Thyroxine affects physiological and morphological development of the ear

Freeman, Sharon; Cherny, Lily; Sohmer, Haim

doi:10.1016/s0378-5955(96)80004-9

Cited by 21 publications

(11 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The maturational sequences of DPOAE response parameters seen in this study are similar to those reported by others in rats [Lenoir and Puel, 1987;Henley et al, 1990; and gerbils [Norton et al, 1991]. These included the following findings: the onset of DPOAEs to higher frequencies preceded those to lower frequencies [Lenoir and Puel, 1987;Henley et al, 1990;Norton et al, 1991;Freeman et al, 1996] and in the younger animals, the responses were initially to the higher-intensity stimuli and with age, responses to lower intensities could be recorded (improvement in threshold) [Henley et al, 1990;Norton et al, 1991;Lenoir and Puel, 1987;Freeman et al, 1996], input-output functions for the higher frequency stimuli were initially monotonic and with age became less monotonic with a change in slope (plateau and/or notch) in the mid-intensity region (65-70 dB SPL); these changes in the input-output functions were first apparent for the higher frequencies [Henley et al, 1990;Norton et al, 1991;Freeman et al, 1996]. Fig.…”

Section: Discussionsupporting

confidence: 89%

“…Doan et al [1996] report that the middle ear bulla was free of fluid by PND 12. Thus prior to PND 15, conductive immaturities could account for much of the OAE development and may possibly explain the fre-quency progression of the DPOAEs and TEOAEs found in this and other studies [Lenoir and Puel, 1987;Henley et al, 1990;Norton et al, 1991;Freeman et al, 1996]. However, from PND 15 onward, other factors must be involved.…”

Section: Discussionmentioning

confidence: 58%

“…The development of OAEs in altricious mammals has previously been studied using cubic distortion product (2f 1 -f 2 ) OAEs (DPOAEs) in rats [Lenoir and Puel, 1987;Henley et al, 1990;Freeman et al, 1996] and in gerbils [Norton et al, 1991]. However, many human clinical studies use transient evoked OAEs (TEOAEs) and these have been difficult to record in most laboratory mammals in the past due to their very short latency and duration, leading to their appearance in close proximity to the stimulus.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Development of Transient Evoked Otoacoustic Emissions in the Neonatal Rat

Khvoles¹,

Freeman²,

Sohmer³

1998

Audiol Neurotol

Self Cite

View full text Add to dashboard Cite

Otoacoustic emissions (OAEs) represent acoustic energy generated by the cochlear amplifier which contributes to auditory sensitivity and frequency discrimination. Therefore the OAEs can serve as a noninvasive tool to study the cochlear amplifier. While transient evoked OAEs (TEOAEs) are generally recorded clinically in man, it has been difficult to record them in animals and instead cubic distortion product OAEs (DPOAEs) have been experimentally studied in animals. In a previous study, we perfected a method of recording TEOAEs routinely in rats and this technique was used here to study the development of OAEs in neonatal rats. TEOAEs were recorded and compared to the DPOAEs on several postnatal days. With increasing postnatal age, TEOAE peak-to-peak amplitude and spectral energy in the 2- to 4-kHz band increased, their threshold decreased and their input-output functions became less monotonic with a change in slope (notch and/or plateau) in the mid-intensity region. The DPOAEs to higher frequencies appeared first, then the TEOAEs, followed by the DPOAEs to lower frequencies. With age, their amplitude also increased, thresholds decreased and a notch appeared in their input-output functions. The TEOAEs were measurable during the continuum of the appearance of the DPOAEs and the developmental sequences of both types of OAEs were similar. This may be evidence that similar mechanisms account for their maturation which probably initially involves a reduction in the air-bone gap with maturation of the outer and middle ears, and then elevation of the endocochlear potential and additional micromechanical maturations.

show abstract

Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Development of Transient Evoked Otoacoustic Emissions in the Neonatal Rat

Khvoles¹,

Freeman²,

Sohmer³

1998

Audiol Neurotol

Self Cite

View full text Add to dashboard Cite

show abstract

“…Also direct driving of the stapes footplate in gerbils elicited cochlear microphonic potentials on PND 10, while to airconducted stimuli only on PND 12 [19], In rats, the external meatus became patent in a few rats on PND 11 and in all rats of the same litter on PND 12. The middle and inner ears acquire almost adult-like morphology by PND 14 [20], Based on the above experi ments and on direct observation, it seems that the chief middle ear conductive maturational Thyroid Hormone and Auditory' Development factors (in addition to opening of the external ear canal) which take place between PND 9 and PND 15 in rats include resorption of mid dle ear mesenchyme and ossicular ossification [20],…”

Section: Conductive (Outer and Middle Ear) Maturationmentioning

confidence: 93%

The Importance of Thyroid Hormone for Auditory Development in the Fetus and Neonate

Sohmer¹,

Freeman²

1996

Audiol Neurotol

Self Cite

View full text Add to dashboard Cite

It seems that many auditory maturational events are regulated by thyroid hormone since elevation in thyroid hormone level always precedes the onset of hearing in the fetus-neonate; low thyroid activity in the developing human fetus or rat neonate leads to hearing loss; earlier, elevated thyroid levels in rat neonate lead to earlier onset of hearing. The hormone, bound to its receptors in the nucleus, acts as a transcription factor activating genes which lead to the synthesis of several proteins and enzymes involved in the structural and functional development of many tissues (e.g. brain, heart, kidney, skeletal muscle) including the ear. Several types of congenital hearing loss of unexplained etiology may be due to abnormalities in one or more stages of this gene cascade since several types of congenital hearing loss have been shown to involve defects in genes related to these events.

show abstract

“…Thyroid hormones acting through TRβ also influence hearing by initiating myelinogenesis of the cochlea and vestibulocochlear nerve (cranial nerve VIII) prior to the onset of hearing (56). In rats, the critical periods of thyroid-sensitive ear development extend from at least GD18 (the onset of fetal thyroid gland function) through PND18 (the period of outer hair cell synaptogenesis in the cochlea) (126)(127)(128). Brucker-Davis et al (121) estimate the critical period of thyroid-sensitive cochlear development in humans extends from the close of the first trimester through the first month of life.…”

Section: Cochlear Developmentmentioning

confidence: 99%

A model of the development of the brain as a construct of the thyroid system.

Howdeshell

2002

Environ Health Perspect

333

237

View full text Add to dashboard Cite

Thyroid hormone is essential for normal brain development. However, little is known about the molecular and cellular mechanisms that mediate thyroid hormone action on the developing brain or the developmental events selectively affected. Consequently, although a large number of environmental chemicals interfere with the thyroid system, there are few neurodevelopmental end points to recruit for toxicological studies. Therefore, my goal here is to review what is known about the relative timing of normal brain construction and thyroid system development, with special focus on the period of in utero development in humans and the comparable developmental period in laboratory rats. These data are presented as a timeline to aid in the identification of thyroid-sensitive end points in brain development and to highlight important data gaps. I discuss the known influence of certain synthetic chemicals on the thyroid system and include a brief review of the effects of developmental exposure to chemicals on thyroid system function. The relationship between the thyroid hormone and retinoic acid systems, as well as the thyroid hormone sensitivity of the developing cochlea, is also discussed.

show abstract

Thyroxine affects physiological and morphological development of the ear

Cited by 21 publications

References 44 publications

Development of Transient Evoked Otoacoustic Emissions in the Neonatal Rat

Development of Transient Evoked Otoacoustic Emissions in the Neonatal Rat

The Importance of Thyroid Hormone for Auditory Development in the Fetus and Neonate

A model of the development of the brain as a construct of the thyroid system.

Contact Info

Product

Resources

About