Prepulse Inhibition Of Acoustic Startle Response Research Articles

Neonatal ventral hippocampus lesion disrupts maternal behavior in rats: An animal model of schizophrenia.

Although individuals with schizophrenia typically present deficits in social interaction, little is known about the quality of their parent-infant interactions. In the present study, we assessed the behavioral effects of neonatal ventral hippocampus lesion (nVHL) in female rats (nVHL is known to induce schizophrenia-like deficits in males). Sexually naïve adult nVHL or sham female rats received cognitive and social tests, and their maternal behavior was observed in independent groups of adult nVHL and sham rats on postpartum days 2, 6, and 12. Compared to Sham females, naïve nVHL rats displayed elevated locomotor activity, less social interaction, and disrupted habituation of the acoustic startle response (ASR), while dorsal immobility (a defensive behavioral response) and prepulse inhibition of ASR were not affected. Although all nVHL mothers retrieved their pups, adopted the crouching posture, and nursed them, they showed disturbances in the display of pup body licking and nest building.Furthermore, a high proportion of nVHL mothers displayed atypical retrieval of pups and re-retrieving of pups, atypical nest-building, excavation, and cannibalism, as well a high level of these behaviors. These data indicate that cognition, locomotor activity, and maternal care is disrupted in nVHL female, suggesting disturbances in mesocorticolimbic dopaminergic systems and/or in social cognition.

Acoustically Enriched Environment during the Critical Period of Postnatal Development Positively Modulates Gap Detection and Frequency Discrimination Abilities in Adult Rats

Throughout life, sensory systems adapt to the sensory environment to provide optimal responses to relevant tasks. In the case of a developing system, sensory inputs induce changes that are permanent and detectable up to adulthood. Previously, we have shown that rearing rat pups in a complex acoustic environment (spectrally and temporally modulated sound) from postnatal day 14 (P14) to P28 permanently improves the response characteristics of neurons in the inferior colliculus and auditory cortex, influencing tonotopical arrangement, response thresholds and strength, and frequency selectivity, along with stochasticity and the reproducibility of neuronal spiking patterns. In this study, we used a set of behavioral tests based on a recording of the acoustic startle response (ASR) and its prepulse inhibition (PPI), with the aim to extend the evidence of the persistent beneficial effects of the developmental acoustical enrichment. The enriched animals were generally not more sensitive to startling sounds, and also, their PPI of ASR, induced by noise or pure tone pulses, was comparable to the controls. They did, however, exhibit a more pronounced PPI when the prepulse stimulus was represented either by a change in the frequency of a background tone or by a silent gap in background noise. The differences in the PPI of ASR between the enriched and control animals were significant at lower (55 dB SPL), but not at higher (65-75 dB SPL), intensities of background sound. Thus, rearing pups in the acoustically enriched environment led to an improvement of the frequency resolution and gap detection ability under more difficult testing conditions, i.e., with a worsened stimulus clarity. We confirmed, using behavioral tests, that an acoustically enriched environment during the critical period of development influences the frequency and temporal processing in the auditory system, and these changes persist until adulthood.

Meta-analysis on the association between genetic polymorphisms and prepulse inhibition of the acoustic startle response

Sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle response (ASR) has been proposed as one of the most promising electrophysiological endophenotypes of schizophrenia. During the past decade, a number of publications have reported significant associations between genetic polymorphisms and PPI in samples of schizophrenia patients and healthy volunteers. However, an overall evaluation of the robustness of these results has not been published so far. Therefore, we performed the first meta-analysis of published and unpublished associations between gene polymorphisms and PPI of ASR. Unpublished associations between genetic polymorphisms and PPI were derived from three independent samples. In total, 120 single observations from 16 independent samples with 2660 study participants and 43 polymorphisms were included. After correction for multiple testing based on false discovery rate and considering the number of analyzed polymorphisms, significant associations were shown for four variants, even though none of these associations survived a genome-wide correction (P<5∗10−8). These results imply that PPI might be modulated by four genotypes – COMT rs4680 (primarily in males), GRIK3 rs1027599, TCF4 rs9960767, and PRODH rs385440 – indicating a role of these gene variations in the development of early information processing deficits in schizophrenia. However, the overall impact of single genes on PPI is still rather small suggesting that PPI is – like the disease phenotype – highly polygenic. Future genome-wide analyses studies with large sample sizes will enhance our understanding on the genetic architecture of PPI.

Cortical electroconvulsive stimulation alleviates breeding-induced prepulse inhibition deficit in rats

In patients with medical-refractory schizophrenia electroconvulsive therapy (ECT), i.e., the induction of therapeutic seizures via cortical surface electrodes, is effectively used. Electroconvulsive stimulation (ECS) in rodents simulates ECT in humans and is applied to investigate the mechanisms underlying this treatment. Experimentally-induced reduced prepulse inhibition (PPI) of the acoustic startle response (ASR), i.e., the reduction of the startle response to an intense acoustic stimulus when this stimulus is shortly preceded by a weaker not-startling stimulus, serves as an endophenotype for neuropsychiatric disorders that are accompanied by disturbed sensorimotor gating, such as schizophrenia. Here we used rats selectively bred for high and low PPI to evaluate whether bifrontal cortical ECS would affect PPI.For this purpose, cortical screw electrodes were stereotactically implanted above the frontal cortex. After recovery ECS was applied for five consecutive days with stimuli of 1ms pulse-width, 100 pulses/s, 1s duration, ranging from 5.5mA to 10mA. PPI of ASR was measured one day before ECS, and on days 1, 7, and 14 after the last ECS.In rats with breeding-induced low PPI ECS increased PPI one week after stimulation. In contrast, ECS decreased PPI in rats with high PPI on the first day after stimulation. The reaction to the startle impulse was reduced by ECS without difference between groups. This work provides evidence that rats with breeding-induced high or low PPI could be used to further investigate the underlying mechanisms of ECT in neuropsychiatric disorders with disturbed sensorimotor gating like schizophrenia.

The acoustic startle response and polymorphism of the gene for catechol-O-methyltransferase in the norm and in schizophrenia

Using 46 healthy subjects and 47 male patients with schizophrenia we studied the influence of the rs4680 polymorphism (Val158Met) in the gene for catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, on the level of catecholamines in the blood plasma and basic parameters and prepulse inhibition of the acoustic startle response (ASR), which are potential neurophysiological markers of the risk of the development of schizophrenia. An effect of the polymorphism of the COMT gene on the prepulse inhibition of ASR was observed only in healthy persons and consisted in a decrease in this index in carriers of the Val/Val genotype. In patients with schizophrenia, polymorphism of the COMT gene was associated with another potential endophenotype of schizophrenia, viz., the basic latent period of ASR; its largest increase, as compared to the norm, was found in homozygous carriers of Met at the 158th position. We found a positive correlation between prepulse inhibition and the ratio of dopamine metabolism in the blood plasma of healthy subjects and the adrenaline level in patients. Binary logistic regression showed that inclusion of the factor of the genotype considerably increases the validity of the diagnostic model, which is based on the evaluation of the neurophysiological indices.

Prepulse inhibition (PPI) disrupting effects of Glycyrrhiza glabra extract in mice: A possible role of monoamines

Liquorice extract was reported to have nootropic and/or antiamnestic effects. Prepulse inhibition (PPI) of startle response is a multimodal, cross-species phenomenon used as a measure of sensorimotor gating. Previous studies indicated that liquorice/its constituents augmented mouse brain monoamine levels. Increased brain monoamines’ transmission was suggested to underlie PPI disruption. However, the effect of antiamnestic dose(s) of the extract on PPI has not been investigated despite the coexistence of impaired memory and PPI deficit in some neurological disorders. The effect of administration of the antiamnestic dose of the extract (150mg/kg for 7 days) was tested on PPI of acoustic startle response in mice. It resulted in PPI disruption and therefore its effect on monoamines’ levels was investigated in a number of mouse brain areas involved in PPI response mediation. Results demonstrated that the extract antiamnestic dose augmented cortical, hippocampal and striatal monoamine levels. It was therefore concluded that liquorice extract (150mg/kg)-induced PPI deficit was mediated through augmenting monoaminergic transmission in the cortex, hippocampus and striatum. These findings can be further investigated in experimental models for autism, psychosis and Huntington's disease to decide the safety of using liquorice extract in ameliorating memory disturbance in disorders manifesting PPI deficit.

Perinatal exposure to low levels of carbon monoxide impairs neurobehavior in adult mice

Maternal smoking is associated with several adverse neurological outcomes including increased risk for SIDS and attention deficit disorder. Perinatal exposure to carbon monoxide (CO) disrupts development of brain structures and associates with neurological disorders.OBJECTIVEto uncover age and sex differences in neurobehavioral phenotype of perinatally CO‐exposed mice. Pregnant mice were exposed to 0, 75, and 150 ppm of CO approximating levels found in smokers from embryonic day 0 until weaning. We utilized the Open Field Test (OFT), Acoustic Startle Response/Prepulse Inhibition (ASR/PPI), and the Neurobehavioral Severity Scale Revised (NSS‐R) to evaluate changes in neurological and behavioral functioning in rodents. Animals were evaluated at 14 and 60 days of life (do).RESULTSAt 14 do: (1) NSS‐R increased (0.33±0.22, 1.56±0.19 and 1.27±0.23 at 0, 75 and 150 ppm respectively) indicating decreased sensory‐motor function after exposure to CO, with females showing greater sensitivity; (2) males and females exposed to CO showed decreased startle with and without pre‐pulse.RESULTSat 60 do: (1) OFT‐horizontal activity decreased without sexual preference; (2) CO‐exposed animals showed some enhanced startle with PPI. We conclude that perinatal exposure to CO is associated with mild neurological impairment in 14 do mice that persists to 60 days.Funding: Flight Attendant Medical Research Institute

Increased Sensorimotor Gating in Recreational and Dependent Cocaine Users Is Modulated by Craving and Attention-Deficit/Hyperactivity Disorder Symptoms

Cocaine dependence has been associated with blunted dopamine and norepinephrine signaling, but it is unknown if recreational cocaine use is also associated with alterations of catecholamine systems. Prepulse inhibition (PPI) of the acoustic startle response-a measure of sensorimotor gating-is highly sensitive for manipulations of the catecholamine system. Therefore, we investigated whether relatively pure recreational users (RCU) and dependent cocaine users (DCU) display alterations of PPI, startle reactivity, and habituation. Moreover, the influences of methylenedioxymethamphetamine and cannabis co-use, craving, and attention-deficit/hyperactivity disorder (ADHD) symptoms on startle measures were examined. In 64 RCU, 29 DCU, and 66 stimulant-naïve control subjects, PPI of acoustic startle response, startle reactivity, habituation, ADHD symptoms, and cocaine craving were assessed. Drug use of all participants was controlled by hair and urine toxicologies. Both RCU and DCU showed increased PPI in comparison with control participants (Cohen's d=.38 and d=.67, respectively), while RCU and DCU did not differ in PPI measures (d=.12). No significant group differences were found in startle reactivity or habituation measures. In cocaine users, PPI was positively correlated with cumulative cocaine dose used, craving for cocaine, and ADHD symptoms. Users with a diagnosis of ADHD and strong craving symptoms displayed the highest PPI levels compared with control subjects (d=.78). The augmented PPI in RCU and DCU suggests that recreational use of cocaine is associated with altered catecholamine signaling, in particular if ADHD or craving symptoms are present. Finally, ADHD might be a critical risk factor for cocaine-induced changes of the catecholamine system.

Effects of periadolescent fluoxetine and paroxetine on elevated plus-maze, acoustic startle, and swimming immobility in rats while on and off-drug

RationaleWhether selective serotonin reuptake inhibitors (SSRIs) exposure during adolescent brain development causes lasting effects remains unresolved.ObjectiveAssess the effects of fluoxetine and paroxetine 60 days after adolescent exposure compared with when on-drug.MethodsMale Sprague-Dawley littermates (41 litters) were gavaged on postnatal days 33-53 with fluoxetine (3 or 10 mg/kg/day), paroxetine (3, 10 or, 17 mg/kg/day), or water; half were tested while on-drug (21 litters) and half after 60 days off-drug (20 litters).ResultsThe highest dose of the drugs reduced body weight gain during treatment that rebounded 1 week post-treatment. On-drug, no significant group differences were found on elevated plus maze time-in-open, zone entries, or latency to first open entry; however, the high dose of paroxetine significantly reduced head-dips (N = 20/group). No significant effects were found on-drug for acoustic startle response/prepulse inhibition (ASR/PPI) although a trend (p < 0.10) was seen, which after combining dose levels, showed a significant increase in ASR amplitude for both fluoxetine and paroxetine (N = 20-21/group). No differences on immobility time were seen in the Porsolt forced swim test or in plasma corticosterone at the end of forced swim (N-19-21/group). Off-drug, no effects were seen in the elevated plus maze (N = 16/group), ASR/PPI (N = 20/group), forced swim (N = 19-20/group), or plasma corticosterone (N = 19/group). At the doses tested, fluoxetine and paroxetine induced minor effects with drug on-board but no residual, long-term adverse effects in rats 60 days after drug discontinuation.ConclusionsThe data provide no evidence that fluoxetine or paroxetine have long-term adverse effects on the behaviors measured here after adolescent to young adult exposure.

P03-140 - Neurotransmitters blood level, ASR prepulse modification and antisaccades deficits in schizophrenia: implication for identification of schizophrenia endophenotypes

ObjectivesStudy of psychophysiological candidate schizophrenia endophenotypes in relation with neurotransmitters blood level and mental disorders.Methods23 patients with schizophrenia and 24 healthy subjects performed horizontal antisaccades. Acoustic startle response (ASR) prepulse modification was studied according to protocol, recommended by Consortium on the genetics of schizophrenia. Neurotransmitters blood plasma level was estimated using HPLC.ResultsSignificant increase of errors and saccade latencies was revealed in patients compared to controls. ASR prepulse inhibition (PPI) at 60 ms lead interval and ASR prepulse facilitation (PPF) at 2500 ms lead interval were impaired in patients. Analysis didn’t reveal any correlations between ASR and antisaccades measures in patients while in healthy controls high initial ASR amplitude correlated with incorrect antisaccades number and PPF level correlated with antisaccades latencies. Significantly higher individual variability of plasma serotonin, glutamate and taurine content was found in patients compared to controls. Positive correlations of PPI with glutamate and taurine content were observed in patients but not in controls. At the same time, correlation between PPI and serotonine turnover ratio was positive in control group and negative in patients. Antisaccade latencies in controls displayed negative correlation with DOPAC and taurine level while in patients they positively correlated with dopamine and negatively with serotonine turnover ratio. It was also found that antisaccades parameters and ASR measures displayed correlations with different PANSS scales.ConclusionThese data support the hypothesis that PPI and antisaccades are associated with different neural networks and have different genetic aetiology.

Sensorimotor Gating of Schizophrenia Patients Depends on Catechol O-Methyltransferase Val158Met Polymorphism

It has been recently shown that Catechol O-methyltransferase (COMT) Val(158)Met polymorphism strongly influences prepulse inhibition (PPI) of the acoustic startle response (ASR) in healthy human volunteers. Given that schizophrenia patients exhibit impairment in PPI and that COMT is a putative susceptibility gene for schizophrenia, we investigated the impact of the COMT Val(158)Met polymorphisms on PPI in schizophrenic inpatients. We analyzed COMT Val(158)Met polymorphisms and assessed startle reactivity, habituation, and PPI of ASR in 68 Caucasian schizophrenia inpatients. Clinical symptoms were measured with the Positive and Negative Syndrome Scale (PANSS). Patients carrying the Val(158)Met Met/Met allele showed elevated PPI levels whereas startle reactivity and habituation did not differ from the other two genotypes. These preliminary results imply that PPI is influenced by COMT Val(158)Met genotype in schizophrenia as well. In concert with other findings, our data suggest that PPI is a polygenic trait.

Sensorimotor Gating of Schizophrenia Patients Is Influenced by 5-HT 2A Receptor Polymorphisms

Schizophrenia patients exhibit impairment in prepulse inhibition (PPI) of the acoustic startle response (ASR), suggesting a sensorimotor gating deficit. The serotonin-2A receptor (5-HT(2A)R) has been implicated in both the pathogenesis of schizophrenia and the PPI deficits of schizophrenia patients. Moreover, both schizophrenia and PPI are thought to be inheritable. We investigated the impact of three 5-HT(2A)R polymorphisms (A-1438G, T102C, H452Y) on PPI in schizophrenia patients. We analyzed the 5-HT(2A)R A-1438G, T102C, and H452Y polymorphisms and assessed startle reactivity, habituation, and PPI of ASR in 68 Caucasian schizophrenia inpatients. Patients were also examined with the Positive and Negative Syndrome Scale. The 5-HT(2A)R A-1438G and T102C polymorphisms were in complete linkage disequilibrium. Patients carrying the T102C TT and the A-1438G AA allele show significantly higher PPI levels and a faster early habituation compared with all other variants. 5-HT(2A)R A-1438G and T102C genotype explained approximately 11% of the PPI and early habituation variance. In contrast, the 5-HT(2A)R H452Y polymorphism did not affect startle parameters. Our findings suggest that PPI and habituation are modulated by 5-HT(2A)R A-1438G and T102C genotype in schizophrenia. Consequently, alterations within brain 5-HT(2A)Rs may contribute to the PPI deficits in schizophrenia.

Prepulse inhibition (PPI) of tactile startle response in recombinant congenic strains of mice: QTL mapping and comparison with acoustic PPI

Prepulse inhibition (PPI) of the startle response is a psychophysiological measure of sensorimotor gating believed to be cross-modal between different sensory systems. We analyzed the tactile startle response (TSR) and PPI of TSR (tPPI), using light as a prepulse stimulus, in the mouse strains A/J and C57BL/6J and 36 recombinant congenic strains derived from them. Parental strains were significantly different for TSR, but were comparable for tPPI. Among the congenic strains, variation for TSR was significant in both genetic backgrounds, but that of tPPI was significant only for the C57BL/6J background. Provisional mapping for loci modulating TSR and tPPI was carried out. Using mapping data from our previous study on acoustic startle responses (ASR) and PPI of ASR (aPPI), no common markers for aPPI and tPPI were identified. However, some markers were significantly associated with both ASR and TSR, at least in one genetic background. These results indicate cross-modal genetic regulation for the startle response but not for PPI, in these mouse strains.

Comparative analysis of anxiety-like behaviors and sensorimotor functions in two rat mutants, ci2 and ci3, with lateralized rotational behavior

There is increasing evidence that developmental anomalies of cerebral asymmetry are involved in the etiology of psychiatric disorders, including schizophrenia, depression and anxiety. Thus, rodents with abnormal cerebral lateralization are interesting tools to study the association between such anomalies and behavioral dysfunction. The most studied indicator of cerebral asymmetry in the rat is that of circling or rotational behavior. We have recently described two rat mutants, ci2 and ci3, in which lateralized rotational behavior occurs either spontaneously or in response to external stimuli, such as new environment or handling. While cochlear and vestibular defects are found in ci2 rats, ci3 rats do not exhibit any inner ear abnormalities. The abnormal motor response to external stimuli raised the possibility that the circling rat mutants may be more likely to express anxiety-related behavior in tests of emotionality. In the present study, we characterized anxiety-related behaviors of ci2 and ci3 rats in the open field, elevated plus-maze and light/dark exploration test. Furthermore, sensorimotor functions of these rats were evaluated by the rotarod, accelerod and wire hang tests. Heterozygous (ci2/+) littermates or rats of the respective background strains (LEW, BH.7A) were used as controls. In contrast to our expectation, both mutants demonstrated less anxiety-related behavior than controls in tests of emotionality. Ci3 rats exhibited normal sensorimotor functions, whereas marked impairment was observed in ci2 rats, which is most likely a consequence of the vestibular dysfunction in these animals. The acoustic startle response (ASR) and prepulse inhibition of ASR did not differ between ci3 rats and controls. The reduced emotionality of the mutant rats indicated by the present experiments may not be specifically linked to anxiety per se, but is maybe more reflective of impulsivity or the inability to normally perceive or process potentially threatening situations. Based on previous findings of dysfunctions of the central dopamine system in ci2 and ci3 mutant rats, we assume that alterations in dopaminergic activity are involved in the maladaptive behavior observed in the present study.

Effect of cefepime on startle amplitude and prepulse inhibition of startle reflex in rats: Manipulation of GABA-A receptor function with midalozam

Disruption of prepulse inhibition (PPI) of startle response is manifested in schizophrenia and Huntington's disease among other neuropsychiatric disorders characterized by sensorimotor gating deficit. Antagonism of GABAA receptor function was documented to reduce PPI response. However, whether GABAA antagonism reduces PPI response is yet to be established because of contradicting reports. Cefepime is one of the fourth-generation cephalosporins documented to antagonize GABAA receptor function. This study investigated the effect of intramuscular injection of cefepime (45 and 90 mg/kg) twice daily for three consecutive days on both PPI of acoustic startle response and acoustic startle amplitude in rats. The effect of administration of the GABAA receptor agonist midazolam (1 mg/kg, i.p.) in conjunction with cefepime on PPI response and startle amplitude was also investigated. Results showed that administration of both dose levels of cefepime caused PPI deficit. Treatment of animals with midazolam in conjunction with cefepime reversed the effect of the lower dose, but not the higher one, on PPI of startle response without affecting startle amplitude in both dose levels. Results of this study, therefore, support the view that GABAA antagonism reduces PPI response. It is also concluded that antagonism of GABAergic transmission may be involved in the effect of the lower dose of cefepime on PPI response. Other mechanisms may mediate the effect of the higher dose of cefepime on PPI response. Clinical investigations are needed to determine the consequence of using cefepime in disorders of sensorimotor gating.

Prepulse inhibition and habituation of acoustic startle response in male MDMA ('ecstasy') users, cannabis users, and healthy controls.

Chronic administration of 3,4-methylenedioxymethamphetamine (MDMA) is associated with long-term depletion of serotonin (5-HT) and loss of 5-HT axons in the brains of rodents and nonhuman primates. Despite the broad database concerning the selective serotonergic neurotoxicity of recreational MDMA consumption by humans, controversy still exists with respect to the question of whether the well-known functional consequences of these neurotoxic effects, such as memory impairment, were caused by chronic 5-HT deficiency. Habituation and prepulse inhibition (PPI) of the acoustic startle response (ASR) can be used as a marker of central serotonergic functioning in rodents and humans. Thus, we investigated the functional status of the central serotonergic system in chronic but abstinent MDMA users by measuring PPI and habituation of ASR. PPI and habituation of ASR were measured in three groups. The first group (MDMA group) included 20 male drug-free chronic users of MDMA; the second group (cannabis group) consisted of 20 male drug-free chronic users of cannabis; and the third group (healthy controls) comprised 20 male participants with no history of illicit drug use. Analysis revealed significantly increased PPI of MDMA users compared to those of cannabis users and healthy controls. Cannabis users and healthy controls showed comparable patterns of PPI. There were no differences in habituation among the three groups. These results suggest that the functional consequences of chronic MDMA use may be explained by 5-HT receptor changes rather than by a chronic 5-HT deficiency condition. Use of cannabis does not lead to alterations of amplitude, habituation, or PPI of ASR.

Concurrent assessment of acoustic startle and auditory P50 evoked potential measures of sensory inhibition

The acoustic startle response (ASR) and midlatency auditory evoked potentials (AEP) have been utilized in the measurement of sensory inhibition. Using these different paradigms, abnormalities suggesting a lack of normal inhibition have been noted in a number of psychiatric syndromes. To date, the most commonly used sensory inhibition paradigms have not been studied in the same individuals, making generalizations across studies tenuous. In this report, reduction of ASR over multiple trials (habituation), prepulse inhibition (PPI) of ASR (decrease in ASR caused by low intensity prepulses) and P50 suppression (P50 AEP amplitude reduction in a paired-click paradigm) were measured in the same individuals. Relationships between these measures of acoustic startle and AEP inhibition were then assessed. Twenty subjects with no personal history of psychiatric disorder were tested and exhibited significant habituation and PPI of ASR as well as P50 suppression. Habituation of ASR was significantly and positively correlated with P50 suppression early, but not late, in AEP testing. Only a modest trend for a positive association between PPI and P50 suppression was noted. Habituation and PPI of startle were both highly correlated (positively) with P50 AEP amplitude. Habituation of startle remained significantly predictive of P50 suppression after controlling for P50 amplitude, whereas the modest association between PPI and P50 suppression was removed when P50 amplitude was factored out. Results indicate that habituation of acoustic startle, but not PPI, is highly associated with P50 suppression in control subjects. An unexpected finding was a robust positive correlation between P50 amplitude and both measures of startle inhibition. These findings and methodologic issues are discussed in terms of possible neural substrates involved in differrent measures of sensory inhibition.