Prepulse Inhibition Of Acoustic Startle Research Articles

Hypoxic preconditioning in rats with low and high prepulse inhibition of acoustic startle is implemented through topographically different sensory inputs. Working hypothesis

Hypoxic preconditioning in rats with low and high prepulse inhibition of acoustic startle is implemented through topographically different sensory inputs. Working hypothesis

Sex-dependent effects of Setd1a haploinsufficiency on development and adult behaviour.

Loss of function (LoF) mutations affecting the histone methyl transferase SETD1A are implicated in the aetiology of a range of neurodevelopmental disorders including schizophrenia. We examined indices of development and adult behaviour in a mouse model of Setd1a haploinsufficiency, revealing a complex pattern of sex-related differences spanning the pre- and post-natal period. Specifically, male Setd1a+/- mice had smaller placentae at E11.5 and females at E18.5 without any apparent changes in foetal size. In contrast, young male Setd1a+/- mice had lower body weight and showed enhanced growth, leading to equivalent weights by adulthood. Embryonic whole brain RNA-seq analysis revealed expression changes that were significantly enriched for mitochondria-related genes in Setd1a+/ samples. In adulthood, we found enhanced acoustic startle responding in male Setd1a+/- mice which was insentitive to the effects of risperidone, but not haloperidol, both commonly used antipsychotic drugs. We also observed reduced pre-pulse inhibition of acoustic startle, a schizophrenia-relevant phenotype, in both male and female Setd1a+/- mice which could not be rescued by either drug. In the open field and elevated plus maze tests of anxiety, Setd1a haplosufficiency led to more anxiogenic behaviour in both sexes, whereas there were no differences in general motoric ability and memory. Thus, we find evidence for changes in a number of phenotypes which strengthen the support for the use of Setd1a haploinsufficient mice as a model for the biological basis of schizophrenia. Furthermore, our data point towards possible underpinning neural and developmental mechanisms that may be subtly different between the sexes.

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus.

Tinnitus is a common annoying symptom without effective and accepted treatment. In this controlled experimental study, photobiomodulation therapy (PBMT), which uses light to modulate and repair target tissue, was used to treat sodium salicylate (SS)-induced tinnitus in a rat animal model. Here, PBMT was performed simultaneously on the peripheral and central regions involved in tinnitus. The results were evaluated using objective tests including gap pre-pulse inhibition of acoustic startle (GPIAS), auditory brainstem response (ABR) and immunohistochemistry (IHC). Harmful neural plasticity induced by tinnitus was detected by doublecortin (DCX) protein expression, a known marker of neural plasticity. PBMT parameters were 808 nm wavelength, 165 mW/cm2 power density, and 99 J/cm2 energy density. In the tinnitus group, the mean gap in noise (GIN) value of GPIAS test was significantly decreased indicated the occurrence of an additional perceived sound like tinnitus and also the mean ABR threshold and brainstem transmission time (BTT) were significantly increased. In addition, a significant increase in DCX expression in the dorsal cochlear nucleus (DCN), dentate gyrus (DG) and the parafloccular lobe (PFL) of cerebellum was observed in the tinnitus group. In PBMT group, a significant increase in the GIN value, a significant decrease in the ABR threshold and BTT, and also significant reduction of DCX expression in the DG were observed. Based on our findings, PBMT has the potential to be used in the management of SS-induced tinnitus.

Allosteric Activation of α7 Nicotinic Acetylcholine Receptors by Novel 2-Arylamino-thiazole-5-carboxylic Acid Amide Derivatives for the Improvement of Cognitive Deficits in Mice.

Enhancing α7 nAChR function serves as a therapeutic strategy for cognitive disorders. Here, we report the synthesis and evaluation of 2-arylamino-thiazole-5-carboxylic acid amide derivatives 6-9 that as positive allosteric modulators (PAMs) activate human α7 nAChR current expressed in Xenopus ooctyes. Among the 4-amino derivatives, a representative atypical type I PAM 6p exhibits potent activation of α7 current with an EC50 of 1.3 μM and the maximum activation effect on the current over 48-fold in the presence of acetylcholine (100 μM). The structure-activity relationship (SAR) analysis reveals that the 4-amino group is crucial for the allosteric activation of α7 currents by compound 6p as the substitution of 4-methyl group results in its conversion to compound 7b (EC50 = 2.1 μM; max effect: 58-fold) characterized as a typical type I PAM. Furthermore, both 6p and 7b are able to rescue auditory gating deficits in mouse schizophrenia-like model of acoustic startle prepulse inhibition.

Neurobehavioral Abnormalities in Offspring of Young Adult Male Rats With a History of Traumatic Brain Injury.

Children of parents with traumatic brain injury (TBI) are more likely to develop psychiatric disorders. This association is usually attributed to TBI-induced changes in parents' personality and families' social environment. We tested the hypothesis that offspring of young adult male rats with TBI develop neurodevelopmental abnormalities in the absence of direct social contact with sires. Male Sprague-Dawley rats (F0 generation) in the TBI group underwent moderate TBI via a midline fluid percussion injury that involved craniectomy under sevoflurane (SEVO) anesthesia for 40 min on post-natal Day 60 (P60), while F0 rats in the control group were placed in a new cage, one per cage, for the equivalent time duration. A subset of F0 rats was sacrificed on P66 to assess acute changes in hypothalamic-pituitary-adrenal (HPA) axis and inflammation markers. The remaining F0 males were mated with naive females on P90 to generate offspring (F1 generation). The F0 males and F1 males and females were sequentially evaluated in the elevated plus maze, for pre-pulse inhibition of acoustic startle, in the Morris water maze, and for resting and stress levels of serum corticosterone starting on ∼P105 (F0) and ∼P60 (F1), followed by tissue collection for further analyses. Acutely, the F0 TBI males had messenger RNA (mRNA) transcripts altered to support an increased hypothalamic and hippocampal Na+-K+-Cl- (Slc12a2) Cl- importer / K+-2Cl- (Slc12a5) Cl- exporter ratio and decreased hippocampal glucocorticoid receptors (Nr3c1), as well as increased serum levels of corticosterone, interleukin-1β (IL-1β), and biomarkers of activated hippocampal microglia and astrocytes. Long-term, F0 TBI rats exhibited increased corticosterone concentrations at rest and under stress, anxiety-like behavior, impaired sensory-motor gating, and impaired spatial memory. These abnormalities were underpinned by reduced mRNA levels of hypothalamic and hippocampal mineralocorticoid receptors (Nr3c2), hippocampal Nr3c1, and hypothalamic brain-derived neurotrophic factor (Bdnf), as well as elevated serum levels of IL-1β, and biomarkers of activated hippocampal microglia and astrocytes. F1 male offspring of TBI sires exhibited abnormalities in all behavioral tests, while their F1 female counterparts had abnormal pre-pulse inhibition responses only. F1 male offspring of TBI sires also had reduced mRNA levels of hippocampal Nr3c1 and Nr3c2, as well as hypothalamic and hippocampal Bdnf, whereas increases in inflammatory markers were more profound in F1 females. These findings suggest that offspring of sires with a history of a moderate TBI that involved craniectomy under SEVO anesthesia for 40 min, develop sex-dependent neurobehavioral abnormalities in the absence of direct social interaction between the sire and the offspring.

Testing Prepulse Inhibition of Acoustic Startle in Rodents.

Prepulse inhibition (PPI) is a measure of sensorimotor gating which is widely used in rodents to study information processing and attention dysfunction. PPI is commonly measured in rats and mice using automated equipment. Here, we present details of aPPI testing protocol extensively used in previous studies. The protocol includes a set pulse-alone startle level and prepulse-pulse combinations with varying interval and intensity. Variations of this protocol can be used depending on the experimental aim or equipment and software version.

Alterations of auditory sensory gating in mice with noise-induced tinnitus treated with nicotine and cannabis extract.

Tinnitus is a phantom sound perception affecting both auditory and limbic structures. The mechanisms of tinnitus remain unclear and it is debatable whether tinnitus alters attention to sound and the ability to inhibit repetitive sounds, a phenomenon also known as auditory gating. Here we investigate if noise exposure interferes with auditory gating and whether natural extracts of cannabis or nicotine could improve auditory pre-attentional processing in noise-exposed mice. We used 22 male C57BL/6J mice divided into noise-exposed (exposed to a 9-11 kHz narrow band noise for 1 h) and sham (no sound during noise exposure) groups. Hearing thresholds were measured using auditory brainstem responses, and tinnitus-like behavior was assessed using Gap prepulse inhibition of acoustic startle. After noise exposure, mice were implanted with multi-electrodes in the dorsal hippocampus to assess auditory event-related potentials in response to paired clicks. The results showed that mice with tinnitus-like behavior displayed auditory gating of repetitive clicks, but with larger amplitudes and longer latencies of the N40 component of the aERP waveform. The combination of cannabis extract and nicotine improved the auditory gating ratio in noise-exposed mice without permanent hearing threshold shifts. Lastly, the longer latency of the N40 component appears due to an increased sensitivity to cannabis extract in noise-exposed mice compared to sham mice. The study suggests that the altered central plasticity in tinnitus is more sensitive to the combined actions on the cholinergic and the endocannabinoid systems. Overall, the findings contribute to a better understanding of pharmacological modulation of auditory sensory gating.

Review of the TAAR1 Agonist Ulotaront: Part I—From Discovery to Clinic

AbstractIntroductionTrace amine-associated receptors (TAARs) are a family of G-protein-coupled receptors (GPCRs) first identified in 2001. TAAR1 has emerged as a promising therapeutic target due to its ability to modulate monoaminergic and glutamatergic neurotransmission. Ulotaront is a trace amine-associated receptor 1 (TAAR1) agonist with serotonin 5-HT1A agonist activity that has received FDA Breakthrough Therapy Designation for the treatment of schizophrenia. Here we provide a brief review of the discovery of ulotaront and preclinical research suggesting efficacy in schizophrenia, leading to the first clinical trial of ulotaront resulting in FDA Breakthrough Therapy Designation.MethodsUlotaront was discovered through a target-agnostic approach optimized to identify drug candidates that demonstrate an antipsychotic-like profile in vivo but lack D2 and 5-HT2A receptor antagonism. Ulotaront was further characterized by in vitro pharmacology, electrophysiology, behavioral, and imaging studies.ResultsUlotaront demonstrated an antipsychotic-like profile in a high-throughput, phenotypic behavior screening platform, as well as efficacy in preclinical models of schizophrenia, including phencyclidine (PCP)-induced hyperactivity, prepulse inhibition of acoustic startle, and subchronic PCP-induced deficits in social interaction. Although not fully elucidated, ulotaront’s mechanism of action appears to be mediated by agonism at trace amine-associated 1 (TAAR1) and 5-HT1A receptors. This was further corroborated with whole cell patch clamp recordings, demonstrating inhibition of dorsal raphe nucleus (DRN) and ventral tegmental area (VTA) neuronal firing via 5-HT1A and TAAR1 receptors. Furthermore, ulotaront attenuated the ketamine-induced increase in striatal dopamine synthesis capacity, suggesting that it may modulate presynaptic dopamine dysfunction which is hypothesized to contribute to the pathophysiology of schizophrenia.ConclusionsPreclinical studies have identified ulotaront as a TAAR1 agonist with antipsychotic-like activity. Ulotaront’s unique receptor profile led to its designation as a member of the new “-taront” class of TAAR1 agonists, distinct in pharmacology from the D2/5-HT2A class of antipsychotics. A companion poster will summarize the efficacy and safety of ulotaront based on initial clinical trials in schizophrenia.FundingSunovion Pharmaceuticals, Inc., and Otsuka Pharmaceutical Development & Commercialization, Inc.

Incorporating Auditory Cortex Potentials and Gap Pre-pulse Inhibition of Acoustic Startle: A Probable Way to Objectively Assess Tinnitus

Background and Objectives: Tinnitus is a complex condition that varies in loudness, quality, location, and distress. Different definitions, heterogeneity, and lack of objective measuring have challenged the understanding the mechanisms involved and definitive cure. The integrative model correlates each of these characteristics to separate parallel and overlapping subnetworks that process tinnitus’s perception and emotional reaction. Many of these networks are common with the gap pre-pulse inhibition of acoustic startle (GPIAS) neural circuity. GPIAS, which measures tinnitus in animals, has recently been used for humans with various recording methods. The present study aimed to review the evidence achieved with gap stimuli in patients with tinnitus to support the potential of cortical responses recorded with the GPIAS stimulus and to objectively detect tinnitus in humans. Methods: Studies were identified by searching electronic databases with relevant keywords. Results: The role of the auditory cortex in processing short gaps, the possibility of evaluating the gap detection ability with GPIAS, and the advantage of cortical responses in reflecting both stimulus properties and different aspects of tinnitus emphasize the importance of this issue. The results of most studies have proven the gap detection deficiency in tinnitus. However, the validity of the auditory startle reflex still needs to be verified due to the inherent variability and different methods. Conclusion: Further human studies are recommended because the perception of tinnitus can be controlled. An appealing research line in this area is multi-channel cortical evoked potentials. Defects of GPIAS with cortical recording can indicate tinnitus.

Comparison of two behavioral tests for tinnitus assessment in mice

Animal research focused on chronic tinnitus associated with noise-induced hearing loss can be expensive and time-consuming as a result of the behavioral training required. Although there exist a number of behavioral tests for tinnitus; there have been few formal direct comparisons of these tests. Here, we evaluated animals in two different tinnitus assessment methods. CBA/CaJ mice were trained in an operant conditioning, active avoidance (AA) test, and a reflexive, gap-induced pre-pulse inhibition of acoustic startle (GPIAS) test, or both. Tinnitus was induced in awake mice by unilateral continuous sound exposure using a 2-kHz- or octave-wide noise centered at 16 kHz and presented at 113- or 116-dB SPL. Tinnitus was assessed 8 weeks after sound overexposure. Most mice had evidence of tinnitus behavior in at least one of the two behaviors. Of the mice evaluated in AA, over half (55%) had tinnitus positive behavior. In GPIAS, fewer animals (13%) were positive than were identified using the AA test. Few mice were positive in both tests (10%), and only one was positive for tinnitus behavior at the same spectral frequency in both tests. When the association between tinnitus behavior and spontaneous activity recorded in the inferior colliculus was compared, animals with tinnitus behavior in AA exhibited increased spontaneous activity, while those positive in GPIAS did not. Thus, it appears that operant conditioning tests, like AA, maybe more reliable and accurate tests for tinnitus than reflexive tests.

Decreasing dorsal cochlear nucleus activity ameliorates noise-induced tinnitus perception in mice

BackgroundThe dorsal cochlear nucleus (DCN) is a region known to integrate somatosensory and auditory inputs and is identified as a potential key structure in the generation of phantom sound perception, especially noise-induced tinnitus. Yet, how altered homeostatic plasticity of the DCN induces and maintains the sensation of tinnitus is not clear. Here, we chemogenetically decrease activity of a subgroup of DCN neurons, Ca2+/Calmodulin kinase 2 α (CaMKII α)-positive DCN neurons, using Gi-coupled human M4 Designer Receptors Exclusively Activated by Designer Drugs (hM4Di DREADDs), to investigate their role in noise-induced tinnitus.ResultsMice were exposed to loud noise (9–11kHz, 90dBSPL, 1h, followed by 2h of silence), and auditory brainstem responses (ABRs) and gap prepulse inhibition of acoustic startle (GPIAS) were recorded 2 days before and 2 weeks after noise exposure to identify animals with a significantly decreased inhibition of startle, indicating tinnitus but without permanent hearing loss. Neuronal activity of CaMKII α+ neurons expressing hM4Di in the DCN was lowered by administration of clozapine-N-oxide (CNO). We found that acutely decreasing firing rate of CaMKII α+ DCN units decrease tinnitus-like responses (p = 3e −3, n = 11 mice), compared to the control group that showed no improvement in GPIAS (control virus; CaMKII α-YFP + CNO, p = 0.696, n = 7 mice). Extracellular recordings confirmed CNO to decrease unit firing frequency of CaMKII α-hM4Di+ mice and alter best frequency and tuning width of response to sound. However, these effects were not seen if CNO had been previously administered during the noise exposure (n = 6 experimental and 6 control mice).ConclusionWe found that lowering DCN activity in mice displaying tinnitus-related behavior reduces tinnitus, but lowering DCN activity during noise exposure does not prevent noise-induced tinnitus. Our results suggest that CaMKII α-positive cells in the DCN are not crucial for tinnitus induction but play a significant role in maintaining tinnitus perception in mice.

Effect of Intrahippocampal Administration of α7 Subtype Nicotinic Receptor Agonist PNU-282987 and Its Solvent Dimethyl Sulfoxide on the Efficiency of Hypoxic Preconditioning in Rats

We have previously suggested a key role of the hippocampus in the preconditioning action of moderate hypobaric hypoxia (HBH). The preconditioning efficiency of HBH is associated with acoustic startle prepulse inhibition (PPI). In rats with PPI > 40%, HBH activates the cholinergic projections of hippocampus, and PNU-282987, a selective agonist of α7 nicotinic receptors (α7nAChRs), reduces the HBH efficiency and potentiating effect on HBH of its solvent dimethyl sulfoxide (DMSO, anticholinesterase agent) when administered intraperitoneally. In order to validate the hippocampus as a key structure in the mechanism of hypoxic preconditioning and research a significance of α7nAChR activation in the hypoxic preconditioning, we performed an in vivo pharmacological study of intrahippocampal injections of PNU-282987 into the CA1 area on HBH efficiency in rats with PPI ≥ 40%. We found that PNU-282987 (30 μM) reduced HBH efficiency as with intraperitoneal administration, while DMSO (0.05%) still potentiated this effect. Thus, direct evidence of the key role of the hippocampus in the preconditioning effect of HBH and some details of this mechanism were obtained in rats with PPI ≥ 40%. The activation of α7nAChRs is not involved in the cholinergic signaling initiated by HBH or DMSO via any route of administration. Possible ways of the potentiating action of DMSO on HBH efficiency and its dependence on α7nAChRs are discussed.

Interference of commissural connections through the genu of the corpus callosum specifically impairs sensorimotor gating

White matter abnormalities in schizophrenic patients are characterized as regional tract-specific. Myelin loss at the genu of the corpus callosum (GCC) is one of the most consistent findings in schizophrenic patients across the different populations. We characterized the axons that pass through the GCC by stereotactically injecting an anterograde axonal tracing viral vector into the forceps minor of the corpus callosum in one hemisphere, and identified the homotopic brain structures that have commissural connections in the two hemispheres of the prefrontal cortex, including the anterior cingulate area, the prelimbic area, the secondary motor area, and the dorsal part of the agranular insular area, along with commissural connections with the primary motor area, caudoputamen, and claustrum. To investigate whether dysmyelination in these commissural connections is critical for the development of schizophrenia symptoms, we generated a mouse model with focal demyelination at the GCC by stereotactically injecting demyelinating agent lysolecithin into this site, and tested these mice in a battery of behavioral tasks that are used to model the schizophrenia-like symptom domains. We found that demyelination at the GCC influenced neither the social interest or mood state, nor the locomotive activity or motor coordination. Nevertheless, it specifically reduced the prepulse inhibition of acoustic startle that is a well-known measure of sensorimotor gating. This study advances our understanding of the pathophysiological contributions of the GCC-specific white matter lesion to the related disease, and demonstrates an indispensable role of interhemispheric communication between the frontal cortices for the top-down regulation of the sensorimotor gating.

Involvement of the thalamic reticular nucleus in prepulse inhibition of acoustic startle

Thalamic reticular nucleus (TRN) is a group of inhibitory neurons surrounding the thalamus. Due to its important role in sensory information processing, TRN is considered as the target nucleus for the pathophysiological investigation of schizophrenia and autism spectrum disorder (ASD). Prepulse inhibition (PPI) of acoustic startle response, a phenomenon that strong stimulus-induced startle reflex is reduced by a weaker prestimulus, is always found impaired in schizophrenia and ASD. But the role of TRN in PPI modulation remains unknown. Here, we report that parvalbumin-expressing (PV+) neurons in TRN are activated by sound stimulation of PPI paradigm. Chemogenetic inhibition of PV+ neurons in TRN impairs PPI performance. Further investigations on the mechanism suggest a model of burst-rebound burst firing in TRN-auditory thalamus (medial geniculate nucleus, MG) circuitry. The burst firing is mediated by T-type calcium channel in TRN, and rebound burst firing needs the participation of GABAB receptor in MG. Overall, these findings support the involvement of TRN in PPI modulation.

Spontaneous firing patterns in the medial geniculate nucleus in a guinea pig model of tinnitus

The mechanism of tinnitus, the perception of sound in the absence of acoustic stimulation, remains as yet unknown. It has been proposed that tinnitus is caused by altered spontaneous activity in the auditory pathway following cochlear damage in combination with inadequate gating at the level of the auditory thalamus, the medial geniculate nucleus (MGN). To investigate this further we made electrophysiological recordings in MGN of guinea pigs (n = 9) with and without tinnitus after acoustic trauma (continuous loud tone at 10 kHz, 124 dB SPL for 2 h). Parameters of interest were spontaneous tonic and burst firing. After acoustic trauma, 5 out of 9 guinea pigs developed signs of tinnitus as determined by the gap prepulse inhibition of acoustic startle. Spontaneous firing rates were significantly increased in the tinnitus animals as compared to the non-tinnitus animals and this change was specific to pure-tone responsive MGN neurons. However, burst firing parameters, including number of bursts per minute, burst duration, number of spikes in each burst, and percentage of spikes occurring in a burst, were not different between tinnitus and non-tinnitus animals. In addition, our data showed a strong dependence of spontaneous firing rates with heart rate, which implies that monitoring physiological status in animals is pertinent to obtaining reliable data when recording at higher levels of the auditory pathway. Our results suggest that increases in the tonic spontaneous fining rate of pure-tone responsive MGN neurons but not changes in burst firing parameters, are a robust neural signature of tinnitus in anaesthetised animals.

Opposite Pathways of Cholinergic Mechanisms of Hypoxic Preconditioning in the Hippocampus: Participation of Nicotinic α7 Receptors and Their Association with the Baseline Level of Startle Prepulse Inhibition.

(1) Background. A one-time moderate hypobaric hypoxia (HBH) has a preconditioning effect whose neuronal mechanisms are not studied well. Previously, we found a stable correlation between the HBH efficiency and acoustic startle prepulse inhibition (PPI). This makes it possible to predict the individual efficiency of HBH in animals and to study its potential adaptive mechanisms. We revealed a bi-directional action of nicotinic α7 receptor agonist PNU-282987 and its solvent dimethyl sulfoxide on HBH efficiency with the level of PPI > or < 40%. (2) The aim of the present study was to estimate cholinergic mechanisms of HBH effects in different brain regions. (3) Methods: in rats pretested for PPI, we evaluated the activity of synaptic membrane-bound and water-soluble choline acetyltransferase (ChAT) in the sub-fractions of ‘light’ and ‘heavy’ synaptosomes of the neocortex, hippocampus and caudal brainstem in the intact brain and after HBH. We tested the dose-dependent influence of PNU-282987 on the HBH efficiency. (4) Results: PPI level and ChAT activity correlated negatively in all brain structures of the intact animals, so that the values of the latter were higher in rats with PPI < 40% compared to those with PPI > 40%. After HBH, this ChAT activity difference was leveled in the neocortex and caudal brainstem, while for membrane-bound ChAT in the ‘light’ synaptosomal fraction of hippocampus, it was reversed to the opposite. In addition, a pharmacological study revealed that PNU-282987 in all used doses and its solvent displayed corresponding opposite effects on HBH efficiency in rats with different levels of PPI. (5) Conclusion: We substantiate that in rats with low and high PPI two opposite hippocampal cholinergic mechanisms are involved in hypoxic preconditioning, and both are implemented by forebrain projections via nicotinic α7 receptors. Possible causes of association between general protective adaptation, HBH, PPI, forebrain cholinergic system and hippocampus are discussed.

Intergenerational Effects of Sevoflurane in Young Adult Rats

Sevoflurane administered to neonatal rats induces neurobehavioral abnormalities and epigenetic reprogramming of their germ cells; the latter can pass adverse effects of sevoflurane to future offspring. As germ cells are susceptible to reprogramming by environmental factors across the lifespan, the authors hypothesized that sevoflurane administered to adult rats could induce neurobehavioral abnormalities in future offspring, but not in the exposed rats themselves. Sprague-Dawley rats were anesthetized with 2.1% sevoflurane for 3 h every other day between postnatal days 56 and 60. Twenty-five days later, exposed rats and nonexposed controls were mated to produce offspring. Adult male but not female offspring of exposed parents of either sex exhibited deficiencies in elevated plus maze (mean ± SD, offspring of both exposed parents vs. offspring of control parents, 35 ± 12 vs. 15 ± 15 s, P < 0.001) and prepulse inhibition of acoustic startle (offspring of both exposed parents vs. offspring of control parents, 46.504 ± 13.448 vs. 25.838 ± 22.866%, P = 0.009), and increased methylation and reduced expression of the potassium ion-chloride ion cotransporter KCC2 gene (Kcc2) in the hypothalamus. Kcc2 was also hypermethylated in sperm and ovary of the exposed rats. Surprisingly, exposed male rats also exhibited long-term abnormalities in functioning of the hypothalamic-pituitary-gonadal and -adrenal axes, reduced expression of hypothalamic and hippocampal Kcc2, and deficiencies in elevated plus maze (sevoflurane vs. control, 40 ± 24 vs. 25 ± 12 s, P = 0.038) and prepulse inhibition of startle (sevoflurane vs. control, 39.905 ± 21.507 vs. 29.193 ± 24.263%, P < 0.050). Adult sevoflurane exposure affects brain development in male offspring by epigenetically reprogramming both parental germ cells, while it induces neuroendocrine and behavioral abnormalities only in exposed males. Sex steroids may be required for mediation of the adverse effects of adult sevoflurane in exposed males.

Memantine Attenuates Salicylate-induced Tinnitus Possibly by Reducing NR2B Expression in Auditory Cortex of Rat.

Memantine, a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, suppresses the release of excessive levels of glutamate that may induce neuronal excitation. Here we investigated the effects of memantine on salicylate-induced tinnitus model. The expressions of the activity-regulated cytoskeleton-associated protein (ARC) and tumor necrosis factor-alpha (TNF α) genes; as well as the NMDA receptor subunit 2B (NR2B) gene and protein, were examined in the SH-SY5Y cells and the animal model. We also used gap-prepulse inhibition of the acoustic startle reflex (GPIAS) and noise burst prepulse inhibition of acoustic startle, and the auditory brainstem level (electrophysiological recordings of auditory brainstem responses, ABR) and NR2B expression level in the auditory cortex to evaluate whether memantine could reduce salicylate-mediated behavioral disturbances. NR2B was significantly upregulated in salicylate-treated cells, but downregulated after memantine treatment. Similarly, expression of the inflammatory cytokine genes TNFα and immediate-early gene ARC was significantly increased in the salicylate-treated cells, and decreased when the cells were treated with memantine. These results were confirmed by NR2B immunocytochemistry. GPIAS was attenuated to a significantly lesser extent in rats treated with a combination of salicylate and memantine than in those treated with salicylate only. The mean ABR threshold in both groups was not significant different before and 1 day after the end of treatment. Additionally, NR2B protein expression in the auditory cortex was markedly increased in the salicylate-treated group, whereas it was reduced in the memantine-treated group. These results indicate that memantine is useful for the treatment of salicylate-induced tinnitus.

Effect of electrical stimulation at auricular points combined with sound masking on the expression of CREB, BDNF and TrkB in the auditory cortex of tinnitus rats

To explore the effect of electrical stimulation at auricular points (EAS) combined with sound masking on the expression of cAMP-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) in the auditory cortex of tinnitus rats. A total of 27 adult male SD rats were randomly divided into a control group, a model group and an EAS group. The rats in the model group and the EAS group were intervened with intraperitoneal injection of sodium salicylate to induce tinnitus model, while the rats in the control group were intervened with injection of 0.9% NaCl solution. After the model was successfully established, the rats in the EAS group were treated with electrical stimulation at "Shenmen" (TF4) and "Yidan" (CO11), combined with sound masking; the treatment was given once a day for 15 days. The gap prepulse inhibition of acoustic startle (GPIAS) and prepulse inhibition (PPI) testing were performed using the acoustic startle reflex starter package for rats. The expression of BDNF, TrkB, CREB and p-CREB in the auditory cortex of each group were measured with Western Blot analysis. ① Compared with the control group, the GPIAS values in 12 kHz, 16 kHz, 20 kHz and 28 kHz were significantly decreased in the model group (all P<0.05); compared with the model group, GPIAS values in 12 kHz, 16 kHz, 20 kHz and 28 kHz were significantly increased in the EAS group (all P<0.05). ② Compared with the control group, the expression of BDNF and p-CREB in the model group was significantly increased (P<0.01), and the expression of TrkB in the model group was significantly increased (P<0.05); the differences of expression of BDNF, TrkB, CREB and p-CREB between the model group and the EAS group had no statistics significance (all P>0.05). EAS could improve the GPIAS values of high-frequency background sound in tinnitus rats, which may be related with the upregulation of the BDNF/TrkB/CREB signaling pathway in the auditory cortex, leading to the reversion of the maladaptive plasticity.

Proposal of conditional random inter-stimulus interval method for unconstrained enclosure based GPIAS measurement systems.

Gap prepulse inhibition of acoustic startle (GPIAS) method has been used effectively for the objective assessment of tinnitus in animals. Among two types of enclosures for the GPIAS, the unconstrained type carries less risk of animal death due to the absence of binding stress in the enclosure, and lack of need for alteration to animal size variation as it grows. However, animals' voluntary movements, which have no relation to the startles evoked by acoustic stimuli, are problematic, as they cannot be excluded in the case of the unconstrained enclosure based GPIAS measurement system. In order to discount voluntary movements which are not associated with external acoustic stimuli, we propose the conditional random inter-stimulus interval (CR ISI) method for unconstrained enclosure based GPIAS measurement. With the proposed ISI method, the unconstrained enclosure based acoustic startle response measurement system has been implemented in this paper. As a result, the effectiveness of the proposed CR ISI method has been verified and compared with those of conventional ISI methods through animal experiments using SD-rats. The experimental results showed that abnormal startle responses and invalid GPIAS values caused by motion were prevented when our proposed CR ISI method was applied to our implemented system. It was also verified that our proposed CR ISI method is advantageous in reducing the total experimental time for acquiring normal startle responses and valid GPIAS values, compared to conventional ISI methods, since our proposed CR ISI can begin the acoustic stimulation only when the animal gets stable and motionless.