Auditory phenotyping of heterozygous sound-responsive (+/dn) and deafness (dn/dn) mice

Stimulus Generalization in Mice during Pavlovian Eyeblink Conditioning

Here, we investigate stimulus generalization in a cerebellar learning paradigm, called eyeblink conditioning. Mice were conditioned to close their eyes in response to a 10-kHz tone by repeatedly pairing this tone with an air puff to the eye 250 ms after tone onset. After 10 consecutive days of training, when mice showed reliable conditioned eyelid responses to the 10-kHz tone, we started to expose them to tones with other frequencies, ranging from 2 to 20 kHz. We found that mice had a strong generalization gradient, whereby the probability and amplitude of conditioned eyelid responses gradually decreases depending on the dissimilarity with the 10-kHz tone. Tones with frequencies closest to 10 kHz evoked the most and largest conditioned eyelid responses and each step away from the 10-kHz tone resulted in fewer and smaller conditioned responses (CRs). In addition, we found that tones with lower frequencies resulted in CRs that peaked earlier after tone onset compared with those to tones with higher frequencies. Together, our data show prominent generalization patterns in cerebellar learning. Since the known function of cerebellum is rapidly expanding from pure motor control to domains that include cognition, reward-learning, fear-learning, social function, and even addiction, our data imply generalization controlled by cerebellum in all these domains.

Exploratory analyses of postanesthetic effects of desflurane using behavioral test battery of mice

Halogenated ethers, such as desflurane, sevoflurane, and isoflurane, are known to exert an array of effects besides sedation. However, the postanesthetic effects of desflurane remain undiscovered as no study has explored these effects systematically. Phenotypic screening using behavioral test batteries is a powerful method to identify such effects. In the present study, we behaviorally phenotyped desflurane-treated mice to investigate postanesthetic effects. We applied comprehensive behavioral test batteries measuring sensorimotor functions, anxiety, depression, sociability, attention, and learning abilities, starting 7 days after anesthesia performed with 8.0% desflurane for 6 h. Although our previous study revealed postanesthetic effects of isoflurane in adult mice, in the current study, desflurane-treated mice exhibited no such effects in any behavioral test. To further examine whether desflurane affect behavior in more early time point, we built up a new additional test battery, which carried out 1 day or 3 days after exposure to desflurane. Mice treated with desflurane 1 day before testing showed more slips than other two groups in the first trial, suggesting mild acute side effects of desflurane on motor coordination. These results suggest the safety of desflurane in clinical settings and imply that postanesthetic effects are unique to each halogenated ether.

Postanesthetic effects of isoflurane on behavioral phenotypes of adult male C57BL/6J mice

Isoflurane was previously the major clinical anesthetic agent but is now mainly used for veterinary anesthesia. Studies have reported widespread sites of action of isoflurane, suggesting a wide array of side effects besides sedation. In the present study, we phenotyped isoflurane-treated mice to investigate the postanesthetic behavioral effects of isoflurane. We applied comprehensive behavioral test batteries comprising sensory test battery, motor test battery, anxiety test battery, depression test battery, sociability test battery, attention test battery, and learning test battery, which were started 7 days after anesthesia with 1.8% isoflurane. In addition to the control group, we included a yoked control group that was exposed to the same stress of handling as the isoflurane-treated animals before being anesthetized. Our comprehensive behavioral test batteries revealed impaired latent inhibition in the isoflurane-treated group, but the concentration of residual isoflurane in the brain was presumably negligible. The yoked control group and isoflurane-treated group exhibited higher anxiety in the elevated plus-maze test and impaired learning function in the cued fear conditioning test. No influences were observed in sensory functions, motor functions, antidepressant behaviors, and social behaviors. A number of papers have reported an effect of isoflurane on animal behaviors, but no systematic investigation has been performed. To the best of our knowledge, this study is the first to systematically investigate the general health, neurological reflexes, sensory functions, motor functions, and higher behavioral functions of mice exposed to isoflurane as adults. Our results suggest that the postanesthetic effect of isoflurane causes attention deficit in mice. Therefore, isoflurane must be used with great care in the clinical setting and veterinary anesthesia.

Criteria for validating mouse models of psychiatric diseases

Animal models of human diseases are in widespread use for biomedical research. Mouse models with a mutation in a single gene or multiple genes are excellent research tools for understanding the role of a specific gene in the etiology of a human genetic disease. Ideally, the mouse phenotypes will recapitulate the human phenotypes exactly. However, exact matches are rare, particularly in mouse models of neuropsychiatric disorders. This article summarizes the current strategies for optimizing the validity of a mouse model of a human brain dysfunction. We address the common question raised by molecular geneticists and clinical researchers in psychiatry, "what is a 'good enough' mouse model"?

Assessment of cochlear function in mice: distortion-product otoacoustic emissions

Distortion-product otoacoustic emissions (DPOAEs) can be measured in the ear canal following the presentation of two tones. These emissions are generated by the outer hair cells (OHCs) of the inner ear and they are reduced or absent when the OHCs are damaged by, for example, exposure to excessive noise or ototoxic drugs. Consequently, DPOAEs provide a powerful and noninvasive means to assess the robustness of OHC function. A detailed method is described for measuring DPOAEs to assess cochlear function in mice. Recommendations are given for the required equipment and instructions are presented for setting up a DPOAE system. Also, a protocol is outlined for measuring DPOAEs in mice and troubleshooting tips are provided. Examples of data analysis procedures following noise exposure in mice are included, as well. These methods are not only applicable to mice, but can be performed using essentially all small laboratory animals.

Spontaneous otitis media in Wistar rats: an overlooked pathology in otological research

The rat is commonly employed in otological research, but spontaneous ear infections can confound the results of experimental procedures--wasting time, money, and animals. The authors focus on the incidence of spontaneous otitis media in Wistar rats. They compare disease incidence in animals housed in standard cages with those housed in barrier units, showing that 20% of their conventionally housed animals developed spontaneous otitis media, whereas only 5% of their animals housed in isolated units were infected. These results underscore the importance of strict control of the shipping, housing conditions, and manipulation of animals to be used in otological research.

GATA3 haploinsufficiency causes a rapid deterioration of distortion product otoacoustic emissions (DPOAEs) in mice

Human HDR (hypoparathyroidism, deafness and renal dysplasia)-syndrome is caused by haploinsufficiency of zinc-finger transcription factor GATA3. The hearing loss due to GATA3 haploinsufficiency has been shown to be peripheral in origin, but it is unclear to what extent potential aberrations in the outer hair cells (OHCs) contribute to this disorder. To further elucidate the pathophysiological mechanism underlying the hearing defect in HDR-syndrome, we investigated the OHCs in heterozygous Gata3-knockout mice at both the functional and morphological level. While the signal-to-noise ratios of distortion product otoacoustic emissions (DPOAE) in wild type mice did not change significantly during the first half-year of live, those in the heterozygous Gata3 mice decreased dramatically. In addition, both light microscopic and transmission electron microscopic analyses showed that the number of OHCs containing vacuoles was increased in the mutants. Together, these findings indicate that outer hair cell malfunctioning plays a major role in the hearing loss in HDR-syndrome.

Impact of conventional anesthesia on auditory brainstem responses in mice

Anesthesia is known to affect the auditory brainstem response (ABR) in animals often used in hearing research. This study describes the differences in ABRs between awake and anesthetized FVB/N mice. Intracranial electrodes connected to a head fixation pedestal were used for click-evoked ABR recordings. This pedestal served to immobilize mice, either awake or under anesthesia, in a 'free' sound field. The presence of myogenic noise in the awake condition obviously increases recording time. However it is demonstrated that recording times can be significantly reduced by increasing the stimulus repetition rate from 23 up to 80 impulses per second. This causes only a small but significant increase in absolute peak latencies in the awake condition, but has no significant effect on the overall ABR-waveform, nor on the ABR-threshold, nor on the ABR interpeak latencies, nor on the absolute peak latencies in the anesthetized condition. Anesthesia with ketamine/xylazine caused a significant prolongation of ABR-peak latencies and interpeak latencies as well as a significant upward shift (8.0+/-1.8 dB) of ABR-thresholds as compared to the awake condition. Under anesthesia the measurement accuracy of peak latencies, interpeak latencies and thresholds decreases. In conclusion, the awake condition is preferable for more accurate measurements of ABR characteristics, in spite of the myogenic noise concomitant with this condition.

Using ontologies to describe mouse phenotypes

By combining ontologies from different sources the authors developed a novel approach to describing phenotypes of mutant mice in a standard, structured manner.

The mouse is an important model of human genetic disease. Describing phenotypes of mutant mice in a standard, structured manner that will facilitate data mining is a major challenge for bioinformatics. Here we describe a novel, compositional approach to this problem which combines core ontologies from a variety of sources. This produces a framework with greater flexibility, power and economy than previous approaches. We discuss some of the issues this approach raises.

Hearing loss following Gata3 haploinsufficiency is caused by cochlear disorder

Patients with HDR syndrome suffer from hypoparathyroidism, deafness, and renal dysplasia due to a heterozygous deletion of the transcription factor GATA3. Since GATA3 is prominently expressed in both the inner ear and different parts of the auditory nervous system, it is not clear whether the deafness in HDR patients is caused by peripheral and/or central deficits. Therefore, we have created and examined heterozygous Gata3 knockout mice. Auditory brainstem response (ABR) thresholds of alert heterozygous Gata3 mice, analyzed from 1 to 19 months of age, showed a hearing loss of 30 dB compared to wild-type littermates. Neither physiological nor morphological abnormalities were found in the brainstem, cerebral cortex, the outer or the middle ear. In contrast, cochleae of heterozygous Gata3 mice showed significant progressive morphological degeneration starting with the outer hair cells (OHCs) at the apex and ultimately affecting all hair cells and supporting cells in the entire cochlea. Together, these findings indicate that hearing loss following Gata3 haploinsufficiency is peripheral in origin and that this defect is detectable from early postnatal development and maintains through adulthood.

Therapy of idiopathic sudden sensorineural hearing loss: antiviral treatment of experimental herpes simplex virus infection of the inner ear

Experimental herpes simplex virus type 1 (HSV-1) labyrinthitis provides a model of idiopathic sudden sensorineural hearing loss (ISSHL). Corticosteroids improve the prognosis for hearing recovery in ISSHL, but the effects of acyclovir are unknown. To establish the therapeutic efficacy of acyclovir (Zovirax) and prednisolone in experimental HSV-1 viral labyrinthitis, we induced HSV-1 labyrinthitis in 12 guinea pigs. Three animals received no treatment, 3 received prednisolone, 3 received acyclovir, and 3 received both. Four other animals served as controls, receiving culture medium only. Hearing, HSV-1 antibody titers, and cochlear damage were evaluated. The HSV-1 labyrinthitis caused hearing loss within 24 hours. Combination treatment consisting of prednisolone and acyclovir resulted in earlier hearing recovery and less extensive cochlear destruction compared to prednisolone or acyclovir as a monotherapy. The beneficial effect of this treatment modality remains to be demonstrated in ISSHL.

The mouse deafness locus (dn) is associated with an inversion on chromosome 19

Recombination data for the mouse deafness locus (dn) on chromosome 19 are consistent with the presence of an inversion for which one of the breakpoints is between D19Mit14 and D19Mit96, a distance of less than 226 kb. Fluorescence in situ hybridization studies using a bacterial artificial chromosome on interphase (G1) nuclei provide additional support for the presence of an inversion. The dn gene is probably the orthologue of the human DFNB7/DFNB11 gene on chromosome 9.

Low intensities and 1.3 ratio produce distortion product otoacoustic emissions which are larger in heterozygous (+/dn) than homozygous (+/+) mice

The f2/f1 frequency ratio of 1.3 in combination with stimulus levels of L1/L2 = 50/60 and 50/50 dB SPL produced a higher level of distortion product otoacoustic emissions (DPOAE) in the heterozygous (+/dn) mice than in the homozygous (+/+) mice. These results suggest that the dn gene carriers have a unique cochlear trait which may be related to the dn gene locus and expressed via a frequency- and intensity-dependent DPOAE function.

N-methyl-D-aspartate antagonists limit aminoglycoside antibiotic-induced hearing loss

The use of aminoglycoside antibiotics is limited by ototoxicity that can produce permanent hearing loss. We report that concurrent administration of N-methyl-D-aspartate (NMDA) antagonists markedly attenuates both the hearing loss and destruction of cochlear hair cells in guinea pigs treated with aminoglycoside antibiotics. These findings indicate that aminoglycoside-induced hearing loss is mediated, in part, through an excitotoxic process. The high correlation (Spearman correlation coefficient: 0.928; P < 0.01) obtained between the relative cochleotoxicities of a series of aminoglycosides in humans and the potencies of these compounds to produce a polyamine-like enhancement of [3H]dizocilpine binding to NMDA receptors is consistent with this hypothesis, and provides a simple in vitro assay that can predict this aspect of aminoglycoside-induced ototoxicity.

Phenotypic patterns of distortion product otoacoustic emission in inbred and F1 hybrid hearing mouse strains

Distortion product otoacoustic emissions (DPOE) were obtained from five different hearing mouse groups: CBA/J, MOLF/Rk, ct (homozygous normal mice of the curly-tail stock), and the F1 hybrid offspring of the matings CBA/J x dn/dn and MOLF/Rk x dn/dn (dn/dn mice are the curly-tail stock with recessive deafness). The DPOE patterns of the CBA/J and ct strains were similar to each other and different from that of the MOLF/Rk. The two sets of F1 hybrid mice, (CBA/J x dn/dn)F1 and (MOLF/Rk x dn/dn)F1, were found to have significantly larger DPOE amplitudes than their hearing parent strains, MOLF/Rk and CBA/J, respectively. In addition, the DPOE amplitudes were greater for the offspring of the MOLF/Rk x dn/dn cross than for those of the CBA/J x dn/dn cross, even though they were lower for MOLF/Rk than for CBA/J. The distinct features of DPOE patterns among these five groups suggest that DPOE testing can be used for auditory phenotyping.