Modeling of Auditory Spatial Receptive Fields With Spherical Approximation FunctionsJenison, Rick L.; Reale, Richard A.; Hind, Joseph E.; Brugge, John F.
doi: N/Apmid: 9819270
Abstract Jenison, Rick L., Richard A. Reale, Joseph E. Hind, and John F. Brugge. Modeling of auditory spatial receptive fields with spherical approximation functions. J. Neurophysiol. 80: 2645–2656, 1998. A spherical approximation technique is presented that affords a mathematical characterization of a virtual space receptive field (VSRF) based on first-spike latency in the auditory cortex of cat. Parameterizing directional sensitivity in this fashion is much akin to the use of difference-of-Gaussian (DOG) functions for modeling neural responses in visual cortex. Artificial neural networks and approximation techniques typically have been applied to problems conforming to a multidimensional Cartesian input space. The problem with using classical planar Gaussians is that radial symmetry and consistency on the plane actually translate into directionally dependent distortion on spherical surfaces. An alternative set of spherical basis functions, the von Mises basis function (VMBF), is used to eliminate spherical approximation distortion. Unlike the Fourier transform or spherical harmonic expansions, the VMBFs are nonorthogonal, and hence require some form of gradient-descent search for optimal estimation of parameters in the modeling of the VSRF. The optimization equations required to solve this problem are presented. Three descriptive classes of VSRF (contralateral, frontal, and ipsilateral) approximations are investigated, together with an examination of the residual error after parameter optimization. The use of the analytic receptive field model in computational models of population coding of sound direction is discussed, together with the importance of quantifying receptive field gradients. Because spatial hearing is by its very nature three dimensional or, more precisely, two dimensional (directional) on the sphere, we find that spatial receptive field models are best developed on the sphere. Footnotes Address for reprint requests: R. L. Jenison, Dept. of Psychology, University of Wisconsin, 1202 West Johnson St., Madison, WI 53706. Copyright © 1998 the American Physiological Society
Differential Effects of GABAA Receptor Antagonists in the Control of Respiratory Neuronal Discharge PatternsDogas, Z.; Krolo, M.; Stuth, E. A.; Tonkovic-Capin, M.; Hopp, F. A.; McCrimmon, D. R.; Zuperku, E. J.
doi: N/Apmid: 9819249
Abstract Dogas, Z., M. Krolo, E. A. Stuth, M. Tonkovic-Capin, F. A. Hopp, D. R. McCrimmon, and E. J. Zuperku. Differential effects of GABA A receptor antagonists in the control of respiratory neuronal discharge patterns. J. Neurophysiol. 80: 2368–2377, 1998. To ascertain the role of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) in shaping and controlling the phasic discharge patterns of medullary respiratory premotor neurons, localized pressure applications of the competitive GABA A receptor antagonist bicuculline (BIC) and the noncompetitive GABA A receptor antagonist picrotoxin (PIC) were studied. Multibarrel micropipettes were used in halothane anesthetized, paralyzed, ventilated, vagotomized dogs to record single unit activity from inspiratory and expiratory neurons in the caudal ventral respiratory group and to picoeject GABA A receptor antagonists. The moving time average of phrenic nerve activity was used to determine respiratory phase durations and to synchronize cycle-triggered histograms of discharge patterns. Picoejection of BIC and PIC had qualitatively different effects on the discharge patterns of respiratory neurons. BIC caused an increase in the discharge rate during the neuron's active phase without inducing activity during the neuron's normally silent phase. The resulting discharge patterns were amplified replicas (×2–3) of the underlying preejection phasic patterns. In contrast, picoejection of PIC did not increase the peak discharge rate during the neuron's active phase but induced a tonic level of activity during the neuron's normally silent phase. The maximum effective BIC dose (15 ± 1.8 pmol/min) was considerably smaller than that for PIC (280 ± 53 pmol/min). These findings suggest that GABA A receptors with differential pharmacology mediate distinct functions within the same neuron, 1 ) gain modulation that is BIC sensitive but PIC insensitive and 2 ) silent-phase inhibition blocked by PIC. These studies also suggest that the choice of an antagonist is an important consideration in the determination of GABA receptor function within the respiratory motor control system. Footnotes Address for reprint requests: E. J. Zuperku, Research Service/151, Zablocki VA Medical Center, Milwaukee, WI 53295. Copyright © 1998 the American Physiological Society
Classification of Caudal Ventrolateral Pontine Neurons With Sympathetic Nerve-Related ActivityBarman, Susan M.; Gebber, Gerard L.
doi: N/Apmid: 9819254
Abstract Barman, Susan M. and Gerard L. Gebber. Classification of caudal ventrolateral pontine neurons with sympathetic nerve-related activity. J. Neurophysiol. 80: 2433–2445, 1998. This study was designed to answer three questions concerning caudal ventrolateral pontine (CVLP) neurons whose naturally occurring discharges are correlated to sympathetic nerve discharge (SND). 1 ) What are the proportions of CVLP neurons that have activity correlated to both the cardiac-related and 10-Hz rhythms in SND, to only the 10-Hz rhythm, and to only the cardiac-related rhythm? 2 ) Do CVLP neurons with activity correlated to the cardiac-related and/or 10-Hz rhythm in SND subserve a sympathoexcitatory or sympathoinhibitory function? 3 ) Do CVLP neurons with activity correlated to the cardiac-related and/or 10-Hz rhythm in SND project to the thoracic spinal cord? To address these issues we recorded from 476 CVLP neurons in 24 urethan-anesthetized cats. Spike-triggered averaging, arterial pulse-triggered analysis, and coherence analysis revealed that the discharges of 66 of these neurons were correlated to inferior cardiac postganglionic SND. For 39 of these neurons, we were able to determine whether their discharges were correlated to one or both rhythms. The results showed that the CVLP contained a heterogeneous population of neurons with sympathetic nerve-related activity. The discharges of 21 neurons were correlated to both the 10-Hz and cardiac-related rhythms in SND, 9 neurons had activity correlated to only the 10-Hz rhythm, and 9 neurons had activity correlated to only the cardiac-related rhythm. The firing rates of CVLP neurons with activity correlated to both rhythms or to only the 10-Hz rhythm were decreased during the inhibition of SND induced by baroreceptor reflex activation (rapid obstruction of the abdominal aorta). These neurons are presumed to exert sympathoexcitatory actions. The time-controlled collision test verified that 11 of 12 CVLP neurons with activity correlated to both rhythms were antidromically activated by stimulation of the first thoracic segment of the spinal cord. Antidromic mapping at this level showed that the site requiring the least stimulus current to elicit the longest latency response (nearest the terminal) was in the vicinity of the intermediolateral nucleus (IML). In contrast, only 1 of 13 CVLP neurons with activity correlated to only one of the rhythms in SND could be antidromically activated by spinal stimulation. These data demonstrate for the first time that there is a direct pathway from the CVLP to the IML that is comprised almost exclusively of sympathoexcitatory neurons whose discharges are correlated to both the 10-Hz and cardiac-related rhythms in SND. Footnotes Address for reprint requests: S. M. Barman, Dept. of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824-1317. Copyright © 1998 the American Physiological Society
Temporal Dynamics of Convergent Modulation at a Crustacean Neuromuscular JunctionJorge-Rivera, Juan Carlos; Sen, Kamal; Birmingham, J. T.; Abbott, L. F.; Marder, Eve
doi: N/Apmid: 9819263
Abstract Jorge-Rivera, Juan Carlos, Kamal Sen, J. T. Birmingham, L. F. Abbott, and Eve Marder. Temporal dynamics of convergent modulation at a crustacean neuromuscular junction. J. Neurophysiol. 80: 2559–2570, 1998. At least 10 different substances modulate the amplitude of nerve-evoked contractions of the gastric mill 4 (gm4) muscle of the crab, Cancer borealis . Serotonin, dopamine, octopamine, proctolin, red pigment concentrating hormone, crustacean cardioactive peptide, TNRNFLRFamide, and SDRNFLRFamide increased and d -allatostatin-3 and histamine decreased the amplitude of nerve-evoked contractions. Modulator efficacy was frequency dependent; TNRNFLRFamide, proctolin, and d allatostatin-3 were more effective when the motor neuron was stimulated at 10 Hz than at 40 Hz, whereas the reverse was true for dopamine and serotonin. The modulators that were most effective at high stimulus frequencies produced a significant decrease in muscle relaxation time; those that were most effective at low stimulus frequencies produced modest increases in relaxation time. Thus modulator actions that appear redundant when examined only at one stimulus frequency are differentiated when a range of stimulus dynamics is studied. The effects of TNRNFLRFamide, serotonin, proctolin, dopamine, and d -allatostatin-3 on the amplitude and facilitation of nerve-evoked excitatory junctional potentials (EJPs) in the gm4 and gastric mill 6 (gm6) muscles were compared. The EJPs in gm4 have a large initial amplitude and show relatively little facilitation, whereas the EJPs in gm6 have a small initial amplitude and show considerable facilitation. Modulators that enhanced contractions also enhanced EJP amplitude; d -allatostatin-3 reduced EJP amplitude. The effects of these modulators on EJP amplitude were modest and showed no significant frequency dependence. This suggests that the frequency dependence of modulator action on contraction results from effects on excitation–contraction coupling. The modulators affected facilitation at these junctions in a manner consistent with a change in release probability. They produced a change in facilitation that is inversely related to their action on EJP amplitude. Footnotes Address for reprint requests: E. Marder, Volen Center MS #013, Brandeis University, 415 South St., Waltham, MA 02454. Copyright © 1998 the American Physiological Society
NMDA Receptor Mechanisms Contribute to Neuroplasticity Induced in Caudalis Nociceptive Neurons by Tooth Pulp StimulationChiang, Chen Yu; Park, Soo Joung; Kwan, Chun L.; Hu, James W.; Sessle, Barry J.
doi: N/Apmid: 9819268
Abstract Chiang, Chen Yu, Soo Joung Park, Chun L. Kwan, James W. Hu, and Barry J. Sessle. NMDA receptor mechanisms contribute to neuroplasticity induced in caudalis nociceptive neurons by tooth pulp stimulation. J. Neurophysiol. 80: 2621–2631, 1998. We recently demonstrated that application of mustard oil (MO), a small-fiber excitant and inflammatory irritant, to the rat maxillary molar tooth pulp induces significant and prolonged increases in jaw muscle electromyographic (EMG) activity that are suggestive of central neuroplasticity. Because small-fiber afferents, including pulp afferents, access nociceptive neurons in trigeminal (V) subnucleus caudalis, this study examined whether pulpal application of MO induces neuroplastic changes in caudalis nociceptive neurons (wide dynamic range and nociceptive specific) and whether central N -methyl- d -aspartate (NMDA) receptor mechanisms are involved in these MO-induced neuroplastic changes. After pretreatment with vehicle (saline, 10 μl i.t.) to the surface of the medulla, the pulpal application of MO to the maxillary molar tooth pulp produced a significant increase in neuronal spontaneous activity, a significant expansion of the pinch and/or tactile mechanoreceptive field (RF), a significant decrease in mechanical threshold, and significant increases in neuronal responses to graded pinch stimuli. Compared with vehicle-treated rats, pretreatment with the NMDA receptor antagonist MK-801 (10 μg/10 μl i.t.) followed by MO application to the pulp in another group of rats significantly reduced or abolished these MO-induced neuroplastic changes in nociceptive neurons. In another group of rats pretreated with saline (intrathecally), mineral oil application to the pulp did not show any significant changes in spontaneous activity or RF properties over the 40-min observation period. The pulpal application of MO in other rats (pretreated with saline, intrathecally) did not produce any significant neuroplastic changes in caudalis low-threshold mechanoreceptive neurons. These results indicate that the MO-induced activation of molar pulpal afferents can produce profound NMDA receptor-related neuroplastic changes in caudalis nociceptive neurons. Such neuroplastic changes may contribute to the hyperalgesia and spread of pain that can be associated with pulpal inflammation. Footnotes Address for reprint requests: B. J. Sessle, Faculty of Dentistry, University of Toronto, 124 Edward St., Toronto, Ontario M5G 1G6, Canada. Copyright © 1998 the American Physiological Society
Neuronal Activity in the Vestibular Nuclei After Contralateral or Bilateral Labyrinthectomy in the Alert Guinea PigRis, Laurence; Godaux, Emile
doi: N/Apmid: 9819248
Abstract Ris, Laurence and Emile Godaux. Neuronal activity in the vestibular nuclei after contralateral or bilateral labyrinthectomy in the alert guinea pig. J. Neurophysiol. 80: 2352–2367, 1998. In the guinea pig, a unilateral labyrinthectomy is followed by an initial depression and a subsequent restoration of the spontaneous activity in the neurons of the ipsilateral vestibular nuclei. In two previous works, we have established the time course of these changes in the alert guinea pig using electrical stimulation as a search stimulus to select the analyzed neurons. The latter criterion was important to capture the many ipsilateral neurons that are silent at rest during the immediate postlabyrinthectomy stage. Because it is known that a pathway originating from the vestibular nuclei on one side crosses the midline and functionally inhibits the activity of the vestibular nuclei on the other side, we investigated in the first part of this study the spiking behavior of the neurons in the vestibular nuclei contralateral to the labyrinthectomy using the same procedure as that used for the ipsilateral neurons. The spiking behavior of 976 neurons was studied during 4-h recording sessions in intact animals and 1 h, 1 day, 2 days, or 1 wk postlabyrinthectomy. Neurons selected according to the electrical activation criterion were classified further as type I (their firing rate increased during ipsilateral rotation), type II (their firing rate increased during contralateral rotation), or unresponsive. The resting activity of type I neurons, which was 38.1 ± 20.9 spikes/s (mean ± SD) in the control state, increased statistically significantly 1 h after the lesion (53.3 ± 29.1 spikes/s) and remained at this level 1 wk later (56.0 ± 20.3 spikes/s). The sensitivity of type I units, which was 0.80 ± 0.46 spikes/s per deg/s in the control population, decreased to 0.49 ± 0.26 spikes/s per deg/s 1 h after the lesion and remained at this level 1 wk later (0.50 ± 0.39 spikes/s per deg/s). When all monosynaptically activated neurons (type I, type II, unresponsive) were pooled, the sensitivity to horizontal rotation fell from 0.58 ± 0.51 spikes/s per deg/s in the control state to 0.15 ± 0.25 spikes/s per deg/s 1 h after the lesion and to 0.20 ± 0.32 spikes/s per deg/s 1 wk later. The major findings of the first part of this study in the alert guinea pig are thus in accord with those of Curthoys et al. and Smith and Curthoys in anesthetized guinea pigs. In the second part of this work, we studied the spiking behavior of the neurons in the vestibular nuclei after bilateral labyrinthectomy. After unilateral labyrinthectomy, the resting discharge of the ipsilateral monosynaptically activated vestibular neurons fell from 36.9 ± 21 spikes/s (basal activity) to 6.7 ± 17.0 spikes/s 1 h after the lesion and then recovered, reaching 17.4 ± 18.9 and 40.8 ± 23.7 spikes/s 1 day and 1 wk after the lesion, respectively. These observations raise the two following questions. What are the relative contributions of the loss of the excitatory influence from the ipsilateral labyrinth (destroyed) and of the persistence of the inhibitory influence from the contralateral labyrinth (intact) in the labyrinthectomy-induced depression of activity? And are the left-right asymmetries caused by a unilateral labyrinthectomy the driving force for restoration of activity? Here, we addressed these two questions by studying the spiking behavior of 473 second-order vestibular neurons in the alert guinea pig after a bilateral labyrinthectomy. In the acute stage, 1 h after bilateral labyrinthectomy, the resting discharge of the second-order vestibular neurons was 16.2 ± 22.4 spikes/s. From comparison with the results obtained in the acute stage after a unilateral labyrinthectomy, we inferred that the ipsilateral excitatory influence was between two and three times more powerful than the contralateral inhibitory influence. After bilateral labyrinthectomy as well as after unilateral labyrinthectomy, the resting activity of the second-order vestibular neurons returned to normal, reaching 20.8 ± 23.1 spikes/s 1 day after the lesion and 38.6 ± 21.1 spikes/s 1 wk after the lesion. From this fact, we concluded that the left-right asymmetries caused by a unilateral labyrinthectomy were not the error signals inducing the restoration of activity. Footnotes Address for reprint requests: E. Godaux, Laboratory of Neurosciences, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium. Copyright © 1998 the American Physiological Society
Raised Object on a Planar Surface Stroked Across the Fingerpad: Responses of Cutaneous Mechanoreceptors to Shape and OrientationLamotte, R. H.; Friedman, R. M.; Lu, C.; Khalsa, P. S.; Srinivasan, M. A.
doi: N/Apmid: 9819255
Abstract LaMotte, R. H., R. M. Friedman, C. Lu, P. S. Khalsa, and M. A. Srinivasan. Raised object on a planar surface stroked across the fingerpad: responses of cutaneous mechanoreceptors to shape and orientation. J. Neurophysiol. 80: 2446–2466, 1998. The representations of orientation and shape were studied in the responses of cutaneous mechanoreceptors to an isolated, raised object on a planar surface stroked across the fingerpad. The objects were the top portions of a sphere with a 5-mm radius, and two toroids each with a radius of 5 mm along one axis and differing radii of 1 or 3 mm along the orthogonal axis. The velocity and direction of stroking were fixed while the orientation of the object in the horizontal plane was varied. Each object was stroked along a series of laterally shifted, parallel, linear trajectories over the receptive fields of slowly adapting, type I (SA), and rapidly adapting, type I (RA) mechanoreceptive afferents innervating the fingerpad of the monkey. “Spatial event plots” (SEPs) of the occurrence of action potentials, as a function of the location of each object on the receptive field, were interpreted as the responses of a spatially distributed population of fibers. That portion of the plot evoked by the curved object (the SEP c ) provided a representation of the shape and orientation of the two-dimensional outline of the object in the horizontal plane in contact with the skin. For both SAs and RAs, the major vector of the SEP c , obtained by a principal components analysis, was linearly related to the physical orientation of the major axis of each toroid. The spatial distribution of discharge rates spatial rate surface profiles (SRSs), after plotting mean instantaneous frequency versus spatial locus within the SEP c represented object shape in a third dimension, normal to the skin surface. The shape of the SA SRSs, well fitted by Gaussian equations, better represented object shape than that of the RA SRSs. A cross-sectional profile along the minor axis spatial rate profile (SRP) was approximately triangular for SAs. After normalization for differences in peak height, the falling slopes of the SA SRPs increased, and the base widths decreased with curvature of the object's minor axis. These curvature-related differences in slopes and widths were invariant with changes in object orientation. It is hypothesized that circularity in object shape is coded by the constancy of slopes of SA SRPs between peak and base and that the constancy of differences in the widths and falling slopes evoked by different raised objects encodes, respectively, the differences in their sizes and shapes regardless of differences in their orientation on the skin. Footnotes Address for reprint requests: R. H. LaMotte, Dept. of Anesthesiology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510. Copyright © 1998 the American Physiological Society
Response Patterns and Force Relations of Monkey Spinal Interneurons During Active Wrist MovementMaier, Marc A.; Perlmutter, Steve I.; Fetz, Eberhard E.
doi: N/Apmid: 9819258
Abstract Maier, Marc A., Steve I. Perlmutter, and Eberhard E. Fetz. Response patterns and force relations of monkey spinal interneurons during active wrist movement. J. Neurophysiol. 80: 2495–2513, 1998. The activity of C 6 –T 1 spinal cord neurons was recorded in three macaques while they generated isometric wrist flexion and extension torques in visually guided step-tracking tasks. Electromyographic activity (EMG) was recorded in ≤12 independent forearm muscles. Spike-triggered averages (STAs) of rectified and unrectified EMG were used to classify neurons into four groups. Motoneurons (MNs) had a clear postspike motor unit signature in the unrectified STA of one muscle. Premotor interneurons (PreM-INs) had postspike effects in at least one muscle, with onset latencies of ≥3.5 ms from the trigger. Synchrony interneurons (Sy-INs) were non-PreM-Ins that had spike-related features with latencies <3.5 ms in at least one muscle. Unidentified interneurons (U-INs) showed no features in any of the STAs. A total of 572 task-related spinal neurons were studied; 29 cells were MNs, 97 PreM-INs, 32 Sy-INs, and 414 U-INs. MNs were activated predominantly in a tonic fashion during the ramp-and-hold torques and were active in one direction only. The most common response pattern for interneurons, irrespective of their class, was phasic-tonic activity, followed by purely tonic and purely phasic activity. Most interneurons (77%) were bidirectionally active in both flexion and extension. For all classes of interneurons, units with phasic response components tended to be activated first, before torque onset, followed by tonic units. The onset times of PreM-INs relative to onsets of their target muscles were distributed broadly, with a mean of −25 ± 128 (SD) ms. For most neurons with tonic response components (all MNs, 71% of PreM-INs, 67% of Sy-INs, and 84% of U-INs), activity during the hold period was correlated significantly with the magnitude of static torque exerted by the monkey. The rate-torque regressions generally had positive slopes with higher mean slopes for extension than for flexion. The phasic response components were correlated significantly with rate of change of torque for a smaller percentage of tested PreM-Ins (50%), Sy-INs (83%), and U-INs (77%). In contrast to other premotor neurons corticomotoneuronal (CM), rubromotoneuronal (RM), and dorsal root ganglion (DRG) afferents previously characterized under similar conditions, a larger proportion of the spinal PreM-INs were activated after onset of their target muscles, probably reflecting a larger proportion of PreM-INs driven by peripheral input. The rate-torque slopes of PreM-INs tended to be less steep than those of CM and RM cells. Unlike the CM and DRG PreM afferents, which were activated unidirectionally, most spinal PreM-INs showed bidirectional activity, like RM cells. Footnotes Address for reprint requests: S. I. Perlmutter, Dept. of Physiology and Biophysics, Box 357330, University of Washington, Seattle, WA 98195-7330. Present address of M. A. Maier: Sobell Dept. of Neurophysiology, Institute of Neurology, Queen Square, London WC1N 3BG, UK. Copyright © 1998 the American Physiological Society
Stereotyped Yawning Responses Induced by Electrical and Chemical Stimulation of Paraventricular Nucleus of the RatSato-Suzuki, Ikuko; Kita, Ichiro; Oguri, Mitsugu; Arita, Hideho
doi: N/Apmid: 9819279
Abstract Sato-Suzuki, Ikuko, Ichiro Kita, Mitsugu Oguri, and Hideho Arita. Stereotyped yawning responses induced by electrical and chemical stimulation of paraventricular nucleus of the rat. J. Neurophysiol. 80: 2765–2775, 1998. Yawning was evoked by electrical or chemical stimulation in the paraventricular nucleus (PVN) of anesthetized, spontaneously breathing rats. To evaluate physiological aspects of yawning, we monitored polygraphic measures as follows; a coordinated motor pattern of yawning was assessed by monitoring breathing intercostal electromyogram (EMG), mouth opening (digastric EMG), and stretching of the trunk (back EMG). We also recorded blood pressure (BP), heart rate, and the electrocorticogram (ECoG) to evaluate autonomic function and arousal responses during yawning. A stereotyped yawning response was reproducibly evoked by electrical stimulation or microinjection of l -glutamate or NOC-7, a nitric oxide (NO)-releasing compound, into the PVN. The stereotyped yawning response consisted of two sequential events, an initial response represented a depressor response and an arousal shift in the ECoG to lower voltage and faster rhythms. These initial changes were followed by a yawning behavior characterized by a single large inspiration with mouth opening and stretching of the trunk. A similar sequence of events occurred during spontaneous yawning; a fall in BP and ECoG arousal preceded a yawning behavior. An increase in the frequency of spontaneous yawns was also observed after microinjection of l -glutamate or NOC-7 into the PVN. Intravenous administration of N G -monomethyl- l -arginine, an inhibitor of nitric oxide synthase (NOS), prevented the stereotyped yawning response evoked by chemical stimulation of the PVN. Histological examination revealed that effective sites for the yawning responses were located in the medial part of the rostral PVN, the site of parvocellular and magnocellular neurons. NADPH-diaphorase histochemistry showed the existence of NOS-containing cells in yawning-evoked sites of the PVN. In summary, the sequential events of yawning may be generated by NOS-containing parvocellular neurons in the medial part of the rostral PVN projecting to the lower brain stem. Footnotes Address for reprint requests: H. Arita, Dept. of Physiology, Toho University School of Medicine, 5-21-16. Omori-nishi, Ota-ku, Tokyo 143-8540, Japan. Copyright © 1998 the American Physiological Society