Extracellular recording of localized electrical activity in denervated frog slow muscle fibres

Pyriformis muscles of Rana temporaria were denervated by cutting the sciatic nerve in the pelvis. Slow muscle fibres were depolarized with intracellular current pulses, and the electrical activity was recorded simultaneously with intracellular and extracellular recording electrodes. When the extracellular electrode was moved along the fibre surface, outward and inward currents of variable amplitude were recorded. Inward currents coincided with the fast rising phase of the intracellularly recorded action potential; up to four inward current peaks could be detected in single fibres investigated over 3.4--8 mm of their length. The distance between inward current peaks was generally 1--2 mm, but greater distances were also observed. Composite action potentials could be shown to be due to inward currents arising in separate areas of the slow fibre membrane. It is concluded that after denervation Na-channels are incorporated into spatially limited areas of the membrane of slow muscle fibres.     

Sheet conductor model of brain slices for stimulation and recording with planar electronic contacts

Current and voltage in a brain slice are considered, taking into account the boundary conditions at the surface to an electrolyte bath and at the substrate of an electron conductor. A sheet conductor model is introduced with ohmic leak conductance to the bath and capacitive coupling to the substrate. It assigns a current-source density of neuronal activity to extracellular field potentials recorded by planar contacts, and it relates the current of planar capacitive contacts to the field potential that elicits neuronal activity. Two examples are analytically solved: the recording across a layered brain slice and the stimulation by a circular electrode. The study forms the basis for neurophysical experiments with brain slices or retinae on microelectronic chips.     

Synaptic effects evoked by supraspinal and intraspinal stimulation in lamprey motoneurons

In experiments onLampetra fluviatilis in response to electrical stimulation of bulbar reticulospinal neurons and descending fibers the postsynaptic potentials of segmental motoneurons and action potentials of single intraspinal axons were recorded intracellularly and the cord dorsum potentials were recorded by a surface electrode. Fast-conducting reticulospinal axons (Müller's axons) were shown to excite spinal motoneurons monosynaptically. Monosynaptic reticulo-motoneuronal EPSPs arise as the result of excitation of a limited number of descending fibers, they reproduce high frequencies of stimulation readily and, in some cases, they are divided into components of which the first may be attributed to an electrical, and the second to a chemical mechanism of transmission. Besides early monosynaptic EPSPs, late, probably polysynaptic, responses also are found.     

Current source-density analysis in the mushroom bodies of the honeybee (Apis mellifera carnica)

Summary Information processing in the mushroom bodies which are an important part of most invertebrate central nervous systems was analysed by extracellular electrophysiological techniques. The mushroom bodies consist of layers of parallel intrinsic neurons which make synaptic contact with extrinsic input and output neurons. The intrinsic neurons (approximately 170,000/mushroom body) have very small axon diameters (0.1–1 m) which makes it difficult to record their activity intracellularly. In order to analyse the functional properties of this neuropil field potentials were measured extracellularly.Series of averaged evoked potentials (AEPs) were recorded along electrode tracks at consecutive depth intervals in different parts of the mushroom bodies of the bee. These potentials were elicited by olfactory, mechanical and visual stimuli.In order to locate the synaptic areas generating these potentials, current source-densities (CSD) were calculated using the consecutively measured evoked potentials. The conductivities of the extracellular space along the electrode tracks in the pedunculus and calyx and in part of the alpha-lobe of the mushroom bodies were found to be constant.The CSD analysis reveals a complex pattern of source-sink distributions in the mushroom bodies. There is a high degree of correlation between current sinks and sources detected by CSD analysis and the morphological distribution of neurons.The CSD analysis shows that the inputs and outputs of the mushroom bodies involve multimodal synaptic interactions, whereas information processing in the intrinsic Kenyon-cells is limited to sensory inputs from the antenna.Comparison of the electrophysiological with the histological results shows that the intrinsic cells of the mushroom bodies are physiologically not a homogeneous group as is often proposed. Among the intrinsic neurons clearly defined areas of current sources and sinks can be identified and attributed to Kenyon-cells in different layers.Abbreviations AEP averaged evoked potentials - AGT antennoglomerular tract - CSD current source-density - PCT antennoglomerular tract     

Slow potentials of the olfactory bulb in the carp

The slow negative potentials evoked in carp olfactory bulb (OB) by some odorants and slow positive potentials evoked by nonspecific irritation (water stream, NaCl solutions) of olfactory epithelium have been studied. The slow potentials of both types were not inverted in deep layers of OB and were resistant to blockade of synaptic transmission by manganese ions. The negative slow potentials were not also affected by hypoxia and associated with local increase of OB tissue resistance. Positive slow potentials were affected by hypoxia and associated with local decrease of OB tissue resistance. The electrical tetanization of local zones of olfactory epithelium evoked in OB steady potential shifts of negative polarity, but diffuse tetanization of olfactory nerve evoked shifts of positive polarity. The results support the hypothesis of glial origin of slow potentials. Possible mechanisms of slow negative and positive potential generation are discussed.     

The origin of slow potentials on the tongue surface induced by frog glossopharyngeal efferent fiber stimulation

When the glossopharyngeal (GP) nerve of the frog was stimulated electrically, electropositive slow potentials were recorded from the tongue surface and depolarizing slow potentials from taste cells in the fungiform papillae. The amplitude of the slow potentials was stimulus strength- and the frequency-dependent. Generation of the slow potentials was not related to antidromic activity of myelinated afferent fibers in the GP nerve, but to orthodromic activity of autonomic post-ganglionic C fibers in the GP nerve. Intravenous injection of atropine abolished the positive and depolarizing slow potentials evoked by GP nerve stimulation, suggesting that the slow potentials were induced by the activity of parasympathetic post-ganglionic fibers. The amplitude and polarity of the slow potentials depended on the concentration of adapting NaCl solutions applied to the tongue surface. These results suggest that the slow potentials recorded from the tongue surface and taste cells are due to the liquid junction potential generated between saliva secreted from the lingual glands by GP nerve stimulation and the adapting solution on the tongue surface.     

Brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 10 common marmosets (Callithrix jacchus) to investigate the effects of recording electrode configurations, stimulus rate, and stimulus frequency on BAEP wave forms and peak latencies. Tone burst stimulations were used to evaluate the effects of pure tone on BAEP wave forms. Five positive peaks superimposed on positive and negative slow potentials were identified in the BAEP recorded at the linkage between the vertex and the dorsal base of the ear ipsilateral to a monaural stimulus. When the reference electrode was placed at the ipsilateral mastoid or the neck, the amplitudes of positive and negative slow potentials and the incidence of wave I increased. There were no significant changes in peak latencies of BAEP waves with changes in stimulus rate from 5 to 20/s. It was possible to record the BAEPs in response to tone burst stimulations at frequencies extending from 0.5 to 99 kHz. Wave I appeared apparently at high stimulus frequencies; while waves III to V, at low frequencies. Wave II was recorded at frequencies ranging from 0.5 to 99 kHz and comprised a superposition of 2 or 3 potentials.     

Extracellular recordings from the motor nervous system of the nematode,Ascaris suum

1. The close association of muscle and neurons in Ascaris suum makes it difficult to determine whether spikes recorded from nerve cords originate in muscle or neurons. We have developed criteria that distinguish muscle and neuronal activity. There are two categories of extracellular spikes. 2. The first category consists of spikes with a wide range of amplitudes, marked by large spikes. These spikes, which can be recorded over lateral muscle and over the dorsal and ventral nerve cords, are abolished when muscle is disrupted or removed, or when curare is applied. Large spikes are relatively infrequent, are correlated with intracellularly recorded muscle events, and respond to polarizations of motor neurons, implying that they originate in muscle. 3. The second spike category, small amplitude spikes, is exclusive to the ventral nerve cord, occurs more frequently than large spikes and displays patterned firing. Small spikes are not affected by muscle removal or by curare, and are correlated with motor neuronal post-synaptic potentials, but not with intracellularly recorded muscle events. We infer that they originate in neurons. 4. Low level activity recorded extracellularly over nerve cords may represent muscle activity due to tonic motor neuronal synaptic transmission. It responds to motor neuronal polarization and is suppressed by curare or muscle removal.     

Analysis of slow hyperpolarizing potentials in frog taste cells induced by glossopharyngeal nerve stimulation

Electrical stimulation of the frog glossopharyngeal (GP) nerve evoked slow hyperpolarizing potentials (HPs) in taste cells. This study aimed to clarify whether slow HPs were postsynaptically induced in taste cells. The slow HPs were recorded intracellularly with a microelectrode. When Ca2+ concentration in the blood plasma was decreased to approximately 0.5 mM, the amplitude of slow HPs reduced and their latency lengthened. When the Ca2+ concentration was increased to approximately 20 mM, the amplitude of slow HPs increased and their latency shortened. Addition of Cd2+ to the plasma greatly reduced the amplitude of slow HPs and lengthened their latency. These data suggest that the slow HPs are dependent on presynaptic activities in the GP nerve terminals in the taste disk. Of various antagonists injected intravenously for blocking receptors of neurotransmitter biogenic amines and peptides, only antagonists for substance P blocked the slow HPs at 2-4 mg/kg body wt. Application of substance P of 2 mg/kg to the plasma induced hyperpolarizing responses in taste cells, whose amplitude was the same as that of the slow HPs induced by GP nerve stimulation. Application of a nonselective cation channel antagonist, flufenamic acid, to the plasma blocked the slow HPs. These results suggest that the slow HPs are generated by closing the nonselective cation channels in the postsynaptic membrane of taste cells following possible release of substance P from the GP nerve terminals in the taste disk.     

Click-evoked responses from the cochlear nucleus: a study in human

Recordings from the vicinity of the cochlear nucleus in 9 patients undergoing microvascular decompression operations to relieve hemifacial spasm, trigeminal neuralgia, tinnitus, and disabling positional vertigo were conducted by placing a monopolar electrode in the lateral recess of the fourth ventricle (through the foramen of Luschka), the floor of which is the dorsolateral surface of the dorsal cochlear nucleus. The click-evoked potentials recorded by such an electrode display a slow negative wave with a peak latency of about 6–7 msec on which several sharp peaks are superimposed. None of the peaks in the recordings from the vicinity of the cochlear nucleus coincided with any vertex-positive peaks of the brain-stem auditory evoked potentials. In recordings from the lateral aspect of the floor of the fourth ventricle near the cochlear nucleus 1 patient showed 2 positive peaks, the earliest of which had a latency close to that of peak II and the second of which had a latency close to the negative peak between peaks III and IV of the brain-stem auditory evoked potentials. There is a distinct negative peak in the responses recorded from the midline of the floor of the fourth ventricle, the latency of which is only slightly shorter than that of peak V of the brain-stem auditory evoked potentials, supporting earlier findings that the sharp tip of peak V of the brain-stem auditory evoked potentials is generated by the termination of the lateral lemniscus in the inferior colliculus.     

Electrophysiological characteristics of reticulospinal neurones in relation to the conduction velocity of their axons

Activity was recorded intracellularly from the bodies of 87 reticulospinal neurones in the cat's gigantocellular nucleus, whose axons had a conduction velocity of 18-148 m.s-1. Slow-conducting neurones (18-45 m.s-1, 23%) were characterized by a wider action potential, higher input resistance (3.8-7.0 M omega) and a lower rheobase (1.0-1.7 nA). They were also very sensitive to changes in membrane polarity and generated regular rhythmic activity. Fast-conducting neurons (45-148 m.s-1) were characterized by a short action potential, low input resistance (0.7-2.9 M omega) and a higher rheobase (1.5-5.2 nA). When depolarizing current pulses were applied, they generated responses with action potentials with a high frequency, especially in the initial phase of depolarization, but their thresholds for the initiation of activity and steady firing were higher than in the case of slow neurones. Slow reticulospinal neurones always responded to stimulation of the spinal funiculi (mainly the dorsal funiculus) by a characteristic large postsynaptic potential on which large numbers of spike potentials were superimposed and which did not occur in fast neurones. The differences observed in membrane properties and in the character of generation of action potentials draw attention to the phasic character of fast, and the tonic character of slow, reticulospinal neurones.     

Elementary polysynaptic potentials of hippocampal neurons

Synaptic connections of 26 pairs of hippocampal neurons were studied in nonanesthetized rabbits by spike-triggered averaging of intracellularly recorded activity. Synchronized activity was detected in 5 pairs and considered to represent common inputs to the neurons recorded. Hyperpolarizing or depolarizing potentials with 3--4 ms latency were revealed in 3 additional pairs. These potentials are considered to be individual postsynaptic potentials (PSPs) evoked in the target neuron by spikes of the adjacent (0.5--2 mm apart) neuron. A quantum analysis of the individual PSPs was performed. The mean quantum content (0.27--0.65) and quantum size (35--200 mkV) were found to be of the same order as those of the excitatory PSPs previously recorded after intracerebral stimulation. It is concluded that most hippocampal synapses are of low efficacy.     

Two classes of spontaneous miniature excitatory junction potentials and one synaptic vesicle class are present in the ray electrocyte

Summary Cross sections (1–2 mm thick) of the ray (Raja) tail were secured to a dish and immersed in elasmobranch saline. Spontaneous miniature excitatory junction potentials (MEJPs) were recorded by advancing a 50 k, KCl filled electrode into the electric organ (20 V peak-to-peak baseline noise). Data were filmed, and/or recorded on magnetic tape for computer analyses. Intracellularly recorded MEJP amplitude histograms showed a peak at 60 V and had a right-hand skew with MEJPs up to 0.5 mV. The small peak amplitude and the skewed amplitude distribution of intracellularly recorded MEJPs result from the relatively low input resistance and the short space constant of the electrocyte coupled with the dispersed synapses on the electrocyte. At 23 °C the intracellularly recorded MEJP frequency ranged from 1–10 MEJPs/s. The MEJPs became larger and became focally recorded as the electrode was advanced against the intracellular surface of the innervated membrane of the electrocyte. Focal extracellular MEJPs (reversed polarity) were also recorded with the electrode positioned against the outside surface of the innervated side of the electrocyte. The frequency of focally recorded intracellular MEJPs was increased (up to 40/s) when the electrode was pushed against the membrane. Focal MEJP frequencies decreased to a few/min within 5–10 min but the mean amplitude of 3–5 mV remained constant. Decreases in amplitude and frequency in focally recorded intracellular MEJPs are attributed to changes in electrode pressure against the membrane. Amplitude histograms were constructed from focally recorded intracellular or extracellular MEJPs which showed the same time characteristics. The focal MEJP amplitude histograms have two distinct classes, each forming a bell-shaped distribution. It is concluded that both classes are generated at the electrode tip. The smaller class of MEJPs has a mean 1/10th that of the larger class and composes about 2% of the MEJPs. The small class is analogous to the sub-MEPP class found in the frog sartorius (Kriebel and Gross 1974) and mouse diaphragm (Kriebel et al. 1976, 1982). Distributions of synaptic vesicle diameters are slightly log normal (right hand skew) such that the mean diameter (57 nm) is slightly larger than the modal value (52 nm). Vesicles touching the membrane were of the same size and diameter distribution as the entire vesicle population. The profiles of the distributions are smooth and suggest only 1 class of synaptic vesicle based on diameter.     

The genesis and transmission of epidermal potentials in an amphibian embryo

The genesis and transmission of action potentials in epidermal cells of the newt (Cynops pyrrhogaster) embryo were investigated with special reference to cellular differentiation during development. Typical action potentials can be recorded from any of the epidermal cells at Stage 31. These potentials consist of a fast spike (18 msec) followed by a slow component (164 msec). The potential is graded with current intensity, and only the slow component initiates action potentials in adjacent cells and induces a transmission to other cells. The fast spike was found in all epidermal cells throughout the embryonic stages examined (Stages 26–47). The slow potential, however, appears at Stage 28, persists until Stage $\text{36}\text{37}$ just before hatching and then disappears at Stage $\text{38}\text{42}$. Electrical recordings from traumatic embryos (embryos without neural crest cells) or from cultured epidermal cell masses isolated from the pregastrula or the ventral region of the neurula, were compared with the intact embryo. No differences were observed in either the form of the action potential or its transmission. Thus these action potentials appear to be derived from epidermal cells, and are not of nervous origin. Evidence suggests that the transient establishment of excitable membranes in epidermal cells during differentiation is closely related to neural cell differentiation.     

Control of flexor motoneuron activity during single leg walking of the stick insect on an electronically controlled treadwheel

In the present study, motoneurons innervating the flexor tibiae muscle of the stick insect (Cuniculina impigra) middle leg were recorded intracellularly while the single leg performed walking-like movements on a treadwheel. Different levels of belt friction (equivalent to a change in load) were used to study the control of activity of flexor motoneurons. During slow leg movements no fast motoneurons were active, but a recruitment of these neurons could be observed during faster leg movements. The firing rate of slow and fast motoneurons increased with incremented belt friction. Also, the force applied to the treadwheel at different frictional levels was adapted closely to the friction of the treadwheel to be overcome. The motoneurons innervating the flexor tibiae were recruited progressively during the stance phase, with the slow motoneurons being active earlier than the fast (half-maximal spike frequency after 10-15% and 50-60% of the stance phase, respectively). The resting membrane potential was more hyperpolarized in fast motoneurons (64.6 +/- 6.5 mV) than in slow motoneurons (-52.9 +/- 5.4 mV). However, the threshold for the initiation of action potentials was not statistically significantly different in both types of flexor motoneurons. Therefore, action potentials were generated in fast motoneurons after a longer period of depolarization and thus later during the stance phase than in slow motoneurons. We show that motoneurons of the flexor tibiae receive substantial common excitatory inputs during the stance phase and that the difference in resting membrane potential between slow and fast motoneurons is likely to play a crucial role in their consecutive recruitment.     

Slow adaptation in spider mechanoreceptor neurons

Slow adaptation of action potential firing is a common but poorly understood property of sensory neurons. We quantified slow adaptation in a cuticular mechanoreceptor organ of the spider, Cupiennius salei, by stimulating with continuous pseudorandom mechanical displacements while recording action potentials intracellularly from the cell bodies. Firing rate declined over a period of several minutes before reaching a steady level at about half the initial rate. This slow adaptation was fitted by an exponential decay with mean time constant of 18.5 s. Recovery from slow adaptation was also fitted by an exponential process, but with a longer time constant of 167 s. The receptor potential produced by the same stimulation protocol did not change its amplitude or dynamics, showing that slow adaptation occurs during action potential encoding from the receptor potential. Experiments with chemical blockers of calcium entry or the known potassium currents failed to reduce the slow adaptation. The Na⁺/K⁺ pump blocker Ouabain decreased the time constant of slow adaptation, suggesting that ion accumulation is involved. In some experiments, a second class of small action potentials were observed, which were tentatively attributed to failed conduction from the sensory dendrite through the soma to the axon.     

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entracce of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50–70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47–50 msec, became evident in recording sites at 30–40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum.We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.     

In vivo magnetic and electric recordings from nerve bundles and single motor units in mammalian skeletal muscle. Correlations with muscle force

Recent advances in the technology of recording magnetic fields associated with electric current flow in biological tissues have provided a means of examining action currents that is more direct and possibly more accurate than conventional electrical recording. Magnetic recordings are relatively insensitive to muscle movement, and, because the recording probes are not directly connected to the tissue, distortions of the data due to changes in the electrochemical interface between the probes and the tissue are eliminated. In vivo magnetic recordings of action currents of rat common peroneal nerve and extensor digitorum longus (EDL) muscle were obtained by a new magnetic probe and amplifier system that operates within the physiological temperature range. The magnetically recorded waveforms were compared with those obtained simultaneously by conventional, extracellular recording techniques. We used the amplitude of EDL twitch force (an index of stimulus strength) generated in response to graded stimulation of the common peroneal nerve to enable us to compare the amplitudes of magnetically recorded nerve and muscle compound action currents (NCACs and MCACs, respectively) with the amplitudes of electrically recorded nerve compound action potentials (NCAPs). High, positive correlations to stimulus strength were found for NCACs (r = 0.998), MCACs (r = 0.974), and NCAPs (r = 0.998). We also computed the correlations of EDL single motor unit twitch force with magnetically recorded single motor unit compound action currents (SMUCACs) and electrically recorded single motor unit compound action potentials (SMUCAPs) obtained with both a ring electrode and a straight wire serving as a point electrode. Only the SMUCACs had a relatively strong positive correlation (r = 0.768) with EDL twitch force. Correlations for ring and wire electrode-recorded SMUCAPs were 0.565 and -0.366, respectively. This study adds a relatively direct examination of action currents to the characterization of the normal biophysical properties of peripheral nerve, muscle, and muscle single motor units.     

Co-cultures of inferior olive and cerebellum: Electrophysiological evidence for multiple innervation of Purkinje cells by olivary axons

Slices of inferior olive (IO) and cerebellum were co-cultured for several weeks by means of the roller tube technique. Recordings were carried out intracellularly from Purkinje cells (PCs) which were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow, or by immunohistochemical stainings with antibodies raised against the 28 kD Ca²⁺-binding protein calbindin. Following stimulation of olivary tissue, an all-or-none full complex spike response was recorded in some PCs consisting of a fast rising spike followed by a depolarizing potential. In other PCs, graded stimulation of the olivary explant induced synaptic potentials which were characterized by step-wise variation in their amplitude and resembled the ones occurring spontaneously. In contrast, only smoothly graded synaptic potentials were observed in cerebellar mono-cultures. These results indicate that some of the PCs in olivo-cerebellar co-cultures are innervated by several olivary neurons.