Characterization of the synaptic properties of olfactory bulb projections

The olfactory bulb directly projects to several diverse telencephalic structures, but, to date, few studies have investigated the physiological characteristics of most of these areas. As an initial step towards understanding the odor processing functions of these secondary olfactory structures, we recorded evoked field potentials in response to lateral olfactory tract stimulation in vivo in urethane-anesthetized Sprague-Dawley rats in the following brain structures: anterior olfactory nucleus, ventral and dorsal tenia tecta, olfactory tubercle, anterior and posterior piriform cortex, the anterior cortical nucleus of the amygdala, and lateral entorhinal cortex. Using paired-pulse stimulation with interpulse intervals of 25-1000 ms, we observed facilitation of the response to the second pulse in every structure examined, although the degree of facilitation varied among the target structures. Additionally, pulse train stimulation at three different frequencies (40, 10 and 2 Hz) produced facilitation of evoked field potentials that also varied among target structures. We discuss the potential utility of such short-term facilitation in olfactory processing.     

The sensory functions of the cerebellum of the thornback ray,Platyrhinoidis triseriata

Summary Single unit spikes and evoked field potentials were recorded in different parts and depths of the corpus cerebelli and auricle of immobilized rays before and after stimulating with light, electric fields, touch, tail bending and direct shock to mechanoreceptive nerves of the lateral line.Discrete areas of the cerebellum are responsive to these modalities and the areas show limited overlap; they are all distinct from the area reported by Plassmann to be responsive to angular acceleration. The visual and tactile-proprioceptive areas are large; the electric area is small. Most units are excited only by one modality.The tail is represented only in the posterior lobe; trigeminal innervation extends from the posterior onto the anterior lobe, suggesting some topographic projection.The dynamic characteristics of the responses were examined particulary in the visual units. To a flash, units discharge up to six bursts of spikes in 500 ms. This pattern is reduced at repetition rates > 1/s; above ca. 4/s units tend to fire irregularly. Various kinds of units are found in respect to the succession of responses to short trains of flashes. Some units fire much better to objects moving in a limited visual field with a certain direction and rate.Abbreviation EP evoked potential     

刺激大鼠颈體背外侧束诱发的脊髓电场电位

电刺激大鼠颈髓背外侧束(DLF),在脊髓腰段用微电极记录到—诱发场电位,将其长时程慢电位正波称为 DLF-FP。DLF-FP 的潜伏期为7.22±1.41ms,达峰时间为15.12±5.58ms,时程为93.92±9.06ms。绘制 DLF-FP 等电位图发现:其负电场中心位于背表面下1.0—1.3mm,与外周传入诱发的场电位(P_1-FP)的起源部位基本一致。印防己毒素抑制DLF-FP,士的宁加强 DLF-FP。在一定时间范围内,先后刺激腓肠神经和 DLF,两者所诱发的场电位具有总和和抑制现象。这些结果表明 DLF-FP 是初级传入末梢去极化的反映,可能和刺激外周神经诱发的场电位共用脊髓环路。     

Scalp topography and dipolar source modelling of potentials evoked by CO2 laser stimulation of the hand

CO₂ laser evoked potentials to hand stimulation recorded using a scalp 19-channel montage in 11 normal subjects consistently showed early N1/P1 dipolar field distribution peaking at a mean latency of 159 ms. The N1 negativity was distributed in the temporoparietal region contralateral to stimulation and the P1 positivity in the frontal region. The N1/P1 response was followed by 3 distinct components: (1) N2a reaching its maximal amplitude at the vertex and ipsilaterally to the stimulated hand, (2) N2b mostly distributed in the frontal region, and (3) P2 with a mid-central topography. Brain electrical source analysis showed that this sequence was explained, with a residual variance below 5%, by a model including two dipoles in the upper bank of the Sylvian fissure of each hemisphere, a frontal dipole close to the midline, and two anterior medial temporal dipoles, thus suggesting a sequential activation of the two second somatosensory areas, anterior cingulate gyrus and the amygdalar nuclei or the hippocampal formations, respectively. This model fitted well with the scalp field topography of grand average responses to stimulation of left and right hand obtained across all subjects as well as when applied to individual data. Our findings suggest that the second somatosensory area contralateral to the stimulation is the first involved in the building of pain-related responses, followed by ipsilateral second somatosensory area and limbic areas receiving noxious inputs from the periphery.     

A comparison of the contractile properties of the human gastrocnemius and soleus muscles

Twitch speeds and potentiating capacities have been determined for human medial and lateral gastrocnemius and soleus muscles. The experiments involved and application of submaximal stimuli to the respective muscle bellies, with monitoring of the evoked compound action potentials (M-waves) during repetitive stimulation. Contrary to an earlier report, the lateral gastrocnemius was found to have a significantly shorter mean contraction time (100.0 +/- 10.8 ms) than the soleus (156.5 +/- 14.7 ms) and this value was also significantly different from that of the medial gastrocnemius (113.7 +/- 19.6 ms). The mean half-relaxation time for each muscle also differed significantly from those for the other two muscles. A further contrast between the muscles was that potentiation of the twitch, following a 3-s tetanus at 50 Hz, was significantly greater in the lateral gastrocnemius than in soleus (mean values 60.4 +/- 43.1% and 2.6 +/- 3.3% respectively.     

Olfactory Evoked Potential Produced by Electrical Stimulation of the Human Olfactory Mucosa

Most physiological studies of the human olfactory system haveconcentrated on the cortical level; the olfactory bulbar levelhas been studied rarely. We attempted to stimulate the humanolfactory mucosa by electrical pulse to detect the bulbar potentials.Electrical stimulation (2 mA, 0.5 ms) of the human olfactorymucosa evoked a change in potential recorded from the frontalsector of the head. A negative peak of the evoked potentialthat occurred at 19.4 ms (grand means, n = 5) after stimulationwas the clearest. The highest amplitude of the potential wasrecorded from the frontal sector of the head on the stimulatedside. Our findings were similar to the experimental resultsobtained from the olfactory bulbs of animals. This evoked potentialwas considered to be the human olfactory bulbar potential. Whenthe subjects were stimulated by applying electricity to theolfactory mucosa, no sensation of smell occurred even thoughevoked potentials were recorded. Evoked potentials were recordedonly when the stimulating electrode was located in the olfactorycleft. When the stimulating electrode was outside the olfactorycleft, the stimulation caused pain. The trigeminal nerve seemedto be stimulated by electricity. Olfactory evoked potentialsproduced by the electrical stimulation of the human olfactorymucosa should aid the research on human olfactory physiology,and may be applicable to clinical tests of olfactory dysfunction.Chem. Senses 22: 77–81, 1997.     

A new electroreceptive teleost:Xenomystus nigri (Osteoglossiformes: Notopteridae)

Summary The African knife fish,Xenomystus nigri, is found to be sensitive to weak electric fields by the method of averaged evoked potentials from the brain. Slow waves and spikes were recorded in or near the lateral line area of the medulla and the torus semicircularis of the mesencephalon in response to long pulses (best > 50 ms) and low frequency sine waves (best ca. 10 Hz) of voltage gradients down to < 10 V/cm. Evoked waves in the lateral line area are a sequence of negative and positive deflections beginning with a first peak at ca. 24 ms; in the torus semicircularis the first peak is at ca. 37 ms. Spikes are most likely in the torus between 50 and 80 ms after ON. At each recording locus there is a best axis of the homogeneous electric field and a better polarity. Effects of stimulus intensity, duration and repetition are described. The physiological properties are similar to those of ampullary receptor systems in mormyriforms, gymnotiforms and siluriforms.Confirming Braford (1982),Xenomystus has a large medullary nucleus resembling the nucleus otherwise peculiar to mormyriforms, gymnotiforms and siluriforms and now called the electrosensory lateral line lobe (ELLL; formerly the posterior lateral line lobe). We describe the projections of anterior and posterior lateral line nerves by HRP applied to the proximal stump of a cut nerve. A descending central ramus of the anterior lateral line nerve and a lateral component of the ascending ramus of the posterior lateral line nerve end in part in the ELLL.Electroreception, including the system of discrete central structures mediating it, is for the first time found to be less than an ordinal or even a family character, but apparently a characteristic of the subfamily Xenomystinae. Species of the other subfamily, Notopterinae as well as of the other families of osteoglossiforms (Osteoglossidae, Hiodontidae and Pantodontidae), lack the ELLL.Notopterus andPantodon are found to lack the evoked potential.The positive finding of evoked activity to feeble electric field is found to be the most practical method for searching widely among fishes for the presence of the electrosense modality and its central pathways. The anatomical criterion of an ELLL can now be taken to be a good criterion for the presence of this sensory system. The absence of evoked response correlates well with the absence of an ELLL.Abbreviations ELLL electrosensory lateral line lobe - HRP horseradish peroxidase - TS torus semicircularis     

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.     

Projections of the posterior area of the hypothalamus to its medial,anterior, and lateral areas

The effect of stimulation of the lateral and medial supramammillary areas of the posterior hypothalamus on spontaneous single unit activity in the anterior, lateral, medial dorsal, and medial ventral areas of the hypothalamus was investigated in acute experiments on rabbits. Single stimulation of the medial area of the posterior hypothalamus evoked responses of 44% of neurons, whereas stimulation of the lateral area did so in only 35% of all neurons recorded. Repetitive stimulation led to an increase in the number of responding neurons (to 57% during stimulation of the lateral and 74% during stimulation of the medial supramammillary area). In response to repetitive stimulation of the medial supramammillary area, activating influences became predominant in all areas, whereas in response to stimulation of the lateral area, they became predominant in the medial, ventral, and lateral areas. The results are assessed from the standpoint of the role of the posterior hypothalamus in the regulation of adenohypophyseal functions.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 377–381, July–August, 1977.     

急性神经损伤引起脊髓背角C-纤维诱发电位长时程增强

神经损伤引起神经病性疼痛,表现为持续性痛超敏和痛觉过敏。目前对神经病性疼痛的机制尚缺乏了解。我们以往的工作表明强直电刺激坐骨神经可引起脊髓背角C-纤维诱发电位的长时程增强(long-term potentiation,LTP),该LTP被认为是病理性疼痛的突触模型。本研究的目的在于探讨急性神经损伤是否能在完整动物的脊髓背角诱发出C-纤维诱发电位LTP。在以测试刺激(10～20V,0．5ms)电刺激坐骨神经的同时在脊髓背角用微电极记录C一纤维诱发电位。分别用强直刺激、剪断或夹捏坐骨神经诱导LTP。结果发现：(1)剪断或夹捏坐骨神经都可以诱导脊髓背角C-纤维诱发电位的LTP,该LTP可持续到实验结束(3～9h),在剪断神经前10min用利多卡因局部阻滞坐骨神经则可完全阻断LTP的产生;(2)神经损伤诱导的LTP可被NMDA受体阻断剂AP5所阻断;(3)用单次强直刺激引起LTP后,切断坐骨神经可使LTP的幅度进一步增大,而用多次强直电刺激使LTP饱和后,损伤神经则不能使LTP进一步增大。切断神经引起LTP后,强直电刺激也不能使LTP进一步增大。这些结果表明,急性神经损伤可以诱导脊髓背角C纤维诱发电位LTP,且切断神经能更有效地诱导LTP。该试验进一步支持我们的设想,即脊髓背角C-纤维诱发电位LTP可能在病理性疼痛的形成中起重要作用。     

Spatial analysis of motor unit potentials of the rat medial gastrocnemius

The spatial analysis of the potentials of single motor units of the rat medial gastrocnemius muscle evoked by stimulation of the fibres of split ventral roots was carried out with a bipolar electrode moving in the direction perpendicular to the longitudinal axis of the muscle fibres. During this movement of the electrode a variability was observed in the time of the biphasic potential from its maximum to minimum, and in the peak-to-peak amplitude of these potentials. The potentials recorded outside the territory of the motor unit had a lower amplitude in relation to the potentials from the territory of the unit. This made localization of the motor unit on the cross-section of the muscle possible. Differences in the duration of the potential from maximal to minimal amplitude (maximum-minimum amplitude time--M-MAT) of each investigated motor unit from successive recording sites reflected the number of fibres contributing to the action potential and the distance of the recording surface of the electrode from the zone of the motor end-plates of this motor unit. The greatest diameter of the territory of the observed motor units reached 2.5 mm.     

Mitral tetrahedron as a geometrical surrogate for chronic ischemic mitral regurgitation

The present study tests the hypothesis that a mitral tetrahedron (MT) is a useful geometrical surrogate for assessment of chronic ischemic mitral regurgitation (CIMR). Fifty-eight subjects were divided into three groups on the basis of left ventricular ejection fraction (LVEF) and the presence or absence of CIMR: LVEF > or =0.5 and negative CIMR (group 1, n = 28), LVEF <0.5 and negative CIMR (group 2, n = 12), and LVEF <0.5 and positive CIMR (group 3, n = 18). MT was defined by its four vertices at the anterior annulus, posterior annulus, and medial and lateral papillary muscle roots, determined by MRI at peak systole. The results showed no clear cutoff values of MT parameters between groups 2 and 1. In contrast, all MT indexes were significantly different between groups 3 and 2 (P < 0.05), and significant cutoff values differentiated the two groups. A scoring system employing parameters of the whole MT confirmed the absence of CIMR with total edge length index <268 mm/BSA(1/3), total surface area index <2,528 mm(2)/BSA(2/3), and volume index <5,089 mm(3)/BSA (where BSA is body surface area). The sensitivity, specificity, and positive and negative predictive values were 1.00. This preliminary study demonstrates that MT might serve as a good geometrical surrogate for assessing CIMR. The derived geometrical criteria of MT may be useful in surgical correction of CIMR.     

Effect of hippocampal stimulation on the feeding behavior of cats

Influence of electrical stimulation (100 cps., 1.0 ms) of medial parts of dorsal and ventral hippocampus (field CA1), and the lateral parts of dorsal and posterior hippocampus (field CA3) on general behaviour, elaboration of instrumental and manifestation of delayed reactions was studied in chronic experiments on cats. Stimulation of medial parts of dorsal and ventral hippocampus elicited a reaction of orienting reflex type to natural stimuli. Stimulation of lateral parts of dorsal and posterior hippocampus evoked arrest reactions. Medial and lateral parts of hippocampus produced different influences on elaboration of conditioned reflexes. In the first case elaboration was possible, but developed slower, while in the second case the ability to learn during stimulation was completely lost due to development of arrest reaction. Stimulation of different parts of the hippocampus disturbed delayed reactions, reducing the number of correct responses.     

Steady-state auditory evoked potentials (SSAEPs) in the rabbit. Contribution of the inferior colliculus

Steady-state auditory evoked potentials (SSAEPs) were recorded in rabbits with both surface and depth electrodes. Surface recording from the bregma provided the largest and most typical SSAEPs as compared to other surface locations when a stimulus rate of 50 Hz was used. The medial geniculate body (MGB) showed no potential corresponding to the surface SSAEP. On the other hand, the latency of SSAEP in the inferior colliculus (IC) corresponded closely to that of the surface potential. Furthermore, the amplitude of the IC potential tended to become large with the stimulus rate of 50 Hz as compared with transient stimuli. Although other auditory nuclei in the brain-stem, the ventral nucleus of the lateral lemniscus, the trapezoid body and the auditory nerve responded to transient stimuli with an amplitude larger than that of the IC, no amplification occurred with 50 Hz stimuli in these nuclei. These findings suggest that the IC contributes to the generation of SSAEP to a great extent.     

Reticular activation by splanchnic afferents: its influence on visual projections at the level of the cerebral cortex in cats]

In an previous work, we have shown a strong increase of visual evoked potentials of the medial lateral gyrus by splanchnic stimulation. This present study demonstrates that this effect is due to the activation of the substantia reticularis. Actually, we observed: 1) an increase of the reticular visual potential by splanchnic stimulus in convergent zone; 2) an increase of the visual evoked potential in the primary cortical area by stimulation of this reticular formation. These results show the existence of a functional pathway including the splanchnic nerve, the reticular formation and the visual cortex.     

Dynamic Processing of Nociception in Cortical Network in Conscious Rats: A Laser-evoked Field Potential Study

(1) Field potential study in conscious rats provides a convenient and effective animal model for pain mechanism and pharmacological research. However, the spatial-temporal character of nociception processing in cortex revealed by field potential technique in conscious rats remains unclear. (2) In the present study, multi-channel field potentials evoked by noxious laser stimulation applied to the hind paw of conscious rats were recorded through 12 chronically implanted skull electrodes. Independent component analysis (ICA) was used to remove possible artifacts and to extract the specific nociception-related component. (3) Two fast sharp responses and one slow blunt response were evoked by noxious laser stimulation. Systemic morphine (5 mg/kg, i.p.) preferentially attenuated the amplitude of the slow blunt response while had no significant effect on the first two sharp responses. ICA revealed that those responses came from activities of contralateral anterior parietal area, medial frontal area and posterior parietal area. A movement artifact was also detected in this study. Partial directed coherence (PDC) analysis showed that there were changes of information flows from medial frontal and posterior parietal area to anterior parietal area after noxious laser stimulation. (4) Characterization of the spatio-temporal responses to noxious laser stimulation may be a valuable model for the study of pain mechanisms and for the assessment of analgesia.     

Differential sensitivity of tongue areas and palate to electrical stimulation: a suprathreshold cross-modal matching study

A cross-modal matching procedure was used, in twelve subjects,to evaluate regional differences in suprathreshold sensitivityof the oral cavity to electrogustometric stimulation. Stimulationof five loci on each side of the oral cavity was performed:tongue tip (one cm from the midline), anterior tongue side (2.5cm from tip on lateral margin), posterior tongue side (regionof the foliate papillae), posterior medial tongue (one cm frommidline on circumvallate papillae), and soft palate (one cmfrom midline, one cm above superior pole of anterior palatinearch). The tip of the tongue was significantly more sensitivethan the other areas to electric stimulation, as evidenced bythe slope and absolute position of the psychophysical powerfunctions. Strong correlations were observed in the sensitivitymeasures across tongue loci and between tongue and palate sides.No effects of subject gender or mouth side were found.     

大鼠脊髓诱发电位与脊髓损伤的关系——Ⅲ.脊髓局部损毁后电位的变化及电位来源分析

本文描述了大鼠脊髓L_1节段后柱、后索、侧索和前角的诱发电位及其损伤后的变化,并观察了切断L_4、L_5脊神经背、腹根与横断高位颈髓对电位的影响,以进行行电位来源分析。结果可见,上述四个区域的诱发电位基本由早反应三相波和晚反应组成。分别电解损毁这些部位后,电位波幅均普遍降低,晚期反应较早反应降低明显。后柱或后索受损对电位影响最大。局部损毁后可见L_1及T_(13)水平的硬膜上电位改变明显,尤其晚反应减弱、波峰平坦。反应时值与潜伏时未见明显改变。切断L_4脊神经背、腹根后、电位基本消失。去大脑对电位未见明显影响。结果表明,刺激坐骨神经诱发的脊髓电位起源于低位腰段传入神经和脊髓内多通路的兴奋传导,在一定程度上受腹根逆行活动的影响,与大脑及脊髓下行传导束活动无直接联系。脊髓诱发电位的幅度与波形改变可作为脊髓损伤的判断指标之一。     

Cerebral-evoked responses elicited by direct stimulation of the lateral spinothalamic tract in the human

The authors recorded cerebral-evoked responses elicited by direct stimulation of the human lateral spinothalamic tract (LST) during percutaneous cordotomy to investigate central conduction of noxious stimuli. These responses consisted of four negative potentials, peak latency being 3.8 (N1), 8.4 (N2), 12.2 (N3) and 21.9 (N4) ms respectively. N1 showed wide distribution over the scalp and was considered to be of subcortical origin. N2-N4 were distributed in both the temporal and central area. The different distribution pattern of N2-N4 from conventional somatosensory-evoked potential suggested a different projection of LST from the medial lemniscus system.     

Physiology of lateral line mechanoreceptive regions in the elasmobranch brain

The physiology of mechanoreceptive lateral line areas was investigated in the thornback guitarfish, Platyrhinoidis triseriata, from medulla to telecephalon, using averaged evoked potentials (AEPs) and unit responses as windows to brain functions. Responses were analysed with respect to frequency sensitivity, intensity functions, influence of stimulus repetition rate, response latency, receptive field (RF) organization and multimodal interaction. 1. Following a quasi-natural vibrating sphere stimulus, neural responses were recorded in the medullary medial octavolateralis nucleus (MON), the dorsal (DMN) and anterior (AN) nucleus of the mesencephalic nuclear complex, the diencephalic lateral tuberal nucleus (LTN), and a telencephalic area which may correspond to the medial pallium (Figs. 2, 3, 13, 14, 15, 16). 2. Within the test range of 6.5-200 Hz all lateral line areas investigated responded to minute water vibrations. Best frequencies (in terms of displacement) were between 75 and 200 Hz with threshold values for AEPs as low as 0.005 microns peak-to-peak (p-p) water displacement calculated at the skin surface (Fig. 6). 3. AEP-responses to a vibrating sphere stimulus recorded in the MON are tonic or phasic-tonic, i.e., responses are strongest at stimulus onset but last for the whole stimulus duration in form of a frequency following response (Fig. 3). DMN and AN responses are phasic or phasic-tonic. Units recorded in the MON are phase coupled to the stimulus, those recorded in the DMN, AN or LTN are usually not (Figs. 5, 8, 9). Diencephalic LTN and telencephalic lateral line responses (AEPs) often are purely phasic. However, in the diencephalic LTN tonic and/or off-responses can be recorded (Fig. 11). 4. For the frequencies 25, 50, and 100 Hz, the dynamic intensity range of lateral line areas varies from 12.8 to at least 91.6 dB (AEP) respectively 8.9 and 92 dB (few unit and single unit recordings) (Fig. 7). 5. Mesencephalic, diencephalic, and telecephalic RFs, based on the evaluation of AEPs or multiunit activity (MUA), are usually contralateral (AN and LTN) or ipsi- and contralateral (telencephalon) and often complex (Figs. 10, 12, 16). 6. In many cases no obvious interactions between different modalities (vibrating sphere, electric field stimulus, and/or a light flash) were seen. However, some recording sites in the mesencephalic AN and the diencephalic LTN showed bimodal interactions in that an electric field stimulus decreased or increased the amplitude of a lateral line response and vice versa (Fig. 13 B).