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PubMed1980

Neurochemical modulation of sensory-motor reactivity: acoustic and tactile startle reflexes.

The present review argues that the startle reflex is particularly well suited as a model system to analyze how drugs alter stimulus reactivity and reflex excitability. It then reviews all the literature to date on how drugs or lesions that are thought to alter neurochemical transmitter systems affect acoustic and/or tactile startle. Hypotheses are presented to account for how serotonin, dopamine, norepinephrine, acetylcholine, and opiates modulate startle. Effects on startle plasticity such as habituation, sensitization, and potentiation resulting from prior associative learning are also included.

Acetylcholine↗

PubMed1986

[Functional characteristics and topography of spinal tracts involved in low- and high-threshold startle reflexes].

Electrophysiological and topographical properties of the spinal tract systems involved in two functional types of startle reflexes were studied in chloralose anesthetized cats: a high threshold reflex evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS, reflex) and low threshold evoked by tactile (T-reflex) and acoustic (A-reflex) stimulation. It was found that the mean maximal conduction velocity of descending transmission of SBS-reflexes was much less (30 m/s) than that of T- (85 m/s) and A-reflexes (100 m/s). Ascending conduction velocities for SBS- and T-reflexes were 70.8 and 40.2 m/s, respectively. It was established by partial spinal cord lesions that ascending tracts for T-reflex passed in dorsal and dorso-lateral funiculi; those for SBS reflexes were found not only in the latter but also in ventro-lateral and partially in ventral funiculi. Descending pathways for SBS reflex passed mainly in ventro-lateral funiculi and partially in the ventral ones. Descending pathways of T- and A-reflexes had a similar organization and were located mainly in the ventral and ventro-lateral funiculi. Functional organization of spinal tracts of all studied types of startle reflexes is discussed.

Acoustic Stimulation↗

PubMed2002

[Correlation between cataleptic freezing and prestimulation inhibition of the startle reflex in rats].

In rats of GC strain bred for predisdposition to cataleptic freezing, a significant negative correlation between the duration of freezing and the level of prepulse inhibition (PPI) of the startle reflex, has been found. Besides, in a group of GC rats specific by their "nervousness" and jumpiness, there was also a negative correlation between the duration of freezing and the habituation to the startle reflex. None of this correlation have been found in Wistar rats. Since impairment of the PPI and habituation of the startle reflex is considered to be characteristic of schizophrenia, it is believed than cataleptic freezing in the GC rats may be used as a model of schizophrenic psychopathology.

Acoustic Stimulation↗

PubMed2004

Correlation between cataleptic freezing and prepulse inhibition of the startle reflex in rats.

GC rats, bred for a predisposition to cataleptic freezing, were found to show a significant negative correlation between the duration of freezing and the level of prepulse inhibition of the startle reflex. In addition, a group of GC rats characterized by increased "nervousness" also showed a negative correlation between the duration of freezing and the extent of habituation of the startle reflex. These correlations were not seen in Wistar rats. Since decreases in the level of prepulse inhibition and habituation of the startle reflex are regarded as characteristic of schizophrenia, it is suggested that cataleptic freezing in GC rats might be used as a model of schizophrenic pyschopathology.

Acoustic Stimulation↗

PubMed1985

Effects of spectrum, background noise, and stimulation rate on the auditory startle reflex in hyperbilirubinemic rats.

The sensory element of the acoustic startle reflex was studied in neonatal rats. Stimulus frequency, background noise, and stimulus presentation rate all affected the reflex. The performance of jaundiced rats with central auditory pathology is initially poorer than that of nonjaundiced rats but rapidly improves to the level of the controls, suggesting that the jaundiced rats may be a model for central auditory disturbances in humans. Startle reflex measurements give no indication that jaundiced rats surviving the testing period had neural hearing loss.

Acoustic Stimulation↗

PubMed2004

Effects of ethanol administration and induction of anxiety-related affective states on the acoustic startle reflex in sons of alcohol-dependent fathers.

BACKGROUND: The high rate of comorbidity between alcoholism and anxiety disorders suggests some causal link. This study used the startle reflex to investigate whether increased reactivity to stimuli inducing fear or related affective states might be one mechanism by which a family genetic risk promotes the development of alcohol use disorders. METHODS: Thirty-one sons of alcoholics (PH+) were recruited from the participants of a longitudinal epidemiologic survey representative of the Munich area population between 18 and 25 years. Thirty male low-risk participants without parental alcoholism (PH-) were matched for age and history of psychiatric disorders. The baseline acoustic startle reflex was elicited before and after subjects drank 0.6 g/kg ethanol or placebo in a randomized, double-blind, placebo-controlled crossover design. Thereafter, the startle response was investigated while the subjects' affective state was manipulated by announcement of aversive electric finger stimuli to induce fear potentiation and by presentation of photographic slides previously rated to be pleasant, unpleasant, or neutral in their emotional valence. RESULTS: Plain startle response was lower in PH+ than PH- participants and was equally dampened by alcohol in PH+ and PH- subjects. Threat of finger shocks increased the startle response to the same extent in both groups. This fear potentiation effect was significantly attenuated by alcohol given on the second experimental day but not if alcohol was administered first and placebo on the second day. Pleasant and unpleasant slides decreased and increased startle response, respectively, and this effect was influenced by neither risk group nor alcohol. CONCLUSIONS: The acoustic startle reflex seems to be reduced in sons of alcoholics. The nonsignificant results during startle modification do not support the concept of increased reactivity to anxiety-related environmental stimuli as a mechanism promoting alcohol use disorders in subjects at increased family genetic risk for alcoholism.

Acoustic Stimulation↗

PubMed1989

The role of 5HT1A receptors in the modulation of the acoustic startle reflex in rats.

The modulatory role of serotonin (5-HT) on the acoustic startle reflex was studied using 5-HT receptor agonists and antagonists. 8-Hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT) (1,2 and 4 mg/kg, SC) and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (1,2 and 4 mg/kg, IP), putative 5-HT1a receptor agonists, increased the magnitude of the startle reflex, while quipazine (5, 10 and 20 mg/kg, SC), an agonist with mixed 5-HT2 and 5-HT1b receptor activity, decreased startle responsiveness. Pretreatment of rats with ketanserin (1, 2 and 4 mg/kg, SC), a 5-HT2 receptor antagonist, had no significant effect on the activity of 8-OHDPAT, 5-MeODMT, or quipazine. Metergoline (0.25, 0.5, 1 and 2 mg/kg, SC), a mixed 5-HT1/5-HT2 receptor antagonist attenuated the augmentation of the reflex by 8-OHDPAT and 5-MeODMT and the suppression produced by quipazine. At the doses used, metergoline produced a non-dose-dependent increase in startle, while ketanserin had no effect. None of the agents specifically affected the ability of a prepulse stimulus to inhibit the acoustic startle response. These data suggest that 5-HT1a and 5-HT1b receptors play opposite roles in the modulation of the acoustic startle response and that 5-HT plays little, if any, role in the prepulse inhibition of the acoustic startle response.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1994

Effects of ethanol on the acoustic startle reflex in humans.

The effect of ethanol on human sensorimotor reactivity was assessed by examining the acoustic startle response. Twelve healthy normal subjects participated in a startle reflex experiment in which placebo or ethanol were given on separate days. Three types of startle probes were used. They consisted of pulse-alone bursts of white noise at 108 dB(A) and 99 dB(A) to explore startle reactivity, and of a 108 dB(A) pulse preceded by a 85 dB(A) prepulse stimulus (prepulse+pulse) to assess prepulse inhibition. Startle amplitude was larger to the 108 dB(A), compared to the 99 dB(A) pulse-alone probes. The prepulse stimulus significantly reduced the amplitude of the startle reflex elicited by the subsequent 108 dB(A) stimulus. The amplitude of the startle response was dramatically reduced by acute ethanol. The effects of ethanol on prepulse inhibition could not be assessed because the startle response was too small in the ethanol condition.

Acoustic Stimulation↗

PubMed1975

Acoustic startle reflexes in the rat during consummatory behavior.

Auditory startle reflexes were elicited in thirsty rats when they were drinking water or were between drinking boutsmthe reaction was greater during drinking, this enhancement developing over the first few seconds after drinking onset. The startle reaction was lowest immediately after the termination of drinking. Reflex enhancement was reduced when thirsty rats drank milk rather than the more preferred water. The reflex was smaller with increased water deprivation, but enhancement produced by drinking was apparent at all levels of deprivation studied, satiety to 4-days deprivation. The inhibitory effect of a preliminary stimulus was not affected by consummatory behavior. Attention is drawn to suggestive parallels between these behavioral effects and other consequences of consummatory activity, primarily having to do with electrophysiological events and arousal processes

Acoustic Stimulation↗

PubMed2001

Roles of the glutamate receptor epsilon2 and delta2 subunits in the potentiation and prepulse inhibition of the acoustic startle reflex.

We examined the regulation of the acoustic startle response in mutant mice of the N-methyl-D-aspartate (NMDA)- and delta-subtypes of the glutamate receptor (GluR) channel, which play important roles in neural plasticity in the forebrain and the cerebellum, respectively. Heterozygous mutant mice with reduced GluRepsilon2 subunits of the NMDA receptor showed strongly enhanced startle responses to acoustic stimuli. On the other hand, heterozygous and homozygous mutation of the other NMDA receptor GluRepsilon subunits exerted no, or only small effects on acoustic startle responses. The threshold of the auditory brainstem response of the GluRepsilon2-mutant mice was comparable to that of the wild-type littermates. The primary circuit of the acoustic startle response is a relatively simple oligosynaptic pathway located in the lower brainstem, whilst the expression of GluRepsilon2 is restricted to the forebrain. We thus suggest that the NMDA receptor GluRepsilon2 subunit plays a role in the regulation of the startle reflex. Ablation of the cerebellar Purkinje cell-specific delta2 subunit of the GluR channel exerted little effect on the acoustic startle response but resulted in the enhancement of prepulse inhibition of the reflex. Because inhibition of the acoustic startle response by a weak prepulse is a measure of sensorimotor gating, the process by which an organism filters sensory information, these observations indicate the involvement of the cerebellum in the modulation of sensorimotor gating.

Acoustic Stimulation↗

PubMed1954