Auditory development in the mouse: Structural maturation of the middle ear

The development of middle-ear structures in the mouse was examined in nine groups of pups between 1 and 45 days of age. The area of the tympanic membrane (pars tensa and pars flaccida), the length of the lever arms of the malleus and incus, the surface area of the oval window, and the volume of the bulla all showed systematic changes during neonatal life. The area of the oval window reached maturity first and the lever arms achieved 90% of their adult size on day 11. The tympanic membrane achieved the same criterion on day 18. These data help us further to understand the processes that contribute to the functional ontogeny of the middle ear.     

Establishment of the afferent function of the striatum in the rabbit during early ontogenesis

The study is dedicated to electrophysiological analysis of development of the caudate nucleus afferent function in rabbits in early postnatal ontogenesis. By amplitude-temporal parameters of the evoked potentials (EPs) of the caudate nucleus, recorded in response to stimulation of afferent inputs from the cortical regions (motor and limbic) and substantia nigra, similar dynamics of these afferent pathways functional maturation is revealed from the beginning of functioning (in the age of 3-5 days) to the definitive level (by the 30th day of life). The most significant changes of the amplitude-temporal parameters of the evoked potential, particularly of latencies are observed during the 3d week of postnatal life. On the basis of the obtained data, the conclusion is made on the formation of a common system of striatum sensory integration in the 3d-4th week of rabbits life. This age period is considered as critical.     

Cyto- and synaptogenesis in the arcuate nucleus of the rat hypothalamus during fetal and early postnatal life

Summary Morphogenesis of the arcuate nucleus of the rat from the 15th fetal day to the 6th postnatal day was investigated light and electron microscopically. The arcuate neurons exhibit a gradual development after the 15th fetal day. All cytoplasmic constituents are present in these nerve cells already during the last days of gestation. Nevertheless, they are not fully differentiated at birth. The first synapse-like structures (presynapses) were observed in 17 day-old, the first synapses in 18 day-old fetuses. During the early postnatal period the number of presynapses decreases, but at the same time there is a gradual increase in the number of the relatively mature synapses. This process starts already during the last days of prenatal life. Although all structural elements of the arcuate nucleus of the adult rat appear to be present at birth, the extent of the neuropil area and the number of the presynapses indicate that the arcuate nucleus is still in a fairly undeveloped stage during the first postnatal days.     

Development of the stratified squamous epithelium of the human tympanic membrane and external canal: the origin of auditory epithelial migration

The development of the stratified squamous epithelium of the tympanic membrane and external canal was studied in 167 embryonic, fetal, and postnatal human ears. It originates as a tube derived from the epithelium of the fundus of the primary external canal (zone 1). The tube is composed of a thin, flat epithelium on the medial side (zone 2), continuous with a thicker one (zone 3) on the lateral side; zone 3 thereafter merges with the external epithelium of the primary external canal (zone 4). Proliferative activity, as indicated by a thickened epithelium, with rete ridges in later fetal life, is present mainly in zones 1 and 3. Cornification at 18 weeks gestation is followed by clearing of keratinous debris to the exterior. Subsequently the canal widens, zone 1 now covering the pars flaccida region, a tongue-shaped area passing inferiorly from it and a part of the postero-superior deep canal adjacent to it; zone 2 covers the pars tensa and zone 3 most of the deep external canal. On the basis of the original embryonic growth, migratory epithelial movement throughout life is postulated to be generated in zone 1 by mitotic interposition and then to pass to zone 2. It then moves en masse through to zone 3, where unilateral progression by mitotic means takes the epithelium up to the cartilaginous canal. Such a pathway is approximately that seen in the marked, living eardrum and canal.     

Scaling of the marsupial middle ear and its functional significance

The marsupial middle ear performs an anatomical impedance matching for acoustic energy travelling in air to reach the cochlea. The size of the middle ear sets constraints for the frequencies transmitted. For generalized placental mammals, it has been shown that the limit for high-frequency hearing can be predicted on the basis of middle ear ossicle mass, provided that the ears fulfil requirements of isometry. We studied the interspecific size variation of the middle ear in 23 marsupial species, with the following measurable parameters: skull mass, condylobasal length, ossicular masses for malleus, incus and stapes, tympanic membrane area, oval window area, and lever arm lengths for malleus and incus. Our results show that the middle ear size grows with negative allometry in relation to body size and that the internal proportions of the marsupial middle ear are largely isometric. This resembles the situation in placental mammals and allows us to use their isometric middle ear model to predict the high-frequency hearing limit for marsupials. We found that the isometry model predicts the high-frequency hearing limit for different marsupials well, indicating that marsupials can be used as auditory models for general therian mammalian hearing. At very high frequencies, other factors, such as the inner ear, seem to constrain mammalian hearing.     

Allometric study of the lachrymal and Harderian glands of the rat during postnatal life.

The authors performed an allometric study of the growth of the rat's lachrymal and Harderian glands, during postnatal life. From the analysis of the results, they could conclude: (1) the growth of these glands in relation to body weight, during postnatal life, could be considered similar, following the allometric law; (2) the differential growth of the glands occurred in two stages: from birth until the 15th day and from the 15th day until the final period of life studied; (3) the two stages of development were separated by a critical period, during which an abrupt modification of the allometric coefficient occurred; (4) during the first days of postnatal life, the development of the Harderian gland was characterized by a high rate of growth and, just after eyelid disjunction and during rest of postnatal life, by a rate of allometric of growth less than 1. It is interesting to observe that the lachrymal and Harderian glands' critical period of development on the 15th day of postnatal life coincides with the time at which the eyelids of the animal open.     

Incudomalleal joint formation: the roles of apoptosis,migration and downregulation

Background  

The middle ear of mammals is composed of three endochondrial ossicles, the stapes, incus and malleus. Joints link the malleus to the incus and the incus to the stapes. In the mouse the first arch derived malleus and incus are formed from a single Sox9 and Type II collagen expressing condensation that later subdivides to give rise to two separate ossicles. In contrast the stapes forms from a separate condensation derived from the second branchial arch. Fusion of the malleus and incus is observed in a number of human syndromes and results in conductive hearing loss. Understanding how this joint forms during normal development is thus an important step in furthering our understanding of such defects.     

Catecholamine concentration in several structures of the cat and rabbit sympathetic nervous systems during postnatal ontogenesis]

Studies have been made on the content of adrenalin and noradrenalin in the nervous fibers and ganglia of the sympathetic nervous system of cats and rabbits during a postnatal life. In all the structures investigated, high catecholamine content was found within the first month of life on the animals. On further development, total catecholamine content decreases. Age changes in catecholamine content of preganglionic sympathetic fibers and different sympathetic ganglia indicate an effective adrenergic regulation in early postnatal ontogenesis of cats and rabbits.     

Localization and proliferation of lymphatic vessels in the tympanic membrane in normal state and regeneration

We clarified the localization of lymphatic vessels in the tympanic membrane and proliferation of lymphatic vessels during regeneration after perforation of the tympanic membrane by using whole-mount imaging of the tympanic membrane of Prox1 GFP mice. In the pars tensa, lymphatic vessel loops surrounded the malleus handle and annulus tympanicus. Apart from these locations, lymphatic vessel loops were not observed in the pars tensa in the normal tympanic membrane. Lymphatic vessel loops surrounding the malleus handle were connected to the lymphatic vessel loops in the pars flaccida and around the tensor tympani muscle. Many lymphatic vessel loops were detected in the pars flaccida. After perforation of the tympanic membrane, abundant lymphatic regeneration was observed in the pars tensa, and these regenerated lymphatic vessels extended from the lymphatic vessels surrounding the malleus at day 7. These results suggest that site-specific lymphatic vessels play an important role in the tympanic membrane.     

Development of the vascular bed in the rabbit ear: scanning electron microscopy of vascular corrosion casts

The development of the vascular bed in the rabbit ear was investigated using vascular corrosion casts from animals of various ages. Examination of the casts revealed that the arrangement of the major auricular arteries and veins was determined before birth and was maintained during postnatal growth of the ear. Furthermore, the number of arteries branching off the central ear artery and the lateral arteries did not increase with increasing ear length. Scanning electron microscopic examination of lateral segments of adult ear casts revealed many anastomoses between marginal arteries and veins. These arteriovenous anastomoses (AVAs) occurred singly, in pairs, or in clusters of three to six. Their size and shape were variable, even in the same cast. The central segment of many AVA casts showed surface impressions of endothelial cell nuclei which were different from the impressions on adjacent arteries and veins. Arteriovenous anastomoses were also detected in ear casts from animals as young as 8 days. The density of AVAs in lateral ear segments ranged from 95-165 cm-2 in 8- to 11-day-old rabbits to 80-115 cm-2 in adults. However, estimates of the total number of AVAs in the lateral ear margin indicated that AVAs continued to be formed at a steady rate during growth of the ear. During the early neonatal period the cutaneous capillary plexuses developed prominent tufts projecting toward the skin surface, which were apparently associated with developing hair follicles. These capillary tufts were not seen in casts from fetal or adult rabbits.     

Auditory epithelial migration on the human tympanic membrane: II. The existence of two discrete migratory pathways and their embryologic correlates

The pathways of movement of dye-markings on the tympanic membranes of 30 ears of 15 volunteers were investigated by photography with a Hopkin's rod. Two discrete pathways were identified. Movement on the pars tensa was centrifugal in all directions from the edge of the handle of malleus surface. This supported our previous suggestion that pars tensa epithelial migration is based on growth of the meatal plate. Movement on the more central part of the handle surface itself, however, was always upwards to the pars flaccida epithelium and then, with all dye on the latter, in a posterosuperior direction only. The covering epithelium of the pars flaccida/handle of malleus arises from the fundus of the early embryonic external canal. To explore the possibility that its migration may also commence early, the fundus was examined histologically in 12 embryo ears. It was shaped like an inverted pear to conform to the primordial head of the malleus above and its handle below. There was distinct flattening of the whole fundal epithelium in contrast to the side wall of the external canal, lending support to the concept of a primordial flux of epithelium in the main fundus and its inferior extension. The meatal plate grew from the rim of the fundus producing the pars tensa and deep external canal epithelia. This process, however, was not associated with significant cytologic alterations or increased expression of the human proliferation antigen, Ki-67, at that rim. This suggests that the pars tensa epithelium grows and moves without the active involvement of the epithelium of the pars flaccida/handle of malleus.     

Study of age-related changes in Middle ear transfer function

Abstract

Osteoporosis (OP) is common with advancing age. Several studies have shown a strong correlation between OP and otosclerosis. However, no studies have investigated OP of the malleus, incus or stapes in the human middle ear, its effect on middle ear transfer function. Here, we investigate whether these three ossicles develop OP, and how this affects middle ear transfer function. The effect of OP on middle ear transfer function was investigated in simulations based on a finite element (FE) method. First, the FE model used in our previous study was refined, and optimized by introducing viscoelastic properties to selected soft tissues of the middle ear. Then, the FE model was used to simulate OP of the three ossicles and assess its influence on middle ear transfer function. Other possible age-related changes, such as stiffness of the joints or ligaments in the middle ear, were also investigated. The results indicated that OP of the ossicles could increase the high frequency displacement of both the umbo and stapes footplate (FP). However, the stiffness of the middle ear soft tissue can lead to the decrease of middle ear gain at lower frequencies. Furthermore, loosening of these joints or ligaments could increase displacement of the umbo and stapes FP. In conclusion, although age-related hearing loss is most commonly conceived of as sensorineural hearing loss (SNHL), we found that age-related changes may also include OP and changes in joint stiffness, but these will have little effect on middle ear transfer function in elderly people.     

Rotation of middle ear ossicles during cetacean development

Cetacean middle ears are unique among mammals in that they have an elongated tympanic membrane, a greatly reduced manubrium mallei, and an incudal crus longum that is shorter than the crus breve. Elongation of the tympanic membrane and reduction of the manubrium is thought to be related to an evolutionary rotation of the incus and malleus out of the plane of the tympanic membrane. We examined if rotation also occurs during ontogeny by comparing the middle ears of two species of dolphins (Delphinus delphis, Stenella attenuata) at different stages of development. We observed that: the incus has the body and crural proportions as in terrestrial mammals early in development; the incudomallear complex rotates approximately 90 degrees following ossification; the tympanic membrane is not elongated until relatively late in development. Therefore, some of the unique characteristics of the cetacean middle ear develop as modifications of an initially terrestrial-like morphology.     

Modulation of the thalamocortical responses of the sensorimotor cortex during stimulation of the lateral hypothalamus in rabbits in ontogeny

It has been demonstrated that rhythmic stimulation of the relay thalamic nucleus in rabbits at the second half of the first month of postnatal life does not significantly affect the amplitude of the second and third positive components (PC-2 and PC-3) of the positive phase of the thalamocortical responses. Combination of rhythmic stimulation of this nucleus and that of lateral hypothalamic structures is accompanied by a significant increase of the amplitude of both positive components of the thalamocortical responses, the degree of potentiation of PC-3 being higher than that of PC-2. The described potentiation is most evident at the third week of postnatal development of rabbits.     

Middle-ear development: II. Morphometric changes in the conducting apparatus of the chick.

The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear.     

Life span changes in the presence of alpha-melanocyte-stimulating-hormone-containing cells in the human pituitary.

Since recent circumstantial evidence has suggested possible functions of alpha-MSH in intrauterine growth and labour, the presence of this hormone in the human pituitary was determined by means of the indirect immunofluorescence procedure during development and adulthood. Cross reaction of the antibodies with other peptides was measured after which they were purified by solid phase absorption. Experiments on the rat pituitary showed that staining of alpha-MSH- and ACTH-containing cells could be obtained well until 48 h after death. In the pars distalis the ability of ACTH-containing cells to take up stain increased during the period of post-mortem storage. In the youngest human fetus studied (15 weeks) only alpha-MSH-containing cells were found in the pars intermedia and no ACTH-containing cells were observed. In the other fetal pituitaries a distinct pars intermedia containing more alpha-MSH cells than ACTH cells was found. In the pars distalis of the fetuses more ACTH- than alpha-MSH-containing cells were observed. From birth to 19 years, progressively fewer alpha-MSH containing cells could be detected in the 'zona intermedia' and pars distalis, while in adults only a few such cells were found in either area. Irrespective of age, sex, cause of death or therapy, alpha-MSH-containing cells were found in all pituitaries throughout life. The number of ACTH containing cells gradually increased in the zona intermedia and pars distalis and reached a high adult level in the latter structure. In the pituitaries of seven anencephalics, no alpha-MSH-containing cells were present. The presence of alpha-MSH in the fetal pars intermedia, the change in the ratio of the alpha-MSH/ACTH cells during the course of development, and the absence of alpha-MSH in anencephaly all support the possibility that human fetal pituitary alpha-MSH is involved in both intrauterine growth and fetal adrenal function and thus also in parturition.     

The effect of ethanol exposure in pregnancy on maturation of monoaminergic systems in the developing rat bran

Simultaneous study of the main neurotransmitter of monoaminergic system of the brain, its metabolites, activity of catechol-O-methyltransferase (COMT) and the state of different subtypes of dopamine (DA) receptors in the developing brain of offspring from mothers alcoholized in gestation and feeding periods revealed a decrease in activity of all monoaminergic systems studied with reduction of noradrenaline and DA level in alcoholized fetus as well as of mPNA of COMT, an enzyme of catecholamine metabolism, in the structures of the forebrain on the 17th day but not on 13th day of prenatal development. In parallel experiments, an increase of the contents of both long and short splice variants of D2 DA receptor was registered. In postnatal period (days 4, 10, 17), further decrease of the DA system activity was observed, particularly a reduction of DOPAC level and DOPAC/DA ratio in rat litter, mothers of whom took alcohol in the gestation period with withdrawal it after birth of offspring. The serotonin system activity was also reduced in alcoholized litter in the postnatal period and was registered in the early stages (on the 4th day of life). Therefore, the serotonin system activity is changing at early stages of development (the 4th day), whereas inhibition of the DA system activity is registered at later stages (the 10th day of life).     

Postnatal changes of some enzymatic activities of energy supplying metabolism in the cortex, inner and outer medulla of the rat kidney

1. In rat kidney cortex, outer and inner medulla the development of activities of seven enzymes was investigated during postnatal ontogeny (10, 20, 30, 60 and 90 days of age). The enzymes were selected in such a manner, as to characterize most of the main metabolic pathways of energy supplying metabolism: hexokinase (glucose phosphorylation, HK), glycerol-3-phosphate dehydrogenase (glycerolphosphate metabolism or shunt, GPDH), triose phosphate dehydrogenase (glycolytic carbohydrate breakdown, TPDH), lactate dehydrogenase (lactate metabolism, LDH), citrate synthase (tricarboxylic acid cycle, aerobic metabolism, CS), malate NAD dehydrogenase (tricarboxylic acid cycle, intra-extra mitochondrial hydrogen transport, MDH) and 3-hydroxyacyl-CoA-dehydrogenase (fatty acid catabolism, HOADH). 2. The renal cortex already differs metabolically from the medullar structures on the 10th day of life. It displays a high activity of aerobic breakdown of both fatty acids and carbohydrates. Its metabolic capacity further increases up to the 30th day of life. 3. The outer medullar structure is not grossly different from the inner medulla on the 10th day of life. Further it differentiates into a highly aerobic tissue mainly able to utilize carbohydrates. It can, however, to some extent, also utilize fatty acids aerobically and produce lactate from carbohydrates anaerobically. 4. The inner medullar structure is best equipped to utilize carbohydrates by anaerobic glycolysis, forming lactate. This feature is already pronounced on the 10th day of life, its capacity increases to some extent during postnatal development, being highest between the 10th and the 60th day of life.     

Ontogenesis of corticotropes and lactotropes in situ in the pituitary gland of the hamster

Summary The development of corticotropes and lactotropes was investigated in the golden Syrian hamster using an anti-porcine ACTH antiserum and a homologous antihamster PRL antiserum. Oval corticotropes were first visible in the ventral region of the pars distalis at 13 days of gestation. By the end of gestation, corticotropes were found throughout the pars distalis and in the pars intermedia. Corticotropes in the pars distalis of postnatal hamsters were either round or irregularly-shaped, often appearing in clusters. Throughout development, corticotropes often appeared to be surrounding other cells. Scarce, very small lactotropes were first observed in the pars distalis of hamsters on the first postnatal day. The number of these cells, which were either round or polyhedral, increased dramatically between 4 and 20 days of postnatal life. These observations indicate that the sequence of appearance of corticotropes and lactotropes in the hamster is similar to that in other species and that lactotropes are confined to the pars distalis of postnatal hamsters.