bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of altering organ of Corti on cochlear distortion products f2 - f1 and 2f1 - f2
Authors: Siegel J. H. , Kim D. O. , Molnar C. E.
Published: December 2017

1. Single cochlear nerve fiber recordings from unexposed chinchillas show spatial distributions of amplitude and phase of the distortion products f2 - f1 and 2f1 - f2 similar to those previously reported for the cat (35, 37, 42). 2. Damaging the organ of Corti in the region corresponding to the frequencies of a two-tone stimulus substantially reduces the amplitude of these distortion products at their characteristic places. 3. The distortion products 2f - f1 and 2f1 - f2 thus appear to be generated in the organ of Corti in the region of the primary-frequency places. 4. The neural responses suggest that the distortion products are propagated in the motion of the cochlear partition like externally applied stimulus tones at the distortion frequencies wih a similar spatial distribution of distortion product amplitude and phase. Models of the cochlea that assume nonlinear cochlear-partition dynamics can account for the similarity by demonstrating that distortion products generated by cochlear-partition nonlinearity can propagate apicalward in the motion of the cochlear partition. 5. Models of the cochlea using a linear-system model for cochlear partition motion, in cascade with a nonlinear transduction stage and a subsequent sharp filter, are inadequate to account for present observations, unless two currently implausible assumptions are made: a) stimulus tones near 4 kHz must propagate in normal cochleas at least as far apically as the 300-Hz place with sufficient amplitude to generate f2 - f1 there, and b) damage to the organ of Corti must interfere with this propagation of 4-kHz stimulus tones to the 300-Hz place. 6. Distortion generation in the cochlea is sensitive to delicate alterations of the organ of Corti. Short moderate-intensity exposures to sound can reversibly reduce the amplitudes of the distortion products f2 - f1 and 2f1 - f2 seen in responses from cochlear nerve fibers with characteristic frequencies (CF) near the distortion frequencies. Since such exposures do ot produce permanent structural changes visible under light microscopy, it seems most reasonable to believe that subtle changes in the organ of Corti (most likely in the hair cells themselves) in the region most responsive to f1 and f2 reduce the generation of mechanically present distortion products.
Slow active potentials and bursting motor patterns in pyloric network of the lobster, Panulirus interruptus
Authors: Russell D. F. , Hartline D. K.
Published: December 2017

1. Neurons in the central pattern generator for the "pyloric" motor rhythm of the lobster stomatogastric ganglion were investigated for the possible involvement of regenerative membrane properties in their membrane-potential oscillations and bursting output patterns. 2. Evidence was found that each class of pyloric-system neurons can possess a capability for generating prolonged regenerative depolarizations by a voltage-dependent membrane mechanism. Such responses have been termed plateau potentials. 3. Several tests were applied to determine whether a given cell possessed a plateau capability. First among these was the ability to trigger all-or-none bursts of nerve impulses by brief depolarizing current pulses and to terminate bursts in an all-or-none fashion with brief hyperpolarizing current pulses. Tests were made under conditions of a high level of activity in the pyloric generator, often in conjunction with the use of hyperpolarizing offsets to the cell under test to suppress ongoing bursting. 4. For each class, the network of synaptic interconnections among the pyloric-system neurons was shown to not be the cause of the regenerative responses observed. 5. Plateau potentials are viewed as a driving force for axon spiking during bursts and as interacting with the synaptic network in the formation of the pyloric motor pattern.
Neurotransmitters producing and modulating opaline gland contraction in Aplysia californica
Authors: Tritt S. H. , Byrne J. H.
Published: December 2017

1. Opaline release in Aplysia provides a simple model system for examining the biochemical and electrophysiological mechanisms underlying glandular secretion and its modulation. The opaline gland is a large multivesicular structure, which is innervated by at least three large identified motor neurons located within the right pleural ganglion (28). In this paper we have investigated the roles of dopamine (DA), acetylcholine (ACh), and serotonin (5-HT) in this simple neural system. 2. DA infusion produces a gland contraction that is similar to the response produced by neural activity in the previously identified opaline motor neurons. 3. The gland response to DA infusion is not affected by blocking synaptic transmission in the gland, suggesting that DA acts directly on muscle cells surrounding the gland and not through interposed interneurons. 4. In addition to its effect of producing contractions of the gland, DA enhances the size of subsequent neurally evoked gland contractions and increases the size of excitatory junctional potentials (EJPs) recorded from the opaline gland. Thus DA may have an additional modulatory role in opaline release. 5. DA antagonists such as fluphenazine and haloperidol inhibit the gland response to DA and also block the gland contraction produced by neural activity in the identified motor neurons. In addition, the DA antagonists reversibly block the EJPs recorded from the gland cells. Compounds known to block the effects of ACh or 5-HT have no effect on the dopamine-induced gland contractions, the contractions produced by firing the motor neurons, or the EJPs evoked by motor neuron stimulation. These results suggest that DA may be the neurotransmitter used by the identified opaline motor neurons. 6. ACh produces a decrease in pressure recorded from the lumen of the opaline gland that can be blocked by hexamethonium. 7. While 5-HT does not directly produce a contraction, treatment of the gland with the transmitter increases the size of subsequent gland responses produced either by DA infusion or activity in the opaline motor neurons. This enhancement has a relatively slow onset and long duration and persists for more than 15 min after the serotonin is washed out. In 60% of the experiments 5-HT also increased the size of the EJPs recorded from the opaline gland. The results suggest a modulatory role for serotonin in opaline secretion similar to the one it plays in other neural systems in Aplysia.
Intracellular alkalinization potentiates slow inward current and prolonged bursting in a molluscan neuron
Authors: Gillette R.
Published: December 2017

1. The bilaterally paired ventral white cells (VWCs) of the buccal ganglion of Pleurobranchaea drive the cyclic motor output of ingestive feeding behavior during prolonged and endogenously sustained burst episodes (7). The capacity to support burst episodes is specifically induced by appetitive (food) stimulation of chemosensory pathways (5). Cyclic 3',5'-adenosine monophosphate (cAMP) and its agonists also induce prolonged burst episodes (8) through potentiation of a slow inward current (6). 2. Intracellular alkalinization of the VWC by externally applied ammonium ion and methylamine (5-20 mM) induces bursting and enhances slow inward current measured under voltage-clamp conditions. The enhancement of slow inward current is seen in the induction or augmentation of a negative slope resistance region in the current-voltage relation and in the enhancement of slowly decaying inward current tails recorded near the K+ equilibrium potential following depolarizing voltage commands. 3. Intracellular injection of alkalinizing agents, bicarbonate ion and a strong buffer solution at pH 8.1, also enhance the inward current. In ammonium saline, enhancement of inward current is dependent on NH3 content, not NH4+; NH3 is the intracellular alkalinizing agent of ammonium saline. Therefore, the change in slow inward current is an effect specific to intracellular pH. 4. The time courses of inward current enhancement and intracellular pH change in NH4+ saline are similar. The results of this study suggest that normal fluctuations in intracellular pH may be significant determinants of the excitability and consequent activity of these and perhaps other neurons. The potential interaction of intracellular pH and cyclic AMP metabolism is discussed.
Descending inhibitory influences from periaqueductal gray, nucleus raphe magnus, and adjacent reticular formation. II. Effects on medullary dorsal horn nociceptive and nonnociceptive neurons
Authors: Dostrovsky J. O. , Shah Y. , Gray B. G.
Published: December 2017

1. This study examined the inhibitory effects elicited by brain stem stimulation on the somatosensory responses of trigeminal medullary dorsal horn (subnucleus caudalis of the spinal trigeminal nucleus) neurons. Single-unit extracellular recordings were obtained in chloralose-anesthetized cats. Neurons were classified as wide dynamic range (WDR), nociceptive specific (NS), or low-threshold mechanoreceptive (LTM). Conditioning stimuli were delivered to the periaqueductal gray (PAG), nucleus cuneiformis (CU), nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis (NGC), and nucleus reticularis magnocellularis (NMC). 2. Over 97% of the neurons tested could be inhibited by stimulation in all regions except PAG. Stimulation in the PAG inhibited 91% of the neurons tested. There was no statistically significant difference in the incidence of inhibition of WDR and NS nociceptive (noci) neurons and the LTM nonnociceptive (nonnoci) neurons. 3. Mean stimulation intensities necessary to produce inhibition were determined for each neuron from each stimulation site. The current thresholds necessary to inhibit the responses of noci neurons were found to be significantly lower, on the average, than those of nonnoci neurons at stimulation sites in the PAG, CU, and NGC. 4. Inhibition of the responses of WDR neurons required a lower mean current than for NS neurons but was statistically significant only for PAG and NGC. Thresholds for inhibiting the responses of NS neurons were similar to those for inhibiting the responses of LTM neurons for all regions except CU, where LTM thresholds were markedly but not significantly higher. 5. Stimulation thresholds were found to be lowest in NMC, while in NGC, NRM, and CU they were all similar and slightly higher. Stimulation in the PAG required the highest currents to produce inhibition. 6. These results indicate that stimulation in NRM and PAG not only inhibits the responses of noci neurons but also those of nonnoci neurons. Furthermore, stimulation in reticular regions adjacent to NRM and PAG is frequently even more effective in inhibiting the responses of both noci and nonnoci neurons. In addition, WDR neurons are more effectively inhibited than NS or LTM neurons. These results are compared with those obtained using similar methods in cat lumbar dorsal horn.
A model of spindle afferent response to muscle stretch
Authors: Hasan Z.
Published: December 2017

1. A unified model of the properties of stretch responses of mammalian spindle endings is proposed. This model encompasses the disparity between sensitivity of spindle endings to small and to large stretch of the muscle as well as the disparity in their dynamic responsiveness for different amplitudes of stretch. 2. In the model the mechanical properties of intrafusal fibers include a property akin to friction, which is hypothesized on the basis of reported observations on amphibian muscle. Transducer and encoder processes are modeled in the light of recent observations on isolated spindles. The model involves five unknown parameters whose values are selected by reference to certain reported observations on deefferented primary and secondary endings. The model can be used to predict responses to length changes of arbitrary time course. 3. Predicted responses to large ramp-and-hold stretch are quantitatively comparable to observations over a wide range of stretch velocities. The quantities compared include the increment in response during ramp stretch as well as the dynamic index, which is a measure of adaptation at stretch plateau. 4. At a fixed frequency of sinusoidal stretch, the relation between amplitudes of stretch and response is predicted in quantitative agreement with measurements. As the frequency of stretch is decreased, the predicted phase lead decreases and then increases, while the sensitivity decreases monotonically, in accord with observations. 5. In the model the high sensitivity for small stretch is not specific to any particular length of the muscle. When stretch is large, the region of high sensitivity is gradually reestablished at the new length, a phenomenon referred to as resetting. The dynamic response to a large stretch can be seen as arising, for the most part, from the dynamic process of resetting. 6. The influences of static or dynamic fusimotor activation on stretch responses of the primary ending are simulated by modifying the parameter values in the model. The modifications are such that static (dynamic) fusimotor activity speeds up (slows down) the resetting of the high-sensitivity region. The predictions mimic qualitatively the observed fusimotor effects not only on the response to large ramp stretch but also the contrasting effects seen with smaller, sinusoidal stretch.
Integration of biphasic synaptic input by electrotonically coupled neuroendocrine caudodorsal cells in the pond snail
Authors: ter Maat A. , Roubos E. W. , Lodder J. C. , Buma P.
Published: December 2017

The ovulation hormone-producing caudodorsal cells (CDCs) of the pond snail Lymnaea stagnalis form two clusters of electrotonically coupled cells, each containing a few specialized (ventral) cells that connect the clusters. The hormone is secreted during a pacemaker-driven discharge. The CDCs receive a biphasic cholinergic postsynaptic potential (PSP), consisting of a rapid excitatory postsynaptic potential (EPSP) and a slow inhibitory postsynaptic potential (IPSP) that is elicited by stimulation of nerves. The effect of the synaptic input on the discharge of the CDCs is described and the location of the synapse investigated by a combination of electrophysiological recordings and morphological techniques. The PSP interrupts the discharge and hastens its termination. In addition, it causes a reversal of the temporal order of the spikes of ventral cells (that normally lead) and dorsal cells (that lead only after the PSP). Ion-substitution experiments indicate that the ionic mechanism underlying the biphasic PSP is conventional, involving a conductance increase for Na+ (EPSP) and K+ (IPSP). Receptors mediating the inhibitory component occur only on the proximal axons of the ventral cells, both components are larger and reverse more readily in ventral cells. These findings suggest that the PSP is generated in the ventral cells. The biphasic PSP has no effect on electrical coupling, suggesting that it is not generated along the electrical pathways among the cells. Horseradish peroxidase (HRP) staining reveals that the lateral branches emerge from the proximal axons of the ventral cells only. In HRP-filled preparations processed for electron microscopy (EM) acetylcholinesterase is demonstrated at these branches where it occurs associated with synapses. The location on fine branches of the ventral cells explains the absence of an effect on electrotonic transmission, whereas the reluctance of components of the PSP to reverse at the expected potentials is due to the distribution of the synapses over more than one cell. It is concluded that the biphasic PSP is received only by the ventral cells and that it is conveyed electrotonically to the other cells.
Apparent discrepancy between single-unit activity and [14C]deoxyglucose labeling in optic tectum of the rattlesnake
Authors: Auker C. R. , Meszler R. M. , Carpenter D. O.
Published: December 2017

Autoradiographic analysis of [1-14C]2-deoxy-D-glucose-6-phosphate ([14C]2-DG-P) accumulation in the rattlesnake brain stem and optic tectum was used in an effort to map infrared and visual neuronal pathways. Visual stimulation with a standard stimulus (a heat lamp) resulted in dense labeling of the superficial layers of the optic tectum. Infrared stimulation with the same standard stimulus resulted in labeling at the first synaptic relay, the lateral descending nucleus of the trigeminal tract (LDN-V), but not at higher levels, including the optic tectum. Systematic comparison of electrophysiological properties of tectal neurons was performed using the standard stimulus. Responses of infrared units in one hemitectum and visual units in the other, elicited by the same stimulus used in the [14C]2-DG-P experiments, were analyzed. There were no clear differences in the number, maximal density, spread, or rates of accommodation of visual units and infrared units, although the locus of maximal density was more superficial for visual units. In general, infrared units generated a greater number of action potentials than did visual units. All infrared units responded only to onset of the stimulus but they varied greatly in their ability to maintain discharge for the full duration of the stimulus. Most visual units exhibited on-, off-, or on-off responses. Four units showed only inhibition of spontaneous activity during the visual stimulation. There were significant differences in the evoked responses elicited by visual and infrared stimulation in response to the standard stimulus. Infrared stimuli generated single, large, triphasic on-responses, whereas visual stimulation generated complex multiphasic and long-lasting on- and off-responses. The major infrared on peak reached maximal amplitude at greater depths and was larger than the major visual on peak. Amplitude of the infrared peak fell off more rapidly with distance from the locus of its maximum than did amplitude of the visual peak. These observations are consistent with the view that infrared stimulation is effective in discharging neurons but is not associated with intense synaptic excitation. In contrast, visual stimulation apparently does produce intense synaptic activity, as suggested by the duration, complexity, and spread of the visual evoked response. Failure of this synaptic activity to produce more spikes in visual units probably reflects either depolarizing spike inactivation or the admixture of excitatory and inhibitory actions. Our observations suggest that 2-deoxy-D-glucose uptake is not necessarily correlated with the degree of action potential activation of specific neuronal pathways. The amount of [14C]2-DG-P labeling may reflect the metabolic requirements for support of synaptic depolarization as well as that supporting action potentials.
Response of ventral pallidal neurons to amygdala stimulation and its modulation by dopamine projections to nucleus accumbens
Authors: Yim C. Y. , Mogenson G. J.
Published: December 2017

It has been shown that the nucleus accumbens receives input from the amygdala and that mesolimbic dopaminergic projection from the ventral tegmental area (VTA) modulates the response of accumbens neurons to amygdala input. Since the nucleus accumbens projects to the ventral pallidum, the purpose of this study was to investigate, using electrophysiological techniques, whether or not the nucleus accumbens relays the projection from the amygdala to the ventral pallidum and whether or not the mesolimbic dopamine projection interacts with this pathway. Extracellular single-unit recordings were obtained from the ventral pallidum of urethan-anesthetized rats, and the responses of these neurons to electrical stimulation of the amygdala were investigated. Of 392 neurons tested, 36% were inhibited and 11% were excited following amygdala stimulation. Latency of onset of inhibitory responses showed a bimodal distribution with peaks in the ranges of 4-6 ms and 16-18 ms, respectively. Fifty-four percent of inhibitory responses with latencies greater than 12 ms were attenuated by 1) injection of procaine hydrochloride into the nucleus accumbens, or 2) injection of d-amphetamine into the nucleus accumbens, or 3) stimulation of VTA with a train of 10 pulses (10 Hz) prior to stimulation of amygdala. Acute administration of haloperidol intraperitoneally or injection of 6-hydroxydopamine into the ipsilateral VTA, 2 days prior to the recording experiment, reduced the attenuating effects of intra-accumbens injection of d-amphetamine and VTA conditioning stimulations on the inhibitory response of ventral pallidal neurons to amygdala stimulation. These results support the hypothesis that the nucleus accumbens provides a link between the amygdala and the ventral pallidum. Since the amygdala is a limbic structure and the ventral pallidum has possible connections with the extrapyramidal motor system, it is suggested that the amygdala to nucleus accumbens to ventral pallidum projection may be a bridge between the limbic and motor systems. We also suggest that this relay of output from the amygdala to the ventral pallidum via the nucleus accumbens is under the modulating influence of the mesolimbic dopamine projection from the ventral tegmental area.
Swimming pattern in intact and decerebrated stingrays
Authors: Droge M. H. , Leonard R. B.
Published: December 2017

Stingrays swim with a rostral-to-caudal wave of elevation and depression of the enlarged pectoral fins. The present study compares the timing relations of swimming before and after decerebration in the same animals using electromyograms (EMGs). EMGs were recorded from several freely swimming, intact animals. Most recordings, however, were from stingrays suspended by vertebral clamps. Activity recorded from restrained animals exhibited the same timing relations as freely swimming animals. Therefore, the restrained preparation was used to compare locomotor rhythm in intact and decerebrate stingrays. The delay from the onset of activity recorded at a rostral segment to the onset of activity at successively caudal recording sites (intersegmental delay) was linearly related to the extent of the segmental separation. This relation was not changed by decerebration. Both the intersegmental delay and the EMG burst duration were linearly related to the period of the swim cycle. The intercepts for both relations fell around the origin. Therefore, stingray swimming demonstrates constant phase coupling. Neither the slopes nor the intercepts of the coupling relations were altered by decerebration. Histological examination of the fins indicates that at least two types of muscles exist. Superficial muscle is activated during slow swimming, while the deeper muscle is recruited during faster swimming.
Effects of rearing kittens with convergent strabismus on development of receptive-field properties in striate cortex neurons
Authors: Chino Y. M. , Shansky M. S. , Jankowski W. L. , Banser F. A.
Published: December 2017

Convergent strabismus was induced surgically in seven kittens at 3 wk of age. Recordings were made in 131 cells in the striate cortex of these strabismic kittens after maturation, and the results were compared to the data obtained from 140 striate neurons in normally reared cats. All our samples had receptive fields (RFs) within 5 degrees of the area centralis. The spatial and temporal response properties were quantitatively analyzed by using drifting sinusoidal gratings of various contrasts as well as spatial and temporal frequencies. In contrast to other reports, the receptive-field properties of the striate neurons exclusively driven or dominated by the deviating eye were quite abnormal. The spatial frequency tuning curves in strabismic cats were different from those obtained from normals in that the optimal spatial frequencies and spatial resolutions were shifted to lower values and the bandwidths were significantly broader. The contrast-response functions show that contrast thresholds, measured at the optimal spatial frequency, were significantly higher and the slope of the functions much flatter in strabismic animals. Moreover, receptive-field sizes were much larger and the sharpness of orientation tuning was reduced in strabismic cats. Direction selectivity, however, was normal in those animals. The temporal frequency tuning curves were also abnormal, particularly in that temporal resolution was considerably reduced in strabismic cats compared with normally reared cats. In addition, many cells in strabismic animals exhibited much longer latencies to visual and optic chiasm (OX) stimulations. All these effects, to our great surprise, were also observed in the striate units controlled by the nondeviating eye, although the magnitude of the alteration depends on the receptive-field property. The abnormalities found in spatial frequency tuning, contrast thresholds, and RF sizes were as severe as those revealed in the deviating eye. On the other hand, the effects on other RF properties were minimal or less severe. These physiological findings correspond very well with results from behavioral measurements of spatial contrast sensitivity in the same cats reported elsewhere. It is concluded from these results that the nondeviating eye in convergent strabismic animals, and perhaps humans, should not always be presumed "normal."
Responses of cat peroneus brevis muscle spindle afferents during recovery from nerve-crush injury
Authors: Hyde D. , Scott J. J.
Published: December 2017

The responses of regenerated muscle spindle afferents to ramp-and-hold stretch of the peroneus brevis muscle in the cat were recorded at periods from 26 to 140 days after crushing the common peroneal nerve. During the early stages of recovery a number of abnormally responding afferents were observed. The most marked abnormality was the absence or rapid failure of firing during the held phase of the stretch. The proportion of abnormal afferents became less as recovery progressed. Electrical stimulation of isolated static and dynamic gamma-axons increased the firing rates of the afferents during the ramp-and-hold stretch such that a gamma static axon would restore the response of an abnormal afferent to the held phase of the stretch. The regenerated afferents have been classified according to the degree of abnormality displayed. These abnormalities can be accounted for by assuming a subtractive reduction in the firing frequency of the regenerated afferents. This is attributed to an increase in the pacemaker threshold.
Factors that control amplitude of EPSPs in dendritic neurons
Authors: Lev-Tov A. , Miller J. P. , Burke R. E. , Rall W.
Published: December 2017

We have used a computer-based mathematical model of alpha-motoneurons and of group Ia synaptic input to them, based on anatomical and electrophysiological data from the cat spinal cord, in order to examine the effects of variations in neuron size and input resistance and of conductance magnitude and duration on the generation of excitatory postsynaptic potentials (EPSPs). The first set of calculations were designed to test the possible role of nonlinear EPSP summation in producing a differential distribution of posttetanic potentiation of group Ia EPSPs, described in the preceding paper (25; see also Refs. 26, 27). The results suggest that the negative correlations observed between the degree of posttetanic potentiation of Ia EPSPs and initial (pretetanic) EPSP amplitude as well as with the input resistance of the postsynaptic motoneurons can be explained in part by the inherent non-linearity between conductance change and the resultant potential change at chemical synapses. In a second set of calculations, we used the same model system to evaluate the effects produced by variations in neuronal membrane area, input resistance, and specific membrane resistivity, as well as of the density of excitatory synaptic input on the peak amplitude of EPSPs. With parameters constrained to match the properties of alpha-motoneurons and group Ia synaptic input, EPSP amplitudes were most sensitive to changes in synaptic density and were much less sensitive to alterations in neuron input resistance and specific membrane resistivity when synaptic density was constant.
Sites of action of segmental and descending control of transmission on pathways mediating PAD of Ia- and Ib-afferent fibers in cat spinal cord
Authors: Rudomin P. , Jimenez I. , Solodkin M. , Duenas S.
Published: December 2017

The present series of investigations was aimed to disclose the possible sites of action of excitatory and inhibitory inputs on tho-interneuron pathway mediating the primary afferent depolarization (PAD) of group I afferents of extensor muscles in the cat spinal cord. To this end we compared the effects produced by stimulation of segmental and descending pathways on the PAD generated either by stimulation of group I fibers of flexor muscles or by intraspinal microstimulation. It was assumed that under the appropriate conditions the PAD produced by intraspinal microstimulation results from the activation of the last-order interneurons in the PAD pathway and may, therefore, allow detection pathway. The PAD of single group I afferent fibers was determined in barbiturate-anesthetized preparations by measuring the test stimulus current required to maintain a constant probability of antidromic firing. This was achieved by means of a feedback system that continuously adjusted the test stimulus current to the required values. The PAD of individual group Ia gastrocnemius soleus (GS) fibers that is produced by activation of the low-threshold afferents of the posterior biceps and semitendinosus nerve was found to be inhibited by conditioning stimulation of the relatively low-threshold cutaneous fibers and also by stimulation of supraspinal structures such as the ipsilateral brain stem reticular formation, the contralateral red nucleus, and the contralateral pyramidal tract. In contrast, the PAD of group Ia fibers produced by microstimulation applied in the intermediate nucleus could be inhibited only by stimulation of the brain stem reticular formation but not by stimulation of the other descending inputs presently tested or by stimulation of cutaneous nerves. PAD of group Ia fibers was produced also by microstimulation applied within the motor nucleus. However, in most fibers the resulting PAD could not be inhibited either by stimulation of the brain stem reticular formation, the red nucleus, the pyramidal tract, or cutaneous nerves. Stimulation of cutaneous and of flexor muscle nerves of the brain stem reticular formation, the red nucleus, and the pyramidal tract all produced PAD of the group Ib GS fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
Receptive-field properties of transcallosal visual cortical neurons in the normal and reeler mouse
Authors: Simmons P. A. , Pearlman A. L.
Published: December 2017

The receptive-field properties of neurons in the striate visual cortex of normal and reeler mutant mice were studied with single-unit recording methods in order to determine whether the connections underlying these properties are altered by the developmental abnormality in neuronal position that characterizes reeler neocortex. Neurons with a projection through the corpus callosum were selected for study because they form a physiologically identifiable class of visual cortical neurons with a characteristic distribution of receptive-field properties that can be compared for normal and reeler cortex. Transcallosal cortical neurons in area 17 near its border with area 18a were identified by antidromic stimulation delivered through bipolar electrodes in the contralateral cortex. A computer controlled the visual stimuli, data acquisition, and analysis. Transcallosal neurons were principally found in layers II-III and V in the normal cortex and in a broand band deep in the reeler cortex. These populations had similar distributions of antidromic latencies, indicating that the neurons sampled from normal and reeler cortex were taken from populations with similar axonal diameters and soma sizes. The receptive-field properties of 46 units in 22 normal mice and 28 units in 11 reeler mice were characterized. Transcallosal neurons in both normal and reeler cortex were usually binocularly responsive and dominated by input from the contralateral eye. They exhibited either nonoriented (31 and 48%, respectively) or oriented (69 and 52%) receptive fields. Tuning 10 stimulus velocity was broad, with peak velocity sensitivities ranging from 1 to 1,000 degrees/s. Directional selectivity was present in 41% of normal units ad 32% of reeler units. There was no significant difference between normal and reeler cortex in the distribution of these properties. Transcallosal neurons were also examined for the presence of an inhibitory surround by comparing their responses to moving or stationary stimuli of varying sizes. Of the tested neurons, most (11/17 in normal cortex, 6/9 in reeler) showed evidence of a decrease in response to large moving stimuli. A large proportion (16/20) of normal neurons tested with stationary flashing stimuli had some degree of surround inhibition whereas significantly fewer (5/17) neurons in reeler cortex had this property. Thus, transcallosal neurons in reeler cortex less frequently had an inhibitory surround demonstrable with stationary flashing stimuli, but this difference between normal and reeler was not apparent with a moving stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)
Integrative properties of crayfish medial giant neuron: steady-state model
Authors: Glantz R. M. , Viancour T.
Published: December 2017

A quantitative morphological description of the crayfish medial giant (MG) neuron was obtained on the basis of 14 individual cells filled with lucifer yellow. The cable parameters of seven MGs were measured in the axon with two or three microelectrodes. The length constant is 4.3 +/- 0.8 mm, the membrane time constant is 3.1 +/- 0.8 ms, the input resistance is 3.6 +/- 0.2 (X10(4) alpha, the mean axon diameter is 208 +/- 34 microns. The specific membrane resistance (Rm) is 2,000 +/- 204 alpha x cm2. The specific axoplasmic resistance (Ri) is 60 +/- 29 alpha x cm and the membrane capacitance is 1.6 +/- microF/cm2. The MG is electrotonically coupled to its symmetrical homolog. The coupling coefficient is 0.46 for both steady-state signals and spike transmission. A steady-state cable model of the MG was calculated on the basis of the axonal Rm and Ri values, the electrotonic coupling coefficient to the MG symmetrical homolog, and the mean dimensions of the 14 MG neurites. The model successfully predicts geometrically determined variations in input resistance and steady-state signal attenuation. A salient feature of the MG steady-state model is the extent to which dendritic input conductance and the attenuation of steady-state voltages is determined by the large input conductance of the axon. Because of the large diameter of the MG neurites, electrotonic distances between dendrite terminals and the integrating segment are short (0.3-0.74 lambda) and the principal basis of excitatory postsynaptic potential (EPSP) attenuation is variation is local input resistance. The time integral of the electrotonic coupling potential between the MGs is diminished by 9.5-21.4% during a monosynaptic sensory EPSP. The magnitude of the inferred synaptic conductance seen at the decussation is inversely related to the electrotonic distance between the decussation and the active dendritic branch. The modest change in input resistance near the electrotonic junction is consistent with the morphological and electrotonic separation of the electrotonic junction and the sites of synaptic action on the dendrites. When the reversal potentials of monosynaptic EPSPs are measured at the integrating segment, the measurements vary systematically with the input pathway selected and overestimate the dendritic reversal potentials by up to 60%.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic organization of eighth nerve afferents to cat dorsal cochlear nucleus
Authors: Manis P. B. , Brownell W. E.
Published: December 2017

The synaptic organization of eighth nerve afferents to the dorsal cochlear nucleus (DCN) of cats was studied using extracellular field potential analyses. The eighth nerve was electrically stimulated and potentials produced in the DCN characterized using single shocks, paired shocks, repetitive stimulation, and one-dimensional current source-density (CSD) analysis. Field potentials and CSD profiles were correlated with the laminated cytoarchitecture of the DCN. At least four major temporally discrete components can be identified in field potentials evoked by a single shock to the eighth nerve. The amplitude and polarity of these events depends on the layers in which they are recorded. A brief positive-negative deflection (the P1-N1) is present in all layers but is maximal in the deeper layers 3 and 4. The N1 has a peak latency of approximately 0.8 ms in these layers. The N1 in the deep layers is followed by a large negative potential, termed the N2, with a peak latency of about 1.6 ms. In the superficial layers (1 and 2), the N1 is followed by a small positive potential (the P2) occurring nearly simultaneously with the N2, Immediately following the N2 is another negative potential that is most clearly observed in layer 2. The layer 2 negative wave is termed N3 and is also identifiable on the repolarizing phase of the N2 in layers 3 and 4. The N3 in layer 2 can be followed by a positive potential, the P4. Simultaneous with the P4 is a small negative wave ion layer 1, termed the N4. The P4-N4 complex is observed in about half the recordings. Frequency-following tests indicate that both the N1 and N2 waves can follow shock trains up to 333 Hz. The N1 remains nearly constant in amplitude up to about 300 Hz and decreases as the stimulus frequency is raised to 500 Hz. The N2 decrements more rapidly than the N1 at frequencies above about 250 Hz and is considerably reduced at 500 Hz. The N2 sometimes shows an increased amplitude (by about 20-40%) between 100 and 250 Hz. A paired-shock paradigm was used to characterize further potentials. The N1 was little affected by prior stimulation for intervals greater than 5 ms. The N2 and N3 generally showed a small facilitation for shock intervals from about 7 to 30 ms, with a return to base line at longer intervals. The N4 and P4 (when present) were profoundly depressed for intervals from 7 to about 30 ms, with recovery to control values by 50 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Spiking local interneurons as primary integrators of mechanosensory information in the locust
Authors: Siegler M. V. , Burrows M.
Published: December 2017

A population of spiking local interneurons in the metathoracic ganglion of the locust is vigorously excited by particular sensory stimuli from the hindlegs and participates in local postural reflexes. We examined the inputs from singly innervated mechanoreceptors (hairs and campaniform sensilla) to these spiking local interneurons, to nonspiking local interneurons, and to motor neurons that are also elements of local reflex pathways. Recordings were made intracellularly from the interneurons and motor neurons and extracellularly from afferent fibers. The physiological evidence is consistent with the spiking local interneurons being excited by direct, chemically mediated synaptic inputs from the afferents. Each afferent spike is followed at a constant latency by an excitatory postsynaptic potential (EPSP) in a spiking local interneuron, even at instantaneous frequencies as high as 300 Hz. The estimated synaptic delay is 1.5 ms, similar to that measured at other presumed monosynaptic connections within the same ganglion. Cobalt stains of individual interneurons, and of the central projections of afferent fibers show that both branch within the same ventral region of neuropil. Afferents from several hairs and campaniform sensilla converge on an individual spiking local interneuron. One interneuron is shown to receive inputs from at least seven hairs and four campaniform sensilla, but these represent only a tiny fraction of the total number of such sensilla on a hindleg. Practical limitations to the number of sensilla that can be tested for each interneuron means that the degree of convergence is likely to be considerably underestimated. We found no evidence that nonspiking local interneurons or motor neurons receive direct inputs from the afferents tested. Neurons of both types are, however, affected by stimulation of individual hairs, and the resulting pattern of postsynaptic potentials (PSPs) is similar to the pattern of spikes evoked in the spiking local interneurons. We infer from the evidence presented here and elsewhere (10, 11) that the spiking local interneurons are involved in at least two types of pathways for local interactions: 1) sensory neuron-spiking local interneuron-motor neuron, and 2) sensory neuron-spiking local interneuron-nonspiking local interneuron-motor neuron. We conclude that the spiking local interneurons are major elements in the primary integration of inputs from external receptors on the hindlegs.
Summation of excitatory postsynaptic potentials in hippocampal pyramidal cells
Authors: Langmoen I. A. , Andersen P.
Published: December 2017

The summation of excitatory postsynaptic potentials (EPSPs) generated in separate parts of the dendritic tree of hippocampal pyramidal cells has been investigated using the in vitro slice preparation. Two separate inputs with known synaptic location were used. The EPSP produced by simultaneous activation of the two inputs (observed sum) was compared to the algebraic sum of the individual EPSPs. Small-amplitude EPSPs (0.5-1.5 mV) added linearly. The shortest distance between the two synaptic groups was 75 micron. With larger amplitudes (greater than 2.5 mV), the EPSP summated nonlinearly. The nonlinear summation was reduced by moderate hyperpolarizations (2-10 mV) of the soma membrane. Also, large EPSPs (greater than 2.5 mV) summated linearly when the peak of the summed EPSP was brought close to the equilibrium potential for the inhibitory postsynaptic potential (IPSP) (EIPSP). When the EPSP peak was made more negative than the EIPSP, summation was again nonlinear but the algebraic sum was now smaller than the observed EPSP sum, i.e., the direction of the nonlinearity was reversed. EPSP summation was linear after the IPSP had been blocked by benzyl penicillin application. We conclude that separate EPSPs in hippocampal pyramids (minimal separation, 75 micron) add linearly but that the addition of an IPSP may complicate this picture. No evidence was found for interaction between the different populations of excitatory synapses.
Fast ballistic arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey. II. Effects of unilateral dentate lesion on discharge of precentral cortical neurons and reaction time
Authors: Spidalieri G. , Busby L. , Lamarre Y.
Published: December 2017

Single-unit recordings from motor cortex (area 4) were obtained before and after dentate lesion in two monkeys executing fast elbow flexions and extensions in response to randomly presented visual, auditory, and somesthetic stimuli. There were no starting or ending reference points or preparatory signals. Monkeys were trained to perform movements larger than 15 degrees within 500 ms of the stimulus presentation. After electrolytic lesion of the dentate nucleus ipsilateral to the trained arm, changes in reaction time (RT) were observed. Mean daily RTs of movements triggered by light and sound were lengthened by 50-70 ms. RTs of movements triggered by somesthetic stimuli were not changed in one monkey, whereas a small increase of only 20 ms was observed in the other animal. Spontaneous firing of precentral neurons was about the same before and after dentate lesion. However, movement-related responses of cortical neurons were affected by the lesion. Whenever there was an increase in RT according to the triggering stimuli, a corresponding increase in the response time of neurons (RS) appeared. Both RS and RT increased by the same amount when movements were triggered by visual and auditory stimuli, whereas they remained about the same when somesthetic stimuli were used to trigger movements. In contrast, the time interval between the appearance of the change of neuronal firing and onset of arm displacement (RM) was not modified after the lesion. Gating of sensory conditioning inputs and modification of RT by the presentation of more than one stimulus were not abolished by dentate lesion. As a whole, the effects of dentate lesion on motor cortical neurons are consistent with the hypothesis that the neocerebellum controls the initiation of simple ballistic limb movements by controlling the discharge of motor cortex neurons. The effects could be attributed to the withdrawal of a facilitatory influence of dentate neurons on the motor cortical cells, particularly for movements triggered by teleceptive inputs.
Responses to head tilt in cat central vestibular neurons. I. Direction of maximum sensitivity
Authors: Schor R. H. , Miller A. D. , Tomko D. L.
Published: December 2017

Responses to head tilt were recorded from vestibular neurons in and around the lateral vestibular nucleus (LVN) of the decerebrate cat. Each animal had all six semicircular canals rendered nonfunctional by a plugging procedure. Each cell was studied by slowly tilting the cat, using one or both of two paradigms. In the first method, sinusoidal tilts (0.05 or 0.1 Hz) were used to produce bidirectional stimuli in up to 12 pairs of directions, including left/right (roll tilt) and fore/aft (pitch). The second method imposed a constant 10 degree tilt; the direction of the tilt was rotated around the animal by an appropriate combination of roll and pitch motions. Neurons responded by maximally increasing their discharge frequency in a particular direction of head tilt from the horizontal. Each cell's response could be described by a vector in the animal's horizontal plane whose orientation is given by the direction of the most effective stimulus and whose length represents the neuron's maximal sensitivity to tilt. The two methods of stimulation yielded equivalent response vectors. Response vectors were obtained for 100 neurons. The distribution of vector directions for these vestibular neurons was not uniform; there was a conspicuous absence of neurons with fore/aft-directed vectors. The sensitivity of these cells (length of the response vector) ranged from 10 to 230 impulses X s-1 X g-1 (median 50). Neurons whose vectors lay in the ipsilateral half-plane (which would be excited by ear-down tilt) tended to be less sensitive than those with contralateral vectors. Neurons excited by ear-up tilt tended to be located ventrally in the LVN, while those excited by ear-down tilt were more evenly distributed. There was no other obvious correlation of vector orientation with the anatomical locus of the cell in the LVN. The directional selectivity of the responses of these neurons to head tilts are similar to those previously reported tin utricular afferents. The broad distribution of response vector orientations provides an appropriate substrate for vestibulospinal reflexes to a wide variety of head tilts.