Pharmacology and behavioral pharmacology of the mesocortical dopamine system

Juvenile fluoxetine treatment affects the maturation of the medial prefrontal cortex and behavior of adolescent female rats

BACKGROUND

Serotonin is strongly involved in the regulation of brain development, including the proper formation of neuronal circuits and synaptic plasticity. One of the factors that can affect brain serotonin levels is exposure to fluoxetine (FLX), a selective serotonin reuptake inhibitor, the first-line pharmacological treatment for depression and anxiety in the pediatric population. The safety of early-life FLX treatment is still questionable. Women are more prone to anxiety and depression from a young age. We hypothesized that juvenile FLX treatment influences the brain maturation and behavior of adolescent females.

METHODS

On postnatal days 20 to 28, juvenile female rats were injected once daily with FLX. Five days later, anxiety- and fear-related behaviors and amphetamine-induced locomotor activity were assessed. On postnatal day 40, the numbers of neurons and glial cells in the medial prefrontal cortex (mPFC) and hippocampus were estimated via stereological methods. Additionally, the mRNA expression of cell survival/apoptosis and synaptic plasticity markers was evaluated via RT‒qPCR.

RESULTS

FLX-treated females showed decreased anxiety level, freezing behavior during fear conditioning and amphetamine-induced locomotor activity when compared to control females. Simultaneously, FLX-injected females presented greater regional volume and numbers of neurons and astrocytes in specific subregions of the mPFC when compared to the control group. Additionally, FLX-treated females showed increased expression of genes regulating cell survival and reduced mRNA levels of AMPA glutamate receptors in the mPFC.

CONCLUSIONS

Juvenile FLX affects the maturation of the mPFC and attenuates anxiety-like behavior, fear memory and the locomotor response to amphetamine in adolescent females.

The influence of high-fat diet on nicotine vapor self-administration, neuronal excitability, and leptin levels in adult mice

With the rise in fast-food culture and the continued high numbers of tobacco-related deaths, there has been a great deal of interest in understanding the relationship between high-fat diet (HFD) and nicotine use behaviors. Using adult mice and a patch-clamp electrophysiology assay, we investigated the influence of HFD on the excitability of ventral tegmental area (VTA) dopamine neurons and pyramidal neurons in the medial prefrontal cortex (mPFC) given their role in modulating the reinforcing effects of nicotine and natural rewards. We then examined whether HFD-induced changes in peripheral markers were associated with nicotine use behaviors. Here, mice were assigned standard diet (SD) or HFD for 6 weeks and then trained to self-administer nicotine using an e-vape® self-administration (EVSA) assay. After the last session, changes in glucose, insulin, and leptin were assessed with ELISA. HFD-assigned mice displayed a decrease in intrinsic excitability of VTA dopamine neurons; but an increase in intrinsic excitability of layer VI prelimbic mPFC neurons. SD-assigned female mice demonstrated enhanced nicotine EVSA during fixed-ratio 3 relative to SD males. HFD-assigned male and female mice displayed increased nicotine EVSA during FR1. However, only HFD-assigned male mice exhibited enhanced nicotine EVSA during FR3. Finally, HFD-assigned male and female mice displayed increased leptin levels. However, we only observed a direct correlation between leptin levels and EVSA responding during FR1 in HFD-fed male mice. These results suggest that high-fat diet alter nicotine intake in a sex-specific manner, and this may be due to diet-induced changes in neuronal excitability and circulating leptin levels.

Mescaline-induced behavioral alterations are mediated by 5-HT2A and 5-HT2C receptors in rats

RATIONALE

Mescaline is a classical psychedelic compound with a phenylethylamine structure that primarily acts on serotonin 5-HT2A/C receptors, but also binds to 5-HT1A and 5-HT2B receptors. Despite being the first psychedelic ever isolated and synthesized, the precise role of different serotonin receptor subtypes in its behavioral pharmacology is not fully understood.

OBJECTIVES

In this study, we aimed to investigate how selective antagonists of 5-HT2A, 5-HT2B, 5-HT2C, and 5-HT1A receptors affect the behavioral changes induced by subcutaneous administration of mescaline (at doses of 10, 20, and 100 mg/kg) in rats.

METHODS

We used adult male Wistar rats in all our experiments. We evaluated locomotor activity using the open field test, and assessed sensorimotor gating deficits by measuring prepulse inhibition (PPI) of acoustic startle reaction (ASR).

RESULTS

While the highest dose of mescaline induced hyperlocomotion (p < 0.001), which almost all the other antagonists reversed (p < 0.05-0.001), the PPI deficits were selectively normalized by the 5-HT2A antagonist (p < 0.05-0.01). The 5-HT2C antagonist partially reversed the small PPI deficit induced by lower doses of mescaline (p = 0.0017).

CONCLUSION

Our findings suggest that mescaline-induced changes in behavior are primarily mediated by the 5-HT2A receptor subtype, with less pronounced contributions from the 5-HT2C receptor. The other antagonists had limited effects.

Dopaminergic Epistases in Schizophrenia

Background: The dopaminergic theory, the oldest and most comprehensively analyzed neurotransmitter theory of schizophrenia, remains a focal point of research. Methods: This systematic review examines the association between combinations of 14 dopaminergic genes and the risk of schizophrenia. The selected genes include dopamine receptors (DRD1-5), metabolizing enzymes (COMT, MAOA, MAOB, DBH), synthesizing enzymes (TH, DDC), and dopamine transporters (DAT, VMAT1, and VMAT2). Results: Recurring functional patterns show combinations with either hyperdopaminergic effects in limbic and striatal regions or high striatal and low prefrontal dopamine levels. The protective statuses of certain alleles or genotypes are often maintained in epistatic effects; however, exceptions exist. This complexity could explain the inconsistent results in previous genetic studies. Investigating individual alleles may be insufficient due to the heterozygous advantage observed in some studies. Conclusions: Schizophrenia may not be a monolithic disease, but rather a sum of different phenotypes which respond uniquely to different treatment and prevention approaches.

Dopamine D1 receptor in medial prefrontal cortex mediates the effects of TAAR1 activation on chronic stress-induced cognitive and social deficits

Trace amine-associated receptor 1 (TAAR1) is an intracellular expressed G-protein-coupled receptor that is widely expressed in major dopaminergic areas and plays a crucial role in modulation of central dopaminergic neurotransmission and function. Pharmacological studies have clarified the roles of dopamine D1 receptor (D1R) in the medial prefrontal cortex (mPFC) in cognitive function and social behaviors, and chronic stress can inhibit D1R expression due to its susceptibility. Recently, we identified TAAR1 in the mPFC as a potential target for treating chronic stress-induced cognitive and social dysfunction, but whether D1R is involved in mediating the effects of TAAR1 agonist remains unclear. Combined genomics and transcriptomic studies revealed downregulation of D1R in the mPFC of TAAR1-/- mice. Molecular dynamics simulation showed that hydrogen bond, salt bridge, and Pi-Pi stacking interactions were formed between TAAR1 and D1R indicating a stable TAAR1-D1R complex structure. Using pharmacological interventions, we found that D1R antagonist disrupted therapeutic effect of TAAR1 partial agonist RO5263397 on stress-related cognitive and social dysfunction. Knockout TAAR1 in D1-type dopamine receptor-expressing neurons reproduced adverse effects of chronic stress, and TAAR1 conditional knockout in the mPFC led to similar deficits, along with downregulation of D1R expression, all of these effects were ameliorated by viral overexpression of D1R in the mPFC, suggesting the functional interaction between TAAR1 and D1R. Collectively, our data elucidate the possible molecular mechanism that D1R in the mPFC mediates the effects of TAAR1 activation on chronic stress-induced cognitive and social deficits.

Preconception ethanol exposure changes anxiety, depressive and checking-like behavior and alter the expression levels of MAO-B in male offspring

Alcohol use, which alters the epigenome, increases the probability that it could affect subsequent generations, even if they were never directly exposed to ethanol or even in utero. We explored the effects of parental ethanol exposure before conception on behavioral changes in the offspring. Considering the role of Monoamine oxidase-B (MAO-B) in dopamine turnover in the prefrontal cortex (PFC) and its influence on behavior, and taking into account that ethanol exposure could alter MAO-B, we assessed the protein levels in the offspring. Male and female rats were exposed to ethanol for 30 days and then allowed ten days of abstinence. Afterward, they were mated with either control or ethanol-exposed rats. The F1 and F2 male offspring underwent tests to assess behavioral changes. Additionally, the levels of MAO-B in the PFC were evaluated. Results revealed that in the F1, anxiety increased only in the bi-parental ethanol-exposed male offspring in the elevated plus maze test (p < 0.05), while depressive-like behavior rose only in maternal and bi-parental ethanol-exposed offspring (p < 0.01). However, compulsive-like behavior increased in all ethanol-exposed offspring (p < 0.01). No significant phenotypic changes were observed in the F2. The levels of MAO-B in the PFC increased in the maternal (p < 0.05) and bi-parental ethanol-exposed offspring (p < 0.01). Our study demonstrates that parental ethanol exposure, even in the days preceding mating, adversely affects behaviors and induces molecular changes in the brain. Given these findings, it becomes imperative to monitor children exposed to parental (especially maternal) ethanol for the prevention of mental disorders.

Memory-specific encoding activities of the ventral tegmental area dopamine and GABA neurons

Although the midbrain dopamine (DA) system plays a crucial role in higher cognitive functions, including updating and maintaining short-term memory, the encoding properties of the somatic spiking activity of ventral tegmental area (VTA) DA neurons for short-term memory computations have not yet been identified. Here, we probed and analyzed the activity of optogenetically identified DA and GABA neurons while mice engaged in short-term memory-dependent behavior in a T-maze task. Single-neuron analysis revealed that significant subpopulations of DA and GABA neurons responded differently between left and right trials in the memory delay. With a series of control behavioral tasks and regression analysis tools, we show that firing rate differences are linked to short-term memory-dependent decisions and cannot be explained by reward-related processes, motivated behavior, or motor-related activities. This evidence provides novel insights into the mnemonic encoding activities of midbrain DA and GABA neurons.

Enhancement of neuronal excitability in the medial prefrontal cortex following prenatal morphine exposure

The clinical use and abuse of opioids during human pregnancy have been widely reported. Several studies have demonstrated that opioids cross the placenta in rats during late gestation, and prenatal morphine exposure has been shown to have negative outcomes in cognitive function. The medial prefrontal cortex (mPFC) is believed to play a crucial role in cognitive processes, motivation, and emotion, integrating neural information from several brain areas and sending converted information to other structures. Dysfunctions in this area have been observed in numerous psychiatric and neurological disorders, including addiction. This current study aimed to compare the electrophysiological properties of mPFC neurons in rat offspring prenatally exposed to morphine. Pregnant rats were injected with morphine or saline twice a day from gestational days 11-18. Whole-cell patch-clamp recordings were performed in male offspring on postnatal days 14-18. All recordings were obtained in current-clamp configuration from mPFC pyramidal neurons to assess their electrophysiological properties. The results revealed that prenatal exposure to morphine shifted the resting membrane potential (RMP) to less negative voltages and increased input resistance and duration of action potentials. However, the amplitude, rise slope, and afterhyperpolarization (AHP) amplitude of the first elicited action potentials were significantly decreased in rats prenatally exposed to morphine. Moreover, the sag voltage ratio was significantly decreased in the prenatal morphine group. Our results suggest that the changes observed in the electrophysiological properties of mPFC neurons indicate an elevation in neuronal excitability following prenatal exposure to morphine.

ADX106772, an mGlu2 receptor positive allosteric modulator, selectively attenuates oxycodone taking and seeking

Opioid abuse and overdose have risen to epidemic proportions in the United States. Oxycodone is the most abused prescription opioid. Treatments for opioid use disorder (OUD) seek to reduce vulnerability to relapse by reducing sources of reinforcement to seek drug (i.e., acute drug effects or drug withdrawal/craving). Accumulating evidence that glutamate release elicits drug-seeking behaviors has generated interest in pharmacotherapies targeting the glutamate system. Agonists and positive allosteric modulators of the metabotropic glutamate 2 (mGlu2) receptor decrease glutamate activity, reducing drug taking and seeking. The present study tested whether the mGlu2 receptor positive allosteric modulator ADX106772 reduces oxycodone self-administration and the conditioned reinstatement of oxycodone seeking without affecting behaviors directed toward a highly palatable nondrug reinforcer (sweetened condensed milk). Male Wistar rats were trained to self-administer oxycodone (0.15 mg/kg/infusion, i.v., 12 h/day) or sweetened condensed milk (SCM; diluted 2:1 v/v in H2O, orally, 30 min/day) for 13 days in the presence of a contextual/discriminative stimulus (SD), and the ability of ADX106772 (0, 0.3, 1, 3 and-10 mg/kg, s. c.) to decrease self-administration was tested. The rats then underwent extinction training, during which oxycodone, SCM, and the SD were withheld. After extinction, the ability of ADX106772 to prevent SD-induced conditioned reinstatement of oxycodone and SCM seeking was tested. ADX106772 reduced oxycodone self-administration and conditioned reinstatement without affecting SCM self-administration or conditioned reinstatement. ADX106772 reduced oxycodone taking and seeking and did not affect the motivation for the palatable conventional reinforcer, SCM, suggesting that activating mGlu2 receptors with a positive allosteric modulator is a potential approach for prescription OUD treatment.

Adolescent neurostimulation of dopamine circuit reverses genetic deficits in frontal cortex function

Dopamine system dysfunction is implicated in adolescent-onset neuropsychiatric disorders. Although psychosis symptoms can be alleviated by antipsychotics, cognitive symptoms remain unresponsive and novel paradigms investigating the circuit substrates underlying cognitive deficits are critically needed. The frontal cortex and its dopaminergic input from the midbrain are implicated in cognitive functions and undergo maturational changes during adolescence. Here, we used mice carrying mutations in Arc or Disc1 to model mesofrontal dopamine circuit deficiencies and test circuit-based neurostimulation strategies to restore cognitive functions. We found that in a memory-guided spatial navigation task, frontal cortical neurons were activated coordinately at the decision-making point in wild-type but not Arc-/- mice. Chemogenetic stimulation of midbrain dopamine neurons or optogenetic stimulation of frontal cortical dopamine axons in a limited adolescent period consistently reversed genetic defects in mesofrontal innervation, task-coordinated neuronal activity, and memory-guided decision-making at adulthood. Furthermore, adolescent stimulation of dopamine neurons also reversed the same cognitive deficits in Disc1+/- mice. Our findings reveal common mesofrontal circuit alterations underlying the cognitive deficits caused by two different genes and demonstrate the feasibility of adolescent neurostimulation to reverse these circuit and behavioral deficits. These results may suggest developmental windows and circuit targets for treating cognitive deficits in neurodevelopmental disorders.

Neurotransmitter systems in the etiology of major neurological disorders: Emerging insights and therapeutic implications

Neurotransmitters serve as chemical messengers playing a crucial role in information processing throughout the nervous system, and are essential for healthy physiological and behavioural functions in the body. Neurotransmitter systems are classified as cholinergic, glutamatergic, GABAergic, dopaminergic, serotonergic, histaminergic, or aminergic systems, depending on the type of neurotransmitter secreted by the neuron, allowing effector organs to carry out specific functions by sending nerve impulses. Dysregulation of a neurotransmitter system is typically linked to a specific neurological disorder. However, more recent research points to a distinct pathogenic role for each neurotransmitter system in more than one neurological disorder of the central nervous system. In this context, the review provides recently updated information on each neurotransmitter system, including the pathways involved in their biochemical synthesis and regulation, their physiological functions, pathogenic roles in diseases, current diagnostics, new therapeutic targets, and the currently used drugs for associated neurological disorders. Finally, a brief overview of the recent developments in neurotransmitter-based therapeutics for selected neurological disorders is offered, followed by future perspectives in that area of research.

Adolescent neurostimulation of dopamine circuit reverses genetic deficits in frontal cortex function

Dopamine system dysfunction is commonly implicated in adolescent-onset neuropsychiatric disorders. Although psychosis symptoms can be alleviated by antipsychotics, cognitive symptoms remain unresponsive to such pharmacological treatments and novel research paradigms investigating the circuit substrates underlying cognitive deficits are critically needed. The frontal cortex and its dopaminergic input from the midbrain are implicated in cognitive functions and undergo maturational changes during adolescence. Here, we used mice carrying mutations in the Arc or DISC1 genes to model mesofrontal dopamine circuit deficiencies and test circuit-based neurostimulation strategies to restore cognitive functions. We found that in a memory-guided spatial navigation task, frontal cortical neurons were activated coordinately at the decision-making point in wild-type but not Arc mutant mice. Chemogenetic stimulation of midbrain dopamine neurons or optogenetic stimulation of frontal cortical dopamine axons in a limited adolescent period consistently reversed genetic defects in mesofrontal innervation, task-coordinated neuronal activity, and memory-guided decision-making at adulthood. Furthermore, adolescent stimulation of dopamine neurons also reversed the same cognitive deficits in DISC1 mutant mice. Our findings reveal common mesofrontal circuit alterations underlying the cognitive deficits caused by two different genes and demonstrate the feasibility of adolescent neurostimulation to reverse these circuit and behavioral deficits. These results may suggest developmental windows and circuit targets for treating cognitive deficits in neurodevelopmental disorders.

The endogenous cannabinoid system modulates male sexual behavior expression

The endocannabinoid system (ECS) plays a key neuromodulatory role in the brain. Main features of endocannabinoids (eCBs) are that they are produced on demand, in response to enhanced neuronal activity, act as retrograde messengers, and participate in the induction of brain plasticity processes. Sexual activity is a motivated behavior and therefore, the mesolimbic dopaminergic system (MSL) plays a central role in the control of its appetitive component (drive to engage in copulation). In turn, copulation activates mesolimbic dopamine neurons and repeated copulation produces the continuous activation of the MSL system. Sustained sexual activity leads to the achievement of sexual satiety, which main outcome is the transient transformation of sexually active male rats into sexually inhibited animals. Thus, 24 h after copulation to satiety, the sexually satiated males exhibit a decreased sexual motivation and do not respond to the presence of a sexually receptive female with sexual activity. Interestingly, blockade of cannabinoid receptor 1 (CB1R) during the copulation to satiety process, interferes with both the appearance of the long-lasting sexual inhibition and the decrease in sexual motivation in the sexually satiated males. This effect is reproduced when blocking CB1R at the ventral tegmental area evidencing the involvement of MSL eCBs in the induction of this sexual inhibitory state. Here we review the available evidence regarding the effects of cannabinoids, including exogenously administered eCBs, on male rodent sexual behavior of both sexually competent animals and rat sub populations spontaneously showing copulatory deficits, considered useful to model some human male sexual dysfunctions. We also include the effects of cannabis preparations on human male sexual activity. Finally, we review the role played by the ECS in the control of male sexual behavior expression with the aid of the sexual satiety phenomenon. Sexual satiety appears as a suitable model for the study of the relationship between eCB signaling, MSL synaptic plasticity and the modulation of male sexual motivation under physiological conditions that might be useful for the understanding of MSL functioning, eCB-mediated plasticity and their relationship with motivational processes.

Modulation of the endoplasmic reticulum stress and unfolded protein response mitigates the behavioral effects of early-life stress

BACKGROUND

Early-life stress (ELS) affects brain development and increases the risk of mental disorders associated with the dysfunction of the medial prefrontal cortex (mPFC). The mechanisms of ELS action are not well understood. Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are cellular processes involved in brain maturation through the regulation of pro-survival or proapoptotic processes. We hypothesized that ER stress and the UPR in the mPFC are involved in the neurobiology of ELS.

METHODS

We performed a maternal separation (MS) procedure from postnatal days 1 to 14 in rats. Before each MS, pups were injected with an inhibitor of ER stress, salubrinal or a vehicle. The mRNA and protein expression of UPR and apoptotic markers were evaluated in the mPFC using RT-qPCR and Western blot methods, respectively. We also estimated the numbers of neurons and glial cells using stereological methods. Additionally, we assessed behavioral phenotypes related to fear, anhedonia and response to psychostimulants.

RESULTS

MS slightly enhanced the activation of the UPR in juveniles and modulated the expression of apoptotic markers in juveniles and preadolescents but not in adults. Additionally, MS did not affect the numbers of neurons and glial cells at any age. Both salubrinal and vehicle blunted the expression of UPR markers in juvenile and preadolescent MS rats, often in a treatment-specific manner. Moreover, salubrinal and vehicle generally alleviated the behavioral effects of MS in preadolescent and adult rats.

CONCLUSIONS

Modulation of ER stress and UPR processes may potentially underlie susceptibility or resilience to ELS.

µ-Opioid Receptors Expressed by Intrinsically Photosensitive Retinal Ganglion Cells Contribute to Morphine-Induced Behavioral Sensitization

Opioid drugs are the most effective tools for treating moderate to severe pain. Despite their analgesic efficacy, long-term opioid use can lead to drug tolerance, addiction, and sleep/wake disturbances. While the link between opioids and sleep/wake problems is well-documented, the mechanism underlying opioid-related sleep/wake problems remains largely unresolved. Importantly, intrinsically photosensitive retinal ganglion cells (ipRGCs), the cells that transmit environmental light/dark information to the brain's sleep/circadian centers to regulate sleep/wake behavior, express μ-opioid receptors (MORs). In this study, we explored the potential contribution of ipRGCs to opioid-related sleep/circadian disruptions. Using implanted telemetry transmitters, we measured changes in horizontal locomotor activity and body temperature in mice over the course of a chronic morphine paradigm. Mice lacking MORs expressed by ipRGCs (McKO) exhibited reduced morphine-induced behavioral activation/sensitization compared with control littermates with normal patterns of MOR expression. Contrastingly, mice lacking MORs globally (MKO) did not acquire morphine-induced locomotor activation/sensitization. Control mice also showed morphine-induced hypothermia in both the light and dark phases, while McKO littermates only exhibited morphine-induced hypothermia in the dark. Interestingly, only control animals appeared to acquire tolerance to morphine's hypothermic effect. Morphine, however, did not acutely decrease the body temperature of MKO mice. These findings support the idea that MORs expressed by ipRGCs could contribute to opioid-related sleep/wake problems and thermoregulatory changes.

Modafinil Administration to Preadolescent Rat Impairs Non-Selective Attention, Frontal Cortex D2 Expression and Mesolimbic GABA Levels

The misuse of psychostimulants is an increasing behavior among young people, highlighting in some countries the abuse of modafinil (MOD) as a neuropotentiator. However, several clinical trials are investigating MOD as an alternative pharmacological treatment for attentional deficit and hyperactivity disorder (ADHD) in children and adolescents. On the other hand, the early use of psychostimulants and the misdiagnosis rates in ADHD make it crucial to investigate the brain effects of this type of drug in young healthy individuals. The aim of this work was to evaluate the effects of chronic MOD treatment on neurochemicals (γ-aminobutyric acid and glutamate), dopamine receptor 2 (D₂) expression and behavior (non-selective attention "NSA") in the mesocorticolimbic system of young healthy Sprague-Dawley rats. Preadolescent male rats were injected with MOD (75 mg/kg, i.p.) or a vehicle for 14 days (from postnatal day 22 to 35). At postnatal day 36, we measured the GLU and GABA contents and their extracellular levels in the nucleus accumbens (NAc). In addition, the GLU and GABA contents were measured in the ventral tegmental area (VTA) and D₂ protein levels in the prefrontal cortex (PFC). Chronic use of MOD during adolescence induces behavioral and neurochemical changes associated with the mesocorticolimbic system, such as a reduction in PFC D₂ expression, VTA GABA levels and NSA. These results contribute to the understanding of the neurological effects of chronic MOD use on a young healthy brain.

Characterization of orexin input to dopamine neurons of the ventral tegmental area projecting to the medial prefrontal cortex and shell of nucleus accumbens

Orexin neurons are involved in homeostatic regulatory processes, including arousal and feeding, and provide a major input from the hypothalamus to the ventral tegmental area (VTA) of the midbrain. VTA neurons are a central hub processing reward and motivation and target the medial prefrontal cortex (mPFC) and the shell part of nucleus accumbens (NAcs). We investigated whether subpopulations of dopamine (DA) neurons in the VTA projecting either to the mPFC or the medial division of shell part of nucleus accumbens (mNAcs) receive differential input from orexin neurons and whether orexin exerts differential electrophysiological effects upon these cells. VTA neurons projecting to the mPFC or the mNAcs were traced retrogradely by Cav2-Cre virus and identified by expression of yellow fluorescent protein (YFP). Immunocytochemical analysis showed that a higher proportion of all orexin-innervated DA neurons projected to the mNAcs (34.5%) than to the mPFC (5.2%). Of all sampled VTA neurons projecting either to the mPFC or mNAcs, the dopaminergic (68.3 vs. 79.6%) and orexin-innervated DA neurons (68.9 vs. 64.4%) represented the major phenotype. Whole-cell current clamp recordings were obtained from fluorescently labeled neurons in slices during baseline periods and bath application of orexin A. Orexin similarly increased the firing rate of VTA dopamine neurons projecting to mNAcs (1.99 ± 0.61 Hz to 2.53 ± 0.72 Hz) and mPFC (0.40 ± 0.22 Hz to 1.45 ± 0.56 Hz). Thus, the hypothalamic orexin system targets mNAcs and to a lesser extent mPFC-projecting dopaminergic neurons of the VTA and exerts facilitatory effects on both clusters of dopamine neurons.

Low-frequency rTMS treatment alters the topographical organization of functional brain networks in schizophrenia patients with auditory verbal hallucination

Auditory verbal hallucinations (AVH) are an important characteristic of schizophrenia. Repeated transcranial magnetic stimulation (rTMS) has been evidence to be effective in treating AVH. We evaluated the topological properties of resting-state functional brain networks in schizophrenia patients with AVH (n = 32) who received 1-Hz rTMS treatment and matched healthy controls (n = 33). The results showed that the psychotic symptoms and certain neurocognitive performances in patients were improved by rTMS treatment. Furthermore, the pretreatment patients showed abnormal global topological metrics compared with the controls, including lower global efficiency (E_glob, represents the relative quality of information transmission between all nodes in the network) and higher characteristic path length (L_p, characterizes the mean shortest distance between any two nodes in the network). The pretreament patients also showed decreased local topological metrics relative to the controls, including the nodal shortest path (NL_p, quantifies the mean distance between the given node and the other nodes in the network) and nodal efficiency (N_e, measures the information interchange among the neighbor nodes when one node is removed), mainly located in the prefrontal cortex, occipital cortex, and subcortical regions. While the abnormal global and local topological patterns were normalized in patients after rTMS treatment. The multiple linear regression analysis indicated that the baseline topological metrics could be associated with the clinical responses after treatment in the patient group. The results suggested that the topological organization of the functional brain network was globally and regionally altered in schizophrenia patients with AVH after rTMS treatment and may be a potential therapeutic effect for AVH in schizophrenia.

Environmental exposure to 17β-trenbolone during adolescence inhibits social interaction in male mice

Puberty is a critical period for growth and development. This period is sensitive to external stimuli, which ultimately affects the development of nerves and the formation of social behaviour. 17β-Trenbolone (17β-TBOH) is an endocrine disrupting chemicals (EDCs), which had been widely reported in aquatic vertebrates. But there is little known about the effects of 17β-TBOH on mammals, especially on adolescent neurodevelopment. In this study, we found that 17β-TBOH acute 1 h exposure can cause the activation of the dopamine circuit in pubertal male balb/c mice. At present, there is little known about the effects of puberty exposure of endocrine disruptors on these neurons/nerve pathways. Through a series of behavioural tests, exposure to 80 μgkg^-1 d^-1 of 17β-TBOH during adolescence increased the anxiety-like behaviour of mice and reduced the control of wheel-running behaviour and the response of social interaction behaviour. The results of TH immunofluorescence staining showed that exposure to 17β-TBOH reduced dopamine axon growth in the medial prefrontal cortex (mPFC). In addition, the results of real-time PCR showed that exposure to 17β-TBOH not only down-regulated the expression of dopamine axon development genes, but also affected the balance of excitatory/inhibitory signals in mPFC. In this research, we reveal the effects of 17β-TBOH exposure during adolescence on mammalian behaviour and neurodevelopment, and provide a reference for studying the origin of adolescent diseases.

Endocannabinoids Released in the Ventral Tegmental Area During Copulation to Satiety Modulate Changes in Glutamate Receptors Associated With Synaptic Plasticity Processes

Endocannabinoids modulate mesolimbic (MSL) dopamine (DA) neurons firing at the ventral tegmental area (VTA). These neurons are activated by copulation, increasing DA release in nucleus accumbens (NAcc). Copulation to satiety in male rats implies repeated ejaculation within a short period (around 2.5 h), during which NAcc dopamine concentrations remain elevated, suggesting continuous neuronal activation. During the 72 h that follow copulation to satiety, males exhibit long-lasting changes suggestive of brain plasticity processes. Enhanced DA neuron activity triggers the synthesis and release of endocannabinoids (eCBs) in the VTA, which participate in several long-term synaptic plasticity processes. Blockade of cannabinoid type 1 receptors (CB1Rs) during copulation to satiety interferes with the appearance of the plastic changes. Glutamatergic inputs to the VTA express CB1Rs and contribute to DA neuron burst firing and synaptic plasticity. We hypothesized that eCBs, released during copulation to satiety, would activate VTA CB1Rs and modulate synaptic plasticity processes involving glutamatergic transmission. To test this hypothesis, we determined changes in VTA CB1R density, phosphorylation, and internalization in rats that copulated to satiety 24 h earlier as compared both to animals that ejaculated only once and to sexually experienced unmated males. Changes in glutamate AMPAR and NMDAR densities and subunit composition and in ERK1/2 activation were determined in the VTA of males that copulated to satiety in the presence or absence of AM251, a CB1R antagonist. The CB1R density decreased and the proportion of phosphorylated CB1Rs increased in the animals that copulated compared to control rats. The CB1R internalization was detected only in sexually satiated males. A decrease in α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR) density, blocked by AM251 pretreatment, and an increase in the proportion of GluA2-AMPARs occurred in sexually satiated rats. GluN2A- N-methyl-D-aspartate receptor (NMDAR) expression decreased, and GluN2B-NMDARs increased in these animals, both of which were prevented by AM251 pre-treatment. An increase in phosphorylated ERK1/2 emerged in males copulating to satiety in the presence of AM251. Results demonstrate that during copulation to satiety, eCBs activate CB1Rs in the VTA, producing changes in glutamate receptors compatible with a reduced neuronal activation. These changes could play a role in the induction of the long-lasting physiological changes that characterize sexually satiated rats.

Nigella sativa oil protects against emamectin benzoate-Induced neurotoxicity in rats

This study evaluated the ameliorative impact of Nigella sativa oil (NSO) on emamectin benzoate (EMB) neurotoxicity. Thirty-five male rats were randomly allocated into 5 groups (n = 7). G1 (control): received distilled water; G2: received NSO (3 ml. Kg^-1 B.W.) for 6 weeks; G3: received EMB (9 mg kg^-1 B.W.) for 6 weeks; G4: was co-treated with NSO and EMB for 6 weeks; G5: was treated with EMB for 4 weeks then, received NSO for 2 weeks. All treatments were given orally every other day. EMB increased serum urea, creatinine levels; brain dopamine, serotonin, malondialdehyde levels; brain expression levels of caspase 3 and TNF-α. While, it decreased serum total protein, albumin, brain GABA, AChE, GSH-Px, CAT, and SOD levels. Histopathological findings revealed hemorrhage, congestion, severe degeneration, and edema of the brain tissues. NSO reversed the EMB-induced biochemical and histopathological alterations. This NSO effect is mostly due to its antioxidant, antiinflammatory, and antiapoptotic activities. These findings suggest NSO as a potential protective and therapeutic agent for EMB-induced neurotoxicity.

Involvement of the dopaminergic system in the reward-related behavior of pregabalin

There has been an increase in cases of drug addiction and prescription drug abuse worldwide. Recently, pregabalin abuse has been a focus for many healthcare agencies, as highlighted by epidemiological studies. We previously evaluated the possibility of pregabalin abuse using the conditioned place preference (CPP) paradigm. We observed that a 60 mg/kg dose could induce CPP in mice and that pregabalin-rewarding properties were mediated through glutamate neurotransmission. Notably, the dopaminergic reward circuitry is also known to play a crucial role in medication-seeking behavior. Therefore, this study aimed to explore the possible involvement of dopaminergic receptor-1 in pregabalin-induced CPP. Mice were randomly allocated to receive saline or the dopamine-1 receptor antagonist SKF-83566 (0.03 mg/kg, intraperitoneal). After 30 min, the mice received either saline or pregabalin (60 mg/kg) during the conditioning phase. Among the control groups that received saline or SKF-83566, the time spent in the two conditioning chambers was not significantly altered. However, among the pregabalin-treated group, there was a marked increase in the time spent in the drug-paired chamber compared to the time spent in the vehicle-paired chamber. Notably, blocking dopamine-1 receptors with SKF-83566 completely prevented pregabalin-induced place preference, thus demonstrating the engagement of the dopaminergic system in pregabalin-induced reward-related behavior.

Chronic oral methylphenidate treatment in adolescent rats promotes dose-dependent effects on NMDA receptor binding

AIM

Examine the effects of chronic oral Methylphenidate (MP) treatment on the N-Methyl-D-aspartic acid (NMDA) glutamate receptor binding in the rat brain using a previously established drinking paradigm that has been shown to deliver MP with similar pharmacokinetic profile as observed clinically.

MAIN METHODS

Briefly, rats were divided into three treatment groups of water, low dose MP (LD; 4/10 mg/kg), or high dose MP (HD; 30/60 mg/kg). Following a 3-month treatment period, some rats were sacrificed while others went through an additional 1-month abstinence period before they were sacrificed. In vitro autoradiography (ARG) was carried out using [3H] MK801 to examine NMDA receptor binding in the brain.

KEY FINDINGS

The dose-dependent effects of MP following 13 weeks of treatment on [3H] MK-801 binding were seen across the brain in the following regions: prelimbic, insular, secondary motor, primary motor, retrosplenial, rhinal, piriform, auditory, visual, dorsolateral striatum, nucleus accumbens core, hippocampus, amygdala, and thalamic regions. No differences were observed in [3H] MK-801 binding levels in animals that underwent the same treatment followed by a 4 week abstinence.

SIGNIFICANCE

These results demonstrate that chronic MP treatment altered NMDA receptor expression throughout the brain, which in turn may impact an individual's drug-seeking behavior, fear memory formation and overall activity. However, these effects of chronic MP were eliminated following cessation of treatment.

Importance of dopaminergic neurotransmission for the RU 24969-induced locomotor activity of male and female rats during the preweanling period

There is disagreement about whether the locomotor activity produced by serotonin (5-HT) _1A/1B receptor agonists is ultimately mediated through a dopaminergic mechanism or is independent of dopamine (DA) system functioning. Using a developing rat model, we examined whether DA neurotransmission is necessary for the locomotor activity produced by 5-HT_1A/1B receptor stimulation. Depending on experiment, male and female preweanling rats were pretreated with vehicle, the monoamine-depleting agent reserpine, the 5-HT synthesis inhibitor 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA), the DA synthesis inhibitor ∝-methyl-DL-p-tyrosine (AMPT), or the D1 and D2 receptor antagonists SCH 23390 and raclopride, respectively. After completing the pretreatment regimen, the behavioral effects of saline and the 5-HT_1A/1B receptor agonist RU 24969 were assessed during a 2-h test session. Locomotor activity in the center and margin of the testing chamber was recorded. RU 24969's locomotor activating effects were sensitive to blockade of the D2 receptor, but not the D1 receptor. The DA synthesis inhibitor (AMPT) significantly attenuated the RU 24969-induced locomotor activity of preweanling rats, as did the 5-HT synthesis inhibitor PCPA. The latter result suggests that presynaptic 5-HT_1A/1B receptors may have a role in mediating RU 24969-induced locomotion during the preweanling period. DA neurotransmission, especially involving D2 receptors, is necessary for the 5-HT_1A/1B-mediated locomotor activity of preweanling rats. The actions of PCPA, reserpine, and SCH 23390 differ substantially between preweanling and adult rats, suggesting that the neural mechanisms underlying these DA/5-HT interactions vary across ontogeny.

Appetitive olfactory conditioning in the neonatal male rat facilitates subsequent sexual partner preference

Pairing a neutral odor with a male rat's initial sexual experiences to ejaculation produces a subsequent conditioned ejaculatory preference (CEP) in which males ejaculate preferentially with receptive females that bear the odor relative to unscented receptive females. In 1986, Fillion and Blass reported that neonatal male rats exposed to a neutral lemon odor (citral) painted on their mother's ventrum while nursing ejaculated faster as adults with sexually receptive, citral-scented females compared to unscented receptive females. The present study examined whether the same odor paired with tactile reward in neonatal male rats would alter the subsequent expression of a CEP. Newborn Long-Evans male rats were separated from their mothers each day beginning on Postnatal Day 1 and placed into a Plexiglas cage that contained either unscented or citral-scented bedding (N = 8/group). During each trial, rats were stroked from head to toe with a soft, narrow paintbrush, after which they were returned to their mothers. Males were weaned at 21 days of age and housed in same-treatment pairs for an intervening 50 days. Following habituation to a large open field, males were presented with two sexually receptive Long-Evans females, one scented with citral, and the other unscented, for a 30-min test of copulation. Males in the Paired group copulated and ejaculated preferentially with the scented female whereas males in the Unpaired group showed no preference. Pairing a neutral odor with a reward state in infancy generates a preference in male rats to ejaculate with sexually receptive females bearing the same odor in adulthood.

Differential Modulation of Ventral Tegmental Area Circuits by the Nociceptin/Orphanin FQ System

The neuropeptide nociceptin/orphanin FQ (N/OFQ) can be released by stressors and is associated with disorders of emotion regulation and reward processing. N/OFQ and its receptor, NOP, are enriched in dopaminergic pathways, and intra-ventricular agonist delivery decreases dopamine levels in the dorsal striatum, nucleus accumbens (NAc), and ventral tegmental area (VTA). We used whole-cell electrophysiology in acute rat midbrain slices to investigate synaptic actions of N/OFQ. N/OFQ was primarily inhibitory, causing outward currents in both immunocytochemically identified dopaminergic (tyrosine hydroxylase positive (TH(+))) and non-dopaminergic (TH(-)) VTA neurons; effect at 1 μm: 20 ± 4 pA. Surprisingly, this effect was mediated by augmentation of postsynaptic GABAAR currents, unlike the substantia nigra pars compacta (SNc), where the N/OFQ-induced outward currents were K+ channel dependent. A smaller population, 17% of all VTA neurons, responded to low concentrations of N/OFQ with inward currents (10 nm: -11 ± 2 pA). Following 100 nm N/OFQ, the response to a second N/OFQ application was markedly diminished in VTA neurons (14 ± 10% of first response) but not in SNc neurons (90 ± 20% of first response). N/OFQ generated outward currents in medial prefrontal cortex (mPFC)-projecting VTA neurons, but inward currents in a subset of posterior anterior cingulate cortex (pACC)-projecting VTA neurons. While N/OFQ inhibited NAc-projecting VTA cell bodies, it had little effect on electrically or optogenetically evoked terminal dopamine release in the NAc measured ex vivo with fast scan cyclic voltammetry (FSCV). These results extend our understanding of the N/OFQ system in brainstem circuits implicated in many neurobehavioral disorders.

The role of NMDA receptors in rat propofol self-administration

BACKGROUND

Propofol is among the most frequently used anesthetic agents, and it has the potential for abuse. The N-methyl-D-aspartate (NMDA) receptors are key mediators neural plasticity, neuronal development, addiction, and neurodegeneration. In the present study, we explored the role of these receptors in the context of rat propofol self-administration.

METHODS

Sprague-Dawley Rats were trained to self-administer propofol (1.7 mg/kg/infusion) using a fixed-ratio (FR) schedule over the course of 14 sessions (3 h/day). After training, rats were intraperitoneally administered the non-competitive NDMA receptor antagonist MK-801, followed 10 min later by a propofol self-administration session.

RESULTS

After training, rats successfully underwent acquisition of propofol self-administration, as evidenced by a significant and stable rise in the number of active nose-pokes resulting in propofol administration relative to the number of control inactive nose-pokes (P < 0.01). As compared to control rats, rats that had been injected with 0.2 mg/kg MK-801 exhibited a significantly greater number of propofol infusions (F (3, 28) = 4.372, P < 0.01), whereas infusions were comparable in the groups administered 0.1 mg/kg and 0.4 mg/kg of this compound. In addition, MK-801 failed to alter the numbers of active (F (3, 28) = 1.353, P > 0.05) or inactive (F (3, 28) = 0.047, P > 0.05) responses in these study groups. Animals administered 0.4 mg/kg MK-801 exhibited significantly fewer infusions than animals administered 0.2 mg/kg MK-801 (P = 0.006, P < 0.01). In contrast, however, animals in the 0.4 mg/kg MK-801 group displayed a significant reduction in the number of active nose-poke responses (F (3, 20) = 20.8673, P < 0.01) and the number of sucrose pellets (F (3, 20) = 23.77, P < 0.01), while their locomotor activity was increased (F (3, 20) = 22.812, P < 0.01).

CONCLUSION

These findings indicate that NMDA receptors may play a role in regulating rat self-administration of propofol.

Competitive and cooperative interactions between medial temporal and striatal learning systems

The striatum and medial temporal lobes (MTL) exhibit dissociable roles during learning. Whereas the striatum and its network of thalamic relays and cortical nodes are necessary for nondeclarative learning, the MTL and associated network are required for declarative learning. Several studies have suggested that these networks are functionally competitive during learning. Since these discoveries, however, evidence has accumulated that they can operate in a cooperative fashion. In this review, we discuss evidence for both competition and cooperation between these systems during learning, with the aim of reconciling these seemingly contradictory findings. Examples of cooperation between the striatum and MTL have been provided, especially during consolidation and generalization of knowledge, and do not appear to be precluded by differences in functional specialization. However, whether these systems cooperate or compete does seem to depend on the phase of learning and cognitive or motor aspects of the task. The involvement of other regions, such as midbrain dopaminergic nuclei and the prefrontal cortex, may promote and mediate cooperation between the striatum and the MTL during learning. Building on this body of research, we propose a model for striatum-MTL interactions in learning and memory and attempt to predict, in general terms, when cooperation or competition will occur.

Effects of dopamine and serotonin synthesis inhibitors on the ketamine-, d-amphetamine-, and cocaine-induced locomotor activity of preweanling and adolescent rats: sex differences

The pattern of ketamine-induced locomotor activity varies substantially across ontogeny and according to sex. Although ketamine is classified as an NMDA channel blocker, it appears to stimulate the locomotor activity of both male and female rats via a monoaminergic mechanism. To more precisely determine the neural mechanisms underlying ketamine's actions, male and female preweanling and adolescent rats were pretreated with vehicle, the dopamine (DA) synthesis inhibitor ∝-methyl-_DL-p-tyrosine (AMPT), or the serotonin (5-HT) synthesis inhibitor 4-chloro-_DL-phenylalanine methyl ester hydrochloride (PCPA). After completion of the pretreatment regimen, the locomotor activating effects of saline, ketamine, d-amphetamine, and cocaine were assessed during a 2 h test session. In addition, the ability of AMPT and PCPA to reduce dorsal striatal DA and 5-HT content was measured in male and female preweanling, adolescent, and adult rats. Results showed that AMPT and PCPA reduced, but did not fully attenuate, the ketamine-induced locomotor activity of preweanling rats and female adolescent rats. Ketamine (20 and 40 mg/kg) caused a minimal amount of locomotor activity in male adolescent rats, and this effect was not significantly modified by AMPT or PCPA pretreatment. When compared to ketamine, d-amphetamine and cocaine produced different patterns of locomotor activity across ontogeny; moreover, AMPT and PCPA pretreatment affected psychostimulant- and ketamine-induced locomotion differently. When these results are considered together, it appears that both dopaminergic and serotonergic mechanisms mediate the ketamine-induced locomotor activity of preweanling and female adolescent rats. The dichotomous actions of ketamine relative to the psychostimulants in vehicle-, AMPT-, and PCPA-treated rats, suggests that ketamine modulates DA and 5-HT neurotransmission through an indirect mechanism.

Ventromedial prefrontal cortex is involved in preference and hedonic evaluation of tastes

The ventromedial prefrontal cortex (vmPFC) of rats has reciprocal connections with the gustatory and the hedonic impact coding structures. The main goal of the present study was to investigate the involvement of local neurons of vmPFC and their catecholaminergic innervations in taste preference and taste reactivity test. Therefore, kainate or 6-hydroxydopamine (6-OHDA) lesions were performed in the vmPFC by iontophoretic method. In the first experiment, taste preference was tested to 250 mM and 500 mM glucose solutions over water in two-bottle choice test. In the second experiment, taste reactivity was examined to 4 concentrations of glucose solutions (250 mM, 500 mM, 750 mM and 1000 mM) and 4 concentrations of quinine solutions (0.125 mM, 0.25 mM, 1.25 mM and 2.5 mM). Our results showed, that kainate microlesion of vmPFC did not modify the preference of 250 mM and 500 mM glucose solutions in two-bottle choice test. In contrast, 6-OHDA microlesion of vmPFC resulted in increased preference to the higher concentration of glucose (500 mM) solution over water. Results of taste reactivity test showed that kainate lesion resulted in more ingestive and less rejective responses to 750 mM glucose solution and elevated rejectivity to the higher concentrations (1.25 mM and 2.5 mM) of quinine solutions. 6-OHDA lesion of vmPFC increased the number of ingestive responses to highly concentrated (500 mM, 750 mM and 1000 mM) glucose solutions and decreased the number of ingestive responses to the lower concentration (0.125 mM) of quinine solution. The present data provide evidence for the important role of vmPFC neurons and catecholaminergic innervation of the vmPFC in the regulation of hedonic evaluation of tastes and in the hedonic consummatory behavior.

Age-dependent effects of dopamine receptor inactivation on cocaine-induced behaviors in male rats: Evidence of dorsal striatal D2 receptor supersensitivity

N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), which irreversibly inactivates dopamine (DA) receptors, causes pronounced age-dependent behavioral effects in rats. For example, EEDQ either augments or does not affect the DA agonist-induced locomotor activity of preweanling rats while attenuating the locomotion of adolescent and adult rats. The twofold purpose of this study was to determine whether EEDQ would: (a) potentiate or attenuate the cocaine-induced locomotor activity of preweanling, adolescent, and adult rats; and (b) alter the sensitivity of surviving D2 receptors. Rats were treated with vehicle or EEDQ (2.5 or 7.5 mg/kg) on postnatal day (PD) 17, PD 39, and PD 84. In the behavioral experiments, saline- or cocaine-induced locomotion was assessed 24 hr later. In the biochemical experiments, dorsal striatal samples were taken 24 hr after vehicle or EEDQ treatment and later assayed for NPA-stimulated GTPγS receptor binding, G protein-coupled receptor kinase 6 (GRK6), and β-arrestin-2 (ARRB2). GTPγS binding is a direct measure of ligand-induced G protein activation, while GRK6 and ARRB2 modulate the internalization and desensitization of D2 receptors. Results showed that EEDQ potentiated the locomotor activity of preweanling rats, while attenuating the locomotion of older rats. NPA-stimulated GTPγS binding was elevated in EEDQ-treated preweanling rats, relative to adults, indicating enhanced functional coupling between the G protein and receptor. EEDQ also reduced ARRB2 levels in all age groups, which is indicative of increased D2 receptor sensitivity. In sum, the present results support the hypothesis that D2 receptor supersensitivity is a critical factor mediating the locomotor potentiating effects of EEDQ in cocaine-treated preweanling rats.

Src deficient mice demonstrate behavioral and electrophysiological alterations relevant to psychiatric and developmental disease

Much evidence suggests that hypofunction of the N-methyl-d-aspartate glutamate receptor (NMDAR) may contribute broadly towards a subset of molecular, cognitive and behavioral abnormalities common among psychiatric and developmental diseases. However, little is known about the specific molecular changes that lead to NMDAR dysfunction. As such, personalized approaches to remediating NMDAR dysfunction based on a specific etiology remains a challenge. Sarcoma tyrosine kinase (Src) serves as a hub for multiple signaling mechanisms affecting GluN2 phosphorylation and can be disrupted by convergent alterations of various signaling pathways. We recently showed reduced Src signaling in post mortem tissue from schizophrenia patients, despite increased MK-801 binding and NMDA receptor complex expression in the postsynaptic density (PSD). These data suggest that Src dysregulation may be an important underlying mechanism responsible for reduced glutamate signaling. Despite this evidence for a central role of Src in NMDAR signaling, little is known about how reductions in Src activity might regulate phenotypic changes in cognition and behavior. As such, the current study sought to characterize behavioral and electrophysiological phenotypes in mice heterozygous for the Src Acl gene (Src+/- mice). Src+/- mice demonstrated decreased sociability and working memory relative to Src+/+ (WT) mice while no significant differences were seen on locomotive activity and anxiety-related behavior. In relation to WT mice, Src+/- mice showed decreased mid-latency P20 auditory event related potential (aERP) amplitudes, decreased mismatch negativity (MMN) and decreased evoked gamma power, which was only present in males. These data indicate that Src+/- mice are a promising new model to help understand the pathophysiology of these electrophysiological, behavioral and cognitive changes. As such, we propose that Src+/- mice can be used in the future to evaluate potential therapeutic approaches by targeting increased Src activity as a common final pathway for multiple etiologies of SCZ and other diseases characterized by reduced glutamate function.

A medium throughput rodent model of relapse from addiction with behavioral and pharmacological specificity

One of most formidable problems in the treatment of addiction is the high rate of relapse. The discovery of medicines to help mitigate relapse are aided by animal models that currently involve weeks of training and require surgical preparations and drug delivery devices. The present set of experiments was initiated to investigate a rapid 8-day screening method that utilizes food instead of intravenous drug administration. Male Sprague-Dawley rats were trained in a reinstatement paradigm in which every lever press produced a 45 mg food pellet concurrently paired with a light and tone. Behavior was subsequently extinguished with lever responses producing neither food nor food-associated stimuli. Reinstatement of responding was evaluated under conditions in which the first three responses of every 5 min time bin produced a food pellet along with food-associated stimuli. The mGlu₅ receptor antagonists MPEP and MTEP produced a significant reduction in reinstatement while failing to alter responding where every response produced food. The cannabinoid CB₁ receptor antagonist rimonabant and the mGlu_2/3 receptor agonist LY379268 also selectively reduced reinstatement. Other compounds including clozapine, d-amphetamine, chlordiazepoxide, ABT-431, naltrexone and citalopram were without effect. The results suggest that relapse-like behavioral effects can be extended to non-pharmacological reinforcers. Drug effects demonstrated both behavioral and pharmacological specificity. The present experimental design thus allows for efficient and rapid assessment of the effects of drugs that might be useful in the treatment of addiction-associated relapse.

Catechol-O-Methyltransferase Val158Met and brain-derived neurotrophic factor Val66Met gene polymorphisms in paraphilic sexual offenders

BACKGROUND

Child sexual abuse (CSA) is an important problem worldwide. The reason of sex abuse is considered as multifactorial. Genetic contribution reported by recent studies is a significant evidence for this pathologic behavior. Catechol-O-Methyltransferase (COMT) is an enzyme in the metabolic inactivation of catecholamine and substances containing catecholamines such as dopamine, epinephrine, and norepinephrine. COMT polymorphism causes functional changes in COMT enzyme activity. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor usually synthesized from central nervous system neurons. With the effect of BDNF, dopamine and serotonin play important roles on neurogenesis, survival, and synaptic plasticity.

AIM

This study aims to examine COMT Val158Met (rs4680) and BDNF Val66Met (rs6265) polymorphisms in CSA.

SETTINGS AND DESIGN

This was a case-control study.

MATERIALS AND METHODS

Seventy paraphilic child sexual abuser patients and seventy age- and gender-matched healthy controls participated in this study. COMT Val158Met and BDNF Val66Met polymorphisms were genotyped by real-time polymerase chain reaction assay.

RESULTS

COMT Val158Met genotype frequencies were determined as GG 31.4%, GA 45.7%, and AA 22.9% in patients; GG 24.3%, GA 45.7%, and AA 8.6% in controls; and exhibited a positive relationship between the groups (P = 0.018). BDNF Val66Met genotype frequencies were determined as GG 77.1%, GA 21.4%, and AA 1.4% in patients; GG 65.7%, GA 31.4%, AA 2.9% in controls; and no significant relationship was observed between the groups (P = 0.317).

CONCLUSIONS

This research investigated COMT (Val158Met) and BDNF (Val66Met) in paraphilic child sexual offenders. A positive relationship was found for COMT gene; however, no significant relation was observed for BDNF gene between paraphilic sexual offenders and controls.

Iron Oxide Nanoparticles Affects Behaviour and Monoamine Levels in Mice

Iron oxide (Fe₂O₃) nanoparticles (NPs) attract the attention of clinicians for its unique magnetic and paramagnetic properties, which are exclusively used in neurodiagnostics and therapeutics among the other biomedical applications. Despite numerous research findings has already proved neurotoxicity of Fe₂O₃-NPs, factors affecting neurobehaviour has not been elucidated. In this study, mice were exposed to Fe₂O₃-NPs (25 and 50 mg/kg body weight) by oral intubation daily for 30 days. It was observed that Fe₂O₃-NPs remarkably impair motor coordination and memory. In the treated brain regions, mitochondrial damage, depleted energy level and decreased ATPase (Mg²⁺, Ca²⁺ and Na⁺/K⁺) activities were observed. Disturbed ion homeostasis and axonal demyelination in the treated brain regions contributes to poor motor coordination. Increased intracellular calcium ([Ca²⁺]_i) and decreased expression of growth associated protein 43 (GAP43) impairs vesicular exocytosis could result in insufficient signal between neurons. In addition, levels of dopamine (DA), norepinephrine (NE) and epinephrine (EP) were found to be altered in the subjected brain regions in correspondence to the expression of monoamine oxidases (MAO). Along with all these factors, over expression of glial fibrillary acidic protein (GFAP) confirms the neuronal damage, suggesting the evidences for behavioural changes.

Theta-gamma coupling in the prelimbic area is associated with heroin addiction

The medial prefrontal cortex (mPFC) is implicated in the regulation of drug-seeking behavior, but the specific contributions of the mPFC prelimbic (PL) subdivision and the precise mechanisms underlying heroin abuse remain largely unclear. In the present study, we examined changes in the rhythmic ensemble activity of PL neurons after induction of heroin addiction in rats. Rats were injected daily with saline (control group) or heroin (addiction group) in the light chamber of a light-dark shuttle box, and a video tracking system was used to measure conditioned place preference (CPP) as a sign of addiction. A wireless telemetry system was used to record local field potentials (LFPs) from the PL area during expression of CPP. Before treatment, there was no difference in CPP between groups (P > 0.05). However, rats in the experimental group exhibited significant CPP (P < 0.05) in the light chamber after heroin treatment compared to before treatment and compared to control rats. During CPP, addicted rats demonstrated substantial alterations in relative θ and γ frequency band power (Ps < 0.05); moreover, the θ wave alteration was strongly coupled to γ waves in heat map analyses (P < 0.05). Collectively, these findings implicate heroin-induced alterations in PL area neural activity and θ-γ coupling in heroin addiction.

Efavirenz exposure, alone and in combination with known drugs of abuse, engenders addictive-like bio-behavioural changes in rats

Efavirenz is abused in a cannabis-containing mixture known as Nyaope. The addictive-like effects of efavirenz (5, 10 and 20 mg/kg) was explored using conditioned place preference (CPP) in rats following sub-acute exposure vs. methamphetamine (MA; 1 mg/kg) and Δ⁹-tetrahydrocannabinol (THC; 0.75 mg/kg). The most addictive dose of efavirenz was then compared to THC alone and THC plus efavirenz following sub-chronic exposure using multiple behavioural measures, viz. CPP, sucrose preference test (SPT) and locomotor activity. Peripheral superoxide dismutase (SOD), regional brain lipid peroxidation and monoamines were also determined. Sub-acute efavirenz (5 mg/kg) had a significant rewarding effect in the CPP comparable to MA and THC. Sub-chronic efavirenz (5 mg/kg) and THC + efavirenz were equally rewarding using CPP, with increased cortico-striatal dopamine (DA), and increased lipid peroxidation and SOD. Sub-chronic THC did not produce CPP but significantly increased SOD and decreased hippocampal DA. Sub-chronic THC + efavirenz was hedonic in the SPT and superior to THC alone regarding cortico-striatal lipid peroxidation and sucrose preference. THC + efavirenz increased cortico-striatal DA and decreased serotonin (5-HT). Concluding, efavirenz has dose-dependent rewarding effects, increases oxidative stress and alters regional brain monoamines. Efavirenz is hedonic when combined with THC, highlighting its abuse potential when combined with THC.

Developmental prefrontal mRNA expression of D2 dopamine receptor splice variants and working memory impairments in rats after early life Interleukin-1β elevation

Long (D2L) and Short (D2S) isoforms of D2 dopamine receptor differ in their biochemical and physiological properties, which could affect functioning of prefrontal cortex. Contribution of distinct D2 dopamine receptor isoforms to cognitive dysfunctions and its developmental regulation are currently not fully elucidated. In the present study, we evaluated developmental mRNA expression of D2S/D2L dopamine receptor isoforms within the rat medial prefrontal cortex (mPFC) in the model of neurodevelopmental cognitive dysfunction. Working memory performance (Y-maze spontaneous alternations) and D2S/D2L mRNA expression in the mPFC (by qRT-PCR) were evaluated in juvenile (P27), adolescent (P42-47) and adult (P75-90) rats after chronic early life treatment with proinflammatory cytokine interleukin (IL)-1β (1 µg/kg i.p. daily P15-21). It was shown that IL-1β elevation during the 3rd week of life leads to working memory deficit originating in juvenile animals and persisting into adulthood. D2S mRNA expression was strongly downregulated during adolescence, and such downregulation was exaggerated in animals injected with IL-1β during P15-21. Early life IL-1β administrations influenced developmental changes in the D2S/D2L mRNA ratio. This measure was found to be decreased in adolescent and adult control (intact and vehicle-treated) rats compared to juvenile control, while in the case of IL-1β-treated animals, the decrease in D2S/D2L ratio was observed only in adulthood but not in adolescence compared to juvenile rats. During the adolescence, D2S mRNA expression was downregulated and D2S/D2L ratio was upregulated in the mPFC of rats treated with IL-1β during the 3rd week of life compared to controls. Based on these data we conclude that changes in the developmental expression of D2 dopamine receptor splice variants within mPFC may underlie long-lasting cognitive deficit associated with neonatal pathology.

A medial prefrontal cortex-nucleus acumens corticotropin-releasing factor circuitry for neuropathic pain-increased susceptibility to opioid reward

Recent studies have shown that persistent pain facilitates the response to morphine reward. However, the circuit mechanism underlying this process remains ambiguous. In this study, using chronic constriction injury (CCI) of the sciatic nerve in mice, we found that persistent neuropathic pain reduced the minimum number of morphine conditioning sessions required to induce conditioned place preference (CPP) behavior. This dose of morphine had no effect on the pain threshold. In the medial prefrontal cortex (mPFC), which is involved in both pain and emotion processing, corticotropin-releasing factor (CRF) expressing neuronal activity was increased in CCI mice. Chemogenetic inhibition of mPFC CRF neurons reversed CCI-induced morphine CPP facilitation. Furthermore, the nucleus acumens (NAc) received mPFC CRF functional projections that exerted excitatory effects on NAc neurons. Optogenetic inhibition of mPCF neuronal terminals or local infusion of the CRF receptor 1 (CRFR1) antagonist in the NAc restored the effects of neuropathic pain on morphine-induced CPP behavior, but not in normal mice. On a molecular level, in CCI mice, CRFR1 protein expression was increased in the NAc by a histone dimethyltransferase G9a-mediated epigenetic mechanism. Local G9a knockdown increased the expression of CRFR1 and mimicked CCI-induced hypersensitivity to acquiring morphine CPP. Taken together, these findings demonstrate a previously unknown and specific mPFC CRF engagement of NAc neuronal circuits, the sensitization of which facilitates behavioral responses to morphine reward in neuropathic pain states via CRFR1s.

Effects of light and dark phase testing on the investigation of behavioural paradigms in mice: Relevance for behavioural neuroscience

Different timing and light phases are critical factors in behavioural neuroscience, which can greatly affect the experimental outcomes of the performed tests. Despite the fact that time of testing is one of the most common factors that varies across behavioural laboratories, knowledge about the consequences of testing time on behavioural readouts is limited. Thus, in this study we systematically assessed the effect of this factor on the readout of a variety of elementary and recurrent behavioural paradigms in C57Bl/6 mice. Furthermore, we investigated potential neuronal correlates of this phenomenon by analysing how testing time influences the expression pattern of genes relevant for neuronal activation functions and the control of brain circadian rhythms. We show that animals tested in the light phase display reduced social approach behaviour and sensorimotor gating and increased locomotor activity, whereas anxiety-related behaviour and working memory are not affected. In addition, animals tested in the light phase also exhibit increased locomotor response to systemic amphetamine treatment, which is paralleled by alterations in the expression patterns of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the Nucleus Accumbens (NAc) and/or Midbrain (Mid). Lastly, we observed that neuronal activation, indexed by the gene expression levels of cFos, was increased in the NAc and Mid of animals tested during the light phase. Our data thus suggest that daily alterations in gene expression in mesolimbic brain structures might be involved in the different behavioural responses of mice tested in the light- versus the dark-phase. At the same time, our study adds further weight to the notion that the specific timing of testing can indeed strongly affect the readout of a given test. As comparison and reproducibility of findings is pivotal in science, experimental protocols should be clarified in detail to allow appropriate data comparison across different laboratories.

Cyproheptadine Regulates Pyramidal Neuron Excitability in Mouse Medial Prefrontal Cortex

Cyproheptadine (CPH), a first-generation antihistamine, enhances the delayed rectifier outward K⁺ current (I_K) in mouse cortical neurons through a sigma-1 receptor-mediated protein kinase A pathway. In this study, we aimed to determine the effects of CPH on neuronal excitability in current-clamped pyramidal neurons in mouse medial prefrontal cortex slices. CPH (10 µmol/L) significantly reduced the current density required to generate action potentials (APs) and increased the instantaneous frequency evoked by a depolarizing current. CPH also depolarized the resting membrane potential (RMP), decreased the delay time to elicit an AP, and reduced the spike threshold potential. This effect of CPH was mimicked by a sigma-1 receptor agonist and eliminated by an antagonist. Application of tetraethylammonium (TEA) to block I_K channels hyperpolarized the RMP and reduced the instantaneous frequency of APs. TEA eliminated the effects of CPH on AP frequency and delay time, but had no effect on spike threshold or RMP. The current-voltage relationship showed that CPH increased the membrane depolarization in response to positive current pulses and hyperpolarization in response to negative current pulses, suggesting that other types of membrane ion channels might also be affected by CPH. These results suggest that CPH increases the excitability of medial prefrontal cortex neurons by regulating TEA-sensitive I_K channels as well as other TEA-insensitive K⁺ channels, probably I_D and inward-rectifier Kir channels. This effect of CPH may explain its apparent clinical efficacy as an antidepressant and antipsychotic.

Electrically Controlled Neurochemical Release from Dual-Layer Conducting Polymer Films for Precise Modulation of Neural Network Activity in Rat Barrel Cortex

Implantable microelectrode arrays (MEAs) are important tools for investigating functional neural circuits and treating neurological diseases. Precise modulation of neural activity may be achieved by controlled delivery of neurochemicals directly from coatings on MEA electrode sites. In this study, a novel dual-layer conductive polymer/acid functionalized carbon nanotube (fCNT) microelectrode coating is developed to better facilitate the loading and controlled delivery of the neurochemical 6,7-dinitroquinoxaline-2,3-dione (DNQX). The base layer coating is consisted of poly(3,4-ethylenedioxythiophene/fCNT and the top layer is consisted of polypyrrole/fCNT/DNQX. The dual-layer coating is capable of both loading and electrically releasing DNQX and the release dynamic is characterized with fluorescence microscopy and mathematical modeling. In vivo DNQX release is demonstrated in rat somatosensory cortex. Sensory-evoked neural activity is immediately (<1s) and locally (<446 µm) suppressed by electrically triggered DNQX release. Furthermore, a single DNQX-loaded, dual-layer coating is capable of inducing effective neural inhibition for at least 26 times without observable degradation in efficacy. Incorporation of the novel drug releasing coating onto individual MEA electrodes offers many advantages over alternative methods by increasing spatial-temporal precision and improving drug selection flexibility without increasing the device's size.

Verbal working memory and functional large-scale networks in schizophrenia

The aim of this study was to test whether bilinear and nonlinear effective connectivity (EC) measures of working memory fMRI data can differentiate between patients with schizophrenia (SZ) and healthy controls (HC). We applied bilinear and nonlinear Dynamic Causal Modeling (DCM) for the analysis of verbal working memory in 16 SZ and 21 HC. The connection strengths with nonlinear modulation between the dorsolateral prefrontal cortex (DLPFC) and the ventral tegmental area/substantia nigra (VTA/SN) were evaluated. We used Bayesian Model Selection at the group and family levels to compare the optimal bilinear and nonlinear models. Bayesian Model Averaging was used to assess the connection strengths with nonlinear modulation. The DCM analyses revealed that SZ and HC used different bilinear networks despite comparable behavioral performance. In addition, the connection strengths with nonlinear modulation between the DLPFC and the VTA/SN area showed differences between SZ and HC. The adoption of different functional networks in SZ and HC indicated neurobiological alterations underlying working memory performance, including different connection strengths with nonlinear modulation between the DLPFC and the VTA/SN area. These novel findings may increase our understanding of connectivity in working memory in schizophrenia.

Aripiprazole, A Drug that Displays Partial Agonism and Functional Selectivity

BACKGROUND

The treatment of schizophrenia is challenging due to the wide range of symptoms (positive, negative, cognitive) associated with the disease. Typical antipsychotics that antagonize D2 receptors are effective in treating positive symptoms, but extrapyramidal side-effects (EPS) are a common occurrence. Atypical antipsychotics targeting 5-HT2A and D2 receptors are more effective at treating cognitive and negative symptoms compared to typical antipsychotics, but these drugs also result in side-effects such as metabolic syndromes.

OBJECTIVE

To identify evidence in the literature that elucidates the pharmacological profile of aripiprazole.s.

METHODS

We searched PubMed for peer reviewed articles on aripiprazole and its clinical efficacy, side-effects, pharmacology, and effects in animal models of schizophrenia symptoms.

RESULTS

Aripiprazole is a newer atypical antipsychotic that displays a unique pharmacological profile, including partial D2 agonism and functionally selective properties. Aripiprazole is effective at treating the positive symptoms of schizophrenia and has the potential to treat negative and cognitive symptoms at least as well as other atypical antipsychotics. The drug has a favorable side-effect profile and has a low propensity to result in EPS or metabolic syndromes. Animal models of schizophrenia have been used to determine the efficacy of aripiprazole in symptom management. In these instances, aripiprazole resulted in the reversal of deficits in extinction, pre-pulse inhibition, and social withdrawal. Because aripiprazole requires a greater than 90% occupancy rate at D2 receptors to be clinically active and does not produce EPS, this suggests a functionally selective effect on intracellular signaling pathways.

CONCLUSION

A combination of factors such as dopamine system stabilization via partial agonism, functional selectivity at D2 receptors, and serotonin-dopamine system interaction may contribute to the ability of aripiprazole to successfully manage schizophrenia symptoms. This review examines these mechanisms of action to further clarify the pharmacological actions of aripiprazole.

Prefrontal mRNA expression of long and short isoforms of D2 dopamine receptor: Possible role in delayed learning deficit caused by early life interleukin-1β treatment

Long (D2L) and short (D2S) isoform of the D2 dopamine receptor are believed to play different roles in behavioral regulation. However, little is known about differential regulation of these isoforms mRNA expression during the process of learning in physiological and pathological states. In this study, we have investigated the combined effect of training in active avoidance (AA) paradigm and chronic early life treatment with pro-inflammatory cytokine interleukin (IL)-1β (1μg/kg i.p., P15-21) on D2S and D2L dopamine receptor mRNA expression in the medial prefrontal cortex (mPFC) of adult rats. We have shown differential regulation of D2 short and long mRNA isoform expression in the mPFC. There was no effect of AA-training on D2S mRNA expression, while D2L mRNA was downregulated in AA-trained control (intact and saline-treated) animals, and this effect was not observed in rats treated with IL-1β. D2S mRNA expression level negatively correlated with learning ability within control (saline-treated and intact) groups but not in IL-1β-treated animals. Thus, prefrontal expression of distinct D2 dopamine receptor splice variants is supposed to be implicated in cognitive decline caused by early life immune challenge.