Development of the statocyst in the freshwater snail Biomphalaria glabrata (Pulmonata, Basommatophora)

Gerbil middle-ear sound transmission from 100 Hz to 60 kHz

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance H(MY) (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from 0.1 to 60 kHz, a range that spans the gerbil's audiometric range. Similar measurements were performed in two laboratories. The H(MY) magnitude (a) increased with frequency below 1 kHz, (b) remained approximately constant with frequency from 5 to 35 kHz, and (c) decreased substantially from 35 to 50 kHz. The H(MY) phase increased linearly with frequency from 5 to 35 kHz, consistent with a 20-29 micros delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around 10 kHz. Cochlear input impedance was estimated from H(MY) and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and 35 kHz and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.

On generation of statoconia in gravireceptors of mollusks

Two models of development of statoconia in the statocyst of mollusks, based on the experimental data [Hearing Res. 49 (1990) 63; Hearing Res. 109 (1997) 125; Hearing Res. 109 (1997) 109;] are proposed. The purpose of the present work is to apply mathematical modeling to the analysis of mechanisms of statoconia formation and generation by supporting cells at the stage of their accumulation in the cyst lumen. In the case of Aplysia californica, it is not clear whether there is a temporal change of statoconia due to their growth in the cyst lumen similar to that in Biomphalaria, or whether the growth of statoconia occurs in supporting cells before they get into the cyst lumen. This question has to do with a more general and insufficiently investigated problem of the mechanisms of statoconia evolution during their stage of accumulation. This is related to A. californica as well as to the initial phase of development of Biomphalaria glabrata. This problem is of practical importance because the majority of experiments related to the study of the effects of altered gravity on the development of gravireceptors in the two mollusks A. californica and B. glabrata deals with the initial phase of statoconia development. It is assumed that two main processes determine the evolution of statoconia in developing mollusks: generation of new statoconia by growing supporting cells and growth of statoconia sizes in the cyst lumen. Analysis of experimental data related to the generation of statoconia in Aplysia and comparison of these data with the results of modeling of accumulation of statoconia suggest that the basic mechanism of evolution of size distribution of statoconia in Aplysia is growth of embryonic statoconia in supporting cells, that follows the growth of animal size. Thus, the large sizes of statoconia are determined by their development within supporting cells rather than by their growth in the cyst lumen. Analysis of the data concerning Biomphalaria allows us to assume that distribution of supporting cells which generate statoconia also varies. The results of modeling of evolution of statoconia specify necessary additional experiments, which are required to refine and test the model.

Morphometry of otoconia in the utricle and saccule of developing Japanese quail

The development of otoconia in the utricular and saccular maculae from initial embryonic formation to adult stages was examined in Japanese quails. Both the morphology and size of the otoconia were quantified at different developmental stages. It was observed that the otoconia were initially formed on embryologic stage E5 in the saccule and E6 in the utricle. Otolith mass areas increased in a sigmoidal growth pattern, with saccular otolith areas being smaller than the utricular mass areas. Saccular otolith masses reached adult values at embryonic stage E12 and utricular areas reached adult values at post-hatch day 7. Mature individual otoconia were characterized by a barrel shape with two trihedral faceted ends. However, initial formation of otoconia at E5 (saccular) and E6 (utricular) maculae was characterized by a double fluted morphology that consisted of an hourglass shape with extended fins forming trihedral angles of 120 degrees. Double fluted otoconia rapidly filled, so that by embryonic day 8 mature otoconia dominated the maculae for the remainder of development through adulthood. Thus, a progression from double fluted to mature forms was noted. Mature utricular otoconia in adult quails averaged 11 microm in length and 5 microm in width, with length/width ratios of approximately 2.5:1, for all size ranges. Saccular otoconia were smaller, having about 70% the size of utricular otoconia in both length and width. During development, the average size and range of individual otoconia increased nearly linearly for both otolith organs. In the utricular macula, large otoconia were concentrated in the lateral regions of the epithelium. In contrast, otoconia of various sizes were distributed uniformly across the surface of the saccular macula.

Histological preparation of developing vestibular otoconia for scanning electron microscopy

The unique nature of vestibular otoconia as calcium carbonate biominerals makes them particularly susceptible to chemical deformation during histological processing. We fixed and stored otoconia from all three otolith endorgans of embryonic, hatchling and adult Japanese quail in glutaraldehyde containing either phosphate or non-phosphate buffers for varying lengths of time and processed them for scanning electron microscopy. Otoconia from all age groups and otolith endorgans processed in 0.1 M phosphate buffer (pH 7.4) showed abnormal surface morphology when compared to acetone fixed controls. Otoconia processed in 0.1 M sodium cacodylate or HEPES buffered artificial endolymph (pH 7.4) showed normal morphology that was similar to controls. The degree of otoconial deformation was directly related to the time exposed to phosphate buffer. Short duration exposure produced particulate deformations while longer exposures resulted in fused otoconia that formed solid sheets. Otoconial surface deformation and fusing was independent of the glutaraldehyde component of the histological processing. These findings should help vestibular researchers to develop appropriate histological processing protocols in future studies of otoconia.

Mathematical model of the evolution of statoconia

A mathematical model of the evolution of statoconia in statocysts of freshwater snails based on the analysis of experimental data [Wiederhold et al., 1990; Pedrozo et al., 1996; Gao et al., 1997; Gao and Wiederhold, 1997; Wiederhold et al., 1999] is proposed. The growth of statoconia is considered as the process of solution crystallization. The model proposed assumes that two main processes determine the evolution of statoconia in developing snails: the generation of new statoconia and the linear growth of statoconia sizes. The analytical solution of the model and qualitative comparison of theoretical results with the experimental data show: (1) there are at least three periods of statoconia evolution; (2) the generation of new statoconia mainly determines the first period of evolution when the shell diameter of snails D < 4 mm; (3) when D > 6 mm the size distribution of statoconia is determined by the growth of their sizes with a constant rate; (4) on the interval deltaD = 4-6 mm the transformation of size distribution with selective dissolution of statoconia takes place. The model agrees well with the experimental data and makes it possible to estimate some parameters of the statoconia kinetics. Additional experiments, which are necessary for further development of the model, and quantitative estimates of the mechanisms of statoconia evolution are formulated.