bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of EPSCs and IPSCs Carrying Rhythmic, Locomotor-Related Information in the Isolated Spinal Cord of the Neonatal Rat
Authors: Raastad Morten , Johnson Bruce R. , Kiehn Ole
Published: December 2017

Raastad, Morten, Bruce R. Johnson, and Ole Kiehn. Analysis of EPSCs and IPSCs carrying rhythmic, locomotor-related information in the isolated spinal cord of the neonatal rat. J. Neurophysiol. 78: 1851–1859, 1997. To understand better the synaptic language used by neurons in active networks, we have analyzed postsynaptic currents (PSCs) received by interneurons in the isolated spinal cord from neonatal rats during 5-hydroxytryptamine- and N-methyl-d-aspartate–induced fictive locomotion. Using a computer algorithm, we identified PSCs in rhythmically active interneurons in laminae VII and X. To test whether the PSCs actually participated in the transmission of the cyclic, locomotor-related signal, we constructed an analytic current trace based on only the identified events. Each identified PSC was fitted by a mathematical function, and the shape of this function was added to a baseline with time delays given by the time positions of the identified PSCs. By averaging the resulting analytic current trace over several cycles, we showed that the identified PSCs built a cyclic signal locked to the rhythmic activity recorded from the ventral roots. Furthermore, subtraction of the analytic from the original current trace reduced the amplitude of the cyclic signal received by these cells. Thus the identified PSCs contributed to the cyclic information, allowing us to analyze how they built the compound cyclic signal. Most often there was an inverse relationship between the contribution from excitatory and inhibitory PSCs during the cyclic modulation, indicating that there was a reciprocal regulation of the presynaptic inhibitory and excitatory cells. Comparing the most inhibitory and most excitatory halves of the locomotor related cycle, there was a considerably larger modulation of the frequency of PSCs than of their amplitude. The small and sometimes insignificant modulation of PSC amplitude suggests that facilitation and depression had little importance for the information transfer. The modest amplitude modification also suggests that the large range of available PSC amplitudes seen in these neurons was not used very efficiently to code the cyclic information.
Passive and Active Membrane Properties of Isolated Rat Intracardiac Neurons: Regulation by H- and M-Currents
Authors: Cuevas J. , Harper A. A. , Trequattrini C. , Adams D. J.
Published: December 2017

Cuevas, J., A. A. Harper, C. Trequattrini, and D. J. Adams. Passive and active membrane properties of isolated rat intracardiac neurons: regulation by H- and M-currents. J. Neurophysiol. 78: 1890–1902, 1997. The electrical characteristics of isolated neonatal rat intracardiac neurons were examined at 22 and 37°C using the perforated-patch whole cell recording technique. The mean resting membrane potential was −52.0 mV at 37°C and exhibited no temperature dependence. Lowering the temperature from 37 to 22°C decreased the mean input resistance from 854 to 345 MΩ, respectively, and reduced the membrane time constant approximately threefold yielding a Q 10 of 2.1. Hyperpolarizing current pulses induced time-dependent rectification of the voltage response in all neurons at both temperatures. This behavior was previously not observed in dialyzed neurons and was reversibly blocked by external Cs+ (2 mM) but not Ba2+ (1 mM). Voltage-clamp studies of isolated neurons revealed a hyperpolarization-activated inward current. This inwardly rectifying conductance was isolated from other membrane currents using external Cs+. The time and voltage dependence of this current is consistent with I h and contributes to the passive electrical properties of rat intracardiac neurons. In >90% of the neurons studied, depolarizing currents evoked firing of multiple, adapting, action potentials at 22°C. The number of action potentials increased with current strength producing a mean discharge of 5.1 (+100 pA, 1 s pulse), which was attenuated at 37°C to a mean of 1.4. The amplitude and kinetics of the slow, muscarine-sensitive inward and outward currents ( I M) were highly temperature dependent. Lowering the temperature from 37 to 22°C reduced the steady-state current amplitude by approximately one-third and the rate of deactivation of I M by six- to ninefold at all voltages examined. The average Q 10 for the time constant of deactivation of I M was 3.7 ± 0.3 (mean ± SE). Acetylcholine (ACh) induced tonic discharges in response to depolarizing currents (+100 pA, 1 s pulse) at both temperatures. This effect of ACh was inhibited by the muscarinic receptor antagonists, pirenzepine (100 nM), and mL-toxin (60 nM). At 37°C, a mean discharge of 1.5 was increased to 23.5 in the presence of ACh. A similar switch from phasic to tonic discharge was also produced by the potassium channel inhibitors, Ba2+ (1 mM) and uridine-5′-triphosphate (UTP; 100 μM), whereas cadmium, 4-aminopyridine, apamin, charybdotoxin, and dendrotoxin did not alter discharge activity. The pharmacological sensitivity profile and temperature dependence of the active membrane properties are consistent with the muscarine-sensitive potassium current ( I M) regulating the discharge activity in rat intracardiac neurons.
Impulse Encoding Mechanisms of Ganglion Cells in the Tiger Salamander Retina
Authors: Fohlmeister J. F. , Miller R. F.
Published: December 2017

Fohlmeister, J. F. and R. F. Miller. Impulse encoding mechanisms of ganglion cells in the tiger salamander retina. J. Neurophysiol. 78: 1935–1947, 1997. A study of nerve impulse generation in ganglion cells of the tiger salamander retina is carried out through a combination of experimental and analytic approaches, including computer simulations based on a single-compartment model. Whole cell recordings from ganglion cells were obtained using a superfused retina-eyecup preparation and studied with pharmacological and electrophysiological techniques, including phase plot analysis. Experimental efforts were guided by computer simulation studies of an excitability model consisting of five voltage- or ion-gated channels, which were identified from earlier voltage-clamp data. The ion channels include sodium, calcium, and three types of potassium channels, namely the A type ( IK,A), Ca-activated potassium ( IK,Ca), and the delayed rectifier ( IK). A leakage channel was included to preserve input resistance continuity between model and experiment. Ion channel densities of Na and Ca currents ( INaand ICa) for the single-compartment model were independently determined from phase plot analysis. The IKand IK,Acurrent densities were determined from the measured width of impulses. The IK,Cawas modeled to respond to Ca influx, and a variable-rate Ca-sequestering mechanism was implemented to remove cytoplasmic calcium. Impulse frequency increases when either ICaor IK,Cais eliminated from the model or blocked pharmacologically in whole cell recording experiments. Faithful simulations of experimental data show that the ionic currents may be grouped into small ( IK,Ca, leakage, and stimulus), and large ( INa, IK, IA, ICa) on the basis of their peak magnitudes throughout the impulse train. This division of the currents is reflected in their function of controlling the interspike interval (small currents) and impulse generation (large currents). Although the single-compartmental model is qualitatively successful in simulating impulse frequency behavior and its controlling mechanisms, limitations were found that specifically suggest the need to include morphological details. The spike train analysis points to a role for electrotonic currents in the control of the duration of the interspike intervals, which can be compensated by prolonged activation of gK,Cain the single-compartment model. A detailed, multicompartmental model of the ganglion cell is presented in the companion paper.
Intravenous Morphine Increases Release of Nitric Oxide From Spinal Cord by an α-Adrenergic and Cholinergic Mechanism
Authors: Xu Zemin , Tong Chuanyao , Pan Hui-Lin , Cerda Sergio E. , Eisenach James C.
Published: December 2017

Xu, Zemin, Chuanyao Tong, Hui-Lin Pan, Sergio E. Cerda, and James C. Eisenach. Intravenous morphine increases release of nitric oxide from spinal cord by an α-adrenergic and cholinergic mechanism. J. Neurophysiol. 78: 2072–2078, 1997. Systemic opioids produce analgesia in part by activating bulbospinal noradrenergic pathways. Spinally released norepinephrine (NE) has been suggested to produce analgesia in part by stimulating α2-adrenoceptors on cholinergic spinal interneurons to release acetylcholine (ACh). We hypothesized that this spinally released ACh would stimulate synthesis of nitric oxide (NO), and that spinally released NO after intravenous (IV) opioid injection thus would depend on a cascade of noradrenergic and cholinergic receptor stimulation. To test these hypotheses, IV morphine was administered to anesthetized sheep, and neurotransmitters in dorsal horn interstitial fluid were measured by microdialysis. IV morphine increased NE and ACh in dorsal horn microdialysates, and these increases were inhibited by IV naloxone or cervical spinal cord transection. IV morphine also increased dorsal horn microdialysate concentrations of nitrite, a stable metabolite of NO. Increases in NE, ACh, and nitrite were antagonized by prior intrathecal injection of the α2-adrenergic antagonist idazoxan, the muscarinic antagonist atropine, or the NO synthase inhibitor N-methyl-l-arginine (NMLA). To examine the concentration-dependent effects of spinal adrenergic stimulation, isolated rat spinal cord tissue was perfused with the α2-adrenergic agonist clonidine. Clonidine increased nitrite in the spinal cord tissue perfusate, an effect blocked by coadministration of idazoxan, atropine, and NMLA. These data support a previously hypothesized cascade of spinally released NE and ACh after systemic opioid administration. These data also suggest that spinally released NO plays a role in the analgesic effects of systemic opioids. In addition, these data imply a positive feedback whereby spinally released nitric oxide increases NE release and that has not previously been described.
Coactivation of Putative Octopamine- and Serotonin-Containing Interneurons in the Medicinal Leech
Authors: Gilchrist Laura S. , Mesce Karen A.
Published: December 2017

Gilchrist, Laura S. and Karen A. Mesce. Coactivation of putative octopamine- and serotonin-containing interneurons in the medicinal leech. J. Neurophysiol. 78: 2108–2115, 1997. Possible interactions between octopamine-immunoreactive (IR) and serotonergic neurons in the CNS of the medicinal leech were investigated. Simultaneous intracellular recordings of serotonin-containing neurons (either the Retzius neuron or cell 21) and the dorsolateral octopamine-IR (DLO) neuron demonstrated that both sets of neurons are coactive at times. Depolarization of either serotonergic cell 21 or the Retzius neuron did not alter the membrane potential of the DLO. Similarly, depolarization of the DLO did not affect the serotonergic neurons examined. Because it was found that the DLO and either the serotonergic cell 21 or Retzius neuron were at times coactive, we looked for possible sources of common excitatory inputs. The centrally located pressure (P)- and touch (T)-sensitive mechanosensory neurons excited the DLOs through a polysynaptic pathway. Stimulation of nociceptive (N) mechanosensory neurons did not cause a measurable depolarization in the membrane potential of the DLO. Through simultaneous recordings of the DLO, cell 21, and a particular identified mechanosensory neuron, it was demonstrated that activity in the T or P cells can excite both serotonergic cell 21 and the octopamine-IR DLO. These findings indicate that, in many instances, both serotonin and octopamine, biogenic amines with neuromodulatory actions in many different invertebrates, may be released simultaneously in the leech.
Relationship Between Sensory Stimuli–Elicited IPSPs in Motoneurons and PGO Waves During Cholinergically Induced Muscle Atonia
Authors: Kohlmeier Kristi A. , López-Rodríguez Faustino , Morales Francisco R. , Chase Michael H.
Published: December 2017

Kohlmeier, Kristi A., Faustino López-Rodrı́guez, Francisco R. Morales, and Michael H. Chase. Relationship between sensory stimuli–elicited IPSPs in motoneurons and PGO waves during cholinergically induced muscle atonia. J. Neurophysiol. 78: 2145–2155, 1997. Inhibitory postsynaptic potentials (IPSPs) can be produced in masseter motoneurons by sensory stimuli after the injection of carbachol into the nucleus pontis oralis (NPO) of α-chloralose–anesthetized cats. We have postulated previously that these IPSPs, which are induced in masseter motoneurons by sensory stimuli, arise as the result of phasic activation of the motor inhibitory system that mediates atonia occurring spontaneously during active sleep. In the present study, we determined that sensory stimuli, which excite different sensory pathways, somatosensory and auditory, also elicit ponto-geniculo–occipital (PGO) waves during the carbachol-induced state. Because the elicitation of PGO waves has been hypothesized to be a central sign of activation of alerting mechanisms, we suggest that these stimuli also excite those CNS structures that are involved in the alerting network. The temporal association of the sensory stimuli-elicited IPSPs and PGO waves also was examined by correlating the intracellular response of masseter motoneurons and the extracellular response of lateral geniculate nuclei neurons to somatosensory and auditory stimuli. Sensory stimuli produced an IPSP that had a similar latency from the foot of the elicited PGO wave as that of spontaneously occurring motoneuron IPSPs and PGO waves that occur during both carbachol-induced muscle atonia and naturally occurring active sleep. In addition, the intensity of the stimulus necessary for elicitation of PGO waves was found to be lower than that required for the elicitation of IPSPs in motoneurons. Additionally, evoked responses in masseter motoneurons during the carbachol-induced state were graded in response to increases in stimulus intensity. The preceding data suggest that some type of processing of sensory input occurs such that only those stimuli that are capable of activating alerting mechanisms involved in the generation of PGO waves result in an increase in activity in the motor inhibitory system. We conclude that there may be a functional link between alerting mechanisms involved in the generation of PGO waves and the motor inhibitory system that generates IPSPs in motoneurons. This functional link may serve to preserve atonia, and thus the state of active sleep, from potentially disruptive PGO-related influences that, during other behavioral states, result in motor activation.
Spatial Distribution and Discharge Characteristics of Superior Colliculus Neurons Antidromically Activated From the Omnipause Region in Monkey
Authors: Gandhi Neeraj J. , Keller Edward L.
Published: December 2017

Gandhi, Neeraj J. and Edward L. Keller. Spatial distribution and discharge characteristics of superior colliculus neurons antidromically activated from the omnipause region in monkey. J. Neurophysiol. 78: 2221–2225, 1997. One proposed role of the superior colliculus (SC) in oculomotor control is to suppress or excite the activity of brain stem omnipause neurons (OPNs) to initiate or terminate saccades, respectively. Although connections from the SC to the OPNs have been demonstrated, the spatial distribution and discharge characteristics of the projecting neurons from the SC remain unknown. We mapped the spatial distribution of the deeper-layer neurons of the SC by stimulating the region of the OPNs to identify antidromic projections and found that the density of direct projections from the SC to the OPNs was greatest in the most rostral region and decreased gradually for more caudal sites. On the basis of saccade-related discharge characteristics, the antidromically driven neurons were predominantly fixation and buildup neurons. The spatially distributed SC projections to the OPNs and the discharge characteristics of the SC neurons suggest that the direct projections from SC to OPNs are excitatory. Finally, we propose how excitation and disfacilitation from SC activity can contribute to modulation of OPN response and control saccades.
Object Representation in the Ventral Premotor Cortex (Area F5) of the Monkey
Authors: Murata Akira , Fadiga Luciano , Fogassi Leonardo , Gallese Vittorio , Raos Vassilis , Rizzolatti Giacomo
Published: December 2017

Murata, Akira, Luciano Fadiga, Leonardo Fogassi, Vittorio Gallese, Vassilis Raos, and Giacomo Rizzolatti. Object representation in the ventral premotor cortex (area F5) of the monkey. J. Neurophysiol. 78: 2226–2230, 1997. Visual and motor properties of single neurons of monkey ventral premotor cortex (area F5) were studied in a behavioral paradigm consisting of four conditions: object grasping in light, object grasping in dark, object fixation, and fixation of a spot of light. The employed objects were six different three-dimensional (3-D) geometric solids. Two main types of neurons were distinguished: motor neurons ( n = 25) and visuomotor neurons ( n = 24). Motor neurons discharged in association with grasping movements. Most of them ( n = 17) discharged selectively during a particular type of grip. Different objects, if grasped in similar way, determined similar neuronal motor responses. Visuomotor neurons also discharged during active movements, but, in addition, they fired also in response to the presentation of 3-D objects. The majority of visuomotor neurons ( n = 16) showed selectivity for one or few objects. The response was present both in object grasping in light and in object fixation conditions. Visuomotor neurons that selectively discharged to the presentation of a given object discharged also selectively during grasping of that object. In conclusion, object shape is coded in F5 even when a response to that object is not required. The possible visual or motor nature of this object coding is discussed.
Properties of Calcium Spikes Revealed During GABAA Receptor Antagonism in Hippocampal CA1 Neurons From Guinea Pigs
Authors: Miura Masami , Yoshioka Masatomo , Miyakawa Hiroyoshi , Kato Hiroshi , Ito Ken-Ichi
Published: December 2017

Miura, Masami, Masatomo Yoshioka, Hiroyoshi Miyakawa, Hiroshi Kato, and Ken-Ichi Ito. Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs. J. Neurophysiol. 78: 2269–2279, 1997. Intracellular electrical responses and changes in intracellular calcium concentration ([Ca2+]i) in response to activation of synaptic inputs and to DC injections were recorded simultaneously from CA1 pyramidal neurons ( n = 42) in guinea pig hippocampal slices. In the presence of the γ-aminobutyric acid-A (GABAA) receptor antagonists, bicuculline (25 μM) and picrotoxin (10 μM), broad (>20 ms) all-or-none spikes were induced by activation of synaptic inputs (20 pulses, 30 Hz) and were accompanied by a simultaneous rapid and large rise in [Ca2+]i (34 of 34 cells). By contrast, direct depolarizing current (0.7 nA, 1 s) induced spikes having short duration, during which time the spike firing pattern was observed not to be significantly affected. When Na+ channels were blocked by QX-314 applied intracellularly through the recording microelectrode in the presence of GABAA receptor antagonists, broad spikes were frequently generated by activation of synaptic inputs (32 of 33 cells). These broad spikes were blocked by Cd2+ (200 μM) or in Ca2+-free medium (6 of 6 cells) but were resistant to either tetrodotoxin (TTX; 1 μM; 6 of 6 cells) or QX-314, whereas short-duration spikes were blocked by both TTX andQX-314. Based on these findings we conclude that broad and short-duration spikes are Ca2+ and Na+ spikes, respectively. To investigate the properties of the Ca2+ spikes, antagonists of a voltage-operated Ca2+ channel were applied to the evoked responses. Nifedipine (30 μM), a L-type Ca2+ channel blocker, suppressed the generation of Ca2+ spikes, whereas Ni2+ (100 μM), theT- and R-type Ca2+ channel blocker, and ω-agatoxin-IVA (ω-Aga-IVA, 60 nM), a P-type Ca2+ channel blocker, had little effect on the generation of Ca2+ spikes. Nifedipine suppressed the rise in [Ca2+]i induced by synaptic inputs up to 26% of the control in the soma and 18–32% in the dendrites ( n = 5), respectively, whereas Ni2+ suppressed the rise by 12–27% ( n = 5) in both soma and dendrites. ω-Aga-IVA showed little effect (less than a 10% change; n = 7). These results suggest that the GABAA inhibitory system tonically suppresses dendritic Ca2+ spikes, and the L-type Ca2+ channel plays a major role in the generation of Ca2+ spikes and in Ca2+ influx.
Reaching Movements With Similar Hand Paths but Different Arm Orientations. II. Activity of Individual Cells in Dorsal Premotor Cortex and Parietal Area 5
Authors: Scott Stephen H. , Sergio Lauren E. , Kalaska John F.
Published: December 2017

Scott, Stephen H., Lauren E. Sergio, and John F. Kalaska. Reaching movements with similar hand paths but different arm orientations. II. Activity of individual cells in dorsal premotor cortex and parietal area 5. J. Neurophysiol. 78: 2413–2426, 1997. Neuronal activity in primary motor cortex (MI) is altered when monkeys make reaching movements along similar handpaths at shoulder level with two different arm orientations, either in the natural orientation with the elbow positioned below the level of the shoulder and hand or in an abducted orientation with the elbow abducted nearly to shoulder level. The present study examines to what degree two other cortical areas, the dorsal premotor (PMd) and parietal area 5, also show modulation of cell activity related to arm geometry during reaching. The activity of most (89%) of the 207 cells in PMd recorded while monkeys made reaching movements showed a statistically significant change in activity between orientations [analysis of variation (ANOVA), P < 0.01]. A common effect of arm orientation on cell activity was a change in the overall level of discharge either before, during, and/or after movement (67%, ANOVA, task main effect, P < 0.01). Many cells (76%) showed a statistical change in their response to movement direction (ANOVA, task × direction interaction term, P < 0.01), including changes in dynamic range and changes in the preferred direction of cells that were directionally tuned in both arm orientations. Overall, these effects were similar qualitatively but not as strong quantitatively as those observed in MI. A sample of cells was recorded in area 5 of one monkey. Most (95%) of the 79 area 5 cells showed a change in activity when reaching movements were performed using different arm orientations (ANOVA, P < 0.01). As in PMd and MI, many area 5 cells (56, 71%) showed changes in their tonic discharge before, during, and/or after movement, and 70 cells (89%) showed changes in their response to movement direction (ANOVA, task × direction interaction term, P < 0.01). The observed changes in neuronal activity related to posture and movement in MI, PMd and area 5 demonstrate that single-cell activity in these cortical areas is not simply related to the spatial attributes of hand trajectory but is also strongly influenced by attributes of movement related to arm geometry.
Electrical Properties of a Cockroach Motor Neuron Soma Depend on Different Characteristics of Individual Ca Components
Authors: Mills Janette D. , Pitman Robert M.
Published: December 2017

Mills, Janette D. and Robert M. Pitman. Electrical properties of a cockroach motor neuron soma depend on different characteristics of individual Ca components. J. Neurophysiol. 78: 2455–2466, 1997. The “fast” coxal depressor motor neuron (Df) of the cockroach is among the most extensively studied of insect neurons. It has been shown that the cell body of this neuron can exhibit active electrical properties, which may change over time or with chemical modulation. To further understand these electrical events and their modulation, inward currents in Dfhave been characterized under conditions in which outward currents have been suppressed. The inward current activated at potentials positive to −60 mV and peaked between −10 and 0 mV when measured in barium saline and between 0 and +10 mV when measured in calcium saline. The inward current was insensitive to Ni2+(100 μM) but reduced by verapamil (50 μM) and abolished by Cd2+(1 mM). Two components of ICawere identified by their sensitivity to either 50 μM nifedipine or micromolar Cd2+. The nifedipine-sensitive component activated positive to −60 mV and peaked between −10 and 0 mV, whereas the Cd2+-sensitive component activated positive to −40 mV and peaked between +10 and +20 mV. Immediately after dissection, depolarization of Dfevoked plateau potentials, whereas 1–4 h after dissection, depolarization evoked action potentials. The plateau potentials were insensitive to 100 μM Cd2+but blocked by 50 μM nifedipine, whereas the spikes required a combination of nifedipine (50 μM) and Cd2+(100 μM) for complete suppression, indicating that only one component of ICacontributes to the plateau potential, whereas both components contribute to action potentials. Currents measured in calcium saline decayed faster than currents measured in barium saline. The inactivation characteristics were investigated with the use of double-pulse voltage-clamp experiments. ICashowed a greater degree of inactivation and slower recovery from inactivation than did IBa. Current decay and the extent of inactivation were reduced after injection of the calcium-chelator 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid (BAPTA). This suggests that the calcium current of this neuron displays calcium-dependent inactivation. An additional mechanism, most probably voltage-dependent inactivation, also occurs because IBa, even in neurons injected with BAPTA, displayed some inactivation. The inactivation characteristics may be important in determining activity displayed by Df. Indirect evidence suggests that intracellular calcium is high immediately after dissection. At this time, the calcium current may therefore be reduced due to calcium-dependent inactivation. This may, at least partly, explain why the cell does not spike shortly after dissection.
Calcium-Dependent Plateau Potentials in Rostral Ambiguus Neurons in the Newborn Mouse Brain Stem In Vitro
Authors: Rekling Jens C. , Feldman Jack L.
Published: December 2017

Rekling, Jens C. and Jack L. Feldman. Calcium-dependent plateau potentials in rostral ambiguus neurons in the newborn mouse brain stem in vitro. J. Neurophysiol. 78: 2483–2492, 1997. The nucleus ambiguus contains vagal and glossopharyngeal motoneurons and preganglionic neurons involved in respiration, swallowing, vocalization, and control of heart beat. Here we show that the rostral compact formation's ambiguus neurons, which control the esophageal phase of swallowing, display calcium-dependent plateau potentials in response to tetanic orthodromic stimulation or current injection. Whole cell recordings were made from visualized neurons in the rostral nucleus ambiguus using a slice preparation from the newborn mouse. Biocytin-labeling revealed dendritic trees with pronounced rostrocaudal orientations confined to the nucleus ambiguus, a morphological profile matching that of vagal motoneurons projecting to the esophagus. Single-stimulus orthodromic activation, using an electrode placed in the dorsomedial slice near the nucleus tractus solitarius, evoked single excitatory postsynaptic potentials (EPSPs) or short trains of EPSPs (500 ms to 1 s). However, tetanic stimulation (5 pulses, 10 Hz) induced voltage-dependent afterdepolarizations or long-lasting plateau potentials (>1 min) with a constant firing pattern. Depolarizing or hyperpolarizing current pulses elicited voltage-dependent afterdepolarizations or plateau potentials lasting a few seconds to several minutes. Constant spike activity accompanied the long-lasting plateau potentials, which ended spontaneously or could be terminated by weak hyperpolarizing current pulses. Current-induced afterdepolarizations and plateau potentials were dependent on extracellularand intracellular Ca2+, as they were blocked completely by extracellular Co2+, Cd2+, or intracellular bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA). Orthodromically induced afterdepolarizations and plateau potentials were blocked by intracellular BAPTA. Afterdepolarizations and plateau potentials were completely blocked by substitution of extracellular Na+ with choline. Afterdepolarizations persisted in tetrodotoxin. We conclude that rostral ambiguus neurons have a Ca2+-activated inward current carried by Na+. Synaptic activation of this conductance may generate prolonged spike activity in these neurons during the esophageal phase of swallowing.
Receptive Properties of Embryonic Chick Sensory Neurons Innervating Skin
Authors: Koltzenburg Martin , Lewin Gary R.
Published: December 2017

Koltzenburg, Martin and Gary R. Lewin. Receptive properties of embryonic chick sensory neurons innervating skin. J. Neurophysiol. 78: 2560–2568, 1997. We describe a new in vitro skin-nerve preparation from chick embryos that allows detailed study of the functional properties of developing sensory neurons innervating skin. Functionally single sensory afferents were isolated by recording from their axons in microdissected filaments of the cutaneous femoralis medialis nerve, which innervates skin of the thigh. A total of 157 single neurons were characterized from embryos [embryonic days 17–21 ( E17–E21), n = 115] and hatchlings up to 3 wk old ( n = 42). Neurons were initially classified on the basis of their conduction velocity; those conducting below 1.0 m/s were being classified as C fibers and faster conducting fibers as A fibers. The proportions of A and C fibers encountered in embryonic and hatchling preparations were not very different, indicating that myelination and axon growth proceeds quite slowly over the period studied. Afferent fibers that could subserve nociceptive and nonnociceptive functions were identified in the time period studied. Subpopulations of low-threshold myelinated afferent units exhibited rapidly or slowly adapting discharges to constant force stimuli and could have tactile functions. Many afferent fibers responded to noxious heat and were excited and sensitized by exposure to inflammatory mediators, suggesting that they are nociceptors. The behavior of these units changed in several respects over the period studied. The discharge of C fibers to noxious heat increased with age as did their mechanical thresholds. A substantial population of heat-responsive neurons (34% of the A fibers) present in embryos were not encountered in hatchling chicks. This indicates that substantial changes in the physiological response properties of sensory afferents occur after hatching. We conclude that this new preparation can be used for quantitative assessment of the receptive properties of developing sensory neurons and has considerable potential for the investigation of factors, such as neurotrophins, that specify and influence the functional phenotype of sensory neurons during embryonic development in vivo.
Inwardly Rectifying and Ca2+-Permeable AMPA-Type Glutamate Receptor Channels in Rat Neocortical Neurons
Authors: Itazawa Shun-Ichi , Isa Tadashi , Ozawa Seiji
Published: December 2017

Itazawa, Shun-Ichi, Tadashi Isa, and Seiji Ozawa. Inwardly rectifying and Ca2+-permeable AMPA-type glutamate receptor channels in rat neocortical neurons. J. Neurophysiol. 78: 2592–2605, 1997. Current-voltage ( I-V) relations and Ca2+ permeability of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)type glutamate receptor channels were investigated in neurons of rat neocortex by using the whole cell patch-clamp technique in brain slices. To activate AMPA receptor channels, kainate was used as a nondesensitizing agonist. A patch pipette was filled with solution containing 100 μM spermine to maintain the inward rectification of Ca2+-permeable AMPA receptor channels. Three types of responses to kainate were observed: type I response with outwardly rectifying I-V relation, type II response with I-V relation of marked inward rectification, and intermediate response with I-V relation of weaker inward rectification. Neurons with type I, type II and intermediate I-V relations were referred to as type I, type II, and intermediate neurons, respectively. Of a total of 223 recorded cells, 90 (40.4%) were type I, 129 (57.8%) intermediate, and 4 (1.8%) type II neurons. Properties of AMPA receptor channels were examined in the former two types of neurons. The value of PCa:PCs, the ratio of the permeability coefficients of Ca2+ and Cs+, was estimated from the reversal potentials of kainate responses in the outside-out patches bathed in Na+-free solution containing 100 mM Ca2+ according to the constant-field equation. They ranged from 0.05 to 0.10 (0.08 ± 0.02, mean ± SD, n = 8) for type I neurons and from 0.14 to 1.29 (0.60 ± 0.37, n = 11) for the intermediate neurons. There was a close correlation between the inward rectification and the Ca2+ permeability in AMPA receptor channels in these neurons. Intermediate neurons stained with biocytin were nonpyramidal cells with ellipsoidal-shaped somata. Type I neurons had either triangular- or ellipsoidal-shaped somata. Excitatory postsynaptic currents (EPSCs) recorded in both type I and intermediate neurons had 6-cyano-7-nitroquinoxaline-2,3-dione-sensitive fast and d−2-amino-5-phosphonovalerate-sensitiveslow components. The I-V relation of the fast component exhibited inward rectification in the intermediate neuron, whereas that in the type I neuron showed slight outward rectification. The fast component of EPSCs in the intermediate neuron was suppressed more prominently (to 56 ± 15% of the control, n = 12) than that in the type I neuron (to 78 ± 6% of the control, n = 6) by bath application of 1 mM spermine. These results indicate that inwardly rectifying and Ca2+-permeable AMPA receptor channels are expressed in a population of neurons of rat neocortex and are involved in excitatory synaptic transmission.
Stochastic Threshold Characterization of the Intensity of Active Channel Dynamical Action Potential Generation
Authors: Schmich Robert M. , Miller Michael I.
Published: December 2017

Schmich, Robert M. and Michael I. Miller. Stochastic threshold characterization of the intensity of active channel dynamical action potential generation. J. Neurophysiol. 78: 2616–2630, 1997. This paper develops a stochastic intensity description for action potential generation formulated in terms of stochastic processes, which are direct analogues of the physiological processes of the pre- and postsynaptic complex of the cochlear nerve: 1) neurotransmitter release is modeled as an inhomogeneous Poisson counting process with release intensity μ t , 2) the excitatory postsynaptic conductance (EPSC) process is modeled as a marked, linearly filtered Poisson process resulting from the linear superposition of standard shaped postsynaptic conductances of size G, and 3) action potential generation is modeled as resulting from the EPSC exceeding a random threshold determined by active channel dynamics of the Hodgkin-Huxley type. The random threshold is defined to be the least upper bound in the size of a standard-shaped neurotransmitter release injected at time t given the previous action potential time and the number of releases occurring in a short preconditioning time increment. The action potential process is modeled as a self-exciting point process with stochastic intensity resulting from the probability that the random threshold process crosses the threshold in some small time increment that is a function of time since previous action potential, release intensity, and the probability that a single synaptic event exceeds the stochastic threshold. The stochastic intensity model is consistent with a direct simulation of the nonlinear Hodgkin-Huxley differential equations over a variety of parameters for the vesicle release intensity, vesicle size, vesicle duration, and temperatures. Results are presented showing that the regularity properties seen in the vestibular primary afferent in the lizard, Calotes versicolor, associated with a slow-to-activate potassium channel resulting in a long afterhyperpolarization can be accommodated directly by the stochastic intensity description. The stimulus dependence of the model is attributed to synaptic transmission and the probabilistic nature to the threshold conductance process, which is dependent upon the EPSC process. The stochastic intensity is seen to have a form consistent with the phenomenologically based Siebert-Gaumond model, a stimulus-related function of time multiplied by a refractory-related function of time since previous action potential.
Independent Coding of Wind Direction in Cockroach Giant Interneurons
Authors: Mizrahi Adi , Libersat Frederic
Published: December 2017

Mizrahi, Adi and Frederic Libersat. Independent coding of wind direction in cockroach giant interneurons. J. Neurophysiol. 78: 2655–2661, 1997. In this study we examined the possible role of cell-to-cell interactions in the localization processing of a wind stimulus by the cockroach cercal system. Such sensory processing is performed primarily by pairs of giant interneurons (GIs), a group of highly directional cells. We have studied possible interactions among these GIs by comparing the wind sensitivity of a given GI before and after removing another GI with the use of photoablation. Testing various combinations of GI pairs did not reveal any suprathreshold interactions. This was true for all unilateral GI pairs on the left or right side as well as all the bilateral GI pairs (left and right homologues). Those experiments in which we were able to measure synaptic activity did not reveal subthreshold interactions between the GIs either. We conclude that the GIs code independently for a given wind direction without local GI–GI interactions. We discuss the possible implications of the absence of local interactions on information transfer in the first station of the escape circuit.
Axotomy Increases the Excitability of Dorsal Root Ganglion Cells With Unmyelinated Axons
Authors: Zhang Jun-Ming , Donnelly David F. , Song Xue-Jun , Lamotte Robert H.
Published: December 2017

Zhang, Jun-Ming, David F. Donnelly, Xue-Jun Song, and Robert H. LaMotte. Axotomy increases the excitability of dorsal root ganglion cells with unmyelinated axons. J. Neurophysiol. 78: 2790–2794, 1997. To better understand the neuronal mechanism of neuropathic pain, the effect of axotomy on the excitability of dorsal root ganglion (DRG) cells with unmyelinated axons (C cells) was investigated. Whole cell patch-clamp recordings were performed on intact DRG cells with intact axons or with axons transected 7–12 days earlier. C cells were identified by 1) soma size, 2) action potential morphology, 3) conduction velocity, and 4) in some cases, injection of Fast Blue into the injured nerve fibers. Axotomy reduced (more negative) action potential threshold but did not significantly change resting membrane potential, action potential duration, or maximal depolarization rate. Axotomy significantly increased the peak sodium current measured under voltage-clamp conditions. In Fast Blue–labeled (injured) cells, thetetrodotoxin (TTX)-sensitive current was enhanced while the TTX-resistant current was reduced. These results suggest that axotomy increased the excitability of C cells, possibly because of a preferential increase in expression of TTX-sensitive sodium currents.
Gain Adaptation of Eye and Head Movement Components of Simian Gaze Shifts
Authors: Phillips James O. , Fuchs Albert F. , Ling Leo , Iwamoto Yoshiki , Votaw Scott
Published: December 2017

Phillips, James O., Albert F. Fuchs, Leo Ling, Yoshiki Iwamoto, and Scott Votaw. Gain adaptation of eye and head movement components of simian gaze shifts. J. Neurophysiol. 78: 2817–2821, 1997. To investigate the site of gaze adaptation in primates, we reduced the gain of large head-restrained gaze shifts made to 50° target steps by jumping the target 40% backwards during a targeting saccade and then tested gain transfer to the eye- and head-movement components of head-unrestrained gaze shifts. After several hundred backstep trials, saccadic gain decreased by at least 10% in 8 of 13 experiments, which were then selected for further study. The minimum saccadic gain decrease in these eight experiments was 12.8% (mean = 18.4%). Head-unrestrained gaze shifts to ordinary 50° target steps experienced a gain reduction of at least 9.3% (mean = 14.9%), a mean gain transfer of 81%. Both the eye and head components of the gaze shift also decreased. However, average head movement gain decreased much more (22.1%) than eye movement gain (9.2%). Also, peak head velocity generally decreased significantly (20%), but peak eye velocity either increased or remained constant (average increase of 5.6%). However, the adapted peak eye and head velocities were appropriate for the adapted, smaller gaze amplitudes. Similar dissociations in eye and head metrics occurred when head-unrestrained gaze shifts were adapted directly ( n = 2). These results indicated that head-restrained saccadic gain adaptation did not produce adaptation of eye movement alone. Nor did it produce a proportional gain change in both eye and head movement. Rather, normal eye and head amplitude and velocity relations for a given gaze amplitude were preserved. Such a result could be explained most easily if head-restrained adaptation were realized before the eye and head commands had been individualized. Therefore, gaze adaptation is most likely to occur upstream of the creation of separate eye and head movement commands.
Functional Role of Peptidergic Anterior Lobe Neurons in Male Sexual Behavior of the SnailLymnaea stagnalis
Authors: A.C.M. De Boer Pamela , Maat Andries Ter , Pieneman Anton W. , Croll Roger P. , Kurokawa Makoto , Jansen René F.
Published: December 2017

De Boer, Pamela A.C.M., Andries Ter Maat, Anton W. Pieneman, Roger P. Croll, Makoto Kurokawa, and René F. Jansen. Functional role of peptidergic anterior lobe neurons in male sexual behavior of the snail Lymnaea stagnalis. J. Neurophysiol. 78: 2823–2833, 1997. A morphologically defined group of peptidergic neurons in the CNS of the hermaphroditic snail, Lymnaea stagnalis, is concerned with the control of a very specific element of male sexual behavior. These neurons are located in the anterior lobe of the right cerebral ganglion (rAL). By using chronically implanted electrodes, we show that the rAL neurons are selectively active during eversion of the penis-carrying structure, the preputium. The preputium is normally contained inside the body cavity and is everted during copulation in the male role. Electrical stimulation of the rAL neurons through the implanted electrodes, induced eversion of the preputium in vivo. Injection of APGWamide (Ala-Pro-Gly-Try-NH2), a small neuropeptide that is present in all rAL neurons, induced eversion of the preputium. Application of APGWamide to in vitro preparations of the preputium caused relaxation of this organ. In contrast, injection of the neuropeptide conopressin, which is co-localized with APGWamide in 60% of the rAL neurons, did not induce any behavior associated with male sexual activities. These results show that the neurons of the rAL can induce an eversion of the preputium as occurs during male copulation by release of APGWamide during a period of electrical activity.
Encoding of Object Curvature by Tactile Afferents From Human Fingers
Authors: Goodwin A. W. , Macefield V. G. , Bisley J. W.
Published: December 2017

Goodwin, A. W., V. G. Macefield, and J. W. Bisley. Encoding of object curvature by tactile afferents from human fingers. J. Neurophysiol. 78: 2881–2888, 1997. Isolated responses were recorded from fibers in the median nerves of human subjects by using microneurography. Mechanoreceptive afferent fibers with receptive fields on the fingerpads were selected. The fingers were immobilized and spherical stimuli were applied passively to the receptive field with a contact force of 40-, 60-, or 80-g weight. The radii of the spheres were 1.92, 2.94, 5.81, or 12.4 mm or ∞ (flat); the corresponding curvatures, given by the reciprocal of the radii, were 694, 340, 172, 80.6, or 0 m−1, respectively. When the spheres were applied to the receptive field center of slowly adapting type I afferents (SAIs), the response increased as the curvature of the sphere increased and also increased as the contact force increased. All SAIs behaved in the same way except for a scaling factor proportional to the sensitivity of the afferent. When a sphere was located at different positions in the receptive field, the shape of the resulting response profile reflected the shape of the sphere; for more curved spheres the profile was higher and narrower (increased peak and decreased width). Slowly adapting type II afferents (SAIIs) showed different response characteristics from the SAIs when spheres were applied to their receptive field centers. As the curvature of the stimulus increased from 80.6 to 172 m−1, the response increased. However, further increases in curvature did not result in further increases in response. An increase in contact force resulted in an increase in the response of SAIIs; this increase was proportionately greater than it was for SAIs. For SAIIs, the shape of the receptive field profile did not change when the curvature of the stimulus changed. For fast-adapting type I afferents (FAIs), the responses were small and did not change systematically with changes in curvature or contact force. Fast-adapting type II afferents (FAIIs) did not respond to our stimuli. Human SAIs, FAIs, and FAIIs behaved like monkey SAIs, FAIs, and FAIIs, respectively. The response of the SAI population contains accurate information about the shape of the sphere and its position of contact on the finger and also indicates contact force. Conversely, whereas SAIIs possess a greater capacity to encode changes in contact force, they provide only coarse information on local shape.