Rapid responses of the cupula in the lateral line of ruffe (Gymnocephalus cernuus)

Source location encoding in the fish lateral line canal

The position of a hydrodynamic dipole source, as encoded in a linear array of mechano-detecting neuromasts in the fish lateral line canal, was electrophysiologically investigated. Measured excitation patterns along the lateral line were compared to theoretical predictions and were found to be in good agreement. The results demonstrate that information on the position of a vibrating source from a fish is linearly coded in the spatial characteristics of the excitation pattern of pressure gradients distributed along the lateral line canal. Several algorithms are discussed that could potentially be used by a fish to decode lateral line excitation patterns, in order to localise a source and its axis of vibration. Specifically, a wavelet transform of a 1-D excitation pattern is shown to reconstruct a 2-D image of dipole sources located within a distance comparable to the body length of a fish and with a close range spatial accuracy twice the inter-neuromast distance.

Hydrodynamic detection by cupulae in a lateral line canal: functional relations between physics and physiology

In the present review, signal-processing capabilities of the canal lateral line organ imposed by its peripheral architecture are quantified in terms of a limited set of measurable physical parameters. It is demonstrated that cupulae in the lateral line canal organ can only partly be described as canal fluid velocity detectors. Deviation from velocity detection may result from resonance, and can be characterized by the extent to which a single dimensionless resonance number, N ( r ), exceeds 1. This number depends on four physical parameters: it is proportional to cupular size, cupular sliding stiffness and canal fluid density, and inversely proportional to the square of fluid viscosity. Situated in a canal, a cupula may benefit from its resonance by compensating for the limited frequency range of water motion that is efficiently transferred into the lateral line canal. The peripheral transfer of hydrodynamic signals, via canal and cupula, leads to a nearly constant sensitivity to outside water acceleration in a bandwidth that ranges from d.c. to a cut-off frequency of up to several hundreds of Hertz, significantly exceeding the cut-off frequency of the lateral line canal. Threshold values of hydrodynamic detection by the canal lateral line organ are derived in terms of water displacement, water velocity, water acceleration and water pressure gradients and are shown to be close to the detection limits imposed by hair cell mechano-transduction in combination with the physical constraints of peripheral lateral line signal transfer. The notion that the combination of canal- and cupular hydrodynamics effectively provides the lateral line canal organ with a constant sensitivity to water acceleration at low frequencies so that it consequently functions as a low-pass detector of pressure gradients, supports the appropriateness of describing it as a sense organ that "feels at a distance" (Dijkgraaf in Biol Rev 38:51-105, 1963).

The effect of althesin, ketamine or pentothal on renal function in saline loaded rats

Rats were prepared with chronic cannulae in the carotid artery, jugular vein and urinary bladder; they were then kept 2 days to allow recovery from surgery. A steady-state continuous saline diuresis was established, then various anaesthetic agents were injected and changes in the urine flow, sodium and potassium excretion rates, GFR, ERPF, ERBF and blood pressure were measured. Five groups of rats were studied: (1) control animals given saline in place of any anaesthetic agent, all parameters measured remained constant; (2) althesin (1.2 mg/kg), all parameters remained constant except for the blood pressure which decreased slightly for 5 min; (3) althesin (12 mg/kg); (4) ketamine (50 mg/kg); (5) pentothal (50 mg/kg). The above anaesthetics altered all of the measured parameters except urine output. Various mechanisms for these anaesthetic agents are discussed. In althesin anaesthetized rats, all the retarded renal parameters recovered within 30 min. It is concluded that for the study of renal function, if a brief anaesthesia is needed, althesin is a more suitable anaesthetic agent.