Spontaneous activity of hair cells of the snail statocyst and its changes during intracellular stimulation

The following conclusions were drawn from an electrophysiological study of statocyst hair cell activity inHelix lucorum using intracellular recording. The maximal input resistance of the receptors is observed with hyperpolarizing currents of not more than 0.1 nA, close in magnitude to that arising during inhibitory synaptic transmission. Background noise, a special type of activity of statocyst hair cells, is neither synaptic nor pacemaker in nature, but depends entirely on the degree of contact between the cilia and statoconia. The hair cells possess pacemaker properties which are manifested on depolarization. The zone of action potential generation of the receptors lies in the axon. Inhibitory interactions take place between hair cells, leading to the generation of IPSPs in their spontaneous activity, which do not disappear after division of the vestibular nerve.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 222–229, March–April, 1985.     

Hair Cell Interactions in the Statocyst of Hermissenda

Hair cells in the statocyst of Hermissenda crassicornis respond to mechanical stimulation with a short latency (<2 ms) depolarizing generator potential that is followed by hyperpolarization and inhibition of spike activity. Mechanically evoked hyperpolarization and spike inhibition were abolished by cutting the static nerve, repetitive mechanical stimulation, tetrodotoxin (TTX), and Co⁺⁺. Since none of these procedures markedly altered the generator potential it was concluded that the hyperpolarization is an inhibitory synaptic potential and not a component of the mechanotransduction process. Intracellular recordings from pairs of hair cells in the same statocyst and in statocysts on opposite sides of the brain revealed that hair cells are connected by chemical and/or electrical synapses. All chemical interactions were inhibitory. Hyperpolarization and spike inhibition result from inhibitory interactions between hair cells in the same and in opposite statocysts.     

Secondary hair cells and afferent neurones of the squid statocyst receive both inhibitory and excitatory efferent inputs

Summary Intracellular recordings were obtained from the hair cells and afferent neurones of the angular acceleration receptor system of the statocyst of the squid,Alloteuthis subulata. Electrical stimulation of the efferent fibres in the crista nerve (minor) evoked responses in all of the secondary hair cells recorded from (n=211). 48% of the secondary air cells responded with a small depolarization, 15% with a hyperpolarization, and 37% with a depolarization followed by a hyperpolarization. The depolarizations and hyperpolarizations had mean stimulus to response delays of 6.7 ms and 24 ms, and reversal potentials of about –1 mV and –64 mV, respectively. Both types of potential increased in amplitude, up to a point, when the stimulus shock was increased and facilitation and/or summation effects could be obtained by applying multiple shocks. These data, together with the fact that both responses could be blocked by bath application of cobalt or cadmium, indicate that the secondary hair cells receive both inhibitory and excitatory efferent inputs and that these are probably mediated via chemical synapses. No efferent responses were seen in the primary hair cells but both depolarizing and hyperpolarizing efferent responses were obtained from the afferent neurones.     

Sensory interaction in the snailHelix lucorum

The activity of hair cells of statocysts inHelix lucorum was investigated by means of intra- and extracellular recording, applying appropriate stimulation of the organs of balance, optic photoreceptors, and the chemoreceptors of the optic tentacle bulb. Mechanical stimulation of the statocysts evoked a firing reaction in the hair cells as a result of generator potentials occurring at the receptors. The amplitude of generator potentials was proportional to the intensity of the reaction. Stimulating the optic photoreceptors by switching on a light produced a spike response in the hair cells with a short latency of 0.3–2 sec. The latent period of this response was inversely proportional to the intensity of the light. Appropriate stimulation of the chemoreceptors of the optic tentacle bulb caused a faint spike response with a long latent period of 20–40 sec in the hair cells. Illumination and stimulation of the chemoreceptors produced an inhibitory response in the form of bursts of IPSP in 2 out of more than 50 hair cells.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 17–26, January–February, 1986.     

Changes in the direction of vestibulomotor response in the course of adaptation to protracted static head turning in man

Vestibulomotor response during the course of adaptation to prolonged (10 min) static head turning to the furthest limit was investigated in healthy subjects standing upright with the eyes closed. The head was either actively or passively maintained in this position. The sensation of a decline in the angle of head turning was experienced during adaptation to the position by five of the 12 subjects tested. Error in appreciating this angle ranged up to 70–80°. Matching changes occurred in the direction of vestibulomotor response to electrical stimulation of the vestibular apparatus. When true and perceived head position conflict, direction of vestibulomotor response thus matches spatial perception rather than actual orientation of the head.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 210–217, March–April, 1989.     

Efferent activity in theOctopus statocyst nerves

Summary Single unit electrophysiological recordings were obtained from efferent fibres in the statocyst nerves ofOctopus vulgaris. A preparation comprising the CNS and a single statocyst was employed. 42% of the efferents displayed a level of resting activity; transient changes in this activity occurred at irregular intervals.The responses of the efferent units were examined during sinusoidal oscillations of the statocyst at stimulus frequencies between 0.01–1 Hz, and amplitudes up to 35°. 84% of the units showed activity synchronised with the imposed oscillations; the time taken to establish this response varied for different units (Fig. 1).The lowest stimulus frequency at which a unit could be entrained varied for different units, with those units with a resting level of activity having the lowest thresholds. The peak firing frequency of the efferents was found to increase with increasing stimulus frequency or amplitude (Fig. 3). However, the change in firing frequency was much smaller than that reported for the statocyst afferents to similar stimuli.The efferent units of the posterior crista nerve were found to respond to clockwise or anticlockwise rotations (Fig. 4), with the individual units having unipolar responses. The phase response of the units changed little with increasing stimulus amplitude but an increase in phase lag occurred with an increase in the stimulus frequency (Fig. 5). The form of this relationship (Fig. 6) was similar to that reported for the statocyst crista afferents.The principal source of the input to the efferents in these experiments was shown to be afferents from the contralateral statocyst. These results are discussed and compared with data from the vertebrate semicircular canal system.     

The cross-ply arrangement of collagen fibres in the submucosa of the mammalian small intestine

Summary Whole-mount preparations of the submucosa were made from the small intestine of rats, guinea-pigs, rabbits and sheep. In the distended intestine the collagen fibres ran straight and approximately parallel to the serosal surface. They formed a characteristic lattice, with two arrays of fibres running diagonally in a clockwise and an anticlockwise direction, and making an angle of 50°–55° with the longitudinal axis of the intestine. This collagenfibre lattice was flexible and changed with the movements of the intestinal wall; when the radial distension predominated, the angle between collagen fibres of the submucosa and longitudinal axis of the intestine increased to 60°–65°, and when the longitudinal distension predominated the angle decreased to about 30°.     

Stimulus-response properties of cricket cereal filiform receptors

The dynamic ranges and stimulus-response properties of a large sample of cereal filiform receptors in Acheta domesticus were investigated electrophysiologically. The relation between receptor response and stimulus velocity was a sigmoid function, the log-linear portion of which spanned 1–1.5 log units of peak air-current velocity. Different receptors responded over different but overlapping velocity ranges, such that the system velocity sensitivity range spanned at least 2.5 log units. Plots of receptor response amplitude vs. stimulus direction were sinusoidal, with a period of 360°. Long-hair receptors responded in phase with air-current velocity, and intermediate-hair receptors responded in phase with air-current acceleration. These results extend those of Shimozawa and Kanou (1984a) and Kämper and Kleindienst (1990), in which the dynamics of receptor responses were shown to depend on hair length. When individual hairs were directly mechanically deflected, their receptors responded in phase with the first derivative of hair deflection. The signal transform between the air-current stimulus and the receptor response is comprised of two processes, one biomechanical/aerodynamic and one membrane biophysical. The results of this study suggest that the parametric sensitivities of receptors are primarily determined by hair biomechanical/aerodynamic properties.Abbreviation IR infrared     

Dynamics of functional reciprocal connections between cerebral motor cortex neurons under stimulation in cats

Activity was recorded from neurons belonging to the representation of the forelimb in the motor cortex (sulcus cruciatus, L 7–9 mm) using multiple multi-channel/barrel electrodes during acute experiments on cats. Cross-correlation analysis of impulse trains was adopted to investigate dynamics of interneuronal connections during passive flexion and electrical stimulation of the limb contralateral to the recording site. It was found that neither passive bending nor electrical stimulation of the limb leads to a significant increase in the total number of direct relationships between cortical neurons. At the same time, passive flexion does produce a considerable decrease in the number of instances of both inputs operating in neighboring neurons (50–100 µm apart) and an increase in cells located further (between 100 and 400 µm) apart. Some increase in the number of direct inhibitory interactions between neighboring neurons was observed during electrical stimulation.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Nentskii Institute of Experimental Biology, Warsaw, Poland. Center of Experimental and Clinical Medicine, Warsaw, Poland. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 73–80, January–February, 1991.     

Structure and function of the Nautilus statocyst.

The two equilibrium receptor organs (statocysts) of Nautilus are avoid sacks, half-filled with numerous small, free-moving statoconia and half with endolymph. The inner surface of each statocyst is lined with 130,000-150,000 primary sensory hair cells. The hair cells are of two morphological types. Type A hair cells carry 10-15 kinocilia arranged in a single ciliary row; they are present in the ventral half of the statocyst. Type B hair cells carry 8-10 irregularly arranged kinocilia; they are present in the dorsal half of the statocyst. Both type of hair cells are morphologically polarized. To test whether these features allow the Nautilus statocyst to sense angular accelerations, behavioural experiments were performed to measure statocyst-dependent funnel movements during sinusoidal oscillations of restrained Nautilus around a vertical body axis. Such dynamic rotatory stimulation caused horizontal phase-locked movements of the funnel. The funnel movements were either in the same direction (compensatory funnel response), or in the opposite direction (funnel follow response) to that of the applied rotation. Compensatory funnel movements were also seen during optokinetic stimulation (with a black and white stripe pattern) and during stimulations in which optokinetic and statocyst stimulations were combined. These morphological and behavioural findings show that the statocysts of Nautilus, in addition to their function as gravity receptor organs, are able to detect rotatory movements (angular accelerations) without the specialized receptor systems (crista/cupula systems) that are found in the statocysts of coleoid cephalopods. The findings further indicate that both statocyst and visual inputs control compensatory funnel movements.     

Neurite growth and formation of connections in pteropodial mollusk neurons in culture

Neurons from the peripharyngeal nerve ring detached from the pteropodial molluskClione limacina were cultured in polylysine prepared in a 25% Leibovitz saltwater medium containing 2% embryonic calf serum. Neurite outgrowth was observed in a proportion of the neurons, reaching its peak rate during the first three days. Neurites grew up to 300 µm in length. Membrane potential of the neurons measured 40–60 mV. The latter generated either single action potentials or volleys of spikes. Neural connections between 70 pairs of cells with overlapping neurites were investigated on days 3–4. An electrical connection was discovered between cells in 20% of the pairs examined and, in 6%, stimulating one neuron of a pair produced an inhibitory postsynaptic potential in the other.Institute of Information Transmission Research, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 81–86, January–February, 1987.     

Reception of millimeter-band electromagnetic radiation by the ampullae of Lorenzini of skates

During recording of impulse activity from single nerve fibers of electroreceptors of the ampullae of Lorenzini of skates, we studied the responses to electromagnetic radiation (EMR) at a frequency of 37–55 GHz and an intensity of 1–100 mW/cm².Exposure of the ampullar canal pore to EMR at an intensity of 1–5 mW/cm² and a distance of 1–10 mm evoked a transient increase in the frequency of low-threshold receptor activity (current threshold was 0.04–0.2 µA). An increase in EMR intensity by more than 8–10 mW/cm² produced, together with elevation of receptor activity, an inhibition due to a rise in temperature of 1–3°C in the region exposed. The phase of increase in frequency of activity was absent in high current-threshold receptors (0.3–2.0 µA) when exposed to EMR. The receptors responded to irradiation of the ampullar canal pore at a distance of 15–20 mm by an increase in discharge frequency for 20 min. Direct irradiation of the ampullae of Lorenzini induced only inhibitory responses in receptor cells regardless of their excitability.The results obtained indicate that the sensory receptors of vertebrates are sensitive to EMR. It is concluded that the excitatory effects are due to direct reception of EMR by electroreceptors, and the inhibitory effects are related to local heating of the Lorenzini ampullar pore.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 325–329, September–October, 1993.     

Structure and kinematics of the prosternal organs and their influence on head position in the blowfly Calliphora erythrocephala Meig.

Summary The blowfly Calliphora has a mobile head and various, presumably proprioceptive, sense organs in the neck region. The prosternal organs are a pair of mechanosensory hair fields, each comprising ca. 110 sensilla. We studied their structure (Figs. 2–4), kinematics (Figs. 5, 6) and, after surgery, their influence on head posture (Figs. 7–11) in order to reveal their specific function.The hair sensilla are structurally polarized, all in roughly the same direction, and are stimulated by dorsoventral bending of the hairs (Figs. 3, 4). This occurs indirectly by flap-movements of two contact sclerites (Figs. 3, 6); they move in the same direction during pitch turns of the head, in opposite directions during roll turns, and barely at all during yaw turns of the head (Fig. 5).Bending and arresting all hairs of one field elicits a head roll bias to the non-operated side (Fig. 7) during tethered flight in visually featureless surroundings. In contrast, shaving all hairs of one field elicits a head roll to the operated side (Figs. 8–10). The surgically induced bias of head posture is not compensated within three days (Fig. 10). Our results show that the prosternal organs of Calliphora sense pitch and roll turns of the fly's head, and control at least its roll position.Abbreviations HP° TP° angular positions of the sagittal planes of the fly's head and thorax, respectively, relative to an external reference - HR° = HP — TP head roll angle of the fly's head relative to its thorax, HR>0° for clockwise head roll, looking in flight direction - N number of flies - n number of measurements - PO prosternal organ - SD standard deviation - SEM standard error of the mean     

The responses of primary and secondary sensory hair cells in the squid statocyst to mechanical stimulation

Summary Intracellular recordings were obtained from primary and secondary sensory hair cells in the anterior transverse crista segment of the squid (Alloteuthis subulata) statocyst during imposed displacements of the overlying cupula. The secondary sensory hair cells were depolarized by ventral movements of the cupula and hyperpolarized by dorsal cupula movements. The displacement/response curve was asymmetric around the zero position and sigmoidal in shape, similar to that already described for vertebrate hair cells. The cells are estimated to have a sensitivity of at least 0.5 mV per degree angle of cilia displacement. The responses showed pronounced adaptation and could be blocked by bath applied alcohols, such as heptanol or octanol, or by high concentrations of aminoglycosides.The primary sensory hair cells were depolarized by dorsal movements of the cupula, usually responding with a burst of action potentials. The displacement/response curve was also sigmoidal in shape and the firing pattern showed strong adaptation to maintained displacements of the cupula.The cupula itself appeared to be irregular in shape, extending much further into the statocyst cavity in its central part than at its edges. This is likely to result in differences in the responses of the underlying hair cells along the length of the crista ridge.     

Bicercal model of the mechanism for consistency in directional detection of mechano-acoustic signals in insects

A model of signal processing in the insect mechano-acoustical cercal system is considered which maintains consistency in the directional detection of air flow and in relation to the position of the sensory organs (cerci) by means of connections between four central neurons and certain groups of receptors located on both cerci. The monocercal mechanism for consistency in directional detection described previously [2–4, 8], according to the data available, would indicate changes in the effectiveness of connections between the central neurons and the receptors belonging to each cercus depending on the location of the latter. One distinguishing feature examined in this article on the bicercal consistency mechanism is that it shapes neither regulation of connections between neural elements nor use of information acquired on the position of the sensory organs at the moment of signal perception. The model is based on the two following properties of the cercal system: firstly, the presence on each cercus of receptors with preferred directions of stimulation, namely parallel and perpendicular to the axis of the cercus, and secondly, symmetrical location of the two cerci in relation to that of the insect's body. A method is suggested for determining direction of the air flow equating to calculation of this factor by projecting the velocity vector against the two unvarying basic directions — alignments which do not change when the cerci move symmetrically together and apart.Institute for Information Transmission Studies, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 53–61, January–February, 1987.     

Optimal Electrical Properties of Outer Hair Cells Ensure Cochlear Amplification

The organ of Corti (OC) is the auditory epithelium of the mammalian cochlea comprising sensory hair cells and supporting cells riding on the basilar membrane. The outer hair cells (OHCs) are cellular actuators that amplify small sound-induced vibrations for transmission to the inner hair cells. We developed a finite element model of the OC that incorporates the complex OC geometry and force generation by OHCs originating from active hair bundle motion due to gating of the transducer channels and somatic contractility due to the membrane protein prestin. The model also incorporates realistic OHC electrical properties. It explains the complex vibration modes of the OC and reproduces recent measurements of the phase difference between the top and the bottom surface vibrations of the OC. Simulations of an individual OHC show that the OHC somatic motility lags the hair bundle displacement by ∼90 degrees. Prestin-driven contractions of the OHCs cause the top and bottom surfaces of the OC to move in opposite directions. Combined with the OC mechanics, this results in ∼90 degrees phase difference between the OC top and bottom surface vibration. An appropriate electrical time constant for the OHC membrane is necessary to achieve the phase relationship between OC vibrations and OHC actuations. When the OHC electrical frequency characteristics are too high or too low, the OHCs do not exert force with the correct phase to the OC mechanics so that they cannot amplify. We conclude that the components of OHC forward and reverse transduction are crucial for setting the phase relations needed for amplification.     

Intersensory Interactions in Hermissenda

Hair cells of the Hermissenda statocyst respond to photic stimulation. This response requires the presence of at least one of the two eyes. Two principal hair cell responses to light were observed. The activity of photoreceptors in response to a light step is interrupted during firing of contralateral hair cells. The intersensory interactions between the statocyst and visual pathway underlying these responses were examined with simultaneous intracellular recordings. Evidence is presented that the statocyst of Hermissenda is an important channel for visual information.     

Direction sensitivity of the filiform hair population of the cricket cereal system

Each cercus on the adult cricket Acheta domesticus bears 1000–2000 filiform hair mechanoreceptors. In order to determine the extent of identifiability of individual hair receptors, the structural characteristics of ten putative identified hairs were measured in 21–25 different animals. For these ten hairs, the sets of preferred directions and circumferential locations had standard deviations of 6.8° and 5.9°, respectively. There was no significant inter-animal covariance between a hair's preferred direction and its circumferential location. The preferred directions of 246 different identified hairs were then measured from 16 animals in order to characterize the distribution of preferred directions of hairs on a single typical cercus. These data were transformed from the frame of reference of the cercus into that of the cricket, generating an estimate of the representation of air-current stimulus direction provided by the entire ensemble of filiform hairs on both cerci. The distribution of hair directional sensitivities was continuous but extremely non-uniform, and more complex than previous studies had suggested.Abbreviations MT medial-transverse - LT lateral-transverse - AL anterior-longitudinal - PL posterior-longitudinal - MAO medial-anterior-oblique - MPO medial-posterior-oblique - LAO lateral-anterior-oblique - LPO lateral-posterior-oblique - T transverse - L longitudinal - O oblique - CNS central nervous system     

Spatio-temporal convergence (STC) in otolith neurons

It has been recently demonstrated that some primary otolith afferents and most otolith-related vestibular nuclei neurons encode two spatial dimensions that can be described by two vectors in temporal and spatial quadrature. These cells are called broadly-tuned neurons. They are characterized by a non-zero tuning ratio which is defined as the ratio of the minimum over the maximum sensitivity of the neuron. Broadly-tuned neurons exhibit response gains that do not vary according to the cosine of the angle between the stimulus direction and the cell's maximum sensitivity vector and response phase values that depend on stimulus orientation. These responses were observed during stimulation with pure linear acceleration and can be explained by spatio-temporal convergence (STC) of primary otolith afferents and/or otolith hair cells. Simulations of STC of the inputs to primary otolith afferents and vestibular nuclei neurons have revealed interesting characteristics: First, in the case of two narrowly-tuned input signals, the largest tuning ratio is achieved when the input signals are of equal gain. The smaller the phase difference between the input vectors, the larger the orientation differences that are required to produce a certain tuning ratio. Orientation and temporal phase differences of 30–40° create tuning ratios of approximately 0.10–0.15 in target neurons. Second, in the case of multiple input signals, the larger the number of converging inputs, the smaller the tuning ratio of the target neuron. The tuning ratio depends on the number of input units, as long as there are not more than about 10. For more than 10–20 input vectors, the tuning ratio becomes almost independent of the number of inputs. Further, if the inputs comprise two populations (with different gain and phase values at a given stimulus frequency), the largest tuning ratio is obtained when the larger population has a smaller gain. These findings are discussed in the context of known anatomical and physiological characteristics of innervation patterns of primary otolith afferents and their possible convergence onto vestibular nuclei neurons.     

Cheese whey: an alternative growth and protective medium for<Emphasis Type="Italic"> Rhizobium loti</Emphasis> cells

Cheese whey (CW)-based growth medium efficiently protects Rhizobium loti cells during freezing and desiccation and can maintain their growth in a manner similar to that of traditional mannitol-based medium (YEM). The cheese-whey-based medium (CW) improved viability when used to re-suspend cell pellets kept at –20 °C and –80 °C and resulted in the survival of over 90% of the cells. Moreover, bacterial pellets obtained from cells grown in CW withstand desiccation better than cells grown in YEM. Survival was over 60% after 30 days at 4 °C. No differences were observed in nodulation efficiency between YEM-grown and CW-grown cells. Fast protein liquid chromatography (FPLC) protocols are presented for total protein profile analyses of sweet and acid cheese whey.In memoriam of Sylvio Cortina Vicepresident of Fundación COREPRO