Synthetic aporphine alkaloids are potential therapeutics for Leigh syndrome.

Mitochondrial diseases are mainly caused by dysfunction of mitochondrial respiratory chain complexes and have a variety of genetic variants or phenotypes. There are only a few approved treatments, and fundamental therapies are yet to be developed. Leigh syndrome (LS) is the most severe type of progressive encephalopathy. We previously reported that apomorphine, an anti- "off" agent for Parkinson's disease, has cell-protective activity in patient-derived skin fibroblasts in addition to strong dopamine agonist effect. We obtained 26 apomorphine analogs, synthesized 20 apomorphine derivatives, and determined their anti-cell death effect, dopamine agonist activity, and effects on the mitochondrial function. We found three novel apomorphine derivatives with an active hydroxy group at position 11 of the aporphine framework, with a high anti-cell death effect without emetic dopamine agonist activity. These synthetic aporphine alkaloids are potent therapeutics for mitochondrial diseases without emetic side effects and have the potential to overcome the low bioavailability of apomorphine. Moreover, they have high anti-ferroptotic activity and therefore have potential as a therapeutic agent for diseases related to ferroptosis.

Kinetic Properties and Pharmacological Modulation of High- and Low-Affinity Dopamine Transport in Striatal Astrocytes of Adult Rats.

Astrocytes actively participate in neurotransmitter homeostasis by bidirectional communication with neuronal cells, a concept named the tripartite synapse, yet their role in dopamine (DA) homeostasis remains understudied. In the present study, we investigated the kinetic and molecular mechanisms of DA transport in cultured striatal astrocytes of adult rats. Kinetic uptake experiments were performed using radiolabeled [3H]-DA, whereas mRNA expression of the dopamine, norepinephrine, organic cation and plasma membrane monoamine transporters (DAT, NET, OCTs and PMAT) and DA receptors D1 and D2 was determined by qPCR. Additionally, astrocyte cultures were subjected to a 24 h treatment with the DA receptor agonist apomorphine, the DA receptor antagonist haloperidol and the DA precursor L-DOPA. [3H]-DA uptake exhibited temperature, concentration and sodium dependence, with potent inhibition by desipramine, nortriptyline and decynium-22, suggesting the involvement of multiple transporters. qPCR revealed prominent mRNA expression of the NET, the PMAT and OCT1, alongside lower levels of mRNA for OCT2, OCT3 and the DAT. Notably, apomorphine significantly altered NET, PMAT and D1 mRNA expression, while haloperidol and L-DOPA had a modest impact. Our findings demonstrate that striatal astrocytes aid in DA clearance by multiple transporters, which are influenced by dopaminergic drugs. Our study enhances the understanding of regional DA uptake, paving the way for targeted therapeutic interventions in dopaminergic disorders.

Long-term safety, tolerability and efficacy of apomorphine sublingual film in patients with Parkinson's disease complicated by OFF episodes: a phase 3, open-label study.

BACKGROUND: Apomorphine sublingual film (SL-APO) is an on-demand treatment for OFF episodes in patients with Parkinson's disease (PD). OBJECTIVE: To assess the long-term (≥ 3 years) safety/tolerability and efficacy of SL-APO. METHODS: Study CTH-301 ( http://www. CLINICALTRIALS: gov NCT02542696; registered 2015-09-03) was a phase 3, multicentre, open-label study of SL-APO in PD patients with motor fluctuations, comprised of a dose-titration and long-term safety phase. All participants received SL-APO. The primary endpoint was safety/tolerability (treatment-emergent adverse events [TEAEs]) during the long-term safety phase. Efficacy assessments included the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III (motor examination), assessed at weeks 24, 36 and 48 during the first year of the long-term safety phase. RESULTS: 496 patients were included and 120 (24.2%) completed the long-term safety phase. Mean duration of SL-APO exposure was 294.3 days. TEAEs related to study drug were experienced by 65.3% of patients (most common: nausea [6.0%], stomatitis [1.8%], lip swelling [1.8%], dizziness [1.6%], oral mucosal erythema [1.6%], mouth ulceration [1.6%]). TEAEs leading to study drug withdrawal were experienced by 34.0% of patients (most common: nausea [5.4%], lip swelling [4.5%], mouth ulceration [2.6%], stomatitis [2.3%]). A clinically meaningful reduction in MDS-UPDRS part III score was observed as soon as 15 min following administration of SL-APO, with peak effects observed approximately 30 min post-dose and sustained up to 90 min post-dose; results were consistent over 48 weeks. CONCLUSIONS: SL-APO was generally well tolerated and efficacious over the long term as an on-demand treatment for OFF episodes in patients with PD.

Apomorphine is a potent inhibitor of ferroptosis independent of dopaminergic receptors.

Originally, apomorphine was a broad-spectrum dopamine agonist with an affinity for all subtypes of the Dopamine D1 receptor to the D5 receptor. We previously identified apomorphine as a potential therapeutic agent for mitochondrial diseases by screening a chemical library of fibroblasts from patients with mitochondrial diseases. In this study, we showed that apomorphine prevented ferroptosis in fibroblasts from various types of mitochondrial diseases as well as in normal controls. Well-known biomarkers of ferroptosis include protein markers such as prostaglandin endoperoxide synthase 2 (PTGS2), a key gene for ferroptosis-related inflammation PTGS2, lipid peroxidation, and reactive oxygen species. Our findings that apomorphine induced significant downregulation of PTSG2 and suppressed lipid peroxide to the same extent as other inhibitors of ferroptosis also indicate that apomorphine suppresses ferroptosis. To our knowledge, this is the first study to report that the anti-ferroptosis effect of apomorphine is not related to dopamine receptor agonist action and that apomorphine is a potent inhibitor of ferroptotic cell death independent of dopaminergic receptors.

The Natural Protoalkaloid Methyl-2-Amino-3-Methoxybenzoate (MAM) Alleviates Positive as well as Cognitive Symptoms in Rat and Mouse Schizophrenia Models.

The development of new antipsychotics with pro-cognitive properties and less side effects represents a priority in schizophrenia drug research. In this study, we present for the first time a preclinical exploration of the effects of the promising natural atypical antipsychotic Methyl-2-Amino-3- Methoxybenzoate (MAM), a brain-penetrable protoalkaloid from the seed of the plant Nigella damascena. Using animal models related to hyperdopaminergic activity, namely the pharmacogenetic apomorphine (D2/D1 receptor agonist)-susceptible (APO-SUS) rat model and pharmacologically induced mouse and rat models of schizophrenia, we found that MAM reduced gnawing stereotypy and climbing behaviours induced by dopaminergic agents. This predicts antipsychotic activity. In line, MAM antagonized apomorphine-induced c-Fos and NPAS4 mRNA levels in post-mortem brain nucleus accumbens and dorsolateral striatum of APO-SUS rats. Furthermore, phencyclidine (PCP, an NMDA receptor antagonist) and 2,5-Dimethoxy-4-iodoamphetamine (DOI, a 5HT2A/2C receptor agonist) induced prepulse inhibition deficits, reflecting the positive symptoms of schizophrenia, which were rescued by treatment with MAM and atypical antipsychotics alike. Post-mortem brain immunostaining revealed that MAM blocked the strong activation of both PCP- and DOI-induced c-Fos immunoreactivity in a number of cortical areas. Finally, during a 28-day subchronic treatment regime, MAM did not induce weight gain, hyperglycemia, hyperlipidemia or hepato- and nephrotoxic effects, side effects known to be induced by atypical antipsychotics. MAM also did not show any cataleptic effects. In conclusion, its brain penetrability, the apparent absence of preclinical side effects, and its ability to antagonize positive and cognitive symptoms associated with schizophrenia make MAM an exciting new antipsychotic drug that deserves clinical testing.

Fabrication and Characterization of Dissolving Microneedles for Transdermal Drug Delivery of Apomorphine Hydrochloride in Parkinson's Disease.

PURPOSE: We fabricated and characterized polyvinyl alcohol (PVA)-based dissolving microneedles (MNs) for transdermal drug delivery of apomorphine hydrochloride (APO), which is used in treating the wearing-off phenomenon observed in Parkinson's disease. METHODS: We fabricated MN arrays with 11 × 11 needles of four different lengths (300, 600, 900, and 1200 µm) by micromolding. The APO-loaded dissolving MNs were characterized in terms of their physicochemical and functional properties. We also compared the pharmacokinetic parameters after drug administration using MNs with those after subcutaneous injection by analyzing the blood concentration of APO in rats. RESULTS: PVA-based dissolving MNs longer than 600 µm could effectively puncture the stratum corneum of the rat skin with penetrability of approximately one-third of the needle length. Although APO is known to have chemical stability issues in aqueous solutions, the drug content in APO-loaded MNs was retained at 25°C for 12 weeks. The concentration of APO after the administration of APO-loaded 600-µm MNs that dissolved completely in skin within 60 min was 81%. The absorption of 200-µg APO delivered by MNs showed a Tmax of 20 min, Cmax of 76 ng/mL, and AUC0-120 min of 2,829 ng・min/mL, compared with a Tmax of 5 min, Cmax of 126 ng/mL, and AUC0-120 min of 3,224 ng・min/mL for subcutaneous injection. The bioavailability in terms of AUC0-120 min of APO delivered by MNs was 88%. CONCLUSION: APO-loaded dissolving MNs can deliver APO via skin into the systemic circulation with rapid absorption and high bioavailability.

[Morphine and Apomorphine, in Sad Cypress].

Christie's Sad Cypress features an impressive trick with morphine and apomorphine. I read the book as if I were this killer, and also thought about the effects of morphine and apomorphine.

Apomorphine Sublingual Film Compared with Subcutaneous Apomorphine for OFF Episodes in Parkinson's Disease: An Open-Label, Randomized, Crossover Study.

BACKGROUND: Apomorphine sublingual film (SL-APO) and subcutaneous apomorphine (SC-APO) have been used for the treatment of OFF episodes in Parkinson's disease (PD). No study has prospectively compared efficacy and safety of these formulations. OBJECTIVE: To compare SL-APO with SC-APO for treatment of OFF episodes in PD. METHODS: An open-label, randomized, crossover study assessed SL-APO versus SC-APO in patients with PD and OFF episodes (N = 113). Doses were optimized in randomly assigned order. SL-APO dose initiation (10 mg) occurred in clinic; further dose optimization (15-30 mg; 5-mg increments) occurred primarily at home. SC-APO dosing (2-6 mg; 1-mg increments) occurred entirely in clinic. After a 3-7-day washout, patients were randomized 1 : 1 to 4 weeks of treatment with their optimized dose of SL-APO or SC-APO, followed by washout and 4 weeks of crossover treatment. RESULTS: Propensity score matching applied on 159 patients (STN-DBS n = 75, MED n = 84) resulted in 40 patients in each treatment group. At 36-month follow-up, STN-DBS led to significantly better PDSS and PDQ-8 change scores, which were significantly correlated. We observed no significant effects for HADS and no significant correlations between change scores in PDSS, HADS, and LEDD. CONCLUSIONS: We report Class IIb evidence of beneficial effects of STN-DBS on quality of sleep at 36-month follow-up, which were associated with QoL improvement independent of depression and dopaminergic medication. Our study highlights the importance of sleep for assessments of DBS outcomes. RESULTS: No difference was observed between SL-APO and SC-APO for change from predose to 90 minutes postdose in Movement Disorder Society Unified Parkinson's Disease Rating Scale Part III score at week 4 (primary endpoint), assessed by a blinded rater (-13.6 vs. -13.8, respectively; p = NS). Overall, 72.2% of patients preferred SL-APO compared with SC-APO/no preference (p = 0.0002) per the Treatment Preference Questionnaire (secondary endpoint). Patients reported greater satisfaction with SL-APO compared with SC-APO, per mean scores of convenience (73.7 vs. 53.5) and global satisfaction (63.9 vs. 57.6) on the Treatment Satisfaction Questionnaire for Medication (other endpoint). The safety profiles of both treatments were generally comparable and were well-tolerated. CONCLUSIONS: Patients reported overall preference for and greater satisfaction with SL-APO over SC-APO.

Apomorphine for Parkinson's disease: pharmacologic and clinical considerations.

INTRODUCTION: In Parkinson's disease, dopamine depletion in the basal ganglia leads to symptoms including bradykinesia, gait abnormalities, and cognitive impairment. Even with treatment, the disease course leads to decreases in the amount of dopamine produced and released into the synapse. As dopamine production falls and the treatment course is insufficient to match the metabolic supply and demand, acute 'off' periods develop that cause reemergence of symptoms. Apomorphine is used to reverse these 'off' periods and restore function in patients with Parkinson's. This review will provide clinicians a concise article to read to learn more about apomorphine and its appropriate utilization. AREAS COVERED: The research discussed is focused on the history, pharmacokinetics, and mechanism of action of Apomorphine. Its utilization as a treatment for Parkinson's Disease and its comparison to currently utilized drugs is also discussed in this review. We focused on articles published on PubMed and Google Scholar within the last 10 years, but in some instances had to go as far back as 1951 to include early articles published about apomorphine. EXPERT OPINION: The expert opinion section focuses on the ways in which apomorphine could be administered in the future to better promote utilization and increase tolerability.

The Nitric Oxide (NO) Donor Molsidomine Attenuates Memory Impairments Induced by the D1/D2 Dopaminergic Receptor Agonist Apomorphine in the Rat.

Several lines of evidence suggest that scarcity of the gaseous molecule nitric oxide (NO) is associated with the pathogenesis of schizophrenia. Therefore, compounds, such as NO donors, that can normalize NO levels might be of utility for the treatment of this pathology. It has been previously shown that the NO donor molsidomine attenuated schizophrenia-like behavioral deficits caused by glutamate hypofunction in rats. The aim of the current study was to investigate the efficacy of molsidomine and that of the joint administration of this NO donor with sub-effective doses of the non-typical antipsychotics clozapine and risperidone to counteract memory deficits associated with dysregulation of the brain dopaminergic system in rats. Molsidomine (2 and 4 mg/kg) attenuated spatial recognition and emotional memory deficits induced by the mixed dopamine (DA) D1/D2 receptor agonist apomorphine (0.5 mg/kg). Further, the joint administration of sub-effective doses of molsidomine (1 mg/kg) with those of clozapine (0.1 mg/kg) or risperidone (0.03 mg/kg) counteracted non-spatial recognition memory impairments caused by apomorphine. The present findings propose that molsidomine is sensitive to DA dysregulation since it attenuates memory deficits induced by apomorphine. Further, the current findings reinforce the potential of molsidomine as a complementary molecule for the treatment of schizophrenia.

Sprague Dawley rats from different vendors vary in the modulation of prepulse inhibition of startle (PPI) by dopamine, acetylcholine, and glutamate drugs.

RATIONALE: Rodent vendors are often utilized interchangeably, assuming that the phenotype of a given strain remains standardized between colonies. Several studies, however, have found significant behavioral and physiological differences between Sprague Dawley (SD) rats from separate vendors. Prepulse inhibition of startle (PPI), a form of sensorimotor gating in which a low-intensity leading stimulus reduces the startle response to a subsequent stimulus, may also vary by vendor. Differences in PPI between rat strains are well known, but divergence between colonies within the SD strain lacks thorough examination. OBJECTIVES: We explored intrastrain variation in PPI by testing SD rats from two vendors: Envigo and Charles River (CR). METHODS: We selected drugs acting on four major neurotransmitter systems that have been repeatedly shown to modulate PPI: dopamine (apomorphine; 0.5, 1.5, 3.0 mg/kg), acetylcholine (scopolamine; 0.1, 0.5, 1.0 mg/kg), glutamate (dizocilpine; 0.5, 1.5, 2.5 mg/kg), and serotonin (2,5-Dimethoxy-4-iodoamphetamine, DOI; 0.25, 0.5, 1.0 mg/kg). We determined PPI and startle amplitude for each drug in male and female Envigo and CR SD rats. RESULTS: SD rats from Envigo showed dose-dependent decreases in PPI after apomorphine, scopolamine, or dizocilpine administration, without significant effects on startle amplitude. SD rats from CR were less sensitive to modulation of PPI and/or more sensitive to modulation of startle amplitude, across the three drugs. CONCLUSIONS: SD rats showed vendor differences in sensitivity to pharmacological modulation of PPI and startle. We encourage researchers to sample rats from separate vendors before experimentation to identify the most suited source of subjects for their specific endpoints.

Contingency learning in zebrafish exposed to apomorphine- and levetiracetam.

Cognitive rigidity (CR) refers to inadequate executive adaptation in the face of changing circumstances. Increased CR is associated with a number of psychiatric disorders, for example, obsessive-compulsive disorder, and improving cognitive functioning by targeting CR in these conditions, may be fruitful. Levetiracetam (LEV), clinically used to treat epilepsy, may have pro-cognitive effects by restoring balance to neuronal signalling. To explore this possibility, we applied apomorphine (APO) exposure in an attempt to induce rigid cue-directed responses following a cue (visual pattern)-reward (social conspecifics) contingency learning phase and to assess the effects of LEV on such behaviours. Briefly, zebrafish were divided into four different 39-day-long exposure groups ( n  = 9-10) as follows: control (CTRL), APO (100 µg/L), LEV (750 µg/L) and APO + LEV (100 µg/L + 750 µg/L). The main findings of this experiment were that 1) all four exposure groups performed similarly with respect to reward- and cue-directed learning over the first two study phases, 2) compared to the CTRL group, all drug interventions, but notably the APO + LEV combination, lowered the degree of reward-directed behaviour during a dissociated presentation of the cue and reward, and 3) temporal and spatial factors influenced the manner in which zebrafish responded to the presentation of the reward. Future studies are needed to explore the relevance of these findings for our understanding of the potential cognitive effects of LEV.

Lacosamide exhibits neuroprotective effects in a rat model of Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder that primarily affects the motor system. Although there are several treatments available to alleviate PD symptoms, there is currently no cure for the disease. Lacosamide, an anti-epileptic drug, has shown promising results in preclinical studies as a potential neuroprotective agent for PD. In this study, we aimed to investigate the neuroprotective effect of lacosamide in a murine model of PD. METHODS: Twenty-one adult male rats were randomly divided into the following three groups (n = 7): 1 group received stereotaxical infusion of dimethyl sulfoxide (vehicle, group 1), and the others received stereotaxical infusion of rotenone (groups 2 and 3). The apomorphine-induced rotation test was applied to the rats after 10 days. Thereafter, group 2 was administered isotonic saline, whereas group 3 was administered lacosamide (20 mg/kg,i.p.) for 28 days. Apomorphine-induced rotation tests were performed to assess the effect of lacosamide on motor function. In addition, immunohistochemistry and biochemistry were used to assess the dopaminergic neuron loss in the substantia nigra and MDA, TNF-α and HVA levels, respectively. RESULTS: In rats with Parkinson's disease induced by rotenone, levels of malondialdehyde and TNF-α significantly increased and HVA levels decreased, whereas in mice treated with lacosamide, levels of malondialdehyde and TNF-α significantly decreased and HVA levels increased. The apomorphine-induced rotation test scores of lacosamide-treated mice were lower compared with the untreated group. Furthermore, treatment with lacosamide significantly mitigated the degeneration of dopaminergic projections within the striatum originating from the substantia nigra and increased tyrosine hydroxylase (TH) immunofluorescence, indicative of preserved dopaminergic neuronal function. CONCLUSION: In conclusion, our study provides evidence that lacosamide has a neuroprotective effect on the rat model of PD. Further studies are required to investigate the underlying mechanisms and evaluate the potential clinical use of lacosamide as a neuroprotective agent for PD.

The dopaminergic D1 receptor modulates the hyperactivity of Bapa mutant mice.

The mutant bate-palmas ("claps"; symbol - bapa) mice induced by the mutagenic chemical ENU present motor incoordination and postural alterations. A previous study showed that bapa mice present increased motor/exploratory behaviors during the prepubertal period due to increased striatal tyrosine hydroxylase expression, suggesting striatal dopaminergic system hyperactivity. This study aimed to evaluate the involvement of striatal dopaminergic receptors in the hyperactivity of bapa mice. Male bapa mice and their wild strain (WT) were used. Spontaneous motor behavior was observed in the open-field test, and stereotypy was evaluated after apomorphine administration. The effects of DR1 and DR2 dopaminergic antagonists (SCH-23,390; sulpiride) and the striatal DR1 and D2 receptor gene expression were evaluated. Relative to WT, bapa mice showed: 1) increased general activity for four days; 2) increased rearing and sniffing behavior and decreased immobility after apomorphine; 3) blockage of rearing behavior after the DR2 antagonist but no effect after DR1 antagonist; 4) blockage of sniffing behavior after the DR1 antagonist in bapa and WT mice but no effect after the DR2 antagonist; 5) increased immobility after the DR1 antagonist but no effect after the DR2 antagonist; 6) increased expression of striatal DR1 receptor gene and reduced the DR2 expression gene after apomorphine administration. Bapa mice showed increased activity in open field behavior. The increased rearing behavior induced by apomorphine of bapa mice resulted from the increased gene expression of the DR1 receptor.

Task Specific Tremor in Parkinson's Disease Responds to Apomorphine.

Background: Task specific tremor (TST) is a poorly understood entity without any standard treatments, that may subsequently develop tremor during additional tasks, later develop postural/kinetic tremor (essential tremor criteria), and later develop Parkinson's disease. The pathophysiology is not understood as it has features of tremor, dystonia, and parkinsonism. Objectives: To assess response of TST to apomorphine and thus infer pathophysiology. Methods: We administered sublingual apomorphine to 8 patients diagnosed with Parkinson's disease based on clinical criteria and dopamine imaging, who all initially presented with TST and later presented other parkinsonian signs and dopamine imaging deficits. Results: Apomorphine improved TST, which was refractory to oral levodopa and other tremor therapies, in 6/8 subjects. Discussion: These results offer a treatment option for TST, which is usually refractory to other pharmacologic treatments, in patients with other parkinsonian features, and infers a dopaminergic pathophysiology of TST.

Adopting the Rumsfeld approach to understanding the action of levodopa and apomorphine in Parkinson's disease.

Dopaminergic therapies dominate the treatment of the motor and non-motor symptoms of Parkinson's disease (PD) but there have been no major advances in therapy in many decades. Two of the oldest drugs used appear more effective than others-levodopa and apomorphine-but the reasons for this are seldom discussed and this may be one cause for a lack of progress. This short review questions current thinking on drug action and looks at whether adopting the philosophy of ex-US Secretary of State Donald Rumsfeld reveals 'unknown' aspects of the actions of levodopa and apomorphine that provide clues for a way forward. It appears that both levodopa and apomorphine have a more complex pharmacology than classical views would suggest. In addition, there are unexpected facets to the mechanisms through which levodopa acts that are either forgotten as 'known unknowns' or ignored as 'unknown unknowns'. The conclusion reached is that we may not know as much as we think about drug action in PD and there is a case for looking beyond the obvious.

Ropinirole has similar efficacy to apomorphine for induction of emesis and removal of foreign and toxic gastric material in dogs.

OBJECTIVE: Assess efficacy of ropinirole versus apomorphine in inducing vomiting in dogs. ANIMALS: 279 client-owned dogs with known or suspected ingestion of a foreign material (n = 129) or toxin (150) between August 2021 and February 2022. PROCEDURES: In this non-randomized non-controlled clinical trial, ropinirole topical ophthalmic solution was applied to dogs' eyes, with a target dose of 3.75 mg/m2. A second dose was administered after 15 minutes based on clinician discretion. Reversal with metoclopramide was provided based on clinician discretion. Results of ropinirole's efficacy were compared to previous literature assessing the efficacy of apomorphine. RESULTS: Of 279 dogs, 255 (91.4%) vomited after ropinirole administration, including 116 of the 129 dogs (89.9%) dogs that ingested foreign material and 139 of the 150 dogs (92.7%) that ingested toxins. Success of emesis did not differ between groups. With a single dose of ropinirole, 78.9% produced vomit. Fifty-nine dogs received 2 doses of ropinirole, resulting in 79.7% that produced vomit. Overall, 74.2% of the dogs vomited all the expected ingested material. Average time to emesis was 11.0 minutes with 50% of dogs vomiting within 7 to 18 minutes. Adverse effects were observed for 17.0% of dog and were self-limiting. Ropinirole was less effective than apomorphine in inducing vomiting (91.4% ropinirole, 95.6% apomorphine [P < .0001]) and equally effective at evacuating all ingested material (74.2% ropinirole, 75.6% apomorphine [P = .245]). CLINICAL RELEVANCE: Ropinirole ophthalmic solution is a safe and effective emetic for use in dogs. It has a small but statistically significant decrease in efficacy compared to IV apomorphine.

Morphine and dopamine: Low dose apomorphine can prevent both the induction and expression of morphine locomotor sensitization and conditioning.

The disinhibition of dopamine neurons in the VTA by morphine is considered an important contributor to the reward potency of morphine. In this report, three experiments were conducted in which a low dose of apomorphine (0.05 mg/kg) was used as a pretreatment to reduce dopamine activity. Locomotor hyperactivity was used as the behavioral response to morphine (10.0 mg/kg). In the first experiment, five treatments with morphine induced the development of locomotor and conditioned hyperactivity that were prevented by apomorphine given 10 min prior to morphine. Apomorphine before either vehicle or morphine induced equivalent reductions in locomotion. In the second experiment, the apomorphine pretreatment was initiated after induction of a conditioned hyperactivity and apomorphine prevented the expression of the conditioning. To assess the effects of apomorphine on VTA and the nucleus accumbens, ERK measurements were carried out after the induction of locomotor and conditioned hyperactivity. Increased ERK activation was found and these effects were prevented by the apomorphine in both experiments. A third experiment was conducted to assess the effects of acute morphine on ERK before locomotor stimulation was induced by morphine. Acute morphine did not increase locomotion, but a robust ERK response was produced indicating that the morphine-induced ERK activation was not secondary to locomotor stimulation. ERK activation was again prevented by the apomorphine pretreatment. We suggest that contiguity between the ongoing behavioral activity and the morphine activation of the dopamine reward system incentivizes and potentiates the ongoing behavior generating equivalent behavioral sensitization and conditioned effects.

Neurobehavioral Profiles of Six Genetically-based Rat Models of Schizophrenia- related Symptoms.

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda.

Dopamine differentially affects retinal circuits to shape the retinal code.

Dopamine has long been reported to enhance antagonistic surrounds of retinal ganglion cells (RGCs). Yet, the retina contains many different RGC subtypes and the effects of dopamine can be subtype-specific. Using multielectrode array (MEA) recordings we investigated how dopamine shapes the receptive fields of RGCs in the mouse retina. We found that the non-selective dopamine receptor agonist apomorphine can either increase or decrease RGCs' surround strength, depending on their subtype. We then used two-photon targeted patch-clamp to target a specific RGC subtype, the transient-Off-αRGC. In line with our MEA recordings, apomorphine did not increase the antagonistic surround of transient-Off-αRGCs but enhanced their responses to Off stimuli in the centre receptive field. Both D1 - and D2 -like family receptor (D1 -R and D2 -R) blockers had the opposite effect and reduced centre-mediated responses, but differently affected transient-Off-αRGC's surround. While D2 -R blocker reduced surround antagonism, D1 -R blocker led to surround activation, revealing On responses to large stimuli. Using voltage-clamp recordings we separated excitatory inputs from Off cone bipolar cells and inhibitory inputs from the primary rod pathway. In control conditions, cone inputs displayed strong surround antagonism, while inputs from the primary rod pathway showed no surround. Yet, the surround activation in the D1 -R blockade originated from the primary rod pathway. Our findings demonstrate that dopamine differentially affects RGC subtypes via distinct pathways, suggesting that dopamine has a more complex role in shaping the retinal code than previously reported. KEY POINTS: Receptive fields of retinal ganglion cells (RGCs) have a centre-surround organisation, and previous work has shown that this organisation can be modulated by dopamine in a light-intensity-dependent manner. Dopamine is thought to enhance RGCs' antagonistic surround, but a detailed understanding of how different RGC subtypes are affected is missing. Using a multielectrode array recordings, clustering analysis and pharmacological manipulations, we found that dopamine can either enhance or weaken antagonistic surrounds, and also change response kinetics, of RGCs in a subtype-specific manner. We performed targeted patch-clamp recordings of one RGC subtype, the transient-Off-αRGC, and identified the underlying circuits by which dopamine shapes its receptive field. Our findings demonstrate that dopamine acts in a subtype-specific manner and can have complex effects, which has implications for other retinal computations that rely on receptive field structure.