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At least 73 records · Page 4Linked to original sources
PubMed1989

Spinal vs. supraspinal sites of action of the alpha 2-adrenergic agonists clonidine and ST-91 on the acoustic startle reflex.

Previous work has shown that stimulation of alpha 2-adrenergic receptors depresses the startle responses in rats. The present study suggests that this depressant effect involves supraspinal rather than spinal alpha 2-adrenergic receptors because intraventricular but not intrathecal infusion of the hydrophilic alpha 2-adrenergic agonist ST-91 depressed the acoustic startle reflex. To determine the point in the acoustic startle pathway where alpha 2-adrenergic receptor activation might ultimately alter neural transmission, startle responses were elicited electrically from different points along the acoustic startle pathway after systemic administration of clonidine. Clonidine depressed acoustically-elicited startle and startle elicited by electrical stimulation of the ventral cochlear nucleus to a comparable magnitude and over a similar time course. It also partially depressed startle elicited by electrical stimulation of the nucleus reticularis pontis caudalis (RPC). Taken together, these data suggest that alpha 2-adrenergic stimulation depresses startle by acting on supraspinal receptors, but that this effect is ultimately expressed, at least in part, by actions at both spinal and brainstem levels of the acoustic startle response pathway. The results are compared to other drugs known to affect the startle reflex.

Acoustic Stimulation↗
PubMed2005

Disruption of the prepulse inhibition of the startle reflex in vasopressin V1b receptor knockout mice: reversal by antipsychotic drugs.

In the present study, we investigated whether mice lacking the arginine vasopressin (AVP) V1b receptor (V1bR) exhibit deficits of prepulse inhibition (PPI) of the startle reflex, reminiscent of the sensorimotor gating deficits observed in a large majority of schizophrenic patients. V1bR knockout (KO) mice displayed significantly reduced levels of PPI of the startle reflex. In addition to PPI deficits, V1bR KO mice showed increased acoustic startle response. However, acoustic startle response was not significantly correlated to the PPI of the startle reflex in V1bR KO mice. V1bR KO mice also showed a decrease in basal levels of extracellular dopamine (DA) in the medial prefrontal cortex, which is thought to be an important brain region for PPI. Moreover, PPI deficits observed in the V1bR KO mice are significantly reversed by atypical antipsychotics such as risperidone and clozapine but not by a typical neuroleptic haloperidol, like in schizophrenic patients. By contrast, we did not observe any significant differences between V1bR KO mice and wild-type mice in the open-field, light/dark, elevated plus maze, and forced swimming tests. The results of the present study indicate that V1bR may be involved in the regulation of PPI of the startle reflex. The V1bR has been considered an important molecular target for the development of antipsychotic drugs.

Acoustic Stimulation↗
PubMed1999

P50 suppression and prepulse inhibition of the startle reflex in humans: a correlational study.

BACKGROUND: Sensory gating is an important feature of the normally functioning brain. When not operating correctly, it can contribute to different kinds of psychiatric illnesses by flooding the higher brain functions with useless information. Over the years, two paradigms have evolved to quantify the amount of sensory gating: the prepulse inhibition (PPI) of the startle reflex and the suppression of the P50 evoked potential. To enable comparison across studies it is important to find out to what extent these paradigms reflect the same processes. In the present study, this relationship was explored. METHODS: Thirty-one healthy male volunteers with no personal or family history of mental illness were tested on their ability to suppress the P50 wave and to inhibit the startle reflex. RESULTS: A significant positive correlation was found between PPI and P50 suppression mainly early in testing, when habituation of the startle reflex is taking place. Furthermore, a significant negative correlation was found between P50 suppression in the second half of testing and the habituation of the startle reflex. CONCLUSIONS: PPI and P50 suppression are correlated at an early stage of testing, when the process of habituation of the startle reflex is active. The role of the habituation in the correlation between these two measures needs to be further explored.

Acoustic Stimulation↗
PubMed1997

The audiogenic startle reflex in Tourette's syndrome.

The motor response pattern of the audiogenic startle reflex was studied in 15 Tourette's syndrome (TS) patients and 15 normal, age-matched control subjects, using auditory stimuli at 88 and 114 dB. The louder stimuli readily elicited responses in the orbicularis oculi (in all subjects), masseter, sternomastoid, trapezius, deltoid, and biceps (in most subjects) muscles, with a few subjects having responses in the forearm flexors and quadriceps. The TS subjects did not differ from controls in the onset latency, amplitude, and first peak latency of the reflex response in any of the muscles. Rates of habituation in the orbicularis oculi muscle were widely variable across the subjects, and the two groups did not differ overall in the habituation rates. Our study does not support the reports of an abnormal audiogenic startle reflex in TS.

Acoustic Stimulation↗
PubMedDate not supplied

Sensitization and aversive conditioning: effects on the startle reflex and electrodermal responding.

Animal data suggest that shock sensitization as well as aversive learning potentiates the acoustic startle reflex. The present experiment tested, whether this shock sensitization also occurs in human subjects and whether it precedes aversive conditioning. Sixty subjects viewed--prior to conditioning--a series of slides of different emotional contents including the to be conditioned stimuli (CSs). Afterwards, the experimenter attached the shock electrodes and initiated shock exposure. Then, subjects were randomly assigned to view a series of two slides, each for eight acquisition trials in which one slide was followed by a shock. Subsequently, extinction trials (12 for each slide) were administered. During preconditioning, acquisition, and extinction, startle probes occurred unpredictably during and between slide viewing. Preconditioning data replicated previous results by Lang and his associates, showing that the startle response magnitude is directly related to the affective valence induced by the slides. Shock exposure strongly facilitated the startle reflex magnitude. This shock sensitization was absent for the skin conductance response. Course of learning also varied for both response systems. The data suggest that startle reflex potentiation indexes the acquisition of an avoidance disposition, which is preceded by a general sensitization of the protective reflexes. Skin conductance learning follows arousal changes and is modulated by cognitive processes.

Adult↗
PubMed1988

Effects of pyrethroids on the acoustic startle reflex in the rat.

The effects of NAK 1901 (Pentafluorbenzyl (1R, cis)-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane-carboxylate) and cypermethrin ((S,R)-alpha-cyano-3-phenoxybenzyl-2,2-dimethyl (1R, 1S, cis, trans)-3-(2,2-dichlorovinyl) cyclopropane-carboxylate) (RU 24 501) on amplitude and prepulse inhibition of the acoustic startle reflex were studied in male Wistar rats. NAK 1901 (0, 1, 2.5, 4 mg/kg p.o.) enhanced the amplitude of the startle reflex in a dose-dependent way. Startle latency was not affected. Cypermethrin (0, 0.5, 1, 2 mg/kg p.o.) had no effect on the amplitude or the latency of the startle reflex. Both NAK 1901 and cypermethrin administration produced a dose-dependent increase in toxic signs and a dose-dependent increase in weight loss during the experimental session. None of the pyrethroids affected prepulse inhibition of the startle reflex. Because the neural substrate of the inhibitory processes involved in prepulse inhibition are probably of supraspinal origin, it is suggested that these substrates are not affected by pyrethroids.

Acoustic Stimulation↗
PubMed2006

Fearful and sexual pictures not consciously seen modulate the startle reflex in human beings.

BACKGROUND: Animal and human studies consistently have demonstrated that the startle reflex elicited by intense auditory stimulation is enhanced by the previous presentation of fear-evoking stimuli. There is also growing and varied evidence of the nonconscious processing of fear stimuli in human beings eliciting brain and autonomic fear responses. METHODS: We report two studies using the startle probe paradigm and the backward-masking procedure to examine the modulation of the eye-blink component of the startle reflex by consciously and nonconsciously presented emotional pictures. RESULTS: Conscious and nonconscious presentation of fearful pictures amplified the magnitude of the startle reflex in both studies. The opposite tendency was observed for conscious and nonconscious presentation of sexually attractive pictures in the second study. CONCLUSIONS: These findings support the notion that negative (and possibly positive) biologically relevant stimuli can be nonconsciously processed, presumably via amygdala activation, and can affect behavioral responding.

Acoustic Stimulation↗
PubMedDate not supplied

Elicitation and modification of the acoustic startle reflex in animals prenatally exposed to cocaine.

In separate experiments, pregnant Long-Evans rats were administered cocaine orally (60 mg/kg/day) on gestation days 14-21, or subcutaneously (40 mg/kg/day) on gestational days 8-21. For each route of administration, a vehicle control group was pair-fed to the group administered cocaine and another control group was left untreated. Throughout pregnancy, the dams that received cocaine gained approximately 15% less weight than the untreated controls, but none of the dosage procedures affected the size of the litters, or the weight and growth of the offspring. When the offspring reached adulthood, various assessments of reflex function were made using the acoustic startle reflex and prepulse inhibition of startle. There were no effects on startle habituation or reflex modification that could be attributed to the prenatal exposure to cocaine.

Administration, Oral↗
PubMed1999

Caffeine and prepulse inhibition of the acoustic startle reflex.

RATIONALE: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. OBJECTIVE: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). METHODS: Caffeine was administrated to human subjects in within-subjects designs (n = 24 and n = 18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. RESULTS: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. CONCLUSIONS: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attended acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.

Acoustic Stimulation↗
PubMed2000

PHNO, a selective dopamine D2 receptor agonist, does not reduce prepulse inhibition of the startle reflex in rats.

RATIONALE: Dopamine agonists nonselective for dopamine receptor subtypes, such as apomorphine, reduce prepulse inhibition of the startle reflex. It has been suggested that either D2 or D3 dopamine receptors mediate this action of apomorphine. OBJECTIVE: The present study investigated whether a selective D2 agonist with relatively low affinity for D3 receptors can reduce prepulse inhibition. METHODS: Rats (n=48) were treated with vehicle or one of three doses ( 15, 30 or 60 microg/kg, s.c.) of the specific dopamine D2 receptor agonist (+)-4-propyl-9-hydroxynaphthoxazine (PHNO) for 11 days. On days 1, 6 and 11 of treatment, the rats (n=12 in each group) were tested for their acoustic startle reflexes (105-dB, 40-ms white noise) and for prepulse inhibition (5-kHz tone, 5 dB above a 65 dB background white noise). Prepulses were presented with a range of stimulus onset asynchronies (SOAs: 5-160 ms) or lead times between the onset of the prepulse and the onset of the startle stimulus. In a second experiment, two groups of rats (n=10 in each group) were tested in a similar manner after vehicle or apomorphine (0.8 mg/kg, s.c.) to verify the sensitivity of the present procedure to agonist-induced reductions in prepulse inhibition. RESULTS: At doses that increased motor activity, PHNO increased prepulse inhibition at SOAs less than 80 ms and had no effect on prepulse inhibition at SOAs of 80 ms or above. However, all doses decreased startle amplitudes on trials in which only the startle-eliciting stimulus was presented. Apomorphine reduced prepulse inhibition under the same conditions. CONCLUSIONS: These findings with PHNO are in contrast to the less-specific D2 agonist, quinpirole, which has been reported to decrease prepulse inhibition. It is concluded that activation of D2 dopamine receptors alone is not sufficient to attenuate prepulse inhibition of the startle reflex.

Analysis of Variance↗
PubMed1997

Audiogenic startle reflex in acute hemiplegia.

The generators of the audiogenic startle reflex (ASR) are located in the bulbopontine reticular formation. We studied the influence of acute vascular supratentorial lesions on ASR. Ten patients with hemiplegia due to hemispheric cerebral infarct were studied within 5 days of stroke onset. ASR and magnetic cortical stimulation were performed the same day. A muscle response to magnetic stimulation was not elicited over the plegic side in any patient. In four of seven patients, ASR was enhanced over the plegic side. We suggest that enhanced ASR is due to the loss of a predominantly inhibitory hemispheric drive on ASR generators.

Acoustic Stimulation↗
PubMedDate not supplied

[The characteristics of the startle reflex to an acoustic stimulus in rats with hereditary stress-sensitive arterial hypertension: the effect of chronic stress in the prepuberty period].

Acoustic startle reflex was studied in young and adult rats with hereditary stress-induced arterial hypertension (HSIAH) in comparison with original normotensive Wistar strain. Immediate and long-lasting effects of chronic handling or chronic unpredictable stress at the age of 4 and 5 weeks on manifestations of the startle reflex were studied. The amplitude of the sensorimotor reaction was lower in both young (38-day-old) and adult (4-month-old) HSIAH rats than in age-matched normotensive Wistar rats. Young and adult hypertensives demonstrated significant inhibition of startle reflex when the startling stimulus was preceded by a weak prepulse. Such prepulse inhibition was not expressed in young or adult Wistar rats. Chronic handling as well as chronic unpredictable stress during the 4th and 5th weeks of life potentiated the startle amplitude in young HSIAH rats. The prepulse inhibition level did not depend on the chronic stress. The long-lasting effect of the prepubertal chronic stress depended on the type of the stress factors.

Acoustic Stimulation↗
PubMed2002

Stability of the acoustic startle reflex, prepulse inhibition, and habituation in schizophrenia.

Prepulse inhibition (PPI) of the acoustic startle reflex has been proposed as a neurophysiological measure of sensorimotor gating. There is high test-retest reliability of both startle magnitude and PPI in non-psychiatric subjects. The present study examined the stability of the acoustic startle reflex and its modulation in patients with schizophrenia. Startle measurements were performed in 19 chronic schizophrenic patients on stable medications and 24 healthy control subjects, three times at one-month intervals. PPI trials with various intervals between the prepulse and the startle stimulus (30, 60. 120, 240, and 2000 ms) were used. Intraclass correlation coefficients (ICC) were computed to assess stability. There was a good test-retest reliability of PPI in both schizophrenic patients (Mean ICC: 0.75) and control subjects (Mean ICC: 0.71). Acoustic startle magnitude was the most stable measure across sessions (Mean ICC schizophrenics: 0.89; Mean ICC controls: 0.89). In both groups, a good test-retest reliability was found in the startle latencies. Habituation and prepulse-induced shortening of latencies exhibited moderate stability. Schizophrenic patients exhibited significantly less PPI than control subjects in the 60 ms prepulse condition. This PPI deficit was evident in all three sessions. These results indicate that PPI is a stable neurobehavioral measure in chronic schizophrenic patients in the absence of changes in clinical state.

Acoustic Stimulation↗
PubMed1987

[Efferent activity in the phrenic nerve during the startle reflex in chloralose-anesthetized cats].

Reflex activity in the phrenic nerve was studied in chloralose anesthetized cats during development of somatic startle reflexes in limb and lower intercostal nerves. It was shown that the main component of this activity during low-threshold reflexes evoked by acoustic, tactile and low-threshold somatic afferent stimulation was depression of phrenic inspiratory activity. The following reflex discharges were prevalent components of phrenic responses to high-threshold afferent stimulation: early, propriospinal (intercostal-to-phrenic reflex) and late, suprasegmental ones. The latter were of two types: inspiratory (observed mainly during inspiration in about 75% of experiments) and expiratory (observed during expiration in 25% of experiments) which could be classified as "phrenic startle reflexes". Modulation of all responses during the respiratory cycle was described. Structural characteristics of reflex responses evoked in the phrenic nerve by stimulation of various respiratory and nonrespiratory bulbar sites as well as their respiratory modulation have been analyzed. Organization of possible neurophysiological mechanisms of phrenic responses during startle reflexes is discussed.

Animals↗
PubMed1990

Directed attention influences the modification of startle reflex probability.

The present study was designed to investigate the effect of directed attention on elicitation and modification of the startle reflex. 30 adult human subjects received 90 dB(A) broadband noise startle stimuli either alone or preceded by a 60 dB(A) prepulse (either 2000-Hz tone, 1000-Hz tone, or broadband noise). Subjects were instructed to attend to one of the three prepulses during half the trials and to ignore all stimuli during the rest of the trials. The probability of responding while attending to a prepulse was significantly lower than the probability of responding while ignoring the prepulses. Responding to the prepulses was also more probable while subjects were attending to the prepulses, and these effects were more pronounced for tone than for noise prepulses. These results suggest that directed attention can influence the probability of the startle reflex without influencing startle amplitude or latency.

Adolescent↗
PubMed1989

[Influence of stimulation of the central gray matter on low- and high-threshold startle reflexes].

Influences of the periaqueductal gray matter (PAG) stimulation on high-threshold jaw opening reflex (JOR) evoked by tooth pulp stimulation and on two functional types of startle reflexes were studied in chloralose anesthetized cats; the startle reflexes were high-threshold ones evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS, reflex) and low-threshold ones evoked by tactile stimuli (tactile spino-reticulo-spinal, TSRS, reflex). Stimulation of the majority of PAG sites induced considerable inhibition of JOR as well as profound depression of SBS-reflexes and moderate depression of TSRS-reflexes. Some PAG sites were found to exert a facilitatory action on the latter reflex. Effects of PAG stimulation were short-term (hundred ms) and/or long-lasting (minutes). Possible mechanisms of these effects are discussed.

Animals↗
PubMed1998

Effects of the hallucinogen psilocybin on habituation and prepulse inhibition of the startle reflex in humans.

Schizophrenic patients exhibit deficits in indices of sensorimotor gating, such as habituation and prepulse inhibition (PPI) of the startle reflex. Hallucinogenic drug-induced states are putative models for the early and acute stages of schizophrenic and schizophrenia-spectrum disorders. Hallucinogenic drugs have been shown to disrupt PPI and/or retard habituation of the startle reflex in animal models of schizophrenia, consistent with the view of hallucinogen-induced states as 'model psychoses'. We evaluated the effects of the hallucinogen psilocybin on PPI and habituation of the startle reflex in a double-blind, placebo-controlled human study with 12 healthy subjects. In contrast to animal studies, in our small human sample, psilocybin increased PPI, while having no clear effect on habituation (n = 6). These findings must be considered preliminary because several factors, including dose regimens and experimental parameters, may influence the results of studies on startle plasticity. Further investigations both with psychotic patients in different stages of the disease and with human and animal models of schizophrenia are needed in order to explore the effects of hallucinogens on sensorimotor gating and the relationship between information processing in hallucinogenic drug-induced states and the naturally occurring psychoses.

Adult↗