The visual response from the compound eye of Oncopeltus fasciatus: Effects of temperature and sensory adaptation

The effects of temperature (10–30°C) on response latency and amplitude were determined in the dark- and light-adapted compound eye of the milkweed bug, Oncopeltus fasciatus. Response amplitude was an inverse function of temperature under dark-adapted conditions, but was nearly independent of temperature when superimposed on a background field. Response amplitude to a test stimulus (S₂) was maximum at 15–20°C when presented 10 sec after an adapting stimulus (S₁). The optimum temperature (10°C or less) for maximum response amplitude from dark-adapted eyes was far below the temperature at which the animals were grown (19–25°C) and lower than previously reported for insect compound eyes. These results are discussed in terms of the adaptive implications for diurnal, terrestrial ectotherms.Response latency from dark-adapted eyes was an inverse exponential function of temperature with an apparent activation energy of 13·6 kcal mole⁻¹. No change in activation energy could be attributed to light adaptation.Reductions of S₂ response latency and amplitude, during the adaptation régimes employed in this study, were different functions of temperature. Adapting stimuli, which were equally effective at reducing S₂ latency, had different effects on S₂ response amplitude. Recovery of S₂ response latency and amplitude were not related at either 20 or 10°C. Therefore, changes in S₂ response latency as a function of adaptation appeared independent of changes in S₂ response amplitude.     

The effects of muscle history on short latency stretch reflex response of soleus muscle.

The purpose of the present study was to investigate the combined effects of muscle history, activation and stretching velocity on short latency stretch response (SLR). Stretches (70, 120 and 200 deg s-1) were elicited to both passive and active (10-25% MVC) triceps surae muscle with constant (ISO), lengthened (LEN) or shortened (SHO) muscle length. Under the passive SHO pre-condition both SLR amplitude and reflex torque (RT) decreased where as latency increased compared with the passive ISO pre-condition. Such observations were absent in active trials. Stretches applied to a lengthening passive muscle (LEN) resulted in smaller SLR amplitude and RT compared with passive ISO. In active muscle the stretch response increased with stretching velocity in ISO and SHO. However, in LEN there was large interindividual variability and no velocity dependent increase in SLR amplitude was observed. Smaller amplitude and longer latency of passive SLR in SHO could result from increased slack in the intrafusal fibres, which may be compensated by fusimotor activation during the active condition. The mechanism behind the smaller amplitude in passive LEN and the lack of velocity dependence in active LEN may be related to changes in motoneuron pool excitability or changes in the spindle sensitivity to stretch.     

Cryotherapy and ankle bracing effects on peroneus longus response during sudden inversion

Cryotherapy and ankle bracing are often used in conjunction as a treatment for ankle injury. No studies have evaluated the combined effect of these treatments on reflex responses during inversion perturbation. This study examined the combined influence of ankle bracing and joint cooling on peroneus longus (PL) muscle response during ankle inversion. A 2 × 2 RM factorial design guided this study; the independent variables were: ankle brace condition (lace-up brace, control), and treatment (ice, control), and the dependent variables studied were PL stretch reflex latency (ms), and PL stretch reflex amplitude (% of max). Twenty-four healthy participants completed 5 trials of a sudden inversion perturbation to the ankle/foot complex under each ankle brace and cryotherapy treatment condition. No two-way interaction was observed between ankle brace and treatment conditions on PL latency (P = 0.283) and amplitude (P = 0.884). The ankle brace condition did not differ from control on PL latency and amplitude. Cooling the ankle joint did not alter PL latency or amplitude compared to the no-ice treatment. Ankle bracing combined with joint cooling does not have a deleterious effect on dynamic ankle joint stabilization during an inversion perturbation in normal subjects.     

Analysis of the middle latency evoked potentials to angular acceleration impulses in man

The middle latency vestibular evoked potential (ML-VsEP) recorded with scalp electrodes in man in response to impulses of angular acceleration is dominated by a forehead positive peak at about 15 ms and a negative peak at about 20 ms; the peak amplitude of this component is about 30 μV. This is followed by slower, smaller amplitude activity. The latency of this initial peak is similar to the latency of the vestibulo-ocular reflex (VOR) in monkeys. The present study was undertaken to elucidate the possible relation between the ML-VsEPs and VOR. This included recordings from forehead-mastoid electrodes (sites used to record VsEP) and other scalp electrodes and the recording of potentials due to eye movement: the electro-oculogram. Direct recording of eye movements was also conducted using an infra-red reflection device in those experiments in which the head was not moved. The recordings were conducted in man during vestibular stimulation eliciting VsEPs, during voluntary eye movements and during caloric and optokinetic stimulation. These experiments indicated that the 15–20 ms component of the ML-VsEP was not due to movements of the eye (corneoretinal dipole). The large amplitude 15–20 ms component of the ML-VsEP was similar in general magnitude, waveform, polarity, duration and rise time to the highly synchronous pre-saccadic spike (neural and/or myogenic) which precedes nystagnys and voluntary saccades. It therefore probably represents vestibular-initiated electrical activity in motor units of the extra-ocular muscles which then produce anti-compensatory saccades.     

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.     

Effect of seduksen (diazepam) on cortical P300 potentials evoked by neutral and emotional words

The influence of seduxen (diazepam) on cortical potentials P300 evoked by neutral and emotional words was studied in adult subjects having life conflicts. The therapeutic dose of seduxen (10 mg) had no significant effect on the amplitude of the late positive cortical response P300 to neutral words. Seduxen depresses the emotional activation of the cerebral cortex; that is manifested in selective elimination of those changes in latency and amplitude of P300 wave which are observed in response to emotionally significant words. Under the action of seduxen, the interhemispheric difference in the latency of cortical response disappears due to latency increase in the right hemisphere.     

Age-dependent amplitude variation of brain-stem auditory evoked potentials

Normative amplitude values of brain-stem auditory evoked potential (BAEP) components are given for normally hearing subjects at 1, 10, 30, 50 and 70 years of age, with an intragroup age variation of only ±6 months. Under these circumstances amplitude standard deviations decreased to less than 20% of the mean values. In contrast with the reduced evolution of latency with age, BAEP amplitude (for components I–V) undergoes a greater oscillation during ontogeny. With the exception of component I, it increased markedly from 1 year to 10 years of age and decreased thereafter constantly up to 50 years, with a mean rate of 10 nV yearly. The decrease slowed down between 50 and 70 years. The amplitude differences between the subgroups are highly significant statistically (P < 0.01). Possible reasons for these changes are discussed.     

Comparison of scalp distribution of short latency somatosensory evoked potentials (SSEPs) to stimulation of different nerves in the lower extremity

SSEPs to stimulation of the CPN at the knee and PTN, PN and SN at the ankle were recorded from 15 cephalic sites and compared in 8 normal subjects. The configuration, amplitude, peak latency and distribution of P27, N35 (CPN) and P37, N45 (PTN, PN and SN) were analyzed. The configuration and distribution of SSEPs to stimulation of the 3 nerves at the ankle were similar across subjects. Both P37 and N45 were greatest in amplitude at the vertex and at recording sites ipsilateral to the side of stimulation. At contralateral sites either negative (N37) or negative, positive, negative potentials were recorded. The peak latency of N37 was the same or slightly less than that of P37. CPN-SSEPs were lower in amplitude and their configuration and scalp distribution showed much greater intersubject variability. This suggests that complex mechanisms which variably interact with one another are reflected in scalp SSEPs to CPN stimulation at the knee. The larger amplitude plus the minimal intersubject variability in morphology and topography of PTN-SSEPs indicate that this nerve is the most suitable for routine clinical use.     

Decreased fibularis reflex response during inversion perturbations in FAI subjects

Investigate reflex responses in muscles throughout the lower limb and low back during sudden inversion perturbations in individuals with and without Functional Ankle Instability (FAI) while walking. Forty subjects participated in the study. Surface electromyogram recordings were obtained from the fibularis (FIB), gluteus medius (GM), erector spinae (ES), and sternocleidomastoid (SCM) of the injured/matched side as well as the uninjured/matched contralateral side (FIB_CLS, GM_CLS, or ES_CLS). Latency and amplitude data were collected while subjects were walking on a custom-built perturbation walkway. The onset of the short-latency stretch reflex of the FIB was significantly later in the injured side of the FAI individuals when compared to the control group (P = 0.009). Both the short and long latency reflex amplitude was significantly smaller in the FIB muscle in the FAI group than in the control group (P < 0.008). No significant differences in latency or amplitude reflex responses were identified between the two groups in the GM, ES, FIB_CLS, GM_CLS, or ES_CLS (P > .05). Interpretation of these results indicate that during a dynamic perturbation task individuals with FAI demonstrate longer fibularis muscle latencies on the injured side while no significant changes in the proximal muscle groups. Additionally, short and long latency reflex amplitude was significantly decreased in FAI individuals.     

High-rate sequential sampling of auditory brain-stem and somatosensory evoked responses in hypoxia

We developed a high-rate sequential recording technique that allowed simultaneous measurements of both auditory brain-stem response (ABR) and somatosensory evoked potential (SEP) every 10 sec. Using this method, a transient increase in amplitude of all the ABR and SEP components in response to hypoxia in dogs could be detected. The increase in amplitude preceded the prolongation of latency. Our study showed that there were succesive changes of evoked potentials in response to hypoxia. A transient increase in amplitude is the first to occur, followed by a latency prolongation and an amplitude decrease for both ABRs and SEPs.     

Changes in somatodendritic but not terminal dopamineregulation in aged rhesus monkeys

For these studies, young (8-9 years), middle-aged (14-17 years) and aged (23-28 years) rhesus monkeys were used as a model of normal aging in humans to investigate changes in dopamine (DA)-containing neurons in senescence. Aged monkeys exhibited significant age-related motoric declines as compared to the young animals. In vivo microdialysis studies showed that basal levels of the DA metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were diminished by 44% and 79%, respectively, in the substantia nigra (SN) of aged monkeys. In addition, d-amphetamine-evoked overflow of DA in the SN was diminished by 30% in the middle-aged animals and 67% in the aged monkeys. Post-mortem measures of DA and DA metabolites showed significant decreases in DA (20%), DOPAC (47%) and HVA (22%) levels in the putamen and a 25% decline in HVA tissue levels in the SN of the aged monkeys as compared to the young animals. Unbiased stereological cell counting of tyrosine hydroxylase (TH)-immunoreactive neurons in the SN showed a small (15-20%) but significant age-related decline in TH-positive neurons. In addition, there was a small (15-20%) but significant decline in TH-positive fiber density and TH-positive cell size. In comparison to the massive loss of DA neurons responsible for the movement dysfunctions seen in Parkinson's disease, pronounced functional changes in DA release in the SN and putamen may significantly contribute to the motoric dysfunctions characterizing normal aging in rhesus monkeys.     

Behavioral evidence of a latency code for stimulus intensity in mormyrid electric fish

Mormryid electric fish (Gnathonemus petersii) respond to novel stimuli with an increase in the rate of the electric organ discharge (EOD). These novelty responses were used to measure the fish's ability to detect small changes in the amplitude and latency of an electrosensory stimulus. Responses were evoked in curarized fish in which the EOD was blocked but in which the EOD motor command continued to be emitted. An artificial EOD was provided to the fish at latencies of 2.4 to 14.4 ms following the EOD motor command.Novelty responses were evoked in response to transient changes in artificial EOD amplitude as small as 1% of baseline amplitude, and in latency as small as 0.1 ms. Changes in latency were effective only at baseline delays of less than 12.4 ms.The sensitivity to small changes in latency supports the hypothesis that latency is used as a code for stimulus intensity in the active electrolocation system of mormyrid fish. The results also indicate that a corollary discharge signal associated with the EOD motor command is used to measure latency.Abbreviations EOD electric organ discharge - ELL electrosensory lateral line lobe - epsp excitatory post synaptic potential     

Effect of Blood Volume in Standard Anaerobic Blood Culture Bottles of the BacT/ALERT 3D System Used for the Detection of Pathogens and Time to Detection

BackgroundBlood volume may profoundly affect the isolation of microorganisms in blood cultures. The effect of blood volume in standard anaerobic bottles of the BacT/ALERT 3D system was investigated.MethodsAdult patients who visited the emergency department and referred for blood culture (n = 824) were enrolled from June to September 2013. Two sets of blood cultures were obtained from each patient. One set consisted of 5 mL that was collected in a standard aerobic bottle (SA5), 5 mL that was collected in a standard anaerobic bottle (SN5), and 10 mL that was collected in a standard anaerobic bottle (SN10). The growth of clinically significant pathogens and the time to detection (TTD) were compared between the SN5 and SN10 samples.ResultsIncreasing the volume of blood collected from 5 to 10 mL yielded a 14.7% improvement in the isolation of microorganisms. There was a statistically significant difference in the isolation of pathogens (14 vs. 30, P = 0.023) between the SN5 and SN10 samples. Gram-positive microorganisms were detected earlier in the SN10 samples than the SN5 samples (P = 0.052). The mean TTD of all pathogens was 13.5 h for the SN5 samples and 12.9 h for the SN10 samples (P = 0.099).ConclusionIncreased blood volume in the SN bottle yielded a significantly higher pathogen detection rate. However, there was no difference in the frequency of earlier detection or TTD between the SN5 and SN10 samples.     

Local vasoconstriction in spinal cord-injured and able-bodied individuals.

Local vasoconstriction plays an important role in maintaining blood pressure in spinal cord-injured individuals (SCI). We aimed to unravel the mechanisms of local vasoconstriction [venoarteriolar reflex (VAR) and myogenic response] using both limb dependency and cuff inflation in SCI and compare these with control subjects. Limb blood flow was measured in 11 male SCI (age: 24-55 yr old) and 9 male controls (age: 23-56 yr old) using venous occlusion plethysmography in forearm and calf during three levels of 1) limb dependency, and 2) cuff inflation. During limb dependency, vasoconstriction relies on both the VAR and the myogenic response. During cuff inflation, the decrease in blood flow is caused by the VAR and by a decrease in arteriovenous pressure difference, whereas the myogenic response does not play a role. At the highest level of leg dependency, the percent increase in calf vascular resistance (mean arterial pressure/calf blood flow) was more pronounced in SCI than in controls (SCI 186 +/- 53%; controls 51 +/- 17%; P = 0.032). In contrast, during cuff inflation, no differences were found between SCI and controls (SCI 17 +/- 17%; controls 14 +/- 10%). Percent changes in forearm vascular resistance in response to either forearm dependency or forearm cuff inflation were equal in both groups. Thus local vasoconstriction during dependency of the paralyzed leg in SCI is enhanced. The contribution of the VAR to local vasoconstriction does not differ between the groups, since no differences between groups existed for cuff inflation. Therefore, the augmented local vasoconstriction in SCI during leg dependency relies, most likely, on the myogenic response.     

The Spatiotemporal Analysis of Odorants at the Level of the Olfactory Receptor Sheet

Activity in two separate regions of the frog olfactory mucosa was sampled by simultaneously recording the summated neural discharges from the olfactory nerve branches originating from them. The difference in the activity from these two regions in response to a stimulus was measured by: (a) the ratio of the response amplitude recorded from the lateral nerve branch to that recorded from the medial nerve branch (LB/MB ratio), (b) the latency difference (or time interval) between these two responses. Equal concentrations of four different odorants were drawn into the nose by an artificially produced sniff of known dimensions. At each concentration in every animal the four chemicals were ranked in order of the magnitudes of their LB/MB ratios and again in order of their latency differences. Regardless of their concentration, the same chemicals fell into the same ranks in different animals. In addition, for each chemical the magnitudes of the ratios and latency differences showed only minimal changes with concentration. Thus, spatiotemporal patterns of relative response magnitudes and latency differences across the mucosa differentially represented the odorants. Such a spatiotemporal code, together with physicochemical considerations, suggested that the nose separates vapors in a manner similar to a gas chromatograph. This is further supported by the previously observed reversal of the ratio patterns with reversal of air flow direction through the olfactory sac.     

Combined electrophysiological assessment of the visual system in central serous retinopathy

Six subjects suffering from idiopathic central serous retinopathy were examined during the acute phase using a battery of neurophysiological tests. The records (using skin electrodes) included the electro-oculogram (EOG), the white light electroretinogram (ERG) during various stages of dark and light adaptation, and the flash and pattern reversal visual evoked potentials. Results obtained from the affected eye were compared with those from the healthy eye. The values of the healthy eye were not significantly different from our normal control group.The EOGs of the affected eyes were not significantly different from those of the healthy eyes. The ‘a’ wave of the ERG during light adaptation was significantly (P<0.05) smaller in the affected eye. The amplitudes of the other components and the latencies of all components were not affected. The latency of the PR-VEP of the affected eye in all subjects was prolonged in comparison with the unaffected eye. In 3 subjects the latency was prolonged by more than 2 S.D.s compared with our control group. The amplitude of the PR-VEP in 5 of our 6 subjects was slightly but significantly (P<0.02) smaller in the affected eye. There was no correlation between amplitude and latency changes.     

Myocardial Depolarizing Response to Glutamate in the Myogenic Heart of the Branchiopod Crustacean Triops longicaudatus

Fine structure of the heart and the effects on the heartbeat of some transmitter candidates in crustacean cardioregulatory system were examined in the myogenic heart of the branchiopod crustacean Triops longicaudatus. Electron microscopy revealed that, in each myocardial cell, myofibrils are confined in the part facing the epicardium and intercalated disks are present between the myofibrillar regions of adjacent myocardial cells. No neural elements were found in the heart, suggesting lack of extrinsic cardioregulatory nerves from the central nervous system. Gamma aminobutyric acid and acetylcholine produced no detect-able changes in the myogenic activity of the heart at concentrations up to 10(-3) M, respectively. Glutamate induced a depolarizing membrane response in the cardiac muscle with a threshold concentration of approximately 1x10(-5) M. The amplitude of the depolarizing response was concetration-dependent and saturated at approximately 1x10(-4) M. The myogenic activity of the heart increased in frequency with glutamate of less than approximately 3x10(-5) M. With higher dose of glutamate, action potential adaptation occurred in the cardiac muscle and the heart exhibited a systolic arrest.     

Frequency-dependent excitability of "membrane" slow responses of Rabbit left atrial trabeculae in the presence of Ba2+ and high K+

Small trabeculae of rabbit left atrium immersed in TKBa solution (Tyrode with 10 mM K+ and 1 mM Ba2+) were used to study frequency dependence of "membrane" slow response excitability at long cycle lengths (greater than 1 s). In TKBa, stimuli generate graded, low- amplitude (2-15 mV) subliminal responses of variable long duration (up to 450 ms). A full all-or-none slow response is generated when a subliminal response depolarizes the membrane to about--35 mV. Subliminal response amplitude and rate of rise augment with stimulus intensity-duration product. For a fixed stimulus, the subliminal response is larger and faster at higher frequencies. Sudden changes in stimulus frequency or time course induce changes in subliminal response tha take four to eight cycles to attain steady state. For a fixed stimulus, slow response latency shortens progressively during the first few cycles after a sudden increase in frequency or when a rested preparation is excited (latency adaptation phenomenon, LAP). Slow response threshold stimulus requirements decrease during LAP (excitability hysteresis). The degree of excitability hysteresis is dependent on stimulation frequency and is more pronounced at higher frequencies. Frequency sensitivity of subliminal response (which causes frequency sensitivity of slow response excitability) is explained in terms of a transient state of enhancement set up by each stimulus. The enhanced state decays between stimuli with a half-time of approximately 4 s, thus allowing cumulative effects to become evident at rates above 0.1 Hz.     

Low doses of radiation increase the latency of spontaneous lymphomas and spinal osteosarcomas in cancer-prone,radiation-sensitive Trp53 heterozygous mice

Mice heterozygous for Trp53 are radiation-sensitive and cancer-prone, spontaneously developing a variety of cancer types. Osteosarcomas in the spine lead to paralysis, while lymphomas lead rapidly to death, distinct events that provide objective measures of latency. The effects of a single low-dose (10 or 100 mGy), low-dose-rate (0.5 mGy/min) (60)Co gamma irradiation on lymphoma or spinal osteosarcoma frequency and latency, defined as time of death or of onset of paralysis, respectively, were examined. Compared to spontaneous lymphomas or to spinal osteosarcomas leading to paralysis in unexposed mice, an exposure of 7-8-week-old Trp53(+/-) mice to 10 or 100 mGy had no significant effect on tumor frequency, indicating no effect on tumor initiation. All tumors are therefore assumed to be of spontaneous origin. However, a 10-mGy exposure reduced the risk of both lymphomas and spinal osteosarcomas by significantly increasing tumor latency, indicating that the main in vivo effect of a low-dose exposure is a reduction in the rate at which spontaneously initiated cells progress to malignancy. The effect of this adaptive response persisted for the entire life span of all the animals that developed these tumors. Exposure to 100 mGy delayed lymphoma latency longer than the 10-mGy exposure. However, the 100-mGy dose increased spinal osteosarcoma risk by decreasing overall latency compared to unexposed control mice. That result suggested that this higher dose was in a transition zone between reduced and increased risk, but that the dose at which the transition occurs varies with the tumor type.