Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats

In this study, short latency (t<12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 μm (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300–1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4–6 clear waves with mean amplitudes (for a 4 g stimulus) of 1–5 μV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P<0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06–0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.     

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.     

Comparison of short-latency trigeminal evoked potentials elicited by painful dental and gingival stimulation

Painful stimulation of tooth pulp and of the maxillary gingiva was undertaken in 16 volunteers. Short-latency evoked potentials (15–20 msec) were recorded over 800 trials in each case at F3-P3 of F4-P4, and the resultant averaged wave forms were compared. The gingival wave was distinct in all subjects and could be averaged across subjects while the dental waves were either noise or very inconsistent over subjects. Averaging of the dental wave forms across subjects yielded an uninterpretable result. It was clear that dental evoked potentials could not be recorded at these sites. These findings could be explained by either or both of two hypotheses: (1) dental afferents are predominantly small fiber, nociceptive end organs that conduct more slowly than soft tissue afferents whereas gingival stimulation activates both large and small fiber populations; and (2) dental representation in somatosensory cortex is different and phylogenetically more primitive than that of neighboring soft tissue. Therefore, the location of the generator sites in cortex and the orientation of the dipole may be different for dental than for gingival wave forms.     

Postsynaptic potentials of facial motoneurons evoked by afferent and corticofugal impulses

Postsynaptic potentials of motoneurons in the facial nerve nucleus, evoked by stimulation of the cranial nerves (trigeminal, hypoglossal, facial) and of the sensomotor cortex were investigated in cats anesthetized with chloralose and pentobarbital. Two functionally opposite groups of motoneurons were found to exist in the facial nucleus. Stimulation of the afferent nerves and cortex evoked the appearance of EPSPs in the first of these groups and IPSPs in the second. The latency and duration of the PSPs indicate that afferent and corticofugal impulses reach the facial motoneurons along polysynaptic pathways. Interneurons on which wide convergence of influences travelling along afferent fibers and of the cortex, were found in the region of the facial nucleus. The possible neuronal pathways concerned with the transmission of afferent and corticofugal impulses to the facial motoneurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 391–400, July–August, 1972.     

The assessment of severe head injury by short-latency somatosensory and brain-stem auditory evoked potentials

The relative prognostic value of short-latency somatosensory evoked potentials (SEPs) and brain-stem auditory evoked potentials (BAEPs) was assessed in 35 patients with post-traumatic coma. Analysis of the evoked potentials was restricted to those recorded within the first 4 days following head injury. Abnormal SEPs were defined as an increase in central somatosensory conduction time or an absence of the initial cortical potential following stimulation of either median nerve. Abnormal BAEPs were classified as an increase in the wave I–V interval or the loss of any or all of its 3 most stable components (waves I, III and V) following stimulation of either ear. SEPs reliably both good and bad outcomes. All 17 patients in whom SEPs were graded as normal had a favourable outcome and 15 of 18 patients in whom SEPs were abnormal had an unfavourable outcome. Although abnormal BAEPs were associated with an unfavourable outcome in almost all patients (6 of 7), only 19 of 28 patients with normal BAEPs had a favourable outcome. The finding of normal BAEPs was therefore of little prognostic significance. These results confirm the superiority and greater sensitivity of the SEP in detecting abnormalities of brain function shortly after severe head trauma.     

Multicomponent synaptic potentials in rubrospinal neurons of cat brain evoked by corticofugal impulses

The compound nature of EPSP occurring in response to stimulation of the sensorimotor area of the cerebral cortex and the association area of the parietal cortex was shown during acute experiments on cats anesthetized by pentobarbital using an intracellular recording technique. The monosynaptic nature of the two first components of EPSP produced by corticofugal impulses spreading at the average rate of 18.5 and 7.5 msec, respectively, was established. It is postulated that these EPSP components are produced by activating the slow conducting pyramidal and corticorubral neurons. In a portion of rubrospinal neurons the first component of EPSP produced by corticofugal impulses was marked by a fast-rising phase and reflected electrophysiological activation of axosomatic synapses. Findings are discussed with regard to mechanisms reorganizing cortical synaptic inputs to the red nucleus neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 665–672, September–October, 1985.     

Oscillatory evoked potentials in the rabbit visual system during experimental retinal pathology induced by administration of monoiodoacetic acid

ERG and EP of the visual cortex (VC) and superior colliculus (SC) were investigated under experimental dystrophy of the retina induced by intravenous injection of monoiodoacetic acid in different doses. The relative resistance of the VC to the derangement of retinal function was established. It was manifested by less marked suppression of its EP as compared with ERG. Taking into consideration the selective projection to the SC of the rod system that was damaged to a greater degree under pathology in question, it is suggested that functional suppression of the SC might facilitate the conduction of visual information through the main retino-geniculo-cortical canal. This might be one of the factors of VC resistance to the impairment of retinal function. This assumption was confirmed in experiments with SC electrocoagulation in which one could observe the facilitation of EP formation of the contralateral VC.     

Neural generators of the somatosensory evoked potentials: Recording from the cuneate nucleus in man and monkeys

The neural generators of the somatosensory evoked potentials (SEPs) elicited by electrical stimulation of the median nerve were studied in man and in rhesus monkeys. Recordings from the cuneate nucleus were compared to the far-field potentials recorded from electrodes placed on the scalp. It was found that the shape of the response from the surface of the human cuneate nucleus to stimulation of the median nerve is similar to that of the response recorded more caudally in the dorsal column, i.e., an initially small positivity followed by a negative wave that is in turn followed by a slow positive wave. The beginning of the negative wave coincides in time with the N14 peak in the SEP recorded from the scalp, and its latency is 13 msec. The response from the cuneate nucleus in the rhesus monkey has a similar shape and its negative peak appears with the same latency as the positive peak in the vertex response that has a latency of 4.5 msec; the peak negativity has a latency of about 6 msec and thus coincides with P6.2 in the vertex recording. Depth recordings from the cuneate nucleus and antidromic stimulation of the dorsal column fibers in the monkey provide evidence that the early components of the response from the surface of the cuneate nucleus are generated by the dorsal column fibers that terminate in the nucleus.The results support the hypothesis that the P14 peak in the human SEP is generated by the termination of the dorsal column fibers and that the cuneate nucleus itself contributes little to the far-field potentials.     

Comparative evaluation of visual evoked potentials in experimental hepatic encephalopathy and in pharmacologically induced coma-like states in rat

Visual Evoked Potential (VEP) was used as a method for the evaluation of Hepatic Encephalopathy (HE) in rats with galactosamine induced Fulminant hepatic Failure (FHF). Two degrees of the coma were documented by two different patterns in VEP recording. Animals under pentobarbital anaesthesia had a VEP waveform clearly different from the coma VEP and, as a further demonstration of the specificity in VEP changes, Amino-oxyacetic acid produced a VEP waveform similar to that due to pentobarbital anaesthesia. Neither ammonia nor amino acids (tryptophan and phenylalanine), believed to be inducers of HE-like neurological symptoms in normal animals, produced a VEP waveform similar to VEP recorded during HE. The authors propose this method for the evaluation, quantification and documentation of the neurological changes during experimental HE and during experiments inducing a HE-like state in normal animals.     

Trial on the objective evaluation of visual acuity and its maturation by the method of evoked visual potentials]

We have developed a method to estimate foveal visual acuity (VA) through analysis of VEPs. It consists in determining the smallest check size in a pattern reversal that elicits a significant cortical response. The VEP is regarded as significant if the P 100 amplitude reaches a pre-established level in the signal to noise ratio. A valid criterion to determine normal VEP-VA emerges from the testing of 84 emmetropic and ametropic eyes: within our stimulation and recording conditions, a significant VEP response to the reversal of seven minutes checks corresponds to normal foveal acuity. This criterion has also proved pertinent to discriminate between normal VAs of 20/20 and decreased VAs (20/40 or less) with four other groups of subjects: 14 adult eyes whose VAs of 20/20 are decreased through Bangerter occlusives, 32 emmetropic and ametropic eyes belonging to five-years-olds children, 28 emmetropic and ametropic eyes of twelve-years-olds. In order to guarantee the validity of our results we carried out a double-blind study with ophthalmologists. The relevance of the method we suggest is related to that of the method which consists in extrapolating the regression line between VEP amplitudes and the pattern element sizes. At least we have aimed at establishing VEP norms for the maturation of VA. We have collected data from the following subjects: 5 infants tested monthly between 1 and 6 months, 31 infants ranging in age from 1 to 16 months, 10 five-year-old children, 13 twelve-year-olds, and 11 subjects aged 20. Within our stimulation and recording conditions a significant evoked response to the reversal of seven minute checks can be observed from 8 months onward. With an eight-month-old infant this response to the reversal of seven minute checks cannot be identified to the same response with an adult. There are two major differences: the latency of the major positive component is longer, and the structure of the evoked response consists of fewer components.     

The trade of medicinal animals in Brazil: current status and perspectives

In cities, the trade of medicinal products derived from animals, especially as raw materials, is concentrated in local and traditional markets. The lack of studies on commercialised medicinal faunas restricts an evaluation of the impact of this activity on the exploited species. Within this context, this work reviewed the literature on the trade of medicinal animals in local markets, focusing on urban zootherapy in Brazil and the social factors involved in these practices. Our results reveal that at least 131 species are sold for medicinal purposes in markets and open fairs in Brazil, but results obtained from statistical estimators suggest that this trade actually encompasses a greater richness of species. The medicinal animals sold in Brazil are used to treat 126 illnesses and/or symptoms. Despite the trade of wild animals, including species that are present on the list of endangered species, being forbidden in Brazil, it has been demonstrated that this activity remains common in some Brazilian cities, occurring illicitly and without due monitoring by competent environmental agencies. The results illustrate the need for further research, which should encompass a larger number of cities, especially in regions where information on this subject is currently lacking.     

The contribution of the lateral semicircular canal to the short latency vestibular evoked potentials in cat

Short latency vestibular evoked potentials (VsEPs) to angular acceleration impulses (maximal intensity 20,000°/sec², rise time 1.5–3 msec) were recorded by skin electrodes in cats before and after various surgical procedures. Under general anesthesia, the animals underwent unilateral labyrinthectomy and the VsEPs in response to stimulation of the remaining inner ear in the plane of the lateral semicircular canal (SCC) with the head flexed 20°–25° were recorded as a baseline. The lateral SCC was then selectively obliterated near its ampulla. This induced major changes in the VsEPs recorded in response to stimulation of the remaining inner ear in this plane: the first 2 VsEP waves were absent, and only longer latency, smaller amplitude waves were present in response to both clockwise and counterclockwise stimulation. On the other hand, obliteration of the anterior and posterior SCCs and, in addition, destruction of both maculae were without major effects on the first 2 VsEP waves in response to excitatory stimulation. The results confirm that when the head is flexed 20°–25° and stimulated with angular acceleration impulses in the horizontal plane, the major site of initiation of the VsEPs in cats and probably in man is the crista ampullaris of the lateral SCC.     

Physiology and physiopathology of somatic sensations studied in man by the method of evoked potentials

The physiology of somatic sensation can be investigated noninvasively in man by recording the electric activity of peripheral nerves, spinal cord and brain. Since these responses have a small voltage, it is necessary to use electronic averaging methods for improving the signal-to-noise ratio. These methods are described and discussed, as well as principles of interpretation of somatosensory evoked potentials. It is agreed that the traces thus obtained involve a series of components (extracellular potentials) which reflect distinct neural generators. These generators have been identified and localized at different levels of the subcortical somatosensory pathway and in different cortical areas. Several components reflect generators located under the recording electrodes (nearfield potentials), while other reflect extracellular potentials diffusing at a distance in the volume conductor of the neck and head (farfield potentials). The analysis of these components provides a wealth of new data for the physiology and pathophysiology of the somatic sensory system in man. Besides so-called "obligatory" components that are present irrespective of the attention of the subject, the studies have uncovered "cognitive" components which reflect neural mechanisms involved in the intellectual processus of perception and decision.     

Laccase applications in biofuels production: current status and future prospects

The desire to reduce dependence on the ever diminishing fossil fuel reserves coupled with the impetus towards green energy has seen increased research in biofuels as alternative sources of energy. Lignocellulose materials are one of the most promising feedstocks for advanced biofuels production. However, their utilisation is dependent on the efficient hydrolysis of polysaccharides, which in part is dependent on cost-effective and benign pretreatment of biomass to remove or modify lignin and release or expose sugars to hydrolytic enzymes. Laccase is one of the enzymes that are being investigated not only for potential use as pretreatment agents in biofuel production, mainly as a delignifying enzyme, but also as a biotechnological tool for removal of inhibitors (mainly phenolic) of subsequent enzymatic processes. The current review discusses the major advances in the application of laccase as a potential pretreatment strategy, the underlying principles as well as directions for future research in the search for better enzyme-based technologies for biofuel production. Future perspectives could include synergy between enzymes that may be required for optimal results and the adoption of the biorefinery concept in line with the move towards the global implementation of the bioeconomy strategy.     

Dependence of nitrazepam metabolism on the method of its administration and species of experimental animals

Intraperitoneal, intravenous and peroral administration of nitrasepam has no effect on its transformation and distribution in the liver tissues, blood and brain of mice. Depending on the products of nitrasepam transformation formed in the animal liver, the enzymic systems providing such transformations have species peculiarities: the rat liver tissues contain nitroreductase, N-acetyl-transferase and desacetylase. And the mice tissues contain only nitroreductase and desacetylase.     

Evaluation of hypoxic state in experimental animals induced by Yersinia pestis antigens

Some characteristics of purine metabolism in experimental animals (white mice, clawed jirds and guinea pigs), injected intraperitoneally with Y. pestis "murine" toxin and capsular antigen (Fraction 1), were studied. Under the influence of sublethal doses of these antigens increased levels of guanine and xanthine in blood were noted. Changes in the content of xanthine oxidase in cells were insignificant. In white mice and clawed jirds the activity of succinate dehydrogenase decreased under the action of "murine" toxin and increased after the injection of Fraction 1.     

Antidromic and synaptic potentials evoked in neurons of the lateral vestibular nucleus by stimulation of the interstitial nucleus of Cajal and Darkshevich's nucleus in cats

Effects of stimulation of the interstitial nucleus of Cajal and Darkshevich's nucleus on unit activity in the lateral vestibular nucleus of Dieters were investigated in cats anesthetized with pentobarbital. Stimulation of the above-mentioned structures was shown to lead to antidromic and orthodromic activation of Dieters neurons. Axon collateral of vestibular neurons, ascending to the above-mentioned brain-stem structures were discovered electrophysiologically. Stimulation of the nuclei of Cajal and Darkshevich was shown to evoke mono- and polysynaptic EPSPs and IPSPs in neurons of Deiters nucleus. Convergence of influences from both nuclei on the neurons studied was demonstrated. The particular features and functional role of the influences observed are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 822–829, November–December, 1984.