DEVELOPMENT AND POTENTIAL BEHAVIORAL SIGNIFICANCE OF PRECISE TONOTOPY IN AN INHIBITORY CIRCUIT OF THE AUDITORY BRAINSTEM

Precise neuronal connections are crucial for normal brain function. Often this is accomplished during development, as initially imprecise connections are refined in a manner that depends on neural activity, both spontaneous and sensory-evoked. In the auditory system, many connections are topographically organized according to frequency, or tonotopically, an organizational scheme important for processing information about sound. In this thesis, I investigated the development of precise tonotopy in the inhibitory connections between the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO), a pathway in the auditory brainstem involved in sound localization. Although MNTB-LSO connections exhibit tonotopy from the outset, tonotopic precision increases during development through a process of silencing imprecise inputs and strengthening maintained connections before hearing onset, followed by anatomical pruning after hearing. I teased apart the relationship between functional and anatomical refinement, as well as the degree to which spontaneous and sound-evoked activity play a role in each. Finally, I attempted to link the tonotopic specificity of this circuit to a specific aspect of auditory perception, frequency discrimination.In Chapter 2, I mapped the tonotopic precision of individual MNTB axons in the LSO over the first three weeks of postnatal development and showed that pruning does not take place before hearing onset, indicating that functional and anatomical refinement take place during distinct developmental periods. In Chapter 3, I showed that anatomical refinement after hearing onset depends on efferent cholinergic transmission in the cochlea, most likely due to its role in patterning pre-hearing spontaneous activity and the functional refinement of connections. In Chapter 4, I showed that eliminating the normal spectrotemporal structure of sound-evoked activity by rearing animals in pulsed white noise does not disrupt pruning. Finally, in Chapter 5, I showed that the loss of tonotopic precision that results from the elimination of cochlear cholinergic transmission is also accompanied by impaired frequency discrimination, providing a link between tonotopic refinement, the efferent system, and auditory perception. I discuss the results in the context of a model of tonotopic refinement and a new role of the efferent system during development

Mice Lacking the Alpha9 Subunit of the Nicotinic Acetylcholine Receptor Exhibit Deficits in Frequency Difference Limens and Sound Localization

Sound processing in the cochlea is modulated by cholinergic efferent axons arising from medial olivocochlear neurons in the brainstem. These axons contact outer hair cells in the mature cochlea and inner hair cells during development and activate nicotinic acetylcholine receptors composed of α9 and α10 subunits. The α9 subunit is necessary for mediating the effects of acetylcholine on hair cells as genetic deletion of the α9 subunit results in functional cholinergic de-efferentation of the cochlea. Cholinergic modulation of spontaneous cochlear activity before hearing onset is important for the maturation of central auditory circuits. In α9KO mice, the developmental refinement of inhibitory afferents to the lateral superior olive is disturbed, resulting in decreased tonotopic organization of this sound localization nucleus. In this study, we used behavioral tests to investigate whether the circuit anomalies in α9KO mice correlate with sound localization or sound frequency processing. Using a conditioned lick suppression task to measure sound localization, we found that three out of four α9KO mice showed impaired minimum audible angles. Using a prepulse inhibition of the acoustic startle response paradigm, we found that the ability of α9KO mice to detect sound frequency changes was impaired, whereas their ability to detect sound intensity changes was not. These results demonstrate that cholinergic, nicotinic α9 subunit mediated transmission in the developing cochlear plays an important role in the maturation of hearing

Caracterização físico-química dos frutos de goiabeira ‘Pedro Sato’ (Psidium guajava L.)

Objetivou-se com o estudo avaliar as seguintes características físico-químicas dos frutos de goiaba da cultivar Pedro Sato: peso, altura, diâmetro, número de sementes e teor de sólidos solúveis (SS) sob diferentes temperaturas

Expert Panel Curation of 113 Primary Mitochondrial Disease Genes for the Leigh Syndrome Spectrum

OBJECTIVE: Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene-disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes. METHODS: The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene-Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS. RESULTS: The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31/114 gene-disease relationships curated (27%); moderate for 38 (33%); limited for 43 (38%); and 2 as disputed (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 autosomal dominant, and 3 X-linked. INTERPRETATION: GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multi-system organ surveillance, recurrence risk counselling, reproductive choice, natural history studies and eligibility for interventional clinical trials. This article is protected by copyright. All rights reserved

Clinical validity assessment of genes frequently tested on intellectual disability/autism sequencing panels.

[en] PURPOSE: Neurodevelopmental disorders (NDDs), such as intellectual disability (ID) and autism spectrum disorder (ASD), exhibit genetic and phenotypic heterogeneity, making them difficult to differentiate without a molecular diagnosis. The Clinical Genome Resource Intellectual Disability/Autism Gene Curation Expert Panel (GCEP) uses systematic curation to distinguish ID/ASD genes that are appropriate for clinical testing (ie, with substantial evidence supporting their relationship to disease) from those that are not. METHODS: Using the Clinical Genome Resource gene-disease validity curation framework, the ID/Autism GCEP classified genes frequently included on clinical ID/ASD testing panels as Definitive, Strong, Moderate, Limited, Disputed, Refuted, or No Known Disease Relationship. RESULTS: As of September 2021, 156 gene-disease pairs have been evaluated. Although most (75%) were determined to have definitive roles in NDDs, 22 (14%) genes evaluated had either Limited or Disputed evidence. Such genes are currently not recommended for use in clinical testing owing to the limited ability to assess the effect of identified variants. CONCLUSION: Our understanding of gene-disease relationships evolves over time; new relationships are discovered and previously-held conclusions may be questioned. Without periodic re-examination, inaccurate gene-disease claims may be perpetuated. The ID/Autism GCEP will continue to evaluate these claims to improve diagnosis and clinical care for NDDs

The ClinGen Syndromic Disorders Gene Curation Expert Panel: Assessing the Clinical Validity of 111 Gene-Disease Relationships.

PURPOSE: The Clinical Genome Resource (ClinGen) Gene Curation Expert Panels (GCEPs) have historically focused on specific organ systems or phenotypes; thus, the ClinGen Syndromic Disorders GCEP (SD-GCEP) was formed to address an unmet need. METHODS: The SD-GCEP applied ClinGen\u27s framework to evaluate the clinical validity of genes associated with rare syndromic disorders. 111 Gene-Disease Relationships (GDRs) associated with 100 genes spanning the clinical spectrum of syndromic disorders were curated. RESULTS: From April 2020 through March 2024, 38 precurations were performed on genes with multiple disease relationships and were reviewed to determine if the disorders were part of a spectrum or distinct entities. 14 genes were lumped into a single disease entity and 24 were split into separate entities, of which 11 were curated by the SD-GCEP. A full review of 111 GDRs for 100 genes followed, with 78 classified as Definitive, 9 as Strong, 15 as Moderate, and 9 as Limited highlighting where further data are needed. All diseases involved two or more organ systems, while the majority (88/111 GDRs, 79.2%) had five or more organ systems affected. CONCLUSION: The SD-GCEP addresses a critical gap in gene curation efforts, enabling inclusion of genes for syndromic disorders in clinical testing and contributing to keeping pace with the rapid discovery of new genetic syndromes

Differential maturation of vesicular glutamate and GABA transporter expression in the mouse auditory forebrain during the first weeks of hearing

Vesicular transporter proteins are an essential component of the presynaptic machinery that regulates neurotransmitter storage and release. They also provide a key point of control for homeostatic signaling pathways that maintain balanced excitation and inhibition following changes in activity levels, including the onset of sensory experience. To advance understanding of their roles in the developing auditory forebrain, we tracked the expression of the vesicular transporters of glutamate (VGluT1, VGluT2) and GABA (VGAT) in primary auditory cortex (A1) and medial geniculate body (MGB) of developing mice (P7, P11, P14, P21, adult) before and after ear canal opening (~P11–P13). RNA sequencing, in situ hybridization, and immunohistochemistry were combined to track changes in transporter expression and document regional patterns of transcript and protein localization. Overall, vesicular transporter expression changed the most between P7 and P21. The expression patterns and maturational trajectories of each marker varied by brain region, cortical layer, and MGB subdivision. VGluT1 expression was highest in A1, moderate in MGB, and increased with age in both regions. VGluT2 mRNA levels were low in A1 at all ages, but high in MGB, where adult levels were reached by P14. VGluT2 immunoreactivity was prominent in both regions. VGluT1(+) and VGluT2(+) transcripts were co-expressed in MGB and A1 somata, but co-localization of immunoreactive puncta was not detected. In A1, VGAT mRNA levels were relatively stable from P7 to adult, while immunoreactivity increased steadily. VGAT(+) transcripts were rare in MGB neurons, whereas VGAT immunoreactivity was robust at all ages. Morphological changes in immunoreactive puncta were found in two regions after ear canal opening. In the ventral MGB, a decrease in VGluT2 puncta density was accompanied by an increase in puncta size. In A1, peri-somatic VGAT and VGluT1 terminals became prominent around the neuronal somata. Overall, the observed changes in gene and protein expression, regional architecture, and morphology relate to—and to some extent may enable— the emergence of mature sound-evoked activity patterns. In that regard, the findings of this study expand our understanding of the presynaptic mechanisms that regulate critical period formation associated with experience-dependent refinement of sound processing in auditory forebrain circuits