of sucrose-seeking. L-SPD had no significant locomotor effects, and did not modulate the robust hyperactivity induced by MDPV. The current findings show for the first time a robust reinstatement effect with MDPV, which can be reduced by L-SPD. These results establish a role for DA receptors in drug-seeking behavior for MDPV.

Role of paraventricular hypothalamic dopaminergic D1 receptors in food intake regulation of food-deprived rats.

Dopaminergic neurons play an important role on central regulatory mechanisms of feeding behavior. Dopamine receptors are distributed within the hypothalamus and densely localized in the paraventricular hypothalamic nucleus (PVN). From these ideas we postulated that PVN D1 receptors may play a role in regulating the food intake behavioral process. In this paper, we considered the effects of SKF38393, a D1 receptor agonist, and the D1 receptor antagonist (SCH23390), on food intake of conscious rats deprived of food for 24h. Our findings revealed that intraparaventricular injections of SKF383993 (0.3-5µg) stimulated food intake behavior in a dose dependent manner. This stimulatory effect of SKF3833 persisted over 2h of the monitoring period. The PVN injections of D1 receptor antagonist were associated with dose-dependent inhibition of food intake. SCH23390 (0.01µg) was also administered 5min before intraparaventricular injection of SKF3833. The results showed that SCH23390 suppressed stimulated food intake induced by SKF38393 (1.2µg). In conclusion, endogenous dopamine impact PVN D1 receptors and may be a factor in regulating the food intake behavioral process.

Electrical stimulation of the hippocampal fimbria facilitates neuronal nitric oxide synthase activity in the medial shell of the rat nucleus accumbens: Modulation by dopamine D1 and D2 receptor activation.

The medial shell region of the nucleus accumbens (msNAc) is a key center for the regulation of goal-directed behavior and is likely to be dysfunctional in neuropsychiatric disorders such as addiction, depression and schizophrenia. Nitric oxide (NO)-producing interneurons in the msNAc are potently modulated by dopamine (DA) and may play an important role in synaptic integration in msNAc networks. In this study, neuronal NO synthase (nNOS) activity was measured in anesthetized rats using amperometric microsensors implanted into the msNAc or via histochemical techniques. In amperometric studies, NO oxidation current was recorded prior to and during electrical stimulation of the ipsilateral fimbria. Fimbria stimulation elicited a frequency and intensity-dependent increase in msNAc NO efflux which was attenuated by systemic administration of the nNOS inhibitor NG-propyl-l-arginine. Parallel studies using NADPH-diaphorase histochemistry to assay nNOS activity produced highly complementary outcomes. Moreover, systemic administration of either a DA D1 receptor agonist or a DA D2 receptor antagonist potentiated nNOS activity in the msNAc elicited by fimbria stimulation. These observations demonstrate for the first time that NO synthesis in nNOS expressing interneurons in the msNAc is facilitated by robust activation of hippocampal afferents in a manner that is differentially modulated by DA D1 and D2 receptor activation.

Dopamine Receptor D1 Agonism and Antagonism Using a Field-Effect Transistor Assay.

The field-effect transistor (FET) has been used in the development of diagnostic tools for several decades, leading to high-performance biosensors. Therefore, the FET platform can provide the foundation for the next generation of analytical methods. A major role of G-protein-coupled receptors (GPCRs) is in the transfer of external signals into the cell and promoting human body functions; thus, their principle application is in the screening of new drugs. The research community uses efficient systems to screen potential GPCR drugs; nevertheless, the need to develop GPCR-conjugated analytical devices remains for next-generation new drug screening. In this study, we proposed an approach for studying receptor agonism and antagonism by combining the roles of FETs and GPCRs in a dopamine receptor D1 (DRD1)-conjugated FET system, which is a suitable substitute for conventional cell-based receptor assays. DRD1 was reconstituted and purified to mimic native binding pockets that have highly discriminative interactions with DRD1 agonists/antagonists. The real-time responses from the DRD1-nanohybrid FET were highly sensitive and selective for dopamine agonists/antagonists, and their maximal response levels were clearly different depending on their DRD1 affinities. Moreover, the equilibrium constants (K) were estimated by fitting the response levels. Each K value indicates the variation in the affinity between DRD1 and the agonists/antagonists; a greater K value corresponds to a stronger DRD1 affinity in agonism, whereas a lower K value in antagonism indicates a stronger dopamine-blocking effect.

Guduchi Sawras (Tinospora cordifolia): An Ayurvedic drug treatment modulates the impaired lipid metabolism in alcoholics through dopaminergic neurotransmission and anti-oxidant defense system.

Tinospora cordifolia (Guduchi Sawras) though has been clearly demonstrated in literature for its hypolipidemic and anti-alcoholism properties but its anti-hyperlipidemia mechanistic approach is still missing. Moreover, its direct implication with alcohol induced hyperlipidemia has also not been reported till date. In order to explore the answers of these questions, phytochemicals of Tinospora cordifolia water extract "Guduchi Sawras" (GS) was analyzed using HPLC-Q-TOF-MS. On the basis of relative peak volumes 110 compounds were selected and identified in GS. Besides that, protein targets of most abundant compounds present in GS were fetched from ChEMBL and protein interaction network (PIN) was constructed. GO enrichment analysis showed that GS targets various pathways including dopamine metabolism, cAMP-dependent signaling pathway, and glycolytic process. Biological processes obtained via PIN were correlated with hyperlipidemia markers and dopamine metabolism in moderate alcohol consumers (n=25) and healthy volunteers (n=27) of age 41±3.8years. Metabolic analysis demonstrated the increased serotonin (1.9-fold) and decreased dopamine (-2.3-fold) levels in alcoholics. Further data analysis revealed a significant increase in urinary BCAAs (>2.0-fold), pantothenic acid (1.8-fold), carnitines (>2-fold) levels, and decrease in PPARα activation markers levels i.e. nicotinamide-1-oxide (-1.7-fold), and N-methylnicotinamide (-1.6-fold) in alcoholics. Biochemical analysis showed the increased AST/ALT ratio (1.91), along with triglycerides (20%), and MDA (34%) and GSH (56%) levels in alcoholics. GS treatment significantly reverted the most of the discussed metabolites levels (p<0.05) and enzymes activities (p<0.05) in alcoholics. The data depict that moderate chronic alcohol consumption lead to hyperlipidemia and oxidative burden; whereas GS treatment ameliorates hyperlipidemia by decreasing oxidative stress, activating PPARα, CREB and SREBP-1 through stimulation of dopamine D1 receptors mediated signalling molecules i.e. cAMP and protein kinase A.

Highlights from the 2016 Schizophrenia International Research Society Conference, April 2-6, 2016.

The 2016 Schizophrenia International Research Society (SIRS) Conference, held in Florence, Italy, attracted approximately 1,800 attendees from over 54 countries to the stately Firenze Fiera Conference Center from April 2-6, 2016. Providing plenary sessions, special sessions, symposia, workshops, oral presentations and poster presentations, this 5th Biennial SIRS Conference focused on "Deconstructing Schizophrenia towards Targeted Treatment." In conjunction with the Schizophrenia Research Forum, a Web project of the Brain and Behavior Research Foundation, and with our thanks to the SIRS organizers and staff, we bring you the following selected highlights.

Dampened Mesolimbic Dopamine Function and Signaling by Saturated but not Monounsaturated Dietary Lipids.

Overconsumption of dietary fat is increasingly linked with motivational and emotional impairments. Human and animal studies demonstrate associations between obesity and blunted reward function at the behavioral and neural level, but it is unclear to what degree such changes are a consequence of an obese state and whether they are contingent on dietary lipid class. We sought to determine the impact of prolonged ad libitum intake of diets rich in saturated or monounsaturated fat, separate from metabolic signals associated with increased adiposity, on dopamine (DA)-dependent behaviors and to identify pertinent signaling changes in the nucleus accumbens (NAc). Male rats fed a saturated (palm oil), but not an isocaloric monounsaturated (olive oil), high-fat diet exhibited decreased sensitivity to the rewarding (place preference) and locomotor-sensitizing effects of amphetamine as compared with low-fat diet controls. Blunted amphetamine action by saturated high-fat feeding was entirely independent of caloric intake, weight gain, and plasma levels of leptin, insulin, and glucose and was accompanied by biochemical and behavioral evidence of reduced D1R signaling in the NAc. Saturated high-fat feeding was also tied to protein markers of increased AMPA receptor-mediated plasticity and decreased DA transporter expression in the NAc but not to alterations in DA turnover and biosynthesis. Collectively, the results suggest that intake of saturated lipids can suppress DA signaling apart from increases in body weight and adiposity-related signals known to affect mesolimbic DA function, in part by diminishing D1 receptor signaling, and that equivalent intake of monounsaturated dietary fat protects against such changes.

Comparing the effects of 17ß-oestradiol and the selective oestrogen receptor modulators, raloxifene and tamoxifen, on prepulse inhibition in female rats.

BACKGROUND: Evidence suggests that oestrogen plays a protective role against the development and severity of schizophrenia. However, while oestrogen may be beneficial as a treatment in schizophrenia, its chronic use is associated with side-effects. Selective oestrogen receptor modulators (SERMs) may provide an alternative, however little is known about the mechanism underlying their effects in schizophrenia. METHODS: We investigated the effect of raloxifene and tamoxifen on dopaminergic-induced disruptions of prepulse inhibition (PPI). PPI measures sensorimotor gating and PPI disruptions are considered an endophenotype for schizophrenia. Adult female Sprague-Dawley rats were either intact, ovariectomized (OVX), OVX and 17ß-oestradiol-treated, OVX and raloxifene-treated (low or high dose), or OVX and tamoxifen-treated (low or high dose). RESULTS: The dopamine D1/D2 receptor agonist, apomorphine (0, 0.1, 0.3 and 1mg/kg), caused the expected dose-dependent disruption in PPI in intact and OVX rats. This PPI disruption was prevented in OVX rats treated with 17ß-oestradiol, a high dose of raloxifene or a high dose of tamoxifen. In untreated OVX rats, average PPI was 55% after saline and 34% after 1mg/kg apomorphine treatment, a reduction of 21%. However, oestradiol-treated and raloxifene-treated OVX rats showed only a 7% PPI reduction, and tamoxifen-treated OVX rats had a 4% PPI reduction caused by apomorphine treatment. Startle amplitude was not different between the groups. CONCLUSION: The SERMs, raloxifene and tamoxifen, can prevent dopamine D1/D2 receptor-mediated disruptions of sensorimotor gating, similar to oestradiol. These data lend support for the use of SERMs as a treatment for schizophrenia.

Dopaminergic Modulation of Lateral Amygdala Neuronal Activity: Differential D1 and D2 Receptor Effects on Thalamic and Cortical Afferent Inputs.

BACKGROUND: In auditory fear conditioning, the lateral nucleus of the amygdala (LA) integrates a conditioned stimulus (CS) from the auditory thalamus (MGN) and the auditory association cortex (Te3) with an aversive unconditioned stimulus. The thalamic input provides a basic version of the CS, while the cortical input provides a processed representation of the stimulus. Dopamine (DA) is released in the LA under heightened arousal during the presentation of the CS. METHODS: In this study we examined how D1 or D2 receptor activation affects LA afferent-driven neuronal firing using in vivo extracellular single-unit recordings with local micro-iontophoretic drug application in anesthetized rats. LA neurons that were responsive (~50%) to electrical stimulation in either the MGN or the Te3 were tested by iontophoresis of either the D1 agonist, SKF38393, or the D2 agonist, quinpirole. RESULTS: We found that most of the LA projection neurons exhibited either facilitatory or attenuating effects (changes in evoked probability >15% relative to baseline) on afferent input by activation of D1 or D2 receptors. In general, it required significantly higher stimulation current to evoke ~50% baseline responses to the cortical input. Activation of the D1 receptor showed no difference in modulation between the thalamic or cortical pathways. On the other hand, activation of the D2 receptor had a stronger inhibitory modulation of the cortical pathway, but a stronger excitatory modulation of the thalamic pathway. CONCLUSIONS: Our results suggest that there is a shift in balance favoring the thalamic pathway in response to DA acting via the D2 receptor.

Differential role of D1 and D2 receptors in the perifornical lateral hypothalamus in controlling ethanol drinking and food intake: possible interaction with local orexin neurons.

BACKGROUND: The neurotransmitter dopamine (DA), acting in various mesolimbic brain regions, is well known for its role in promoting motivated behaviors, including ethanol (EtOH) drinking. Indirect evidence, however, suggests that DA in the perifornical lateral hypothalamus (PF/LH) has differential effects on EtOH consumption, depending on whether it acts on the DA 1 (D1) or DA 2 (D2) receptor subtype, and that these effects are mediated in part by local peptide systems, such as orexin/hypocretin (OX) and melanin-concentrating hormone (MCH), known to stimulate the consumption of EtOH. METHODS: The present study in brain-cannulated Sprague-Dawley rats measured the effects of dopaminergic compounds in the PF/LH on drinking behavior in animals trained to consume 7% EtOH and also on local peptide mRNA expression using digoxigenin-labeled in situ hybridization in EtOH-naïve animals. RESULTS: Experiments 1 and 2 showed that the D1 agonist SKF81297 (10.8 nmol/side) in the PF/LH significantly increased food intake, while tending to increase EtOH intake, and the D1 antagonist SCH23390 significantly decreased EtOH intake without affecting food intake. In contrast, the D2 agonist quinelorane (6.2 nmol/side) in the PF/LH significantly reduced EtOH consumption, while the D2 antagonist sulpiride increased it. Experiments 3 and 4 revealed differential effects of PF/LH injection of the DA agonists on local OX mRNA, which was increased by the D1 agonist and decreased by the D2 agonist. These DA agonists had no impact on MCH expression. CONCLUSIONS: These results support a stimulatory role of the PF/LH D1 receptor in promoting the consumption of both EtOH and food, in contrast to a suppressive effect of the D2 receptor on EtOH drinking. They further suggest that these receptors affect consumption, in part, through local OX-expressing neurons. These findings provide new evidence for the function of PF/LH DA receptor subtypes in controlling EtOH and food intake.

Experimental confirmation of new drug-target interactions predicted by Drug Profile Matching.

We recently introduced Drug Profile Matching (DPM), a novel affinity fingerprinting-based in silico drug repositioning approach. DPM is able to quantitatively predict the complete effect profiles of compounds via probability scores. In the present work, in order to investigate the predictive power of DPM, three effect categories, namely, angiotensin-converting enzyme inhibitor, cyclooxygenase inhibitor, and dopamine agent, were selected and predictions were verified by literature analysis as well as experimentally. A total of 72% of the newly predicted and tested dopaminergic compounds were confirmed by tests on D1 and D2 expressing cell cultures. 33% and 23% of the ACE and COX inhibitory predictions were confirmed by in vitro tests, respectively. Dose-dependent inhibition curves were measured for seven drugs, and their inhibitory constants (Ki) were determined. Our study overall demonstrates that DPM is an effective approach to reveal novel drug-target pairs that may result in repositioning these drugs.

SKF 38393 and SCH 23390 inhibit reuptake of serotonin by rat hypothalamic synaptosomes.

BACKGROUND/AIMS: Both the dopamine receptor D(1) agonist SKF 38393 and the antagonist SCH 23390 are benzazepine derivatives that have been widely used as pharmacological tools and radioligands. Evidence suggests that behavioral effects of both compounds do not always correspond to their established receptor subtype selectivity. Here, we assessed the effects of SKF 38393 and SCH 23390 on the synaptosomal uptake of tritiated serotonin. METHODS: Uptake experiments were performed by using [(3)H]serotonin and synaptosomal fractions prepared from the hypothalamus of rat brain. RESULTS: Both SKF 38393 and SCH 23390 inhibited synaptosomal uptake of [(3)H]serotonin, with IC(50) values of 910 ± 60 nmol/l and 1,400 ± 80 nmol/l, respectively. Clomipramine, a known inhibitor of serotonin uptake, and (+)-amphetamine, a weak inhibitor, had IC(50) values of 14 ± 1 nmol/l and more than 10,000 nmol/l, respectively, under the same experimental conditions. The IC(50) values for SKF 38393 and SCH 23390 fall within the broad range of corresponding values for antidepressants that have been shown to inhibit the uptake of serotonin. This finding indicates that SKF 38393 and SCH 23390 can enhance the activity of the serotonergic system in the brain, a mechanism that may be responsible for some of the effects of these drugs. CONCLUSION: SKF 38393 and SCH 23390 are useful tools to differentiate D(1) from D(2) receptors, but their indirect effects on serotonergic mechanisms have to be considered.

Dopamine enhances the excitability of somatosensory thalamocortical neurons.

The thalamus conveys sensory information from peripheral and subcortical regions to the neocortex in a dynamic manner that can be influenced by several neuromodulators. Alterations in dopamine (DA) receptor function in thalami of Schizophrenic patients have recently been reported. In addition, schizophrenia is associated with sensory gating abnormalities and sleep-wake disturbances, thus we examined the role of DA on neuronal excitability in somatosensory thalamus. The ventrobasal (VB) thalamus receives dopaminergic innervation and expresses DA receptors; however, the action of DA on VB neurons is unknown. In the present study, we performed whole cell current- and voltage-clamp recordings in rat brain slices to investigate the role of DA on excitability of VB neurons. We found that DA increased action potential discharge and elicited membrane depolarization via activation of different receptor subtypes. Activation of D2-like receptors (D(2R)) leads to enhanced action potential discharge, whereas the membrane depolarization was mediated by D1-like receptors (D(1R)). The D(2R-mediated) increase in spike discharge was mimicked and occluded by α-dendrotoxin (α-DTX), indicating the involvement of a slowly inactivating K(+) channels. The D1R-mediated membrane depolarization was occluded by barium, suggesting the involvement of a G protein-coupled K(+) channel or an inwardly rectifying K(+) channel. Our results indicate that DA produces dual modulatory effects acting on subtypes of DA receptors in thalamocortical relay neurons, and likely plays a significant role in the modulation of sensory information.

D(1)/D(2) receptor-targeting L-stepholidine, an active ingredient of the Chinese herb Stephonia, induces non-rapid eye movement sleep in mice.

L-stepholidine, an active ingredient of the Chinese herb Stephonia, is the first compound known to have mixed dopamine D(1) receptor agonist/D(2) antagonist properties and to be a potential treatment medication for schizophrenia. In schizophrenic patients insomnia is a common symptom and could be partly related to the presumed over-activity of the dopaminergic system. To elucidate whether stepholidine modulates sleep behaviors, we observed its effects on sleep-wake profiles in mice. The results showed that stepholidine administered i.p. at doses of 20, 40 or 80 mg/kg significantly shortened the sleep latency to non-rapid eye movement (non-REM, NREM) sleep, increased the amount of NREM sleep, and prolonged the duration of NREM sleep episodes, with a concomitant reduction in the amount of wakefulness. Stepholidine at doses of 40 and 80 mg/kg increased the number of state transitions from wakefulness to NREM sleep and subsequently from NREM sleep to wakefulness. However, stepholidine had no effect on either the amount of REM sleep or electroencephalogram power density of either NREM or REM sleep. Immunohistochemistry study showed that stepholidine dose-dependently increased c-Fos expression in neurons of the ventrolateral preoptic area, a sleep center in the anterior hypothalamus, as compared with the vehicle control. These results indicate that stepholidine initiates and maintains NREM sleep with activation of the sleep center in mice, suggesting its potential application for the treatment of insomnia.

The effect of a full agonist/antagonist of the D1 receptor on locomotor activity, sensorimotor gating and cognitive function in dizocilpine-treated rats.

Cognitive impairment has been found across all subtypes of schizophrenia. The location and function of dopamine-1 receptors (D1Rs) make them attractive targets for the treatment of cognitive impairment in schizophrenia. Here we investigate the systemic effect of a D1R agonist (A77636) and antagonist (SCH 23390) on hyperlocomotor activity and cognitive deficit induced by an NMDA receptor antagonist (MK-801). Wistar rats (250-300 g) received A77636 (0.1, 0.5 or 1 mg/kg) or SCH 23390 (0.02 or 0.05 mg/kg) with MK-801 (0.1 mg/kg) or saline for 4 d. On day 4 we assessed the prepulse inhibition of the acoustic startle response, locomotor activity in a novel arena and active allothetic place avoidance (spatial memory task) 15 min after the last injection. Systematic administration of the D1R agonist at 0.1 mg/kg ameliorates cognitive dysfunction in our model of schizophrenia, but increases stereotypy and locomotor activity (model of psychotic symptoms) at higher doses (0.5 or 1 mg/kg). Administration of the D1R antagonist had no effect on cognitive function, but decreased hyperlocomotion induced by MK-801. Thus, based on our results, over-activation of D1Rs may exacerbate psychotic symptoms in patients with schizophrenia.

D2-like but not D1-like dopamine receptors are involved in the ventrolateral orbital cortex-induced antinociception: a GABAergic modulation mechanism.

The ventrolateral orbital cortex (VLO) is part of an endogenous analgesic system consisting of an ascending pathway from the spinal cord to VLO via the thalamic nucleus submedius (Sm) and a descending pathway to the spinal cord relaying in the periaqueductal gray (PAG). This study examines whether activation of D(1)-like and D(2)-like dopamine receptors in VLO produces antinociception and whether GABAergic modulation is involved in the VLO, D(2)-like dopamine receptor activation-evoked antinociception. The radiant heat-evoked tail flick (TF) reflex was used as an index of nociceptive response in lightly anesthetized rats. Microinjection of the D(2)-like (D(2)/D(3)) dopamine receptor agonist quinpirole (0.1-2.0 microg), but not D(1)-like (D(1)/D(5)) receptor agonist SKF-38393 (1.0, 5.0 microg), into VLO produced dose-dependent antinociception which was antagonized by the D(2)-like (D(2)/D(3)) receptor antagonist raclopride (1.5 microg). We also found that VLO application of the GABA(A) receptor antagonist bicuculline or picrotoxin (100 ng) enhanced the quinpirole-induced inhibition of the TF reflex, whereas the GABA(A) receptor agonist muscimol (250 ng) or THIP (1.0 microg) significantly attenuated the quinpirole-induced inhibition. These results suggest that D(2)-like, but not D(1)-like, dopamine receptors are involved in VLO-induced antinociception and that GABAergic disinhibitory mechanisms participate in the D(2)-like receptor mediated effect. These findings provide support for the hypothesis that D(2)-like receptor activation may inhibit the inhibitory action of the GABAergic interneurons on the output neurons projecting to PAG leading to activation of the brainstem descending inhibitory system and depression of nociceptive inputs at the spinal dorsal horn.

Acute dopamine D(1) and D(2) receptor stimulation does not modulate mismatch negativity (MMN) in healthy human subjects.

RATIONALE: Schizophrenia is commonly associated with an impairment in pre-attentive change detection, as represented by reduced mismatch negativity (MMN), an auditory event related potential. While the neurochemical basis of MMN has been linked to the integrity of the glutamatergic system involving N-methyl-D-aspartate (NMDA) receptors, the role of the dopaminergic system and in particular, the role of D(1) and D(2) receptors on MMN is yet to be determined. OBJECTIVES: The aim of the present project was to investigate the acute effects of dopamine D(2) (bromocriptine) and D(1)/D(2) (pergolide) receptor stimulation on the human MMN in healthy subjects. METHODS: Fifteen healthy male subjects participated in a double-blind, placebo-controlled, cross-over design in which each subject was tested under three acute treatment conditions separated by a 1-week wash out period; placebo, bromocriptine (2.5 mg) and pergolide (0.1 mg). The subjects were exposed to a duration-MMN paradigm with 50 ms standard tones (91%) and 100 ms deviant tones (9%). RESULTS: The results showed that neither D(2) receptor stimulation with bromocriptine, nor simultaneous D(1) and D(2) receptor stimulation with pergolide, modulated MMN. CONCLUSIONS: These findings suggest that acute D(1) and D(2) receptor stimulation does not modulate MMN. While the role of dopamine cannot be completely ruled out, the findings support the view that the aberrant MMN reported in schizophrenia may be linked primarily to glutamate dysfunction involving NMDA receptors.