bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal features of afferent inhibition of thalamocortical relay cells
Authors: Janig W. , Spencer W. A. , Younkin S. G.
Published: December 2017

1. The temporal and spatial features of the afferent inhibition of thalamocortical relay (TCR) cells in the ventrobasal complex of the thalamus have been examined using paired conditioning and test air jets. 2. The response of TCR units to air jets may be divided into three parts: a) an early response of 1--6 impulses, which begins after a latency of 8--10 ms and lasts for 10--25 ms; b) a period of 70--80 ms following the early response, during which the spontaneous activity is inhibited; and c) a period of late activity, which follows the inhibitory period. 3. The inhibition of TCR units generated by an air jet lasts about 80 ms. The time course of inhibition is the same in hair units and in units activated by Pacinian corpuscles. Evidence is presented that suggests that inhibition decays at the same rate throughout the inhibitory receptive field. 4. The spatial features of inhibition demonstrated in this study are: a) that the excitatory and inhibitory receptive-field centers coincide; b) that these fields have different shape; and c) that there is a significant area in which the inhibitory receptive field surrounds the excitatory receptive field.
Segmental and descending influences on intraspinal thresholds of single C-fibers
Authors: Hentall I. D. , Fields H. L.
Published: December 2017

1. The effect was studied of various conditioning stimuli on the threshold of single C-fibers near their spinal terminals. Spikes were recorded in L6 and L7 dorsal root ganglia of cats. A stimulating electrode in the superficial dorsal horn delivered periodic pulses whose widths were adjusted automatically to near threshold for antidromic spike production. Most units were classified according to their adequate cutaneous stimuli, as C-mechanoreceptors, high-threshold mechanoreceptors, or polymodal nociceptors. 2. Orthodromic activity in all units increased their threshold for up to several minutes; the maximum and rate of decay depended on the amount of activity. This phenomenon parallels the hyperpolarizing afterpotential of C-fibers in peripheral nerve and, we suggest, is probably due to the aftereffect of impulses. 3. Cutaneous conditioning stimuli were applied for 10-20 s near the receptive fields of tested units, but without activating them. During the brushing of skin hair, all threshold changes were decreases; during pinching most changes were increases; during noxious heating the numbers of increases and decreases were similar. It will be necessary to analyze the responses of postsynaptic cells in order to know the physiological significance of these threshold changes. 4. Stimulation in the nucleus raphe magnus caused in half the units higher intraspinal thresholds. If this result is causally related to the previously reported inhibition of neuronal responses in the dorsal horn by the nucleus raphe magnus (NRM), then increased thresholds could reflect either direct presynaptic inhibition or facilitation of inhibitory connections. 5. No correlation between receptive-field classification and the response of terminals to natural cutaneous stimulation or stimulation of the NRM could be discovered. However, the terminals of all kinds of C-fibers differ from A-fibers in their reaction to noxious cutaneous and NRM stimulation, suggesting they are subject to a different system of control.
Glycogen-depletion method of intrafusal distribution of gamma-axons that increase sensitivity of spindle secondary endings
Authors: Jami L. , Lan-Couton D. , Petit J.
Published: December 2017

1. The glycogen-depletion method was used in cat tenuissimus muscles to investigate whether the action of static gamma-axons that increase the sensitivity of spindle secondary endings to muscle length is associated with a specific pattern of distribution of these axons to intrafusal muscle fibers. 2. In each experiment, a single gamma-axon acting on a secondary ending of a precisely located spindle was repetitively stimulated, and subsequently the intrafusal muscle fibers of that spindle were examined for glycogen depletion. 3. The gamma-axons whose repetitive stimulation increased the length sensitivity of secondary endings depleted all the chain fibers in one or both poles of the spindle, with the bag fibers being inconstantly involved. The gamma-axons whose stimulation did not exert this effect produced much more restricted patterns of glycogen depletion. 4. The length sensitivities of two secondary endings belonging to the same spindle were similarly affected by a single gamma-axon, whereas a gamma-axon could increase the sensitivity of a secondary ending without altering that of the primary ending of the same spindle. 5. The action exerted by single gamma-axons on secondary endings appears related to their intrafusal distribution since enhancement of the secondary endings sensitivity was observed only when all the chain fibers of at least one spindle pole were activated. 6. If several static gamma-axons supplying a given spindle are firing together, an increase in the length sensitivity of the secondary endings of that spindle can be expected since probably all chain fibers are activated.
Competition for survival among developing ciliary ganglion cells
Authors: Pilar G. , Landmesser L. , Burstein L.
Published: December 2017

1. Functionally different subgroups, each innervating a different part of the peripheral target, were defined within the ciliary population of the avian ciliary ganglion by electrical stimulation of the various ciliary nerve branches. 2. Although neurons innervating defined parts of the peripheral target consistently sent their axons through certain nerves, the technique of retrograde horseradish peroxidase (HRP) transport showed that the ganglion cell bodies were not spatially grouped but distributed throughout the ganglion, both before and after the period of naturally occurring cell death. However, such neurons tended to be clustered into groups of two or greater. 3. Ciliary and choroid populations, however, were found to be for the most spatially separate and recognizable by location and soma size before the period of cell death. Choroid cells did not project out the ciliary nerves even prior to the cell death period, confirming previous observations of selective axon outgrowth in the two populations. 4. Competition for survival was demonstrated within the ciliary population by experimentally removing approximately two-thirds of the neurons by axotomy-induced cell death at stage 32-34 just prior to the normal cell death period. This reduction in the number of competing neurons resulted in rescue of approximately 40% of the neurons that would have died, as assessed both by the number of axon profiles in the remaining intact nerve branch, as well as the number of somata that could be retrogradely labeled from this nerve. 5. It was concluded that many of the neurons that are normally removed during the cell death period are not destined to die, but can be rescued by reducing the number of neurons competing for a limited supply of some aspect of the peripheral target. Further, the postulated interaction with the target was shown to occur relatively late, just prior to the onset of cell death. 6. At the time of the peripheral interaction, the target was found to consist primarily of myoepithelial cells, which had migrated into the target region following the arrival of the ciliary axons. The target per se, therefore, cannot be involved in the selective growth of ciliary axons to the appropriate region. Well-defined synapses were rare, although many axonal endings were observed in close contact with both myoepithelial cells and the sparser differentiated muscle fibers, which increased to account for 60% of the target by the end of the cell death period. 7. Competition was also found to retard the rate of neuronal maturation because intact axons in the partially axotomized ganglion developed more rapidly than control axons, as assessed by axon diameter, conduction velocity, and degree of glial ensheathment. 8. Finally, at least some of the neurons in the partially axotomized ganglion expanded to innervate the peripheral territory of the axotomized branches, suggesting that competition between neurons is involved in the establishment of the observed peripheral innervation pattern.
Action-potential broadening and endogenously sustained bursting are substrates of command ability in a feeding neuron of Pleurobranchaea
Authors: Gillette R. , Gillette M. U. , Davis W. J.
Published: December 2017

1. The ventral white cells (VWC's) of the buccal ganglion of Pleurobranchaea, so named for their position and color, are a bilateral pair of neuron somata. Each sends a single axon out its contralateral stomatogastric nerve and has a dendritic field originating close to the soma. 2. The vwcs exhibit spontaneous episodes of prolonged depolarization (duration 1--4 min) accompanied by repetitive action-potential activity and separated by regular intervals of 3--30 min. Such prolonged burst episodes can be triggered by short pulses of depolarizing current. During the repetitive activity of the spontaneous bursts or that driven by imposed depolarization, the action potentials progressively broaden to 5--16 times their initial duration. 3. During spontaneous bursting or activity driven by imposed depolarization, the cyclic motor output of the feeding network is initiated or accelerated with a latency corresponding with the development of appreciable VWC spike broadening. When broadening of antidromic VWC spikes is suppressed by imposed hyperpolarization of the soma, the frequency of feeding cycles is significantly lower than when broadened spikes are allowed to develop. When trains of spikes are driven by depolarizing current, the motor output of the feeding network is not initiated until the VWC spikes have broadened to a repeatable "threshold" duration, regardless of the intensity of the depolarizing current. 4. The endogenous production of prolonged burst episodes, triggered by depolarizing current pulses, and progressive spike broadening can be demonstrated in the surgically isolated VWC soma. 5. The paired VWCs are strongly electrically coupled and display highly synchronous activity. They receive synaptic inputs from many previously identified interneurons of the feeding network and are thus reciprocally coupled within the network. 6. These results demonstrate that the capacity of this neuron to generate broadened action potentials during repetitive activity confers the ability to command coordinated motor-network output. The appropriate repetitive activity can be produced endogenously in the form of prolonged bursts of spikes.
Spatial localization in cats reared with strabismus
Authors: Olson C. R.
Published: December 2017

1. The capacity for judging the location of an object relative to the body (egocentric localization) was assessed in cats by measuring the landing position attained when the cat jumped toward a platform viewed from a known distance. 2. Normal cats and kittens land at center of the platform when using one eye or both. In contrast, nine animals tested immediately after tenotomy of the medial rectus muscle of one eye all landed consistently off-center when using the operated eye. The direction of the error was predictable from the assumption that the cat was unaware of the eye's deviation from its natural position. Thus, proprioceptive reafference is not capable, under these conditions, of supporting an accurate awareness of eye position. 3. After initial testing, all cats were maintained in a normal environment with both eyes open and were tested intermittently. Jumps guided by the deviated eye became accurate over a period of weeks in kittens younger than 4 mo. In contrast, behavioral adjustment in older kittens required many months. An adult cat displayed almost no adjustment over a period of 9 mo. 4. Five additional kittens were first tested several months after the onset of strabismus. These animals manifested accurate use of the operated eye from the first trial onward. Therefore, acquisition of accurate use of the deviated eye is not dependent on repeated testing. 5. Two kittens subjected to early exodeviation of one eye displayed a reduced capacity for adjustment when subjected to late exodeviation of the second eye. Thus, changes in neural function resulting from early strabismus (for instance, the loss of binocular connectivity in striate cortex) do not produce persistent behavioral flexibility. 6. In two strabismic kittens with a fully developed compensatory adjustment of monocular egocentric localization, the capacity for judging the relative location of two objects viewed simultaneously through separate eyes was assessed through use of a two-choice visual discrimination paradigm. One animal made predictable systematic errors, while the other exhibited correct judgments. Thus, it appears that a compensatory shift of retinal correspondence may occur in some strabismic kittens, but that such a change is not necessary for accurate use of the deviated eye in monocular visual guidance. 7. A number of observations are described that tend to indicate that cats reared with strabismus continue to use both the deviated and the nondeviated eye for visual guidance under binocular viewing conditions, unlike many human strabismics.
Cells of origin of medullary projections in central gray of rat mesencephalon
Authors: Sakuma Y. , Pfaff D. W.
Published: December 2017

1. Seventy-four neurons in the central gray of the mesencephalon were antidromically activated by electrical stimulation of the gigantocellular and magnocellular nuclei region of the ipsilateral medullary reticular formation in urethan-anesthetized female rats. An additional eight cells were located contralaterally. With control of the lordosis reflex (facilitated from central gray) in mind, each cell was characterized by the properties of its antidromic response and by its response to pressure stimulation of the hindquarters of the hindquarters of the animal. 2. The antidromically activated spikes had constant latencies between 1.0 and 25.5 ms, with a mean of 10.7 +/- 0.7 ms. 3. Cells of origin of the descending projections were located in all parts of the central gray and adjacent mesencephalic reticular field except within the inner ring of the central gray that surrounds the cerebral aqueduct. A particularly dense group of cells was noted in the ventrolateral aspect of the central gray. Fewer were found in the dorsal central gray over the cerebral aqueduct. 4. These cells had very low rates of spontaneous discharge or none at all. No specific changes in activity could be elicited by lordosis-relevant somatosensory stimuli. Therefore, these cells appear not to be involved in stimulus-bound reflexive control of lordosis behavior. Instead, they may be engaged in mediating influences descending from hypothalamus, known to control lordosis (see Ref. 48). In turn, they could modulate activity in reflex arcs completed at lower levels of the neuraxis.
Excitability of female rat central gray cells with medullary projections: changes produced by hypothalamic stimulation and estrogen treatment
Authors: Sakuma Y. , Pfaff D. W.
Published: December 2017

1. Effects of estrogen on the excitability of 74 neurons in the central gray of the mesencephalon (CG) antidromically identified from the medulla were investigated extracellularly in female rats under urethan anesthesia. 2. The mean rate of spontaneous discharge of the identified CG cells was higher in estrogen-treated (2.9 Hz) than in untreated ovariectomized rats (0.3 Hz). In the estrogen-treated preparations, 18.5% of the identified cells had discharge rates exceeding 3.0 Hz, while none were found in this range in the untreated animals. 3. Two types of positive-negative biphasic antidromic spike potentials were distinguished. In one ("fast") the initial positive deflection was completed within 500-700 microseconds, while it took longer than 1 ms in the other ("slow" spikes). Slow spikes had a notch in the rising phase of their initial positive deflection, at which antidromic propagation was often blocked. Mean antidromic spike latency for the fast spikes was 6.8 ms, while the value for the slow spikes was 14.7 ms. 4. In slow spikes, the percentage of successful antidromic spike invasions into the somatodendritic complex remained constant for a long time when the response was elicited by repetitive antidromic stimuli at 0.5 Hz. Antidromic propagation into the somatodendritic complex occurred more frequently in the slow spikes recorded from estrogen-treated preparations (94.2%) than in those of ovariectomized untreated animals (55.7%). 5. Electrical stimulation of the preoptic area (POA) reduced the frequency of successful antidromic propagation into the somatodendritic complex. Stimulation of the ventromedial nucleus of the hypothalamus (VMN) increased it. Conversely, electrolytic lesion of the POA facilitated, while VMN lesion reduced antidromic spike invasion. 6. Thus, excitability of some neurons in the CG is facilitated by estrogen. Similar effects of VMN stimulation and POA lesion suggest that the estrogenic effect could be mediated by these structures. The pattern of effects on these CG neurons is that required for their control of lordosis behavior, an estrogen-dependent postural reflex in female rodents. These cells may modulate medullary reticulospinal cells, which in turn govern the reflex.
A dorsal spinal neural network in cat. I. Responses to single impulses in single type I cutaneous input fibers
Authors: Tapper D. N. , Wiesenfeld Z.
Published: December 2017

1. We have studied some properties of a sacral dorsal spinal gray matter network. the lamina 4:type 1 afferent fiber network (L4:T1 network) in 24 adult cats that were anesthetized with urethan and the spinal cord transected at the thoracolumbar junction. 2. The network in the first sacral segment is composed of a subgroup of lamina 4 cells as principal neurons that are connected to type 1 afferent fibers emerging from the skin, the manipulable input channels. Other primary afferent fibers and axons of central cells of other segments may also be input elements. Cells of the substantia gelatinosa (SG) and of the marginal layer constitute the intrinsic neurons. We monitored the output of the network by unit recording of the lamina 4 cell's impulse activity. 3. We activated the network by single impulses delivered via single type 1 afferent fibers. We stimulated fibers individually by focused electrical stimulation and monitored the selectivity of the stimulus by a computer-averaging procedure. The basic stimulus paradigm (each stimulus trial) consisted of 100 single impulses delivered 1 impulse/3 s. For nine networks, each of the accessible type 1 fibers was used as an input channel. 4. The typical pattern of response to the 100 impulses was composed of: a) an early discharge lasting for 5 ms after the input impulse invades the central arbor of the type 1 fiber, b) a late discharge of variable duration terminated by c) a postresponse reduction in ongoing discharge rate. Early-only and late-only discharges were occasionally observed. We conclude that the response pattern reflects the specific neuronal and synaptic configuration that is engaged by each input channel. 5. Across input channels, the early discharge was characterized by: a) a bimodal distribution of low- and high-probability responses, reflecting two predominating groups of type 1 input channels, one believed to be weakly coupled and the other strongly coupled to the principal neuron; b) relatively little multiple discharge; c) modal response during the first 2 ms of the discharge; d) response produced via a monosynaptic connection of the type 1 fiber with the lamina 4 neuron and average synaptic delay of 0.53 +/- 0.01 ms (mean +/- SE, n = 100); e) in general, a stable response throughout the 5-min stimulus trial, although an occasional habituating response was noted. 6. The late discharge was characterized by: a) a multiple discharge and a wide response jitter; b) mean duration approximately 29 ms; c) in general, high-probability response; d) a tendency for the response to wane during the course of the stimulus trial. 7. We observed no relationship between the magnitude of the early or late response and the level of ongoing discharge when considered across input channels. However, for a given input channel over time, the output response was often highly correlated with the level of ongoing discharge. The effect was best described by a log-log relationship...
Spinal and medullary lamina I projection to nucleus submedius in medial thalamus: a possible pain center
Authors: Craig A. D. , Burton H.
Published: December 2017

1. Results obtained with the anterograde horseradish peroxidase (HRP) and autoradiographic techniques have revealed a dense and compact spinal and trigeminal projection to the dorsal portion of the nucleus submedius (Sm) in the medial thalamus of the cat. A homologous projection was observed in two cases in the monkey and in three cases in the rat with the anterograde HRP method. 2. The projection to Sm in topographically organized rostrocaudally, with trigeminal terminations located caudally and spinal terminations rostrally. The rostrocaudal extent of the trigeminal field in Sm (ca. 1 mm) is larger than that of the spinal field (ca. 0.8 mm). There is a considerable ipsilateral trigeminal projection, whereas there is a minimal uncrossed spinal projection to Sm. 3. Retrogradely labeled cells were analyzed in cases with small injections of HRP in medial thalamus in the cat. The results indicate that the projections to Sm identified in the anterograde experiments arise from lamina I cells of the spinal and medullary dorsal horm, probably exclusive of lamina V and other spinothalamic cells. The retrograde results corroborate the topographic observations made in the anterograde experiments. 4. These results suggest that Sm may be critically involved in specific nociception.
Physiological activity of newly differentiated olfactory receptor neurons correlated with morphological recovery from olfactory nerve section in the salamander
Authors: Simmons P. A. , Getchell T. V.
Published: December 2017

1. Extracellular unitary recordings were made from the olfactory epithelium of the salamander, Ambystoma tigrinum, at numerous time points following olfactory nerve section. Unitary response properties were correlated with histological examination of the same tissues. 2. At 10 days following nerve section, unitary activity was rarely recorded in all regions of the epithelium. Histological examination indicated that virtually the entire mature olfactory receptor cell population had undergone retrograde degeneration. Transneuronal degeneration was not observed in the olfactory bulb, although the olfactory nerve and glomerular layers were substantially reduced in size. 3. At subsequent times, unitary impulse activity gradually returned, consisting of both spontaneous activity and odor-evoked discharges. Anatomical recovery of the olfactory epithelium preceded that of the olfactory bulb. A positive correlation was found between neuronal differentiation in the olfactory epithelium and the recovery of receptor cell function. 4. Patterns of spontaneous activity, odor specificities, intensity-response functions, and adaptive properties studied in newly differentiated olfactory receptor neurons were indistinguishable from those observed in control units. This indicated that these properties were intrinsic to the receptor neurons. 5. Spontaneously active and responsive units were encountered prior to olfactory nerve connection with the bulb. It is concluded that receptor neurons pass through two phases of functional maturity: the first independent of bulbar contact and the second dependent on presumed synaptic contact with bulbar neurons.
Membrane potential, synaptic activity, and excitability of hindlimb motoneurons during wakefulness and sleep
Authors: Glenn L. L. , Dement W. C.
Published: December 2017

1. The membrane potential and excitability of hindlimb motoneurons was recorded in chronically implanted, restrained cats during natural sleep and wakefulness. 2. The potential of all motoneurons varied in a systematic and predictable manner during the sleep-wake cycle, suggesting that all motoneurons contributed to variations in muscle tension across the cycle. 3. Motoneuron excitability and level of polarization did not change at sleep onset. 4. During REM sleep, motoneurons had a sustained hyperpolarization, a diminished probability of antidromic and monosynaptic activation, and a reduced responsiveness to depolarizing current pulses. Motoneuron excitability is thus reduced in this phase of sleep. 5. Synaptic activity, but not necessarily synaptic noise, was higher during REM sleep. Hindlimb motoneuron hyperpolarization in REM sleep in concluded to arise from augmented asynchronous inhibitory synaptic activity distributed on the soma.
Dynamic analysis of a rhythmic neural circuit in the leech Hirudo medicinalis
Authors: Peterson E. L. , Calabrese R. L.
Published: December 2017

1. The results of perturbation experiments demonstrate the functional diversity of the interneurons (HN cells) that generate heartbeat in the medicinal leech. 2. HN cells were individually stimulated by single current pulses. The induced activity of HN cells in the first four ganglia (cell pairs HN(1)-HN(4)) reset the rhythm of the interneuron network; induced activity of those in the fifth through seventh ganglia (cell pairs HN(5)-HN(7)) did not. 3. Cells HN(1)-HN(4) can entrain every other interneuron of the network; cells HN(5)-HN(7) cannot. 4. Thus the HN interneuron network includes two distinct subsets: cells HN(1)-HN(4) form the network's timing oscillator; cells HN(5)-HN(7), driven by the timing oscillator, force one of the two coordination states on the heart motor neurons. 5. In general the dynamic behavior of the heart interneuron network was predictable given the web of identified synapses between HN cells. Nevertheless, the unexpected capacity of cells HN(3) and HN(4) to entrain the network shows that there are functional connections still to be found. Burst termination experiments suggest that cells HN(3) and HN(4) inhibit directly the more rostral HN cells. 6. The timing oscillation seems to arise from a balance between the endogenous polarization rhythms of interneurons HN(1)-HN(4) and selective reciprocal inhibition between these same cells.
Nonlinear feedback model of neuronal populations in hippocampal CAl region
Authors: Leung L. S.
Published: December 2017

1. A lumped-circuit model is proposed for the local interactions within the hippocampal CAl region. Each neuronal population is represented by a linear differential equation or a linear transfer function in the Laplace domain. Interactions between neuronal populations are represented by gain factors. Recurrent inhibition of pyramidal cells by the inhibitory interneurons is the important interaction represented by an asymmetric, bidirectionally saturating gain curve. The inputs to the model are orthodromic or antidromic inputs to the pyramidal cells and a tonic input from the brain stem. The outputs are the response ot pyramidal cells and interneurons. 2. The model is evaluated by data of intracellular and extracellular recordings from the hippocampus. Extracellular recordings consist of the average evoked potentials (AEPs), unitary poststimulus time histograms (PSTHs), and the spontaneous electroencephalogram (EEG). On account of the regular structure of the hippocampus, extracellular potentials are expected to correspond to the average intracellular potential among a local neuronal population. 3. Under deep anesthesia, all neuronal responses evoked by an electrical shock to the hippocampal afferents end in a prolonged inhibition of pyramidal cells. The model further predicts that the duration of inhibition increases with stimulus intensity, which is verified experimentally. 4. In the awake rat, especially during behaviors accompanied by a hippocampal theta rhythm (e.g., walking), the AEPs evoked by stimulation of afferent input to the CAl region were oscillatory with a frequency of 20-50 cycles/s. In the model an excitatory bias from the brain stem is assumed to linearize the local circuits, resulting in oscillatory responses similar to those obtained experimentally. 5. As observed by spectral analysis, the hippocampal EEG of the frequency 40-70 Hz varied in power and resonance during various behaviors of the rat. Except for the theta rhythm, analysis of the output(s) of the model given a Gaussian white-noise input showed similar power spectra as the EEG in vivo. The increase in power of the 40-70 Hz EEG in some behaviors, e.g., walking, is reproduced by assuming that during such behaviors a modulating bias from the brain stem linearizes the local CAl circuits. This latter circumstances underlies the generation of oscillatory AEPs and the high-frequency EEG. 6. When recurrent excitatory-inhibitory feedback is very large, the model produces a limit cycle of 50-65 cycles/s. The limit cycle is suggested to be the cause of a particular type of high-frequency (50-65 cycles/s) hippocampal afterdischarge that occurs after tetanization of the input pathways. The amplitude, frequency, and waveform of the model generated and experimental data are similar. 7. In conclusion, a nonlinear recurrent excitatory-inhibitory feedback model of the hippocampus explains and integrates various existing experimental data. The model further predicts results that can be experimentally tested.
Reversibility of Ia EPSP investigated with intracellularly iontophoresed QX-222
Authors: Flatman J. A. , Engberg I. , Lambert J. D.
Published: December 2017

1. Cat lumbosacral motoneurons were impaled by two individually advanced microelectrodes: one to record membrane potential (EM), the second to pass depolarizing currents. 2. During the passage of depolarizing current ramps the repetitive action-potential firing and the later high conductance (GM) state obscured and distorted Ia excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of hindlimb muscle afferents. 3. Intracellular iontophoresis of QX-222 (a trimethyl analogue of lignocaine) or methylxylocholine, prevented action-potential generation and reduced the GM increase during current depolarization so that positive levels of EM could be reached. 4. Following QX-222 treatment it was possible to demonstrate a reversal of the Ia EPSP including its first part, at EM values between -13 and +32 mV. Reversal was seen in 13 of the 22 motoneurons tested. 5. Reversal was easiest to obtain in motoneurons of the deep peroneal group. More positive levels of EM were needed to show a reversal in neurons of the gastrocnemius-so-leus group. (The 10-90% rise times of the EPSPs were rather similar for both groups.) 6. In a few motoneurons the initial part of the Ia EPSP reversed at a more negative EM than a later part. This was best seen after subtraction of the extracellular field potentials from the records.
Dietary choline augments blood choline and cholinergic transmission in terrestrial mollusk Limax maximus
Authors: Barry S. R. , Gelperin A.
Published: December 2017

1. A radioenzymatic assay was used to determine the concentration of choline in the hemolymph of the terrestrial mollusk Limax maximus maintained on choline-enriched and choline-deficient diets. The levels of free choline in the slug's hemolymph varied with the availability of choline in the diet. The concentration of choline in the plasma of choline-enriched animals averaged 5.5 microM while the mean circulating choline level of choline-deprived slugs was 3.3 microM. The difference in choline levels between the two groups was statistically significant. 2. Neurophysiological measurements of transmission at the isolated cholinergic synapses between the salivary burster neuron (SB) and the salivary duct muscle (SD) showed that this synapse was sensitive to fluctuations in the external choline concentration within the physiological range. Increases in exogenous choline from 0.5 to 2.0 microM, from 2.5 to 5.0 microM, and from 5.0 to 15.0 microM were followed by increases in the amplitudes of SB-elicited junction potentials recorded from the SD by a focal extracellular electrode. 3. Thus, the SB-SD synapse is sensitive to the fluctuations in exogenous choline that can occur with a change in diet.
Specificity of electrical coupling among neurons innervating forelimb muscles of the adult bullfrog
Authors: Westerfield M. , Frank E.
Published: December 2017

1. The specificity of electrical connections among sensory fibers and motoneurons in the bullfrog's spinal cord was studied by recording intracellularly from brachial motoneurons. Synaptic potentials evoked by stimulation of individual muscle nerves were recorded in normal and reduced-calcium solutions and after acute section of dorsal or ventral roots. 2. Homonymous motoneurons are electrically coupled. After the dorsal roots were cut to abolish sensory input, short-latency potentials were almost always evoked anti-dromically in a motoneuron by stimulation of its own muscle nerve but rarely by stimulation of nerves innervating other muscles. These potentials differed from chemically mediated synaptic potentials in this preparation; they had a shorter latency and remained after perfusion with reduced-calcium solutions. This evidence suggests that they are mediated electrically. 3. Some motoneurons that innervate functionally equivalent muscles are electrically coupled. Approximately two-thirds of the motoneurons innervating the internal or external heads of the triceps muscles received coupling potentials on stimulation of the other nerve, although never on stimulation of the heteronymous, medial, triceps nerve. 4. The monosynaptic potentials evoked by muscle sensory afferents in motoneurons often have both electrical and chemical components. The electrical component occurred with short delay and persisted in reduced-calcium solutions. The chemical component occurred 1.5-2.0 ms later, at 14 degrees C, and was abolished by reducing calcium in the bathing solution. Muscle sensory afferents make these mixed synapses on homonymous, heteronymous, and other motoneurons.
Electrophysiology of retinal ganglion cells in the mouse: a study of a normally pigmented mouse and a congenic hypopigmentation mutant, pearl
Authors: Balkema G. W. , Pinto L. H.
Published: December 2017

1. The organization of the receptive fields of retinal ganglion cells in te normal mouse was studied qualitatively in recordings from 43 single axons in the optic nerve and optic tract, and the light sensitivity was studied quantitatively in 26 of these cells by measuring incremental sensitivity. 2. The receptive fields of normal animals were elliptical, had concentric center and peripheral subdivisions, and had an antagonistic center/surround organization; the receptive-field centers ranged from 1.95 to 83 degrees in diameter, with a median of 7 degrees. 3. The incremental sensitivity to white light was measured using a criterion response of 10 extra spikes; the most sensitive dark-adapted cell required a stimulus luminance of 3.5 x 10(-3) cd/m2 to generate a criterion response. 4. The action spectrum measured at seven different wavelengths (433-619 nm) from ganglion cells in the normally pigmented mouse resembled the CIE (International Commission on Illumination, CIE 1957 (11)) relative scotopic luminous efficiency function (41) and is consistent with a curve having a peak around 500 nm. 5. On light adaptation with blue light (less than 460 nm), the sensitivity to longer wavelength stimuli increased by 0.2-0.5 log units relative to the sensitivity to the shorter wavelengths; these results are compatible with the presence of a photoreceptor sensitive to long wavelengths in the normally pigmented mouse (C57BL/6J+/+). 6. The organization of the receptive fields of 48 retinal ganglion cells from the hypopigmentation mutant pearl (C57BL/6J-pe) was also studied qualitatively; the receptive field organization was similar to that of the normally pigmented mouse. 7. In 25 cells from dark-adapted pearl mice, the incremental sensitivity to white light was, on the average, 1.6 log units less than that for normal mice. 8. The dark-adapted action spectrum of pearl mice was similar to that of normally pigmented mice. However, a shift in sensitivity to longer wavelengths did not occur on selective light adaptation with the most luminous blue light (less than 460 nm) background that we could produce. 9. We conclude that pearl is one of the mammalian genes that codes for functions that affect dark-adapted retinal sensitivity. The results of this study and past studies suggest that the pearl gene's action on light sensitivity is predominantly within the retina and before (distal to) the ganglion cells.
Mechanisms underlying pattern generation in lobster stomatogastric ganglion as determined by selective inactivation of identified neurons. II. Oscillatory properties of pyloric neurons
Authors: Miller J. P. , Selverston A. I.
Published: December 2017

1. The motor program controlling the rhythmic movements of the pyloric region of the lobster stomach is generated by neurons in the stomatogastric ganglion. Neurons within this "pyloric network" were tested for their ability to generate bursting pacemaker potentials (BPPs). For these experiments, each neuron to be tested was isolated from other cells within the stomatogastric ganglion by use of the dye-sensitized photoinactivation technique. All extraganglionic inputs to the stomatogastric ganglion were blocked. 2. Only one cell in the pyloric network, the anterior burster (AB) cell, continued to generate BPPs when isolated in this manner. The AB cell is also the only interganglionic interneuron in the pyloric network. 3. Two other neurons that were previously thought to be endogenous bursters, the pyloric dilator (PD) cells, fired tonically when isolated from synaptic input. However, tonic stimulation of the stomatogastric nerve elicited BPP generation in the PD cells. These membrane-potential oscillations were generated for periods of up to a minute following cessation of the stimulus. 4. Stimulation of the stomatogastric nerve also elicited BPP generation in two other pyloric cell types: the ventricular dilator (VD) and lateral pyloric (LP) cells. 5. A reduced subset of the pyloric network was obtained by photoinactivation of several cells, including the spontaneously oscillatory AB interneuron. When inputs to this reduced network were blocked, all pattern generation ceased. A short stimulus to the stomatogastric nerve induced an episode of coordinated patterned activity from these cells. Thus, BPP production contributes to the production and stability of the pyloric motor program.
Responses of isolated Golgi tendon organs of cat to sinusoidal stretch
Authors: Wilkinson R. S. , Fukami Y.
Published: December 2017

1. Receptor potential and tension have been recorded from isolated Golgi tendon organs in response to sinusoidal stretch. Responses depended on amplitude and frequency of stretch and on the initial (resting) tension of the preparation. 2. Both tension and receptor potential behaved as power functions of stretch amplitude over most of the range corresponding to physiological tendon strains. However, for very small stretch amplitudes (less than 8 microns), a more linear response was seen. Those characteristics of responses that depended on stretch amplitude behaved similarly at all frequencies examined. 3. Frequency dependence of tension was slight. Its character, a gradual monotonic increase in response with increasing stretch frequency and a constant phase lead of a few degrees, did not change over the examined frequency range from 0.12 to 80 Hz. In contrast, receptor potential displayed a marked frequency dependence, increasing rapidly with increasing frequency of stretch in the range from approximately 1 to 20 Hz, then slowly declining as frequency was further increased. 4. Changes in initial tension of the preparation produced marked parallel changes in the amplitude dependence of tension and receptor potential. Frequency response was not significantly affected. 5. By comparing tension and receptor potential responses, the relative contributions of mechanical and electrical properties of the receptor to the sensory transduction process was examined. The present results suggest that in tendon organs the observed nonlinear dependence on amplitude of stretch originates primarily in the mechanical stage of transduction. Dynamic sensitivity, however, seems largely attributable to ionic processes within the sensory terminal membranes.
Role of proprioceptive reflexes in control of feeding muscles of Aplysia
Authors: Jahan-Parwar B. , Wilson A. H. , Fredman S. M.
Published: December 2017

Stretching the muscles of the buccal mass of Aplysia evoked proprioceptive reflexes. These consisted of a direct reflex in which the stretched muscle contracted and a crossed reflex in which the contralateral homolog of the stretched muscle contracted as well. Both reflexes were accompanied by corresponding changes in neural activity in the buccal nerves. The muscle contraction and efferent neural activity were abolished by blocking synaptic transmission in the buccal ganglia. Blocking neuromuscular transmission blocked the contractions but not the stretch-induced afferent neural activity. Proprioceptive responses were obtained from isolated buccal nerve-muscle preparations. Both tonic on- and on-off responses were observed. These responses persisted after blocking synaptic transmission at the muscle, indicating that they were due to afferent fibers rather than peripheral interneurons. Proprioceptive neurons with centrally located cell bodies were found. These included previously identified neurons B4 and B5 as well as small cells. Proprioceptive neurons responded to muscle stretch with peripherally initiated axonal spikes that conducted into the central nervous system (CNS) and preceded their somatic spikes. These responses persisted after blocking synaptic transmission in the CNS. Several motor neurons were found. When intracellularly stimulated, these evoked contractions of their target muscle even after blocking synaptic transmission in the CNS. The motor neurons responded synaptically to stretching the ipsilateral muscle. Some responded to stretching of the contralateral homologous muscle as well. The motor neurons differed in their axonal projections, with some projecting only ipsilaterally, others bilaterally. The majority of motor neurons were inhibited by muscle stretch due to inhibitory monosynaptic input from the proprioceptive cells B4 and B5. The stretch reflex occurred when the motor neurons fired due to postinhibitory rebound. The synaptic organization of the reflex was considered.
Response to sudden torques about ankle in man: V effects of peripheral ischemia
Authors: Gottlieb G. L. , Agarwal G. C. , Jaeger R. J.
Published: December 2017

Sudden dorsiflexions and plantar flexions of the foot were imposed by a torque motor while blood flow to the lower leg was occluded by a sphygmomanometer cuff. Seated subjects were instructed to resist the torques and restore the foot to its original position as rapidly as possible. Measurements of the first two electromyographic (EMG) responses were made in the soleus (SOL) and anterior tibial (TA) muscles. These are the myotatic reflex at about 40 ms and the postmyotatic response at about 120 ms. In the anterior tibial muscle, the myotatic component often occurs at 60- to 90-ms latency and is continuous with the postmyotatic component. After about 20 min of ischemia, there is a rapid and eventually complete loss of the myotatic component of the response in the stretched muscle. Concurrent with the loss of the myotatic reflex there is usually a reduction of the postmyotatic component. The latency of postmyotatic component remains unchanged, even after the myotatic reflex is abolished. Voluntary restoration of the foot to its original position in opposition to the motor torque is delayed and slowed by the time that the myotatic reflex has vanished. By measuring electromyographic responses to visually triggered reactions, we demonstrate that the reduction of the postmyotatic response is not due to failure of the efferent pathway. On this basis we discuss the possible contributions made by myotatic mechanisms to the tasks of load compensation and maintenance of muscle tone. Hoffmann reflexes were evoked in similar experiments with stimulation of the posterior tibial nerve at the popliteal fossa, distal to the cuff. The maximal direct motor response and muscle twitch are unaffected by loss of the H-reflex. Myotatic and Hoffmann reflexes were both evoked with torque perturbations and with a stimulating electrode proximal to a below-the-knee cuff. In this case, the myotatic reflex failed while the maximal H-reflex was slightly facilitated. The loss of the myotatic reflex was accompanied by a modest reduction in the direct motor response to electrical stimulation and a somewhat greater reduction in the postmyotatic response to torque perturbation. The data are interpreted to support a dual role for the primary afferent pathway in the control of voluntary movements. It provides the fastest path for the activation of a stretched muscle to initiate a load-compensating contraction. It also provides a form of servo assistance in modulating descending control signals. The degree of this assistance is estimated. In this simple experimental paradigm, functional contributions of the reflex arc are demonstrated.