Diffusion Tensor Imaging of Auditory Pathway in Patients With Crigler-Najjar Syndrome Type I: Correlation With Auditory Brainstem Response

AIM

To evaluate the role of diffusion tensor imaging of the auditory pathway in patients with Crigler Najjar syndrome type I and its relation to auditory brainstem response.

METHODS

Prospective study was done including 12 patients with Crigler Najjar syndrome type I and 10 age- and sex-matched controls that underwent diffusion tensor imaging of brain. Mean diffusivity and fractional anisotropy at 4 regions of the brain and brainstem on each side were measured and correlated with the results of auditory brainstem response for patients.

RESULTS

There was significantly higher mean diffusivity of cochlear nucleus, superior olivary nucleus, inferior colliculus, and auditory cortex of patients versus controls on both sides for all regions (P = .001). The fractional anisotropy of cochlear nucleus, superior olivary nucleus, inferior colliculus, and auditory cortex of patients versus controls was significantly lower, with P values of, respectively, .001, .001, .003, and .001 on the right side and .001, .001, .003, and .001 on left side, respectively. Also, a negative correlation was found between the maximum bilirubin level and fractional anisotropy of the left superior olivary nucleus and inferior colliculus of both sides. A positive correlation was found between the mean diffusivity and auditory brainstem response wave latency of the right inferior colliculus and left cochlear nucleus. The fractional anisotropy and auditory brainstem response wave latency of the right superior olivary nucleus, left cochlear nucleus, and inferior colliculus of both sides were negatively correlated.

CONCLUSION

Diffusion tensor imaging can detect microstructural changes in the auditory pathway in Crigler Najjar syndrome type I that can be correlated with auditory brainstem response.

Mutation of Npr2 leads to blurred tonotopic organization of central auditory circuits in mice

Tonotopy is a fundamental organizational feature of the auditory system. Sounds are encoded by the spatial and temporal patterns of electrical activity in spiral ganglion neurons (SGNs) and are transmitted via tonotopically ordered processes from the cochlea through the eighth nerve to the cochlear nuclei. Upon reaching the brainstem, SGN axons bifurcate in a stereotyped pattern, innervating target neurons in the anteroventral cochlear nucleus (aVCN) with one branch and in the posteroventral and dorsal cochlear nuclei (pVCN and DCN) with the other. Each branch is tonotopically organized, thereby distributing acoustic information systematically along multiple parallel pathways for processing in the brainstem. In mice with a mutation in the receptor guanylyl cyclase Npr2, this spatial organization is disrupted. Peripheral SGN processes appear normal, but central SGN processes fail to bifurcate and are disorganized as they exit the auditory nerve. Within the cochlear nuclei, the tonotopic organization of the SGN terminal arbors is blurred and the aVCN is underinnervated with a reduced convergence of SGN inputs onto target neurons. The tonotopy of circuitry within the cochlear nuclei is also degraded, as revealed by changes in the topographic mapping of tuberculoventral cell projections from DCN to VCN. Nonetheless, Npr2 mutant SGN axons are able to transmit acoustic information with normal sensitivity and timing, as revealed by auditory brainstem responses and electrophysiological recordings from VCN neurons. Although most features of signal transmission are normal, intermittent failures were observed in responses to trains of shocks, likely due to a failure in action potential conduction at branch points in Npr2 mutant afferent fibers. Our results show that Npr2 is necessary for the precise spatial organization typical of central auditory circuits, but that signals are still transmitted with normal timing, and that mutant mice can hear even with these deficits.

Childhood autism and auditory system abnormalities

Hearing disorders are common among children with autism, ranging from peripheral and sensorineural hearing deficit or loss to auditory hypersensitivity with bizarre reactions to sounds. The auditory abnormalities and consequent sensory deprivation exacerbate the communication deficit of autism, and early auditory assessment holds an important place in the planning of intervention and the overall prognosis of patients. Physiologic, pathologic, imaging, and neurochemical studies have revealed an array of aberrations in the perception and processing of the audiologic stimuli, including (among others) maturational defects, atypical lateralization, and serotonin dysfunction.

Auditory event-related responses in children with semi-lobar holoprosencephaly

The purpose of this study was to evaluate auditory sensory and discrimination responses in children with semi-lobar holoprosencephaly (HPE). Event-related potential (ERP) signals were recorded to tone pair stimuli at 62 electrode sites from the scalp using an oddball paradigm (a two-block design, inter-stimulus interval=70 or 300 ms; frequency of tone pair=100 vs. 100 Hz for the frequent and 100 vs. 300 Hz for the infrequent). Latencies and amplitudes of P150, N250, and mismatch negativity (MMN)-like components were compared between children with HPE and controls. Our results revealed less organized ERP waveforms to both stimuli in children with HPE, with diminished P150 and N250 components across brain area. Robust and delayed MMN-like responses were elicited from the children with HPE, with decreased MMN amplitudes in the central, parietal, occipital, and posterior temporal areas. Our results suggest that while brain sensory responses to auditory tones may be impaired in children with semi-lobar HPE, subcomponents of auditory discrimination processes remain functional.

BetaIVSigma1 spectrin stabilizes the nodes of Ranvier and axon initial segments

Saltatory electric conduction requires clustered voltage-gated sodium channels (VGSCs) at axon initial segments (AIS) and nodes of Ranvier (NR). A dense membrane undercoat is present at these sites, which is thought to be key for the focal accumulation of channels. Here, we prove that βIVΣ1 spectrin, the only βIV spectrin with an actin-binding domain, is an essential component of this coat. Specifically, βIVΣ1 coexists with βIVΣ6 at both AIS and NR, being the predominant spectrin at AIS. Removal of βIVΣ1 alone causes the disappearance of the nodal coat, an increased diameter of the NR, and the presence of dilations filled with organelles. Moreover, in myelinated cochlear afferent fibers, VGSC and ankyrin G clusters appear fragmented. These ultrastructural changes can explain the motor and auditory neuropathies present in βIVΣ1 −/− mice and point to the βIVΣ1 spectrin isoform as a master-stabilizing factor of AIS/NR membranes.

Hearing loss in early infancy affects maturation of the auditory pathway

The influence of early cochlear hearing loss on maturation of the auditory pathway was studied by measuring auditory brainstem responses (ABR). In a retrospective study, 85 children with normal hearing (46 males, 39 females; age range 2 months to 14 years) and 165 children with binaural cochlear hearing impairment (89 males, 76 females; age range 1 month to 16 years) were examined. A significant positive correlation (p<0.001) between the degree of hearing loss and interpeak latencies I-V (IPL(I-V)) of the ABR was observed. No significant correlation (p=0.85) was found between hearing loss and interpeak latencies I-III (IPL(I-III)). These findings can be interpreted as indicating a marked delay in maturation of higher brainstem structures due to reduced auditory input during infancy. The correlation differs notably from results of comparable studies of adults published in recent literature. This leads to the assumption that the developing human brain is particularly sensitive to auditory deprivation. Thus, our results indicate the importance of a normal acoustic environment during sensitive periods in early childhood to ensure normal hearing and speech development.

Episodic exposure to ethanol during development differentially affects brainstem nuclei in the macaque

Neuronal vulnerability to ethanol may be non-specific, i.e., vulnerability may be conferred by the developmental state of the population or by the site of derivation. To address these issues, the effect of developmental exposure to ethanol on three brainstem nuclei; the trigeminal motor (MoV), facial motor (MoVII) and medial superior olivary (MSO) nuclei was determined. MoVII and MSO are generated at the same time and from the same rhombomere, r4. MoV is generated earlier from r2. Macaca nemestrina were exposed to ethanol or a control solution one day per week for six or 24 weeks of gestation. Brainstems of the mature offspring were sectioned and stained. The number of neurons and volume of each nucleus were determined stereologically. Neuron number was lower in MoV and MSO following exposure to ethanol whereas MoVII appeared unaffected. No significant effects of ethanol exposure were seen on the volume and weight of the brainstem, or the volume of the individual nuclei. These findings show that ethanol differentially affects brainstem nuclei in a targeted, rather than non-specific, manner. Furthermore, they show that serious ethanol-induced neurological deficits can be present without gross morphological changes.

The neurochemical basis of cognitive deficits induced by brain iron deficiency: involvement of dopamine-opiate system

Iron is an essential element in maintaining normal structure and functions of the central nervous system. Dangerous effects of decreases in the bioavailability of iron in the brain are shown to affect brain biochemistry, neurotransmitters production and function, mainly in the dopamine-opiate systems well as cognitive functions (learning and memory) and a number of physiological variables such motor activity and thermoregulation. Recent research has shown the added complications and deficits that are introduced in the endocrine and the immune system activity. While iron deficiency is not perceived as a life threatening disorder, it is the most prevalent nutritional disorder in the world and a better understanding of the modes and sites of action, can help devise better treatment programs for those who suffer from it.

[Morphological and functional modifications of the acoustic system in golden hamsters with acoustic generalized epilepsy]

We studied the role of the neuronal circuit consisting of the superior olive-cochlear hair cells-auditory nerve complex in the pathophysiology of reflex audiogenic generalized epilepsy in the epileptic golden hamster. A direct role of the auditory function can be assumed from the genetic lesions found in these animals' acoustic system. These animals are a model of the anatomopathologic substrate of a type of hereditary neurosensorial hypoacusia.

Genetic factors affecting hearing development

Both genetic background and single gene mutations may affect the development of the auditory system. A classification system is presented for those single gene mutations causing hearing impairment. The new feature of this classification is the inclusion of a category for hereditary deafness of central origin. The other categories involve peripheral abnormalities and are: morphogenetic defects, in which the overall structure of the labyrinth is deformed; neuroepithelial degeneration, in which the primary defect appears to occur in the organ of Corti; and cochleo-saccular degeneration, where the stria vascularis is abnormal and Reissner's membrane collapses, leading to further degeneration.

Visual and auditory anomalies in Chediak-Higashi syndrome

Albinism is correlated with misrouting of decussating retinal fibers in the brain. There is also evidence of anomalies of decussating auditory pathways in albinos. The Chediak-Higashi syndrome (CHS) is a rare form of partial albinism which includes increased susceptibility to infections, a hemorrhagic tendency and peripheral polyneuropathies. Binocular and monocular pattern-onset visually evoked potentials (VEPs) and monaural auditory brain stem responses (ABRs) were recorded from 4 subjects with CHS. Three of the CHS demonstrated asymmetric monocular VEPs and failed the Titmus stereovision test. All 4 CHS produced asymmetric ABRs similar to those reported for albinos. Although the hair, skin and irises are relatively well pigmented in CHS, these individuals apparently have anomalies of their central visual and auditory pathways.