bluuebunny/crossref_metadata_2025 huggingface dataset:
Human Brain Regions Involved in Direction Discrimination
Authors: Cornette L. , Dupont P. , Rosier A. , Sunaert S. , Hecke P. Van , Michiels J. , Mortelmans L. , Orban G. A.
Published: December 2017

Cornette, L., P. Dupont, A. Rosier, S. Sunaert, P. Van Hecke, J. Michiels, L. Mortelmans, and G. A. Orban. Human brain regions involved in direction discrimination. J. Neurophysiol. 79: 2749–2765, 1998. To obtain further evidence for the functional specialization and task-dependent processing in the human visual system, we used positron emission tomography to compare regional cerebral blood flow in two direction discrimination tasks and four control tasks. The stimulus configuration, which was identical in all tasks, included the motion of a random dot pattern, dimming of a fixation point, and a tone burst. The discrimination tasks comprised the identification of motion direction and successive direction discrimination. The control tasks were motion detection, dimming detection, tone detection, and passive viewing. There was little difference in the activation patterns evoked by the three detection tasks except for decreased activity in the parietal cortex during the detection of a tone. Thus attention to a nonvisual stimulus modulated different visual cortical regions nonuniformly. Comparison of successive discrimination with motion detection yielded significant activation in the right fusiform gyrus, right lingual gyrus, right frontal operculum, left inferior frontal gyrus, and right thalamus. The fusiform and opercular activation sites persisted even after subtracting direction identification from successive discrimination, indicating their involvement in temporal comparison. Functional magnetic resonance imaging (fMRI) experiments confirmed the weak nature of the activation of human MT/V5 by successive direction discrimination but also indicated the involvement of an inferior satellite of human MT/V5. The fMRI experiments moreover confirmed the involvement of human V3A, lingual, and parietal regions in successive discrimination. Our results provide further evidence for the functional specialization of the human visual system because the cortical regions involved in direction discrimination partially differ from those involved in orientation discrimination. They also support the principle of task-dependent visual processing and indicate that the right fusiform gyrus participates in temporal comparison, irrespective of the stimulus attribute.
Temporal Integration Can Readily Switch Between Sublinear and Supralinear Summation
Authors: Margulis Michael , Tang Cha-Min
Published: December 2017

Margulis, Michael and Cha-Min Tang. Temporal integration can readily switch between sublinear and supralinear summation. J. Neurophysiol. 79: 2809–2813, 1998. Temporal summation at dendrites of cultured rat hippocampal neurons was examined as a function of the interval separating two dendritic inputs. A novel method that relies on single-mode optical fibers to achieve rapid photorelease of glutamate was developed. Dendritic excitation achieved with this approach resembles that associated with miniature excitatory postsynaptic currents (mEPSCs), but the strengths, sites, and timing of the inputs can be precisely controlled. Dendritic summation deviated markedly from behavior predicted by passive cable theory. Subthreshold temporal summation varied as a triphasic function of the interpulse interval. As the interpulse interval decreased, local dendritic Na+ conductances were recruited to generate a marked transition from sublinear to supralinear summation. These results suggest that active dendritic conductances acting in concert with passive cable properties may serve to boost coincident synaptic inputs and attenuate noncoincident inputs.
Three-Dimensional Analysis of Spontaneous and Thalamically Evoked Gamma Oscillations in Auditory Cortex
Authors: Sukov William , Barth Daniel S.
Published: December 2017

Sukov, William and Daniel S. Barth. Three-dimensional analysis of spontaneous and thalamically evoked gamma oscillations in auditory cortex. J. Neurophysiol. 79: 2875–2884, 1998. The purpose of this study was to investigate interactions among laminar cell populations producing spontaneous and evoked high-frequency (∼40 Hz) gamma oscillations in auditory cortex. Electrocortical oscillations were recorded using a 64-channel epipial electrode array and a 16-channel linear laminar electrode array while electrical stimulation was delivered to the posterior intralaminar (PIL) nucleus. Spontaneous gamma oscillations, and those evoked by PIL stimulation, are confined to a location overlapping primary and secondary auditory cortex. Current source-density and principal components analysis of laminar recordings at this site indicate that the auditory evoked potential (AEP) complex is characterized by a stereotyped asynchronous activation of supra- and infragranular cell populations. Similar analysis of spontaneous and evoked gamma waves reveals a close spatiotemporal similarity to the laminar AEP, indicating rhythmic interactions between supra- and infragranular cell groups during these oscillatory phenomena. We conclude that neural circuit interactions producing the laminar AEP onset in auditory cortex are the same as those generating evoked and spontaneous gamma oscillations.
Contribution of Ca2+-Activated K+ Channels to Central Chemosensitivity in Cultivated Neurons of Fetal Rat Medulla
Authors: Wellner-Kienitz M.-C. , Shams H. , Scheid P.
Published: December 2017

Wellner-Kienitz, M.-C., H. Shams, and P. Scheid. Contribution of Ca2+-activated K+ channels to central chemosensitivity in cultivated neurons of fetal rat medulla. J. Neurophysiol. 79: 2885–2894, 1998. Neurons in fetal rat medullary slices that exhibited spontaneous electrical activity after blockade of synaptic transmission were investigated for their response to decreases in extracellular pH. Increases in [H+] (induced either by fixed acid or increases in PCO2) induced a significant increase in the frequency of action potentials, associated with a membrane depolarization, and/or increases in the slope of the interspike depolarization. In addition, CO2/H+ prolonged the repolarizing phase of action potentials and reduced the afterhyperpolarization, suggesting that K+ channels were the primary site of CO2/H+ action. The type of K+ channel that was modulated by CO2/H+ was identified by application of agents that inhibited Ca2+-activated K+ channels either directly (tetraethylammonium chloride, TEA) or indirectly (Cd2+ ions) by inhibiting Ca2+ influx. CO2/H+ effects on neuronal activity were abolished after application of these blockers. The contribution of Ca2+-activated K+ channels to H+ sensitivity of these neurons was confirmed further in voltage-clamp experiments in which outward rectifying I-V curves were recorded that revealed a zero current potential of −70 mV. CO2/H+ induced a prominent reduction in outward currents and shifted the zero current potential to more positive membrane potentials (mean −63 mV). The CO2/H+-sensitive current reversed at −72 mV and was blocked by external application of TEA. It is concluded that CO2/H+ exerts its stimulatory effects on fetal medullary neurons by inhibition of Ca2+-activated K+ channels, either directly or indirectly, by blocking voltage-dependent Ca2+ channels, which in turn results in a reduction of K+ efflux and in cell depolarization.
Effects of Intrathecal α1- and α2-Noradrenergic Agonists and Norepinephrine on Locomotion in Chronic Spinal Cats
Authors: Chau Connie , Barbeau Hugues , Rossignol Serge
Published: December 2017

Chau, Connie, Hugues Barbeau, and Serge Rossignol. Effects of intrathecal α1- and α2-noradrenergic agonists and norepinephrine on locomotion in chronic spinal cats. J. Neurophysiol. 79: 2941–2963, 1998. Noradrenergic drugs, acting on α adrenoceptors, have been found to play an important role in the initiation and modulation of locomotor pattern in adult cats after spinal cord transection. There are at least two subtypes of α adrenoceptors, α1 and α2 adrenoceptors. The aim of this study was to investigate the effects of selective α1 and α2 agonists in the initiation and modulation of locomotion in adult chronic cats in the early and late stages after complete transection at T13. Five cats, chronically implanted with an intrathecal cannula and electromyographic (EMG) electrodes were used in this study. Noradrenergic drugs including α2 agonists (clonidine, tizanidine, and oxymetazoline) and an antagonist, yohimbine, one α1 agonist (methoxamine), and a blocker, prazosin, as well as norepinephrine were injected intrathecally. EMG activity synchronized to video images of the hindlimbs were recorded before and after each drug injection. The results show differential effects of α1 and α2 agonists in the initiation of locomotion in early spinal cats (i.e., in the first week or so when there is no spontaneous locomotion) and in the modulation of locomotion and cutaneous reflexes in the late-spinal cats (i.e., when cats have recovered spontaneous locomotion). In early spinal cats, all three α2 agonists were found to initiate locomotion, although their action had a different time course. The α1 agonist methoxamine induced bouts of nice locomotor activity in three spinal cats some hours after injection but only induced sustained locomotion in one cat in which the effects were blocked by the α1 antagonist prazosin. In late spinal cats, although α2 agonists markedly increased the cycle duration and flexor muscle burst duration and decreased the weight support or extensor activity (effects blocked by an α2 antagonist, yohimbine), α1 agonist increased the weight support and primarily the extensor activity of the hindlimbs without markedly changing the timing of the step cycle. Although α2 agonists, especially clonidine, markedly reduced the cutaneous excitability and augmented the foot drag, the α1 agonist was found to increase the cutaneous reflex excitability. This is in line with previously reported differential effects of activation of the two receptors on motoneuron excitability and reflex transmission. Noradrenaline, the neurotransmitter itself, increased the cycle duration and at the same time retained the cutaneous excitability, thus exerting both α1 and α2 effects. This work therefore suggests that different subclasses of noradrenergic drugs could be used to more specifically target aspects of locomotor deficits in patients after spinal injury or diseases.
Cooperative Mechanisms Between Leg Joints ofCarausius morosusI. Nonspiking Interneurons That Contribute to Interjoint Coordination
Authors: Brunn Dennis E.
Published: December 2017

Brunn, Dennis E. Cooperative mechanisms between leg joints of Carausius morosus. I. Nonspiking interneurons that contribute to interjoint coordination. J. Neurophysiol. 79: 2964–2976, 1998. Three nonspiking interneurons are described in this paper that influence the activity of the motor neurons of three muscles of the proximal leg joints of the stick insect. Interneurons were recorded and stained intracellularly by glass microelectrodes; motor neurons were recorded extracellularly with oil-hook electrodes. The motor neurons innervate the two subcoxal muscles, the protractor and retractor coxae, and the thoracic part of the depressor trochanteris muscle. The latter spans the subcoxal joint before inserting the trochanter, thus coupling the two proximal joints mechanically. The three interneurons are briefly described here. First, interneuron NS 1 was known to become more excited during the swing phase of the rear and the stance phase of the middle leg. When depolarized it excited several motor neurons of the retractor coxae. This investigation revealed that it inhibits the activity of protractor and thoracic depressor motor neurons when depolarized as well. In a pilocarpine-activated animal, the membrane potential showed oscillations in phase with the activity of protractor motor neurons, suggesting that NS 1 might contribute to the transition from swing to stance movement. Second, interneuron NS 2 inhibits motor neurons of protractor and thoracic depressor when depolarized. In both a quiescent and a pilocarpine-activated animal, hyperpolarizing stimuli excite motor neurons of both muscles via disinhibition. In one active animal the disinhibiting stimuli were sufficient to generate swing-like movements of the leg. In pilocarpine-activated preparations the membrane potential oscillated in correlation with the motor neuronal activity of the protractor coxae and thoracic depressor muscle. Hyperpolarizing stimuli induced or reinforced the protractor and thoracic depressor bursts and inhibited the activity of the motor neurons of the retractor coxae muscle, the antagonistic muscle of the protractor. Therefore interneuron NS 2 can be regarded as an important premotor interneuron for the switching from stance to swing and from swing to stance. Finally, interneuron NS 3 inhibits the spontaneously active motor neurons of both motor neuron pools in the quiescent animal. During pilocarpine-induced protractor bursts, depolarizing stimuli applied to the interneuron excited several protractor motor neurons with large action potentials and one motor neuron of the thoracic depressor. No oscillations of the membrane potentials were observed. Therefore this interneuron might contribute to the generation of rapid leg movements. The results demonstrated that the two proximal joints are coupled not only mechanically but also neurally and that the thoracic part of the depressor appears to function as a part of the swing-generating system.
Cooperative Mechanisms Between Leg Joints ofCarausius morosusII. Motor Neuron Activity and Influence of ConditionalBursting Interneuron
Authors: Brunn Dennis E. , Heuer Antje
Published: December 2017

Brunn, Dennis E. and Antje Heuer. Cooperative mechanisms between leg joints of Carausius morosus. II. Motor neuron activity and influence of conditional bursting interneuron. J. Neurophysiol. 79: 2977–2985, 1998. The activity of the motor neuron pools of the protractor coxae muscle and of the thoracic part of the depressor trochanteris muscle during forward walking in the stick insect was investigated, and a spiking local interneuron, able to produce “endogenous bursting” and innervating both motor neuron pools, was identified. Extracellular recordings of the motor neurons innervating the protractor and the thoracic depressor of front, middle, and rear legs, respectively, were made with oil-hook electrodes from the peripheral nerves nl2c and nl4a while the animals were walking on a styrofoam treadwheel. The corresponding leg movements were registered and phase histograms were created with the software Spike2. Intracellular recordings were made in the neuropile of the metathoracic ganglion with glass electrodes filled with the dye Lucifer yellow. In all three legs measured (front, middle, and rear), both motor neuron pools increased their activity during the swing movement. The increase in the activity of the protractor motor neurons started at the end of the stance ∼100 ms before reaching the posterior extreme position (PEP), and the activity of the large-sized depressor motor neurons increased as soon as the tarsus was lifted at the PEP. A local spiking interneuron was identified that excited both motor neuron pools. In 4 of 23 recordings the interneuron started to burst in synchrony with protractor and thoracic depressor motor neurons. During bursting a depolarizing stimulus reinforced and a hyperpolarizing stimulus inhibited the activity of both motor neuron pools. Thus we conclude that the thoracic part of the depressor trochanteris muscle might be a component of the neuromuscular system that shapes the swing movement. The two proximal joints, subcoxal and coxa-trochanter, connected mechanically via the thoracic part of the depressor trochanteris muscle, are also connected neurally by segmental and intersegmental spiking interneurons (this paper) and by nonspiking local interneurons (see companion paper).
Neurophysiological Correlates of Unconditioned and Conditioned Feeding Behavior in the Pond SnailLymnaea stagnalis
Authors: Staras Kevin , Kemenes György , Benjamin Paul R.
Published: December 2017

Staras, Kevin, György Kemenes, and Paul R. Benjamin. Neurophysiological correlates of unconditioned and conditioned feeding behavior in the pond snail Lymnaea stagnalis. J. Neurophysiol. 79: 3030–3040, 1998. We used a behavioral appetitive learning paradigm followed by electrophysiological analysis to investigate the neuronal expression of appetitive conditioning in Lymnaea. We first established the levels of unconditioned and conditioned feeding responses in intact animals. We then demonstrated that neuronal correlates of both unconditioned responses to touch and food and a conditioned response to touch could be found in semi-intact preparations of the same animals that had been subjected to behavioral tests and conditioning trials. In the conditioning experiments, the experimental animals received 15 trials in which touch to the lips, the conditioned stimulus (CS), was paired with sucrose, the unconditioned food stimulus (US). Control animals received 15 presentations of either CS or US, or both, applied in a random manner. After training, a strong conditioned response to touch was established in the experimental but not in the control groups. For subsequent electrophysiological analysis of posttraining neuronal responses to the touch CS, semi-intact preparations were set up from the same animals that had been behaviorally conditioned or subjected to control procedures. Intracellular recordings, made from previously identified motoneurons of the feeding system, allowed the fictive feeding response to the CS to be monitored. In experimental preparations, touch applied to the lips evoked significantly more fictive feeding cycles than in controls, and this demonstrated the existence of a neurophysiological correlate of the appetitively conditioned response observed in the whole animals.
Functional Specialization in Auditory Cortex: Responses to Frequency-Modulated Stimuli in the Cat's Posterior Auditory Field
Authors: Heil Peter , Irvine Dexter R. F.
Published: December 2017

Heil, Peter and Dexter R. F. Irvine. Functional specialization in auditory cortex: responses to frequency-modulated stimuli in the cat's posterior auditory field. J. Neurophysiol. 79: 3041–3059, 1998. The mammalian auditory cortex contains multiple fields but their functional role is poorly understood. Here we examine the responses of single neurons in the posterior auditory field (P) of barbiturate- and ketamine-anesthetized cats to frequency-modulated (FM) sweeps. FM sweeps traversed the excitatory response area of the neuron under study, and FM direction and the linear rate of change of frequency (RCF) were varied systematically. In some neurons, sweeps of different sound pressure levels (SPLs) also were tested. The response magnitude (number of spikes corrected for spontaneous activity) of nearly all field P neurons varied with RCF. RCF response functions displayed a variety of shapes, but most functions were of low-pass characteristic or peaked at rather low RCFs (<100 kHz/s). Neurons with strong responses to high RCFs (high-pass or nonselective RCF response function characteristics) all displayed spike count—SPL functions to tone burst onsets that were monotonic or weakly nonmonotonic. RCF response functions and best RCFs often changed with SPL. For most neurons, FM directional sensitivity, quantified by a directional sensitivity (DS) index, also varied with RCF and SPL, but the mean and width of the distribution of DS indices across all neurons was independent of RCF. Analysis of response timing revealed that the phasic response of a neuron is triggered when the instantaneous frequency of the sweep reaches a particular value, the effective F i. For a given neuron, values of effective F i were independent of RCF, but depended on FM direction and SPL and were associated closely with the boundaries of the neuron's frequency versus amplitude response area. The standard deviation (SD) of the latency of the first spike of the response decreased with RCF. When SD was expressed relative to the rate of change of stimulus frequency, the resulting index of frequency jitter increased with RCF and did so rather uniformly in all neurons and largely independent of SPL. These properties suggest that many FM parameters are represented by, and may be encoded in, orderly temporal patterns across different neurons in addition to the strength of responses. When compared with neurons in primary and anterior auditory fields, field P neurons respond better to relatively slow FMs. Together with previous studies of responses to modulations of amplitude, such as tone onsets, our findings suggest more generally that field P may be best suited for processing signals that vary relatively slowly over time.
Brain Stem Omnipause Neurons and the Control of CombinedEye-Head Gaze Saccades in the Alert Cat
Authors: Paré Martin , Guitton Daniel
Published: December 2017

Paré, Martin and Daniel Guitton. Brain stem omnipause neurons and the control of combined eye-head gaze saccades in the alert cat. J. Neurophysiol. 79: 3060–3076, 1998. When the head is unrestrained, rapid displacements of the visual axis—gaze shifts (eye-re-space)—are made by coordinated movements of the eyes (eye-re-head) and head (head-re-space). To address the problem of the neural control of gaze shifts, we studied and contrasted the discharges of omnipause neurons (OPNs) during a variety of combined eye-head gaze shifts and head-fixed eye saccades executed by alert cats. OPNs discharged tonically during intersaccadic intervals and at a reduced level during slow perisaccadic gaze movements sometimes accompanying saccades. Their activity ceased for the duration of the saccadic gaze shifts the animal executed, either by head-fixed eye saccades alone or by combined eye-head movements. This was true for all types of gaze shifts studied: active movements to visual targets; passive movements induced by whole-body rotation or by head rotation about stationary body; and electrically evoked movements by stimulation of the caudal part of the superior colliculus (SC), a central structure for gaze control. For combined eye-head gaze shifts, the OPN pause was therefore not correlated to the eye-in-head trajectory. For instance, in active gaze movements, the end of the pause was better correlated with the gaze end than with either the eye saccade end or the time of eye counterrotation. The hypothesis that cat OPNs participate in controlling gaze shifts is supported by these results, and also by the observation that the movements of both the eyes and the head were transiently interrupted by stimulation of OPNs during gaze shifts. However, we found that the OPN pause could be dissociated from the gaze-motor-error signal producing the gaze shift. First, OPNs resumed discharging when perturbation of head motion briefly interrupted a gaze shift before its intended amplitude was attained. Second, stimulation of caudal SC sites in head-free cat elicited large head-free gaze shifts consistent with the creation of a large gaze-motor-error signal. However, stimulation of the same sites in head-fixed cat produced small “goal-directed” eye saccades, and OPNs paused only for the duration of the latter; neither a pause nor an eye movement occurred when the same stimulation was applied with the eyes at the goal location. We conclude that OPNs can be controlled by neither a simple eye control system nor an absolute gaze control system. Our data cannot be accounted for by existing models describing the control of combined eye-head gaze shifts and therefore put new constraints on future models, which will have to incorporate all the various signals that act synergistically to control gaze shifts.
Single Olivocochlear Neurons in the Guinea Pig. I. Binaural Facilitation of Responses to High-Level Noise
Authors: Brown M. C. , Kujawa S. G. , Duca M. L.
Published: December 2017

Brown, M. C., S. G. Kujawa, and M. L. Duca. Single olivocochlear neurons in the guinea pig. I. Binaural facilitation of responses to high-level noise. J. Neurophysiol. 79: 3077–3087, 1998. Single medial olivocochlear (MOC) neurons were recorded from the cochlea of the anesthetized guinea pig. We used tones and noise presented monaurally and binaurally and measured responses for sounds up to 105 dB sound pressure level (SPL). For monaural sound, MOC neuron firing rates were usually higher for noise bursts than tone bursts, a situation not observed for afferent fibers of the auditory nerve that were sampled in the same preparations. MOC neurons also differed from afferent fibers in having less saturation of response. Some MOC neurons had responses that continued to increase even at high sound levels. Differences between MOC and afferent responses suggest that there is convergence in the pathway to olivocochlear neurons, possibly a combination of inputs that are at the characteristic frequency (CF) with others that are off the CF. Opposite-ear noise almost always facilitated the responses of MOC neurons to sounds in the main ear, the ear that best drives the unit. This binaural facilitation depends on several characteristics that pertain to the main ear: it is higher in neurons having a contralateral main ear (contra units), it is higher at main-ear sound levels that are moderate (∼65 dB SPL), and it is higher in neurons with low discharge rates to main-ear stimuli. Facilitation also depends on parameters of the opposite-ear sound: facilitation increases with noise level in the opposite ear until saturating, is greater for continuous noise than noise bursts, and is usually greater for noise than for tones. Using optimal opposite-ear facilitators and high-level stimuli, the firing rates of olivocochlear neurons range up to 140 spikes/s, whereas for moderate-level monaural stimuli the rates are <80 spikes/s. At high sound levels, firing rates of olivocochlear neurons increase with CF, an increase that may compensate for the known lower effectiveness of olivocochlear synapses on outer hair cells responding to high frequencies. Overall, our results demonstrate a high MOC response for binaural noise and suggest a prominent role for the MOC system in environments containing binaural noise of high level.
Voltage-Clamp Analysis and Computer Simulation of a Novel Cesium-Resistant A-Current in Guinea Pig Laterodorsal Tegmental Neurons
Authors: Sanchez Russell M. , Surkis Alisa , Leonard Christopher S.
Published: December 2017

Sanchez, Russell M., Alisa Surkis, and Christopher S. Leonard. Voltage-clamp analysis and computer simulation of a novel cesium-resistant A-current in guinea pig laterodorsal tegmental neurons. J. Neurophysiol. 79: 3111–3126, 1998. Increased firing of cholinergic neurons of the laterodorsal tegmental nucleus (LDT) plays a critical role in generating the behavioral states of arousal and rapid eye movement sleep. The majority of these neurons exhibit a prominent transient potassium current ( I A) that shapes firing but the properties of which have not been examined in detail. Although I A has been reported to be blocked by intracellular cesium, the I A in LDT neurons appeared resistant to intracellular cesium. The present study compared the properties of this cesium-resistant current to those typically ascribed to I A. Whole cell recordings were obtained from LDT neurons ( n = 67) in brain slices with potassium- or cesium-containing pipette solutions. A transient current was observed in cells dialyzed with each solution (KGluc-85%; CsGluc-79%). However, in cesium-dialyzed neurons, the transient current was inward at test potentials negative to about −35 mV. Extracellular 4-aminopyridine (4-AP; 2–5 mM) blocked both inward and outward current, suggesting the inward current was reversed I A rather than an unmasked transient calcium current as previously suggested. This conclusion was supported by increasing [K]o from 5 to 15 mM, which shifted the reversal potential positively for both inward and outward current (+17.89 ± 0.41 mV; mean ± SE). Moreover, recovery from inactivation was rapid (τ = 15.5 ± 4 ms; n = 4), as reported for I A, and both inward and outward transient current persisted in calcium-free solution [0 calcium/4 mM ethylene glycol-bis(β-aminoethyl ether)- N,N,N′,N′-tetraacetic acid; n = 4] and during cadmium-blockade of calcium currents ( n = 3). Finally, the transient current was blocked by intracellular 4-AP indicating that adequate dialysis occurred during the recordings. Thus the Cs-resistant current is a subthreshold I A. We also estimated the voltage-dependence of activation ( V 1/2 = −45.8 ± 2 mV, k = 5.21 ± 0.62 mV, n = 6) and inactivation ( V 1/2 = −59.0 ± 2.38 mV, k = −5.4 ± 0.49 mV, n = 3) of this current. Computer simulations using a morphologically accurate model cell indicated that except for the extreme case of only distal A-channels and a high intracellular resistivity, our parameter estimates were good approximations. In conclusion, guinea pig LDT neurons express subthreshold A-channels that are resistant to intracellular cesium ions. This suggests that these channels differ fundamentally in their ion permeation mechanism from those previously studied. It remains to be determined if Cs+ resistance is common among brain A-channels or if this property is conferred by known A-channel subunits.
Model of Cortical-Basal Ganglionic Processing: Encoding the Serial Order of Sensory Events
Authors: Beiser David G. , Houk James C.
Published: December 2017

Beiser, David G. and James C. Houk. Model of cortical-basal ganglionic processing: encoding the serial order of sensory events. J. Neurophysiol. 79: 3168–3188, 1998. Several lines of evidence suggest that the prefrontal (PF) cortex and basal ganglia are important in cognitive aspects of serial order in behavior. We present a modular neural network model of these areas that encodes the serial order of events into spatial patterns of PF activity. The model is based on the topographically specific circuits linking the PF with the basal ganglia. Each module traces a pathway from the PF, through the basal ganglia and thalamus, and back to the PF. The complete model consists of an array of modules interacting through recurrent corticostriatal projections and collateral inhibition between striatal spiny units. The model's architecture positions spiny units for the classification of cortical contexts and events and provides bistable cortical-thalamic loops for sustaining a representation of these contextual events in working memory activations. The model was tested with a simulated version of a delayed-sequencing task. In single-unit studies, the task begins with the presentation of a sequence of target lights. After a short delay, the monkey must touch the targets in the order in which they were presented. When instantiated with randomly distributed corticostriatal weights, the model produces different patterns of PF activation in response to different target sequences. These patterns represent an unambiguous and spatially distributed encoding of the sequence. Parameter studies of these random networks were used to compare the computational consequences of collateral and feed-forward inhibition within the striatum. In addition, we studied the receptive fields of 20,640 model units and uncovered an interesting set of cue-, rank- and sequence-related responses that qualitatively resemble responses reported in single unit studies of the PF. The majority of units respond to more than one sequence of stimuli. A method for analyzing serial receptive fields is presented and utilized for comparing the model units to single-unit data.
Role of the Basal Forebrain Cholinergic Projection in Somatosensory Cortical Plasticity
Authors: Sachdev Robert N. S. , Lu Shao-Ming , Wiley Ron G. , Ebner Ford F.
Published: December 2017

Sachdev, Robert N. S., Shao-Ming Lu, Ron G. Wiley, and Ford F. Ebner. Role of the basal forebrain cholinergic projection in somatosensory cortical plasticity. J. Neurophysiol. 79: 3216–3228, 1998. Trimming all but two whiskers in adult rats produces a predictable change in cortical cell-evoked responses characterized by increased responsiveness to the two intact whiskers and decreased responsiveness to the trimmed whiskers. This type of synaptic plasticity in rat somatic sensory cortex, called “whisker pairing plasticity,” first appears in cells above and below the layer IV barrels. These are also the cortical layers that receive the densest cholinergic inputs from the nucleus basalis. The present study assesses whether the cholinergic inputs to cortex have a role in regulating whisker pairing plasticity. To do this, cholinergic basal forebrain fibers were eliminated using an immunotoxin specific for these fibers. A monoclonal antibody to the low-affinity nerve growth factor receptor 192 IgG, conjugated to the cytotoxin saporin, was injected into cortex to eliminate cholinergic fibers in the barrel field. The immunotoxin reduces acetylcholine esterase (AChE)-positive fibers in S1 cortex by >90% by 3 wk after injection. Sham-depleted animals in which either saporin alone or saporin unconjugated to 192 IgG is injected into the cortex produces no decrease in AChE-positive fibers in cortex. Sham-depleted animals show the expected plasticity in barrel column neurons. In contrast, no plasticity develops in the ACh-depleted, 7-day whisker-paired animals. These results support the conclusion that the basal forebrain cholinergic projection to cortex is an important facilitator of synaptic plasticity in mature cortex.
Synaptic Connectivity of Distinct Hilar Interneuron Subpopulations
Authors: Forti Matteo , Michelson Hillary B.
Published: December 2017

Forti, Matteo and Hillary B. Michelson. Synaptic connectivity of distinct hilar interneuron subpopulations. J. Neurophysiol. 79: 3229–3237, 1998. Dual intracellular recordings of hilar interneurons and CA3 pyramidal cells were performed in transverse slices of guinea pig hippocampus in the presence of the convulsant compound 4-aminopyridine (4-AP) and ionotropic glutamate receptor antagonists. Under these conditions, interneurons burst fire synchronously, producing synchronized inhibitory postsynaptic potentials (sIPSPs) in pyramidal cells. Three different hilar interneuron subpopulations that contributed to the sIPSP were identified based on their projection properties and morphology. These three types were pyramidal-like stellate interneurons, spheroid interneurons, and oviform interneurons. Physiologically, pyramidal-like stellate interneurons could be differentiated from the other interneuron subpopulations because they generated short synchronized bursts of action potentials coincident with the hyperpolarizing and depolarizing γ-aminobutyric acid-A (GABAA)-mediated inhibitory postsynaptic potentials (IPSPs) recorded in pyramidal cells. The bursts in pyramidal-like stellate cells were abolished by theGABAA-receptor blocker, bicuculline. In contrast, spheroid interneurons of the dentate-hilus (D-H) border and oviform hilar interneurons exhibited prolonged bicuculline-resistant bursts that occurred coincident with the GABAB pyramidal cell sIPSPs. Pyramidal-like stellate interneurons likely did not contribute to the generation of synchronized GABAB responses in hippocampal pyramidal cells. Spheroid interneurons were unique among these subpopulations of interneurons in that the bicuculline-resistant bursts in spheroid interneurons were sustained by a synaptic depolarization that persisted in the presence of antagonists of ionotropic glutamate, GABAA and GABAB receptors [6-cyano-7-nitroquinoxaline-2,3-dione, 20 μM; 3-3(2-carboxipiperazine-4-yl)propyl-1-phosphonate, 20 μM; bicuculline, 10–15 μM; CGP 55845A, 20 μM]. This novel depolarizing potential reversed between −30 and 0 mV. No noticeable synaptic depolarization sustaining burst firing could be isolated in oviform interneurons, suggesting that firing in this interneuron subpopulation was synchronized by nonsynaptic mechanisms. The results of the present study indicate that the hilar inhibitory circuit is composed of at least three different subpopulations of interneurons, distinguishable by their morphological characteristics and synaptic inputs and outputs. These findings give further support to the hypothesis that there are distinct populations of interneurons producing GABAA and GABAB responses with defined functional roles within the hippocampal inhibitory circuit. Notably, we found that spheroid interneurons were unique among the hilar interneurons studied, in that the synchronized bursts observed in these cells are sustained by a novel ionotropic glutamate and GABA receptor-independent synaptic depolarization.
Modulation of the Ca2+-Activated K+Current sIAHPby aPhosphatase-Kinase Balance Under Basal Conditions inRat CA1 Pyramidal Neurons
Authors: Pedarzani Paola , Krause Michael , Haug Trude , Storm Johan F. , Stühmer Walter
Published: December 2017

Pedarzani, Paola, Michael Krause, Trude Haug, Johan F. Storm, and Walter Stühmer. Modulation of the Ca2+-activated K+current s IAHPby a phosphatase-kinase balance under basal conditions in rat CA1 pyramidal neurons. J. Neurophysiol. 79: 3252–3256, 1998. The slow Ca2+-activated K+current, s IAHP, underlying spike frequency adaptation, was recorded with the whole cell patch-clamp technique in CA1 pyramidal neurons in rat hippocampal slices. Inhibitors of serine/threonine protein phosphatases (microcystin, calyculin A, cantharidic acid) caused a gradual decrease of s IAHPamplitude, suggesting the presence of a basal phosphorylation-dephosphorylation turnover regulating s IAHP. Because selective calcineurin (PP-2B) inhibitors did not affect the amplitude of s IAHP, protein phosphatase 1 (PP-1) or 2A (PP-2A) are most likely involved in the basal regulation of this current. The ATP analogue, ATP-γ-S, caused a gradual decrease in the s IAHPamplitude, supporting a role of protein phosphorylation in the basal modulation of s IAHP. When the protein kinase A (PKA) inhibitor adenosine-3′,5′-monophosphorothioate, Rp-isomer (Rp-cAMPS) was coapplied with the phosphatase inhibitor microcystin, it prevented the decrease in the s IAHPamplitude that was observed when microcystin alone was applied. Furthermore, inhibition of PKA by Rp-cAMPS led to an increase in the s IAHPamplitude. Finally, an adenylyl cyclase inhibitor (SQ22,536) and adenosine 3′,5′-cyclic monophosphate-specific type IV phosphodiesterase inhibitors (Ro 20–1724 and rolipram) led to an increase or a decrease in the s IAHPamplitude, respectively. These findings suggest that a balance between basally active PKA and a phosphatase (PP-1 or PP-2A) is responsible for the tonic modulation of s IAHP, resulting in a continuous modulation of excitability and firing properties of hippocampal pyramidal neurons.
Role of Platelet-Activating Factor in Long-Term Potentiation of the Rat Medial Vestibular Nuclei
Authors: Grassi Silvarosa , Francescangeli Ermelinda , Goracci Gianfrancesco , Pettorossi Vito E.
Published: December 2017

Grassi, Silvarosa, Ermelinda Francescangeli, Gianfrancesco Goracci, and Vito E. Pettorossi. Role of platelet-activating factor in long-term potentiation of the rat medial vestibular nuclei. J. Neurophysiol. 79: 3266–3271, 1998. In rat brain stem slices, we investigated the role of platelet activating factor (PAF) in long-term potentiation (LTP) induced in the ventral part of the medial vestibular nuclei (MVN) by high-frequency stimulation (HFS) of the primary vestibular afferent. The synaptosomal PAF receptor antagonist, BN-52021 was administered before and after HFS. BN-52021 did not modify the vestibular potentials under basal conditions, but it reduced the magnitude of potentiation induced by HFS, which completely developed after the drug wash-out. The same effect was obtained by using CV-62091, a more potent PAF antagonist at microsomal binding sites, but with concentrations higher than those of BN-52021. By contrast both BN-52021 and CV-6209 had no effect on the potentiation once induced. This demonstrates that PAF is involved in the induction but not in the maintenance of vestibular long-term effect through activation of synaptosomal PAF receptors. In addition, we analyzed the effect of the PAFanalogue,  1 - O - hexadecyl - 2 - O - (methylcarbamyl) - sn - glycero - 3phosphocoline (MC-PAF) and the inactive PAF metabolite, 1- O-hexadecyl- sn-glycero-3-phosphocoline (Lyso-PAF) on vestibular responses. Our results show that MC-PAF, but not Lyso-PAF induced potentiation. This potentiation was prevented by d,l-2-amino 5-phosphonopentanoic acid, suggesting an involvement of N-methyl-d-aspartate receptors. Furthermore, under BN-52021 and CV-6209, the MC-PAF potentiation was reduced or abolished. The dose-effect curve of MC-PAF showed a shift to the right greater under BN-52021 than under CV-6209, confirming the main dependence of MC-PAF potentiation on the activation of synaptosomal PAF receptors. Our results suggest that PAF can be released in the MVN after the activation of postsynaptic mechanisms triggering LTP, and it may act as a retrograde messenger which activates the presynaptic mechanisms facilitating synaptic plasticity.
Limbic Gamma Rhythms. II. Synaptic and Intrinsic Mechanisms Underlying Spike Doublets in Oscillating Subicular Neurons
Authors: Stanford Ian M. , Traub Roger D. , Jefferys John G. R.
Published: December 2017

Stanford, Ian M., Roger D. Traub, and John G. R. Jefferys. Limbic gamma rhythms. II. Synaptic and intrinsic mechanisms underlying spike doublets in oscillating subicular neurons. J. Neurophysiol. 80: 162–171, 1998. Gamma oscillations were evoked in the subiculum in rat transverse hippocampal slices by tetanic stimulation (200 ms/100 Hz) of either CA1 or subiculum. Gamma oscillations in the subiculum differed from those in CA1 in containing population spike doublets as well as singlets. The present study addresses the origin of this more complex form of gamma oscillation in the subiculum. Intracellular recordings from subicular neurons revealed that 63% of them fired double action potentials on cycles of the gamma oscillation that generated population spike doublets after tetanic stimulation of either CA1 or subiculum. The remaining cells produced excitatory postsynaptic potentials (EPSPs), and occasional single spikes, on each cycle. Neurons that fired occasional single action potentials during gamma rhythms were “regular spiking” cells. They did not produce burst discharges during depolarizing steps, had minimal membrane potential sags on hyperpolarizing steps, and responded to single afferent volleys with a single action potential on an EPSP followed by a large inhibitory postsynaptic potential complex. Fast spiking cells were observed too infrequently to be studied in detail. Neurons that fired doublets during gamma rhythms were “intrinsic burst” (IB) cells. They generated bursts of action potentials on step membrane depolarizations, had significant membrane potential sags on step hyperpolarizations with an anodal break potential on return to rest, and fired multiple action potentials in response to high-intensity single afferent volleys. IB neurons did not fire action potential doublets during 1-s membrane depolarizations. Double action potentials, however, were evoked in these cells by depolarizing pulses at 40 Hz from hyperpolarized membrane potentials (−100 mV). Computer simulations suggest that the hyperpolarization between the depolarizations was essential for action potential doublets. The results in this and the previous paper suggest the following: either CA1 or subiculum alone can generate gamma oscillations gated by local networks of interneurons, oscillations in CA1 project through pyramidal cell axons to subiculum with a time lag expected from axon conduction delays, and oscillating sequences of EPSPs and intrinsic and/or synaptic hyperpolarizing potentials in IB subicular neurons generate gamma frequency spike doublets, which depend on both the intrinsic properties of these neurons and their temporally patterned synaptic input. This phenomenon could amplify gamma output from CA1 and modify its coupling to gamma oscillations in the wider limbic system.
Effects of Mitochondrion on Calcium Transients at Intact Presynaptic Terminals Depend on Frequency of Nerve Firing
Authors: Peng Yan-Yi
Published: December 2017

Peng, Yan-Yi. Effects of mitochondrion on calcium transients at intact presynaptic terminals depend on frequency of nerve firing. J Neurophysiol. 80: 186–195, 1998. The rate and the total amount of Ca2+ elevation in the presynaptic terminals of bullfrog sympathetic ganglia depend on the firing frequency of the terminals. Carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, was used for testing whether mitochondrial Ca2+ uptake is one of the mechanisms that underlie this frequency dependence. Fura-2 fluorimetry was used for measurement of intraterminal Ca2+. When stimulations of different durations (30 and 1.5 s) and frequencies (4 and 20 Hz) evoked Ca2+ transients with similar peak amplitudes (264 ± 22 nM vs. 251 ± 18 nM, means ± SE), CCCP augmented the responses to the 4-Hz stimulation 8.9 times more strongly than it did the responses to the 20-Hz stimulation (249.7 ± 81.5% vs. 25.3 ± 10.2%). When stimulations delivered at the two frequencies had the same durations (1.5, 3, 6, 10, 20, and 30 s), CCCP enlarged the responses to the 4-Hz stimulations up to 4.2 times more than it did the responses to the 20-Hz stimulations. When the same number of stimuli (120) was delivered at the two frequencies, the effects of CCCP on the responses evoked by the 4-Hz train were again 6.8 times stronger than its effects on the responses to the 20-Hz stimulation. Therefore neither the peak amplitudes of the responses nor the durations of the stimulations dictated the extent to which the mitochondria modulated the peak [Ca2+]i. Instead, the extent of the modulation was governed by the frequency of stimulation. Specifically, the less frequent the Ca2+ influx, the stronger the mitochondrial modulation. Also, during nerve firing Ca2+ release from the ryanodine-sensitive store had a higher potential to influence the [Ca2+]i transients than did Ca2+ removal by the mitochondria for the first 6 s of the responses. On cessation of stimulation, CCCP reduced the initial rapid rate of Ca2+ decay. Thus uptake by the mitochondria was an important mechanism for Ca2+ removal after repetitive firing at the presynaptic terminals.