bluuebunny/crossref_metadata_2025 huggingface dataset:
Ligand-gated currents of alpha and beta ganglion cells in the cat retinal slice
Authors: Cohen E. D. , Zhou Z. J. , Fain G. L.
Published: December 2017

1. We studied the receptor pharmacology of the ligand-gated currents of ON- and OFF- alpha and beta ganglion cells in a cat retinal slice preparation using the whole cell recording variation of the patch-clamp technique. Cat retinal slices were cut in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffer and incubated in a bicarbonate-buffered solution. Ganglion cells were voltage clamped at -70 mV in HEPES-buffered Ringer solution. The pipette solution contained a low concentration of Cl- to distinguish mixed cationic from Cl(-)-mediated conductances, and Lucifer yellow (0.5%) was included for identification of the cell type. 2. In Ringer solution containing 1.2 mM Mg2+, current-voltage (I-V) curves of responses to the excitatory amino acid agonist (EAA) N-methyl-D-aspartate (NMDA) (200 microM) revealed a J-shaped function. In Mg(2+)-free Ringer solution containing 200 microM Cd2+ to block synaptic transmission, NMDA (200 microM) elicited an inward current 5-8 times larger at -70 mV. In both conditions I-V curves of the NMDA-induced currents reversed near 0 mV. These results suggest that there are NMDA EAA receptors present directly on the dendrites of alpha and beta ganglion cells. Responses to NMDA were blocked by +/- 2-amino-7-phosphonoheptanoic acid (AP7) (200 microM). 3. In Ringer solution containing 200-1,000 microM Cd2+ to block synaptic transmission, both ON- and OFF- alpha and beta cells responded to kainic acid (10-50 microM), alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) (20-70 microM), and quisqualic acid (0.1-30 microM) with inward currents that reversed near 0 mV. These responses were blocked by the quinoxaline EAA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 microM). The metabotropic agonists 1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) (25 microM) and L-2-amino-4-phosphonobutyric acid (L-APB) (50 microM) and L-2-amino-4-phosphonobutyric acid (L-APB) (50 microM) in the presence of Cd2+ evoked little or no response for all cells tested. 4. In the presence of Cd2+, alpha and beta cells responded to gamma-amino-butyric acid (GABA) (200 microM) and glycine (200 microM) with inward currents that reversed near -35 mV, the calculated chloride equilibrium potential Ecl. Responses to GABA and glycine were both strongly desensitizing. (+)Bicuculline methyl chloride (20 microM) blocked an average of 90% of the inward current evoked by 200 microM GABA on all ganglion cell types.(ABSTRACT TRUNCATED AT 400 WORDS)
Dynamics of propagating waves in the olfactory network of a terrestrial mollusk: an electrical and optical study
Authors: Kleinfeld D. , Delaney K. R. , Fee M. S. , Flores J. A. , Tank D. W. , Gelperin A.
Published: December 2017

1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives ipsilateral axonal projections from superior and inferior noses. This network exhibits an approximately 0.7-Hz intrinsic oscillation in its local field potential (LFP). 2. Intracellular recordings show that the lobe contains at least two classes of neurons with activity phase locked to the oscillation. Neurons in one class produce periodic bursts of spikes, followed by a period of hyperpolarization and subsequently a depolarizing afterpotential. There is a small but significant chance for a second burst to occur during the depolarizing afterpotential; this leads to a double event in the LFP. Bursting neurons constitute approximately 10% of the neurons in the lobe. 3. Neurons in the other class fire infrequently and do not produce periodic bursts of action potentials. However, they receive strong, periodic inhibitory input during every event in the LFP. These nonbursting cells constitute the major fraction of neurons in the lobe. There is a clear correlation between the periodic burst of action potentials in the bursting neurons and the hyperpolarization seen in nonbursting neurons. 4. Optical techniques are used to image the spatially averaged transmembrane potentials in preparations stained with voltage-sensitive dyes. The results of simultaneous optical and electrical measurements show that the major part of the optical signal can be interpreted as a superposition of the intracellular signals arising from the bursting and nonbursting neurons. 5. Successive images of the entire PC lobe show waves of electrical activity that span the width of the lobe and travel its full length along a longitudinal axis. The direction of propagation in the unperturbed lobe is always from the distal to the proximal end. The wavelength varies between preparations but is on the order of the length of the preparation. 6. One-dimensional images along the longitudinal axis of the lobe are used to construct a space-time map of the optical activity, from which we calculate the absolute contribution of bursting and nonbursting neurons to the optical signal. The contribution of the intracellular signals from the two cell types appears to vary systematically across the lobe; bursting cells dominate at middle and proximal locations, and nonbursting cells dominate at distal locations. 7. The direction and form of the waves can be perturbed either by microsurgical manipulation of the preparation or by chemical modulation of its synaptic and neuronal properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Neurokinin 1 and 2 antagonists attenuate the responses and NK1 antagonists prevent the sensitization of primate spinothalamic tract neurons after intradermal capsaicin
Authors: Dougherty P. M. , Palecek J. , Paleckova V. , Willis W. D.
Published: December 2017

1. Activation of neurokinin receptors contributes to the excitation of many dorsal horn neurons by cutaneous sensory stimuli, particularly noxious stimuli. In the present study we investigate the role of neurokinin receptors in the activation of primate spinothalamic tract (STT) neurons by cutaneous mechanical stimuli and by intradermal injection of capsaicin. This was done by testing the responses of these neurons to a battery of cutaneous stimuli before and during infusion by microdialysis of antagonists selective for NK1 and NK2 receptors. 2. The NK1 receptor antagonists cis-3-(2-methoxybenzyl-amino-2-benzhydrylquinuclidine (CP96345) and D-Pro9-[Spiro-y-lactam]-Leu10,Trp11)-Physalaemin(1-11) (GR82334) did not significantly reduce the responses of STT cells to mechanical stimulation of the skin. Both NK1 antagonists did, however, produce a significant reduction in the responses of STT neurons to an intradermal injection of capsaicin. Finally, despite having no effects on responses to mechanical stimuli, both NK1 antagonists prevented the sensitization of the responses to cutaneous stimuli that is usually observed after intradermal injections of capsaicin. 3. The NK2 selective antagonists PhCO-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (GR98400) and [Tyr5,D-Trp6,8,9,Lys10]-NKA (4–10) (MEN10376) had effects very similar to those of the NK1 antagonists, but with an important difference. Neither NK2 antagonist affected the responses of STT neurons to noxious or innocuous mechanical stimulation of the skin, but they did reduce the responses to intradermal capsaicin injections. These compounds failed to prevent capsaicin-induced sensitization. In fact, cells exposed to GR98400 or MEN10376 showed unusually sustained increases in the responses to mechanical stimuli after the first capsaicin injection, suggesting that these compounds actually induced sensitization. 4. These results support the contention that both neurokinin receptors participate in the processing of nociceptive information in the dorsal horn, especially responses to strong stimuli such as intradermal injection of capsaicin. NK1 receptors are also involved in the sensitization of STT neurons after peripheral injury. A clearer understanding of the role of NK2 receptors in sensitization requires further studies with improved antagonists.
Independent control of limb position and contact forces in cat posture
Authors: Lacquaniti F. , Maioli C.
Published: December 2017

1. It has previously been demonstrated that a set of geometric and kinetic parameters are invariant in cats standing at their preferred interfoot distance and weight distribution. Thus the length and the angle of orientation relative to the vertical of each limb axis remain approximately constant when the supporting platform is tilted in the sagittal plane. The direction of the tangential contact forces is similarly constrained in response to horizontal translations. The main aim of the present study is to assess whether or not the control of limb position is independent of the control of the contact forces at the feet. To this end we have examined cat posture under a number of different conditions expressly designed to increase the range of postural variability. We considered that if the specification of limb position is a mere byproduct of the neural control of contact forces (or vice versa), geometric and kinetic parameters would covary interdependently. If instead limb position and contact forces are controlled in parallel and independently of each other, they will tend to follow different laws of variation. 2. Limb position and contact forces were measured in intact cats standing freely on a support platform. In a first series of experiments the pitch angle of the platform was randomly changed, as were the interfoot distance and head orientation. In another series of experiments cats were tilted in the presence of an external load tending to shift the weight distribution. The same load was applied in two different manners: 1) it made contact with a very limited surface of the body, and 2) it was attached by means of a long vest that made contact with most of the trunk and produced abnormal somesthesic cues to the body. 3. The range of different experimental conditions resulted in substantial trial-to-trial variations of the length and orientation of the axis of the limbs, as well as variations of the magnitude and orientation of the net contact forces. We found that the changes of the orientation of the contact force vector are uncorrelated with the corresponding changes of limb orientation, thus providing a first line of evidence in favor of the existence of a separate neural control of geometric and kinetic parameters. 4. Another line of evidence is provided by the specific form of the laws of variation of geometric parameters and tangential forces in different animals. Under normal (unloaded) conditions the values of the limb joint angles tend to covary linearly.(ABSTRACT TRUNCATED AT 400 WORDS)
The synaptic activation of N-methyl-D-aspartate receptors in the rat medial vestibular nucleus
Authors: Kinney G. A. , Peterson B. W. , Slater N. T.
Published: December 2017

1. We examined the synaptic activation of N-methyl-D-aspartate (NMDA) receptors by stimulation of primary vestibular afferent projections to second-order neurons in the medial vestibular nucleus (MVN) using whole cell patch-clamp recording methods in rat brain stem slices maintained in vitro. 2. Stimulation of the vestibular nerve (nVIII) evoked monosynaptic excitatory postsynaptic potentials (EPSPs) in second-order MVN neurons. Bath application of the gamma-aminobutyric acid receptor antagonist bicuculline (10 microM) revealed a late, slow EPSP that was blocked by the NMDA receptor antagonist D-2-amino-5-phosphonovalerate (D-AP5; 50 microM) and displayed a voltage-dependent reduction at hyperpolarized potentials in the presence of external magnesium (1 mM). The early component of the nVIII-evoked EPSP in the presence of bicuculline was blocked by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 microM) and displayed linear current-voltage relations in the presence of external magnesium. 3. In some cells both components of the EPSP were blocked by DNQX, whereas only the late component was sensitive to D-AP5, indicating that NMDA receptors also mediate excitation via intrinsic pathways within MVN. 4. The NMDA receptor-mediated excitatory postsynaptic current (EPSC) evoked by nVIII stimulation was recorded in voltage-clamped MVN neurons in a magnesium-free saline containing bicuculline (10 microM) and DNQX (10 microM). At -80 mV the NMDA receptor-mediated EPSC (latency = 2.7 ms) displayed a slow rise time (10–90%, 5.8 ms) and exhibited a biexponential decay [time constant of fast component of decay (tau s) = 27.6 ms, time constant of slow component of decay (tau s) = 147.4 ms].(ABSTRACT TRUNCATED AT 250 WORDS)
The learning of novel finger movement sequences
Authors: Gordon A. M. , Casabona A. , Soechting J. F.
Published: December 2017

1. Experienced typists typed phrases containing words in which one isolated letter was typed with one hand, while the remaining letters were typed with the contralateral hand. 2. The translational and rotational motion of the fingers and wrist of the right hand were obtained optoelectronically from the location of reflective markers placed on the fingers. 3. Midway through the experiment, the key corresponding to the isolated letter was physically switched with another key on the keyboard, and subjects typed the letter in its new location (for 140 trials). The letter “n,” typed with the right index finger, was either switched with letters normally typed with the same finger (u), with a different finger but same hand (o), with the same finger of the left hand (v), or with a different finger of the left hand (w). 4. When the words were typed normally, the interkey intervals were relatively short, and the onset of movement of the right hand began before the preceding keypress with the left hand. Thus the movement of the two hands overlapped. Furthermore, the movement to the isolated key was highly stereotypical, with little trial-to-trial variability. 5. After the transposition of keys, there were prolongations in the interkey intervals, with the largest delay occurring directly before the typing of the transposed key. Switches between homologous fingers (involving mirror movements) delayed the onset of keypresses to a lesser extent than did other switches. With practice, these delays were reduced but never reached the control level. 6. After the keyswitch, the onset of movement to the isolated key did not occur on average until after the last keypress with the contralateral hand, except when the switch involved the use of homologous fingers. In the latter case, overlapping movement of the two hands was maintained. Thus the learning of a series of discrete movements does not necessarily require that each movement segment be performed sequentially. 7. After the transposition of keys, the movement pattern and time course to a given key were similar to the movement patterns for that key observed during control trials in all conditions. Thus the learning of a series of movements may involve the use of previously learned movements under new conditions. 8. The results suggest that typing movements may be organized at several levels, including the individual keystroke and word level.
Interactions between the eye and hand motor systems: disruptions due to cerebellar dysfunction
Authors: van Donkelaar P. , Lee R. G.
Published: December 2017

1. We tested the hypothesis that interactions occur between eye and hand movements produced in conjunction. This was accomplished by having human subjects with cerebellar dysfunction and age-matched controls perform two tasks: 1) tracking a moving target with the hand and 2) performing a pointing movement to intercept the target. Our prediction was that the inaccuracies that are characteristic of eye and hand movements generated in isolation by cerebellar subjects would be accentuated in each system during combined eye-hand tasks. 2. The cerebellar subjects took longer to respond to the onset of target motion in both tasks. This was true for both the eyes and hand, regardless of whether the eye and hand movements were generated in isolation or in conjunction with each other. 3. The cerebellar subjects also displayed a larger degree of error and/or variability in their hand movements than the control subjects. A significant amount of this increased variability was due to systematic changes in the trajectory of the hand during the critical periods leading up to and after each ocular saccade. These systematic changes were consistent with an overestimation of target velocity in the perifoveal visual field. 4. The increased variability of the cerebellar subjects' hand movements was markedly reduced by restricting eye movements. A similar reduction in variability occurred when vision of the hand was restricted in the tracking task. This effect was accompanied by improved eye movements. 5. For both sets of subjects the eye movements were affected by the hand movements produced in the tracking task. In particular, eye movement accuracy was improved in the controls and degraded in the cerebellar subjects when compared with the eye movements generated in isolation. In contrast, no changes were observed in the interception task. 6. Taken together, these results imply that a reciprocal interaction occurs between the eye and hand motor systems and/or that common “upstream” sites influence each of these systems in a similar manner. The functional anatomy and neurophysiological characteristics of several sites where such interactions may take place are discussed.
Encoding of amplitude and rate of forces applied to the teeth by human periodontal mechanoreceptive afferents
Authors: Trulsson M. , Johansson R. S.
Published: December 2017

1. The encoding of force amplitude and force rate by human periodontal mechanoreceptive afferents was studied. Recordings were obtained from 19 single periodontal afferents in the inferior alveolar nerve with the use of tungsten microelectrodes. Loads consisting of a force increase (loading ramp), a phase of maintained force (static phase), and a force decrease (unloading ramp) were applied to the receptor bearing tooth, which was most often an incisor. The static forces applied ranged between 0.05 and 5 N, and the rate of force applied during the loading ramps ranged between 0.4 and 70 N/s. The forces were primarily applied in one of six directions (lingual, labial, mesial, distal, upward, or downward) that evoked the greatest discharge activity. 2. For each force application, the steady-state response was defined as the mean discharge rate during a 1-s period starting 0.5 s after the end of the loading ramp. Most afferents (15/19) exhibited a “hyperbolic” (viz., negatively accelerating) relationship between the amplitude of the stimulation force and the steady-state response, featuring a pronounced saturation tendency: the highest sensitivity to changes in static force was observed at force levels below 1 N. At higher force levels the sensitivity gradually diminished. Moreover, the dynamic sensitivity similarly decreased with increasing amplitude of static background force. For a subsample of afferents studied, comparable stimulus-response relationships were obtained in directions other than the most responsive one, but the discharge rates were lower. 3. In contrast to the response of most afferents, four (4/19) differed in that they consistently exhibited a nearly linear relationship between force amplitude and the steady-state response. Moreover, these afferents maintained their dynamic sensitivity as the amplitude of the background force was increased. 4. The steady-state response of all afferents was well described as a constant times F/ (F + c), where F represents the steady-state force, and c the force generating one-half the estimated maximum discharge rate that could be evoked by steady-state force stimulation. The c-parameter was on average 0.42 N (range 0.05–1.1 N) for the afferents exhibiting hyperbolic stimulus-response relationships. In contrast it ranged between 5 and 22 N for those exhibiting “nearly linear” relationships. A hypothetical model of the mechanics of the periodontal ligament supporting the F/(F + c) transform is proposed. 5. A general transfer function was developed to predict the instantaneous discharge rate of an individual afferent to arbitrary force profiles applied to the receptor bearing tooth.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of a muscarinic current that regulates excitability of an identified insect motoneuron
Authors: Trimmer B. A.
Published: December 2017

1. Application of the muscarinic agonist oxotremorine-M (oxo-M) to isolated abdominal ganglia of larval Manduca sexta excited an identified proleg retractor motoneuron called PPR. This excitation consisted of a persistent depolarization and an increased tendency to generate action potentials. Previous work has established that the action of oxo-M is probably mediated by muscarinic acetylcholine receptors (mAChRs) on PPR and that oxo-M mimics an afferent-induced long-lasting depolarization called the slow excitatory postsynaptic potential (sEPSP). 2. Action potentials in the ganglion could be blocked by applying tetrodotoxin (TTX) in the bath saline. Under these conditions all excitatory postsynaptic potentials in PPR were also blocked, but the depolarizing action of oxo-M was unaffected. In the absence of background activity PPR could be voltage clamped using a single-electrode switching clamp to study the currents underlying the response to oxo-M. 3. At a membrane potential of -50 mV, application of oxo-M to the ganglion in the bath saline (3-6 x 10(-7) M) or by brief (20–40 ms) pulses from a micropipette into the neuropil (1 x 10(-5) M) evoked an apparently inward current called Iox. The mean peak current change in response to pulses was -0.80 +/- 0.04 nA (n = 48 preparations). 4. The voltage dependence of Iox was determined by subtracting the current-voltage relationship for PPR in control saline from that during a response to oxo-M. Iox was maximal near the resting potential of PPR (-45 to -40 mV), decreasing slightly with hyperpolarization and strongly with depolarization. 5. Peak Iox was directly dependent on the bath Na+ concentration. Complete replacement of Na+ with N-methyl-D-glucamine in the saline blocked Iox. Changes in the bath K+ concentration (extracellular K+ concentration, [K+]o) had only a small effect on Iox. Reducing [Cl-]o from 140 to 74.5 mM had no significant effect on Iox during a 15-min exposure. Intracellular injections of Cl- from a KCl-containing electrode also had no measurable effect on Iox. 6. Changes in the bath Ca2+ concentration above or below 2 mM inhibited Iox. Furthermore, the divalent cations Ni2+, Co2+, Mg2+, and Ba2+ at millimolar concentrations and the Ca2+ channel blocking agents nifedipine and Cd2+ at micromolar concentrations inhibited Iox. 7. These results suggest that mAChRs on PPR activate an inward current that is persistent, TTX insensitive, voltage dependent and carried predominantly by Na+. However, the results cannot eliminate the possibility that changes in K+ or Cl- conductances might also be involved.(ABSTRACT TRUNCATED AT 400 WORDS)
Cross-correlation analysis of cuneothalamic interactions in the rat somatosensory system: influence of receptive field topography and comparisons with thalamocortical interactions
Authors: Alloway K. D. , Wallace M. B. , Johnson M. J.
Published: December 2017

1. We simultaneously recorded neuronal responses to cutaneous stimulation from matched somatotopic representations in the nucleus cuneatus and ventrobasal complex of intact, halothane-anesthetized rats. A total of 95 cuneate and 86 thalamic neurons representing hairy skin on the forelimb were activated by hair movements produced by air jets at multiple skin sites. Mean responsiveness was higher among neurons in nucleus cuneatus (34.4 spikes per stimulus) than in thalamus (23.7 spikes per stimulus), a result that was consistent with the greater proportion of “sustained” responses recorded in nucleus cuneatus (80%) than in the thalamus (62%). 2. Cross-correlation analysis of 166 pairs of cuneate and thalamic neurons showed that 56 neuron pairs displayed time-locked correlations in activity that were characterized primarily by excitatory interactions (44 pairs) or a combination of excitatory and inhibitory interactions (10 pairs). Unilateral interactions in the cuneothalamic direction (31 pairs) and reverse direction (11 pairs) were observed, as well as multiphasic interactions in both directions (14 pairs). Most excitatory interactions involved intervals of 1–7 ms between successive cuneate and thalamic discharges, whereas most inhibitory influences involved intervals > 7 ms. Connection strength, defined by the ratio of time-linked interactions to the number of cuneate discharges, varied widely among neuron pairs but was largest for interactions involving interspike intervals of < or = 15 ms. 3. The relationship between connection strength and receptive field topography was analyzed in 103 cuneate-thalamic neuron pairs. The region of skin shared by both neurons varied substantially among neuron pairs and the probability of detecting interactions increased proportionately with larger amounts of receptive field overlap. Neuron pairs with moderate (25–50%) amounts of receptive field overlap had connection strengths 3–4 times greater than neuron pairs with minimal (0–25%) overlap. Connection strength was essentially identical, however, for neuron pairs with moderate or large (> 50%) amounts of overlap. 4. Cuneate-thalamic neuron pairs displaying functional connections were usually tested at multiple peripheral sites, but only 37% (18 of 49) of these neuron pairs displayed interactions at more than one stimulation site. Stimulation at different sites altered the timing of interactions in seven neuron pairs, including three that showed timing shifts across time zero in the cross-correlation histogram. In neuron pairs displaying interactions at multiple sites, connection strengths for 67% of the cases were strongest when stimulation was delivered within the region of receptive field overlap.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of neck posture on the activation of feline neck muscles during voluntary head turns
Authors: Thomson D. B. , Loeb G. E. , Richmond F. J.
Published: December 2017

1. To determine whether neck posture affects the usage of neck muscles during a specific motor task, we recorded the electromyographic (EMG) patterns of neck muscles in four cats, which made horizontal, head-turning movements to fixate eccentrically placed targets. In some trials, the cervical column was oriented vertically whereas in other trials, the cervical column was oriented more horizontally. 2. During horizontal head movements, five muscles (obliquus capitis inferior, splenius, levator scapulae, complexus, and biventer cervicis) displayed activation patterns that were consistent from cat to cat and did not change when the cats adopted a different neck posture. Most of these muscles are large, superficial muscles that attach to the skull and span many cervical joints. 3. Posturally dependent patterns of activation were observed in five other neck muscles (semispinalis cervicis, longissimus capitis, levator scapulae ventralis, scalenus anterior, and obliquus capitis superior). Most of these muscles lie deeper and more laterally within the neck musculature and generally span fewer cervical joints than the muscles that displayed invariant patterns of activation. 4. These results suggest that the set of invariantly activated muscles may compose part of a basic motor program that is triggered during head movements in the horizontal plane. This motor program appears to be modified by the selective activation of ancillary muscles, which are recruited in a manner related to the neck posture. The deep positioning of the ancillary muscles may permit them to regulate the mobility of the cervical column and to adjust the net muscular force applied across the neck to the skull. Organizing the motor output in this manner might simplify the task of computing the appropriate patterns of neck-muscle activation.
Synchronization properties of spindle oscillations in a thalamic reticular nucleus model
Authors: Golomb D. , Wang X. -J. , Rinzel J.
Published: December 2017

Pages 1109–1126: D. Golomb, X.-J. Wang, and J. Rinzel. “Synchronization properties of spindle oscillations in a thalamic reticular nucleus model.” The following errors were inadvertently introduced when this article was printed. Page 1125, in the list of references, all the journal titles written as Physiol. Rev. should be Phys. Rev., and all the journal titles written as Physiol. Rev. Lett. should be Phys. Rev. Lett.
Motor cortical activity during voluntary gait modifications in the cat. II. Cells related to the hindlimbs
Authors: Widajewicz W. , Kably B. , Drew T.
Published: December 2017

1. To determine whether the motor cortex is involved in the modification of the hindlimb trajectory during voluntary adjustments of the locomotor cycle, we recorded the discharge patterns of 72 identified pyramidal tract neurons (PTNs) within the hindlimb region of pericruciate area 4 during a task in which cats stepped over obstacles attached to a moving treadmill belt. Data were also recorded from representative flexor and extensor muscles of the fore- and hindlimbs contralateral to the recording site. 2. To step over the obstacles, the cats increased flexion sequentially at the knee, ankle, and then the hip to bring the leg above and over the obstacle. This flexion movement was followed by a strong extension of the whole limb that repositioned the foot on the treadmill belt. These changes in limb trajectory were associated with large changes in the level of the activity of many flexor and extensor muscles of the hindlimb, and especially of the knee flexor, semitendinosus. On the basis of the time of onset of the knee and ankle extensor muscles in those steps when the limb was the first to be brought over the obstacle, the swing phase of the modified step cycle was subdivided into two parts, Phase I and Phase II, which correspond respectively to the flexion of the limb (F) and the initial extension (E1). 3. The temporal sequence of the movement was the same whether the hindlimb was the first (lead) or second (trail) to step over the obstacle, although the relative time between flexion at the three joints was changed in the two conditions. 4. Seventy-two PTNs were recorded from the posterior bank of the cruciate sulcus during the voluntary gait modifications. Sixty-three (63/72) of these PTNs had receptive fields that were confined to the contralateral hindlimb, or were recorded from penetrations in which such cells were found. Nine (9/72) PTNs had receptive fields on both the contralateral fore- and hindlimbs. Microstimulation applied through the recording electrode evoked, in all cases, brief twitch responses only in contralateral hindlimb musculature. 5. Forty-two (42/63) of those PTNs with receptive fields confined to the hindlimb showed a significant increase in their discharge frequency when the limb contralateral to the recording site was the first to step over the obstacle (lead limb). Twenty-nine PTNs (29/63) discharged maximally during the swing phase (18 in Phase I and 11 in Phase II), including two PTNS that also increased their discharge frequency during stance.(ABSTRACT TRUNCATED AT 400 WORDS)
Global synchronous response to autogenous song in zebra finch HVc
Authors: Sutter M. L. , Margoliash D.
Published: December 2017

1. The spatial distribution of neuronal responses to autogenous song (AS) was investigated in the HVc of urethan-anesthetized adult male zebra finches (Taeniopygia guttata). In seven birds, penetrations covered the entire mediolateral, rostrocaudal, or dorsoventral extents of HVc. In an eighth, control birth penetrations were made near to but outside of HVc. Reconstruction of recording sites from histological material indicated a good correspondence between sites that exhibited stronger responses to AS than to tone or noise bursts, and sites that were within HVc. 2. Within each experimental bird but not in the control, multiple-unit responses to AS were similar across the entire spatial extent of HVc (up to 1.3 mm). For each experimental bird, the strongest responses occurred within a narrow range of times. The middle of this range of times is called the time of maximum synchronization (TMS). Across birds, 34–75% of recording sites exhibited the same TMS. With the use of a criterion of > 33% of sites exhibiting their strongest responses at the TMS, the temporal scatter around the TMS varied between 6 and 138 ms across individuals. In six of the seven experimental birds, the position of the TMS was not affected by changing the window of integration from 10 to 150 ms. In two experimental birds, short windows of integration tended to emphasize beginning portions of the song. In one case this effect was sufficiently strong to change the TMS for short windows of integration. 3. Each TMS was associated with a syllable of maximum synchronization (SMS). The positions of the SMS varied considerably across birds. In four birds the SMS was one of the syllables of the first motif (a motif is a temporal sequence of syllables that can be repeated > or = 1 times to form a song), in two birds the SMS was the introductory note of song, and in one bird the SMS was the second syllable of the last (3rd) motif. Syllables of the same type as the SMS but occurring in other motifs typically elicited much weaker responses, in many cases weaker than other syllables in those motifs. Syllables that elicited strong responses in non-SMS motifs did not necessarily elicit strong responses in the SMS motif, even if they preceded the SMS. There were no apparent acoustical features of the SMS or the preceding syllable that could account for the global synchronous response to song.(ABSTRACT TRUNCATED AT 400 WORDS)
FRF peptides in the ARC neuromuscular system of Aplysia: purification and physiological actions
Authors: Cropper E. C. , Brezina V. , Vilim F. S. , Harish O. , Price D. A. , Rosen S. , Kupfermann I. , Weiss K. R.
Published: December 2017

1. One preparation that has proven to be advantageous for the study of neuromuscular modulation is the accessory radula closer (ARC) muscle of Aplysia californica and its motor neurons B15 and B16. In this study three members of a new peptide family have been purified from this well-characterized preparation. Because these peptides terminate in Phe-Arg-Phe-amide, we have named them FRFA, FRFB, and FRFC. The FRFs are thus RFamide peptides and are related to the widely studied neuropeptide FMRFamide. 2. The FRFs are present in the ARC motor neuron B15 in small quantities. 3. When they are exogenously applied, the FRFs decrease the size of ARC muscle contractions elicited by stimulation of either motor neuron B15 or B16. They appear to do this by a combination of presynaptic and postsynaptic actions. 4. Presynaptically, the FRFs appear to act like the buccalins, another family of inhibitory ARC neuropeptides. Both families of peptides reduce the size of motor neuron-elicited excitatory junction potentials (EJPs) presumably by decreasing presynaptic acetylcholine (ACh) release. 5. Postsynaptically, the FRFs appear to depress contractions because they activate a characteristic voltage-dependent, 4-amino-pyridine-sensitive K current in the ARC muscle. The same current is activated by a second class of ARC modulators: those that exert potentiating actions at low doses and inhibitory actions at high doses, i.e., serotonin, the small cardioactive peptides (SCPs), and particularly the myomodulins. Receptors mediating activation of the K current by the FRFs and the other modulators do, however, appear to be different. 6. We hypothesize that the inhibitory actions of the FRFs prevent excessively large muscle contractions. If contraction size is limited, then contraction duration is also limited. This may allow faster and more energetically favorable switching between contractions of antagonistic muscles.
Calcium current and inactivation in identified neurons in Hermissenda crassicornis
Authors: Yamoah E. N. , Kuzirian A. M. , Sanchez-Andres J. V.
Published: December 2017

1. N-type (omega-conotoxin sensitive) calcium currents (ICa) were recorded in identified neurons in Hermissenda crassicornis using low-resistance patch electrodes (0.7 +/- 0.3 M omega; n = 101) under conditions that eliminated inward Na+ currents (choline ions substitution) and suppressed outward K+ currents (Cs+, tetraethylammonium, and 4-AP). Step depolarization from a holding potential of -60 mV to potentials above -30 mV elicited ICa, which peaked approximately 20 mV and declined with increasing depolarizations. 2. Evidence for a low-threshold current was present. Step depolarization from a more hyperpolarizing potentials (e.g., -90 mV) revealed a small shoulder (< 100 pA) at -60 to -40 mV that was sensitive to Co2+ and Ni2+. However, under the conditions examined here (holding potential of -60 mV), the high-voltage-activated current predominated. 3. Barium (Ba2+) and strontium (Sr2+) permeate the Ca2+ channel with similar activation kinetics (ease of permeation; Ba2+ > Ca2+ > Sr2+). Steady-state activation of permeability versus membrane potentials for Ca2+, Ba2+, and Sr2+ as charge carriers could be fitted with the Boltzmann equation, with half-activation voltage and slope factor of 2.9 and 7.7 mV for ICa, -13.1 mV and 7.8 for Ba2+ current (IBa) and -2.3 mV and 7.8 for Sr2+ current (ISr). The time course of activation was monotonic with time constant (tau) for ICa ranging from 2 to 8 ms. 4. The inactivation profile was complex. At negative step potentials (e.g., -20 mV), inactivation of the current was slow. Depolarization steps to relatively positive voltages (e.g., 10 mV) showed more rapid inactivation than those at more positive potentials (e.g., 40 mV). When extracellular Ca2+ was raised from 5 to 10 mM, a biphasic decay (tau fast of 25 +/- 4 ms; and tau slow of 473 +/- 64 ms; mean +/- SD, n = 9) was seen. Such an observation suggested a current-mediated inactivation. 5. With a pulse duration of approximately 350 ms, ISr showed inactivation whereas Ba2+ virtually removed the decay. However, IBa turned off with more prolonged depolarization. 6. A twin-pulse protocol was used to assess the voltage dependence of inactivation: an incomplete U-shaped inactivation curve was observed for ICa, IBa, and ISr. Channels available for inactivation were increased in the presence of Ca2+ ions. 7. Inactivation was further studied with the Ca2+ chelators, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and bis(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA). With 10 mM of BAPTA, in the pipette, inactivation was reduced but not removed.(ABSTRACT TRUNCATED AT 250 WORDS)
Reflex patterns in postganglionic neurons supplying skin and skeletal muscle of the rat hindlimb
Authors: Habler H. J. , Janig W. , Krummel M. , Peters O. A.
Published: December 2017

1. Reflex patterns were analyzed in spontaneously active postganglionic vasoconstrictor neurons supplying skeletal muscle [muscle vasoconstrictor (MVC) neurons] and hairy skin [cutaneous vasoconstrictor (CVC) neurons] of the rat hindlimb. Postganglionic activity was recorded from single units and from filaments containing the axons of several spontaneously active neurons (multiunit preparations). The animals were freely breathing or artificially ventilated and maintained, in different experiments, under three different types of anesthesia (pentobarbital, chloralose, urethan). Reflexes were elicited by stimulation of arterial baroreceptors, chemoreceptors, cutaneous nociceptors, and cold receptors and visceral receptors from urinary bladder and colon. 2. Spontaneous activity of single postganglionic neurons ranged from 0.3 to 3.6 imp/s (median 1.15 imp/s and 1.0 imp/s in MVC and CVC neurons, respectively). Postganglionic axons conducted at 0.56 +/- 0.15 m/s (mean +/- SD, MVC neurons) and 0.53 +/- 0.11 m/s (CVC neurons). There was almost no difference in the rate of spontaneous activity under the three anesthetics used and whether the animals were artificially ventilated or breathing freely. 3. Stimulation of arterial baroreceptors by increasing arterial blood pressure by > 30 mmHg with intravenous injections of phenylephrine or angiotensin led to a depression of the activity in almost all vasoconstrictor neurons. In simultaneous recordings, with an identical increase of blood pressure, the magnitude of inhibition was greater in MVC neurons than in CVC neurons. Phasic stimulation of the arterial baroreceptors by the pulse pressure wave evoked a pronounced cardiac rhythmicity in the activity of the majority of MVC neurons (78%), but in only a small fraction of CVC neurons (18%). In most CVC neurons the cardiac rhythmicity was weak (33%) or absent (49%). When quantified the difference in the degree of cardiac rhythmicity between simultaneously recorded MVC and CVC neurons was highly significant (P < 0.001). 4. Noxious mechanical stimulation of skin of the ipsilateral hindpaw activated 20/35 MVC preparations (57%) and inhibited 25/47 CVC preparations (53%). Some CVC neurons (19%) were also activated, whereas the remainder of neurons were not affected. The quality of responses to noxious stimulation was correlated with the degree of cardiac rhythmicity that the sympathetic neurons displayed in their activity. A similar reciprocal response pattern in CVC and MVC neurons, albeit less pronounced, was observed to intense cold stimuli (chlor-ethyl spray) applied to the hindlimb. 5. This reciprocal pattern of the responses of MVC and CVC neurons was not observed when nociceptors from the contralateral hindlimb were stimulated and when cold stimuli were applied to the abdominal skin.(ABSTRACT TRUNCATED AT 400 WORDS)
Proprioceptive activity in primate primary somatosensory cortex during active arm reaching movements
Authors: Prud'homme M. J. , Kalaska J. F.
Published: December 2017

1. We studied the activity of 254 cells in the primary somatosensory cortex (SI) responding to inputs from peripheral proprioceptors in a variety of tasks requiring active reaching movements of the contralateral arm. 2. The majority of cells with receptive fields on the proximal arm (shoulder and elbow) were broadly and unimodally tuned for movement direction, often with approximately sinusoidal tuning curves similar to those seen in motor and parietal cortex. 3. The predominant temporal response profiles were directionally tuned phasic bursts during movement and tonic activity that varied with different arm postures. 4. Most cells showed both phasic and tonic response components to differing degrees, and the population formed a continuum from purely phasic to purely tonic cells with no evidence of separate distinct phasic and tonic populations. This indicates that the initial cortical neuronal correlates of the introspectively distinguishable sensations of movement and position are represented in an overlapping or distributed manner in SI. 5. The directional tuning of the phasic and tonic response components of most cells was generally similar, although rarely identical. 6. We tested 62 cells during similar active and passive arm movements. Many cells showed large differences in their responses in the two conditions, presumably due to changes in peripheral receptor discharge during active muscle contractions. 7. We tested 86 cells in a convergent movement task in which monkeys made reaching movements to a single central target from eight peripheral starting positions. A majority of the cells (46 of 86, 53.5%) showed a movement direction-related hysteresis in which their tonic activity after movement to the central target varied with the direction by which the arm moved to the target. The directionality of this hysteresis was coupled with the movement-related directional tuning of the cells. 8. We recorded the discharge of 93 cells as the monkeys performed the task while compensating for loads in different directions. The large majority of cells showed a statistically significant modulation of activity as a function of load direction, which was qualitatively similar to that seen in motor cortex under similar task conditions. Quantitatively, however, the sensitivity of SI proprioceptive cells to loads was less than that seen in motor cortex but greater than in parietal cortex. 9. We interpret these results in terms of their implications for the central representation of the spatiotemporal form (“kinematics”) of arm movements and postures. Most importantly, the results emphasize the important influence of muscle contractile activity on the central proprioceptive representation of active movements.
Electrotonic architecture of cat gamma motoneurons
Authors: Burke R. E. , Fyffe R. E. , Moschovakis A. K.
Published: December 2017

1. Experimental measures of input resistance, RN, and responses to brief hyperpolarizing current pulses were obtained in identified gamma-motoneurons in pentobarbital-anesthetized cats using conventional sharp micropipettes. The same cells were subsequently injected with horseradish peroxidase and completely reconstructed. In two cells, the electrophysiological and morphological data were of sufficient quality to permit estimation of specific membrane resistance, Rm, using biologically plausible ranges of specific cytoplasmic resistance, Ri, and membrane capacitance, Cm. 2. A combination of steady-state and dynamic computer models were employed to reconcile cell morphology with RN and the trajectories of the voltage decay following brief current pulses delivered to the soma. Simulated transient responses matched the tails of the observed transient when generated with the same current injections used experimentally. With Cm < or = 1.0 microF cm-2, the most satisfactory fits were obtained when the values of Rm assigned to the soma, Rms, were much smaller than the spatially uniform value assigned to the dendrites, Rmd and Ri = 60–70 omega cm. With Cm = 1.0 microF cm-2, Rms ranged from 260 to 427 omega cm2, whereas Rmd was approximately 33 K omega cm2. With Cm = 0.8 microF cm-2, Rms ranged from 235 to 357 omega cm2 and Rmd was between 62 and 68 K omega cm2. When Rm was constrained to be spatially uniform (i.e., Rm = Rms), implausibly high values of Cm (2.5–5.0 microF cm-2; Ri = 70 omega cm) were required to match the observed tail time constant, tau o,peel, but the simulated transients did not otherwise match those obtained experimentally. 3. With best fit values of Rms and Rmd, both gamma-motoneurons were electronically relatively compact (80% of total membrane area within 0.85 length constants from the soma). However, the calculated average steady-state inward attenuation factor (AFin) for voltages generated at any point within the dendrites increased rapidly with distance from the soma, reaching levels of < or = 90 and < or = 45 for the proximal 80% of membrane area for the respective motoneurons in the presence of a somatic shunt (Rms ≪ Rmd). If we assume that the somatic shunt is an artifact of sharp micropipette penetration (i.e., that Rms = Rmd for uninjured cells), then AFin decreased to < or = 20 and < or = 15, respectively, for the proximal 80% of cell membrane.(ABSTRACT TRUNCATED AT 400 WORDS)