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Results for “Reflex, Startle”

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At least 523 records · Page 29Linked to original sources

PubMed2002

5-HT(1A) receptor antagonist p-MPPI attenuates acute ethanol effects in mice and rats.

The effect of a selective 5-HT(1A) antagonist, 4-(2'-methoxy-)phenyl-1-[2'-(N-2"-pyridinyl)-p-iodobenzamino-]ethyl-piperazine (p-MPPI), on acute ethanol-induced hypothermia, sleep and suppression of acoustic startle reflex in C3H/He mice and Wistar rats was studied. Administration of p-MPPI at the doses of 0.4, 0.7 and 1.0 mg/kg reduced in a dose-dependent manner the ethanol-induced hypothermia and the sleep time and attenuated the ethanol-induced decrease of acoustic startle reflex magnitude in mice. Similar p-MPPI (0.4 mg/kg) effects on ethanol-induced sleep and hypothermia were obtained in rats. It was concluded that 5-HT(1A) receptors were involved in the mechanisms of the ethanol-induced hypothermia and sleep, and that 5-HT(1A) antagonist increased acute ethanol tolerance.

Acute Disease↗

PubMed1996

A behavioral animal model of posttraumatic stress disorder featuring repeated exposure to situational reminders.

The purpose of this study was to evaluate an animal model of posttraumatic stress disorder (PTSD) in mice. The model featured repeated exposures to situational reminders of a traumatic stress, which consisted of a brief electric shock, and included assessment of two behavioral parameters and the startle reflex. The findings indicated an initial, but unsustained, increase in locomotor activity in a neutral environment due to traumatic stress. Exposure to situational reminders was associated with a persistent bidirectional abnormal behavioral pattern in a fear-provoking environment and a progressive increase over time in the magnitude of the startle reflex. Exposure to situational reminders also produced an increase in aggressive behavior. This animal model appears to produce behavioral changes analogous to those seen in patients with PTSD.

Adaptation, Psychological↗

PubMed2004

Brain activity underlying emotional valence and arousal: a response-related fMRI study.

Emotional behavior is organized along two psychophysiologic dimensions: (1) valence, varying from negative to positive, and (2) arousal, varying from low to high. Behavioral responses along these dimensions are assumed to be mediated by different brain circuits. We recorded startle reflex modulation and skin conductance responses in healthy volunteers during functional magnetic resonance imaging (fMRI) while they viewed a set of emotional pictures and took verbal ratings of the emotional valence and arousal of each picture after scanning. Response-related multiple correlation analysis revealed differential brain activity in five brain regions. Startle reflex changes, associated with the valence of a stimulus, correlated with activity in the amygdala, while verbal reports of negative emotional valence varied with insular activity. Peripheral physiologic and verbal responses along the arousal dimension varied with thalamic and frontomedial activity. Peripheral physiologic responses along both dimensions correlated with activity in somatosensory association areas in the anterior parietal cortex. In the valence dimension, activity in the left anterior parietal cortex was associated with highly correlating peripheral physiologic and verbal responses, suggesting that verbal reports of emotional valence might depend partly on brain circuits representing peripheral physiologic changes. Our data provide direct evidence for a functional segregation of brain structures underlying peripheral physiologic responses and verbal ratings along the emotional dimensions of valence and arousal.

Adult↗

PubMed1990

Reversible neural inactivation by cooling in anesthetized and freely behaving rats.

The design and use of a miniaturized cryoprobe to allow reversible neural inactivation were investigated in the rat. Tissue temperature measurements around the cryoprobe in the cerebellum of anesthetized rats established that significant heat loss (lower than 20 degrees C) was localized within 1.5 mm of the cryoprobe tip. To physiologically test the effectiveness of the cryoprobe, two specific behaviors mediated by well defined neural structures were measured; electrically elicited hindleg flexion in ketamine-anesthetized rats, mediated by the pyramidal tract; and the acoustic startle reflex in freely behaving rats, mediated by the ventral nucleus of the lateral lemniscus. Cooling of the pyramidal tract at a tip temperature of -5 degrees C reversibly blocked electrically elicited hindleg flexions within about 21 s. Cooling of the ventral nucleus of the lateral lemniscus at 0 degrees C reversibly blocked the acoustic startle reflex. These effects were obtained when the cryoprobe tip was within 0.5 mm of the respective neural targets. The results suggest that cooling produces fully reversible neural blockade with a very rapid onset and offset. The advantages and limitations of cooling in the rat are discussed.

Anesthesia↗

PubMed1997

Changes in sensorimotor inhibition across the menstrual cycle: implications for neuropsychiatric disorders.

The startle reflex is inhibited when the starting noise is preceded 30-500 msec by a weak prepulse. "Prepulse inhibition" (PPI) is reduced in specific neuropsychiatric disorders characterized clinically by impaired inhibition of sensory, motor, or cognitive information. PPI is sexually dimorphic, with men exhibiting significantly more PPI than women. We examined possible neuroendocrine substrates for this sex difference in PPI. The startle reflex, and a measure of visuospatial priming, were measured in 10 men, and in 46 normal women at different points in their menstrual cycle. In women, PPI was significantly reduced in the luteal vs follicular phase of the menstrual cycle. This reduction in PPI was most notable during the period corresponding to midluteal elevations of both estrogen and progesterone. In a task of visuospatial priming, follicular-phase women demonstrated a predominance of inhibition over facilitation, but this pattern reversed across the menstrual cycle.

Acoustic Stimulation↗

PubMed1996

The CCK-B antagonist LY288513 blocks the effects of nicotine withdrawal on auditory startle.

In order to explore the potential clinical utility of CCK-B antagonists for the treatment of nicotine withdrawal symptoms, the auditory startle reflex was examined in rats undergoing withdrawal from the chronic administration of nicotine. Rats were exposed to nicotine continuously for 12 days (6 mg kg-1 day-1) via osmotic minipumps. After 12 days the pumps were removed and the animals allowed to go through spontaneous withdrawal for several days. Acute treatment with the CCK-B antagonist LY288513, at doses that have no effect on startle responses in naive rats, blocked the nicotine withdrawal-induced increase in the acoustic startle reflex. These results indicate that CCK-B antagonists may be an efficacious treatment for some nicotine withdrawal symptoms in man and may represent a novel pharmacotherapy for smoking cessation.

Animals↗

PubMed1978

Excitatory and inhibitory components of the eyeblink responses to startle evoking stimuli, studied in the human subject.

Integrated EMG recordings have been used to study the eyeblink component of the human startle reflex. They have shown that the response, to either an auditory or a painful stimulus, consists of an initial excitation followed by a more prolonged period during which a second stimulus, of the same or different sensory modality, fails to evoke a response, or evokes one which is reduced in amplitude. The period of reduced responsiveness does not follow voluntary or spontaneous eyeblinks. Increasing the duration of the startle evoking stimulus has little effect on the excitatory component of the response, but prolongs the subsequent period of reduced responsiveness. When stimuli of one modality are presented repetitively to the subject, the eyeblink response is habituated; the response to a subsequent testing stimulus, of a different sensory modality, is then smaller than that evoked by the testing stimulus alone, but greater than that evoked by the testing stimulus when it follows a single conditioning stimulus. It is concluded that the excitatory and inhibitory components of the startle reflex are at least partially separable and that stimulus novelty has some significance in eliciting a response.

Acoustic Stimulation↗

PubMed2003

Temporal course of emotional startle modulation in schizophrenia patients.

The temporal course of startle reflex modulation to emotional pictures was investigated in 49 relatively asymptomatic schizophrenia outpatients and 46 normal controls. Participants viewed pleasant, neutral and unpleasant pictures, which were presented for 6 s and acoustic startle probes were delivered at five different times after picture onset. Replicating previous findings schizophrenia patients showed the same affective modulation of the startle reflex as healthy controls when probes were presented later during the picture-viewing period (3800 ms). For the early probe times (300 and 800 ms), affective pictures proved to be the effective prepulse stimuli resulting in a clear Prepulse inhibition (PPI) effect in both groups. In contrast to previous findings, the PPI of startle response was not stronger during processing emotional stimuli relative to neutral stimuli. For control subjects, blink reflexes were larger for unpleasant pictures compared with neutral and pleasant pictures, representing an early activation of motivational systems. Schizophrenia patients on the other hand, did not show this early affective modulation of the acoustic startle reflex.

Adult↗

PubMed2005

Routine post-weaning handling of rats prevents isolation rearing-induced deficit in prepulse inhibition.

Rats reared under isolation conditions from weaning present a number of behavioral changes compared to animals reared under social conditions (group housing). These changes include deficits in prepulse inhibition (PPI) of the startle reflex to a loud sound. PPI refers to the reduction of the magnitude of the startle reflex when a relatively weak stimulus (the prepulse) precedes by an appropriate time interval the intense startle-elicing stimulus (the pulse). PPI is useful for studying sensorimotor integration. The present study evaluated the effect of handling on the impairment of PPI induced by isolation-rearing. Male Wistar rats (N = 11-15/group) were housed in groups (5 per cage and handled three times a week) or isolated (housed individually) since weaning (21 days) for 10 weeks when they reach approximately 150 g. The isolated rats were divided into "minimally handled" animals (handled once a week for cleaning purposes only) or "handled" animals (handled three times a week). This handling consisted of grasping the rat by the tail and moving it to a clean cage (approximately 5 s). A statistically significant reduction (52%) in the PPI test was found only in the isolated group with minimal handling while no difference was seen between grouped animals and isolated handled animals. These results indicate that isolation rearing causes disruption in the PPI at adult age, which serves as an index of attention deficit. This change in the sensory processing of information induced by post-weaning isolation can be prevented by handling during the development of the animal.

Animals↗

PubMedDate not supplied

[Behavioral consequences of isolation in early ontogeny in rats: selectivity of anxiety conditions].

Multiparameter scale for evaluation of anxiety-phobic state in rats reveals significant enhancement of anxiety in rat pups after 6-week isolation (beginning from the 21st day from birth) as compared to grouped controls of the same litter: the locomotion and exploration that appear in test areas are suppressed, and species-specific fear reactions are enhanced. These changes considered as signs of situational anxiety are not eliminated by 2.5-month keeping in groups. Nevertheless, they are not correlated with parameters of the acoustic startle reflex that (by the data of literature) is thought to be related with fear and anxiety. On the basis of the discrepancy it is proposed that state of anxiety is selective. This suggestion is confirmed by individual behavioral variations characterized by a combination of a low level of situational anxiety and a high level of acoustic anxiety observed in both experimental and control groups. These variations may explain the existence of atypical "emotional resonance"-like behavior according to P.V. Simonov. Attention is given to selectively enhanced acoustic startle reflex in the group of active control as an evidence for critical importance of any manipulations with social context in early ontogeny.

Animals↗

PubMed1999

Effects of sustained cocaine exposure on sensorimotor gating of startle in rats.

Deficient sensorimotor gating, as measured by a relative loss of prepulse inhibition (PPI) of the startle reflex, has been reported in schizophrenia patients and in rats treated acutely with dopamine (DA) agonists or other psychotomimetic agents. For this reason, PPI has been used as a cross-species measure for studying the neurochemistry of specific information processing deficits in schizophrenia. Cocaine is a DA reuptake inhibitor which can precipitate psychosis after sustained use in humans. In rats, sustained exposure to cocaine results in neuropathological and neurochemical changes in several brain regions, and is also associated with specific prolonged behavioral abnormalities. In the present study, we examined the effects of both acute and sustained cocaine administration on PPI and other measures of the startle reflex in rats. Cocaine produced a significant, dose-dependent reduction in PPI, both after acute administration, and after 3 days of sustained administration via implanted subcutaneous pellets. PPI returned to control levels when rats were tested 10 days after sustained (5 day) cocaine administration. The effects of acute cocaine administration on PPI are consistent with those of other DA agonists and psychotomimetics, but PPI does not appear to be sensitive to lasting effects of a method of prolonged cocaine administration associated with neuropathological and neurochemical changes in several brain regions.

Acoustic Stimulation↗

PubMed1983

Early weight gain and behavioral responsivity as predictors of dietary obesity in rats.

Variance in diet-induced weight gain was examined for possible relationships with variations in early weight gain and three tests of behavioral responsivity. Female Sprague-Dawley rats were reared in litters of 4, 8, or 20. When animals reached adulthood, each animal's acoustic startle reflex, tail-pinch feeding responses and activity in an open field containing a palatable food were assessed. After completing these behavioral tests, rats were exposed to either palatable foods or a control diet for 59 days, following which all subjects were maintained on the control diet for 66 days. Body weights, food intakes, and naso-anal lengths were measured. Preweaning body weight gain for all rats correlated positively with later diet-induced weight gain. Rats reared in litters of 4 or 20 both gained less weight after exposure to palatable foods than did rats reared in litters of 8. Diet-induced weight gain correlated positively with magnitude of acoustic startle reflex and with latency to eat in response to tail pinch. These results tentatively identify specific predictive factors which may be useful in future studies of dietary obesity.

Aging↗

PubMed2001

Enhanced startle reactions to acoustic stimuli in patients with obsessive-compulsive disorder.

OBJECTIVE: Anxiety states induced experimentally or occurring naturally potentiate the startle reflex elicited by sudden sensory stimuli in both animals and human beings. The authors investigated whether patients with obsessive-compulsive disorder (OCD) show exaggerated startle reactions to acoustic probes, especially during negative-affect-toned stimuli, compared with healthy subjects. METHOD: Ten patients with OCD and 10 age- and sex-matched comparison subjects were shown a series of film clips. Two of the film clips had positive valence, two had negative valence, and two had relatively neutral valence. The subjects' eyeblink startle response was measured in reaction to startle-eliciting stimuli presented three times binaurally during each film clip. RESULTS: Patients with OCD produced larger startle reflexes and shorter latencies to onset of startle response than the comparison subjects over the entire session. CONCLUSIONS: Patients with OCD were excessively responsive to startle-eliciting stimuli. This effect may be associated with the development or maintenance of OCD.

Acoustic Stimulation↗

PubMed2005

Impaired cognitive performance in rats after complete epithalamus lesions, but not after pinealectomy alone.

In the midbrain, the epithalamus comprises the habenular nuclei and the pineal gland. Based on evidence including imaging studies in schizophrenia patients, several investigators have postulated that dysfunction of this structure is causally involved in symptoms of schizophrenia. Recently, we showed that bilateral habenula lesions in the rat induced some schizophrenia-like behavioural changes, namely memory and attention impairments, but unaltered social interaction in a brief encounter and prepulse inhibition (PPI) of the startle reflex. Here, the possible involvement of the pineal gland in the same behaviours was assessed, by examining them in two series of experiments. In the first, these behaviours were examined in pinealectomized rats compared to sham-operated controls. In the second, they were examined in rats with combined lesion of habenula plus pinealectomy compared to sham-operated controls, to examine whether pinealectomy induced further deficits when combined with habenula damage. Lesions of habenula were confirmed histologically and neurochemically by reduction of choline acetyltransferase in the interpeduncular nucleus. Pinealectomy was confirmed post mortem by careful visual inspection. Pinealectomy induced no deficits in any test, while combined lesions led to the same pattern of deficits as previously observed after habenula lesion, i.e. marked memory impairment in the Morris water maze without affecting the amount of social interaction or PPI of the startle reflex. Thus, loss of pineal function causes no deficits in these behaviours and does not alter the qualitative pattern of deficits resulting from habenula damage.

Acoustic Stimulation↗

PubMed1989

Comparison of vestibular and auditory startle responses in the rat and cat.

Cats, humans, and many other animals show stereotyped EMG responses in limb and axial muscles if suddenly dropped into free-fall. In cats, these free-fall responses (FFR) consist of highly synchronized bursts in most limb and axial muscles at 18-22 ms. We have used FFR to evaluate descending motor function and recovery in chronic spinal injured cats. Here FFR are compared with auditory evoked startle reflexes (ASR) in the hindlimb muscles of the rat and cat to determine whether they are related, and whether they could be used to evaluate descending motor function in the rat. ASR and FFR in the two species were similar except that the earliest components for both responses occurred around 9 ms in the rat versus 18-20 ms in the cat. Also, FFR in cats were usually more consistent and greater in amplitude during repeated drops than in rats, while the converse was true for ASR. Rat FFR amplitudes increased significantly after administering ketamine or 4-aminopyridine (4-AP), especially with both drugs together, while ASR amplitudes did not. FFR in cats recorded under ketamine analgesia were not normally improved by 4-AP. Finally, both FFR and ASR were suppressed by pentobarbital, chloralose, or motor activity. These data suggest that: (1) FFR appears to be a vestibular evoked startle reflex; (2) in the rat, ASR should be useful as a test of descending motor function following spinal injury, and (3) the combination of ketamine and 4-AP may be useful in revealing the presence of functional spinal pathways after CNS trauma.

4-Aminopyridine↗

PubMedDate not supplied

Effect of voluntary muscle contraction on the startle response to auditory stimuli.

Startle reflex responses were studied in 15 normal human subjects using weak (88 dB) and strong (114 dB) auditory stimuli in the orbicularis oculi, masseter, sternocleidomastoid, trapezius, deltoid, biceps, forearm flexors and quadriceps muscles. With the subjects in the relaxed state, no consistent responses were seen with the weak stimuli, and with the strong stimuli responses were only present in orbicularis oculi muscles. When the above muscles were in a state of voluntary contraction, the strong stimuli produced complex responses which were not always excitatory in nature, with muscle relaxation being noted in a number of stimulation sequences. Repetitive weak and strong stimuli were used to study habituation effects in the orbicularis oculi muscles. The repetitive strong stimuli produced a wide range of response patterns, indicating a high inter-individual variability in habituation. In two subjects, no habituation effects were present. Our study supports the high intra-individual variability of the startle response, and suggests that this response is affected by the state of muscle contraction at the time of stimulation. Startle response is more easily elicited in a state of muscular contraction. Future studies of startle reflex should take this into consideration.

Acoustic Stimulation↗

PubMed1998

Effects of bromocriptine and haloperidol on prepulse inhibition of the acoustic startle response in man.

Experiments with animals have shown that D2 dopamine (DA) receptors are involved in prepulse inhibition of the acoustic startle reflex (suppression of the reflex response evoked by a loud sound by prior presentation of a low-intensity stimulus). The present experiment attempted to extend this observation to man. Twelve healthy males (18-30 years), screened for normal hearing thresholds, participated in four sessions in which they received oral doses of placebo, bromocriptine 1.25 mg (a D2 receptor agonist), haloperidol 3 mg (a D2 receptor antagonist) and combined treatment with bromocriptine 1.25 mg+haloperidol 3 mg, according to a balanced double-blind protocol. Thirty-minute electromyographic recordings from the orbicularis oculi muscle of the right eye were carried out 120 min after ingestion of haloperidol and/or 90 min after ingestion of bromocriptine. Subjects received 36 40-msec sound pulses (115 dB), separated by variable intervals (mean 25 sec); in 24 of the trials the pulse was preceded by a 40-msec prepulse (75 dB in 12 trials and 85 dB in 12 trials; prepulse-pulse interval, 120 msec). The amplitude of the startle response was not significantly altered by any of the active treatments. Under the placebo condition, both 75- and 85-dB prepulses inhibited the startle response. Bromocriptine significantly attenuated this prepulse inhibition; haloperidol also produced a small but statistically significant attenuation of prepulse inhibition. Haloperidol significantly antagonized the attenuation of prepulse inhibition produced by bromocriptine. Neither drug altered self-rated alertness, physiological finger tremor, systolic or diastolic blood pressure or salivation. Bromocriptine significantly suppressed and haloperidol significantly elevated serum prolactin levels, these changes being absent when the two drugs were given in combination. The results provide evidence for the involvement of D2 DA receptors in prepulse inhibition of the startle reflex in man.

Acoustic Stimulation↗

PubMed1990

Animal models of anxiety based on classical conditioning: the conditioned emotional response (CER) and the fear-potentiated startle effect.

Stimuli consistently paired with shock become capable of suppressing ongoing operant or consummatory behavior (the conditioned emotional response--CER) or elevating the amplitude of the startle reflex (fear-potentiated startle). These changes are used to infer a central state of fear which involves the central nucleus of the amygdala and its efferent projections to the brainstem. The present paper reviews how psychoactive drugs affect these measures. Both the CER and fear-potentiated startle are reduced by benzodiazepines, barbiturates and opiates. Advantages and disadvantages of these animal tests of anxiety are discussed.

Animals↗