bluuebunny/crossref_metadata_2025 huggingface dataset:
Presynaptic inhibition of transmission from identified interneurons in locust central nervous system
Authors: Pearson K. G. , Goodman C. S.
Published: December 2017

1. Intracellular recordings near the output terminals of an identified interneuron (the descending contralateral movement detector, DCMD) in the locust revealed the occurrence of depolarizing synaptic potentials. These presynaptic depolarizing potentials were evoked by spikes in both DCMDs, by auditory stimuli, and by electrical stimulation of the pro- to mesothoracic connectives. The occurrence of the depolarizing potentials decreased the amplitude of the action potentials close to the output terminals. 2. The stimuli that produced depolarizing potentials in the presynaptic terminals reduced the amplitude of the monosynaptic excitatory postsynaptic potentials evoked by the DCMDs in identified follower interneurons. We conclude that at least part of this reduction in transmission from the DCMDs results from presynaptic inhibition and that the presynaptic inhibition is related to a reduction in the amplitude of the presynaptic action potentials. 3. We propose that the function of the presynaptic inhibition of the DCMDs is to ensure that the interneurons triggering a jump are never activated by the DCMDs in the absence of proprioceptive signals from the legs indicating the animal's readiness to jump.
Is there a high concentration of color-selective cells in area V4 of monkey visual cortex?
Authors: Schein S. J. , Marrocco R. T. , de Monasterio F. M.
Published: December 2017

1. Recordings were made from neurons located within the central-field representation of the V4 area of extrastriate visual cortex using a semichronic, nitrous-oxide preparation; the properties of 174 cells were examined in sufficient detail to permit their classification. Cyto- and myeloarchitectural studies confirmed the identification of the area. 2. Color-selective cells with either color-biased or color-opponent properties represented about 20% of the examined population. Their incidence was not significantly different from that of similar cells encountered in penetrations into the central-field representation of area V2. 3. Most color-selective cells had color-biased properties, responding best to wave-lengths shorter than 460 nm, or longer than 580 n, or both. No examples of "green-biased" cells were found. Some color-biased cells responded to photopically matched white light, while others did not. Very few cells showed overt color-opponent responses. The spectral sensitivity of color-selective cells was not unusually narrow. 4. Cells lacking color selectivity and responding equally well to chromatic and achromatic lights of equal photopic luminosity, were the most commonly encountered cell type in penetrations of different parts of the V4 area (56%). Other than color, these cells showed stimulus preferences like those of color-selective cells. 5. One-fourth of V4 cells could not be systematically driven with the various stimuli used. This finding is consistent with recent results of recordings from the prelunate gyrus of the behaving monkey suggesting that some V4 cells receive extraretinal signals. 6. Our results do not support recent claims that V4 is specialized in the detailed analysis of color information.
Afferent contributions to stretch-evoked myoelectric responses
Authors: Jaeger R. J. , Gottlieb G. L. , Agarwal G. C. , Tahmoush A. J.
Published: December 2017

1. Step torque perturbations were applied to flex or extend the wrists of normal human subjects who were instructed to restore the joint to its initial position as quickly as possible. The resulting electromyographic (EMG) activity was recorded from the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi radialis. Experiments were performed under control and three altered conditions of the limb: 1) ischemia, 2) vibration, and 3) local ulnar nerve anesthesia. The effects of the procedures on the EMG responses in four poststimulus intervals--the myotatic (30-60 ms), late myotatic (60-120 ms), postmyotatic (120-200 ms), and stabilizing (200-400 ms)--were studied. 2. Ischemia was induced in the forearm by means of a sphygmomanometer cuff inflated to 150 mm of mercury around the upper arm. After about 20 min of ischemia the stretch-evoked EMG activity over the 30-60-ms and 60-120-ms intervals were abolished, while the longer latency responses persisted. 3. Vibration at frequencies between 50 and 120 Hz was applied to the tendon of the stretched muscle. Vibration consistently reduced the EMG activity only in the 30-60-ms interval. 4. The ulnar nerve was blocked near the elbow joint by local anesthetic. Varying degrees of block were obtained, from a mild sensory impairment to a complete block. At intermediate degrees of block, EMG activity in the 30-60-ms and 60-120-ms intervals were attenuated with little alteration in later responses. 5. The data are used to differentiate functionally the myoelectric responses evoked in four poststimulus time segments in the stretched muscle by step torque perturbations.
Left-right cortical asymmetries of regional cerebral blood flow during listening to words
Authors: Nishizawa Y. , Olsen T. S. , Larsen B. , Lassen N. A.
Published: December 2017

1. Regional cerebral blood flow (rCBF) was measured during rest and during listening to simple words. The xenon-133 intracarotid technique was used and results were obtained from 254 regions of seven right hemispheres and seven left hemispheres. The measurements were performed just after carotid angiography, carried out to exclude space occupying lesions. In all subjects the angiogram was normal. All were right handed. 2. Mean hemispheric blood flow of both left and right hemispheres increased 10% from the resting measurement during the listening task. This increase was due in part to activation of the entire hemisphere. The focal rCBF increases were localized to the superior part of the temporal regions, the prefrontal regions, the frontal eye fields, and the orbitofrontal regions. Significant asymmetries were found in particular in the superior temporal region with the left side showing a more widespread and intense increase, averaging 29% as compared to 18% on the right side. This left-sided dominance during verbal stimulation should be compared to the right-sided dominance of rCBF during nonverbal sound discrimination reported by Roland et al. (25, 26), who used precisely the same technique as in the present study.
Somatotopic organization of hindlimb cutaneous nerve projections to cat dorsal horn
Authors: Koerber H. R. , Brown P. B.
Published: December 2017

1. The dorsal horn lamina III-IV projections of 10 hindlimb nerves innervating most of the hindlimb have been studied in the cat using transganglionic transport of horseradish peroxidase (HRP). The somatotopic organization of whole cutaneous nerve projections was largely in register with the somatotopic organization of dorsal horn cells. That is, nerves projected to areas of dorsal horn where their innervation fields overlap the receptive fields of dorsal horn cells. 2. However, long-ranging projections were observed that were more extensive than predicted from the somatotopy of dorsal horn cells: these long-ranging projections may reflect the presence of normally ineffective synapses (synapses that do not cause postsynaptic discharge during receptive-field mapping of dorsal horn cells,) or a misconception of dorsal horn cell somatotopy in S2 and caudal segments, or the existence of a functionally separate cell group in ventral lamina IV and lamina V of these segments. 3. The cutaneous innervation fields of homologous nerves possessed high bilateral symmetry, as did their lamina III-IV projection fields. The degree of separation or overlap of two cutaneous nerves' projection fields was predictable from the degree of separation or overlap of their cutaneous innervation fields.
Factors influencing motoneuron rhythmic firing: results from a voltage-clamp study
Authors: Schwindt P. C. , Crill W. E.
Published: December 2017

1. The rhythmic firing properties of cat lumbar motoneurons were determined by intracellular injection of constant-current pulses. The activation thresholds of various membrane current components were subsequently determined in the same neurons using the technique of somatic voltage clamp. Voltage steps were employed that traversed the same voltage range as the membrane potential between rhythmic spikes (the "pacemaker potential"). 2. At fast firing rates (e.g., secondary-range firing), the pacemaker potential remains entirely within the range of voltages over which a previously described (42), persistent, inward, calcium current (Ii) is activated during voltage clamp. Thus Ii is tonically activated and counters the repolarizing, outward, potassium currents during fast firing. At slower firing rates (e.g., primary-range firing), the pacemaker potential only partially enters the voltage range where Ii is activated, and this voltage range may not be entered at all the slowest firing rates. Cells in which Ii deteriorated could not be made to fire at fast rates although they could still fire at slow rates. 3. The use of two independent intracellular microelectrodes allowed accurate measurement of the somatic voltage at which spike initiation occurred ("firing level"). In all cells, firing level increased significantly as steady firing rate increased. During a given injected-current pulse, firing level also exhibited a more moderate variation with time. 4. The variation in firing level was caused by the accommodative properties of the axon initial segment. Except at the fastest firing rates, firing level occurs at less depolarized voltages than the somatic sodium conductance threshold. In addition, somatic sodium current shows minimal inactivation over the voltage range traversed by the pacemaker potentials during slower firing rates. An inactivation of about 50% is attained during the maximum firing rate. 5. We discuss the ways by which Ii activation and thr progressive rise in firing level influence motoneuron rhythmic firing. We propose that the basic role of Ii is to aid in maintaining a linear f-I curve, especially at faster firing rates. We hypothesize that the relative balance between persistent inward and outward ionic currents plays a major role in determining the f-I curve slope among different neurons and between primary- and secondary-range firing of cat lumbar motoneurons.
Muscle spindle discharge in response to contraction of single motor units
Authors: McKeon B. , Burke D.
Published: December 2017

1. In human subjects, microelectrode recordings were made from 25 muscle spindle afferents and two tendon organ afferents coming from muscles innervated by the peroneal nerve. 2. Stimulation at low intensity through the recording microelectrode activated efferent axons innervating motor units in close proximity to the muscle spindle or tendon organ. There was a clear alteration in the discharge of 17 afferents (15 muscle spindle, 2 tendon organ) in response to twitch contractions that involved only one, two, or three motor units. With three other afferents there was a less overt but statistically significant alteration in discharge rate by the twitch contraction of a single motor unit. 3. The sensitivity of 21 receptors (20 spindles, 1 tendon organ) to twitch contractions of anatomically close motor units was contrasted with their sensitivity to twitches of more remote motor units in the muscle. In no instance was the sensitivity to the contraction of remote motor units greater than that to the contraction of local motor units stimulated through the microelectrode; with remote stimulation many units usually had to be activated before the resulting twitch contraction altered the discharge of an afferent. 4. It is concluded that muscle spindles as well as tendon organs can play a role in monitoring the activity of motor units anatomically close to the receptor.
Some features of binaural input to single neurons in physiologically defined area AI of cat cerebral cortex
Authors: Phillips D. P. , Irvine D. R.
Published: December 2017

1. In the ectosylvian cortex of 24 barbiturate-anesthetized cats, area AI was identified by its frequency organization and the responses to tonal stimuli of single neurons in that field were examined using sealed stimulating systems incorporating calibrated probe microphone assemblies. 2. The responsiveness to monaural and binaural best-frequency stimuli was examined quantitatively for 282 single units in AI. One hundred thirty-nine cells (49%) were excited by independent stimulation of only one ear and were classified as EO cells. In general, the effective monaural excitatory input was derived from the contralateral ear. One hundred ten (39%) neurons were excited by independent stimulation of each ear and were classified as EE units. For these neurons, the contralateral responses were generally stronger, shorter in latency, and lower in threshold than were their ipsilateral responses. Thirty-three cells (12%) gave weak or no responses to monaural stimuli but responded securely to binaural stimuli. These cells were classified as predominantly binaural (PB). 3. Binaural interactions were examined by comparison of the response to binaural, equally intense stimuli to the stronger monaural response. Among EO cells suppression was the most common form of interaction, while for EE cells summation was the more common. Less than 8% of cells were found to be monaural. 4. In electrode penetrations radial to the cortex surface, cells received their stronger or sole monaural excitatory input from a common ear, generally the contralateral. Within such penetrations, however, cells commonly differed with regard to the nature of their input from the other ear and/or in their binaural interactions. 5. Comparison of these data with data previously reported for subcortical auditory nuclei revealed that AI preserves many of the stimulus specificity characteristics of the lower nuclei. The reasons for the preservation of these characteristics at the cortex and the implications of the present data for the binaural column hypothesis are discussed.
Connections of midbrain periaqueductal gray in the monkey. II. Descending efferent projections
Authors: Mantyh P. W.
Published: December 2017

1. We have defined the descending efferent projections of the midbrain periaqueductal gray (PAG) by injecting small amounts of [3H]leucine into the various regions of the squirrel monkey PAG. 2. Despite the fact that different regions of the PAG were injected in separate animals, the majority of the brain stem areas labeled remained constant. 3. The PAG exhibited a dense projection to the superior colliculus, the nucleus cuneiformis, and the locus ceruleus. Parts of the reticular formation (nucleus reticularis: pontis oralis, pontis caudalis, gigantocellularis, magnocellularis, and ventralis) received a projection from the PAG, as did the nucleus parabrachial pars lateralis, ambiguous, the nucleus raphe magnus, and raphe pallidus. 4. In contrast to the brain stem, the deep laminae of the nucleus caudalis and the deep laminae of the cervical spinal cord were labeled only after injections of the lateral aspect of the PAG. 5. The main route for the PAG leads to brain stem projections is through the lateral edge of the paramedian reticular formation. The great majority of the anterograde labeling was ipsilateral to the injection although a small contralateral projection was present. 6. These results indicate that the PAG projects to the brain stem and spinal cord in the monkey. Many of the brain stem areas that the PAG projects to are known to project to the spinal cord. These secondary spinal projections coupled with the direct PAG leads to spinal projection provide a wide variety of routes through which the PAG may influence spinal cord activity.
Response of cat semicircular canal afferents to sinusoidal polarizing currents: implications for input-output properties of second-order neurons
Authors: Ezure K. , Cohen M. S. , Wilson V. J.
Published: December 2017

1. We studied the response of cat vestibular afferents, most likely innervating the semicircular canals, to sinusoidal polarizing currents applied to an electrode implanted near the horizontal ampulla. 2. Electrode implantation abolished responses to natural stimulation and reduced the level of resting activity compared to a population of afferents from unimplanted animals. The distribution of coefficients of variation of resting activity was, however, similar to that seen when the labyrinth is intact. 3. Many fibers were modulated sinusoidally by polarizing currents in the frequency range 0.175-4 Hz. Phase was mainly constant and typically led stimulus negativity by approximately 14 degrees, although about half the regular fibers had a phase lead that increased with frequency. Mean sensitivity (spikes X s-1 X microA-1) of regular and irregular fibers increased by a factor of about 1.5 over the frequency studied. Absolute sensitivity was about 7 times higher for irregular than for regular fibers. The overall behavior of the afferents could be well described by a transfer function in the form, sk, with 0 less than k less than 1. 4. We compared the response of afferent fibers to sinusoidal current with the response of second-order neurons studied under similar conditions in earlier experiments (15, 23). While the slopes of the sensitivities were similar, second-order neurons developed a phase advance over afferents at frequencies around 1 Hz. This difference in dynamics can be described by a transfer function in the form tau S + 1, with tau = 12 ms. This predicts that second-order neurons can develop a phase lead of about 25 degrees with respect to afferents at 6 Hz, a frequency still in the physiological range. It remains to be determined whether this applies to a particular subset of second-order neurons contributing to vestibulocollic reflexes.
Responses of neurons in VPL and VPL-VL region of the cat to algesic stimulation of muscle and tendon
Authors: Kniffki K. D. , Mizumura K.
Published: December 2017

1. The responses evoked by electrical stimulation of cutaneous and muscle nerves, by noxious and innocuous mechanical stimulation of muscle, tendon, and cutaneous tissues, and by intra-arterial (ia) injection of algesic substances (potassium, bradykinin) into arteries supplying the gastrocnemius-soleus muscle (GS) were studied in single neurons located in the ventroposterolateral nucleus (VPL) and in the transitional zone between VPL and the ventrolateral nucleus (VL) of cats lightly anesthetized with thiopenthal. Such chemical stimulation of the muscles has been shown to activate muscular groups III and IV axons specifically (43, 44) and presumably is nociceptive in character (14, 17, 31). 2. One hundred eight neurons were tested. Eighty-three of the units responded only to various types of cutaneous stimulation of the hindlimb. The other 25 responded to algesic stimulation of muscle and/or tendon. Of these latter 25, 7 had no apparent cutaneous receptive field although 4 of them responded to electrical stimulation of the common peroneal and/or sural nerve. Thus, only three neurons responded exclusively to algesic chemical and noxious mechanical stimulation of the muscle. Of the other 18 neurons, 14 had cutaneous receptive fields restricted to the hindlimb and often responded to non-noxious repetitive light stroking and to noxious pinching with a high-frequency discharge. Four cells (two of which had cutaneous input only from low-threshold mechanoreceptors) had complex and large receptive fields extending to more than one limb. 3. Potassium was a more potent muscle receptor stimulant than bradykinin, the latter only weakly exciting 3 neurons of 24 tested with both substances. The responses to potassium were rapid (approximately 4.0 s in latency) and tended to be greater (have higher response rates) for the units that responded to cutaneous as well as muscle/tendon stimulation. 4. Most neurons that responded to noxious deep stimulation had a threshold for the GS nerve volley in the group III fiber range. The few neurons with thresholds slightly below the group III range did not respond to activation of group I or II muscle spindle afferents by intra-arterial application of succinylcholine or by stretching the muscle. 5. Neurons with responses to any of the muscle, tendon, or cutaneous nociceptive stimuli were located at the ventral and dorsal periphery of VPL and in the VPL-VL transitional zone. 6. These results strongly suggest that there exist regions within the lateral diencephalon of cats that are capable of processing nociceptive information and that these regions are located at the periphery of VPL.
Neurons in ventrobasal region of cat thalamus selectively responsive to noxious mechanical stimulation
Authors: Honda C. N. , Mense S. , Perl E. R.
Published: December 2017

1. A survey was made of neurons located in the ventral posterior lateral nucleus of the cat thalamus and its immediate vicinity for elements with specifically nociceptive properties. 2. Pipette microelectrodes filled with a dye solution were used to obtain extracellular recordings of unitary activity in 34 animals anesthetized with chloralose. 3. The great majority of the over 1,000 different single units responding to sciatic nerve stimulation noted in this series of experiments could also be excited by innocuous mechanical stimulation of skin or subcutaneous tissues. An infrequent but consistently noted group of units excited by A-alpha beta delta sciatic nerve volleys did not respond to innocuous mechanical manipulation or A-alpha beta sciatic nerve volleys; they were excited only by either noxious levels of mechanical stimulation or when volleys included the activity of more slowly conducting myelinated fibers. The latencies of such "high-threshold" units to sciatic volleys were longer than those of the other units. 4. Histologically identified recording sites marked by dye were recovered for 17 high-threshold units. Twelve of the 17 could be excited by noxious manipulations of restricted parts of the contralateral hindlimb. Nine of the 12 had cutaneous receptive fields, whereas 3 responded only to stimulation of subcutaneous tissues. None of the 17 high-threshold units evidenced additional discharges that could be correlated with the C-fiber component of sciatic nerve volleys. 5. The high-threshold units typically exhibited a low level of irregular background activity, which increased on repeated noxious stimulation of the peripheral receptive fields. Tactile units of the same or adjacent penetrations usually had a much greater degree of ongoing activity, often marked by bursts at a relatively high frequency. 6. The recording sites for the 17 high-threshold neurons were located dorsal and ventrolateral to the core of the ventrobasal nuclei and were not found in the midst of the low-threshold, cutaneous, mechanoreceptive population. During vertical stereotaxic penetrations, high-threshold units were noted dorsal or ventral to the location of ventrobasal tactile units in a pattern consistent with the core's somatotopic arrangement. 7. These results support the concept that the cat ventrolateral thalamus receives a small but distinct selectively nociceptive projection. The nociceptive neurons appear to be located in a shell that surrounds the main tactile projection to the ventral posterior lateral nucleus and that retains at least part of the topographic arrangement characteristic of the tactile core. Presumably, this projection is part of an organization identifying and localizing noxious stimulation.
Auditory response properties of neurons in deep layers of cat superior colliculus
Authors: Wise L. Z. , Irvine D. R.
Published: December 2017

1. The auditory responses of 207 single neurons in the intermediate and deep layers of the superior colliculus (SC) of barbiturate -or chloralose-anesthetized cats were recorded extracellularly. Sealed stimulating systems incorporating calibrated probe microphone assemblies were employed to present tone- and noise-burst stimuli. 2. All acoustically activated neurons responded with onset responses to noise bursts. Of those neurons also tested with tonal stimuli, approximately 30% were unresponsive over the frequency range tested (0.1-40 kHz), while the others had higher thresholds to tones than to noise. 3. Details of frequency responsiveness were obtained for 55 neurons; 21 were broadly tuned, while 34 were sharply tuned with clearly defined characteristic frequencies (CFs). All sharply tuned neurons had CFs greater than or equal to 10 kHz. 4. The majority of neurons (81%) responded with latencies in the range 8-20 ms; only 11% of neurons had latencies greater than 30 ms. 5. Binaural response properties were examined for 165 neurons. The great majority (79%) received monaural excitatory input only from the contralateral ear (EO). However, most EO cells were binaurally influenced, the contralateral response being either inhibited (EO/I; 96 of 131 units) or facilitated (EO/F; 33 of 131 units) by simultaneous ipsilateral stimulation. Small subgroups were monaurally excited by either ear (EE cells; 8%) or were unresponsive monaurally but responded strongly to binaural stimulation (OO/F cells; 7%). 6. EO/I, EO/F, and OO/F neurons showed characteristic forms of sensitivity to interaural intensity differences (IIDs). The IID functions of EO/I neurons would be expected to produce large contralateral spatial receptive fields with clearly defined medial borders, such as have been described in studies of deep SC neurons employing free-field stimuli. 7. Preliminary evidence suggests a possible topographic organization of IID sensitivity in deep SC, such that the steeply sloping portion of the function (corresponding to the medial edge of the receptive field) is shifted laterally for EO/I neurons located more caudally in the nucleus. 8. The auditory properties of deep SC neurons are compared with previous reports and implications for the organization of auditory input are considered. The binaural properties and auditory spatial fields of deep SC neurons suggest that any representation of auditory space in this structure is unlikely to be based on restricted spatial fields.
Organization of electrical coupling between frog lumbar motoneurons
Authors: Collins W. F.
Published: December 2017

1. The organization of electrical coupling between lumbar motoneurons in the isolated frog spinal cord was investigated. Intracellular recordings were made from unidentified and identified thigh muscle motoneurons in segment 9. Excitatory postsynaptic potentials (EPSPs) elicited by stimulation of individual muscle nerves with dorsal roots cut (VR-EPSPs) were observed when the cord was perfused with either normal frog Ringer solution or calcium-free Ringer solution containing 2, 2.5, or 5 mM magnesium. 2. The VR-EPSPs recorded following stimulation of the homonymous muscle nerve were greater in amplitude and occurred with a shorter latency than the VR-EPSPs observed following stimulation of muscle nerves to different muscles. In addition, the latter VR-EPSPs had a shorter half-decay time. 3. Electrical connections made by motoneurons innervating synergistic muscles had a similar distribution, as indicated by the linear correlation observed between the amplitudes of VR-EPSPs in the same motoneuron elicited by stimulation of muscle nerves innervating synergistic muscles. No such linear correlation was observed between VR-EPSP amplitudes when muscle nerves innervating antagonistic muscles were stimulated. 4. Small-amplitude, spikelike potentials were often observed on top of the muscle nerve VR-EPSPs. In the case of VR-EPSPs elicited by stimulation of muscle nerves not containing the axon from the recorded motoneuron, the spikelike component accounted for a major part of the response. These spikelike potentials had a rapid time course (half-decay time, 2.5-5.9 ms) and in a few cases were observed to be all or none. These observations are consistent with dendritic action potentials in the recorded motoneuron as well as electrotonic coupling between a small number of neurons close to the recording site in the impaled motoneuron. 5. These results are interpreted to mean that a high degree of specificity exists in the organization of electrical coupling among frog lumbar motoneurons.
Descending inhibitory influences from periaqueductal gray, nucleus raphe magnus, and adjacent reticular formation. I. Effects on lumbar spinal cord nociceptive and nonnociceptive neurons
Authors: Gray B. G. , Dostrovsky J. O.
Published: December 2017

1. This study examined the inhibitory effects of conditioning stimuli delivered to the periaqueductal gray (PAG), nucleus cuneiformis (CU), nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis (NGC), and nucleus reticularis magnocellularis (NMC) on functionally identified neurons of the lumbar spinal cord dorsal horn in chloralose-anesthetized or decerebrate cats. 2. Neurons were classified according to their responses to a variety of cutaneous stimuli as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), or nociceptive specific (NS). The major aim of this study was to determine whether there was a difference in the effectiveness of the brain stem stimulation-produced inhibition of nociceptive (noci) neurons (consisting of both WDR and NS neurons) and the LTM non-nociceptive (nonnoci) neurons. There were no statistical differences in the susceptibility of WDR and NS neurons to brain stem-induced inhibition. 3. Most neurons tested could be inhibited by stimulation of any of the brain stem regions tested. In all cases the percentage of noci neurons inhibited from a given region was higher than the percentage of nonnoci neurons; however, this difference was only statistically significant in the case of NMC stimulation. 4. Threshold current intensities necessary to produce inhibition were determined for each neuron from each stimulation site. Although there was a trend for noci neurons to require slightly lower current intensities, there was in fact no statistically significant difference in the inhibitory thresholds between noci and nonnoci neurons for any of the regions tested. 5. A comparison of the mean threshold currents for the five regions studied revealed that the lowest stimulation currents were obtained in NMC with NRM, CU, NGC, and PAG, each requiring progressively higher current intensities in order to produce inhibition. 6. These results indicate that stimulation in PAG and NRM not only inhibits the responses of noci neurons but also those of nonnoci neurons. Moreover, stimulation in reticular regions adjacent to these two regions is effective in inhibiting the responses of both noci and nonnoci neurons.
Stochastic properties of spontaneous unit discharges in somatosensory cortex and mesencephalic reticular formation during sleep-waking states
Authors: Yamamoto M. , Nakahama H.
Published: December 2017

1. We compared renewal and Markovian characteristics of neuronal discharge sequences in deeper layers (V and VI) of the somatosensory area I (SI) and the mesencephalic reticular formation (MRF) of unanesthetized cats in the following five behavioral states: active wakefulness with movements (AW), motionless quiet waking (QW), slow-wave sleep (SWS), and paradoxical sleep with and without rapid eye movements (REM-PS and non-REM-PS). 2. The profile of the pooled renewal properties for the shorter interspike-interval component predicted by the exponential tail of interval distribution during a sleep-wakefulness cycle was quite different from that for the total intervals including the longer ones; e.g., the mean rate of the SI neuronal group for the shorter interval component during SWS was as high as that during REM-PS in spite of the lowest rate for the total intervals. 3. In the SI and MRF neurons, the group mean of the degree of Markovian characteristics of the shorter intervals was much larger during AW, SWS, and REM-PS then QW and non-REM-PS, indicating that successive interspike intervals of spontaneous activity are time dependent in the AW, SWS, and REM-PS states, while they tend to be independent during QW and non-REM-PS. This tendency was more conspicuous for SI than MRF. On the other hand, the longer intervals in the five states did not contribute to the revealment of the Markov property. 4. The time-independent activities during QW and non-REM-PS were markedly similar especially for SI, suggesting that these activities may be regarded as autochthonous ones inherent to the neuron and its surrounding network under study. 5. The degree of Markovian properties was much higher in the MRF neurons than in the SI neurons during each of the states of vigilance except for AW, suggesting that the MRF neuronal group has a tonically modulated unit activity even in the absence of external stimuli.
Ammonia does not selectively block IPSPs in rat hippocampal pyramidal cells
Authors: Alger B. E. , Nicoll R. A.
Published: December 2017

Intracellular recordings from CA1 pyramidal cells in the rat hippocampal slice preparation have been used to study the action of ammonia on inhibitory postsynaptic potentials (IPSPs). Concentrations of ammonia less than 2 mM had little effect on IPSPs or the action of iontophoretically applied gamma-aminobutyric acid (GABA). This concentration has been reported to be fully effective in blocking hyperpolarizing IPSPs in spinal cord and neocortex. Concentrations above 2 mM did cause a depolarizing shift in the IPSP and GABA reversal potentials, but this effect was accompanied by several generalized effects. The conductance increase during the IPSP but not during the GABA response was depressed, indicating that ammonia has a presynaptic depressant effect on the IPSP. Ammonia also depressed excitatory postsynaptic potentials (EPSPs), presynaptic fiber potentials, and pyramidal cell population spikes. In addition, the calcium-dependent potassium response elicited by depolarizing current pulses was depressed. This depression was due, in part, to a depolarizing shift in the reversal potential for this response. Responses recorded with potassium-sensitive microelectrodes indicate that ammonia releases potassium into the extracellular space. The possibility is discussed that the shifts in IPSP reversal potential seen with high concentrations of ammonia are a consequence of generalized nonspecific effects. We conclude that the relative insensitivity of hippocampal IPSPs to blockade by ammonia suggests that a mechanism fundamentally unlike an ammonia-sensitive chloride pump must maintain the hippocampal IPSP gradient.
Synaptic interactions between mammalian central neurons in cell culture. II. Quantal Analysis of EPSPs
Authors: Nelson P. G. , Marshall K. C. , Pun R. Y. , Christian C. N. , Sheriff W. H. , Macdonald R. L. , Neale E. A.
Published: December 2017

The presynaptic release mechanism involved in excitatory synaptic connections between neurons in cell cultures of fetal mouse spinal cord were studied by statistical analysis of intracellularly recorded postsynaptic responses. Quantal parameters were determined for the EPSPs evoked in spinal cord (SC) neurons by stimulation of either other SC or dorsal root ganglion (DRG) neurons. Transmitter release was manipulated by varying the Ca2+ and Mg2+ content of the culture medium. The release process was represented better by binomial than by Poisson statistics. A method was derived for obtaining the probability of release and the number of release elements. The quantal content and the number of release elements were substantially higher for the SC-SC connection than for the DRG-SC connection. This was partially compensated for by a larger quantal amplitude for the DRG-SC connection. There was some indication that the probability of release was higher for the SC-SC connection. The relationship between transmitter output and effective external Ca2+ ion concentration was approximately linear.
Control of extrinsic feeding muscles in Aplysia
Authors: Jahan-Parwar B. , Fredman S. M.
Published: December 2017

The extrinsic buccal muscles in Aplysia are responsible for the overall protraction and retraction of the buccal mass during feeding. The six pairs of extrinsic muscles are organized into two groups, consisting of three protractors and three retractors. Insights into how the extrinsic muscles are controlled were obtained by examining the organization of the motor neurons that innervated them. The extrinsic buccal muscles are innervated by cerebral ganglion nerves and neurons. All the muscles examined appear to be multiply innervated. Identified neurons in the cerebral B, E, and G clusters were found to be motor neurons for individual extrinsic muscles. Some extrinsic muscles had both excitatory and inhibitory innervation. Two synergistic muscles, the extrinsic ventrolateral protractor (ExVLP) and the extrinsic dorsal protractor (ExDP), had common excitatory innervation by identified neuron E5. Two antagonistic muscles, the ExVLP and the extrinsic ventral retractor (ExVR), also had common innervation. Identified neuron E1 appeared to be an inhibitory motor neuron for the ExVLP but an excitatory motor neuron for the ExVR. Common innervation provides a simple mechanism for coordinating synergistic and antagonistic extrinsic muscles. On the basis of these data, a model for the control of buccal mass protraction and retraction is proposed. Bursting by extrinsic buccal muscles was coordinated with cyclic activity in the intrinsic muscles of the buccal mass. Antagonistic extrinsic muscles burst antiphasically and synergistic extrinsic muscles burst in phase when the buccal mass was fully protracted and exhibited a series of rhythmic contractions. Additionally, cerebral E cluster neurons burst in phase with stereotyped rhythmic buccal motor neuron discharges recorded from buccal nerves. The cerebral E cluster motor neurons were coordinated by common synaptic input. No monosynaptic connections were observed; homologous neurons in each E cluster received synaptic input with similar but not identical timing, indicating that the interneurons that coordinate the homologous motor neurons are synchronized. The source of the rhythm that drives synaptically mediated cerebral extrinsic muscle motor neuron bursting was in the buccal ganglia. Cutting one cerebral-buccal connective eliminated E neuron bursting on that side but had no effect on homologous neurons on the intact side. This suggests that a single oscillator in the buccal ganglia may coordinate both the extrinsic and intrinsic buccal muscles during feeding.
Jaw muscle afferent firing during an isotonic jaw-positioning task in the monkey
Authors: Larson C. R. , Finocchio D. V. , Smith A. , Luschei E. S.
Published: December 2017

The activity of jaw muscle receptors was studied by recording neurons in the mesencephalic nucleus of the trigeminal nerve in monkeys trained to control the position and movement of their mandible. Jaw position was measured by a weighted lever resting on the mandibular incisors. The force required to maintain the position of the lever was varied; in most cases it was either 25 or 360 g. Firing rates of neurons were related to stationary mandibular positions and to the velocity of movements during intervals when the movement velocity was constant. Of 49 neurons studied in detail, 21 fired at rates that were consistently and linearly related to static incisal openings. This static position sensitivity was typically about 5 spikes/mm of incisal opening. Most position-sensitive neurons fired at higher rates during opening movements and at lower rates during closing movements than would be accounted for by their position sensitivity. This sensitivity to the velocity of movement was not linear, however; slow closing movements sometimes did not produce a decrease in firing rate, and an actual increase during muscle shortening was seen in a few instances. The position sensitivity of eight neurons was evaluated during different loading conditions; in no case did it change substantially. Of the remaining 28 neurons, 26 fired at high rates during all opening movements and either stopped firing or fired at low, sporadic rates during closing movements. The static position sensitivity of these neurons was weak and variable both within and between neurons. The velocity sensitivity of these stretch-sensitive neurons was very nonlinear. Except for a range of slow movements (+/- 5 mm/s), the firing rate was maximal (200 spikes/s or higher) for most opening movements and zero for most closing movements. Maximal firing rates were higher when the loads being moved were increased from 25 to 360 g. The majority of position-sensitive neurons exhibited a large interspike-interval variability at wide incisal opening. In most of these neurons, this interspike-interval variability was periodic, usually at a rate of about 10 periods/s, and took the form of "saw-tooth" modulation on a record of instantaneous firing rate. Neurons that exhibited this modulation in a very prominent form also exhibited, in many instances, a substantial increase in firing rate during closing jaw movements.
Graded synaptic transmission between identified spiking neurons
Authors: Graubard K. , Raper J. A. , Hartline D. K.
Published: December 2017

Graded synaptic transmission between spiking motoneurons of the pyloric group was studied in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus. Intracellular microelectrodes were placed in the cell bodies of both pre- and postsynaptic neurons. Graded synaptic transmission was found between all tested cell pairs that were known to display spike-evoked synaptic transmission, including PD to LP, PD to PE, PD to PL, PL to LP, and LP to PD. Graded synaptic transmission was effective below the threshold for spikes. Thus, it was possible to study the influence of graded synaptic transmission in normally active ganglia without blockage of spikes by tetrodotoxin. PD and LP neurons that were known to produce spike-evoked inhibitory postsynaptic potentials (IPSPs) were also capable of producing inhibitory effects on postsynaptic cells below the threshold for spikes. When tetrodotoxin (TTX) was used to eliminate both spikes and endogenous membrane oscillations, depolarization of presynaptic neurons produced hyperpolarization of postsynaptic cells. The presynaptic response to a current step usually showed a small early peak and a maintained, slightly lower plateau. The postsynaptic response had a delay, then a rise to a pronounced peak, and a roughly exponential decline to a maintained plateau. There was a presynaptic voltage threshold for any postsynaptic response; beyond the threshold, both pre- and postsynaptic peak and plateau responses increased with increasing current. PD neurons normally are depolarized beyond their release threshold in tetrodotoxin and, thus, released transmitter tonically for the many-hour duration of these experiments. Chemical, tonic synaptic transmission, here called graded synaptic transmission, was demonstrated by the presence of the following criteria: 1) reversal in sign of the postsynaptic response, 2) synaptic delay, 3) reversal potential, 4) postsynaptic conductance increase, 5) graded and reversible block by reduction of external Ca2+, and 6) specific graded block of the LP-to-PD synapse without effect on the PD-to-LP synapse by less than 10 microM picrotoxin added to the bathing medium.
Lateral geniculate nucleus unitary discharge in sleep and waking: state- and rate-specific aspects
Authors: McCarley R. W. , Benoit O. , Barrionuevo G.
Published: December 2017

The relationship between behavioral state, discharge pattern, and discharge rate was investigated in 26 lateral geniculate nucleus (LGN) units recorded in cats in the dark during waking (W), synchronized sleep (S), and desynchronized sleep (D). A distinctive state-dependent discharge pattern was the presence of stereotyped bursts of 2-7 spikes that occurred in 63% of the units. These bursts were most frequent in S, much less frequent in D, and rarely occurred in W. Lack of association with discharge rate changes between states showed the bursting to be a true state-dependent phenomenon. A burst consisted of 2-7 spikes, with each successive interspike interval being longer than the preceding one; in the 200 ms prior to burst occurrence, discharge probability decreased markedly. This structure of burst organization suggested a model of generation wherein each burst was caused by a unitary event of varying intensity, perhaps a rebound following a hyperpolarization. Spectral and autocorrelational analyses showed bursts occurred rhythmically in three cells at a frequency of 3-4 Hz and in two cells at a frequency of 10-12 Hz, indicating a possible linkage with slow-wave generators. While the number of bursts in the various behavioral states was a state-dependent phenomena, other aspects of discharge pattern were shown to be rate dependent. To evaluate discharge pattern apart from the occurrence of bursts, a "primary event spike train" was formed; this consisted of individual spikes and the first spike of each burst. This analysis showed that, within S, the probability of burst occurrence was highest when the primary spike rate was low. Quantitative analyses showed that first-order pattern measures (the form of the interspike interval histogram, IH) were dependent on the mean interspike interval (ISI, the inverse of mean rate). This association explained 83-89% of the variance in a power series approximation of IH form. Joint interval histograms (JIH) were used to evaluate the signature of bursts and of the form of the primary spike train. As with interval histograms, the main features of the form of the primary spike JIH were dependent on the primary spike rate. Thus, we concluded that first- and second-order discharge patterns of primary events were rate dependent and not state dependent. Our data are compatible with a model where in the absence of retinal input, the frequency of LGN primary spikes over behavioral state changes is largely determined by brain stem reticular formation input.(ABSTRACT TRUNCATED AT 400 WORDS)