Increase In Startle Amplitude Research Articles

Cell‐type specific expression of GluN2C and GluN2D subunits and their role in schizophrenic phenotypes

IntroductionFunctional deficit in NMDA‐receptors on parvalbumin (PV)‐positive interneurons (PV‐NMDARs) is central to the pathophysiology of schizophrenia. NMDA channel blockers like ketamine and MK‐801 have shown to produce psychosis by inhibiting GluN2C and GluN2D subunits with greater affinity than other subunits. Recent neuroanatomical and electrophysiological studies have reported expression of GluN2D subunit in PV positive interneurons in corticolimbic regions but the precise distribution of GluN2C subunit especially in PV interneurons remains unknown.Hence, the objective of the study was to identify the expression pattern of GluN2C subunit in neuronal and non‐neuronal cell population and to perform a side‐by‐side comparison of the effect of partial and complete ablation of GluN2C and GluN2D subunit on pure C57BL/6N mouse strain.Methods and ResultsImmunohistochemistry was used to determine the heterogenous expression of GluN2C using a novel eGFP reporter mouse model. We found the expression of EGFP (GluN2C) with PV positive neurons in nucleus reticularis of the thalamus, globus pallidus externa and interna, ventral pallidum and substantia nigra. Interestingly, EGFP (GluN2C) showed co‐localization with astrocytic marker in the striatum, cortex, hippocampus and amygdala but not with PV positive neurons. GluN2C was found to be enriched in several thalamic relay nuclei including first order and higher order nuclei. GluN2D knockout mouse exhibited hypo‐locomotion and anxiety‐like behavior in the open field test. We found a significant increase in startle amplitude in GluN2C HET but not GluN2C KO and no change in prepulse inhibition (PPI) in either genotype was observed. Increase in startle response was found for GluN2D heterozygous and GluN2D knockout along with lower prepulse inhibition at some decibels. We also found CIQ, a selective positive allosteric modulator for GluN2C/GluN2D subunit, reversed the MK801 induced impairment in PPI in GluN2C wildtype and heterozygous mice but not in GluN2C KO mice. Furthermore, we observed that GluN2C knockout mice but not GluN2D knockout mice were less sensitive to phencyclidine‐induced hyperlocomotion, a model of psychosis. The cell‐type specific expression of both GluN2C and GluN2D subunit may provide more insights into schizophrenia‐like behaviors. Hence, we will confirm psychotic and sensorimotor deficits by selectively deleting GluN2D subunit from PV‐positive interneurons and GluN2C subunit from astrocytes using Cre‐lox strategy.ConclusionTogether, these results identify the unique expression pattern of GluN2C subunit in neuronal and non‐neuronal cell population. It also demonstrates the preferential involvement of GluN2C‐ containing receptors in phencyclidine‐induced hyperlocomotion and that facilitation of GluN2C subunit may reverse the schizophrenic phenotypes.Support or Funding InformationR21 NS104705This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Spatial hearing ability of the pigmented Guinea pig (Cavia porcellus): Minimum audible angle and spatial release from masking in azimuth

Despite the common use of guinea pigs in investigations of the neural mechanisms of binaural and spatial hearing, their behavioral capabilities in spatial hearing tasks have surprisingly not been thoroughly investigated. To begin to fill this void, we tested the spatial hearing of adult male guinea pigs in several experiments using a paradigm based on the prepulse inhibition (PPI) of the acoustic startle response. In the first experiment, we presented continuous broadband noise from one speaker location and switched to a second speaker location (the “prepulse”) along the azimuth prior to presenting a brief, ∼110 dB SPL startle-eliciting stimulus. We found that the startle response amplitude was systematically reduced for larger changes in speaker swap angle (i.e., greater PPI), indicating that using the speaker “swap” paradigm is sufficient to assess stimulus detection of spatially separated sounds. In a second set of experiments, we swapped low- and high-pass noise across the midline to estimate their ability to utilize interaural time- and level-difference cues, respectively. The results reveal that guinea pigs can utilize both binaural cues to discriminate azimuthal sound sources. A third set of experiments examined spatial release from masking using a continuous broadband noise masker and a broadband chirp signal, both presented concurrently at various speaker locations. In general, animals displayed an increase in startle amplitude (i.e., lower PPI) when the masker was presented at speaker locations near that of the chirp signal, and reduced startle amplitudes (increased PPI) indicating lower detection thresholds when the noise was presented from more distant speaker locations. In summary, these results indicate that guinea pigs can: 1) discriminate changes in source location within a hemifield as well as across the midline, 2) discriminate sources of low- and high-pass sounds, demonstrating that they can effectively utilize both low-frequency interaural time and high-frequency level difference sound localization cues, and 3) utilize spatial release from masking to discriminate sound sources. This report confirms the guinea pig as a suitable spatial hearing model and reinforces prior estimates of guinea pig hearing ability from acoustical and physiological measurements.

The Effects of Prior Stress on Anxiety-Like Responding to Intra-BNST Pituitary Adenylate Cyclase Activating Polypeptide in Male and Female Rats.

Chronic or repeated exposure to stressful stimuli can result in several maladaptive consequences, including increased anxiety-like behaviors and altered peptide expression in anxiety-related brain structures. Among these structures, the bed nucleus of the stria terminalis (BNST) has been implicated in emotional behaviors as well as regulation of hypothalamic-pituitary-adrenal (HPA) axis activity. In male rodents, chronic variate stress (CVS) has been shown to increase BNST pituitary adenylate cyclase activating polypeptide (PACAP) and its cognate PAC1 receptor transcript, and BNST PACAP signaling may mediate the maladaptive changes associated with chronic stress. Here, we examined whether CVS would sensitize the behavioral and/or endocrine response to a subthreshold BNST PACAP infusion. Male and cycling female rats were exposed to a 7 day CVS paradigm previously shown to upregulate BNST PAC1 receptor transcripts; control rats were not stressed. Twenty-four hours following the last stressor, rats were bilaterally infused into the BNST with a normally subthreshold dose of PACAP. We found an increase in startle amplitude and plasma corticosterone levels 30 min following intra-BNST PACAP infusion in male rats that had been previously exposed to CVS. CVS did not enhance the startle response in cycling females. Equimolar infusion of the VPAC1/2 receptor ligand vasoactive intestinal polypeptide (VIP) had no effect on plasma corticosterone levels even in previously stressed male rats. These results suggest that repeated exposure to stressors may differentially alter the neural circuits underlying the responses to intra-BNST PACAP, and may result in different anxiety-like responses in males and females.

Emotion regulation of the affect-modulated startle reflex during different picture categories.

Previous studies on emotion regulation of the startle reflex found an increase in startle amplitude from down-, to non-, to up-regulation for pleasant and unpleasant stimuli. We wanted to clarify whether this regulation effect remains stable for different picture categories within pleasant and unpleasant picture sets. We assessed startle amplitude of 31 participants during down-, non-, or up-regulation of feelings elicited by pleasant erotic and adventure and unpleasant victim and threat pictures. Startle amplitude was smaller during adventure and erotic compared to victim and threat pictures and increased from down-, to non-, to up-regulation independently of the picture category. Results indicate that the motivational priming effect on startle modulation elicited by different picture categories is independent of emotion regulation instructions. In addition, the emotion regulation effect is independent of motivational priming effects.

Neuropsychological Deficits in Mice Depleted of the Schizophrenia Susceptibility Gene CSMD1

Recent meta-analyses of schizophrenia genome-wide association studies (GWASs) have identified the CUB and SUSHI multiple domains 1 (CSMD1) gene as a statistically strong risk factor. CSMD1 is a complement control-related protein suggested to inhibit the classical complement pathway, being expressed in developing neurons. However, expression of CSMD1 is largely uncharacterized and relevance for behavioral phenotypes is not previously demonstrated. Here, we assess neuropsychological behaviors of a Csmd1 knockout (KO) mouse in a selection of standard behavioral tests. Deregulation of neuropsychological responses were observed in both the open field and the elevated plus maze tests, in which KO mice spent 55% and 33% less time than WT littermate mice in open areas, respectively. Altered behaviors were also observed in tail suspension and to higher acoustic stimuli, for which Csmd1 KO mice showed helplessness and moderate increase in startle amplitude, respectively. Furthermore, Csmd1 KO mice also displayed increased weight-gain and glucose tolerance, similar to a major phenotype of the metabolic syndrome that also has been associated to the human CSMD1 locus. Consistent with a role in the control of behaviors, Csmd1 was found highly expressed in the central nervous system (CNS), and with some expression in visceral fat and ovary, under tissue-specific control by a novel promoter-associated lncRNA. In summary, disruption of Csmd1 induces behaviors reminiscent of blunted emotional responses, anxiety and depression. These observations suggest an influence of the CSMD1 schizophrenia susceptibility gene on psychopathology and endophenotypes of the negative symptom spectra.

The role of the read through variant of acetylcholinesterase in anxiogenic effects of predator stress in mice

This study examined the role of the read through variant of acetylcholinesterase (AChE-R) in lasting changes in murine affective behavior produced by a brief predator stress. AChE-R is elevated by stress in limbic cholinergic circuits implicated in anxiogenic effects of predator stress. The expression of AChE-R was blocked with a systemically administered central acting antisense oligonucleotide for AChE-R (EN101). EN101 was injected at multiple points prior to and after a predator stress in male C57 mice. Seven days after the last injection, behavior was tested. Predator stress caused a significant increase in startle amplitude, which EN101 blocked. This effect was specific to EN101, as the negative control inactive form of EN101, INVEN101 was without effect on stress effects on startle. Neither EN101 nor INVEN101 altered the anxiogenic effects of predator stress on behavior in the elevated plus maze, and both drugs partially reduced stress suppression of time active in the hole board. In the light dark box test, INVEN101 exhibited a weak block of stress effects on behavior for reasons which are unclear. Taken together, findings support the view that multiple neural systems are responsible for the different changes in behavior produced by predator stress. Present findings also suggest a role for AChE-R in specific anxiogenic (hyperarousal) effects following predator stress. Since AChE-R manipulations took place starting 23 h prior to predator stress and continued 48 h after predator stress, further research is necessary to determine the role of AChE-R in initiation and/or consolidation of hyperarousal effects of predator stress.

Anatomically discrete functional effects of adenoviral clostridial light chain gene-based synaptic inhibition in the midbrain

The gene for the Light Chain fragment of Tetanus Toxin (LC) induces synaptic inhibition by preventing the release of synaptic vesicles. The present experiment applied this approach within the rat midbrain in order to demonstrate that LC gene expression can achieve functionally and anatomically discrete effects within a sensitive brain structure. The deep layers of the superior colliculus/deep mesencephalic nucleus (dSC/DpMe) that are located in the rostral midbrain has been implicated in fear-induced increase of the acoustic startle reflex (fear potentiated startle) but exists in close proximity to neural structures important for a variety of critical functions. The dSC/DpMe of adult rats was injected bilaterally with adenoviral vectors for LC, green fluorescent protein, or vehicle. Synaptobrevin was depleted in brain regions of adenoviral LC expression. LC gene expression in the dSC/DpMe inhibited the increase in startle amplitude seen with the control viral infection, and blocked context-dependent potentiation of startle induced by fear conditioning. Although LC gene expression reduced the absolute amount of cue-specific fear potentiated startle, it did not decrease percent potentiated startle to a cue, nor did it reduce fear-induced contextual freezing, nonspecific locomotor activity, or general health, indicating that its effects were functionally and anatomically specific. Thus, vector-driven LC expression inhibits the function of deep brain nuclei without altering the function of surrounding structures supporting its application to therapeutic neuromodulation.

Effects of anticholinergic drugs selective for muscarinic receptor subtypes on prepulse inhibition in mice

The effects of anticholinergic drugs selective for muscarinic receptor subtypes on prepulse inhibition of acoustic startle response were determined in mice. The prepulse inhibition is associated with sensorimotor information processing in the brain. The anticholinergic agent scopolamine (0.3 mg/kg, s.c.) significantly attenuated prepulse inhibition, while the drug (1–10 mg/kg, s.c.) had no effects on startle amplitude as an indicator of startle response. The muscarinic M1 receptor antagonist pirenzepine (0.1–10 μg/mouse, i.c.v.) and the muscarinic M2 receptor antagonist AF-DX116 (11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one) (0.1–10 μg/mouse, i.c.v.) had no effects on prepulse inhibition or startle amplitude. The muscarinic M3 receptor antagonist 4-DAMP (1,1-dimethyl-4-diphenylacetoxy-piperidinium iodide) (30 μg/mouse, i.c.v.) and the muscarinic M4 receptor antagonist tropicamide (0.1 μg/mouse, i.c.v.) significantly attenuated prepulse inhibition, while tropicamide (0.01 μg/mouse, i.c.v.) but not 4-DAMP (10 and 30 μg/mouse, i.c.v.) produced a significant increase in startle amplitude. These results suggest that the blockade of muscarinic M3 and M4 receptors leads to the disruption of prepulse inhibition.

Estrogen and progesterone prevent disruption of prepulse inhibition by the serotonin-1A receptor agonist 8-hydroxy-2-dipropylaminotetralin.

The aim of the present study was to investigate the effect of estrogen and progesterone treatment on 5-hydroxytryptamine (serotonin)-1A (5-HT(1A)) receptor-mediated disruption of prepulse inhibition (PPI) of acoustic startle. The age-at-onset of schizophrenia is later in women than men, and it has been suggested that women may be protected from schizophrenia by the sex steroid hormone estrogen. 5-HT(1A) receptors have been implicated in the development of schizophrenia and the action of antipsychotics. PPI is a model of sensorimotor gating that is deficient in schizophrenia and other illnesses. Female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated. Some OVX rats received silastic implants filled with a low dose of estrogen (E20), a high dose of estrogen (E100), progesterone (P), or both the E20- and P-filled (E/P) silastic implants. Two weeks later, the rats were randomly treated with saline, or 0.02 or 0.5 mg/kg of the 5-HT(1A) receptor agonist 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT). Treatment with 8-OH-DPAT resulted in a dose-dependent increase in startle amplitude in all rat groups. PPI was significantly reduced after injection of 0.5 mg/kg 8-OH-DPAT in sham-operated rats, untreated OVX rats, E20-treated OVX rats, and P-treated OVX rats. In contrast, in E100- and E/P-treated OVX rats, PPI was not significantly reduced by 0.5 mg/kg 8-OH-DPAT. These data suggest that treatment with a high dose of estrogen, or with a combination of estrogen and progesterone, prevents 8-OH-DPAT-induced disruption of PPI. Thus, these hormones could be protective against sensorimotor gating deficits, at least those induced by 5-HT(1A) receptor stimulation, and may therefore be beneficial against some symptoms of schizophrenia.

Exposure of mice to a predator odor increases acoustic startle but does not disrupt the rewarding properties of VTA intracranial self-stimulation

The present investigation assessed the propensity of an acute psychogenic stressor exposure to induce behavioral change in paradigms assessing fear/anxiety (acoustic startle) and motivation/anhedonia (intracranial self-stimulation) in CD-1 mice. In the acoustic startle paradigm, a 10-min exposure of 2–4 month old mice (young adult mice) to fox odor (2,5-dihydro-2,4,5-trimethylthiazoline; TMT) was associated with decreased acoustic startle relative to mice exposed to the control odor, butyric acid (BA), immediately and relative to both saline and BA exposure 24 h following odor exposure in the home cage. In contrast, a 2-min exposure of young adult mice to TMT was associated with an increase in startle relative to saline and BA during the immediate post-odor test session only. In young adult mice a 2-min and a 10-min exposure to BA resulted in a startle profile of mice reminiscent of saline-treated mice. In comparison to young adult mice, a 2-min exposure of mature adult mice (5–7 months old) to TMT enhanced startle for up to 48 h relative to both saline and BA, while a 10-min exposure of mature adult mice to TMT enhanced startle for 168 h post-odor exposure relative to saline-exposed mice only. However, the greatest increase in startle amplitude (i.e. 48 h) was acquired following the 2-min exposure of mature mice to TMT. Among mature adult mice, a 10-min exposure to BA in the home cage eventuated in enhanced startle relative to saline-exposed animals 168 h following odor exposure. In comparison, exposure of mice to 10 min of TMT depressed responding for VTA brain stimulation at the initial 80 Hz frequency, but was ineffective in elevating reward thresholds relative to mice merely exposed to saline. Mice assessed in the ICSS paradigm were approximately 2–4 months old at the time of surgery and 5–7 months old at the completion of testing. These data suggest that acute odor exposure may induce a fear gradient dependent upon the perceived stressor severity and that the resultant anxiety-like effects are dependent on the duration of odor exposure, age of the animals and the temporal interval between odor presentation and behavioral testing. Moreover, the anxiogenic properties of psychogenic stressors can be separated from their anhedonic effects. The implications of these data for clinical psychopathology are discussed.

Prepulse inhibition of the acoustic startle reflex using visual and auditory prepulses: disruption by apomorphine

The amplitude of the acoustic startle reflex can be reduced reliably when preceded at short intervals by a weak stimulus (prepulse) which itself does not elicit startle. The magnitude of this prepulse inhibition effect is attenuated by several dopamine agonists, such as apomorphine, especially when there is a relatively small difference between the intensity of the prepulse and the intensity of the background noise over which the prepulse is superimposed. One goal of the present experiment was to test the generality of this disruptive effect of apomorphine on prepulse inhibition by using either an auditory prepulse that included both a change in intensity and a change in frequency relative to the background noise or a visual prepulse stimulus. Apomorphine reduced auditory prepulse inhibition when induced by a small change in stimulus intensity, but not when induced by a change in both intensity and frequency. Apomorphine consistently reduced visual prepulse inhibition with a complete blockade at 100-ms test interval. However, it did not fully block the usual reduction in startle onset latency or even attenuate the increase in startle amplitude when a visual prepulse was presented 5, 10 or 15 ms before the startle stimulus. Consistent with conclusions from other laboratories using auditory prepulse inhibition, these data suggest that apomorphine did not prevent the animal from detecting prepulse presentation under conditions where the drug completely blocked prepulse inhibition. Moreover, they indicate that the blockade of prepulse inhibition by apomorphine was independent of prepulse modality, adding generality to the original finding. Visual prepulse inhibition may be a useful alternative procedure for evaluating the effects of drugs on this attentional process.

Lesions of the central nucleus of the amygdala block the excitatory effects of septal ablation on the acoustic startle reflex

Many studies have investigated the role of the septum and the amygdala in emotional behavior. While the literature is somewhat inconsistent, most studies suggest a role for the septal nuclei in the inhibition of fear and stress responses (at the behavioral, autonomic and hormonal levels) while the central nucleus of the amygdala is involved in the production of such responses. The present study examined the ability of lesions of the central nucleus of the amygdala to block the excitatory effects of complete septal ablation on the acoustic startle reflex. Septal ablation produced a significant increase in startle amplitude which was blocked by concomitant lesions of the central nucleus of the amygdala. These results suggest that the increase in startle amplitude resulting from septal damage might be due to a disinhibition of neuronal activity in the central nucleus of the amygdala, a structure known to mediate the increase in startle associated with conditioned and unconditioned fear, or from antagonistic interactions at other target sites which themselves modulate startle.

Effects of nicotine on the acoustic startle reflex amplitude in rats

The acoustic startle reflex was used to measure changes in sensorimotor reactivity in response to nicotine administration and cessation. Male rats received saline, 6 mg/kg/day or 12 mg/kg/day nicotine delivered subcutaneously by osmotic minipumps. The pumps delivered their contents during a 10-day period of implantation, after which time they were explanted. Animals were tested for startle reflex amplitudes using two levels of white noise bursts prior to pump implantation, on days 1 and 7 of nicotine or saline administration, and on several days following drug cessation. Nicotine produced a dose-dependent increase in startle amplitude during the period of administration that decreased during cessation. Results are interpreted in terms of nicotine's actions to enhance attentional processes.

Role of the inferior colliculus in the inhibition of acoustic startle in the rat

Fifteen rats were tested for amplitude reduction of the acoustic startle response using auditory and visual prestimuli. Eight subjects then received large lesions of the inferior colliculus, and the remaining subjects served as normal controls. All animals were reassessed on a post-test identical to the pre-test. In addition, all subjects were tested for latency reduction of startle using auditory prestimuli. There were no significant differences between groups on the pre-test for startle amplitude, visual amplitude reduction, or auditory amplitude reduction, nor did the control group differ significantly on these measures from pre-test to post-test. After surgery, the lesion group displayed a large, significant increase in startle amplitude. Auditory prestimuli were no longer effective in reducing startle amplitude in this group, but visual prestimuli still produced reliable amplitude reduction. Both groups displayed reliable latency reduction to auditory prestimuli; the groups were not significantly different from each other on this measure. These data support the proposition that the inferior colliculus is part of a neural circuit for startle amplitude reduction by auditory prestimuli.

Excitatory effects of the vasodilator hydralazine on acoustic startle in the rat

Several drugs that functionally depress noradrenergic transmission depress acoustic startle amplitude (e.g., clonidine, phenoxybenzamine). Since these agents also depress blood pressure, the current study was designed to investigate the effects of hypotension per se (in the absence of decrease noradrenergic transmission) on the acoustic startle response. The vasodilator hydralazine was chosen because it produces marked hypotension in conscious rats, yet results in a compensatory increase in noradrenergic transmission (sympathetic rebound), rather than a decrease, as is seen with many other hypotensive agents. Hydralazine (0.3–20 mg/kg, IP) produced a marked and long-lasting increase in startle amplitude, compared to saline-treated controls. In a similar group of subjects, IP administration of 2.5 mg/kg hydralazine decreased mean arterial blood pressure by about 50% in conscious rats. Since, at the doses and treatment times employed in the present study, hydralazine decreases blood pressure but not startle amplitude, these data suggest that there is no relationship between changes in blood pressure and changes in startle amplitude across all drugs. Moreover, since hydralazine-induced hupotension results in an increase in noradrenergic transmission (sympathetic rebound), these data are consistent with the hypothesis that increases in central noradrenergic transmission increase acoustic startle amplitude. Lastly, since the most prominent direct action of hydralazine occurs in the periphery, hydralazine may alter startle through central actions that are triggered in the periphery.

Strychnine: Brainstem and spinal mediation of excitatory effects on acoustic startle

The present study investigated the effects of the glycine antagonist strychnine on the acoustic startle response in rats. Strychnine (0.25, 0.50, 1.0, 1.25, 1.5 and 2.0 mg/kg) administered intraperitoneally (i.p.) was found to produce a dose-dependent increase in startle amplitude that reached is greatest magnitude within 10–15 min after injection. These doses did not produce convulsions or behavioral activation. In order to localize the site of action of this excitatory strychnine effect, rats were implanted with catheters in the lumbar region of the spinal cord (intrathecal implantation), in the cisterna magna, or in the lateral ventricle and later tested for startle after microinjections of strychnine. Dose-dependent excitatory effects on acoustic startle were found when strychnine was injected onto the spinal cord (3.12–12.5 μg) or into the cisterna magna (6.25–25.0 μg), whereas infusion into the lateral ventricle produced inhibition (6.25–25.0 μg). The peak increases in startle following intrathecal (164%) and intracisternal (144%) strychnine were similar to the increase seen following systemic strychnine (160%). Thus, the excitatory effect of systemic strychnine appears to be mediated in the spinal cord and/or brainstem, consistent with data showing that glycine receptors are primarily localized in the caudal regions of the central nervous system. Furthermore, these results suggest that glycine exerts a tonic inhibitory influence on acoustic startle. The possible relation of such a system to phenomena that involve reduction in startle amplitude (e.g., habituation, pre-pulse inhibition) is discussed.

Involvement of norepinephrine in startle arousal after acute and chronic d-amphetamine administration.

Treatment with d-amphetamine produced a dose-dependent increase in startle amplitude in response to a buzzer. This increase appeared to be a reflection of a sensitization effect, i.e., enhanced responsivity as a function of repeated stimulus presentations. Treatment with alpha-methyl-p-tyrosine, which reduced whole brain concentrations of dopamine (DA) and norepinephrine (NE), or treatment with FLA-63, which reduced only NE, antagonized the effects of d-amphetamine on the startle reflex, suggesting a role of NE in this behavior. Startle amplitude was also reduced following chronic d-amphetamine treatment. The effect of d-amphetamine on startle was found to be independent of changes in drug-induced locomotor excitation. The data of the present investigation, together with earlier reports, suggests that tolerance occurs to those behaviors that involve a noradrenergic component.