Long rise times of sound pulses in grasshopper songs improve the directionality cues received by the CNS from the auditory receptors

Auditory receptors of the locust (Locusta migratoria) were investigated with respect to the directionality cues which are present in their spiking responses, with special emphasis on how directional cues are influenced by the rise time of sound signals. Intensity differences between the ears influence two possible cues in the receptor responses, spike count and response latency. Variation in rise time of sound pulses had little effect on the overall spike count; however, it had a substantial effect on the temporal distribution of the receptor's spiking response, especially on the latencies of first spikes. In particular, with ramplike stimuli the slope of the latency vs. intensity curves was steeper as compared to stimuli with steep onsets (Fig. 3). Stimuli with flat ramplike onsets lead to an increase of the latency differences of discharges between left and right tympanic receptors. This type of ramplike stimulus could thus facilitate directional hearing. This hypothesis was corroborated by a Monte Carlo simulation in which the probability of incorrect directional decisions was determined on the basis of the receptor latencies and spike counts. Slowly rising ramps significantly improved the decisions based on response latency, as compared to stimuli with sudden onsets (Fig. 4). These results are compared to behavioural results obtained with the grasshopper Ch. biguttulus. The stridulation signals of the females of this species consist of ramplike pulses, which could be an adaptation to facilitate directional hearing of phonotactically approaching males.Abbreviations HFR high frequency receptor - ILD interaural level difference - LFR low frequency receptor - SPL sound pressure level - WN white noise     

Multisensory control of escape in the cockroach Periplaneta americana

1. All giant interneurons (GIs) were ablated from the nerve cord of cockroaches by electrocautery, and escape behavior was analyzed with high-speed videography. Animals with ablations retained the ability to produce wind-triggered escape, although response latency was increased (Table 1, Fig. 4). Subsequent lesions suggested that these non-GI responses depended in part on receptors associated with the antennae.
2. Antennal and cereal systems were compared by analyzing escape responses after amputating either cerci or antennae. With standard wind stimuli (high peak velocity) animals responded after either lesion. With lower intensity winds, animals lost their ability to respond after cereal removal (Fig. 6).
3. Removal of antennae did not cause significant changes in behavioral latency, but in the absence of cerci, animals responded at longer latencies than normal (Fig. 7).
4. The cercal-to-GI system can mediate short latency responses to high or low intensity winds, while the antennal system is responsive to high intensity winds only and operates at relatively longer latencies. These conclusions drawn from lesioned animals were confirmed in intact animals with restricted wind targeting the cerci or antennae only (Fig. 9).
5. The antennae do not represent a primary wind-sensory system, but may have a direct mechanosensory role in escape.

     

Escape reaction performance of myelinated and non-myelinated calanoid copepods

Calanoid copepods from seven families in three superfamilies were exposed to a controlled near-field hydrodynamic stimulus and their escape reactions were recorded using high-speed videographic techniques. Copepod species have two distinct mechanisms for increasing conduction speed of neural signals: larger diameter nerve axons and insulated axons, i.e., myelination. Myelinated axons have been found in certain species of the more recently-evolved calanoid superfamilies. Copepod representatives from these superfamilies were expected to have shorter response latencies than species from more ancestral superfamilies due to the increased conduction speed of nerve impulses in myelinated neurons. Using frame-by-frame playback and computerized motion analysis techniques, response latency, jump speed, and acceleration were measured. Kinetic performance of copepods was highly variable, with mean escape speeds ranging between 100-250 mm s^− 1 and accelerations of 9-230 m s^− 2. Minimum behavioral response latencies of 2 ms were recorded for both myelinated and non-myelinated calanoids. There was no significant difference between the response latencies of copepods from the myelinated and non-myelinated superfamilies. Furthermore, no relationships were found between copepod latency and size for either myelinated or non-myelinated species. Previous research may suggest that myelin may shorten the response latencies of certain calanoid species. However, our results show that non-myelinated copepods are also capable of responding rapidly, within as few as 2 ms, to hydrodynamic stimuli and produce similar kinetic performance to myelinated species. The main advantage of myelination over giant nerve axons is their more efficient transfer of nerve impulses resulting in a metabolic energy savings. Although this energetic reward would be important for copepods in food-limited environments, for coastal copepods, in food-rich habitats, either mechanism is a viable solution.     

Auditory sensitivity of the diencephalon of the leopard frogRana p. pipiens

Summary Evoked potentials were recorded from the posterocentral nucleus in the dorsal diencephalon of leopard frogs (Rana p. pipiens) in response to acoustic stimulation. This electrophysiological study confirms the anatomical study by Neary (1974) of the existence of an auditory area within this nucleus.The response of the auditory thalamic area showed a selectivity for stimuli that simultaneously excited both the amphibian and the basilar papillae in the inner ear. The magnitude of the evoked potential to the combination of either low (300 Hz) and high (1 700 Hz) or mid (600 Hz) and high (1700 Hz) frequency tones was much greater than the sum of the responses to the component tones individually (Fig. 5). This selective convergence is not seen in the torus semicircularis: in this midbrain center the sum of the responses to the individual tones is approximately equal to the magnitude of the response to the combination tone (Fig. 7).The selectivity of the thalamic center for stimuli with patterned energy distributions is compared to the spectral combinations occurring within several of this species' vocal signals. This comparison indicates that the extraction of spectral patterns involves a hierarchical organization within the anuran's auditory system which probably plays a major role in processing complex sounds.This research was supported by the U.S. Public Health Service (NIH Research Grant NS-09244). We would like to thank Anne Moffat for her assistance in collecting data on the tuning characteristics of the VIIIth nerve units.     

Recording of short-latency vestibular evoked potentials induced by acceleration impulses in experimental animals: current status of the method and its applications

The short-latency vestibular evoked potential (VsEP) induced by angular acceleration impulses (maximal amplitude 30,000 deg/sec², rise time 2–3 msec) was recorded by skin electrodes in intact cats after various surgical and pharmacological procedures. The normal VsEP consists of 5–8 waves, several microvolts in amplitude, during the first 10 msec. The latency of the first wave (P1) is about 2 msec with respect to the start of head acceleration. The first and the second waves (P1 and P2) were shown to originate from the vestibular nerve and nucleus, respectively.The VsEP disappears permanently after bilateral labyrinthectomy, excision of the 8th nerves, or administration of large doses of gentamicin. Temporary disappearance is caused by anoxia induced for a brief period of time or injection of lidocaine (4%) into the vestibular nerve or into the inner ear after contralateral labyrinthectomy.The VsEPs in the intact cat are similar whether clockwise or counterclockwise stimuli are used and are not affected by changing the position of the head. Unilaterally labyrinthectomized animals, however, show asymmetric response whereby excitatory stimulation of any of the intact semicircular canals evokes prominent P1 and P2 waves which are absent with inhibitory stimulation.The rate and input-output intensity functions of the VsEP are described. The threshold of the VsEP was found to be 1000–1500 deg/sec².In addition to the neurogenic waves, 2 other potentials appear occasionally in the response: (1) large-amplitude and longer-duration waves with latencies of 8–20 msec, which are of myogenic origin, and (2) smaller waves with shorter latency which probably represent vestibular microphonics and generator potentials. Extracellular recordings of the responses of single second-order neurons in the vestibular nuclei to the same acceleration impulses confirmed that the kinetic vestibular neurons can respond to these stimuli with a latency as short as 3.5 msec.This method for inducing and recording VsEPs has proved to be a powerful tool for the evaluation of vestibular function in experimental animal models.     

Selective depressant action of antidromic impulses on gustatory nerve signals

The depressant action of antidromic volleys of impulses on gustatory nerve signals from the tongues of bullfrogs was studied. Electrical stimulation of the glossopharyngeal nerve at a rate of 100 Hz for 10 s and at supramaximal intensity slightly depressed the integrated glossopharyngeal nerve responses to quinine and to mechanical taps to the tongue. The same antidromic stimuli resulted in a 30-40% reduction in the responses to salt, acid, water, and warmed saline, but depressed greater than 80% of the afferent impulses firing spontaneously. The magnitude of responses to quinine and NaCl and the number of spontaneous discharges decreased gradually with an increase in either the frequency or the duration of antidromic stimuli. Similar results were obtained with intensities above the threshold for exciting gustatory and slowly adapting mechanosensitive fibers. The time required to recover from termination of the antidromic stimuli to two-thirds of the maximal amount of depression ranged between 6 and 7 min, with no significant differences among the depressions. The possible mechanisms involved in the antidromic depression of gustatory nerve signals are discussed.     

Propagation failure of action potentials at the bifurcation point of the slow axon innervating the extensor tibiae muscle ofDecticus albifrons (Orthoptera)

Summary Failure of conduction of nerve impulses has been observed at the bifurcation point of the metathoracic slow extensor tibiae motor axon (SETi) ofDecticus albifrons. Records from the region proximal and distal to the bifurcation point of the axon showed that during prolonged and repetitive stimulation and after a certain number of stimuli, proportional to the stimulating frequency, some SETi action potentials failed to cross this point (Fig. 1).Cross-sections of the metathoracic extensor motor nerve ofD. albifrons show that at the region of axonal bifurcation, both the neural lamella and the layer of glial cells (the sheath) around the SETi axons became thinner than the region proximal and distal to the bifurcation (Fig. 2).The possible role of the conduction block in the neuronal control of the muscle has been discussed.Abbreviations ETi extensor tibiae - SETi slow extensor tibiae - PE proximal electrode - DE distal electrode - SE stimulating electrode     

The concentration of free Ca(2+) in the sarcoplasmic reticulum of frog cut twitch skeletal muscle fibers estimated with tetramethylmurexide

One aim of this article was to determine the resting concentration of free Ca²⁺ in the sarcoplasmic reticulum (SR) of frog cut skeletal muscle fibers ([Ca²⁺]_SR,R) using the calcium absorbance indicator dye tetramethylmurexide (TMX). Another was to determine the ratio of [Ca²⁺]_SR,R to TMX's apparent dissociation constant for Ca²⁺ (K_app) in order to establish the capability of monitoring [Ca²⁺]_SR(t) during SR Ca²⁺ release – a signal needed to determine the Ca²⁺ permeability of the SR. To reveal the properties of TMX in the SR, the surface membrane was rapidly permeabilized with saponin to rapidly dissipate myoplasmic TMX. Results indicated that the concentration of Ca-free TMX in the SR was 2.8-fold greater than that in the myoplasm apparently due to binding of TMX to sites in the SR. Taking into account that such binding might influence K_app as well as a dependence of K_app on TMX concentration, the results indicate an average [Ca²⁺]_SR,R ranging from 0.43 to 1.70 mM. The ratio [Ca²⁺]_SR,R/K_app averaged 0.256, a relatively low value which should not depend on factors influencing K_app. As a result, the time course of [Ca²⁺]_SR(t) in response to electrical stimulation is well determined by, and approximately linearly related to, the active TMX absorbance signal.     

Response patterns of two auditory interneurons in a freely moving grasshopper (Chorthippus biguttulus L.)

Summary Summated nerve potentials were recorded from the neck connectives in intact, freely moving grasshoppers of the speciesChorthippus biguttulus by means of chronically implanted hook electrodes. The action potentials of two auditory interneurons, known as the G₁- and the B₁-neuron, respectively (Kalmring 1975a, b), were distinguishable (Fig. 1) in the recordings and the neurons were identified by their morphology (Fig. 2).The G-neuron exhibits a very rapid and another, much slower, response decrement; the times required for recovery from both these effects show the opposite time courses (Fig. 3). The response versus intensity curve of the G-neuron has the shape of a saturating characteristic for noise stimuli and high frequencies whereas at low frequencies inhibitory effects can be observed for high intensities. The B-neuron has a bell-shaped intensity characteristic at all frequencies with position and width of the bell being frequency-dependent (Fig. 5). The directional characteristic of the G-neuron is nearly circular (for noise stimuli); the B-neuron responds preferentially to sound from the ipsilateral side (Fig. 6). With increasing temperature the threshold, latency, and spike interval of the G-neuron strongly decrease, while the number of spikes per stimulus increases (Fig. 7).In general, the response properties of both auditory interneurons as determined in almost intactChorthippus biguttulus, largely resemble those previously reported forLocusta migratoria in extensively dissected preparations. However, a few, probably interspecific, differences were observed.     

Predominant membrane localization is an essential feature of the bacterial signal recognition particle receptor

Background  

The signal recognition particle (SRP) receptor plays a vital role in co-translational protein targeting, because it connects the soluble SRP-ribosome-nascent chain complex (SRP-RNCs) to the membrane bound Sec translocon. The eukaryotic SRP receptor (SR) is a heterodimeric protein complex, consisting of two unrelated GTPases. The SRβ subunit is an integral membrane protein, which tethers the SRP-interacting SRα subunit permanently to the endoplasmic reticulum membrane. The prokaryotic SR lacks the SRβ subunit and consists of only the SRα homologue FtsY. Strikingly, although FtsY requires membrane contact for functionality, cell fractionation studies have localized FtsY predominantly to the cytosolic fraction of Escherichia coli. So far, the exact function of the soluble SR in E. coli is unknown, but it has been suggested that, in contrast to eukaryotes, the prokaryotic SR might bind SRP-RNCs already in the cytosol and only then initiates membrane targeting.     

How Does Stochastic Ryanodine Receptor-Mediated Ca Leak Fail to Initiate a Ca Spark?

Spontaneous calcium (Ca) sparks are initiated by single ryanodine receptor (RyR) opening. Once one RyR channel opens, it elevates local [Ca] in the cleft space ([Ca]_Cleft), which opens other RyR channels in the same Ca release unit (CaRU) via Ca-induced Ca-release. Experiments by Zima et al. (J. Physiol. 588:4743–4757, 2010) demonstrate that spontaneous Ca sparks occur only when intrasarcoplasmic-reticulum (SR) [Ca] ([Ca]_SR) is above a threshold level, but that RyR-mediated SR Ca leak exists without Ca sparks well below this threshold [Ca]_SR. We examine here how single RyR opening at lower [Ca]_SR can fail to recruit Ca sparks at a CaRU, while still contributing to SR Ca leak. We assess this using a physiologically detailed mathematical model of junctional SR Ca release in which RyR gating is regulated by [Ca]_SR and [Ca]_Cleft. We find that several factors contribute to the failure of Ca sparks as [Ca]_SR declines: 1), lower [Ca]_SR reduces driving force and thus limits local [Ca]_Cleft achieved and the rate of rise during RyR opening; 2), low [Ca]_SR limits RyR open time (τ_O), which further reduces local [Ca]_Cleft attained; 3), low τ_O and fast [Ca]_Cleft dissipation after RyR closure shorten the opportunity for neighboring RyR activation; 4), at low [Ca]_SR, the RyR exhibits reduced [Ca]_Cleft sensitivity. We conclude that all of these factors conspire to reduce the probability of Ca sparks as [Ca]_SR declines, despite continued RyR-mediated Ca leak. In addition, these same factors explain the much lower efficacy of L-type Ca channel opening to trigger local SR Ca release at low [Ca]_SR during excitation-contraction coupling. Conversely, all of these factors are fundamentally important for increasing the propensity for pro-arrhythmic Ca sparks and waves in cardiac myocytes at high [Ca]_SR.     

Cardioacceleratory reflexes triggered by mechanoproprioceptors of the swimmerets in the stomatopod crustacean Squilla oratoria

The heart of Squilla oratoria is innervated by processes arising from the cardiac ganglion, which lies on the outer surface of the heart wall. The ganglion is regulated by one pair of cardioinhibitory nerves and two pairs of cardioacceleratory nerves. Cardiac acceleration accompanied activation of the five pairs of swimmerets in the first to the fifth abdominal segments. The cardioacceleratory nerves were activated when swimmerets beat strongly. Activation of the cardioacceleratory nerves was caused by electrical stimuli to a nerve branch extending to the swimmerets from the first nerve root of the abdominal ganglion. Bursts of afferent impulses were recorded from the nerve branch of the first nerve root corresponding to periods of protractive and retractive swimmeret movements. Afferent impulses were recorded from the nerve branch when the articular membrane was artificially boosted up. Cardiac acceleration during active swimmeret movements in Squilla is attributable to a reflexive response triggered by the movements. Putative mechanoproprioceptors on the articular membrane between the sterna and basipodite in the swimmerets may be responsible for the cardioacceleratory reflex.     

Calcium buffering properties of sarcoplasmic reticulum and calcium-induced Ca2+ release during the quasi-steady level of release in twitch fibers from frog skeletal muscle

Experiments were performed to characterize the properties of the intrinsic Ca²⁺ buffers in the sarcoplasmic reticulum (SR) of cut fibers from frog twitch muscle. The concentrations of total and free calcium ions within the SR ([Ca_T]_SR and [Ca²⁺]_SR) were measured, respectively, with the EGTA/phenol red method and tetramethylmurexide (a low affinity Ca²⁺ indicator). Results indicate SR Ca²⁺ buffering was consistent with a single cooperative-binding component or a combination of a cooperative-binding component and a linear binding component accounting for 20% or less of the bound Ca²⁺. Under the assumption of a single cooperative-binding component, the most likely resting values of [Ca²⁺]_SR and [Ca_T]_SR are 0.67 and 17.1 mM, respectively, and the dissociation constant, Hill coefficient, and concentration of the Ca-binding sites are 0.78 mM, 3.0, and 44 mM, respectively. This information can be used to calculate a variable proportional to the Ca²⁺ permeability of the SR, namely d[Ca_T]_SR/dt ÷ [Ca²⁺]_SR (denoted release permeability), in experiments in which only [Ca_T]_SR or [Ca²⁺]_SR is measured. In response to a voltage-clamp step to −20 mV at 15°C, the release permeability reaches an early peak followed by a rapid decline to a quasi-steady level that lasts ∼50 ms, followed by a slower decline during which the release permeability decreases by at least threefold. During the quasi-steady level of release, the release amplitude is 3.3-fold greater than expected from voltage activation alone, a result consistent with the recruitment by Ca-induced Ca²⁺ release of 2.3 SR Ca²⁺ release channels neighboring each channel activated by its associated voltage sensor. Release permeability at −60 mV increases as [Ca_T]_SR decreases from its resting physiological level to ∼0.1 of this level. This result argues against a release termination mechanism proposed in mammalian muscle fibers in which a luminal sensor of [Ca²⁺]_SR inhibits release when [Ca_T]_SR declines to a low level.     

Primary afferent fibers conduct impulses in both directions under physiological stimulus conditions

Summary In electric fish of the family Mormyridae some primary afferent fibers conduct impulses not only from electroreceptors to the brain but also from the brain to the receptors. The efferent impulses may be elicited by electrical stimulation which is within the physiological range, i.e., by stimulation which is similar in amplitude and duration to the stimulation that is caused by the fish's own electric organ discharge. Afferent and efferent impulses in the same afferent fiber were identified by: simultaneously recording from a fiber at two different points, at the receptor and at the nerve trunk (Figs. 2C-H; 3B-D); by cutting the afferent fiber between the brain and the recording site as well as between the recording site and the periphery; and by intra-axonal recording from the afferent fiber near its entry into the brain (Fig. 4). The efferent impulses result from the central integration of a corollary discharge of the electric organ motor command with excitatory and inhibitory input from several different receptors near the one from which afferent impulses originate (Fig. 4). The centrally originating impulse may be capable of modifying the effect of signals originating in the periphery.Abbreviations ELLL electrosensory lateral line lobe - EOCD electric organ corollary discharge - EOD electric organ discharge - epsp excitatory postsynaptic potential - NPLL posterior lateral line nerve     

Processing of calling songs by an L-shaped neuron in the prothoracic ganglion of the female cricket, Acheta domesticus

ABSTRACT. An L-shaped auditory intemeuron (LI) has been recorded from extracellularly and intracellularly, and identified morphologically (by Lucifer yellow or cobalt injection) in the prothoracic ganglion of mature female Acheta domesticus. The morphology of the LI is very similar to ascending, prothoracic acoustic interneurons that are most sensitive to higher carrier frequencies in both A. domesticus and other gryllid species. Its terminations in the brain are similar to ascending acoustic interneurons found in other gryllids. The LI neuron is most sensitive to 4–5 kHz model calling songs (CSs), the main carrier frequency of the natural call. Thresholds to high frequencies (8–15 kHz) are 15–20 dB higher. Increasing CS intensities of up to 15 dB above threshold at 4–5 kHz result in increased firing rates by the LI. More than 15 dB increase in intensity causes saturation with little increase in spiking rate until the intensity surpasses 80 dB. In response to 70 dB or higher stimulus intensities, the LI responds to the second and third CS syllables with one or two spikes, pauses, and then produces a burst of nerve impulses with the same or greater latency than for lower intensity stimuli. In response to CS syllables of changing duration (10–30 ms) this neuron responds with a rather constant duration burst of impulses. Syllable periods of the CS stimuli were accurately encoded by the LI. Progressively stronger injection of hyperpolarizing current reduces, and ultimately stops spiking of the LI in response to CS stimuli. More intense stimulation with reduced hyperpolarization shows an initial spike, pause and burst of spikes. Intracellular recording from axonal regions of the neuron shows large spikes, small EPSPs and a developing hyperpolarization through the response to a CS chirp. Inhibitory input to the LI is demonstrated at 4.5, 8 and 16 kHz. This probably explains the specialized response characteristics of the LI which enhanced its encoding of CS syllable period.     

Physiological characteristics of the tympanic organ in noctuoid moths

Summary We show the variations in the spike activity of both auditory receptors inSpodoptera frugiperda, Mocis latipes, Ascalapha odorata (Noctuidae),Maenas jussiae andEmpyreuma pugione (Arctiidae) immediately after 45 ms and 5 s acoustic stimuli at different intensities. The frequency of the applied stimuli was 34 kHz forE. pugione and 20 kHz for the other species. The electrical activity of the auditory receptors was recorded at the tympanic nerve with a stainless steel hook electrode. When the 45 ms pulses cease there is an afterdischarge from both auditory receptors in all the species. The number of spikes in the afterdischarge activity of both receptor cells (A₁ and A₂) shows a linear relation with stimulus intensity (Table 1). This number increases monotonically with increments in stimulus intensity, except for the A₁ cell activity inE. pugione, which decreases at intensities higher than 55 dB (Fig. 1). There are significant species-specific differences in the slope values of the number of spikes in the afterdischarge of both auditory receptors. After a 5 s stimulusM. latipes andM. jussiae show a rapid recovery of the standard spontaneous A₁-cell discharge level. Poststimulus A₁-cell spike activity inS. frugiperda shows a silent period, the duration of which increases with stimulus intensity (Fig. 3).E. pugione andA. odorata show such a silent period after low and moderately intense stimuli, but at high intensities the post-stimulus activity exceeds the pre-stimulus spontaneous discharge (Fig. 3). We demonstrate statistically that these variations cannot be explained by the random fluctuations of the standard spontaneous discharge. They are thus considered a silent and a rebound period respectively (Fig. 5). The presence and duration of either type of period seem to depend on the magnitude of the response to the acoustic stimulus. They thus seem related to the adaptation rate and the previously suggested existence of peripheral inhibitory interaction between the auditory receptors.     

Response characteristics of wide-field non-habituating non-directional motion detecting neurons in the optic lobe of the locust,Locusta migratoria

1. Extracellular recordings from wide-field nonhabituating non-directional (ND) motion detecting neurons in the second optic chiasma of the locust Locusta migratoria are presented. The responses to various types of stepwise moving spot and bar stimuli were monitored (Fig. 1)
2. Stepwise motion in all directions elicited bursts of spikes. The response is inhibited at stimulus velocities above 5°/s. At velocities above 10°/s the ND neurons are slightly more sensitive to motion in the horizontal direction than to motion in the vertical direction (Fig. 2). The ND cells have a preference for small moving stimuli (Fig. 3).
3. The motion response has two peaks. The latency of the second peak depends on stimulus size and stimulus velocity. Increasing the height from 0.1 to 23.5° of a 5°/s moving bar results in a lowering of this latency time from 176 to 130 ms (Fig. 4). When the velocity from a single 0.1° spot is increased from 1 to 16°/s, the latency decreases from 282 to 180 ms (Figs. 5–6).
4. A change-of-direction sensitivity is displayed. Stepwise motion in one particular direction produces a continuous burst of spike discharges. Reversal or change in direction leads to an inhibition of the response (Fig. 7).
5. It shows that non-directional motion perception of the wide-field ND cells can simply be explained by combining self-and lateral inhibition.

     

The latency of the response of Limulus photoreceptors to inositol trisphosphate lacks the calcium-sensitivity of that to light

Summary The latent period before depolarization of Limulus ventral photoreceptors by light flashes was compared with that following brief, intracellular, pressure-injection of d-myo-inositol 1,4,5 trisphosphate. At temperatures between 18 °C and 22 °C and with an extracellular calcium concentration of 10 mM, the responses of 4 cells to light and to injections of 100 M inositol trisphosphate displayed average latencies of 71 and 56 ms, respectively. The latencies of responses to InsP₃ included an estimated 20 ms dead-time inherent in the injection method. Reducing the temperature lengthened the latency of the response to light (Q₁₀ approximately 3.2 between 7 and 22 °C) more than that to inositol trisphosphate (Q₁₀ approximately 2.3). Bathing the photoreceptors in seawater containing no added calcium and 1 mM of the calcium chelator EGTA greatly increased the latency of the light response at all temperatures, but did not increase the latency of the response to inositol trisphosphate. We conclude that the response to inositol trisphosphate lacks the calcium- and temperature-sensitive latent period which characterizes the response to light. If inositol trisphosphate acts, via the release of stored calcium, to stimulate an intermediate in the visual cascade, then that intermediate would appear to be downstream from the latency-generating mechanism.Abbreviations InsP ₃ D-myo-inositol 1,4,5 trisphosphate - ASW Artificial seawater - Ca _i Cytosolic free calcium ion concentration - Ca ₀ Extracellular calcium ion concentration     

Temporal resolution of odour pulses by three types of pheromone receptor cells inAntheraea polyphemus

Summary Temporal response characteristics of three cell types of maleA. polyphemus, each responding to a different pheromone component, have been measured using series of short (20 ms) pheromone pulses. The stimuli were delivered through capillaries 20 m in diameter and applied to single olfactory sensilla trichodea. Two of three cell types sensitive to (E,Z)-6,11-hexadecadienal and (E,Z)-4,9-tetradecadienyl acetate are able to resolve at least 5 stimuli/s whereas the third, responding to the major pheromone component (E,Z)-6,11-hexadecadienyl acetate, is slower, resolving only about 2 stimuli/s. These results suggest that receptor cells are able to respond to pulses of pheromone concentration as they occur downwind from a point source. The time-averaged number of nerve impulses does not seem to be a reliable measure of the amount of pheromone reaching the sensillum. Responses of the cells thus reflect the non-uniform distribution of pheromone in a plume rather than the average concentration.