bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions between bilateral clusters of neuroendocrine cells in Aplysia
Authors: Haskins J. T. , Blankenship J. E.
Published: December 2017

1. Activity of bilateral clusters of electrotonically coupled neuroendocrine cells (the bag cells) was studied using multiple-site intracellular and extracellular recording techniques in isolated parietovisceral ganglia of three species of Aplysia. Bilateral afterdischarges typically began with spike initiation on one side near the neurite terminals along the pleurovisceral connective; propagation of action potentials then proceeded toward the somata with potentiation to full somatic invasion in the ipsilateral bag cell cluster. This activity potentiated across the parietovisceral ganglion until contralateral spikes were initiated at a point near the bag cell somata (designated site A) and compound bag cell activity was then propagated both inward toward the somata and outward toward the circumesophageal ring of head ganglia. This sequence of events, i.e., "in one side, out the other," could occur several times during an afterdischarge, although outward propagation of activity was rarely maintained for more than 20 spikes. Synchrony between clusters was best during these periods of activity. Usually after a few episodes of this sequence, the sites of spike initiation spontaneously shifted to near the neurite terminals of each side and activity was initiated distally and propagated inward. Asychrony between clusters commonly developed when the sites for spike initiation were near the neurite terminals of each side. 2. Waveforms and temporal sequence of recorded events indicate that at least two sites for spike initiation exist within the neuritic tree of each bag cell cluster. These are the distal terminations of the neurites and a proximal site near the somata. Action potentials could be generated at this proximal site spontaneously or when electrotonically driven by contralateral activity. Removal of the bag cell somata did not interfere with bilateral behavior of the bag cell system. The proximal site is, therefore, not somatic. Activity initiated there was always more synchronous and propagated with a higher conduction velocity than activity initiated at the distal ends of the neurites. 3. Experiments were performed with and without the circumesophageal ring of head ganglia intact. Removal of the head ganglia had no effect on bilaterality of or synchrony within the bag cell system. Systematic stimulations and cuts of head ring connectives suggested that the cerebral ganglion may participate in orthodromic activation of the bag cells. 4. Our findings indicate the bag cells of Aplysia are a homogeneous population of neuroendocrine cells with multiple sites for spike initiation. Either cluster can serve as a pacemaker for the other through potentiation and electrotonic activation of the contralateral cluster at proximal sites on the neurites.
Interactions among an ensemble of chordotonal organ receptors and motor neurons of the crayfish claw
Authors: Lindsey B. G. , Gerstein G. L.
Published: December 2017

1. Action potentials of crayfish propodite-dactyl (PD) chordotonal organ receptors and two claw motor neurons, the opener inhibitor (OI) and slow closer excitor CE) were simultaneously monitored during imposed step and ramp movements of the dactyl or while the dactyl was held at various positions. 2. The activities of the cells during imposed displacements were analyzed using peristimulus time histograms and response and contour planes. The proprioceptive fields (PFs) of individual receptors resemble components of the more complex motor neuron PFs. Some receptors are briefly active after each successive opening step, while others do not respond to steps near the closed position but respond as the joint angle increases, becoming active when the claw is held open. Another type of receptor responds to closing movements. 3. Interactions among the various types of receptors and the two motor neurons were detected and analyzed by various statistical methods and intracellular recording techniques. The results indicate that receptors activated during opening movements and when the dactyl is held at open positions excite OI and CE via divergent functional connections. The efficacies of the connections made by a receptor may differ. Receptors activated by closing movements produce hyperpolarizing synaptic potentials in both efferents, possible directly or via interneurons. 4. It is concluded that several types of chordotonal organ receptors form an ensemble of parallel input channels, which modulates the activities of OI and CE and contributes to the generation of the spatial-temporal nonuniformities of their proprioceptive reflex responses.
Disorders in somesthesis following lesions of parietal lobe
Authors: LaMotte R. H. , Mountcastle V. B.
Published: December 2017

1. We determined the effects of lesions of the parietal lobe on the capacities of monkeys to detect and discriminate between mechanical sinusoids delivered to the hand. Tests of discrimination measured the capacity to discriminate between frequencies of flutter (24--36 Hz) and the capacity to make gross discriminations of frequency of flutter-vibration over the range of 10--50 Hz. 2. A unilateral removal of the parietal lobe impaired sensory capacities only on the contralateral hand; detection threshold was elevated, the capacity to discriminate between frequenceis of flutter was permanently lost, and the capacity to discriminate between and identify frequencies of 10--50 Hz was grossly impaired. No defects were found on the hand ipsilateral to the lesion. Detection thresholds, but not discrimination thresholds, decreased during postoperative testing, but in most cases did not recover to preoperative values. The impairments in frequency discrimination remained through the last day of postoperative testing. 3. A unilateral, subtotal parietal lesion that completely destroyed the primary and secondary somatic areas and Brodmann's area 5 resulted in the same sensory impairments as those produced by total removal of the parietal lobe. In most cases, detection threshold was elevated; flutter-frequency discrimination was lost, and the capacity to discriminate between frequencies of 10--50 Hz over the extended range of flutter and vibration was impaired. 4. The loss in discriminative capacity following lesions of the somatosensory cortex is interpreted as due to the absence of a cortical mechanism that determined differences in the temporal pattern of cyclically entrained activity in the somatic afferent pathway. This loss was dissociated from the remaining capacity, although impaired, to detect the presence of any neural activity in the afferent pathways or to determine gross differences in the frequency of mechanical sinusoids by a mechanism of coding by the labeled line.
Hippocampal pyramidal cells: significance of dendritic ionic conductances for neuronal function and epileptogenesis
Authors: Traub R. D. , Llinas R.
Published: December 2017

1. Starting with published data derived mainly from hippocampal slice preparations, we have used computer-modeling techniques to study hippocampal pyramidal cells (HPCs). 2. The dendrites of the HPC apparently have a short electrotonic length. Calcium spikes are apparently generated by a voltage-dependent mechanism whose kinetics are slow in comparison with those generating sodium spikes of the soma. Inward calcium currents are assumed to trigger a long-lasting potassium conductance. This slow calcium-potassium system, which in our model is located predominantly on the dendrites, provides a heuristic model to describe the mechanism for a) the after-depolarization following an HPC soma (sodium) spike, b) the long afterhyperpolarization following repetitive firing, c) bursts of spikes that sometimes occur after orthodromic or antidromic stimulation, and d) the buildup of the "depolarizing shift" during the strong synaptic input presumed to occur during seizures. 3. Fast prepotentials or d-spikes are shown to arise most probably from dendritic "hot spots" of sodium-regenerative membrane. The limited amplitude and short duration of these prepotentials imply that the hot spots are located on small dendrites. 4. Dendritic electroresponsiveness, first postulated for the HPC by Spencer and Kandel (52), is analyzed quantitatively here and is shown to provide rich integrative possibilities for this cell. Our model suggests that, for these nerve cells, alterations in specific membrane properties, particularly calcium electroresponsiveness, can lead to bursting behavior that resembles epileptogenic neuronal responses.
Quantitative analysis of relative contribution of central and peripheral neurons to gill-withdrawal reflex in Aplysia californica
Authors: Carew T. J. , Castellucci V. F. , Byrne J. H. , Kandel E. R.
Published: December 2017

1. There is general agreement that the gill-withdrawal reflex elicited by weak tactile stimuli (less than 2 g to the siphon skin) is mediated almost entirely by the central nervous system (CNS) (13, 15, 18, 23). However, there was disagreement concerning the effects of moderate intensity (2--4 g) stimuli. Kupfermann et al. (18) found that the CNS mediates approximately 94% of the reflex elicited by moderate-intensity stimuli, whereas Peretz et al. (23) found that in this stimulus range, the amplitude of the reflex was, on average, unaltered when the CNS was removed. 2. To resolve this difference we first carried out pilot experiments in collaboration with B. Peretz, J. W. Jacklet, and K. Lukowiak using isolated mantle preparations, and then performed a systematic study using both the isolated mantle and intact animals. The main difference that seemed to account for the discrepancy in the results was the magnitude of the reflex response that was selected for study. Previous studies from this laboratory used a minimum-response criterion whereby only brisk and clearly observable responses of at least 35% maximum were examined. By contrast, Peretz et al. (23) examined all responses, even those that were extremely small. In addition, the two groups used different methods of stimulation so that stimulus intensities could not really be compared. 3. By comparing the effects of moderate-intensity stimuli in experiments with and without a response criterion in isolated mantle preparations, we found that when a minimal response-amplitude criterion is imposed the CNS mediates 90--95% of the gill-withdrawal reflex, whether it is elicited by the "tapper" stimulus used by Peretz et al. (23) or by the servo-controlled probe previously used in this laboratory. On the other hand, when no minimal response criterion is used and small responses are also examined, the response to the probe is still significantly reduced by 85% when the CNS is removed, whereas the reflex response to the tapper is more variable, sometimes increasing and other times decreasing with deganglionation. 4. We have also tested, in intact animals, the role of the CNS in mediating gill withdrawal. Water-jet stimuli were delivered to the siphon to elicit the reflex, as in previous behavioral studies. As was the case with probe stimulation in the isolated mantle preparation, in intact animals the CNS mediates 90% of the reflex evoked by moderate-intensity stimuli when a minimal response-amplitude criterion is imposed. 5. Our experiments indicate that, using response criteria and methods of stimulation, one can reliably study the reflex as predominantly mediated by the CNS.
Serotonergic activation of tonic-type enteric neurons in guinea pig small bowel
Authors: Wood J. D. , Mayer C. J.
Published: December 2017

1. Electrical stimulation of interganglionic fiber tracts of Auerbach's plexus released a chemical substance, which produced a slow EPSP associated with an increase in input resistance in the postsynaptic neuron. 2. This effect of fiber tract stimulation was mimicked by microiontophoretic application of serotonin (5-HT) to the neurons. Both the endogenous transmitter substance and exogenous 5-HT produced membrane depolarization, both increased the input resistance of the neuron, both reduced or abolished hyperpolarizing afterpotentials of the action potentials, and both augmented membrane excitability. 3. During tachyphylaxis to excess 5-HT (1 micron) in the perfusion solution, the response to fiber tract stimulation was also reversibly blocked. 4. Methysergide (30 micron) blocked both the response to fiber tract stimulation and to exogenous 5-HT. 5. Cholinergic agonists and antagonists did not alter the slow EPSP and the response to exogenous 5-HT. 6. The evidence suggests that 5-HT is the neurotransmitter substance that produces the slow EPSP in myenteric neurons.
Cutaneous masking. II. Geometry of excitatory andinhibitory receptive fields of single units in somatosensory cortex of the cat
Authors: Laskin S. E. , Spencer W. A.
Published: December 2017

1. The responses of single neurons in the primary somatosensory cortex of the cat to brief air-pulse stimuli were quantitatively examined. These controlled natural stimuli activated almost exclusively rapidly adapting hair units which, on systematic movement of the stimulus through the receptive field, gave unit-response profiles that showed the classical unimodal tent-shaped distribution. 2. Conditioning stimulus-induced inhibition of a response evoked by a fixed test stimulus was measured by systematically moving the conditioning stimulus through the receptive field. The spatial distribution of in-field inhibitory activity was unimodal and highly covariant with that of the conditioning excitation, the peak inhibition corresponding to the functional center of the excitatory receptive field. 3. Nearly one-half of the units studied evidenced inhibition extending beyond the excitatory receptive field, forming a "surround" inhibitory region; but these were usually restricted areas with rather weak inhibitory effects. 4. Time-course measuring revealed, on the average, inhibition effects measureable from 10 ms before to some 70 ms following conditioning stimulation, with peak inhibition delayed some 10--15 ms from the conditioning stimulus onset. We showed the backward inhibition, occurring with the test stimulus delivered before the onset of the conditioning stimulus, to be a property of the test response duration. Inhibition measured in the surround areas had essentially the same time course as the inhibition calculated from measurements made within the receptive fields. 5. The spatial and temporal profiles of the excitatory and inhibitory cortical unitary activity are thus very similar to the parametric features of psychophysical enhancement and masking. These findings suggest that the excitatory and inhibitory activities related to individual stimuli interact in multipoint stimulus paradigms so that simple unimodal composite profiles are synthesized.
Forward masking of auditory nerve fiber responses
Authors: Harris D. M. , Dallos P.
Published: December 2017

1. Responses of single fibers were obtained from the auditory nerve of chinchillas. Tone-burst stimuli consisted of a masking stimulus followed by a probe stimulus. Forward masking of a fiber's response is defined as a reduction in the magnitude of the probe-evoked response caused by the addition of the masking stimulus. 2. The recovery of probe response magnitude as a function of the time interval between masker offset and probe onset (delta T) follows an exponential time course. A relationship between the time course or magnitude of poststimulus recovery and the characteristic frequency (CF) of a fiber was not detected. 3. The iso-forward masking contour near the threshold of the masking effect across masker frequencies approximates a fiber's frequency threshold curve (FTC). In other words, forward masking tuning curves are essentially the same as frequency threshold curves. 4. The frequency dependence of forward masking is compared to that of two-tone suppression. Tonal stimuli outside the boundaries of a fiber's FTC that produce two-tone suppression are ineffective forward maskers. Certain frequency/intensity combinations within the FTC may produce both suppression and forward masking and tones within the remaining area of the FTC produce no suppression but are effective forward maskers. 5. Both the time course and the magnitude of the forward masking effect are dependent on the discharge rate evoked by the masker regardless of the masker's absolute level or spectral content. An increase in masker-evoked excitation causes an increase in time constant and a greater reduction in probe response magnitude, rd. The function relating rd to masker level parallels the firing rate/masker level function up to 40 dB above response threshold. 6. A decrease in masker duration from 100 ms leads to a decrease in both rd and the time constant of recovery. There is no significant difference between the 100 and 200 ms duration conditions. 7. Forward masking in single fibers is related to the period of poststimulus recovery of spontaneous activity, a component of a fiber's response pattern to the masker, and this component is tentatively identified as a period of recovery from short-term adaptation.
Studies on sensory neurons of the mouse with intracellular-recording and horseradish peroxidase-injection techniques
Authors: Yoshida S. , Matsuda Y.
Published: December 2017

1. Dorsal root ganglion (DRG) cells were dissected from the adult mouse with their peripheral nerves, and electrophysiological and morphological studies were performed. 2. The peripheral nerves were stimulateradish peroxidase (HRP) was injected into the cell body, and the size of stained cell body and axon, together with the state of myelination, were examined. 4. F-neurons, whose somatic spike is a tetrodotoxin (TTX)-sensitive Na spike, had a large or medium-sized cell body with a myelinated axon, and shoed a fast conduction velocity (A fibers). 5. A-neurons, whose somatic spike is a TTX-resistant Na spike, had a small cell body with an unmyelinated axon, and showed a slow conduction velocity (C fibers). 6. Most H-neurons, whose somatic spike is a TTX-resistant combined Na-Ca spike, proved to have conduction velocity and morphological features similar to A-neurons, whereas the rest of them had features similar to F-neurons. 7. A roughly linear correlation was exhibited between each pair of cell body size, axon diameter, and conduction velcoity. 8. Spike conduction along axons to cell bodies were blocked in all neurons either by an elimination of Na ions from the medium or by an application of TTX. 9. The possibility of transmission of different information by different DRG cells and the developmental differentiation of sensory neurons are discussed.
Postnatal rat sympathetic neurons in culture. I. A comparison with embryonic neurons
Authors: Wakshull E. , Johnson M. I. , Burton H.
Published: December 2017

1. A morphological and physiological comparison was made between embryonically and postnatally derived superior cervical ganglion neurons (SCGN) grown in dissociated cell culture. It was found that while morphologically distinct, the physiological properties of the postnatal neurons were the same as their embryonic counterparts. 2. Intracellular injection of horseradish peroxidase (HPR) demonstrated that SCGN from any age of animal elaborated two basic types of processes, although the pattern of process ramification was unique for each neuron. The two types of proceses were 1) the large, smooth, rapidly tapering; and 2) the thin, nontapering variety, which often contained varicosities along its length. It is suggested that the former are dendritic in function, while the latter act as axons. 3. A difference was noted in somal size and the number of primary processes extended by the embryonic and postnatal neurons, with the latter more closely resembling the in vivo morphology. 4. Resting potentials and action-potential amplitudes of postnatal SCGN were comparable to those found previously for embryonic SCGN in vitro. 5. Iontophoretic application of putative neurotransmitter substances revealed the presence of acetylcholine receptors (AChR) on both embryonic and postnatal SCGN. Picrotoxin-sensitive depolarizing responses to iontophoresed gamma-aminobutyric acid (GABA) was seen on a few embryonic neurons, but not on the older cells. No responses were detected when norepinephrine (NE), glutamate, cAMP, substance P, or dopamine were applied to the SCGN of either age group. 6. Synatpic interaction between postnatal SCGN were found at an earlier in vitro age (12 days) than was the case for embryonic neurons (20 days). 7. Synaptic transmission was found to be chemical in nature. This was shown by 1) a dependence on external Ca2+ concentrations; 2) steplike fluctuations in synpatic potential amplitude, and 3) a variation in potential amplitude with changes in membrane potential. 8. It is concluded that the postnatal SCGN are able to survive in culture even when taken from animals up to 12.5 wk old. The elaboration of processes is in many ways strikingly similar to sympathetic neurons in the animal, and they are able to form functional synaptic interactions.
Postnatal rat sympathetic neurons in culture. II. Synaptic transmission by postnatal neurons
Authors: Wakshull E. , Johnson M. I. , Burton H.
Published: December 2017

1. It was shown in the preceding paper that postnatally derived rat superior cervical ganglion neurons (SCGN) will grow in dissociated cell culture and form functional synaptic connections with each other. In this report, synaptic transmission by the postnatal SCGN is detailed. 2. Synaptic interactions between SCGN were blocked by the nicotinic cholinergic antagonist hexamathonium (C-6), indicating that acetylcholine was the transmitter substance used by these neurons. This was found to be the case even for neurons taken from 12.5-wk-old animals. 3. In a few cases, the beta-adrenergic blocking agent, propranolol, was found to block synaptic potentials, suggesting that a catecholamine might be involved in the transmission process. The possible mechanisms of this involvement are discussed. 4. SCGN taken from up to 10-wk-old rats were able to form functional synaptic contacts with cocultured skeletal muscle cells. These interactions were sensitive to low external Ca2+ and to 1--2 microM d-tubocurarine (d-TC). 5. It is concluded that even adult SCGN retain a certain amount of neurotransmitter "plasticity" when grown under appropriate culture conditions. From the data on the neuron-neuron and SCGN-skeletal muscle interactions, it is suggested that a matching of presynaptic transmitter with postsynaptic receptor is a sufficient condition for the formation of functional nerve-target interactions.
Auditory cortex lesions and interaural intensity and phase-angle discrimination in cats
Authors: Cranford J. L.
Published: December 2017

1. A currently unresolved question concerning the effects of auditory decortication on sound localization is whether or not operated animals have a normal capacity for discriminating the small interaural differences in phase angle or intensity that result from the spatial separation of sound sources relative to the head. The present experiment was designed to provide data relevant to this question. 2. Four normal and three operated cats (bilateral ablations of AI, AII Ep, SII, I-T), wearing stereo headsets, were tested with an active avoidance procedure to detect reversals in the interaural phase-angle or intensity relations of binaural 1-kHz tones. For both groups of cats, the detection thresholds for interaural intensity and phase angle were found to be close to 1 dB and 5 degrees, respectively. 3. In addition, we found that both unoperated and operated cats exhibited positive transfer from the original lateralization task involving the detection of interaural reversals of phase angle or intensity to a new test, which required the cats to identify, in an absolute sense, which ear received the leading or louder signals. 4. Thus, the present investigation provides additional evidence that the neocortex has no primary sensory role in sound localization.
Potentials evoked by alvear tract in hippocampal CA1 region of rats. I. Topographical projection, component analysis, and correlation with unit activities
Authors: Leung L. W.
Published: December 2017

1. The field potentials and unit activities evoked by the alvear tract (AT) in CA1 region of the dorsal hippocampus of rats were studied under sodium pentobarbital anesthesia. 2. The localized activity evoked anterior to an AT stimulus began as a compound action potential, followed by a slower negative wave, and ended in a long-lasting, slow positive wave. Observed with a 64-electrode recording array, topographical projections of the AT in CA1 were seen as parallel strips inclined at an angle of 5-30 degrees medially from the sagittal plane. 3. Three overlapping components in the averaged evoked potentials (AEPs) were distinguished. The first event (component I) was a brief compound antidromic action potential of pyramidal cells. The second field event (component II) reversed from surface negative to deep positive at 200 micrometer from the ventricular surface, increased rapidly with stimulus intensity, potentiated with double shocks, and followed stimulus frequency up to 50/s. The third component was long lasting (up to 200 ms), surface positive and ventral negative (turnover at 150 micron below the pyramidal layer), followed stimulus frequency up to about 10/s, and saturated at a low stimulus intensity (about 3 x threshold). 4. In some preparations, another fast negative peak of about 2 ms duration was found to follow the axon compound action potential on the hippocampal surface and appeared to propagate from the pyramidal layer to the ventricular surface. It was probably of nonsynaptic origin, perhaps due to the centrifugal basal dendritic spikes of the pyramidal cells. 5. Single units were recorded in CA1. Antidromic units were identified by their firing at a fixed latency (1.5 ms) and ability to follow high stimulus frequencies. Units firing at about 2.7 ms latency possessed characteristics of monosynaptic excitation. Under light anesthesia, many of the latter units also showed a late, prolonged suppression of background firing. Tentative interneuronal types fired with peak latencies of 4-5 ms or showed prolonged increase in firing rate. 6. From the correlation with unit post-stimulus time histograms, AEP component II was inferred to be the extracellular, monosynaptic, excitatory postsynaptic potentials, and component III the di- or polysynaptic inhibitory postsynaptic potentials. These postsynaptic potentials were generated by the pyramidal cells and interneurons.
A comparison of visual-response properties in cat's parabigeminal nucleus and superior colliculus
Authors: Sherk H.
Published: December 2017

1. The visual-response properties of single cells in the cat's superior colliculus and parabigeminal nucleus were compared. In the colliculus, 151 cells (restricted to the upper layer) were studied, and in the parabigeminal nucleus, 134 cells. 2. Response characteristics in the two structures were similar in many respects: among these were receptive-field size, ocular dominance, and lack of specificity for stimulus shape and contrast (light versus dark). 3. Quantitatively, there were some significant differences between the two populations of cells. Parabigeminal neurons tended to respond more brisky and reliably, while being less selective for those stimulus parameters tested (size, velocity, and direction of movement). Spontaneous activity was much higher in the parabigeminal nucleus than in the colliculus. Finally, parabigeminal cell responses to stationary stimuli were somewhat brisker than those of tectal cells. 4. These data suggest that a physiologically distinct population of tectal cells sends input to the parabigeminal nucleus, probably with some convergence on individual cells.
Responses of Purkinje cells of cerebellar vermis to sinusoidal rotation of neck
Authors: Denoth F. , Magherini P. C. , Pompeiano O. , Stanojevic M.
Published: December 2017

1. The response of Purkinje (P) cells located in the vermal cortex of the cerebellar anterior lobe to sinusoidal rotation of the neck was investigated in precollicular decerebrate cats. The head of the animal was fixed in a sterotaxic frame while the spinous process of the second cervical vertebra was held by a clamp rigidly fixed to the tilting table. It was then possible to elicit a selective neck input by rotating the neck and the body simultaneously along the longitudinal axis of the animal while maintaining the head in horizontal position. 2. Among the 95 P-cells tested for neck stimulation, 35 units showed a mossy fiber (MF) or a climbing fiber (CF) response to sinusoidal rotation of the axis vertebra at the frequency of 0.026 Hz and at the peak amplitude of displacement of 5--10 degrees. The response consisted in a periodic modulation of the discharge frequency during sinusoidal rotation of the neck. Most of these units were excited during side-down rotation of the neck, but were inhibited during side-up rotation. 3. The threshold amplitude of neck rotation responsible for the MF-induced responses varied in different units from 1 to 3 degrees at the frequency of 0.026 Hz. The sensitivity of the units, expressed in percentage change of the average firing rate per degree of displacement, either did not change or very slightly decreased as a result of increasing amplitude of stimulation from 1--3 degrees to 10--15 degrees at the frequency of 0.026 Hz or by increasing frequency of neck rotation from 0.015 to 0.15 Hz at the amplitude of neck displacement of 5--10 degrees. 4. Changes in amplitude or frequency of stimulation at the parameters reported above did not greatly modify the phase of the unit responses relative to the side-down position of the neck. These findings indicate that the MF and CF responses of P-cells to sinusoidal rotation of the neck depended on changes in neck position and not on changes in velocity of neck rotation. 5. The observation that the majority of responding P-cells located in the vermal cortex of the cerebellar anterior lobe increased their firing rate during side-down rotation of the neck is discussed in relation to the results of stimulation and lesion experiments, indicating that postural changes can be elicited either during asymmetric stimulation of neck receptors or by unilateral interruption of the neck afferents.
Differential inhibitory effects of medial and lateral midbrain stimulation on spinal neuronal discharges to noxious skin heating in the cat
Authors: Carstens E. , Klumpp D. , Zimmermann M.
Published: December 2017

1. The inhibitory effects of electrical stimulation in midbrain periaqueductal gray (PAG) and lateral reticular formation (LRF) on spinal dorsal horn neuronal responses to noxious skin heating were investigated in cats anesthetized with Nembutal and N2O. 2. Thirty-one dorsal horn units driven by electrical stimulation of the posterior tibial and/or superficial peroneal nerves at A- and C-fiber strength responded to noxious radiant heating (e.g., 50 degrees C) of the skin of the hindpaw. All units tested were inhibited by electrical stimulation (100-Hz trains, 3/s) of both PAG and LRF. 3. Systematic tracking with the stimulating electrode revealed that descending inhibition is generated at sites throughout the mediolateral extent of the midbrain. Particularly effective sites were in LRF and PAG. 4. More powerful descending inhibition was generated from LRF than from PAG sites, based on quantitative comparison in the same unit of a) degree of inhibition of spinal unit heat-evoked discharges by PAG and LRF stimulation at the same current intensity, b) current threshold for inhibition by PAG and LRF stimulation, and c) slope of curves plotting degree of inhibition in relation to intensity of PAG and LRF stimulation. 5. Dorsal horn neurons show a linear relationship between response magnitude and temperature of skin heating during a series of heat stimuli (42-50 degrees C) applied at 3-min intervals. When the series is repeated during PAG stimulation, the slope of the linear temperature-response curve is reduced without a change in the response threshold. In contrast, repetition of the heating series during LRF stimulation produced a parallel rightward shift in the linear temperature-response curve, with commensurate increase in response threshold. 6. The results indicate that functionally separate descending inhibitory systems are activated by stimulation of PAG and LRF. Possible inhibitory mechanisms and the functional significance of descending inhibition from PAG and LRF are discussed.
Visual pontocerebellar projections in the cat
Authors: Mower G. , Gibson A. , Robinson F. , Stein J. , Glickstein M.
Published: December 2017

1. Projections of pontine visual cells onto the cat cerebellar cortex were studied by antidromic activation and by the retrograde transport of horseradish peroxidase (HRP). 2. Cells in the medial pontine visual area, which receive visual cortex projections, were activated antidromically principally from the contralateral cerebellar hemisphere. Cells in the dorsolateral pontine visual area, which receive an input from the superior colliculus, were activated principally from the vermis and ipsilateral hemisphere. There is some overlap in the projections of these two different populations of pontine cells, which probably occurs by way of bifurcated axons. 3. The HRP technique confirmed that there is a major difference in the pattern of projections from these two pontine visual regions. Many cells in the rostral-medial portion of the pontine nuclei, which receive their input from visual cortex, were labeled following HRP injections in the contralateral cerebellar hemisphere. Far fewer of these cells were labeled following vermal injection. Cells in the dorsolateral pontine nucleus, which receive visual input from the superior colliculus, were labeled following an HRP injection in the vermis or the ipsilateral hemisphere. Cells in the region of pontine nuclei that receive input from the ventral lateral geniculate nucleus were also labeled after a vermian injection. 4. If the vermis is related to the control of whole-body movements and the hemisphere to control of ipsilateral limbs, these results suggest that the corticopontocerebellar and the tectopontocerebellar pathways may be involved in different classes of visually guided movement.
Spatial organizations of catfish retinal neurons. II. Circular stimulus
Authors: Chan R. Y. , Naka K.
Published: December 2017

1. Temporal dynamics of receptive-field components were identified by use of circular stimuli whose diameter was modulated in white-noise fashion. 2. A thin ring of light evoked a complex response from the horizontal-cell soma but not from its axon. 3. All bipolar cells had a biphasic receptive field whose incremental sensitivities were comparable for the field's center and surround. 4. Type-N cells had a biphasic field whose two components were segregated both in time and space. 5. Type-C cells showed nonlinearities, which did not depend on the types of light inputs and which were intrinsic to the cell. 6. Ganglion cells could be classified roughly into two classes: small- and large-field cells. Their main nonlinearity was rectification. 7. Our studies on the catfish retna have shown that the distal cells are essentially linear in time and space and can be identified functionally by any type of input. The proximal cells, however, have a complex functional repertoire whose identification poses considerable difficulty.
Axonal branching patterns and location of nigrothalamic and nigrocollicular neurons in the cat
Authors: Anderson M. E. , Yoshida M.
Published: December 2017

1. Antidromic activation from the thalamus and the superior colliculus was used to identify the axonal projections of neurons in the substantia nigra. 2. Up to 43% of the nigral neurons studied in individual animals had branching axons that could be activated antidromically from both the ipsilateral ventromedial thalamus and the ipsilateral superior colliculus. 3. For several neurons, the conduction time spent in the unbranched axonal segment could be calculated using measurable collision and antidromic latency times. Time in the unbranched segment was less than 20% of the antidromic latency for most neurons studied. 4. Latencies for antidromic activation from the thalamus were measured and would be appropriate if these axons were to mediate the monosynaptic nigrothalamic inhibition reported earlier. 5. Stimulation of the caudate nucleus produced inhibition of spontaneous activity of both collicular- and thalamic-projecting neurons.
Synaptic organization of defined motor-unit types in cat tibialis anterior
Authors: Dum R. P. , Kennedy T. T.
Published: December 2017

1. Synaptic potentials were recorded intracellularly in tibialis anterior (TA) motoneurons following stimulation of a descending brain stem pathway, the medial longitudinal fasciculus (MLF), and three segmental inputs, the homonymous and heteronymous group Ia afferents, the group I afferents from the antagonist, and the cutaneous and muscle afferents. Intracellular stimulation of the motoneurons was used to classify them, based on the properties of the innervated muscle units, into types FF, F(int), FR, and S (6, 16). 2. The sum of the monosynaptic EPSP amplitudes resulting from stimulation of homonymous and heteronymous group Ia afferents (summed group Ia EPSP) was inversely related to motoneuron size, as assessed by motoneuron input resistance, and was inversely related to motor-unit tetanic tension. Type-FF, -FR, and -S motoneurons showed significant differences in the mean amplitude of their summed group Ia EPSPs. 3. The amplitudes of disynaptic IPSPs resulting from stimulation of group I afferents in the antagonist muscle also showed an inverse relationship to motoneuron size. The observed relationships between motoneuron size and the monosynaptic group Ia EPSP amplitude or the disynaptic group I IPSP amplitude are compatible with the “size principle” of motor-unit recruitment (26). 4. The amplitudes of the monosynaptic EPSPs evoked in TA motoneurons by stimulation of the MLF were distributed rather randomly among all types of TA motoneurons. A slight tendency of larger monosynaptic EPSPs to occur in motoneurons with larger tetanic tensions was observed. 5. The polysynaptic effects from cutaneous and muscle afferents in sural and gastrocnemius-soleus nerves were frequently excitatory on type-FF motoneurons, but were primarily inhibitory on type-FR and -S motoneurons. Clearly, the polysynaptic cutaneous and muscle inputs and the monosynaptic MLF input onto TA motoneurons show a different pattern of synaptic organization than the group I inputs. 6. In general, the synaptic organization of the TA motor nucleus is similar to that of its extensor antagonist, medial gastrocnemius (MG) (2--5, 7, 8), when analogous neural circuits are compared. This parallel organization suggests a commonality of motor-control systems for both flexor and extensor muscles.
Location and properties of dorsal horn neurons at origin of spinoreticular tract in lumbar enlargement of the rat
Authors: Menetrey D. , Chaouch A. , Besson J. M.
Published: December 2017

1. Spinoreticular tract neurons at the rat lumbar cord level were identified by antidromic activation following stimulation at mainly pontine and mesencephalic levels. These units, which were found in the dorsal half of the cord, could be separated into two groups according to their spinal location, electrophysiological properties, and their central projections. 2. Units in the dorsolateral funiculus nucleus projected mainly to the cuneiformis area and adjacent structures with frequent bilateral projections. They had the slowest conduction velocities, sometimes in the unmyelinated range. Generally, they were driven only by stimulation of subcutaneous and/or deep structures. 3. Neurons located in the dorsal horn mainly projected contralaterally to pontine and mesencephalic levels. their conduction velocities and the electrophysiological properties were identical to those observed for the rat spinothalamic tract (22). Almost all (86%) had clear cutaneous sensitivity and generally large receptive fields: 40% responded to nonnoxious and noxious mechanical cutaneous stimuli and frequently to noxious radiant heat, 26% were exclusively excited by light tactile stimuli, and 20% required noxious cutaneous mechanical stimulation for activation. There was a good correlation between responses to natural and transcutaneous electrical stimulation: units driven by noxious mechanical stimuli received A-delta- and/or C-fiber inputs. The remaining units (14%) had more complex receptive fields associated with both excitatory and inhibitory inputs originating from a single peripheral area. 4. The functional heterogeneity of the rat spinoreticular tract is reminiscent of that demonstrated for the rat and monkey spinothalamic tracts. Similarly, the rat spinoreticular neurons are under the influence of descending inhibitory controls originating from the nucleus raphe magnus and bulbar reticular formation. 5. Responses of the rat spinoreticular tract neurons are consistent with the involvement of this pathway in the transmission of messages of both innocuous and noxious origins.
Control of multiple impulse-initiation sites in a leech interneuron
Authors: Calabrese R. L.
Published: December 2017

1. Several heart interneurons (HN cells) of the leech nerve cord have impulse-initiation sites in every segmental ganglion through which their single axons pass. All these initiation sites are capable of producing rhythmic impulse bursts. However, under normal conditions a dominant primary initiation site in the ganglion where the cell body is located suppresses the activity of the other secondary sites. 2. Hyperpolarization of the primary initiation site by injected current permits immediate expression of rhythmic activity by a secondary site, usually the one located in the next posterior ganglion. 3. The free-running impulse burst rhythm of the primary site is stronger than that of the secondary site, having a greater burst duration and a tendency toward a higher burst frequency. 4. Bursts of primary-site impulses intercalated into the secondary-site impulse burst rhythm have a twofold effect. First, early to midway through the secondary-site's burst cycle, they phase delay its impulse burst rhythm. Second, early in the secondary-site's burst cycle, they tend to suppress ongoing impulse bursts, and late in the secondary-site's burst cycle, they tend to suppress the next expected impulse burst. The amount of burst suppression seen early and late in the secondary-site burst cycle depends on the burst duration and intraburst impulse frequency of the intercalated burst. 5. The ability of a train of primary-site impulse bursts to completely suppress secondary-site activity depends on burst duration, intraburst impulse frequency, and burst period. 6. Primary-site impulse trains with burst parameters close to those of naturally occurring primary-site bursts completely suppress secondary-site activity. 7. These results are consistent with the notion that the primary-site impulse burst rhythm of an HN cell suppresses the activity of its secondary site because, cycle by cycle, it delays and/or suppresses the next secondary-site burst so that no secondary-site bursts are produced. Dominance of the primary site over the secondary site is ensured by virtue of the primary-site's stronger impulse burst rhythm.
Mechanism of long-lasting synaptic inhibition in Aplysia neuron R15
Authors: Adams W. B. , Parnas I. , Levitan I. B.
Published: December 2017

1. Long-lasting inhibition is a synaptically mediated response found in certain molluscan nerve cells that fire action potentials in bursts. It is elicited by repetitive stimulation of a presynaptic nerve and may last for minutes or hours after stimulation. 2. Voltage-clamp techniques were employed to measure the voltage dependence of the synaptically elicited current. Current-voltage curves were obtained by stepping or sweeping the voltage over the range -40 to -120 mV. 3. Long-lasting inhibition was found to be mediated by two separate conductance mechanisms. A component that reverses near -80 mV is most prominent at times up to 5 min following stimulation. A component with no reversal potential between -40 and -120 mV predominates at later times. 4. The reversible component is attenuated by reducing the intensity of stimulation of the presynaptic nerve, by injection of TEA into the postsynaptic cell, or by activation of a potassium conductance with serotonin prior to stimulation of the nerve. Thus, the reversible component appears to be mediated by an increase in potassium conductance. 5. The effects of the nonreversible component measured in the soma appear to be too large to attribute it to a conductance change that is electrically "distant" from the soma. It is attenuated by turning off a resting inward ion conductance with dopamine prior to stimulation of the nerve. It is not affected by short exposure to ouabain, but is attenuated by longer exposures that reduce the sodium and calcium gradients. Thus, the nonreversible component may be mediated by a decrease in voltage-dependent inward current flow carried by sodium or calcium.
Reinnervation of glabrous skin in baboons: properties of cutaneous mechanoreceptors subsequent to nerve transection
Authors: Terzis J. K. , Dykes R. W.
Published: December 2017

1. A total of 758 fibers were isolated from previously transected and repaired ulnar nerves of five baboons. These fibers were compared to fibers from normal and previously crushed nerves studied in an earlier experiment. 2. The conduction velocities of the proximal portion of the injured axons dropped below normal, and this reduction persisted until reinnervation appeared nearly complete. 3. The receptive-field organization and response characteristics of 79 cutaneous afferent fibers serving the glabrous skin were studied in detail and compared to cutaneous afferent fibers of normal and previously crushed nerves studied earlier. 4. Initially, receptive fields were small and irregular, and often one fiber served several distinct skin regions. Ten months later, most of these abnormalities were no longer apparent. 5. Thresholds for single impulses elicited by von Frey hairs remained elevated for up to 4 mo after the receptive field reappeared, but then dropped abruptly to a near-normal range. 6. After reinnervation, rapidly adapting fibers displayed tuning curves characteristic of their submodality, but thresholds were elevated and only began to approach the normal range 6 mo after reinnervation. 7. After reinnervation, slowly adapting fibers displayed stimulus-response curves with elevated thresholds and they tended to saturate at lower stimulus intensities than normal fibers. 8. When compared to the return of function following a crushing injury, axons that had been transected displayed a slower time course for the return to normal values of conduction velocity and threshold. Receptive-field organization also remained abnormal for a longer time period. 9. These data support the hypotheses that a) breaking the continuity of the Schwann cells and extracellular matrix that occurs during transection but not during crush is a major factor leading to errors of axonal regeneration in the distal stump, b) submodality specificity is a property of the regenerating axon, and c) regenerating axons are influenced by an internal or external cue, causing them to form and maintain a single relatively homogeneous receptive field.