bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic potentials in motoneurons during fictive swimming in spinal Xenopus embryos
Authors: Roberts A. , Dale N. , Evoy W. H. , Soffe S. R.
Published: December 2017

Embryos spinalized at the 3rd to 6th postotic myotome and immobilized in 10(-4) M tubocurarine can respond to a brief skin stimulus with motor root activity suitable for swimming. Embryos spinalized at the more caudal levels give shorter episodes of fictive swimming. We have previously described the synaptic inputs to motoneurons during fictive swimming in intact embryos (23). In the present paper we look to see if similar synaptic inputs are present in spinal embryos and are therefore spinal in origin. All motoneuron firing during fictive swimming is associated with a tonic depolarization that falls away slowly once firing stops, is increased by hyperpolarizing current, and is reduced by depolarizing current. A slow depolarizing potential evoked by lower levels of skin stimulation has similar properties and rate of fall. In 1-2 mM PDA, an excitatory amino acid antagonist, only a small remnant of the depolarization remains, and motoneuron firing stops. The NMDA antagonist 50 microM APV reduces the depolarization less but also blocks firing. Motoneurons fire one spike per swimming cycle, in phase with nearby motor root discharge. Spikes are preceded by a depolarizing prepotential. This increases with hyperpolarizing current, which can block the spike to reveal an underlying depolarizing potential. In phase with motor root discharge on the opposite side of the body, motoneurons receive a midcycle inhibitory postsynaptic potential, which increases with depolarizing current, decreases with hyperpolarizing current, and is blocked by 10(-6) M strychnine. Strychnine, 5 X 10(-7) M, leads first to broadening of motor root bursts then to loss of the alternating swimming pattern of activity, which is replaced by synchronous bursts on both sides of the body. We conclude that the synaptic inputs to motoneurons during fictive swimming in spinal embryos are very similar in properties and pharmacology to those in intact embryos. These inputs, including the tonic depolarization always associated with motoneuron firing during swimming, must be at least partly spinal in origin.
Rectification of single GABA-gated chloride channels in adult hippocampal neurons
Authors: Gray R. , Johnston D.
Published: December 2017

The properties of single chloride channels activated by gamma-aminobutyric acid (GABA) were investigated with hippocampal slices from adult guinea pigs. After the slices were treated with proteolytic enzymes, gigaseal recordings were made from excised patches of pyramidal or granule cell membranes. This newly developed preparation permits the application of patch-clamp techniques to the adult mammalian central nervous system. Guinea pig hippocampal slices were prepared in a conventional manner. Once prepared, the slices were treated with two different enzymes for brief periods and gently agitated. Slices generally split apart along the boundaries of the cell body regions, exposing neuronal somata. Standard patch-clamp techniques were used for the gigaseal recordings from excised patches. Solutions for both sides of the patches consisted of symmetrical concentrations of chloride, with all cation channels blocked. GABA at concentrations of 0.5-1.0 microM was added to the solution for the extracellular side of the patches. At transmembrane potentials negative to the chloride reversal potential (0 mV), the conductance through the GABA-gated chloride channels was approximately 20 pS. When the transmembrane potential was changed to positive values, the chloride conductance increased dramatically. For example, at +40 mV the conductance through the GABA-gated channels was almost 40 pS. Ramp-clamp commands were used to measure the current-voltage (I-V) relationship through single open channels. The open-channel I-V curves displayed outward rectification. The relationship between open-channel conductance and voltage could be fitted reasonably well by a single energy-barrier model for the channel, with the higher energy barrier placed near the cytoplasmic side of the membrane (at a fractional distance through the membrane of 0.73).(ABSTRACT TRUNCATED AT 250 WORDS)
Nonspiking local interneuron in the motor pattern generator for the crayfish swimmeret
Authors: Paul D. H. , Mulloney B.
Published: December 2017

We describe a type of nonspiking premotor local interneuron (interneuron IA) in the abdominal nervous system of Pacifasticus leniusculus. All of its branches are restricted to one side of the midline. These interneurons are identifiable and occur as bilateral pairs, one neuron on each side of abdominal ganglia 3, 4, and 5. The membrane potential of interneuron IA oscillated in phase with the swimmeret rhythm, a motor pattern generated in each of these ganglia, because the neuron received postsynaptic potentials in phase with the rhythm. Sustained hyperpolarization of an individual interneuron IA initiated generation of the swimmeret rhythm in all the ganglia of a quiescent nervous system. Sustained depolarization stopped the swimmeret rhythm in all the active ganglia of a nervous system that was generating the rhythm. Currents injected into one interneuron reset the rhythm. Comparisons of the shapes of the IA interneurons in different ganglia showed that they are similar to each other and distinct from other local interneurons in these ganglia. Interneuron IA has a large integrative segment and relatively few branches that are largely restricted to the lateral neuropil, to which all other kinds of swimmeret neurons also project. We conclude that this interneuron occurs only once in each hemiganglion in abdominal segments 3, 4, and 5, and that it is identifiable. Furthermore, this interneuron is an essential component of the circuit in each hemiganglion that generates the swimmeret rhythm. The interneuron was dye coupled to a particular identifiable motor neuron and not to any other neurons. The motor neuron was not dye-coupled to any other local interneurons. The ability of this motor neuron to reset the rhythm is attributed to its being electrically coupled to interneuron IA in its ganglion.
Inferior olivary neurons in the awake cat: detection of contact and passive body displacement
Authors: Gellman R. , Gibson A. R. , Houk J. C.
Published: December 2017

We have recorded from 306 neurons in the inferior olive of six alert cats. Most of the cats were trained to perform a simple task with the forelimb. We observed the neural responses to a wide variety of cutaneous and proprioceptive stimuli, as well as responses during spontaneous and learned active movements. Neurons responsive to somatosensory stimulation were found in all parts of the inferior olive, and they were roughly evenly divided between those responsive to cutaneous stimulation and those responsive to proprioceptive stimulation. In the dorsal accessory olive all neurons were responsive to somatosensory stimulation. In the medial accessory nucleus 88% and in the principal olive 74% of cells were responsive to somatosensory stimulation. Cells responsive to cutaneous stimulation usually had small receptive fields, commonly on the paw. These cells had low-threshold responses to one or more forms of cutaneous stimulation and typically fired one spike at the onset of the stimulus on 80% or more of stimulus applications. Cells responsive to proprioceptive stimulation most commonly responded to passive displacements of a limb. These cells were often very sensitive, responding to linear displacements of less than 1 cm in one specific direction. No cells in our sample responded reliably during active movement by the animal. Only 21% of cells responding to passive proprioceptive stimulation showed any modulation during active movement, and the modulation was weak. Likewise, cells responsive to cutaneous stimulation generally failed to respond when a similar stimulus was produced by an active movement by the animal. Exceptions to this were stimuli produced during exploratory movements or when the receptive field unexpectedly made contact with an object during active movement. Electrical stimulation applied in the inferior olive failed to evoke movements or to modify ongoing movement. Our results are consistent with the hypothesis that inferior olivary neurons function as somatic event detectors responding particularly reliably to unexpected stimuli.
T2-T5 spinothalamic neurons projecting to medial thalamus with viscerosomatic input
Authors: Ammons W. S. , Girardot M. N. , Foreman R. D.
Published: December 2017

Spinothalamic tract neurons projecting to medial thalamus (M-STT cells), ventral posterior lateral nucleus (VPL) of the thalamus (L-STT cells), or both thalamic regions (LM-STT cells) were studied in 19 monkeys anesthetized with alpha-chloralose. Twenty-seven M-STT cells were antidromically activated from nucleus centralis lateralis, nucleus centrum medianum, or the medial dorsal nucleus. Stimulation of VPL elicited antidromic responses from 22 cells and 13 cells were activated from both VPL and medial thalamus. Antidromic conduction velocities of M-STT cells were significantly slower than those of L-STT or LM-STT cells. M-STT cells were located in laminae I, IV, V, and VII with greater numbers found in the deepest laminae. L-STT cells were located mostly in lamina IV, whereas most LM-STT cells were found in lamina V. Twenty-four of 27 M-STT cells, all L-STT cells, and all LM-STT cells received input from both cardiopulmonary sympathetic and somatic afferent fibers. WDR cells were most common among the L-STT and LM-STT groups, whereas HT cells were the most common class in the M-STT cell group. Excitatory receptive fields of M-STT cells were large, and often bilateral. Receptive fields of L-STT cells were simple and never bilateral. Receptive fields of LM-STT cells could be similar to M-STT or L-STT cells. Thirty-three percent of the M-STT cells, 37% of the L-STT cells, and 62% of the LM-STT cells had inhibitory receptive fields. Inhibition was elicited most often by a noxious pinch of the hindlimbs. Sixteen of 23 (70%) M-STT cells received C-fiber cardiopulmonary sympathetic input in addition to A-delta-fiber input. The other 7 cells received only A-delta-fiber input. Only 45% of the L-STT cells and 38% of the LM-STT cells received both A-delta- and C-fiber inputs. The maximum number of spikes elicited by A-delta-input was related to segmental locations for L-STT cells with greatest responses in T2 and lesser responses in more caudal segments; however, no such trend was apparent for M-STT cells or for responses to C-fiber input for either group. Electrical stimulation of the left thoracic vagus nerve inhibited 7 of 18 M-STT cells, 10 of 16 L-STT cells, and 6 of 12 LM-STT cells. These results are the first description of visceral input to cells projecting to medial thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)
Mixing of color signals by turtle cone photoreceptors
Authors: Normann R. A. , Perlman I. , Daly S. J.
Published: December 2017

The direct mixing of red and green cone signals in the outer plexiform layer of the turtle retina was studied by using intracellular recordings from red cone photoreceptors. Cone photoresponses were a function of the wavelength of the photons that stimulated them, even when small-diameter stimuli were used. The intensity response curves measured with red and green test flashes had different shapes. The kinetics of approximately equal amplitude red and green responses also differed. To quantify the short wavelength input onto red cones, differential chromatic adaptation was used. The relative sensitivity of the red cone to red and green test flashes was a function of the color and intensity of the background illumination; red backgrounds decreased relative red sensitivity, and green backgrounds increased relative red sensitivity. The spectral sensitivity of the additional short wavelength input onto red cones was determined by using differential chromatic adaptation, and was found to peak approximately 550 nm. We conclude that red cones receive an additional excitatory input from green cones (and possibly blue cones). A model of the cone mosaic suggests that approximately 50% of the red cone response (linear range) to a dim green test flash arises from neighboring green cones.
Action of the efferent vestibular system on primary afferents in the toadfish, Opsanus tau
Authors: Highstein S. M. , Baker R.
Published: December 2017

Spinalized toadfish were held in a lucite chamber and perfused through the mouth with running seawater. Primary vestibular afferents and vestibular efferent axons and somas were studied with glass microelectrodes. Vestibular semicircular canal afferent and efferent axons were visually identified and penetrated with glass microelectrodes. Afferents responded to pulses of injected current with trains of action potentials, whereas efferents responded with only a single spike. This differential response to injected current served to further distinguish these two classes of nerve fibers that share the same canal nerve for part of their course. When current pulses were injected into efferent somadendritic recording sites, cells responded with trains of action potentials similar to those seen in other central nervous system neurons. Semicircular canal afferents were spontaneously active and occupied the same spectrum of regularity as vestibular afferents recorded in other species. Behavioral arousal evoked by lightly touching the fish on the snout or over the eye resembled spontaneous arousal observed in the field and consisted of eye withdrawal, fin erection, and attempted swimming. Efferent vestibular neurons were spontaneously active and increased their frequency of discharge when the fish was behaviorally aroused. Most efferents were briskly activated by behavioral arousal, but the time constant of the decay of their responses was variable ranging from 100 to 600 ms. Not only touch, but multimodal stimuli were capable of increasing the level of spontaneous activity of efferent vestibular neurons. The shortest latency to behavioral activation was 160 ms. Vestibular primary afferents also manifested increase in neuronal activity with behavioral activation. Irregularly discharging afferents were much more responsive than regularly discharging afferents. One rare case of transient inhibition in a regularly discharging afferent is illustrated. Severing the efferent vestibular nerve blocked behavioral activation in vestibular primary afferents. Electrical stimulation of the efferent vestibular nerve produced excitatory postsynaptic potentials (EPSPs) at latencies within the monosynaptic range in vestibular primary afferents. These monosynaptic EPSPs could produce action potentials in primary afferents or could sum with subthreshold depolarizations produced by current passed through the microelectrode to initiate impulses.(ABSTRACT TRUNCATED AT 400 WORDS)
Regeneration of cutaneous afferent unmyelinated (C) fibers after transection
Authors: Shea V. K. , Perl E. R.
Published: December 2017

The cutaneous receptive properties of C-fiber units were studied 1-8 mo after transection and repair of the rabbit's great auricular nerve. The proportions of C-fiber units that could be excited by the cutaneous stimuli known to excite normal C-fiber afferent elements of the same nerve increased with time of recovery and approached the normal range within 5 mo after transection. No evidence was obtained that suggests that any specific receptor type regenerated more rapidly than others. No differences were established between the cutaneous receptive properties of normal and regenerated low-threshold mechanoreceptors or specific thermoreceptors. However, the properties of regenerated polymodal nociceptors were different from those of normal polymodal nociceptors. Mechanical thresholds for regenerated polymodal nociceptors were greater than normal at 2 mo after transection but not later, and nearly 20% of regenerated polymodal units had heat thresholds lower than normal. It is argued that the abnormal properties of some regenerated polymodal nociceptors could explain, in part, the elevated thresholds to noxious mechanical stimulation and the thermal hyperalgesia reported during recovery from nerve transection in man.
Failure of sympathetic stimulation to affect responsiveness of rabbit polymodal nociceptors
Authors: Shea V. K. , Perl E. R.
Published: December 2017

The responses of polymodal nociceptors with unmyelinated (C) fibers of the rabbit's great auricular nerve were examined with and without intermittent stimulation of the ipsilateral cervical sympathetic trunk. The receptive field of each polymodal nociceptor was heated twice in a stepwise manner from 30 to 50 or 55 degrees C in 5 degree C steps. For each unit, one heating trial was a control trial and the other was accompanied by sympathetic stimulation. The order of the control and sympathetic stimulation trials and the maximum testing temperature were varied systematically among the units examined. The initial responses of polymodal nociceptors in the first heating trial in the presence of sympathetic stimulation were similar to the responses of units whose first heating was a control trial. Units whose receptive fields were tested to a maximum temperature of 50 degrees C in the first trial displayed enhanced responses to heat in their second trial (sensitization), while units tested initially to 55 degrees C responded less briskly during their second heating trial (depression). However, the occurrence of sympathetic stimulation in the second heating trials had no apparent effect on the responses to heat of sensitized or depressed elements. Alterations in the numbers of impulses, instantaneous frequency, or pattern of impulse activity of individual units could not be attributed to sympathetic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Temporal and spatial integration in the rat SI vibrissa cortex
Authors: Simons D. J.
Published: December 2017

Glass micropipettes were used to record the activity of 124 single units in the somatosensory vibrissa cortex (SI) of 16 rats in response to combined deflections of contralateral vibrissae. Compact multiangular electromechanical stimulators were used to stimulate individual vibrissal hairs alone or in combinations of two or three adjacent whiskers. Each whisker was stimulated independently to produce controlled temporal and spatial patterns of mechanical stimuli. Following displacement of a vibrissa, unit discharges to subsequent deflections of adjacent whiskers are reduced in a time-dependent fashion. Response suppression is strongest at short interdeflection intervals, i.e., 10-20 ms and decreases progressively during the 50-100 ms following the first deflection. In many cases this period also corresponds with a reduction in ongoing unit discharges. Response suppression was not observed for first-order neurons recorded in the trigeminal ganglion of barbiturate-anesthetized rats. In the cortex, the presence and/or degree of response suppression depends on a number of spatial factors. These include 1) the angular direction(s) in which the individual hairs are moved, 2) the sequence in which two whiskers are deflected, that is, which one is deflected first, 3) the particular combination of whiskers stimulated, and 4) the number (2 or 3) of vibrissae comprising the multiwhisker stimulus. Within a vertical electrode penetration, one particular whisker typically elicits the strongest excitatory and inhibitory effects; other, nearby vibrissae elicit variable (or no) excitation or inhibition. Excitatory and inhibitory subregions of a receptive field could thus be distributed asymmetrically around the maximally effective whisker. In these cases, the receptive fields displayed spatial orientations. Quantitative criteria were used to classify 30 cortical units on the basis of the distribution of inhibitory subregions on either side of the maximally effective whisker. Twenty-one of these cells had receptive fields (RFs) with symmetrical inhibitory side regions. Responses of the other nine units were strongly suppressed by a preceding deflection of a vibrissa on one side but relatively unaffected, or even slightly facilitated, by preceding deflection of the whisker on the other side.(ABSTRACT TRUNCATED AT 400 WORDS)
Primate frontal eye fields. II. Physiological and anatomical correlates of electrically evoked eye movements
Authors: Bruce C. J. , Goldberg M. E. , Bushnell M. C. , Stanton G. B.
Published: December 2017

We studied single neurons in the frontal eye fields of awake macaque monkeys and compared their activity with the saccadic eye movements elicited by microstimulation at the sites of these neurons. Saccades could be elicited from electrical stimulation in the cortical gray matter of the frontal eye fields with currents as small as 10 microA. Low thresholds for eliciting saccades were found at the sites of cells with presaccadic activity. Presaccadic neurons classified as visuomovement or movement were most associated with low (less than 50 microA) thresholds. High thresholds (greater than 100 microA) or no elicited saccades were associated with other classes of frontal eye field neurons, including neurons responding only after saccades and presaccadic neurons, classified as purely visual. Throughout the frontal eye fields, the optimal saccade for eliciting presaccadic neural activity at a given recording site predicted both the direction and amplitude of the saccades that were evoked by microstimulation at that site. In contrast, the movement fields of postsaccadic cells were usually different from the saccades evoked by stimulation at the sites of such cells. We defined the low-threshold frontal eye fields as cortex yielding saccades with stimulation currents less than or equal to 50 microA. It lies along the posterior portion of the arcuate sulcus and is largely contained in the anterior bank of that sulcus. It is smaller than Brodmann's area 8 but corresponds with the union of Walker's cytoarchitectonic areas 8A and 45. Saccade amplitude was topographically organized across the frontal eye fields. Amplitudes of elicited saccades ranged from less than 1 degree to greater than 30 degrees. Smaller saccades were evoked from the ventrolateral portion, and larger saccades were evoked from the dorsomedial portion. Within the arcuate sulcus, evoked saccades were usually larger near the lip and smaller near the fundus. Saccade direction had no global organization across the frontal eye fields; however, saccade direction changed in systematic progressions with small advances of the microelectrode, and all contralateral saccadic directions were often represented in a single electrode penetration down the bank of the arcuate sulcus. Furthermore, the direction of change in these progressions periodically reversed, allowing particular saccade directions to be multiply represented in nearby regions of cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
Velocity selectivity in the cat visual system. II. Independence from interactions between different loci
Authors: Duysens J. , Orban G. A. , Cremieux J.
Published: December 2017

To investigate the dependence of velocity characteristics on spatiotemporal interactions the velocity selectivity of 15 geniculate and 72 cortical cells (areas 17 and 18) was examined with light and dark bars before and after masking all but the most sensitive part of the receptive field. The use of a 0.3 degree window proved effective in eliminating enough spatiotemporal interactions to abolish cortical direction selectivity. The same window improved the responsiveness at high velocities in only 26% of the cortical cells preferring low velocities and having a receptive field with nonoverlapping ON and OFF subregions. The remaining 74% showed various degrees of velocity-independent decrease in response amplitude. The only two geniculate cells that had a velocity upper cutoff lost this cutoff when tested with the mask. Cortical units preferring high velocities lost their responsiveness at high velocities in the mask condition, provided that their receptive fields contained nonoverlapping ON and OFF subregions. Cortical units, which responded best at intermediate velocities and which had receptive fields with nonoverlapping subregions, lost their sharp velocity tuning when tested with a mask. We conclude that inhibitory spatiotemporal interactions can account for the preference for low velocities in at most a quarter of the cells with nonoverlapping subregions. In contrast, facilitatory interactions seem to be important for cortical cells preferring high or intermediate velocities and having receptive fields with nonoverlapping subregions.
Electrotonic parameters of neurons following chronic ethanol consumption
Authors: Durand D. , Carlen P.
Published: December 2017

The electronic parameters of nerve cells in the dentate gyrus following long-term ingestion of ethanol were studied in vitro. The ethanol was administered in a liquid diet for a period of 20 wk followed by a 3-wk withdrawal period. A control group received a similar diet with the ethanol replaced by maltose-dextrins. Intracellular recordings were obtained from 44 neurons, and the voltage decays following current injections were analyzed with a recent electrical model of granule cells to take into account a somatic shunt already detected in previous studies. The new model accurately accounted for the fast voltage transients and showed that the membrane time constant in the dendrites is, on average, five times larger than the somatic time constant. Injection of horseradish peroxidase into the neurons for the morphological analysis showed that neurons in the ethanol group have a longer dendritic tree than neurons in the control group. Estimation of the membrane surface area showed that the membrane area in the dendrites is at least 60% greater (in both control and ethanol groups) when the membrane foldings and irregularities are taken into account. The results of the modeling analysis showed that the membrane time constant and the input resistance are not affected by ethanol. However, the membrane resistance is significantly increased in the ethanol group (6,632 versus 18,460 omega X cm2), and the capacitance is significantly decreased (4.48 versus 1.71 microF/cm2). The electrotonic length is also increased by chronic ethanol treatment (0.85 versus 0.94). Higher values of membrane specific resistance (Rm) mean larger transmission coefficients. However, since the neurons from the ethanol group are on average longer than neurons in the control group, it is suggested that the change in Rm compensates for the increase in the length of the dendrites, thereby maintaining a value of the electrotonic length under 1.0. The observed changes in the passive parameters are in opposite direction from the recently measured effect of acute doses of ethanol on hippocampal neurons. These results support a model of chronic alcohol intake where homeostatic adaptive changes lead to the development of long-term changes in cellular physiology.
Cross-reinnervated motor units in cat muscle. I. Flexor digitorum longus muscle units reinnervated by soleus motoneurons
Authors: Dum R. P. , O'Donovan M. J. , Toop J. , Burke R. E.
Published: December 2017

The properties of flexor digitorum longus (FDL) muscles and of individual motor units were studied in cats 30-50 wk after self-reinnervation by FDL motoneurons (FDL----FDL) or cross-reinnervation by soleus (SOL) motoneurons (SOL----FDL). Individual motor units were functionally isolated by intracellular recording and stimulation of identified SOL alpha-motoneurons. Glycogen-depletion methods permitted histochemical study of muscle fibers belonging to physiologically characterized muscle units. The observations were compared with data from normal cat FDL muscles and motor units (27). Intentionally self-reinnervated FDL muscles (FDL----FDL; n = 5) were normal in size and wet weight. FDL----FDL motor units could be classified into the same physiological categories found in normal FDL [types: fast contracting, fatigable (FF), fast contracting, fatigue resistant (FR), and slow (S); n = 24], with approximately the same proportions as normal. The histochemical muscle fiber types associated with these categories were also qualitatively normal although there was evidence of marked distortion of the normal histochemical mosaic. These data confirm other studies of self-reinnervation and suggest that self-reinnervation can produce complete interconversion of muscle fiber types. Cross-reinnervation of FDL muscle by SOL motoneurons (SOL----FDL; n = 12) produced muscles that were smaller (about half the normal wet weight) and more red than normal. SOL----FDL muscle contracted more slowly than normal or FDL----FDL muscles and had much higher proportions of histochemical type I muscle fibers. In those SOL----FDL muscles, in which little or no unwanted self-reinnervation could be demonstrated, greater than 95% of the muscle fibers were type I. Forty-one individual motor units in SOL----FDL muscles were isolated by intracellular penetration in functionally identified SOL alpha-motoneurons. Their muscle units were all type S by physiological criteria (absence of "sag" in unfused tetani and marked resistance to fatigue). SOL----FDL muscle units had contraction times and fatigue properties that were essentially identical to those of type S units in the normal FDL. All of the seven units, successfully studied by glycogen depletion, exhibited histochemical type I fibers. SOL motoneurons that innervated FDL muscle units had slightly shorter afterhyperpolarization durations than normal SOL cells, but axonal conduction velocities were normal.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of groups of propriospinal interneurons on fictive swimming in the isolated spinal cord of the lamprey
Authors: Rovainen C. M.
Published: December 2017

Fictive swimming activity was induced in isolated spinal cords of adult lampreys Ichthyomyzon unicuspis and Petromyzon marinus by addition of D-glutamate or N-methyl-D,L-aspartate (NMA) to the bathing fluid. Propriospinal interneurons are defined as nerve cells within the spinal cord with projections longer than 1 segment. The hypothesis that propriospinal interneurons contribute to intersegmental coordination during fictive swimming was tested using electrical stimulation, extracellular recording, and separated compartments. Stimulation of the split caudal end of the spinal cord indirectly excited ascending propriospinal interneurons, which enhanced and entrained bursts in rostral contralateral ventral roots. Indirect electrical stimulation of descending propriospinal interneurons could delay and diminish bursts in caudal contralateral ventral roots. Extracellular recordings from the rostral and caudal split ends of the spinal cord sometimes showed spike activities in phase with contralateral or ipsilateral ventral roots. Inhibition of 1-3 segments by spot applications of glycine or gamma-aminobutyric acid (GABA) did not interrupt normal coordination or rostrocaudal phase lag. When a middle region of spinal cord was inhibited in a compartment with GABA or glycine, the caudal spinal cord could entrain the bursts in rostral ventral roots. In a few preparations the caudal region induced antiphasic bursts in previously silent rostral roots through the inhibited region. The maximum separation for caudal-upon-rostral antiphasic entrainment was approximately 20 segments in Ichthyomyzon and 36 segments in Petromyzon. Increased concentrations of an excitatory amino acid in a rostral compartment could produce descending entrainment of bursts in an adjacent caudal compartment at a higher frequency with rostrocaudal phase lag. The rostral-upon-caudal entrainment could still occur through spot applications of GABA or glycine but not through long inhibited regions. Two hypothetical groups of propriospinal interneurons are proposed for the coordination of swimming activities in the isolated spinal cords of adult lampreys. 1) Crossed, ascending interneurons may be excited in phase with nearby motoneurons and may excite and entrain rostral pattern generators on the opposite side. 2) Short, commissural interneurons may be excited in phase with nearby motoneurons and may inhibit contralateral generators.
Trained slow tracking. I. Muscular production of wrist movement
Authors: Schieber M. H. , Thach W. T.
Published: December 2017

Electromyographic (EMG) activity was recorded from those forearm muscles that act across the wrist as highly trained monkeys tracked slow hold-ramp-hold target trajectories with angular wrist position. During performance of this task, the forearm flexors and extensors had a common "basic pattern" of EMG activity. Flexor digitorum sublimis (FDS) and extensor digitorum communis (EDC), though commonly classified as prime movers of the fingers, were the most active flexor and extensor muscles during these movements at the wrist. The basic pattern of EMG activity was analyzed by varying independently 1) the movement direction, 2) the initial and final held wrist positions, 3) the ramp-movement velocity, and 4) the direction and magnitude of maintained external torque load. Most of the modulation of the basic pattern was related to wrist position: EMG amplitude was greatest at the extreme of muscle shortening. There was a slight difference in EMG activity between flexion and extension ramps that was related purely to the direction of movements, independent of wrist position, velocity, and external load; EMG amplitude was greater when a muscle was shortening and less when it was lengthening. During ramp movement, there was little or no observed EMG activity related to velocity (8-28 degrees/s). The magnitude of EMG activity varied in proportion to the external torque load, but this load-related component was additive, and the basic pattern of activity (related to direction and position) did not change with load. From these results we infer that a muscle's EMG activity was determined by 1) passive elastic properties of the wrist and the active length-tension characteristics of the muscle itself (position), 2) asymmetries in the muscle's contractile force depending on whether it was lengthening or shortening (direction), and 3) magnitude of the external torque load (force). By contrast, since no EMG activity was related to velocity in these slow movements, passive viscous properties and velocity-related cross-bridge kinetics were apparently so slight as to make undetectable the small additional EMG activity and contractile force presumably required to overcome them. A model of the muscle forces acting at the wrist incorporates these experimental observations.
Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons
Authors: Bourque C. W. , Randle J. C. , Renaud L. P.
Published: December 2017

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)
Intersegmental coordination of the leech swimming rhythm. I. Roles of cycle period gradient and coupling strength
Authors: Pearce R. A. , Friesen W. O.
Published: December 2017

The isolated leech nervous system generates a metachronally coordinated rhythmic output that is the neuronal correlate of swimming activity. We investigated two factors that contribute to intersegmental coordination: the swim-cycle periods expressed by segmental ganglia and the strength of neuronal coupling between ganglia. To determine the regional variation in swim-cycle periods, we severed both of the lateral intersegmental connectives. We left intact the median connective, which conveys tonic excitation but little phasic information. We obtained a reduction in intersegmental coupling strength by severing a single lateral intersegmental connective. Cycle periods were manipulated by cooling restricted sections of the nerve cord. Our experiments revealed an anterior-posterior gradient of cycle periods in ganglia of the isolated nerve cord; that is, chains of ganglia obtained from the anterior nerve cord exhibited longer cycle periods than those obtained from the posterior end of the cord. This gradient extends posteriorly to approximately ganglion 12 and may reverse posterior to ganglion 13. Increasing local cycle periods by cooling restricted sections of the nerve cord caused delay in activity cycles in the cooled ganglia, relative to the cycles of ganglia at the control temperature. This finding demonstrates that the observed gradient in cycle period provides for smaller intersegmental phase lags than would occur if there were no period gradients. Reduction of coupling strength by severing a lateral connective led to altered phase relationships across the lesion, both at the motor and oscillator levels. For those ganglion chains in which the anterior ganglia had greater periods, the reduced coupling led to reduced or even reversed phase relationships across the lesion but left unchanged the phase lag between the ends of the chain. In contrast, reduced coupling between halves of a chain in which the posterior ganglia had greater cycle periods led to increased phase lags across the lesion and between the ends. These altered phase relationships arise from a relative increase in the contribution of period differences when coupling strength is decreased. We conclude that the anterior-to-posterior progression of neuronal activity in the isolated leech nerve cord during swimming activity is provided by the intersegmental coupling signals. Furthermore, the period gradient expressed in our preparations acts to provide for smaller phase lags than would be generated by these coupling signals in the absence of such a gradient.(ABSTRACT TRUNCATED AT 400 WORDS)
Intersegmental coordination of the leech swimming rhythm. II. Comparison of long and short chains of ganglia
Authors: Pearce R. A. , Friesen W. O.
Published: December 2017

Preparations of the nearly isolated leech nerve cord containing as few as two ganglia are sufficient to generate intersegmentally coordinated swim oscillations, provided that they receive tonic excitation from other segments via the median connective (Faivre's nerve). Due to their greatly reduced complexity, these preparations should provide useful experimental models of neuronal coordination. As a step in the development of such models, we have characterized the intersegmental coordination of nerve-cord chains ranging from 2 to 18 ganglia in length. We found that increases in swim-cycle period give rise to increases in intersegmental delay between homologous motoneuron bursts. Thus the intersegmental phase relationships are nearly independent of period. The relationship between intersegmental delay and period is approximately linear and extrapolates to intersect the period axis at approximately 0.3 s. This value is in close agreement with the analogous measure derived from tension measurements in the intact swimming leech. Chain length (number of connected ganglia in a preparation) has a pronounced influence on the magnitude of intersegmental phase lag. The longest chains (18 ganglia) exhibited phase lags of approximately 8 degrees per segment, whereas for pairs of ganglia the phase lag was approximately 40 degrees per segment. This dependence of phase lags on chain length was apparent at both the motor and oscillator levels. The intersegmental phase lag is not the same in all parts of the nerve cord. Rather, it increases steadily toward the posterior end of the chain, providing a deceleration in the rearward progression of the metachronal activity. The rearward increase in intersegmental phase lag is paralleled by a propensity of chains taken from more posterior sections of the nerve cord to exhibit larger phase lags. That is, there appears to be a phase-lag gradient intrinsic to the nerve cord to account for the deceleration of activity. The anterior and posterior ends of an isolated nerve cord continue to exhibit phase-locked bursting when an intervening section of five ganglia is bathed in elevated Mg2+ saline. Thus, information sufficient to coordinate oscillations in separate ganglia travels at least six segments. The phase lag across the blocked section is reduced but within each unblocked section is increased so that the phase lag between extreme ends is nearly unchanged. This altered burst pattern is due to a combination of synaptic block in segmental ganglia and conduction block in through-fibers.
Location of membrane conductance changes by analysis of the input impedance of neurons. II. Implementation
Authors: Fox S. E. , Chan C. Y.
Published: December 2017

Mathematical modeling has shown that it should be possible to determine the electrotonic location of membrane conductance changes in single neurons by analysis of the associated changes in the magnitude of the alternating-current (AC) input impedance. The form of the plot of change in the magnitude of the input impedance as a function of frequency (delta [Zn(f)]) should differ for changes in membrane conductance located at different electrotonic distances from the recording/current-injection site. Due to the axial resistance and the membrane capacitance, the higher frequencies are attenuated with distance to a greater degree than are the lower frequencies. Thus delta [Zn(f)] should drop to zero more rapidly with increasing frequency for distal than for proximal conductance changes. For distal changes in conductance, the sign of the change in the magnitude of the input impedance can even reverse in the higher frequency range, so that increases in conductance would produce increases in impedance. This effect may explain the paradoxical increases in impedance at 100 Hz reported for motor neuron inhibitory postsynaptic potentials. Sine-wave impedance measurements were made in single embryonic chick spinal neurons in tissue culture, and gamma-aminobutyric acid (GABA) was iontophoretically applied alternately to the soma and to a neurite at a measured distance from the soma. The impedance changes produced by the GABA-induced conductance changes were consistent with the expectations from the mathematical modeling, but the results suggest that the axial resistance of the neurites must be quite high in some cases. Distortions due to microelectrode capacitance and stray capacitances in the input stage of single-electrode bridge amplifiers can make sine-wave impedance measurements impossible. This difficulty was eliminated by modifications to the capacity compensation circuit of an active bridge amplifier. Noise and distortion of several other types can also introduce serious errors. Methods for minimizing such problems are discussed. In spite of its limitations, this method can be of great practical value, because it can give the electrotonic location of spontaneously occurring membrane conductance changes in single neurons even when unitary synaptic potentials cannot be resolved. These methods are currently being applied to hippocampal pyramidal cells in vivo to locate conductance changes during the electroencephalogram (EEG) theta-rhythm in rats. In such laminated structures, the determination of the anatomical source of a group of active synapses can be aided by location of the resultant membrane conductance changes.
Effects of eye position on saccades evoked electrically from superior colliculus of alert cats
Authors: McIlwain J. T.
Published: December 2017

Electrical stimulation was carried out in the intermediate and deep gray layers of the superior colliculus in alert cats. The heads of the animals were fixed, and their eye movements were recorded with the scleral search coil method. Stimulation in the anterior two-thirds of the colliculus with long-duration pulse trains produced multiple saccades, as in the primate (45, 51), but their directions and amplitudes were influenced significantly by the initial position of the eye. Stimulation in the posterior part of the colliculus evoked saccades that appeared to be "goal-directed," whereas stimulation at the extreme caudal edge of the colliculus yielded centering saccades. These observations confirm previous reports of Roucoux and Crommelinck (48) and Guitton et al. (24). Saccades evoked during bilateral simultaneous stimulation of the superior colliculi were also dependent on the initial position of the eye. At certain relative intensities of stimulation on the two sides, saccades failed to occur when the eye was within a particular part of the oculomotor range. When the eye was outside this region, the same stimuli triggered an eye movement that drove the eye toward the zone of saccade failure. These findings indicate that saccadic commands resulting from focal collicular stimulation in the cat can be modified by information about current eye position. It is not certain where in the brain this occurs or by what neural mechanisms, but a local feedback model of the saccadic control system (46) can account for the main observations. The functional significance of these findings depends in large measure on the degree to which focal collicular stimulation reproduces naturally occurring patterns of neural activity.