Dorsal striatum D1-expressing neurons are involved with sensorimotor gating on prepulse inhibition test

A Computational Model for the Simulation of Prepulse Inhibition and Its Modulation by Cortical and Subcortical Units

The sensorimotor gating is a nervous system function that modulates the acoustic startle response (ASR). Prepulse inhibition (PPI) phenomenon is an operational measure of sensorimotor gating, defined as the reduction of ASR when a high intensity sound (pulse) is preceded in milliseconds by a weaker stimulus (prepulse). Brainstem nuclei are associated with the mediation of ASR and PPI, whereas cortical and subcortical regions are associated with their modulation. However, it is still unclear how the modulatory units can influence PPI. In the present work, we developed a computational model of a neural circuit involved in the mediation (brainstem units) and modulation (cortical and subcortical units) of ASR and PPI. The activities of all units were modeled by the leaky-integrator formalism for neural population. The model reproduces basic features of PPI observed in experiments, such as the effects of changes in interstimulus interval, prepulse intensity, and habituation of ASR. The simulation of GABAergic and dopaminergic drugs impaired PPI by their effects over subcortical units activity. The results show that subcortical units constitute a central hub for PPI modulation. The presented computational model offers a valuable tool to investigate the neurobiology associated with disorder-related impairments in PPI.

The projection-specific signals that establish functionally segregated dopaminergic synapses

Dopaminergic projections regulate various brain functions and are implicated in many neuropsychiatric disorders. There are two anatomically and functionally distinct dopaminergic projections connecting the midbrain to striatum: nigrostriatal, which controls movement, and mesolimbic, which regulates motivation. However, how these discrete dopaminergic synaptic connections are established is unknown. Through an unbiased search, we identify that two groups of antagonistic TGF-β family members, bone morphogenetic protein (BMP)6/BMP2 and transforming growth factor (TGF)-β2, regulate dopaminergic synapse development of nigrostriatal and mesolimbic neurons, respectively. Projection-preferential expression of their receptors contributes to specific synapse development. Downstream, Smad1 and Smad2 are specifically activated and required for dopaminergic synapse development and function in nigrostriatal vs. mesolimbic projections. Remarkably, Smad1 mutant mice show motor defects, whereas Smad2 mutant mice show lack of motivation. These results uncover the molecular logic underlying the proper establishment of functionally segregated dopaminergic synapses and may provide strategies to treat relevant, projection-specific disease symptoms by targeting specific BMPs/TGF-β and/or Smads.

Regulation of sensorimotor gating via Disc1/Huntingtin-mediated Bdnf transport in the cortico-striatal circuit

Sensorimotor information processing underlies normal cognitive and behavioral traits and has classically been evaluated through prepulse inhibition (PPI) of a startle reflex. PPI is a behavioral dimension deregulated in several neurological and psychiatric disorders, yet the mechanisms underlying the cross-diagnostic nature of PPI deficits across these conditions remain to be understood. To identify circuitry mechanisms for PPI, we performed circuitry recording over the prefrontal cortex and striatum, two brain regions previously implicated in PPI, using wild-type (WT) mice compared to Disc1-locus-impairment (LI) mice, a model representing neuropsychiatric conditions. We demonstrated that the corticostriatal projection regulates neurophysiological responses during the PPI testing in WT, whereas these circuitry responses were disrupted in Disc1-LI mice. Because our biochemical analyses revealed attenuated brain-derived neurotrophic factor (Bdnf) transport along the corticostriatal circuit in Disc1-LI mice, we investigated the potential role of Bdnf in this circuitry for regulation of PPI. Virus-mediated delivery of Bdnf into the striatum rescued PPI deficits in Disc1-LI mice. Pharmacologically augmenting Bdnf transport by chronic lithium administration, partly via phosphorylation of Huntingtin (Htt) serine-421 and its integration into the motor machinery, restored striatal Bdnf levels and rescued PPI deficits in Disc1-LI mice. Furthermore, reducing the cortical Bdnf expression negated this rescuing effect of lithium, confirming the key role of Bdnf in lithium-mediated PPI rescuing. Collectively, the data suggest that striatal Bdnf supply, collaboratively regulated by Htt and Disc1 along the corticostriatal circuit, is involved in sensorimotor gating, highlighting the utility of dimensional approach in investigating pathophysiological mechanisms across neuropsychiatric disorders.

Intra-dorsal striatal acetylcholine M1 but not dopaminergic D1 or glutamatergic NMDA receptor antagonists inhibit consolidation of duration memory in interval timing

The striatal beat frequency model assumes that striatal medium spiny neurons encode duration via synaptic plasticity. Muscarinic 1 (M1) cholinergic receptors as well as dopamine and glutamate receptors are important for neural plasticity in the dorsal striatum. Therefore, we investigated the effect of inhibiting these receptors on the formation of duration memory. After sufficient training in a peak interval (PI)-20-s procedure, rats were administered a single or mixed infusion of a selective antagonist for the dopamine D1 receptor (SCH23390, 0.5 µg per side), N-methyl-D-aspartic acid (NMDA)-type glutamate receptor (D-AP5, 3 µg), or M1 receptor (pirenzepine, 10 µg) bilaterally in the dorsal striatum, immediately before initiating a PI-40 s session (shift session). The next day, the rats were tested for new duration memory (40 s) in a session in which no lever presses were reinforced (test session). In the shift session, the performance was comparable irrespective of the drug injected. However, in the test session, the mean peak time (an index of duration memory) of the M1 + NMDA co-blockade group, but not of the D1 + NMDA co-blockade group, was lower than that of the control group (Experiments 1 and 2). In Experiment 3, the effect of the co-blockade of M1 and NMDA receptors was replicated. Moreover, sole blockade of M1 receptors induced the same effect as M1 and NMDA blockade. These results suggest that in the dorsal striatum, the M1 receptor, but not the D1 or NMDA receptors, is involved in the consolidation of duration memory.

Dorsal striatal dopamine induces fronto-cortical hypoactivity and attenuates anxiety and compulsive behaviors in rats

Dorsal striatal dopamine transmission engages the cortico-striato-thalamo-cortical (CSTC) circuit, which is implicated in many neuropsychiatric diseases, including obsessive-compulsive disorder (OCD). Yet it is unknown if dorsal striatal dopamine hyperactivity is the cause or consequence of changes elsewhere in the CSTC circuit. Classical pharmacological and neurotoxic manipulations of the CSTC and other brain circuits suffer from various drawbacks related to off-target effects and adaptive changes. Chemogenetics, on the other hand, enables a highly selective targeting of specific neuronal populations within a given circuit. In this study, we developed a chemogenetic method for selective activation of dopamine neurons in the substantia nigra, which innervates the dorsal striatum in the rat. We used this model to investigate effects of targeted dopamine activation on CSTC circuit function, especially in fronto-cortical regions. We found that chemogenetic activation of these neurons increased movement (as expected with increased dopamine release), rearings and time spent in center, while also lower self-grooming. Furthermore, this activation increased prepulse inhibition of the startle response in females. Remarkably, we observed reduced [¹⁸F]FDG metabolism in the frontal cortex, following dopamine activation in the dorsal striatum, while total glutamate levels- in this region were increased. This result is in accord with clinical studies of increased [¹⁸F]FDG metabolism and lower glutamate levels in similar regions of the brain of people with OCD. Taken together, the present chemogenetic model adds a mechanistic basis with behavioral and translational relevance to prior clinical neuroimaging studies showing deficits in fronto-cortical glucose metabolism across a variety of clinical populations (e.g. addiction, risky decision-making, compulsivity or obesity).

Impaired response to sleep deprivation in heterozygous Disc1 mutant mice

OBJECTIVES

Sleep/circadian rhythm disturbances are environmental stress factors that might interact with genetic risk factors and contribute to the pathogenesis of psychiatric disorders.

METHODS

In this study, the multiple-platform method was used to induce sleep deprivation (SD). We evaluated the impact of 72-hour SD in behavioural, anatomical, and biochemical aspects in heterozygous Disc1 mutant (Disc1 Het) mice, an animal model of schizophrenia.

RESULTS

The sleep pattern and circadian activity were not altered in Disc1 Het mice. Yet, we observed differential responses to SD stress between genotypes. Increased microglial density and reduced neuronal proliferative activity were found in the dentate gyrus, a neurogenic niche, in Het-SD mice. Notably, SD-induced Bdnf mRNA elevations were evident in both WT and Het mice, while only in WT-SD mice did we observe increased BDNF protein expression. Our results suggested an SD-induced physical response featured by the elevation of BDNF protein expression to counteract the harmful influences of SD and sufficient DISC1 is required in this process.

CONCLUSIONS

The present study proposes that sleep disturbance could be pathogenic especially in genetically predisposed subjects who fail to cope with the stress. Potential therapeutic strategies for psychiatric disorders targeting the mRNA translation machinery could be considered.

Effects of Chemogenetic Inhibition of D1 or D2 Receptor-Containing Neurons of the Substantia Nigra and Striatum in Mice With Tourette Syndrome

As tourette syndrome (TS) is a common neurobehavioral disorder, the primary symptoms of which include behavioral stereotypies. Dysfunction of the substantia nigra-striatum network could be the main pathogenesis of TS, which is closely associated with dopamine (DA) and its receptors. TS is often resistant to conventional treatments. Therefore, it is necessary to investigate the neurobiological mechanisms underlying its pathogenesis. In this study, we investigated whether chemogenetic activation or inhibition of dopaminergic D1 receptor (D1R)- or D2 receptor (D2R)-containing neurons in the substantia nigra pars compacta (SNpc) or dorsal striatum (dSTR) affected the stereotyped behavior and motor functions of TS mice. Intraperitoneal injection of 3,3'-iminodipropionitrile (IDPN) was used to induce TS in mice. Stereotyped behavior test and open-field, rotarod, and grip strength tests were performed to evaluate stereotyped behavior and motor functions, respectively. Immunofluorescence labeling was used to detect the co-labeling of virus fluorescence and D1R or D2R. We found that chemogenetic inhibition of D1R- or D2R-containing neurons in the SNpc and dSTR alleviated behavioral stereotypies and motor functions in TS mice. Chemogenetic activation of D1R-containing neurons in the dSTR aggravated behavioral stereotypies and motor functions in vehicle-treated mice, but neither was aggravated in TS mice. In conclusion, chemogenetic inhibition of D1R- or D2R-containing neurons in the SNpc and dSTR alleviated behavioral stereotypies of TS, providing a new treatment target for TS. Moreover, the activation of D1R-containing neurons in the dSTR may contribute to the pathogenesis of TS, which can be chosen as a more precise target for treatment.

HIV-Associated Apathy/Depression and Neurocognitive Impairments Reflect Persistent Dopamine Deficits

Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.

Disruption of prepulse inhibition is associated with compulsive behavior severity and nucleus accumbens dopamine receptor changes in Sapap3 knockout mice

Obsessive compulsive disorder (OCD) is associated with disruption of sensorimotor gating, which may contribute to difficulties inhibiting intrusive thoughts and compulsive rituals. Neural mechanisms underlying these disturbances are unclear; however, striatal dopamine is implicated in regulation of sensorimotor gating and OCD pathophysiology. The goal of this study was to examine the relationships between sensorimotor gating, compulsive behavior, and striatal dopamine receptor levels in Sapap3 knockout mice (KOs), a widely used preclinical model system for OCD research. We found a trend for disruption of sensorimotor gating in Sapap3-KOs using the translational measure prepulse inhibition (PPI); however, there was significant heterogeneity in both PPI and compulsive grooming in KOs. Disruption of PPI was significantly correlated with a more severe compulsive phenotype. In addition, PPI disruption and compulsive grooming severity were associated with reduced dopamine D1 and D2/3 receptor density in the nucleus accumbens core (NAcC). Compulsive grooming progressively worsened in Sapap3-KOs tested longitudinally, but PPI disruption was first detected in high-grooming KOs at 7 months of age. Through detailed characterization of individual differences in OCD-relevant behavioral and neurochemical measures, our findings suggest that NAcC dopamine receptor changes may be involved in disruption of sensorimotor gating and compulsive behavior relevant to OCD.

Estimating the causal effect of prenatal lead exposure on prepulse inhibition deficits in children and adolescents

During pregnancy, maternal lead from earlier exposures mobilizes and crosses placental barriers, placing the developing fetus at risk for lead exposure and neurodevelopmental deficits. Some neuronal circuits known to be affected in neurodevelopment disorders can be probed with simple physiological behavioral paradigms. One such neural biomarker is Pre-Pulse Inhibition (PPI), an indicator of adequate sensorimotor gating processing. In clinical studies, deficits in PPI have been associated with neurodevelopmental disorders in human subjects. To our knowledge, no studies have examined the use of PPI as a biomarker of toxicant effects on the brain in epidemiological studies. We aimed to estimate the causal effect of prenatal lead exposure, assessed by maternal cortical bone lead concentrations, on PPI in 279 children from Mexico City. in vivo maternal cortical bone lead measurements were taken at four weeks postpartum at the mid-tibia shaft using a K-Shell X-ray fluorescence instrument. PPI recording occurred in an isolated clinical setting and eye blink responses were measured using electromyography. We assessed if the conditions for causal inference held in our study and used the results of our assessment to estimate the causal effect of prenatal lead exposure on PPI using an ordinary least squares regression model, a marginal structural model, and the parametric g-formula. Results were consistent across the three modeling approaches. For the parametric g-formula, a one standard deviation (10.0 μg/g) increase in prenatal lead significantly reduced PPI by approximately 19.0 % (95 % CI: 5.4 %, 34.3 %). This decrease is similar in magnitude to clinical studies on schizophrenia, which have observed PPI impairments in patients with schizophrenia as compared to controls. Our results are consistent with findings from other studies establishing an association between lead exposure and neurodevelopmental disorders in children and suggest that PPI may be useful as an objective biomarker of toxicant effects on the brain.

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

Dosage sensitivity intolerance of VIPR2 microduplication is disease causative to manifest schizophrenia-like phenotypes in a novel BAC transgenic mouse model

Recent genome-wide association studies (GWAS) have identified copy number variations (CNVs) at chromosomal locus 7q36.3 that significantly contribute to the risk of schizophrenia, with all of the microduplications occurring within a single gene: vasoactive intestinal peptide receptor 2 (VIPR2). To confirm disease causality and translate such a genetic vulnerability into mechanistic and pathophysiological insights, we have developed a series of conditional VIPR2 bacterial artificial chromosome (BAC) transgenic mouse models of VIPR2 CNV. VIPR2 CNV mouse model recapitulates gene expression and signaling deficits seen in human CNV carriers. VIPR2 microduplication in mice elicits prominent dorsal striatal dopamine dysfunction, cognitive, sensorimotor gating, and social behavioral deficits preceded by an increase of striatal cAMP/PKA signaling and the disrupted early postnatal striatal development. Genetic removal of VIPR2 transgene expression via crossing with Drd1a-Cre BAC transgenic mice rescued the dopamine D2 receptor abnormality and multiple behavioral deficits, implicating a pathogenic role of VIPR2 overexpression in dopaminoceptive neurons. Thus, our results provide further evidence to support the GWAS studies that the dosage sensitivity intolerance of VIPR2 is disease causative to manifest schizophrenia-like dopamine, cognitive, and social behavioral deficits in mice. The conditional BAC transgenesis offers a novel strategy to model CNVs with a gain-of -copies and facilitate the genetic dissection of when/where/how the genetic vulnerabilities affect development, structure, and function of neural circuits. Our findings have important implications for therapeutic development, and the etiology-relevant mouse model provides a useful preclinical platform for drug discovery.

Muscimol injection into the substantia nigra but not globus pallidus affects prepulse inhibition and startle reflex

Behavioral arrest is an essential feature of an animal's survival. Acoustic startle reflex (ASR) is an involuntary whole-body contraction of the skeletal musculature to an unexpected auditory stimulus. This strong reaction can be decreased by prepulse inhibition (PPI) phenomenon; which, for example, is important in reducing distraction during the processing of sensory input. Several brainstem regions are involved in the PPI and startle reflex, but a previous study from our laboratory showed that the main input structure of Basal Ganglia (BG) - the striatum - modulates PPI. The pallidum and nigra are connected with striatum and these brainstem structures. Here, we investigated the role of these striatum outputs in the brain regions on startle amplitude, PPI regulation, and exploratory behavior in Wistar rats. The temporary bilateral inhibition of the globus pallidus (GP) by muscimol lead to motor impairment, without disturbing startle amplitude or PPI. Similarly, inhibition of the entopeduncular nucleus (EPN) specifically disrupted the exploratory behavior. On the other hand, the substantia nigra reticulata (SNr) inhibition interfered in all measured behaviors: decreased the PPI percentage, increased ASR and impaired the locomotor activity. The nigra is a key BG output structure which projects to the thalamus and brainstem. These findings extend our previous study showing that the striatum neurons expressing D1 receptors involvement in PPI occurs via the direct pathway to SNr, but not to the pallidum which more likely occurs by its connection with the caudal pontine nucleus, superior colliculus and/or pedunculopontine nucleus pivotal structures for startle reflex modulation.

Histamine H3 receptor activation reduces the impairment in prepulse inhibition (PPI) of the acoustic startle response and Akt phosphorylation induced by MK-801 (dizocilpine), antagonist at N-Methyl-d-Aspartate (NMDA) receptors

We have investigated the effect of the local activation of histamine H₃ receptors (H₃Rs) in the rat prefrontal cortex (PFCx) on the impairment of pre-pulse inhibition (PPI) of the startle response induced by the systemic administration of MK-801, antagonist at glutamate N-Methyl-d-Aspartate (NMDA) receptors, and the possible functional interaction between H₃Rs and MK-801 on PFCx dopaminergic transmission. Infusion of the H₃R agonist RAMH (19.8 ng/1 μl) into the PFCx reduced or prevented the inhibition by MK-801 (0.15 mg/kg, ip) of PPI evoked by different auditory stimulus intensities (5, 10 and 15 dB), and the RAMH effect was blocked by the H₃R antagonist/inverse agonist ciproxifan (30.6 ng/1 μl). MK-801 inhibited [³H]-dopamine uptake (-45.4 ± 2.1%) and release (-32.8 ± 2.6%) in PFCx synaptosomes or slices, respectively, and molecular modeling indicated that MK-801 binds to and blocks the rat and human dopamine transporters. However, H₃R activation had no effect on the inhibitory action of MK-801 on dopamine uptake and release. In PFCx slices, MK-801 and the activation of H₃Rs or dopamine D₁ receptors (D₁Rs) stimulated ERK-1/2 and Akt phosphorylation. The co-activation of D₁Rs and H₃Rs prevented ERK-1/2 and Akt phosphorylation, and H₃R activation or D₁R blockade prevented the effect of MK-801. In ex vivo experiments, the intracortical infusion of the D₁R agonist SKF-81297 (37 ng/1 μl) or the H₃R agonist RAMH increased Akt phosphorylation, prevented by D₁R/H₃R co-activation. These results indicate that MK-801 enhances dopaminergic transmission in the PFCx, and that H₃R activation counteracts the post-synaptic actions of dopamine.

Enhanced Dopamine in Prodromal Schizophrenia (EDiPS): a new animal model of relevance to schizophrenia

One of the most robust neurochemical abnormalities reported in patients living with schizophrenia is an increase in dopamine (DA) synthesis and release in the dorsal striatum (DS). Importantly, it appears that this increase progresses as a patient transitions from a prodromal stage to the clinical diagnosis of schizophrenia. Here we have recreated this pathophysiology in an animal model by increasing the capacity for DA synthesis preferentially within the DS. To achieve this we administer a genetic construct containing the rate-limiting enzymes in DA synthesis—tyrosine hydroxylase (TH), and GTP cyclohydrolase 1 (GCH1) (packaged within an adeno-associated virus)—into the substantia nigra pars compacta (SNpc) of adolescent animals. We refer to this model as “Enhanced Dopamine in Prodromal Schizophrenia” (EDiPS). We first confirmed that the TH enzyme is preferentially increased in the DS. As adults, EDiPS animals release significantly more DA in the DS following a low dose of amphetamine (AMPH), have increased AMPH-induced hyperlocomotion and show deficits in pre-pulse inhibition (PPI). The glutamatergic response to AMPH is also altered, again in the DS. EDiPS represents an ideal experimental platform to (a) understand how a preferential increase in DA synthesis capacity in the DS relates to “positive” symptoms in schizophrenia; (b) understand how manipulation of DS DA may influence other neurotransmitter systems shown to be altered in patients with schizophrenia; (c) allow researchers to follow an “at risk”-like disease course from adolescence to adulthood; and (d) ultimately allow trials of putative prophylactic agents to prevent disease onset in vulnerable populations.

A study for the mechanism of sensory disorder in restless legs syndrome based on magnetoencephalography

In spite of the relatively high incidence rate, the etiology and pathogenesis of restless legs syndrome (RLS) are still unclear. Long-term drug treatments fail to achieve satisfying curative effects, which is reflected by rebound and augmentation of related symptoms. An electrophysiological endophenotype experiment was done to investigate the mechanism of somatosensory disorder among RLS patients. Together with 15 normal subjects as the control group, with comparable ages and genders to the RLS patients, 15 primitive RLS patients were scanned by Magnetoencephalography (MEG) under natural conditions; furthermore, the somatosensory evoked magnetic field (SEF) with single and paired stimuli, was also measured. Compared to the control group, the SEF intensities of RLS patients' lower limbs were higher, and the paired-pulse depression (PPD) for SEF in RLS patients was attenuated. It was also revealed by time-frequency analysis of somatosensory induced oscillation (SIO) in RLS patients, that 93.3% of somatosensory induced Alpha (8-12 Hz) oscillations were successfully elicited, while 0% somatosensory induced Gamma (30-55 Hz) oscillations were elicited; which was significantly different from the control group. Additionally, in RLS patients exhibit increased excitability of the sensorimotor cortex, a remarkable abnormality existing in early somatosensory gating control (GC) and an attenuated inhibitory interneuron network, which consequently results in a compensatory mechanism through which RLS patients increase their attention-driven lower limb sensory gating control via somatosensory-induced Alpha (8-12 Hz) oscillation. This hyperexcitability, partially due to an electrocortical disinhibition, may have an important therapeutical implication, and become an important target of neuromodulatory interventions.

Anandamide Effects in a Streptozotocin-Induced Alzheimer's Disease-Like Sporadic Dementia in Rats

Alzheimer's disease (AD) is characterized by multiple cognitive deficits including memory and sensorimotor gating impairments as a result of neuronal and synaptic loss. The endocannabinoid system plays an important role in these deficits but little is known about its influence on the molecular mechanism regarding phosphorylated tau (p-tau) protein accumulation - one of the hallmarks of AD -, and on the density of synaptic proteins. Thus, the aim of this study was to investigate the preventive effects of anandamide (N-arachidonoylethanolamine, AEA) on multiple cognitive deficits and on the levels of synaptic proteins (syntaxin 1, synaptophysin and synaptosomal-associated protein, SNAP-25), cannabinoid receptor type 1 (CB₁) and molecules related to p-tau degradation machinery (heat shock protein 70, HSP70), and Bcl2-associated athanogene (BAG2) in an AD-like sporadic dementia model in rats using intracerebroventricular (icv) injection of streptozotocin (STZ). Our hypothesis is that AEA could interact with HSP70, modulating the level of p-tau and synaptic proteins, preventing STZ-induced cognitive impairments. Thirty days after receiving bilateral icv injections of AEA or STZ or both, the cognitive performance of adult male Wistar rats was evaluated in the object recognition test, by the escape latency in the elevated plus maze (EPM), by the tone and context fear conditioning as well as in prepulse inhibition tests. Subsequently, the animals were euthanized and their brains were removed for histological analysis or for protein quantification by Western Blotting. The behavioral results showed that STZ impaired recognition, plus maze and tone fear memories but did not affect contextual fear memory and prepulse inhibition. Moreover, AEA prevented recognition and non-associative emotional memory impairments induced by STZ, but did not influence tone fear conditioning. STZ increased the brain ventricular area and this enlargement was prevented by AEA. Additionally, STZ reduced the levels of p-tau (Ser199/202) and increased p-tau (Ser396), although AEA did not affect these alterations. HSP70 was found diminished only by STZ, while BAG2 levels were decreased by STZ and AEA. Synaptophysin, syntaxin and CB₁ receptor levels were reduced by STZ, but only syntaxin was recovered by AEA. Altogether, albeit AEA failed to modify some AD-like neurochemical alterations, it partially prevented STZ-induced cognitive impairments, changes in synaptic markers and ventricle enlargement. This study showed, for the first time, that the administration of an endocannabinoid can prevent AD-like effects induced by STZ, boosting further investigations about the modulation of endocannabinoid levels as a therapeutic approach for AD.

Inhibition of the substantia nigra pars reticulata produces divergent effects on sensorimotor gating in rats and monkeys

The basal ganglia are an evolutionarily old group of structures, with gross organization conserved across species. Despite this conservation, there is evidence suggesting that anatomical organization of a key output nucleus of the basal ganglia, the substantia nigra pars reticulata (SNpr), diverges across species. Nevertheless, there are relatively few comparative studies examining the impact of manipulations of SNpr across species. Here, we evaluated the role of SNpr in a highly conserved behavior: prepulse inhibition of the acoustic startle response (PPI). We performed parallel experiments in both rats and rhesus macaques using intracranial microinfusions of GABAA agonist muscimol to investigate the role of SNpr in PPI. SNpr inactivation significantly disrupted PPI in rats, congruent with prior studies; however, in macaques, SNpr inactivation resulted in facilitation of PPI. We suggest that this difference in circuit function results from a divergence in anatomical connectivity, underscoring the importance of circuit dissection studies across species.