Amphetamine-induced Locomotor Activity Research Articles

Low-Impact Ampakine CX1739 Exerts Pro-Cognitive Effects and Reverses Opiate-Induced Respiratory Depression in Rodents

AMPA-glutamate receptors (AMPARs) are expressed throughout the CNS and mediate the majority of fast excitatory synaptic transmission. Ampakines are orally available small molecules that bind allosterically to AMPARs and enhance excitatory currents elicited by the endogenous agonist glutamate. In preclinical studies, ampakines are effective in ameliorating symptoms in a battery of neurodegenerative and neuropsychiatric diseases in which excitatory transmission is compromised. However, the development of ampakines as medicines was slowed by the emergence of neurotoxicity and seizures in rodents due to some ampakines. Here, we describe the preclinical pharmacology of a novel ampakine, N-methyl-N-(tetrahydro-2H-pyran-4-yl)benzo[c][1,2,5] oxadiazole-5-carboxamide (CX1739), that does not induce seizures in animals or humans at efficacious doses. CX1739 dose-dependently enhanced long-term potentiation in vivo in rats, a process thought to be a molecular substrate of learning and memory. Correspondingly, CX1739 dose-dependently enhanced performance in assays that probed multiple aspects of cognition—the novel object recognition test, the win shift radial arm maze, and the five-choice serial reaction time task in rats. CX1739 also abrogated amphetamine-induced locomotor activity, demonstrating that it may be given in conjunction with stimulants for pro-cognitive gains while mitigating the side effects of stimulant-based ADHD medications. CX1739 also rapidly reversed opioid-induced respiratory depression. While efficacy in these tests occurred at doses of 0.03–18 mg/kg, there were no adverse events detected in safety studies in rats up to 2000 mg/kg. These preclinical findings suggest that CX1739 can be translated safely into the clinical setting to potentially treat dementia, neuropsychiatric disorders, and the life-threatening complication of opiate-induced suppression of endogenous inspiratory breathing rhythms.

Sex-Dependent Attentional Impairments in a Subchronic Ketamine Mouse Model for Schizophrenia

BackgroundThe development of more effective treatments for schizophrenia targeting cognitive and negative symptoms has been limited, partly due to a disconnect between rodent models and human illness. Ketamine administration is widely used to model symptoms of schizophrenia in both humans and rodents. In mice, subchronic ketamine treatment reproduces key dopamine and glutamate dysfunction; however, it is unclear how this translates into behavioral changes reflecting positive, negative, and cognitive symptoms. MethodsIn male and female mice treated with either subchronic ketamine or saline, we assessed spontaneous and amphetamine-induced locomotor activity to measure behaviors relevant to positive symptoms, and used a touchscreen-based progressive ratio task of motivation and the rodent continuous performance test of attention to capture specific negative and cognitive symptoms, respectively. To explore neuronal changes underlying the behavioral effects of subchronic ketamine treatment, we quantified expression of the immediate early gene product, c-Fos, in key corticostriatal regions using immunofluorescence. ResultsWe showed that spontaneous locomotor activity was unchanged in male and female subchronic ketamine–treated animals, and amphetamine-induced locomotor response was reduced. Subchronic ketamine treatment did not alter motivation in either male or female mice. In contrast, we identified a sex-specific effect of subchronic ketamine on attentional processing wherein female mice performed worse than control mice due to increased nonselective responding. Finally, we showed that subchronic ketamine treatment increased c-Fos expression in prefrontal cortical and striatal regions, consistent with a mechanism of widespread disinhibition of neuronal activity. ConclusionsOur results highlight that the subchronic ketamine mouse model reproduces a subset of behavioral symptoms that are relevant for schizophrenia.

Glycogen Synthase Kinase 3β Is a Key Regulator in the Inhibitory Effects of Accumbal Cocaine- and Amphetamine-Regulated Transcript Peptide 55-102 on Amphetamine-Induced Locomotor Activity.

Microinjection of cocaine- and amphetamine-regulated transcript (CART) peptide 55-102 into the nucleus accumbens (NAcc) core significantly attenuates psychostimulant-induced locomotor activity. However, the molecular mechanism remains poorly understood. We examined the phosphorylation levels of Akt, glycogen synthase kinase 3β (GSK3β), and glutamate receptor 1 (GluA1) in NAcc core tissues obtained 60 min after microinjection of CART peptide 55-102 into this site, followed by systemic injection of amphetamine (AMPH). Phosphorylation levels of Akt at Thr308 and GSK3β at Ser9 were decreased, while those of GluA1 at Ser845 were increased, by AMPH treatment. These effects returned to basal levels following treatment with CART peptide 55-102. Furthermore, the negative regulatory effects of the CART peptide on AMPH-induced changes in phosphorylation levels and locomotor activity were all abolished by pretreatment with the S9 peptide, an artificially synthesized indirect GSK3β activator. These results suggest that the CART peptide 55-102 in the NAcc core plays a negative regulatory role in AMPH-induced locomotor activity by normalizing the changes in phosphorylation levels of Akt-GSK3β, and subsequently GluA1 modified by AMPH at this site. The present findings are the first to reveal GSK3β as a key regulator of the inhibitory role of the CART peptide in psychomotor stimulant-induced locomotor activity.

Neuron-specific cilia loss differentially alters locomotor responses to amphetamine in mice.

The neural mechanisms that underlie responses to drugs of abuse are complex, and impacted by a number of neuromodulatory peptides. Within the past 10years it has been discovered that several of the receptors for neuromodulators are enriched in the primary cilia of neurons. Primary cilia are microtubule-based organelles that project from the surface of nearly all mammalian cells, including neurons. Despite what we know about cilia, our understanding of how cilia regulate neuronal function and behavior is still limited. The primary objective of this study was to investigate the contributions of primary cilia on specific neuronal populations to behavioral responses to amphetamine. To test the consequences of cilia loss on amphetamine-induced locomotor activity we selectively ablated cilia from dopaminergic or GAD2-GABAergic neurons in mice. Cilia loss had no effect on baseline locomotion in either mouse strain. In mice lacking cilia on dopaminergic neurons, locomotor activity compared to wild- type mice was reduced in both sexes in response to acute administration of 3.0mg/kg amphetamine. In contrast, changes in the locomotor response to amphetamine in mice lacking cilia on GAD2-GABAergic neurons were primarily driven by reductions in locomotor activity in males. Following repeated amphetamine administration (1.0mgkg-1 day-1 over 5days), mice lacking cilia on GAD2-GABAergic neurons exhibited enhanced sensitization of the locomotor stimulant response to the drug, whereas mice lacking cilia on dopaminergic neurons did not differ from wild-type controls. These results indicate that cilia play neuron-specific roles in both acute and neuroplastic responses to psychostimulant drugs of abuse.

Virus-mediated overexpression of radixin in the nucleus accumbens inhibits the development of amphetamine-induced conditioned locomotor activity

Virus-mediated overexpression of radixin in the nucleus accumbens inhibits the development of amphetamine-induced conditioned locomotor activity

Effect of estrous cycle on schizophrenia-like behaviors in MAM exposed rats

Although there are clear sex differences in individuals with schizophrenia, preclinical research has historically favored the use of male rats for behavioral studies. The methylazoxymethanol acetate (MAM) model is a gestational disruption model of schizophrenia and has been reported to produce robust behavioral, neurophysiological and anatomical alterations in male rats; however, whether similar effects are observed in female rats is less well known. In this study, we characterize the behavioral, electrophysiological and molecular alterations induced by prenatal MAM administration in female rats while also examining the potential effects of the estrous cycle on schizophrenia-like behaviors. Specifically, MAM-treated female offspring demonstrated deficits in sensorimotor gating, latent inhibition, and social interaction, consistent with those observed in male animals. Interestingly, amphetamine-induced locomotor activity, latent inhibition, and social interaction were also affected by the estrous cycle. To examine the potential cellular mechanisms associated with these behavioral alterations, we analyzed hippocampal parvalbumin (PV) interneurons. Deficits in PV interneuron number and high-frequency gamma oscillations were disrupted in female MAM-treated rats regardless of the stage of the estrous cycle; however, alterations in PV protein expression were more prominent during metestrus/diestrus. Taken together, these data suggest that prenatal MAM exposure in female rats produces robust behavioral, molecular, and physiological deficits consistent with those observed in the male MAM model of schizophrenia. Moreover, our results also suggest that specific schizophrenia-like symptoms can also be influenced by the estrous cycle, and further emphasize the importance of sex as a biological variable when using preclinical models.

Melatonin receptors limit dopamine reuptake by regulating dopamine transporter cell-surface exposure.

Melatonin, a neuro-hormone released by the pineal gland, has multiple effects in the central nervous system including the regulation of dopamine (DA) levels, but how melatonin accomplishes this task is not clear. Here, we show that melatonin MT1 and MT2 receptors co-immunoprecipitate with the DA transporter (DAT) in mouse striatal synaptosomes. Increased DA re-uptake and decreased amphetamine-induced locomotor activity were observed in the striatum of mice with targeted deletion of MT1 or MT2 receptors. In vitro experiments confirmed the interactions and recapitulated the inhibitory effect of melatonin receptors on DA re-uptake. Melatonin receptors retained DAT in the endoplasmic reticulum in its immature non-glycosylated form. In conclusion, we reveal one of the first molecular complexes between G protein-coupled receptors (MT1 and MT2) and transporters (DAT) in which melatonin receptors regulate the availability of DAT at the plasma membrane, thus limiting the striatal DA re-uptake capacity in mice.

Regulator of G protein signaling-12 modulates the dopamine transporter in ventral striatum and locomotor responses to psychostimulants.

Regulators of G protein signaling are proteins that accelerate the termination of effector stimulation after G protein-coupled receptor activation. Many regulators of G protein signaling proteins are highly expressed in the brain and therefore considered potential drug discovery targets for central nervous system pathologies; for example, here we show that RGS12 is highly expressed in microdissected mouse ventral striatum. Given a role for the ventral striatum in psychostimulant-induced locomotor activity, we tested whether Rgs12 genetic ablation affected behavioral responses to amphetamine and cocaine. RGS12 loss significantly decreased hyperlocomotion to lower doses of both amphetamine and cocaine; however, other outcomes of administration (sensitization and conditioned place preference) were unaffected, suggesting that RGS12 does not function in support of the rewarding properties of these psychostimulants. To test whether observed response changes upon RGS12 loss were caused by changes to dopamine transporter expression and/or function, we prepared crude membranes from the brains of wild-type and RGS12-null mice and measured dopamine transporter-selective [3H]WIN 35428 binding, revealing an increase in dopamine transporter levels in the ventral-but not dorsal-striatum of RGS12-null mice. To address dopamine transporter function, we prepared striatal synaptosomes and measured [3H]dopamine uptake. Consistent with increased [3H]WIN 35428 binding, dopamine transporter-specific [3H]dopamine uptake in RGS12-null ventral striatal synaptosomes was found to be increased. Decreased amphetamine-induced locomotor activity and increased [3H]WIN 35428 binding were recapitulated with an independent RGS12-null mouse strain. Thus, we propose that RGS12 regulates dopamine transporter expression and function in the ventral striatum, affecting amphetamine- and cocaine-induced increases in dopamine levels that specifically elicit acute hyperlocomotor responses.

Impaired contextual fear-conditioning in MAM rodent model of schizophrenia

The methylazoxymethanol acetate (MAM) rodent neurodevelopmental model of schizophrenia exhibits aberrant dopamine system activation attributed to hippocampal dysfunction. Context discrimination is a component of numerous behavioral and cognitive functions and relies on intact hippocampal processing. The present study explored context processing behaviors, along with dopamine system activation, during fear learning in the MAM model.Male offspring of dams treated with MAM (20mg/kg, i.p.) or saline on gestational day 17 were used for electrophysiological and behavioral experiments. Animals were tested on the immediate shock fear conditioning paradigm, with either different pre-conditioning contexts or varying amounts of context pre-exposure (0–10 sessions). Amphetamine-induced locomotor activity and dopamine neural activity was measured 1-week after fear conditioning.Saline, but not MAM animals, demonstrated enhanced fear responses following a single context pre-exposure in the conditioning context. One week following fear learning, saline rats with 2 or 7min of context pre-exposure prior to fear conditioning also demonstrated enhanced amphetamine-induced locomotor response relative to MAM animals. Dopamine neuron recordings showed fear learning-induced reductions in spontaneous dopamine neural activity in MAM rats that was further reduced by amphetamine. Apomorphine administration confirmed that reductions in dopamine neuron activity in MAM animals resulted from over excitation, or depolarization block.These data show a behavioral insensitivity to contextual stimuli in MAM rats that coincide with a less dynamic dopamine response after fear learning.

Parenteral nanoemulsions of risperidone for enhanced brain delivery in acute psychosis: Physicochemical and in vivo performances

This work aimed to deepen the lately acquired knowledge about parenteral nanoemulsions as carriers for brain delivery of risperidone, a poorly water-soluble antipsychotic drug, through establishing the prospective relationship between their physicochemical, pharmacokinetic, biodistribution, and behavioral performances. For this purpose, two optimized risperidone-loaded nanoemulsions, stabilized by lecithin or lecithin/polysorbate 80 mixture, and costabilized by sodium oleate, were produced by high-pressure homogenization. The characterization revealed the favorable droplet size, narrow size distribution, high surface charge, with proven stability to autoclaving and long-term stability for at least one year at 25±2°C. Pharmacokinetic and tissue distribution results demonstrated improved plasma, liver, and brain pharmacokinetic parameters, resulting in 1.2–1.5-fold increased relative bioavailability, 1.1–1.8-fold decreased liver distribution, and about 1.3-fold improved brain uptake of risperidone active moiety following intraperitoneal administration of nanoemulsions relative to solution in rats. In behavioral study, investigated nanoemulsions showed pronounced reduction in basal and, more pertinently, amphetamine-induced locomotor activity in rats, with an early onset of antipsychotic action, and this effect lasted at least 90min after drug injection. Together, these findings corroborate the applicability of parenteral nanoemulsions as carriers for enhanced brain delivery of risperidone, further suggesting their promise in acute psychosis treatment or other emergency situations.

Modeling hypohedonia following repeated social defeat: Individual vulnerability and dopaminergic involvement

Social defeat in rodents putatively can model hypohedonia. The present studies examined models for assessing hypohedonia-like behavior and tested the hypotheses that 1) individual differences in baseline reward sensitivity predict vulnerability, and 2) defeat elicits changes in pharmacological measures of striatal dopaminergic function. Male Wistar rats (n=142) received repeated defeat (3 “triad” blocks of 3 defeats) or control handling. To determine whether defeat influenced consumption of SuperSac (glucose-saccharin) over an isocaloric, less preferred, glucose solution, a 2-choice paradigm was used. To determine repeated defeat effects on the reinforcing efficacy of SuperSac, a progressive-ratio schedule of reinforcement was used. Amphetamine-induced locomotor activity (0.08mg/kg, s.c.) was determined as a measure sensitive to striatal dopaminergic function. Defeat reduced SuperSac consumption during the first two triads—an effect seen in the third triad only in defeated rats with High vs. Low baseline SuperSac intake. The characteristic escalation in PR breakpoint for SuperSac normally seen in controls was absent in defeated rats, leading to a significant difference by the third triad. Defeat-induced blunting of the escalation in PR performance was greater in rats with High antecedent PR breakpoints and persisted 2.5weeks post-defeat. Repeated defeat also blunted amphetamine-induced locomotion 13days post-defeat. Thus, hypohedonic-like effects of social defeat were detected and accompanied by persistently attenuated striatal dopamine function. Early effects were seen for consumption of differentially-palatable solutions, and persistent effects were seen for the “breakpoint” motivational measure. The results implicate initial reward sensitivity as a risk factor for stress-induced hypohedonia.

The Sodium Channel β4 Auxiliary Subunit Selectively Controls Long-Term Depression in Core Nucleus Accumbens Medium Spiny Neurons.

Voltage-gated sodium channels are essential for generating the initial rapid depolarization of neuronal membrane potential during action potentials (APs) that enable cell-to-cell communication, the propagation of signals throughout the brain, and the induction of synaptic plasticity. Although all brain neurons express one or several variants coding for the core pore-forming sodium channel α subunit, the expression of the β (β1–4) auxiliary subunits varies greatly. Of particular interest is the β4 subunit, encoded by the Scn4b gene, that is highly expressed in dorsal and ventral (i.e., nucleus accumbens – NAc) striata compared to other brain regions, and that endows sodium channels with unique gating properties. However, its role on neuronal activity, synaptic plasticity, and behaviors related to drugs of abuse remains poorly understood. Combining whole-cell patch-clamp recordings with two-photon calcium imaging in Scn4b knockout (KO) and knockdown mice, we found that Scn4b altered the properties of APs in core accumbens medium spiny neurons (MSNs). These alterations are associated with a reduction of the probability of MSNs to evoke spike-timing-dependent long-term depression (tLTD) and a reduced ability of backpropagating APs to evoke dendritic calcium transients. In contrast, long-term potentiation (tLTP) remained unaffected. Interestingly, we also showed that amphetamine-induced locomotor activity was significantly reduced in male Scn4b KO mice compared to wild-type controls. Taken together, these data indicate that the Scn4b subunit selectively controls tLTD by modulating dendritic calcium transients evoked by backpropagating APs.

Inositol Phosphate Accumulation in Vivo Provides a Measure of Muscarinic M1 Receptor Activation.

The rationale for using M1 selective muscarinic acetylcholine receptor activators for the treatment of cognitive impairment associated with psychiatric and neurodegenerative disease is well-established in the literature. Here, we investigate measurement of inositol phosphate accumulation, an end point immediately downstream of the M1 muscarinic acetylcholine receptor signaling cascade, as an in vivo biochemical readout for M1 muscarinic acetylcholine receptor activation. Five brain penetrant M1-subtype selective activators from three structurally distinct chemical series were pharmacologically profiled for functional activity in vitro using recombinant cell calcium mobilization and inositol phosphate assays, and a native tissue hippocampal slice electrophysiology assay, to show that all five compounds presented a positive allosteric modulator agonist profile, within a narrow range of potencies. In vivo characterization using an amphetamine-stimulated locomotor activity behavioral assay and the inositol phosphate accumulation biochemical assay demonstrated that the latter has utility for assessing functional potency of M1 activators. Efficacy measured by inositol phosphate accumulation in mouse striatum compared favorably to efficacy in reversing amphetamine-induced locomotor activity, suggesting that the inositol phosphate accumulation assay has utility for the evaluation of M1 muscarinic acetylcholine receptor activators in vivo. The benefits of this in vivo biochemical approach include a wide response window, interrogation of specific brain circuit activation, an ability to model responses in the context of brain exposure, an ability to rank order compounds based on in vivo efficacy, and minimization of animal use.

Medicinal plant Combretum leprosum mart ameliorates motor, biochemical and molecular alterations in a Parkinson's disease model induced by MPTP

Ethnopharmacological relevanceCombretum leprosum is a popular medicinal plant distributed in north and northeastern regions of Brazil. Many different parts of this plant are used in traditional medicine to treat several inflammatory diseases. Parkinson's disease (PD) is a disorder associated with inflammatory toxic factors and the treatments available provide merely a delay of the neurodegeneration. Aim of the studyWe investigated the potential neuroprotective properties of the C. leprosum ethanolic extract (C.l.EE) in a murine model of PD using the toxin 1-methyl-4 phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Materials and methodsThe mice were split into four groups: V/S (vehicle/saline), E/S (extract/saline), V/M (vehicle/MPTP) and E/M (extract/ MPTP). Mice received MPTP (30mg/kg, i.p.) or vehicle (10ml/kg, i.p.) once a day for 5 consecutive days and vehicle (10ml/kg) or C.l.EE (100mg/kg) orally by intra-gastric gavage (i.g.) during a 14-d period, starting 3 days before the first MPTP injection. All groups were assessed for behavioural impairments (amphetamine-induced locomotor activity and muscle strength), dopamine content in striatum using high performance liquid chromatography (HPLC), tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene expressions using qPCR. ResultsAnimals were injected with d-amphetamine (2mg/kg) and the activity was recorded. Amphetamine-induced hyperlocomotion was observed in all groups; however animals treated with MPTP showed exacerbated hyperlocomotion (approximately 3 fold increase compared to control groups). By contrast, mice treated with MPTP that received C.l.EE exhibited attenuation of the hyperlocomotion and did not differ from control groups. Muscle strength test pointed that C.l.EE strongly avoided muscular deficits caused by MPTP (approximately 2 fold increase compared to V/M group). Dopamine and its metabolites were measured in the striatum. The V/M group presented a dopamine reduction of 80%. On the other hand, the E/M group exhibited an increase in dopamine and its metabolites levels (approximately 3 fold increase compared to V/M group). Tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene expressions were significantly reduced in the V/M group (60%). Conversely, C.l.EE treatment was able to increase the mRNA levels of those genes in the E/M group (approximately 2 fold for TH and DAT). ConclusionsThese data show, for the first time, that C. leprosum ethanolic extract prevented motor and molecular changes induced by MPTP, and partially reverted dopamine deficit. Thus, our results demonstrate that C.l.EE has potential for the treatment and prevention of PD.

Parvalbumin and GAD65 interneuron inhibition in the ventral hippocampus induces distinct behavioral deficits relevant to schizophrenia.

Hyperactivity within the ventral hippocampus (vHPC) has been linked to both psychosis in humans and behavioral deficits in animal models of schizophrenia. A local decrease in GABA-mediated inhibition, particularly involving parvalbumin (PV)-expressing GABA neurons, has been proposed as a key mechanism underlying this hyperactive state. However, direct evidence is lacking for a causal role of vHPC GABA neurons in behaviors associated with schizophrenia. Here, we probed the behavioral function of two different but overlapping populations of vHPC GABA neurons that express either PV or GAD65 by selectively inhibiting these neurons with the pharmacogenetic neuromodulator hM4D. We show that acute inhibition of vHPC GABA neurons in adult mice results in behavioral changes relevant to schizophrenia. Inhibiting either PV or GAD65 neurons produced distinct behavioral deficits. Inhibition of PV neurons, affecting ∼80% of the PV neuron population, robustly impaired prepulse inhibition of the acoustic startle reflex (PPI), startle reactivity, and spontaneous alternation, but did not affect locomotor activity. In contrast, inhibiting a heterogeneous population of GAD65 neurons, affecting ∼40% of PV neurons and 65% of cholecystokinin neurons, increased spontaneous and amphetamine-induced locomotor activity and reduced spontaneous alternation, but did not alter PPI. Inhibition of PV or GAD65 neurons also produced distinct changes in network oscillatory activity in the vHPC in vivo. Together, these findings establish a causal role for vHPC GABA neurons in controlling behaviors relevant to schizophrenia and suggest a functional dissociation between the GABAergic mechanisms involved in hippocampal modulation of sensorimotor processes.

The effects of mGluR2/3 activation on acute and repeated amphetamine-induced locomotor activity in differentially reared male rats.

Environmental stimuli play a key role in affecting the likelihood to abuse drugs. Environmental enrichment can reduce that likelihood. The neurotransmitter glutamate contributes to both drug reward and rearing-induced changes in the brain. The current study investigated the effects of the Group-2 metabotropic glutamate receptor (mGluR2/3) agonist, LY-379268 (0.5, 1.0 mg/kg), on acute and repeated amphetamine-induced locomotor activity in differentially reared male rats. Male Sprague-Dawley rats were randomly assigned to one of 3 environmental conditions postweaning: enriched (EC), isolated (IC), or standard (SC), where they reared for 30 days. The effect of LY-379268 on acute amphetamine-induced locomotor activity was assessed. Rats were injected with either LY-379268 (0.5, 1.0 mg/kg) or saline prior to an amphetamine (0.5 mg/kg) or saline challenge injection. Rats were also administered amphetamine (0.5 mg/kg) or saline injections prior to 5 locomotor sessions. Following a rest period of 14-15 days, the effects of repeated amphetamine exposure were evaluated using LY-379268 (0.5, 1.0 mg/kg) or saline injections 30 min prior to receiving amphetamine (0.5 mg/kg). Results showed that LY-379268 administration dose-dependently attenuated acute amphetamine-induced locomotor activity, with EC rats generally displaying less attenuation than IC or SC rats. After repeated amphetamine administrations, the ability of LY-379268 to attenuate the final expression of amphetamine-induced locomotor activity in differentially reared rats was dose-dependent. The differing effect of LY-379268 observed in EC rats suggests enrichment-induced glutamatergic alterations that may protect against sensitivity to psychostimulants.

Optogenetic inhibition of neurons by internal light production.

Optogenetics is an extremely powerful tool for selective neuronal activation/inhibition and dissection of neural circuits. However, a limitation of in vivo optogenetics is that an animal must be tethered to an optical fiber for delivery of light. Here, we describe a new method for in vivo, optogenetic inhibition of neural activity using an internal, animal-generated light source based on firefly luciferase. Two adeno-associated viruses encoding luciferase were tested and both produced concentration-dependent light after administration of the substrate, luciferin. Mice were co-infected with halorhodopsin- and luciferase-expressing viruses in the striatum, and luciferin administration significantly reduced Fos activity compared to control animals infected with halorhodopsin only. Recordings of neuronal activity in behaving animals confirmed that firing was greatly reduced after luciferin administration. Finally, amphetamine-induced locomotor activity was reduced in halorhodopsin/luciferase mice pre-injected with luciferin compared to controls. This demonstrates that virally encoded luciferase is able to generate sufficient light to activate halorhodopsin and suppress neural activity and change behavior. This approach could be used to generate inhibition in response to activation of specific molecular pathways.

Neonatal Exposure to Estradiol Valerate Increases Dopamine Content in Nigrostriatal Pathway During Adulthood in the Rat

Research in programming has focused in the study of stimuli that affect sensitive periods of development such as prenatal and neonatal stage. We previously showed that exposure to estradiol valerate to female rats during the first 12 h of life increased catecholamine content in ventromedial-arcuatus hypothalamus of the adult rat. However, changes in others dopaminergic circuits have not been studied. The purpose of this work was to determine the neurotransmitters changes induced by neonatal estradiol valerate (0.1 mg/50 μl s. c. per rat) administration on nigrostriatal pathway of adult female rats. Sesame oil (50 μl s. c. per rat) was administered in a control parallel group. EV-1 adult rats presented effective markers of long-term estrogenization as decreased serum levels of progesterone and a reduction in the size of estrogen-sensitive organs. In the brain, neonatal estradiol valerate administration led to a significant increase in dopamine content in striatum, substantia nigra and ventral tegmental area. With respect to the contents of dopamine metabolites, only 3-methoxytyramine content increased in substantia nigra and ventral tegmental area. In addition, the content of noradrenaline increased only in striatum. Interestingly, estrogenized rats lacked locomotor activity induced by acute dose of amphetamine (1 mg/kg i. p.). Altogether, these results show that neonatal exposure to estradiol valerate permanently modified the content of monoamine neurotransmitters in nigrostriatal pathway and amphetamine-induced locomotor activity of adult female rats. This might imply that estrogenized rats could have changes in the expression of key proteins in dopaminergic regulation, as tyrosine hydroxylase and dopamine transporter.

Estrogen potentiates the behavioral and nucleus accumbens dopamine response to continuous haloperidol treatment in female rats

Estrogen has been shown to enhance the effects of antipsychotics in humans. To investigate the mechanisms of how this may occur, the current study examined estradiol's effects on dopaminergic transmission and behavior in amphetamine-sensitized and non-sensitized female rats. Sixty-four ovariectomized female Sprague-Dawley rats were used for this study. Half of the rats were sensitized to four once-daily injections of 1mg/kg amphetamine and the other half served as controls. Rats received chronic administration of either low-dose haloperidol (0.25mg/kg/day) or saline vehicle via osmotic minipumps implanted subcutaneously. The groups were further subdivided with respect to estradiol treatment: low chronic estrogen (subcutaneous estradiol implant, 0.36mg/pellet: 90-day release, plus an additional oil vehicle injection every second day) and high pulsatile estrogen (subcutaneous estradiol implant plus an additional 10μg/kg estradiol injection every second day). Motor activity was assessed at day2 and day12 during haloperidol treatment, while nucleus accumbens dopamine availability was assessed via microdialysis 10days into antipsychotic treatment. Haloperidol treatment along with high, but not low, estradiol replacement was effective in reducing amphetamine-induced locomotor activity in sensitized rats. High estradiol treatment also augmented the effects of chronic haloperidol in reducing dopaminergic release in sensitized rats. These data suggest that estradiol levels affect both the behavioral and the dopamine responses to chronic antipsychotic treatment.

Repeated aripiprazole treatment causes dopamine D2 receptor up-regulation and dopamine supersensitivity in young rats

Aripiprazole is a second-generation antipsychotic that is increasingly being prescribed to children and adolescents. Despite this trend, little preclinical research has been done on the neural and behavioral actions of aripiprazole during early development. In the present study, young male and female Sprague-Dawley rats were pretreated with vehicle, haloperidol (1 mg/kg), or aripiprazole (10 mg/kg) once daily on postnatal days (PD) 10-20. After 1, 4, or 8 days (i.e. on PD 21, PD 24, or PD 28), amphetamine-induced locomotor activity and stereotypy, as well as dorsal striatal D2 receptor levels, were measured in separate groups of rats. Pretreating young rats with aripiprazole or haloperidol increased D2 binding sites in the dorsal striatum. Consistent with these results, dopamine supersensitivity was apparent when aripiprazole- and haloperidol-pretreated rats were given a test day injection of amphetamine (2 or 4 mg/kg). Increased D2 receptor levels and altered behavioral responding persisted for at least 8 days after conclusion of the pretreatment regimen. Contrary to what has been reported in adults, repeated aripiprazole treatment caused D2 receptor up-regulation and persistent alterations of amphetamine-induced behavior in young rats. These findings are consistent with human clinical studies showing that children and adolescents are more prone than adults to aripiprazole-induced side effects, including extrapyramidal symptoms.