The motion of the cupula in the supra-orbital lateral line canal of the ruff in response to sinusoidal water movements was measured in vivo by means of a novel laser interferometer microscope. The ...interferometer utilized the laser light scattered back from a small bead (phi approximately equal to 1 micron) which was positioned under visual control on a selected location inside the cupula. The displacement of the cupula was measured in the range of 0.3 to 300 nm. The stimulus-response relation is found to be linear in this range. The frequency response of the cupula measured at the top is identical to that measured at the base near the sensory hair bundles. From this result it is concluded that the cupula is sliding over the sensory epithelium during motion in the physiological displacement range. A hydrodynamical model of cupular motion which incorporates a frequency dependent boundary layer around the cupula is presented. The model accurately describes the experimental data.
The stimulus response relation of the epidermal lateral-line organ of Xenopus laevis was studied by recording activity of single afferent nerve fibres in isolated preparations. Linear frequency ...response analysis over a frequency range of 0.1--100Hz was performed under steady-state conditions, using small amplitude, sinusoidal water displacements produced by a glass sphere at a short distance from the skin. Period histograms of afferent nerve activity were computed, and amplitude, phase and mean activity of the response were determined by means of Fourier analysis. A standardization procedure at the start of each experiment made scaling of the frequency responses of different preparations unnecessary. The results show that for small stimulus amplitudes the response of the lateral-line organ over the whole range of frequencies studied can adequately be described as a modulation of the spontaneous activity. The amplitude of the response is proportional to the stimulus amplitude, and the phase of the response is independent of stimulus amplitude. The lateral-line organ of Xenopus laevis can thus be regarded as a linear system for stimuli which produce modulation of the spontaneous activity. The frequency response demonstrates unequivocally that the lateral-line organ of Xenopus laevis functions as a water velocity detector. For frequencies of stimulation from 0.1--20Hz the gain increases with a slope of 7.5 dB/oct, and up to 5Hz the response is almost in phase with the water velocity. The extent to which the different transmission steps between stimulus and response will contribute to the frequency response is discussed.
Myoelectric activity of the small intestine was recorded digitally in fasted, freely moving rats fitted with multiple pairs of electrodes in the antimesenterial smooth muscle. The electrodes were ...implanted under strict aseptic conditions to safeguard the animal's health and thereby benefit experimental results.
As in many other mammalian species, the fasted electrical and mechanical activity of the small intestine in the rat consists of alternating periods of activity and quiescence jointly called the Migrating Motility Complex (MMC). Existing methods for the analysis of small bowel myoelectric activity either integrate spike activity over longer periods of time or describe characteristics of single bursts. We have developed a computer program for fast, automated analysis that distinguishes the three characteristic phases of the MMC. The computer program recognizes periods of varying spike burst frequency and then produces a graphical and numerical output of the length and mean burst frequency of the different phases of each MMC that correlates well with the results of visual evaluation. The techniques used are discussed in relation to existing recording and analysis methods, and specific decisions in the program are motivated. The system will be a useful tool in assessing the effects of drugs, peptides, or stress on small bowel motility.
The effects of the inflammatory mediator prostaglandin E2 (PGE2) on myenteric neurons were investigated by intracellular recordings in a conventional plexus preparation. Bath application of PGE2 ...(1-1,000 nM) evoked a concentration-dependent and reversible slow depolarization and an augmentation of excitability in 23 of 26 AH and 12 of 13 S neurons. The amplitude of the slow depolarization ranged from 4 +/- 1 mV at 1 nM to 13 +/- 3 mV at 1 microM in S and AH neurons. In AH neurons, PGE2 evoked an increase in membrane resistance and a reduction of afterhyperpolarization. In S neurons, PGE2 evoked either an increase or a decrease in membrane resistance. PGE2 slightly reduced the amplitude of electrically evoked fast excitatory postsynaptic potentials and had no effect on slow excitatory postsynaptic potentials. Moreover, PGE2 evoked bursts of fast excitatory postsynaptic potentials and action potentials in S neurons, indicative of cyclical neural activity in the myenteric plexus. It is concluded that the inflammatory mediator PGE2 can act as an excitatory neuromodulator of gastrointestinal motility through direct action on neurons in the myenteric plexus.
The isolated lateral-line organ of Xenopus laevis was used to study reversible effects of low concentrations of aminoglycoside antibiotics on sensory hair cell functioning. Extracellular receptor ...potentials and single fibre afferent nerve activity were recorded during stimulation of the lateral-line organ with sinusoidal water movements. The results show that dihydrostreptomycin in concentrations between 2.5 and 17.5 micrograms/ml caused an increase in spontaneous afferent nerve activity, probably by increasing the spontaneous transmitter release at the afferent synapse. In addition, the same concentrations of dihydrostreptomycin markedly affected the mechano-electric transduction process, resulting in a phase lag in th receptor potential, the magnitude of which increased with increasing concentration up to a value of 0.4 pi radians. The effect of dihydrostreptomycin on the amplitude of the receptor potentials depended on the stimulus frequency. Other aminoglycoside antibiotics, namely streptomycin, gentamycin and kanamycin, produced similar effects but at different concentrations. It is concluded that low concentrations of aminoglycoside antibiotics have a dual action upon the sensory hair cells. They increase the spontaneous activity by affecting the hair cell membrane and at the same time they impair the mechano-electric transduction process resulting in a large phase lag in the receptor potentials. The latter effect, which is antagonized by Ca2+, may be due to interference by the antibiotics with the mode of motion of the sensory hairs.
The effects of cholecystokinin (CCK-8) on myenteric S neurons were investigated by intracellular recording techniques, with the aim to determine the CCK receptor subtypes involved. CCK-8 (1-1000 nM) ...evoked concentration-dependent long-lasting excitatory responses in 45 of 54 neurons. CCK receptor antagonists were applied to 15 neurons in which CCK-8 evoked an excitatory response. In 5 of these neurons, application of the CCKA antagonist L-364,718 (100-500 nM) antagonized the action of CCK-8 and the CCKB antagonist L-365,260 (500 nM) had no effect. L-365,260 (100-500 nM) antagonized the CCK-8 induced response in 5 neurons, on which L-364,718 had no effect. In the other 5 neurons each antagonist (500 nM) partly inhibited the CCK-8 evoked excitation and application of both antagonists (500 nM) caused a complete blockade of the response to CCK-8. The selective CCKB receptor agonist CCK-8NS had similar excitatory effects as CCK-8, but only on the neurons in which CCK-8 evoked effects were antagonized by L-365,260. The results demonstrate that the excitatory effects of CCK-8 are mediated by both CCKA and CCKB receptor subtypes. Further, the results indicate that some neurons possess exclusively the CCKA or the CCKB receptor subtype, but others possess both subtypes.
