Electroreceptor mechanisms of the ampullae of lorenzini in skates

Responses of the receptor epithelium of single electrically isolated ampullae of Lorenzini and spike responses of nerve fibers connected to them to electrical stimulation under voltage clamping conditions were studied in experiments on the Black Sea skateRaja clavata. The preparations had an input resistance of 200–800 KΩ, a transepithelial resting potential of between 0 and ?2 mV, and the usual spontaneous spike activity in their afferent fibers. Thresholds of the electroreceptors were 2–10 µV (current about 10^?11 A). Within the working range of the electroreceptors (up to ±500 µV, current up to 1 nA) the current-voltage characteristic curve of the epithelium was linear without any evidence of spike or wave activity of the receptor cells. With negative currents of over 1–10 nA a regenerative spike appeared on the epithelium and was accompanied by an uncharacteristic pattern of spike discharge of the nerve fiber. It is concluded that, contrary to Bennett's hypothesis, spike or oscillatory activity bears no relationship to normal working of electroreceptors. It is postulated that "secondarily sensitive" receptor cells share a common functional organization, which is based on a chemical synapse with high electrical sensitivity.     

Cardiogenic reflexes after immune injury of the heart

Afferent and efferent spike activity from the parasympathetic (vagus) and sympathetic cardiac nerves were recorded simultaneously with ECG, and indices of heart function were measured in acute experiments on anesthetized dogs, which allowed us to study the modifications of cardio-cardiac reflex influences after a local immune heart injury. After an injury nidus has been formed in the heart, cardiogenic depressor reflexes evoked by an intracoronary application of veratrine or bradykinin were considerably suppressed or even abolished, and afferent spike activity in the vagus cardiac nerves noticeably decreased. At the same time, both the facilitation of activity in sympathetic afferent fibers and pressor reflex effects were preserved after the heart injury. Different localization of vagus and sympathetic afferent structures in the heart and their specialized sensitivity to the biologically active substances are suggested as the factors determining the pattern of cardiogenic reflex influences after a heart injury.Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 18–25, January–February, 1995.     

Afferent flow patterns in a cat cutaneous nerve during painful and painless mechanical stimulation of the skin

Quantitative characteristics of afferent flows coding information from a number of receptors were obtained by the gliding impulses method. The frequency spectrum of activity in a cutaneous nerve, the relative numbers of active A, A, and C fibers and their distribution by impulse transition frequency during stimulation of the cat's skin with pins and needles were determined. The afferent flow recorded in the nerve during pricking of the skin is characterized by high density, due to the number of excited fibers and the frequency of activity in them. The higher density of the afferent flow during the application of a painful than of a painless stimulus is mainly due to activity in C fibers. Unmyelinated fibers subjected to the action of the same stimulus and of chemically active substances liberated from the cells during tissue injury are excited directly and generate high-frequency spikes which increase the flow density in the nerve. The number of active myelinated fibers and the spike frequency during the action of a painful stimulus are only a little greater than the corresponding characteristics of the afferent discharge during painless stimulation.Scientific-Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 391–399, July–August, 1976.     

Neuronal organization of the left celiac ganglion in the cat

Unit responses of the isolated left celiac ganglion to stimulation of various nerves of the solar plexus were studied by intracellular microelectrode recording in cats before and after degeneration of the preganglionic fibers. The resting potential of the ganglionic neurons was ?62.2±2.9 mV and the amplitude of the spike potential 72.4±3.2 mV. The spike was followed by after-hyperpolarization with a mean amplitude of 24% of the spike amplitude and a duration of between 25 and 180 msec. A characteristic feature of the ganglion was the presence of orthodromic unit responses to stimulation of peripheral nerve fibers of the solar plexus. The higher threshold of activation of the neurons by peripheral fibers than by preganglionic fibers and the preservation of orthodromic unit responses to stimulation of peripheral nerves after degeneration of the preganglionic fibers are evidence that the peripheral reflex arc is closed in this ganglion. Neurons of the left celiac ganglion are divided into three groups. Only preganglionic fibers of the splanchnic nerve with different properties converge on the neurons of the first group (the most numerous); only afferent fibers of peripheral nerves converge on the neurons of the third group (the least numerous); both types of fibers terminate on neurons of the second group. This convergence may lie at the basis of the mechanism of the centrifugal and peripheral reflex interaction in the ganglion for coordinated visceral activity.     

GM1 ganglioside contributes to retain the neuronal conduction and neuronal excitability in visceral and baroreceptor afferents

GM1 ganglioside has a great impact on the function of nodes of Ranvier on myelinated fiber, suggesting its potential role to maintain the electrical and neuronal excitability of neurons. Here we first demonstrate that visceral afferent conduction velocity of myelinated and unmyelinated fibers are reduced significantly by tetrodotoxin (TTX) or cholera toxin-B subunits (CTX-B), and only the effects mediated by CTX-B are prevented by GM1 pre-treatment. At soma of myelinated A and unmyelinated C-type nodose ganglion neurons (NGNs), the action potential spike frequency reduced by CTX-B is also prevented by GM1. Additionally, the current density of both TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na⁺ channels were significantly decreased by CTX-B without changing the voltage-dependent property. These data confirm that endogenous GM1 may play a dominant role in maintaining the electrical and neuronal excitability via modulation of sodium (Na⁺) channel around nodes and soma as well, especially TTX-S Na⁺ channel, which is also confirmed by the reduction of spike amplitude and depolarization. Similar data are also extended to fluorescently identified and electrophysiologically characterized aortic baroreceptor neurons. These findings suggest that GM1 plays an important role in the neural modulation of electric and neuronal excitability in visceral afferent system.     

Effects of aspartic acid on skate electroreceptors

The effects of L-aspartic acid (L-ASP) on spontaneous and evoked activity in afferent nerve fibers were investigated by perfusing the basal membrane of sea skate electroreceptors (the ampullae of Lorenzini) with this substance. It was found that perfusion with physiological saline containing L-ASP exerted a primarily excitatory effect on afferent activity (threshold concentration: 10^–7 M). When synaptic transmission was blocked by magnesium ions, activity was restored in the afferent fibers if L-ASP was added to the solution and spike activity persisted for longer; this would imply the presence of desensitizing processes in the postsynaptic receptors of the ampullae. Finding would lead to the conclusion that L-ASP and L-glutamate fulfill a set of criteria for likely neurotransmitters in the ampullae of Lorenzini.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 61–67, January–February, 1987.     

Integrative Synaptic Mechanisms in the Caudal Ganglion of the Crayfish

A study of activity recorded with intracellular micropipettes was undertaken in the caudal abdominal ganglion of the crayfish in order to gain information about central fiber to fiber synaptic mechanisms. This synaptic system has well developed integrative properties. Excitatory post-synaptic potentials can be graded, and synaptic potentials from different inputs can sum to initiate spike discharge. In most impaled units, the spike discharge fails to destroy the synaptic potential, thereby allowing sustained depolarization and multiple spike discharge following single pulse stimulation to an afferent input. Some units had characteristics which suggest a graded threshold for spike generation along the post-synaptic fiber membrane. Other impaled units responded to afferent stimulation with spike discharges of two distinct amplitudes. The smaller or "abortive" spikes in such units may represent non-invading activity in branches of the post-synaptic axon. On a few occasions one afferent input was shown to inhibit the spike discharge initiated by another presynaptic input.     

Extra spike formation in sensory neurons and the disruption of afferent spike patterning

The peculiar pseudounipolar geometry of primary sensory neurons can lead to ectopic generation of "extra spikes" in the region of the dorsal root ganglion potentially disrupting the fidelity of afferent signaling. We have used an explicit model of myelinated vertebrate sensory neurons to investigate the location and mechanism of extra spike formation, and its consequences for distortion of afferent impulse patterning. Extra spikes originate in the initial segment axon under conditions in which the soma spike becomes delayed and broadened. The broadened soma spike then re-excites membrane it has just passed over, initiating an extra spike which propagates outwards into the main conducting axon. Extra spike formation depends on cell geometry, electrical excitability, and the recent history of impulse activity. Extra spikes add to the impulse barrage traveling toward the spinal cord, but they also travel antidromically in the peripheral nerve colliding with and occluding normal orthodromic spikes. As a result there is no net increase in afferent spike number. However, extra spikes render firing more staccato by increasing the number of short and long interspike intervals in the train at the expense of intermediate intervals. There may also be more complex changes in the pattern of afferent spike trains, and hence in afferent signaling.     

Detection of cold pain, cold allodynia and cold hyperalgesia in freely behaving rats

In mammals, somatosensory input activates feedback and feed-forward inhibitory circuits within the spinal cord dorsal horn to modulate sensory processing and thereby affecting sensory perception by the brain. Conventionally, feedback and feed-forward inhibitory activity evoked by somatosensory input to the dorsal horn is believed to be driven by glutamate, the principle excitatory neurotransmitter in primary afferent fibers. Substance P (SP), the prototypic neuropeptide released from primary afferent fibers to the dorsal horn, is regarded as a pain substance in the mammalian somatosensory system due to its action on nociceptive projection neurons. Here we report that endogenous SP drives a novel form of feed-forward inhibitory activity in the dorsal horn. The SP-driven feed-forward inhibitory activity is long-lasting and has a temporal phase distinct from glutamate-driven feed-forward inhibitory activity. Compromising SP-driven feed-forward inhibitory activity results in behavioral sensitization. Our findings reveal a fundamental role of SP in recruiting inhibitory activity for sensory processing, which may have important therapeutic implications in treating pathological pain conditions using SP receptors as targets.     

Information processing at a central synapse suggests a noise filter in the auditory pathway of the noctuid moth

1. The central projections of the A1 afferent were confirmed via intracellular recording and staining with Lucifer Yellow in the pterothoracic ganglion of the noctuid moths, Agrotis infusa and Apamea amputatrix (Fig. 1). Simultaneous recordings of the A1 afferent in the tympanal nerve (extracellularly) and in the pterothoracic ganglion (intracellularly) confirm the identity of the stained receptor as being the A1 cell. 2. The major postsynaptic arborizations of interneurone 501 in the pterothoracic ganglion were also demonstrated via intracellular recording and staining (Fig. 2). Simultaneous recordings of the A1 afferent (extracellularly) and neurone 501 (intracellularly) revealed that each A1 spike evokes a constant short latency EPSP in the interneurone (Fig. 2Bi). Neurone 501 receives only monaural input from the A1 afferent on its soma side as demonstrated by electrical stimulation of each afferent nerve (Fig. 2Bii). EPSPs evoked in neurone 501 by high frequency (100 Hz) electrical stimulation of the afferent nerve did not decrement (Fig. 2Biii). These data are consistent with a monosynaptic input to neurone 501 from the A1 afferent. 3. The response of neurone 501 to a sound stimulus presented at an intensity near the upper limit of its linear response range (30 ms, 16 kHz, 80 dB SPL) was a plateau-like depolarization, with tonic spiking activity which continued beyond the end of the tone. The instantaneous spike frequency of the response was as high as 800 Hz, and was maintained at above 600 Hz for the duration of the tone (Fig. 3). 4. The relationship between the instantaneous spike frequency in the A1 afferent and that recorded simultaneously in neurone 501 is linear over the entire range of A1 spike frequencies evoked by white noise sound stimuli (Fig. 4). Similarly, the relationship between instantaneous spike frequency in the A1 afferent and the mean depolarization evoked in neurone 501 is also linear for all A1 spike frequencies tested (Fig. 5). No summation of EPSPs occurred for A1 spike frequencies below 100 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)     

Static and dynamic properties of synaptic transmission at the cyto- neural junction of frog labyrinth posterior canal

The properties of synaptic transmission have been studied at the cyto-neural junction of the frog labyrinth posterior canal by examining excitatory postsynaptic potential (EPSP) activity recorded intraaxonally from the afferent nerve after abolishing spike firing by tetrodotoxin. The waveform, amplitude, and rate of occurrence of the EPSPs have been evaluated by means of a procedure of fluctuation analysis devised to continuously monitor these parameters, at rest as well as during stimulation of the semicircular canal by sinusoidal rotation at 0.1 Hz, with peak accelerations ranging from 8 to 87 deg.s-2. Responses to excitatory and inhibitory accelerations were quantified in terms of maximum and minimum EPSP rates, respectively, as well as total numbers of EPSPs occurring during the excitatory and inhibitory half cycles. Excitatory responses were systematically larger than inhibitory ones (asymmetry). Excitatory responses were linearly related either to peak acceleration or to its logarithm, and the same occurred for inhibitory responses. In all units examined, the asymmetry of the response yielded nonlinear two-sided input-output intensity functions. Silencing of EPSPs during inhibition (rectification) was never observed. Comparison of activity during the first cycle of rotation with the average response over several cycles indicated that variable degrees of adaptation (up to 48%) characterize the excitatory response, whereas no consistent adaptation was observed in the inhibitory response. All fibers appeared to give responses nearly in phase with angular velocity, at 0.1 Hz, although the peak rates generally anticipated by a few degrees the peak angular velocity. From the data presented it appears that asymmetry, adaptation, and at least part of the phase lead in afferent nerve response are of presynaptic origin, whereas rectification and possible further phase lead arise at the encoder. To confirm these conclusions a simultaneous though limited study of spike firing and EPSP activity has been attempted in a few fibers.     

Radular mechanosensory neuron in the buccal ganglia of the terrestrial slug,Incilaria fruhstorferi

A radular mechanosensory neuron, RM, was identified in the buccal ganglia of Incilaria fruhstorferi. Fine neurites ramified bilaterally in the buccal ganglia, and main neurites entered the subradular epithelium via buccal nerve 3 (n3). When the radula was distorted by bending, RM produced an afferent spike which was preceded by an axonic spike recorded at n3. The response of RM to radular distortion was observed even in the absence of Ca²⁺, which drastically suppressed chemical synaptic interactions. Therefore, RM was concluded to be a primary radular mechanoreceptor.During rhythmic buccal motor activity induced by food or electrical stimulation of the cerebrobuccal connective, RM received excitatory input during the radular retraction phase. In the isolated buccal ganglia connected to the radula via n3s, the afferent spike, which had been evoked by electrical stimulation of the subradular epithelium, was broadened with the phasic excitatory input. Since the afferent spike was also broadened by current injection into the soma, depolarization due to the phasic input may have produced the spike broadening.Spike broadening was also observed during repetitive firing evoked by current injection. The amplitude of the excitatory postsynaptic potential in a follower neuron increased depending on the spike broadening of RM.Abbreviations CBC cerebrobuccal connective - EPSP excitatory postsynaptic potential - n1,n3 buccal nerves 1 and 3 - RBMA rhythmic buccal motor activity - RM radular mechanosensory neuron - SMT supramedian radular tensor neuron     

电刺激大鼠巨细胞网状核对小脑浦肯野细胞自发和诱发电活动的影响

本研究在麻醉并制动的大鼠上观察了电刺激巨细胞网状核(Gi)对小脑浦肯野细胞(PC)自发及诱发简单锋电位的影响。结果如下:(1)刺激Gi可使PC的简单锋电位出现潜伏期小于20ms的抑制性或兴奋性反应,并以抑制性反应为主。抑制性反应持续40-100ms,而兴奋性反应的时程可达200ms以上;(2)注射5-HT_2型受体阻断剂methysergide可以减弱或阻断电刺激Gi对PC自发简单锋电位的抑制作用;(3)条件性Gi刺激可以显著压抑或加强由刺激对侧大脑皮层感觉运动区引起的PC诱发简单锋电位反应。以上结果说明:在大鼠存在Gi-小脑通路,这一通路中的部分纤维是5-HT能的。Gi-小脑纤维可能通过突触和/或非经典突触的化学传递方式对PC的电活动产生某种调制性的影响。推测Gi-小脑传入纤维投射可能在某些小脑功能活动,如肌紧张及姿势的调节等方面发挥重要作用。     

The influence of an unmyelinated terminal on repetitive firing of a mammalian receptor afferent fiber

The distal end of a myelinated receptor afferent fiber consists of an unmyelinated terminal membrane which is assumed to be the site of sensory transduction, whereas the action potential encoding appears at a distal node of Ranvier. In the present paper a model of a mammalian myelinated nerve fiber was augmented by an unmyelinated terminal segment into which stimulating current was injected thus modelling the situation at a myelinated receptor afferent fiber. It was found that the introduction of the unmyelinated terminal reduces the repetitive firing rate shown by the model. However, also the amplitude of the spikes at the site of action potential generation diminishes through the large electrical load which the unmyelinated terminal imposes onto the active parts of the nerve fiber model. This "loss" of spike amplitude can abolish the ability of the model to show repetitive activity, if the unmyelinated terminal increases in size. On the other hand, the incorporation of sodium channels into the terminal membrane compensates the spike amplitude reduction introduced by the electrical load of that membrane. This allows repetitive firing at a lower frequency than would be possible for a model with an equivalent sodium-channel-free terminal. The results show that the unmyelinated terminal present at the distal end of myelinated receptor afferent fibers has not only the ability to provide sensory transduction but evokes also a reduction in the discharge rate of the encoding membrane.     

Multiscale spike train variability in primary electrosensory afferents.

Spike train variability is of fundamental importance for understanding how information is encoded and processed in the nervous system. Most studies in this area have focused on short-term variability, as characterized by the coefficient of variation of the interspike interval distribution. Here we discuss the importance of extending the analysis of spike train variability to longer time scales that span multiple interspike intervals. Recent experimental and modeling studies of probability coding (P-type) electrosensory afferent nerve fibers in weakly electric fish have provided new insights into the functional importance of multiscale spike train variability. P-type afferent spike trains are moderately irregular on short time scales of a few milliseconds, but show significantly enhanced regularity on time scales of a few hundred milliseconds. This increased regularity is beyond what would be expected for a renewal process model in which successive intervals are uncorrelated. Modeling studies suggest that the correlation structure that underlies spike train regularization arises from relative refractory effects associated with a dynamic spike threshold. Spike train regularization in P-type afferents has been shown to significantly enhance signal detectability and information transmission on time scales that are functionally relevant for electrolocation behavior.     

自发和诱发神经放电序列的内在时序特性

运用Fano因子分析法,考察豚鼠听神经单纤维的自发放电序列、小鼠海马CAl区神经元的自发放电序列以及蟾蜍缝匠肌肌梭传入神经的诱发放电序列的时序特性,结果显示自发和诱发放电时间序列均存在Fano因子随计算窗口时间的增大而持续增长的特点,而原始数据的随机重排替代数据则没有这一特性,说明这些神经放电时间序列与一般的随机点过程不同,存在长时程相关性,在时序上具有某种结构特征。进一步的研究表明,这一时序结构特征可以通过将随机产生的一维正态分布序列数据,与神经放电时间序列数据进行跟随排序后而体现,提示这一特征与放电间隔的分布特点无关。     

Phantoms in the brain: Ambiguous representations of stimulus amplitude and timing in weakly electric fish

In wave-type weakly electric fish, two distinct types of primary afferent fibers are specialized for separately encoding modulations in the amplitude and phase (timing) of electrosensory stimuli. Time-coding afferents phase lock to periodic stimuli and respond to changes in stimulus phase with shifts in spike timing. Amplitude-coding afferents fire sporadically to periodic stimuli. Their probability of firing in a given cycle, and therefore their firing rate, is proportional to stimulus amplitude. However, the spike times of time-coding afferents are also affected by changes in amplitude; similarly, the firing rates of amplitude-coding afferents are also affected by changes in phase. Because identical changes in the activity of an individual primary afferent can be caused by modulations in either the amplitude or phase of stimuli, there is ambiguity regarding the information content of primary afferent responses that can result in ‘phantom’ modulations not present in an actual stimulus. Central electrosensory neurons in the hindbrain and midbrain respond to these phantom modulations. Phantom modulations can also elicit behavioral responses, indicating that ambiguity in the encoding of amplitude and timing information ultimately distorts electrosensory perception. A lack of independence in the encoding of multiple stimulus attributes can therefore result in perceptual illusions. Similar effects may occur in other sensory systems as well. In particular, the vertebrate auditory system is thought to be phylogenetically related to the electrosensory system and it encodes information about amplitude and timing in similar ways. It has been well established that pitch perception and loudness perception are both affected by the frequency and intensity of sounds, raising the intriguing possibility that auditory perception may also be affected by ambiguity in the encoding of sound amplitude and timing.     

Depolarization of primary afferents during fictitious scratching in thalamic cats

The dorsal cord and dorsal root potentials were recorded in immobilized thalamic cats during fictitious scratching evoked by mechanical stimulation of the ear. Depolarization of primary afferents was shown to be simulated by the central scratching generator. Antidromic spike discharges appeared at the peak of the primary afferent depolarization waves in certain afferent fibers. Similar discharges arise in the resting state in response to stimulation of limb mechanoreceptors. It is suggested that during real scratching primary afferent depolarization and antidromic spikes evoked by it may effectively modulate the level of the afferent flow to spinal neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 173–176, March–April, 1978.     

Primary afferent depolarization induced by activation of intersegmental connections of the substantia gelatinosa in the cat spinal cord

Depolarization of primary afferent terminals induced by selective activation of intersegmental connections of the substantia gelatinosa was investigated in cats anesthetized with pentobarbital. Depolarization was found to develop most rapidly in fibers of high-threshold muscular and cutaneous sensory nerves, but it was present only to a very slight degree in fibers of group Ia muscular afferents. It is suggested that the spread of activity inducing depolarization takes place in the substantia gelatinosa along a chain of excessively excited neurons. The possible role of primary afferent depolarization as a factor stabilizing coordinated activity of spinal neurons is discussed.     

Static response of infrared neurons of crotaline snakes—normal distribution of interspike intervals

Background discharges (static responses) of warm fibers in the pit organs (infrared receptive organs) of two species of crotaline snakes were recorded at various temperatures (water, 18-33 degrees C; air, 19-28 degrees C). Mean interspike intervals (means), standard deviations (SD), and coefficients of variation (CV) were calculated, and the goodness of fit of interspike interval histograms to a corresponding normal distribution (i.e., one having the same mean and SD) were tested. Means, SD, and CV were smallest at a certain temperature, which might be the optimum receptor temperature for the species. More than half of the histograms (22/42 for water, 7/10 for air) showed a normal distribution at a significance level of 0.01. This suggests that the spike intervals generated at the spike initiation site are constant, with some random error. Background discharges of three pure infrared secondary neurons from the lateral descending nucleus were analyzed in the same way and compared to the peripheral discharges. There were no histograms with a normal distribution in these central neurons, which might indicate that the constant interspike intervals which appear in the primary afferent fibers are not utilized for information processing at this level but occur only as part of a receptor mechanism which is still unknown. The discharge patterns of primary afferent fibers are also discussed in relation to the known discharge patterns of cold fibers in other animals.