Cytomegalovirus in the perilymphatic fluid

OBJECTIVE: The incidence of congenital cytomegalovirus (CMV) infection is approximately 1% of neonates. Ninety percent of congenitally infected infants are "asymptomatic;" they have no signs or symptoms at birth. The prevalence of congenital CMV in the profoundly deaf population and the pathogenesis of deafness from CMV are unknown. The objective of this study is to determine whether CMV can be demonstrated and quantified in perilymphatic fluid of patients with congenital CMV infection and sensorineural hearing loss (SNHL) using a quantitative real-time polymerase chain reaction (QRTPCR). STUDY DESIGN: Prospective case series. METHODS: Perilymphatic fluid was collected at the time of cochlear implantation from children with known or radiologic evidence of congenital CMV infection and analyzed for the presence of CMV using QRTPCR. Blood was collected and analyzed for CMV using QRTPCR, serology, and culture. CMV was quantified in perilymphatic fluid and compared with that present in the patient's blood. RESULTS: Perilymphatic fluid and blood was collected from six children. QRTPCR was positive for CMV in the perilymphatic fluid of four patients. Blood analyzed with QRTPCR, and culture was negative in all patients. CONCLUSIONS: CMV can be demonstrated and quantified in perilymphatic fluid using QRTPCR. Refinements in our technique and sampling of perilymphatic fluid from a large population of children with congenital SNHL and unknown etiology can determine the prevalence of CMV-mediated profound HL.     

Changes of glucose uptake in vestibular and auditory nuclei induced by high perilymphatic potassium ion concentration--autoradiographic study

Characteristic nystagmus could be provoked by introducing potassium ion into the unilateral perilymphatic space of healthy guinea pigs. At first, irritative nystagmus appeared for some time to the K+ introduced ear side, and then, it was followed by paralytic nystagmus which directed to the non introduced ear side. During this experiment, the excitabilities of the vestibular nuclei and the central auditory nuclei were investigated by [14C] deoxyglucose method. In the period of "irritative nystagmus", the increment of glucose uptake in the ipsilateral vestibular nucleus, especially in the superior, median and inferior part, was noticed more significantly than the contralateral vestibular nucleus. On the other hand, the period of "paralytic nystagmus" showed the significant increment of glucose uptake in all parts of the contralateral vestibular nucleus. As to the excitability of the central auditory nuclei, the significant decrement of glucose uptake, which was noticed in all periods of this experiment, was predominant in the ipsilateral cochlear nucleus and other superior auditory nuclei of the contralateral side.     

Recurrence of perilymphatic fistula

Recurrence of the perilymphatic fistula is not rare and may be a tough problem for surgical treatment. This is because a graft is usually applied on the ruptured window(s) from the middle ear and therefore the perilymphatic pressure directly acts on the graft. The recurrence may be caused by a technical failure, use of an unsuitable graft material, poor postoperative bedrest, trauma, increased inner ear pressure, etc. In our clinic, the recurrence occurred in 7 of 48 cases surgically treated. Vertigo accompanied with spontaneous or positional nystagmus was seen in all 7 recurrent cases, while only 2 of them complained of worsening of the existing hearing loss. Re-operation was carried out in two patients. In the first case, closure of the round window by the previous operation was found incomplete, and the perilymph leaked through the gap around the graft. In the second case, closure of the round window was complete, but perilymph leaked from the oval window. In order to prevent the recurrence, the operation should be carefully performed by using strong and adhesive tissue as a graft material, applying a glue between the graft and the inner ear window(s), and keeping strict postoperative bedrest.     

Neuroplasticity in the auditory system

An increasing interest on neuroplasticity and nerve regeneration within the auditory receptor and pathway has developed in recent years. The receptor and the auditory pathway are controlled by highly complex circuits that appear during embryonic development. During this early maturation process of the auditory sensory elements, we observe the development of two types of nerve fibers: permanent fibers that will remain to reach full-term maturity and other transient fibers that will ultimately disappear. Both stable and transitory fibers however, as well as developing sensory cells, express, and probably release, their respective neuro-transmitters that could be involved in neuroplasticity. Cell culture experiments have added significant information; the in vitro administration of glutamate or GABA to isolated spiral ganglion neurons clearly modified neural development. Neuroplasticity has been also found in the adult. Nerve regeneration and neuroplasticity have been demonstrated in the adult auditory receptors as well as throughout the auditory pathway. Neuroplasticity studies could prove interesting in the elaboration of current or future therapy strategies (e.g.: cochlear implants or stem cells), but also to really understand the pathogenesis of auditory or language diseases (e.g.: deafness, tinnitus, dyslexia, etc.).     

Experimental study on the perilymphatic pressure

The hydrostatic pressure was successfully and accurately measured through the round window membrane of the cat over a wide pressure range and long duration using glass micropipets of 1-5 micrometer tip inner diameter and an active nulling pressure measuring system. The dynamic changes in perilymphatic pressure occurring after inhalation of different gas mixtures (5 percent CO2 and 95 percent O2/carbogen, 5 percent and 10 percent CO2 in room air) were recorded. The maximal oxygenation of the perilymph combined with minimal increase in pressure was achieved following inhalation of carbogen. The correlation between variations of pressure of the perilymph and of the systemic blood circulation shows that a regulatory system is present in the inner ear vessels. The pressure measuring system used has proven to have all the requirements that are needed for its use in humans.     

Periodicity coding in the auditory system

Periodic envelope fluctuations are a common feature of acoustic communication signals, and as a result of physical constraints, many natural, nonliving sound sources also produce periodic waveforms. In human speech and music, for example, periodic sounds are abundant and reach a high degree of complexity. Under noisy conditions these amplitude fluctuations may be reliable indicators of a common sound source responsible for the activation of different frequency channels of the basilar membrane. To make use of this information, a central periodicity analysis is necessary in addition to the peripheral frequency analysis.

The present review summarizes our present knowledge about representation and processing of periodic signals, from the cochlea to the cortex in mammals, and in homologous or analogous anatomical structures as far as these exist and have been investigated in other animals. The first sections describe important physical and perceptual attributes of periodic signals, and the last sections address some theoretical issues.     

Protecting the auditory system with glucocorticoids

Glucocorticoids are hormones released following stress-related events and function to maintain homeostasis. Glucocorticoid receptors localize, among others, to hair cells, spiral ligament and spiral ganglion neurons. Glucocorticoid receptor-induced protection against acoustic trauma is found by i) pretreatment with glucocorticoid agonists; ii) acute restraint stress; and iii) sound conditioning. In?contrast, glucocorticoid receptor antagonists exacerbate hearing loss. These findings have important clinical significance since synthetic glucocorticoids are commonly used to treat hearing loss. However, this treatment has limited success since hearing improvement is often not maintained once the treatment has ended, a fact that reduces the overall appeal for this treatment. It must be realized that despite the widespread use of glucocorticoids to treat hearing disorders, the molecular mechanisms underlying this treatment are not well characterized. This review will give insight into some physiological and biochemical mechanisms underlying glucocorticoid treatment for preventing hearing loss.     

Neurotransmission in the auditory system.

Neurotransmitters and neuromodulators thought to be active on neurons in the cochlea, CN, and SOC have been reviewed. The variety of neurotransmitters and neuromodulators present and likely colocalized in these neurons are the chemical substrates that link morphologically and physiologically diverse neurons to process sound information. The impact of the limited number of neurotransmitters and neuromodulators in the auditory system is magnified by their interaction with structurally diverse receptors; thus great functional diversity is possible. Moreover, the effects of neurotransmitters and neuromodulators are not limited to synaptic transmission but serve as trophic agents for the establishment of neuronal circuitry during development and the rearrangement of synapses as a result of sensory experience or injury. An understanding of the neurochemical aspects of sensory processing at these diverse synapses then is of fundamental importance in understanding the organization of the auditory system.     

Electrophysiological studies of the auditory system.

Electrophysiological measures of cochlear function can be obtained using the techniques of transtympanic electrode and surface electrocochleography. These provide measures of the basic parameters of the cochlear microphonic, cochlear nerve and auditory brainstem nuclei action potentials, which enable the functional mechanisms of the cochlea and auditory pathway to be defined for normally hearing subjects and, by comparison, give diagnostic information about the pathologies involved in auditory disorders. Data are presented on the values and variability of the responses obtained from normally hearing subjects. The comparative values of each technique in estimating auditory threshold, cochlear function and in evaluating neurological conditions are discussed using data from clinical patients.     

Traumatic perilymphatic fistulae of the lateral semicircular canal

Fifteen patients with perilymphatic fistulae were evaluated. Of these patients, three had CSF leaks in addition to the perilymphatic fistulae. Eight patients had fistulae of one or both windows; two had fistulae confined to the lateral semicircular canal; and two had combined fistulae of both round window and lateral semicircular canals. All improved dramatically following surgical repair. In the following study, we have shown that perilymphatic fistulae can occur in the lateral semicircular canal, and we suggest exploration of this area when indicated.     

Antigen Diffusion from the perilymphatic space of the cochlea

The diffusion pattern of horseradish peroxidase (HEP) injected into the scala tympani of the cochlear basal turn of guinea pigs was studied to test whether antigen presented in this manner can gain access to the endolymphatic sac. By two hours, HEP reaction product was found throughout the cochlea, with the greatest amounts in the spiral ligament, spiral lim-bus, basilar membrane, and organ of Corti. In several cochleas, very weak labeling was seen in the stria vascularis. HEP reaction product was maximal in the basal turn. By two hours, HEP reaction product was also observed in the endolymphatic sac lumen, epithelial cells, subepithelial tissue, and perisaccular connective tissue. It was more common in the proximal portion. At this time, macrophages within the lumen already appeared to have phagocytosed the HEP. By 72 hours after injection, the inner ear was cleared of HEP. The results of this study support the hypothesis that antigen in the scala tympani gains access to the endolymphatic sac lumen, where it may be presented by macrophages to the systemic immune system. Antigen most likely does not gain access to the endolymphatic space in the cochlea, but it gets to the endolymphatic sac through the perilymph and the Derisaccular tissue.     

Etiology of labyrinthine perilymphatic fistula]

The examination of 120 patients with verified labyrinthine fistulas (LFs) has demonstrated that perilymphatic LFs most often are caused by rupture of the cochlear window's membrane (54%). Among other reasons were broken base of the stapes (6%), the defect in the area of both windows (17%), rupture of the annular ligament of the stapes (15%), defects in the area of semicircular canals. Incompetence of the stapedial piston prosthesis is documented.