Proportional inhibition in the cricket medial giant interneuron.

Inhibitory effects on the number of wind-evoked impulses were studied in the medial giant interneuron of the cricket, Gryllus bimaculatus. The interneuron receives an inhibitory input from wind receptors on cercus ipsilateral to its soma. Using a dual channel wind stimulator, the intensity of inhibitory input was changed over 1,000-fold and effects on the number of spikes were observed. The ipsilateral inhibition reduced the number of outgoing spikes from a level elicited by excitation alone and it did so in proportion to the level of wind responsiveness displayed by each cell. A proportional coefficient of inhibition was derived and its value depended on the level of total excitation of the medial giant interneuron. The medial giant interneurons with high excitation showed a smaller value of the coefficient than those with low excitation. The proportional inhibition of the medial giant interneuron by the ipsilateral cercus suppresses the number of its spikes to a reasonable level for a wide range of stimulus intensities under natural conditions.

Analysis of neural spike trains with interspike interval reconstruction.

As a method for the analysis of neural spike trains, we examine fundamental characteristics of interspike interval (ISI) reconstruction theoretically with a leaky-integrator neuron model and experimentally with cricket wind receptor cells. Both the input to the leaky integrator and the stimulus to the wind receptor cells are the time series generated from the Rossler system. By numerical analysis of the leaky integrator, it is shown that, even if ISI reconstruction is possible, sometimes the entire structure of the Rössler attractor may not be reconstructed with ISI reconstruction. For analysis of the in vivo physiological responses of cricket wind receptor cells, we apply ISI reconstruction, nonlinear prediction and the surrogate data method to the experimental data. As a result of the analysis, it is found that there is a significant deterministic structure in the spike trains. By this analysis of physiological data, it is also shown that, even if ISI reconstruction is possible, the entire attractor may not be reconstructed.

Change of motion and localization of cholesterol molecule during L(alpha)-H(II) transition.

Formation of the inverted hexagonal (H(II)) phase from the lamellar (L(alpha)) phase of bovine brain-extracted phosphatidylcholine (BBPC) and phosphatidylethanolamine (BBPE) was investigated using 31P-NMR with or without cholesterol. When the ratio of BBPC to BBPE was 1:1, the H(II) formation was observed in the presence of 33 mol% cholesterol (i.e., BBPC:BBPE:cholesterol = 1:1:1) at 47 degrees C. The fraction of the H(II) phase in the BBPC/BBPE/cholesterol system could be controlled by the addition of dioleoylglycerol. The change of molecular motion of cholesterol affected by the H(II) formation was measured at various ratios of the L(alpha) to H(II) phase with the time-resolved fluorescence depolarization method, using dehydroergosterol as a fluorescent probe. It is observed that the motion of cholesterol became vigorous in the mixture state of the L(alpha) and the H(II) phases compared to that in the L(alpha) or the H(II) phase only. These facts show that cholesterol has the strong ability to induce the H(II) phase, probably by special molecular motion, which includes change of its location from the headgroup area to the acyl-chain area.

Restricted motion of photoexcited bacteriorhodopsin in purple membrane containing ethanol.

The molecular motion of retinal within the purple membrane was investigated by flash-induced absorption anisotropies with or without ethanol. In the absence of ethanol, the measured anisotropies at several wavelengths exhibited almost the same slow decay. This slow decay was attributed to only the rotation of purple membrane sheet itself in the aqueous suspension. In the presence of ethanol, however, we observed the wavelength-dependent anisotropies. The fluidity of the purple membrane, investigated with a fluorescence anisotropy method, was increased by the addition of ethanol. These facts indicated that the characteristic motion of bacteriorhodopsin is induced in perturbed purple membrane with ethanol. The data analysis was performed, taking account of the overlapping of absorption from ground-state bacteriorhodopsin and photointermediates. The results showed that the rotational motion of photointermediates within the membrane was more restricted than that of nonexcited bacteriorhodopsin. The addition of ethanol facilitated the rotation of nonexcited protein, whereas it did not significantly affect the motion of photointermediates. The restricted motion of photointermediates is probably caused by a conformational change in them, which may hinder the rotation of monomer protein and/or induce the interaction between photointermediate and neighboring proteins.

Culture temperature affects the molecular motion of bacteriorhodopsin within the purple membrane.

We measured the absorption anisotropies of bacteriorhodopsin (bR) within a purple membrane suspension after photo-excitation in the millisecond time range. The purple membranes used were isolated from Halobacterium salinarium grown at three different culture temperatures, 37.0, 43.0 and 47.5 degrees C. For the membranes from the 37.0 degrees C culture, the observed anisotropies at wavelengths of 410, 570 and 680 nm showed almost the same slow decay. The slow decaying of the anisotropies originated from the rotation of the membrane itself. Using the membranes from the 43.0 and 47.5 degrees C culture, however, we found that the anisotropy change varied at each wavelength measured. In these cases, it is shown from detailed data analysis that 1) the rotational motion of photo-intermediates within the membrane is more restricted than that of non-excited bR and 2) the distorted arrangements of the proteins within the membrane remain, even after photo-intermediates return to ground-state bR. This restricted motion is probably caused by the conformational changes in photo-intermediates, which prevent the rotation of the monomer protein and/or lead photo-intermediates to bind with neighboring proteins.

The molecular motion of bacteriorhodopsin mutant D96N in the purple membrane.

We measured the flash-induced absorption anisotropies of mutant bacteriorhodopsin (bR), D96N, in the purple membrane suspension. The measured anisotropy decay at 410 nm differed from that at 570 nm. These wavelength-dependent anisotropies show that the motion of absorption dipole of non-excited bR is faster than that of M-intermediate. The motion of non-excited bR is considered as the rotational motion of whole protein in the purple membrane. This fact suggests that the photo-excitation induces the conformational change of the protein and/or the inter-protein interaction within the membrane, which prevents the motion of M-intermediate.

The fertilization potential provides a fast block to polyspermy in lamprey eggs.

At fertilization, the membrane potential of the egg of the lamprey, Lampetra japonica, shifted rapidly from its resting value of -12 to +36 mV and gradually returned to about the same resting level (fertilization potential). The amplitude of depolarization was influenced by the external Cl- concentration and by an anion channel blocker, DIDS, indicating that the positive shift of membrane potential resulted from Cl- efflux. A similar change in membrane potential (activation potential) was observed when the unfertilized egg was pricked with a fine needle or treated with A23187 to induce parthenogenetic activation. Pricking at the animal pole region (predetermined site for sperm entry) resulted in the occurrence of an immediate activation potential and the initiation of cortical granule exocytosis. A time lag between the pricking and the occurrence of the activation potential was observed when the egg was pricked at a distance from the animal pole. In this instance, the activation potential was produced immediately before the propagating cortical granule exocytosis initiated at the pricked site reached the animal pole region. Sperm-egg fusion was blocked in eggs voltage-clamped at +20 to +40 mV and inseminated, whereas it took place in eggs clamped at -60 to 0 mV. However, most eggs clamped at +20 to +40 mV did activate, indicating that the voltage dependence of egg activation differs from that of sperm-egg fusion. Although eggs voltage-clamped at negative membrane potentials permitted multiple sperm to fuse with the egg plasma membrane, the nucleus of the fused sperm did not necessarily enter the ooplasm. We conclude that: (1) A fast electrical block against polyspermy operates in this species and is effective for about 160 sec of the onset of the positive shift; (2) the opening of Cl- channels is responsible for the potential change; (3) the channels are largely localized in the animal pole region; (4) during voltage clamp at positive potentials, eggs can be activated without sperm-egg fusion; and (5) during voltage clamp at negative potentials, sperm-egg fusion occurs, but sperm entry into the egg cytoplasm does not always proceed.

Effects of aging on the cardiopulmonary receptor reflex in hypertensive patients.

In order to evaluate the effects of aging on cardiopulmonary receptor function in hypertensive patients, hemodynamic responses after unloading were studied in middle aged and older hypertensive patients. Twenty-one hypertensive patients were divided into 2 groups according to age. The younger group consisted of 9 patients less than 65 years old (mean age: 57.2 years) and the older group contained 12 patients more than 65 years old (77.2 years). Following 10 min rest, deactivation of cardiopulmonary receptors was obtained by reducing central venous pressure through the application of graded negative pressures of -10, -20, and -40 mmHg to the lower body. Blood pressure, pulse rate, and forearm blood flow were measured at baseline and at each level of negative pressure. Furthermore, plasma norepinephrine and plasma renin activity levels were measured at baseline and at -40 mmHg. Forearm blood flow was measured by venous occlusive plethysmography using a Silastic strain gauge applied around the forearm. Forearm peripheral vascular resistance was calculated by dividing the mean arterial pressure by the forearm blood flow. Baseline mean blood pressure, pulse rate, and peripheral vascular resistance were similar in both age groups. Following lower body negative pressure (LBNP), mean blood pressure and pulse rate did not change, suggesting the selective deactivation of cardiopulmonary receptors. The increase in peripheral vascular resistance at LBNP of -40 mmHg in the older group (20.0 +/- 6.2) was significantly lower than that in the younger group (15.5 +/- 8.9, p less than 0.05). Furthermore, the increase in peripheral vascular resistance after LBNP was inversely related to age (Y = -0.32X + 38.8, r = -0.43, p less than 0.05). Increases in plasma norepinephrine and plasma renin activity in the older group were not different from those in the younger group. It is concluded that the sensitivity of cardiopulmonary baroreceptor function in hypertensive patients deteriorates with increasing age.

Cardiac performance in elderly hypertensive patients with left ventricular hypertrophy: responses to isometric exercise and beta-agonists.

To assess the cardiac functional reserve of elderly hypertensive patients with left ventricular hypertrophy (LVH) we studied cardiac function after isometric exercise and beta-adrenergic stimulation. Forty-five elderly hypertensive and 16 normotensive patients (NC group) were recruited for the study. The hypertensive patients were divided into two groups: those with LVH (n = 17) mass index (LV mass index greater than 130 g/m2; H1 group) and those without LVH (n = 28) (H2 group). Echocardiographic studies were performed before and after isometric exercise (handgrip) and isoproterenol (ISP) administration. We measured the LV mass index, fractional shortening (FS), isovolumic relaxation time (IRT), and the ratio of late and early diastolic transmitral flow velocity (A/E). The FS at rest in the H1 group was significantly higher than those in the H2 and NC groups. In the H1 group, the IRT was elongated and A/E was greater than in the NC group, which indicated the impaired diastolic function in the H1 group. After the HG stress, the FS in the H1 group significantly decreased whereas it did not change in the H2 or NC groups. The FS increased in all three groups after the infusion of ISP, although the increment of FS was smaller in the H1 group. In conclusion, (a) diastolic function was impaired whereas systolic function was supranormal at rest in the hypertrophied heart of the elderly hypertensive patients and (b) when exercise or pharmacological stress was loaded, the systolic function deteriorated, suggesting the impairment of cardiac reserve in those patients.

Suppression of inherited muscle degeneration in a Drosophila mutant by mechanical and genetical immobilizations.

The aperC (abnormal proboscis extension reflex C) mutation of Drosophila causes the degeneration of a particular pair of head muscles involved in the proboscis extension. To define the mechanisms underlying the muscle degeneration, we studied the influence of use or disuse on the muscle degeneration by two kinds of immobilization experiments. In the first experiment, the rostrum was fixed onto the cranium and the extension of the proboscis was mechanically prevented. In the second experiment, we created an aperC aperA double mutant, genetically preventing proboscis extension with the aperA mutation. Both immobilizations suppressed the muscle degeneration in aperC mutant flies.

Auditory space representation in the superior colliculus of the big brown bat, Eptesicus fuscus.

The auditory response areas of 123 superior collicular (SC) units of Eptesicus fuscus were studied under free-field acoustic stimulus conditions. A stimulus was delivered from a loudspeaker placed 14 cm in front of a bat. The best frequency of a unit was determined by changing the stimulus frequency until the minimum threshold was measured. A best frequency stimulus was then delivered as the loud-speaker was moved across the auditory space to determine the response center of the auditory response area of each unit. The response center was defined as the direction at which the unit had its lowest minimum threshold. The stimulus intensity was then raised 2-20 dB above the lowest minimum threshold of the unit and the response area for each stimulus intensity was determined. The response area of a unit expands with stimulus intensity, but the expansion is not even in all directions. The size of the response area of a unit does not correlate with its minimum threshold, best frequency, or recording depth. Response centers of 7 units were located directly in front of the animal, but most response centers were located in a limited portion of the contralateral auditory space. Although each unit has a response center which is the point of maximal sensitivity, the point-to-point representation of the auditory space is not systematically organized. We suggest that an animal with highly mobile external pinnae may not need an orderly auditory space map in its neural tissue for accurate sound localization.

The ecdysis of hair mechanoreceptors in crayfish.

The fine structure of hair mechanoreceptors in crayfish during moulting was investigated with special attention to the interface apparatus between cuticular hairs and sensory cells: the chorda. The chordae are lost with old exuviae at every moulting. They are drawn out from a moulting canal at the tip of the new hair. The chordae are regenerated from a material secreted by sheath cells after moulting. Therefore, the chorda is an inward projection of the cuticular exoskeleton, and it has direct contact with the sensory element, the scolopidium. The scolopidium has been found in both hair mechanoreceptors and subcuticular chordotonal organs in crustaceans, and is thought to be a primitive type of mechano-sensory transducing element. The present observation gives additional evidence for the homology of two sensory elements in arthropods, i.e., the cuticular hair sensilla and subcuticular chordotonal organs.

Lucifer yellow, neuronal marking and paraffin sectioning.

An unusual procedure with the dye lucifer yellow has provided stable neuronal marking that survives paraffin embedding and sectioning. Lucifer yellow CH was dissolved in an electrolyte containing formaldehyde and injected into the large interneurons of a cricket. Intense fluorescence in the axoplasm was retained even after conventional histological procedures.

The structure of the a hair mechanoreceptor in the antennule of crayfish (Crustacea).

In this study we examine the fine structure of mechanosensory hairs in the antennule of crayfish. The sensory hair is a stiff shaft with feather-like filaments. The hair's base is a large expansion of membrane which allows the hair shaft to deflect. The sensory transducing elements are located far from the hair, but are coupled mechanically with the hair shaft by a fine extracellular chorda. The sensory element is a type of scolopidium which consists of a scolopale cell and three sensory cells with a 9 + 0 type ciliary process. This type of scolopidium is characteristic of the chordotonal organ that has no cuticular structure on the surface of the exoskeleton. In this crustacean hair receptor, the deflection on the cuticular hair is transmitted through the chorda to the scolopidium which is a tension-sensitive transducer. The present study reveals that the mechanosensory hair of decapod crustaceans is a chordotonal organ accompanied by a cuticular hair structure. We also discuss comparative aspects of cuticular and subcuticular chordotonal organs in arthropods.

Site of neural attenuation of responses to self-vocalized sounds in echolocating bats.

Bats of the genus Myotis emit intense orientation sounds for echolocation. If such sounds directly stimulated their ears, the detection of echoes from short distances would be impaired. In addition to the muscular mechanism in the middle ear, the bat has a neural mechanism in the brain for attenuation of responses to self-vocalized orientation and nonorientation sounds. This neural attenuating mechanism operates in the nucleus of the lateral lemniscus, reducing its activity by about 15 decibels, and it is synchronized with vocalization.