bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of directional selectivity in simple neurons of the cat's visual cortex analyzed with stationary flash sequences
Authors: Ganz L. , Felder R.
Published: December 2017

The properties of simple neurons showing selectivity to direction of motion in area 17 of the cat cortex were examined. We analyzed in particular a sample of cells receiving a projection from 0 to 10 degrees in visual angle from the area centralis of the cat retina. Three categories of simple neurons were examined: directionally asymmetric (DA) neurons, directionally selective neurons of the unimodal type (DS1), and bimodal types (DS2). Poststimulus time histograms (PSTH) were obtained to moving white and black bars as well as to static onset sequences and static offset sequences. Our analysis involves a comparison of responses to single static flashes at various receptive-field locations with responses to sequence pairs of static flashes at those same locations. We find that DA neurons are not sensitive to the direction in which a pair of stimuli are presented. Inhibitory and excitatory responses show properties of linear summation whatever the direction of the stimulus sequence. Their behavior is reminiscent of retinal and LGN neurons. The synergy model accounts well for a DA neurons's directional asymmetry. If pairs of stimuli are close enough (usually an interstimulus distance of 20' or less for the central 10 degrees of the cat's visual field), then DS neurons show striking departures from linear summation. Specifically, this departure entails an anisotropic distribution of inhibition. The directional selectivity of DS neurons cannot be explained on the basis of a simple linear combination of their on and off region's responses. Directional selectivity is produced entirely within an on-excitatory discharge region or entirely within an off-excitatory discharge region. The excitatory discharge center of even the simplest unimodal DS neuron can be shown to be decomposable into subunits smaller than that discharge center. The fact that the spread of this anisotropy of inhibition is often much more restricted than the entire extent of the DS neuron's excitatory discharge center argues strongly that underlying subregions or modules are contributing their inputs to DS neurons. A DS neuron does not analyze motion as an isolated unit; to the contrary, it is probably embedded in a pool of mutually "cooperative" DS neurons. The basic module of directional analysis is responsive either to an on-on sequence or an off-off sequence but not to both. It is not selective to an on-off sequence. Therefore, unimodal DS neurons (DS1) are performing an analysis of single moving edges.(ABSTRACT TRUNCATED AT 400 WORDS)
Rat hippocampal neurons in culture: properties of GABA-activated Cl- ion conductance
Authors: Segal M. , Barker J. L.
Published: December 2017

The actions of gamma-aminobutyric acid (GABA) on the membrane properties of rat hippocampal neurons maintained in dissociated cell culture were studied using intracellular recording techniques. All the neurons tested were responsive to GABA applied by pressure from micropipettes containing 10-20 microM GABA. The response consisted of a marked increase in conductance associated with a potential change. The inversion potential was sensitive to the Cl- ion gradient across the cells. It was about -60 mV when measured during recordings utilizing K acetate-filled microelectrodes, about -15 mV when measured during recordings with KCl-filled microelectrodes, and about +15 mV when measured with KCl electrodes in a medium containing low [Cl-]o. These results indicate that the membrane conductance evoked by GABA primarily involves Cl- ions. There were no apparent differences between the inversion potential of responses elicited at the level of the cell body and those evoked on processes. The two-electrode voltage-clamp technique was used to study the membrane mechanisms underlying these responses. GABA generated current responses that were associated with an increase in both conductance and membrane current variance. At a given potential both the conductance change and increase in variance were directly proportional to the amplitude of the current response. Spectral analysis of the membrane current variance evoked by GABA revealed that many of the computed spectra could be fitted by a single Lorentzian equation, suggesting that GABA activates two-state (open-closed) Cl- ion channels whose durations are exponentially distributed. The mean duration of these channel openings was estimated to be 22.9 +/- 2.1 ms, while the average conductance was estimated to be 19.8 +/- 2.7 pS in 13 cells. Large-amplitude GABA responses evoked at -70 mV frequently faded in amplitude, often by as much as 50%, with little or no change in the associated conductance. Since the membrane current variance decreased in direct relation to the fading current response, while estimates of channel lifetime did not change, the results suggest that the fading is due to a shift in the Cl- gradient. Responses to constant amounts of GABA evoked at different membrane potentials showed that the macroscopic conductance activated by GABA varied with membrane potential. Often 4-5 times more conductance was generated at depolarized (0 to +10 mV) relative to hyperpolarized potentials (-60 to -70 mV).(ABSTRACT TRUNCATED AT 400 WORDS)
Integration of retinal and motor signals of eye movements in striate cortex cells of the alert cat
Authors: Toyama K. , Komatsu Y. , Shibuki K.
Published: December 2017

Responses of saccade-depressed (SD) and saccade-excited (SE) cells in the striate cortex to eye movements of alert cats under presentation of a visual pattern were studied under reinforcement of the eye movements with rewards of water. These responses were compared to those on passive displacement of the visual pattern reproducing the movements of the retinal image occurring during eye movements while eye movements were suppressed by withdrawal of reinforcement. Passive displacement of the visual pattern produced in the SD cells depression closely resembled the depression occurring during eye movements under presentation of the visual pattern, in time course as well as in amplitude. Both the saccade depression and the depression due to passive movement of the visual pattern were nonselective to the direction of eye movements. Saccade excitation of the SE cells frequently contained two components occurring at 20 and 80 ms after the onsets of eye movements. Passive displacement of the visual pattern produced in the SE cells excitation comparable with the early component of the saccade excitation. These findings suggest that saccade depression in the SD cells and the early component of the saccade excitation in the SE cells are related to retinal reafference of eye movement. During presentation of visual patterns, saccade excitation in the SE cells was closely related to parameters of eye movements, such as direction, amplitude, duration, and velocity. The correlations were completely lost or strongly reduced in darkness. Lines of evidence were provided that the saccade excitation of the SE cells in darkness or the later component of the saccade excitation under presentation of a visual pattern represents efference copy signals of eye movement transferred to the striate cortex through the Clare-Bishop (CB) cortex. Excitation comparable with saccade excitation in darkness occurred in synchrony with activities of the oculomotor nuclei even after retrobulbar paralysis of eye movement, indicating that the excitation is related to efference copy signals rather than proprioceptive reafference of eye movement.(ABSTRACT TRUNCATED AT 400 WORDS)
Potassium distribution and membrane potential of sensory neurons in the leech nervous system
Authors: Schlue W. R. , Deitmer J. W.
Published: December 2017

The intracellular K activity (aKi) and membrane potential of sensory neurons in the leech central nervous system were measured in normal and altered external K+ concentrations, [K+]o, using double-barreled, liquid ion-exchanger microelectrodes. In control experiments membrane potential measurements were made using potassium chloride-filled single-barreled microelectrodes. All values are means +/- SD. At the normal [K+]o (4 mM) the mean aKi of all cells tested was 72.6 +/- 10.6 mM (n = 40) and the average membrane potential was -47.3 +/- 5.2 mM (n = 40). When measured with single-barreled microelectrodes, the membrane potential averaged -45.3 +/- 2.9 mV (n = 12). Assuming an intracellular K+ activity coefficient of 0.75, the intracellular K+ concentration of sensory neurons would be 96.8 +/- 14.1 mM). With an extracellular K+ concentration of 5.8 mM in the intact ganglion compared to the K+ concentration of 4 mM in the bath, the K+ equilibrium potential was -71.5 mV. When the ganglion capsule was opened, the extracellular K+ concentrations in the ganglion were similar to that of the bathing medium and the calculated K+ equilibrium potential was -81 mV. The membrane of sensory neurons depolarized following the changes to elevated [K+]o (greater than or equal to 10-100 mM), whereas aKi changed only little or not at all. At very low [K+]o (0.2, 0 mM) aKi and membrane potential showed little short-term (less than 3 min) effect but began to change after longer exposure (greater than 3 min). Reduction of [K+]o from 4 to 0.2 mM (or 0 mM) produced first a slow, and then a more rapid decrease of aKi and membrane resistance, accompanied by a slow membrane hyperpolarization. Following readdition of normal [K+]o, the membrane first depolarized and then transiently hyperpolarized, eventually returning slowly to the normal membrane potential.(ABSTRACT TRUNCATED AT 400 WORDS)
Control of complex motor gestures: orofacial muscle responses to load perturbations of lip during speech
Authors: Abbs J. H. , Gracco V. L.
Published: December 2017

The contribution of ascending afferents to the control of speech movement was evaluated by applying unanticipated loads to the lower lip during the generation of combined upper lip-lower lip speech gestures. To eliminate potential contamination due to anticipation or adaptation, loads were applied randomly on only 10-15% of the trials. Physical characteristics of the perturbations were within the normal range of forces and movements involved in natural lip actions for speech. Compensatory responses in multiple facial muscles and lip movements were observed the first time a load was introduced, and achievement of the multimovement speech goals was never disrupted by these perturbations. Muscle responses were seen in the lower lip muscles, implicating corrective, feedback processes. Additionally, compensatory responses to these lower lip loads were also observed in the independently controlled muscles of the upper lip, reflecting the parallel operation of open-loop, sensorimotor mechanisms. Compensatory responses from both the upper and lower lip muscles were observed with small (1 mm) as well as large (15 mm) perturbations. The latencies of these compensatory responses were not discernible by conventional ensemble averaging. Moreover, responses at latencies of lower brain stem-mediated reflexes (i.e., 10-18 ms) were not apparent with inspection of individual records. Response latencies were determined on individual loaded trials through the use of a computer algorithm that took into account the variability of electromyograms (EMG) among the control trials. These latency measures confirmed the absence of brain stem-mediated responses and yielded response latencies that ranged from 22 to 75 ms. Response latencies appeared to be influenced by the time relation between load onset and the initiation of muscle activation. Examination of muscle activity changes for individual loaded trials revealed complementary variations in the magnitude of responses among multiple muscles contributing to a movement compensation. These observations may have implications for limb movement control if multimovement speech gestures are considered analogous to a limb action requiring coordinated movements around multiple joints. In this context, these speech motor control data might be interpreted to suggest that for complex movements, both corrective feedback and open-loop predictive processes are operating, with the latter involved in the control of coordination among multiple movement subcomponents.
Linear and nonlinear components of human electroretinogram
Authors: Baker C. L. , Hess R. F.
Published: December 2017

We compared electroretinographic (ERG) responses to uniform-field and a variety of pattern stimuli using both transient and steady-state analyses. Evidence is provided that for all of these stimuli, the peak at high temporal frequencies in the steady-state response corresponds to the fast wave of the transient response and that the peak at low temporal frequencies corresponds to the slow wave of the step response. A variety of contrast-modulated grating stimuli were used to demonstrate that the fast, high-frequency response can be regarded as the sum of two components, an "odd-symmetric" component, which behaves linearly and is independent of spatial frequency, and an "even-symmetric" component, which behaves nonlinearly and has a band-pass spatial-frequency dependence. The prevailing distinction that is made between pattern and uniform-field ERGs is a consequence of the fact that the uniform-field ERG is dominated by the odd-symmetric (linear) component, whereas the so-called pattern (contrast reversal) ERG reveals the even-symmetric (nonlinear) component in isolation. Since a uniform field can also drive the nonlinear component, the present dichotomy ("luminance" versus "pattern") can be better understood in terms of the linear and nonlinear components of the response rather than in terms of the stimuli that produce them.
Transmitter identification of pyloric neurons: electrically coupled neurons use different transmitters
Authors: Marder E. , Eisen J. S.
Published: December 2017

The neurotransmitters mediating the synaptic interactions among the neurons of the pyloric system of the stomatogastric ganglion (STG) of the lobster, Panulirus interruptus, were examined using a combination of electrophysiological, pharmacological, and biochemical techniques. Iontophoretically applied L-glutamate inhibited all motor neurons of the pyloric system. This inhibitory response was blocked by low concentrations of picrotoxin but unaffected by atropine. The anterior burster (AB) interneuron, pyloric dilator (PD) motor neurons, and ventricular dilator (VD) motor neuron were depolarized and excited by iontophoretically applied acetylcholine (ACh). The lateral pyloric (LP) and pyloric (PY) constrictor motor neurons were inhibited by ACh and by the cholinergic agonist, carbachol. These inhibitory cholinergic responses were blocked by atropine but not by picrotoxin. The inhibitory postsynaptic potentials (IPSPs) evoked by the constrictor motor neurons were blocked by picrotoxin but not by atropine. Taken together with previously published data (15, 18), this suggests that the constrictor motor neurons release glutamate at both their excitatory neuromuscular junctions and their inhibitory intraganglionic junctions. The lucifer yellow photoinactivation technique (27) was used to study separately the neurotransmitters released by the electrically coupled PD and AB neurons. The AB-evoked IPSPs were blocked by picrotoxin but not by atropine. The PD-evoked IPSPs were blocked by atropine and other muscarinic antagonists but not by picrotoxin. Somata of PD neurons contained choline acetyltransferase (CAT) activity, but somata of AB neurons contained no detectable CAT activity. On the basis of the data in this paper and previously published data (17, 18), we conclude that the PD neurons release ACh at both their excitatory neuromuscular junctions and their inhibitory intraganglionic connections. Although the AB neuron is electrically coupled to the PD neurons, the AB neuron is not cholinergic. Glutamate is a likely transmitter candidate for the AB neuron. These data show that electrically coupled neurons can release different transmitters. Furthermore, these data show that an IPSP can be the result of the combined actions of two different neurotransmitters, each released from a different neuron. The functional consequences of these conclusions are explored in the following papers (9, 22).
Properties of subthreshold response and action potential recorded in layer V neurons from cat sensorimotor cortex in vitro
Authors: Stafstrom C. E. , Schwindt P. C. , Flatman J. A. , Crill W. E.
Published: December 2017

Properties of the action potential and subthreshold response were studied in large layer V neurons in in vitro slices of cat sensorimotor cortex using intracellular recording and stimulation, application of agents that block active conductances, and a single-microelectrode voltage clamp (SEVC). A variety of measured parameters, including action-potential duration, afterpotentials, input resistance, rheobase, and membrane time constant, were similar to the same parameters reported for large neurons from this region of cortex in vivo. Action-potential amplitudes and resting potentials were greater in vitro. Most measured parameters were distributed unimodally, suggesting that these parameters are similar in all large layer V neurons irrespective of their axonal termination. The voltage response to subthreshold constant-current pulses exhibited both time and voltage dependence in the great majority of cells. Current pulses in either the hyperpolarizing or subthreshold depolarizing direction cause the membrane potential to attain an early peak and then decay (sag) to a steady level. On termination of the pulse, the membrane response transiently overshoots resting potential. Plots of current-voltage relations demonstrate inward rectification during polarization on either side of resting potential. Subthreshold inward rectification in the depolarizing direction is abolished by tetrodotoxin (TTX). The ionic currents responsible for subthreshold rectification and sag were examined using the SEVC. Steady inward rectification in the depolarizing direction is caused by a persistent, subthreshold sodium current (INaP) (54). Sag observed in response to a depolarizing current pulse is due to activation of a slow outward current, which superimposes on and partially counters the persistent sodium current. Both sag in response to hyperpolarizing current pulses and rectification in the hyperpolarizing direction are caused by a slow inward "sag current" that is activated by hyperpolarizing voltage steps. The sag current is unaltered by TTX, tetraethylammonium, (TEA), Co2+, Ba2+, or 4-aminopyridine. Fast-rising, short-duration action potentials can be elicited by an intracellular current pulse or by orthodromic or antidromic stimulation. Spikes are blocked by TTX. The form of the afterpotential following a directly evoked spike varies among cells with similar resting potentials. Biphasic afterhyperpolarizations (AHPs) with fast and slow components were most frequently seen. About 30% of the cells displayed a depolarizing afterpotential (DAP), which was often followed by an AHP. Other cells displayed a purely monophasic AHP.(ABSTRACT TRUNCATED AT 400 WORDS)
Role of corpus callosum in functional organization of cat striate cortex
Authors: Payne B. R. , Pearson H. E. , Berman N.
Published: December 2017

The short-term (3-51 days) and long-term (31-42 wk) effects of corpus callosum transection on the receptive-field properties of neurons were assessed at the single-cell, architectural, and topographical levels of organization in the cat striate cortex. Corpus callosum transection decreased the proportion of neurons that could be activated from both eyes. In short-term animals, the reduction in binocularity was restricted to the representation of a vertical strip of visual space extending from the vertical meridian to at least 12 degrees lateral. In the long-term animals, the reduction in binocularity was restricted to the representation of visual space 4 degrees lateral to the vertical meridian. Therefore, the reduction in the representation of 4-12 degrees was only temporary. In both groups, the reduction in binocularity was less in the representation of area centralis than at other retinal locations in the same vertical strip. The region of area 17 affected permanently by the transection receives fibers from the contralateral hemisphere in normal animals. The region affected temporarily by the transection contains callosal cells but does not contain callosal terminals. Binocularity was assessed separately for simple I, simple II, and complex receptive-field types. The reduction in binocularity in the 12 degrees strip in short-term animals and in the 4 degrees strip in long-term animals was accounted for mainly by a reduction in binocularity of simple I and complex cells. As in normal animals, complex cells in callosum-transected cats were always more binocular than the other cell types. An analysis of the effects of corpus callosum transection on different cortical layers showed that a greater proportion of cells in the supragranular layers II and III showed a reduction in binocularity than in the infragranular layers V and VI. The proportion of binocular neurons in layer IV was not significantly different from normal. The major decreases in binocularity occurred in layers II, III, and VI for simple I and simple II cells and in layers II, III, and V for complex cells. The binocularity of simple II cells in layer IV and complex cells in layer VI was not affected. The effects of the transection on the columnar organization of the cortex were assessed by making electrode tracks that passed in the radial or laminar dimensions of the cortex. Reconstructions of the radial tracks showed that cells within one radial column tended to be dominated by the same eye. In adjacent columns, cells tended to be dominated by different eyes.(ABSTRACT TRUNCATED AT 400 WORDS)
Monosynaptic excitation of dorsal medullary respiratory neurons by slowly adapting pulmonary stretch receptors
Authors: Averill D. B. , Cameron W. E. , Berger A. J.
Published: December 2017

The discharges of individual slowly adapting pulmonary stretch receptors (PSRs) and single respiratory neurons of the dorsal respiratory group (DRG) within the ventrolateral subnucleus of the solitary tract were recorded simultaneously in anesthetized, paralyzed, artificially ventilated cats. DRG neurons were classified as P-cell, I-alpha, or I-beta, based on the alteration in activity during respiratory cycles when lung inflation was withheld compared to activity when the lungs were inflated in phase with central inspiratory drive. In some cases, vagal stimulation was also used to classify respiratory neurons. Synaptic input of PSRs onto DRG neurons was examined by the construction of cross-correlograms for the simultaneously recorded discharge of individual PSRs (reference events) and individual DRG neurons (correlated events). Monosynaptic excitatory connections were demonstrated by peaks in 26% of the cross-correlograms of PSR and P-cell pairs and 20% of the cross-correlograms of PSR and I-beta neuron pairs. The ratio of the peak number of occurrences to the background number of occurrences (k value) was comparable for P-cells and I-beta neurons: 2.96 +/- 2.09 and 1.62 +/- 0.36 (mean +/- SD), respectively. P-cells and I-beta neurons also had similar short latencies for the peak of increased probability of discharge: 2.74 +/- 0.53 and 2.57 +/- 0.63 ms, respectively. No evidence was obtained demonstrating synaptic connectivity between PSRs and I-alpha neurons. Interpretations of this negative result are discussed.
Tonotopic organization in ventral nucleus of medial geniculate body in the cat
Authors: Imig T. J. , Morel A.
Published: December 2017

Responses of single units and clusters of units to tone burst stimulation were recorded at 100-micron intervals along vertical electrode penetrations through the medial geniculate bodies of eight barbiturate-anesthetized cats. Marking lesions were placed at two or three locations along most penetrations to aid in histological reconstruction of electrode tracks. Best frequencies and suprathreshold-response latencies were studied at each location along a penetration. The ventral nucleus is physiologically characterized as a region containing narrowly tuned, short-latency (less than or equal to 40 ms) responses and an orderly tonotopic organization. Best frequencies were plotted as a function of depth along single electrode penetrations, and the sequences from different locations in the ventral nucleus were compared. Two-dimensional best-frequency maps were obtained at different rostrocaudal levels. Each map was constructed from best frequencies encountered along several electrode penetrations in the same transverse plane in one brain. We divided the ventral nucleus into seven different rostrocaudal levels, each characterized by a different pattern of tonotopy. Caudolaterally, isofrequency contours parallel the ventrolateral border of the medial geniculate body. At middle levels, low- and mid-frequency contours course ventromedially from the dorsal border of the ventral nucleus toward its medial border, then turn sharply and continue ventrolaterally. Higher-frequency contours parallel this course, but consist of discontinuous dorsal and ventral segments. Rostrally, isofrequency contours are vertically oriented. A model of the three-dimensional tonotopic organization of the ventral nucleus is described that is consistent with the two-dimensional best-frequency maps obtained at different rostrocaudal levels and with locations of ventral nucleus neurons labeled by horseradish peroxidase injections into low-, mid-, and high-frequency representations in auditory cortex. The model includes a planar component and a concentric component. Within the planar component, low frequencies are represented laterally and high frequencies are represented rostromedially. Within the concentric component, low frequencies are represented in a central column that extends mediolaterally through a hole in the mid-frequency representation. The mid-frequency representation in turn is partially surrounded by the high-frequency representation. There is a continuous representation of a "single" frequency in both the planar and concentric components of the model.(ABSTRACT TRUNCATED AT 400 WORDS)
Raphe magnus inhibition of feline T1-T4 spinoreticular tract cell responses to visceral and somatic inputs
Authors: Chapman C. D. , Ammons W. S. , Foreman R. D.
Published: December 2017

Background activity of spinoreticular tract neurons in the T1-T4 segments was on average inhibited 80% by electrical stimulation of nucleus raphe magnus. Nucleus raphe magnus stimulation inhibited responses of spinoreticular tract neurons to somatic input produced by touching the skin and hair (innocuous stimulus) or pinching the skin and muscle (noxious stimulus). Inhibition of responses to noxious and innocuous somatic inputs was not significantly different. Inhibition produced during nucleus raphe magnus stimulation was less effective when the activity of spinoreticular tract cells increased. This relationship was consistent for both background activity and responses to somatic noxious or innocuous input. Nucleus raphe magnus stimulation inhibited responses of spinoreticular tract neurons to visceral input produced by electrical stimulation of cardiopulmonary sympathetic afferent fibers. Responses to C-fiber sympathetic afferent fibers were more effectively inhibited than were responses to A-delta sympathetic afferent fibers. In conclusion, stimulation of the nucleus raphe magnus inhibits T1-T4 spinoreticular tract neuronal responses to visceral and somatic inputs. Since spinoreticular neurons project to the medullary reticular formation, activation of the nucleus raphe magnus could modulate affective-motivational behavior and cardiovascular adjustments that often occur during angina pectoris.
Excitatory and inhibitory postsynaptic potentials in alpha-motoneurons produced during fictive locomotion by stimulation of the mesencephalic locomotor region
Authors: Shefchyk S. J. , Jordan L. M.
Published: December 2017

We tested the hypothesis that stimulation of the mesencephalic locomotor region (MLR) activates polysynaptic pathways that project to lumbar spinal motoneurons and are involved in the initiation of locomotion. Fictive locomotion was produced by MLR stimulation, and intracellular records of evoked postsynaptic potentials (PSPs) in alpha-motoneurons were computer analyzed. Stimulation of sites in the MLR that were maximally effective for the initiation of locomotion produced excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) in all the motoneurons examined. The amplitudes of the PSPs increased as locomotion commenced. The EPSPs were largest during the depolarized phase of the step cycle, and in 17 of our 22 cells the EPSP was replaced by an IPSP of slightly longer latency during the hyperpolarized phase. The mean latency of the EPSPs measured from the stimulus artifact produced by stimulation of the MLR was 5.1 ms (3.0-7.0 ms). In all cases, the IPSP occurred 0.6 ms or more after the onset of the EPSP in the same cell. Later PSPs were sometimes observed as well. The effects of constant current injection on the membrane potential oscillations associated with fictive locomotion (locomotor drive potentials) were examined. The results showed that the amplitudes of the locomotor drive potentials (LDPs) could be affected by depolarizing and hyperpolarizing current injection. The data is consistent with the LDP having a predominant inhibitory component, which is more readily altered by current injection than is the excitatory component. The effect of constant current injections on the MLR-evoked PSPs was also examined, and it was observed that both EPSPs and IPSPs could be affected by the injected currents. The EPSPs increased in amplitude with constant hyperpolarizing current injection, and this fact rules out the possibility that the EPSP is actually a reversed IPSP. The IPSP was decreased in amplitude by hyperpolarizing current injection. Combined stimulation of the MLR and the ipsilateral high-threshold muscle or cutaneous afferents produced facilitation of both short- and long-latency MLR-evoked PSPs, suggesting that the two pathways share common interneurons. The possibility that the long-latency PSPs are produced by rapid oscillation in the locomotor central pattern generator is discussed. We concluded that MLR stimulation that evokes fictive locomotion produces both excitation and inhibition of spinal motoneurons. Spinal interneuronal systems are implicated and may be those involved in the initiation and control of locomotion. The probable relay sites for the descending pathway from the MLR to motoneurons are discussed.
Interactions between rostral pontine and ventral medullary respiratory neurons
Authors: Segers L. S. , Shannon R. , Lindsey B. G.
Published: December 2017

Lesioning studies have demonstrated that the respiratory rhythm is generated within the brain stem and that connections between the pons and the medulla must be intact for the generation of eupneic breathing in the decerebrate or anesthetized vagotomized cat. However, the nature of proposed functional connections between pontine and medullary respiratory neurons is not well understood. The possibility of interactions between respiratory neurons of the rostral pons (n. parabrachialis medialis, Kolliker-Fuse nucleus) and the ipsilateral ventral respiratory group (VRG; n. retroambigualis, n. ambiguus, retrofacial nucleus) was investigated because of neuroanatomical and electrophysiological evidence for such connections. Phrenic nerve activity and pontine and medullary single-unit respiratory related activities were recorded extracellularly in 44 decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Cross-correlation analysis was employed to detect and evaluate functional associations of pairs of cells. Eighteen (7%) of the 255 pairs of respiratory neurons analyzed showed evidence of short time scale correlations indicative of a functional interaction. The interpretations of the detected correlations suggest that some cell pairs were correlated due to mono- or paucisynaptic connections, while others were correlated due to the influence of an unobserved shared input. The interpretations for 11 of the 15 cell pairs for which a monosynaptic connection may be postulated involve a projection from a tonically active respiratory neuron. Twelve of the 18 positive correlations involved neurons whose maximum rates of discharge occurred during different parts of the respiratory cycle. The results of this study provide the first evidence of functional connections among pontine and medullary respiratory neurons based on the evaluation of simultaneously recorded spike trains and suggest that the role of the rostral pontine respiratory neurons in the control of the respiratory rhythm may be mediated by various types of interactions. When considered with the results of other studies, our data suggest that monosynaptic interactions between VRG and rostral pontine respiratory neurons play a limited role in the control of the respiratory cycle in the decerebrate vagotomized cat. It is likely that the influence of the pons on ventral medullary neurons (and vice-versa) is also exerted via polysynaptic pathways and/or via brain stem neurons not sampled in this study.
Spontaneous and driven responses of semicircular canal primary afferents in the unanesthetized pigeon
Authors: Anastasio T. J. , Correia M. J. , Perachio A. A.
Published: December 2017

Spontaneous activity from 120 vestibular semicircular canal (SC) primary afferents and driven responses from 20 SC primary afferents to 2.3-decade bandwidth (0.029-6.152 Hz) sum of sinusoidal angular rotations were characterized in 10 unanesthetized pigeons. The results were compared with those previously gathered from barbiturate anesthetized pigeons. The average spontaneous mean firing rate (MFR) of SC primary afferents in unanesthetized pigeons was found to be 168 impulses per second (I/s), n = 120, and is approximately 80% higher than that for SC primary afferents in anesthetized pigeons [93 I/s, n = 149 (Ref. 9) and 92 I/s, n = 124 (Ref. 22)]. The spontaneous discharge of SC primary afferents from unanesthetized pigeons was classified according to the coefficient of variation (CV) of 512-1,024 interspike intervals (ISIs) into regular (CV less than 0.1), intermediate (0.1 less than or equal to CV less 0.4), and irregular (0.4 less than or equal to CV) categories. The percentages of SC primary afferents falling within each CV category were similar for unanesthetized and anesthetized pigeons (22). The relation between the spontaneous mean ISI and its standard deviation (SD) for SC primary afferents in the unanesthetized pigeon is best described by a power function model, which provides a significantly better fit than does a linear model. The parameters of this power function model are similar for SC primary afferents in unanesthetized and anesthetized pigeons (10). The spontaneous ISIs of individual SC primary afferents in the unanesthetized pigeon were found to be distributed either normally, log-normally, or according to the first passage time of the Wiener-Levy (WL) process. The gain of anterior SC primary afferents at 0.25 Hz is similar for anesthetized (2.93 I X s-1 X deg-1 X s-1, n = 14) (11) and for unanesthetized (3.01 I X s-1 X deg-1 X s-1, n = 14) pigeons. Bode plots constructed from the responses to sum sinusoidal angular accelerations reveal that SC primary afferents in unanesthetized pigeons display a phase lead and gain enhancement at frequencies between 0.6 and 6 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)
Intracellular analysis of the innervation of a crayfish sensory interneuron by regenerating afferents
Authors: Strandburg R. J. , Krasne F. B.
Published: December 2017

Mechanoreceptors of the crayfish tail fan have peripheral somata and send their axons to the last (sixth) abdominal ganglion via five bilateral pairs of nerve roots (R1-R5). Comparisons were made between normal crayfish and regenerate preparations in which R4 had been cut and directed back to an extensively denervated sixth abdominal ganglion; 8 to 15 weeks postoperatively, an identified target interneuron (A) in this ganglion was impaled, and its response to water currents, electrical excitation of R4, and stimulation of individual sensory hairs supplying axons to R4 was studied along with several other properties of the pre- and post-synaptic neurons. Normal levels of excitability in A to R4 stimulation were achieved within six weeks as judged by extracellular criteria. Subsequent intracellular analysis revealed that few differences exist between regenerated and normal inputs: probability of (re-) connection, unitary EPSP amplitude and time course distributions, resting membrane potentials, and critical firing levels were comparable in the two groups; input impedance, however, may have been lower in regenerates. Compound electrically elicited EPSPs were similar in amplitude, rise time, and half amplitude width, but differed slightly in latency to onset (regenerates greater than normals). This was accounted for by differences in conduction time to the ganglion in regenerates, and central delay estimates suggest that connections in both groups are monosynaptic. The body root (R1) providing input to A that remained intact in the regenerate preparations increased in efficacy; over 12 postoperative weeks the response of A to R1 activation by water drops steadily increased and at 12 weeks unitary increments to ascending electrical stimulation of R1 were significantly larger than in normals. The response to giant interneuron activation demonstrated that recurrent inhibitory inputs were normal in regenerates. In addition, synaptic depression, normally responsible for behavioral habituation in this system, was comparable across groups. Further, protection from habituation was observed in both normals and regenerates if R4 stimulation was preceded by giant interneuron activation, thus indicating that normal presynaptic inhibitory inputs to the regenerated afferent terminals have also successfully regenerated.(ABSTRACT TRUNCATED AT 400 WORDS)
Processing of vibrissa sensory information within the rat neocortex
Authors: Ito M.
Published: December 2017

Neuronal response properties were compared among different layers of the urethan-anesthetized rat vibrissa cortex. Measurements were made of the receptive-field (RF) size, the degree of directional selectivity, the latency of driving, the velocity threshold, and the tuning-curve slope. The RF size was defined by the number of whiskers that, when deflected individually, activated a neurons. For the center whisker of the RF (usually whisker C3), the response to deflection in the most preferred direction was compared with that in the opposite direction to classify the neuron as either strongly directional, weakly directional, or nondirectional. For the most preferred direction of the center whisker, the minimum velocity of deflection required to drive the unit was defined as the velocity threshold, the latency of driven response to a standard supramaximal velocity was measured, and finally, using exponential ramp-and-hold deflection, the threshold amplitude was determined at different values of time constant to construct a tuning-curve slope. Cortical layer IV neurons, as a whole, have the lowest threshold velocity. Layer Vb neurons stand on the opposite extreme in having the highest mean velocity threshold value. Although this difference is consistent with the generally held view that the "barrels" in layer IV represent the input stage of cortical information processing, the lack of laminar differences in latency and RF size support the idea that neurons of other cortical layers also receive direct thalamocortical inputs. The population of cortical neurons thus appears quite homogeneous across different layers as far as the results of examination with short-pulsed stimulation are concerned. Correlation of pairs of parameters (RF, directionality, velocity threshold, and latency) was tested in the two layers (layer IV and layer Vb). The latency and velocity threshold are highly correlated within both layers. Also, most of correlation coefficients of the corresponding pairs of the two layers are similar. However, the use of exponential ramp-and-hold deflection of whiskers revealed a difference in tuning-curve slope between layer IV and layer Vb (also layers II-III); layer IV neurons show flatter tuning-curve slopes (more oriented for detection of the amplitude component of whisker deflection) than neurons of layer Vb and layers II-III, which are more oriented for velocity detection. During the hold phase of whisker deflection, layer IV neurons tend to show sustained discharges, whereas layer Vb (also layers II-III) neurons mainly exhibit transient responses.(ABSTRACT TRUNCATED AT 400 WORDS)
Velocity selectivity in the cat visual system. III. Contribution of temporal factors
Authors: Duysens J. , Orban G. A. , Cremieux J. , Maes H.
Published: December 2017

In 149 units from area 17 and 48 units from area 18 the responses to stationary stimulation of different durations were compared with the responses to the same stimulus (a 0.3 degrees-wide light or dark bar) moving at different velocities. The aim was to test the hypothesis that the range of effective velocities depends on the time needed for the bar to cross the receptive field. Forty-two percent of the area 17 cells and 8% of the area 18 cells responded poorly or not at all to briefly presented stationary stimulation. These cells were unable to respond at high velocities, and for these "duration-sensitive" cells the velocity characteristics are well predicted on the basis of responses to stationary stimulation of different durations. Cells that responded equally well to periods of stationary stimulation ranging from 12.5 to 3,200 ms ("duration-insensitive cells") were found to be able to respond at all equivalent velocities, but their preference for either high, low, or intermediate velocities was not reflected in differences in responsiveness to the different durations tested. Duration-sensitive cells in area 17 tended to have a receptive field near the area centralis, and 73% of them were classified as S-family cells, one third being end-stopped S-cells. In contrast only 18% of the duration-insensitive cells were of the S family, and these S-family cells were rarely end-stopped (1/12) or rarely had receptive fields within 5 degrees of the fovea (3/12). Duration-sensitive cells had very long latencies (median 285 ms) in response to a stationary flashed light bar of 1 s duration but much shorter latencies (median 91 ms) when tested with a slowly moving light bar. This difference was not seen in duration-insensitive cells (median latencies = 61 and 59 ms). The ability to respond at high velocity was contrast dependent. At a low contrast level all cells failed to respond to brief stimulation, whether moving or stationary. At high contrast levels only the duration-insensitive cells showed an increased responsivity to brief stimuli. The absence of responses in duration-sensitive cells to brief stimuli of high contrast may depend upon suppressive influences reaching these cells before the excitatory influences. We conclude that the velocity upper cutoff of most S-family cells with a central receptive field can be predicted from a knowledge of the minimum duration of stationary presentation required for their activation (median ON duration threshold, 200 ms).(ABSTRACT TRUNCATED AT 400 WORDS)
Cross-reinnervated motor units in cat muscle. II. Soleus muscle reinnervated by flexor digitorum longus motoneurons
Authors: Dum R. P. , O'Donovan M. J. , Toop J. , Tsairis P. , Pinter M. J. , Burke R. E.
Published: December 2017

The properties of whole soleus (SOL) muscles and of individual motor units were studied in cats 30-50 wk after self-reinnervation by soleus (SOL) motoneurons (SOL----SOL) or cross-reinnervation by flexor digitorum longus (FDL) motoneurons (FDL----SOL). As in the preceding paper (22), intracellular and glycogen-depletion methods were used to examine the physiological and histochemical properties of individual motor units. The results were compared with data from normal SOL motor units (8, 12). Intentionally self-reinnervated SOL muscles (SOL----SOL; n = 6) were normal in size and wet weight, and all of the five SOL----SOL motor units studied had physiological and histochemical characteristics that matched those of normal SOL units. Cross-reinnervation of SOL by FDL alpha-motoneurons (FDL----SOL; n = 7) produced muscles with wet weights and appearance essentially identical to normal SOL. However, whole-muscle twitch contraction times were much shorter (mean 60.4 ms) than those of normal (mean 136.9 ms, n = 18) or SOL----SOL muscles (mean 115.3 ms; n = 6). Despite this difference, none of the FDL----SOL muscles contained more than 7% histochemical type II muscle fibers, all of which were type IIA. Normal cat SOL muscles can contain up to 5% type IIA fibers, but none of our SOL----SOL muscles showed any type II fibers. Two FDL----SOL muscles had significant amounts of unintended self-reinnervation, permitting side-by-side comparison of FDL----SOL and SOL----SOL muscle fibers. The twitch contraction times of the two populations differed markedly, but they were histochemically indistinguishable except for the fact that SOL----SOL fibers had high neutral fat content (as do normal SOL fibers), whereas FDL----SOL showed much lower fat content. The 23 FDL----SOL muscle units studied were classified as physiological type S by criteria ("sag" test and fatigue resistance) used to identify motor-unit types in normal cat muscles. All five of the FDL----SOL units studied histochemically after glycogen depletion showed the type I histochemical profile, which is characteristic of the normal cat SOL. In marked contrast to the preceding study, cross-reinnervation of cat SOL by FDL motoneurons produced no conversion of muscle-unit properties into those associated with fast-twitch unit types, despite significant decreases in isometric twitch contraction time. The altered twitch speed was not associated with evident changes in conventional myofibrillar adenosine triphosphatase (ATPase) histochemistry.(ABSTRACT TRUNCATED AT 400 WORDS)