The relationship between body size and evoked potentials from the statocysts of the prawn Palaemon serratus.

The organisation of the statocyst hair cells and auditory evoked potentials (AEPs) generated by the afferents in three body size classes of prawn (Palaemon serratus) have been studied using a combination of anatomical, electron microscopic and electrophysiological approaches. The statistical examination of the relationship between the sensory setae and body size showed an increase in both the length and number of statocyst hair cells as the animal grows. In view of this finding, the response of the statocyst organ to a 500 Hz tone burst was recorded from four specimens from each size class using two subcutaneous electrodes, positioned in the carapace close to the supraoesophageal ganglion and statocyst. Neither body size nor the number of afferents in the statocyst has any significant impact on the amplitude of AEPs in response to the 500 Hz tone burst. The findings of this study show that P. serratus is capable of hearing a 500 Hz tone regardless of body size, a finding that is of ecological importance when considering the effect of anthropogenic sound on crustaceans.

The inner ear ultrastructure from the paddlefish (Polyodon spathula) using transmission electron microscopy.

The structure of the hair cells on each sensory macula from the inner ear of the paddlefish (Polyodon spathula) was studied using scanning and transmission electron microscopy, revealing the nucleated cell bodies and peripheral nerve fibres of the saccule utricle and lagena. Examination of the structures within the cell body revealed comparable features with those found in the inner ear hair cells from bony fish species, although in P. spathula the afferent cell body is almost twice the size. This is the first time that the inner ear hair cells from an Acipenseriform fish have been studied using transmission microscopy, thus providing benchmark anatomical information in relation to the cellular morphology of the afferent receptors from a 'healthy' P. spathula ear. Structural information is of assistance in the study of aquatic animal hearing for environmental monitoring purposes, as morphological data can be used to confirm if evidence of raised hearing thresholds from animals exposed to intense anthropogenic noise or other destructive agents (determined using electrophysiological or behavioural techniques) are a direct result of damage to the ultrastructure of the inner ear.

The inner ear morphology and hearing abilities of the Paddlefish (Polyodon spathula) and the Lake Sturgeon (Acipenser fulvescens).

Concern regarding the spread of silver carp (Hypopthalmichthys molitrix) and bighead carp (Aristichthysc nobilis) through the Illinois River has prompted the development of an Acoustic Fish Deterrent (AFD) system. The application of this technology has resulted in a need to understand the auditory physiology of fish other than the target species, in order to minimise the effect of the AFD barrier on the ecology of indigenous fish populations. To this end, both the structures involved in sound reception and the hearing abilities of the paddlefish (Polyodon spathula) and the lake sturgeon (Acipenser fulvescens) are studied here using a combination of morphological and physiological approaches, revealing that both fish are responsive to sounds ranging in frequency from 100 to 500 Hz. The lowest hearing thresholds from both species were acquired from frequencies in a bandwidth of between 200 and 300 Hz, with higher thresholds at 100 and 500 Hz. The rationale for studying hearing in P. spathula and A. fulvescens in particular, is the value placed on them by both the commercial caviar producing industry and by the recreational fisheries sector. The hearing abilities of twelve P. spathula and twelve A. fulvescens were tested in sound fields dominated by either sound pressure or particle motion, with the results showing that acipenseriform fish are responsive to the motion of water particles in a sound field, rather than the sound pressure component. In this study, we measure the intensity of the sound field required to evoke threshold responses using a pressure sensitive hydrophone, as pressure dominated sound fields are the most audible acoustic condition for specialists like H. molitrix and A. nobilis (the target species). The results of the auditory examination clearly show that P. spathula and A. fulvescens are not sensitive to sound pressure, and will therefore have a significantly higher deterrent threshold than H. molitrix and A. nobilis in a pressure dominated sound field.

The polarisation of hair cells from the ear of the European bass (Dicentrarchus labrax).

The polarisation of ciliary bundles on the macula of the saccule in the European bass (Dicentrarchus labrax L) has been studied using a scanning electron microscope (SEM). These data show that D. labrax possesses ciliary bundles arranged in four dichotomous quadrants with a standard orientation, comparable to hearing generalists from the order Perciformes. The spacing between ciliary bundles was investigated in three size classes of fish, with the results indicating that the addition of receptor cells in the ear of D. labrax continues for at least the first 2 years of development. The lengths of the kinocilia from ciliary bundles in each quadrant of the macula were also studied, and found to be of uniform length. In addition, we look at the internal structure of the afferent using transmission electron microscopy (TEM), revealing the nucleated cell body and peripheral nerve fibres of the saccule consistent with other TEM examinations of saccular ultrastructure. This information is required to gain an insight into the inner ear of D. labrax, as part of a larger study of the morphology and physiology of the hearing systems of both vertebrate and invertebrate marine animals.

The hearing abilities of the prawn Palaemon serratus.

The mechanism of sound reception and the hearing abilities of the prawn (Palaemon serratus) have been studied using a combination of anatomical, electron microscopic and electrophysiological approaches, revealing that P. serratus is responsive to sounds ranging in frequency from 100 to 3000 Hz. It is the first time that the Auditory Brainstem Response (ABR) recording technique has been used on invertebrates, and the acquisition of hearing ability data from the present study adds valuable information to the inclusion of an entire sub-phylum of animals when assessing the potential impact of anthropogenic underwater sounds on marine organisms. Auditory evoked potentials were acquired from P. serratus, using two subcutaneous electrodes positioned in the carapace close to the supraesophageal ganglion and the statocyst (a small gravistatic organ located below the eyestalk on the peduncle of the bilateral antennules). The morphology of the statocyst receptors and the otic nerve pathways to the brain have also been studied, and reveal that P. serratus possesses an array of sensory hairs projecting from the floor of the statocyst into a mass of sand granules embedded in a gelatinous substance. It is the purpose of this work to show that the statocyst is responsive to sounds propagated through water from an air mounted transducer. The fundamental measure of the hearing ability of any organism possessing the appropriate receptor mechanism is its audiogram, which presents the lowest level of sound that the species can hear as a function of frequency. The statocyst of P. serratus is shown here to be sensitive to the motion of water particles displaced by low-frequency sounds ranging from 100 Hz up to 3000 Hz, with a hearing acuity similar to that of a generalist fish. Also, recorded neural waveforms were found to be similar in both amplitude and shape to those acquired from fish and higher vertebrates, when stimulated with low-frequency sound, and complete ablation of the electrophysiological response was achieved by removal of the statocyst.

Late surface opacification of Hydroview intraocular lenses.

PURPOSE: To describe clinical and pathological features of Hydroview intraocular lenses undergoing delayed surface opacification resulting in visual deterioration. METHODS: Twenty one eyes which underwent uncomplicated phacoemulsification and Hydroview lens implantation with good visual recovery, presenting at 46-146 weeks post-surgery with visual deterioration and glare symptoms resulting from opacification of the implants, were included in the study. Twelve eyes had severe opacification, of which nine underwent intraocular lens exchange and three more are still awaiting surgery. The method of explantation is described. The explanted intraocular lenses were examined using light microscopy, scanning electron microscopy and x-ray microanalysis using a light element detector. RESULTS: Light microscopy and scanning electron microscopy revealed diffuse granular deposits of approximately 5 microm diameter covering the optic surfaces but sparing the lens haptics. Light microscopic staining techniques and x-ray microanalysis confirm the major component of the deposits to be calcium phosphate salts. CONCLUSIONS: Late opacification of Hydroview intraocular lens implants is uncommon and aetiology seems to be multifactorial. Implant exchange is necessary to restore sight in some cases. As new materials are increasingly used it is important to highlight such unusual occurrences.