bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Analysis of Firing Properties of Pyramidal Neurons From Layer 5 of Rat Sensorimotor Cortex
Authors: Schwindt Peter , O'Brien Jennifer A. , Crill Wayne
Published: December 2017

Schwindt, Peter, Jennifer A. O'Brien, and Wayne Crill. Quantitative analysis of firing properties of pyramidal neurons from layer 5 of rat sensorimotor cortex. J. Neurophysiol. 77: 2484–2498, 1997. Quantitative aspects of repetitive firing evoked by injected current steps and ramps were studied in layer 5 pyramidal neurons in brain slices of rat sensorimotor cortex to answer the following questions. Do the tonic firing properties of burst-firing and regular-spiking (nonbursting) neurons differ significantly? Does burst firing denote a discrete class of neurons or represent a continuum of firing properties? Is firing rate during the burst of action potentials related to stimulus amplitude? What aspect of the stimulus might the initial firing rate code? How stable are a neuron's firing properties over time? All recorded neurons fired tonically to a long-lasting current above a minimum value, and the tonic firing properties of most neurons were quite similar irrespective of their initial response to a current step. Only a group of high-resistance neurons had significantly different tonic firing properties. When slow current ramps (rising between 0.5 and ≈20 nA/s) were applied, the relation between firing rate and current during the ramp was very similar to the relation between tonic firing rate and current obtained from long-lasting current steps. Low-resistance cells exhibited three distinct initial responses to a current step: fast adaptation, high-threshold bursts, and low-threshold bursts, observed in 54, 28, and 10% of recorded cells, respectively. High-resistance cells exhibited a distinctive slow adaptation of firing rate. Slowly adapting, fast-adapting (FA), and high-threshold burster (HTB) neurons exhibited no adaptation near the minimum current that evoked repetitive firing ( I o). FA and HTB cells exhibited two-spike adaptation to a final tonic firing rate during currents up to 1.6 times I o. Only a higher current (2.1 times I o) evoked a burst in HTB cells, whereas a burst was evoked at I o in the low-threshold burster cells. In most cells analyzed, the initial firing rate, whatever its nature, increased monotonically with current step amplitude. The response to fast current ramps indicated that firing rate during adaptation or bursting may code rate of change of current. Repeated measurements during long-duration impalements indicated that both transient and tonic firing properties are stable over time. We discuss how the different tonic firing properties of large and small pyramidal neurons could be more important functionally than the different transient responses (burst/nonburst) of the large neurons. We conclude that the large neurons would perform a better linear transduction of time-varying synaptic current that reaches their somata. We compare the responses evoked by somatically injected current with those evoked by dendritic glutamate iontophoresis in previous studies.
Effects of the Volatile Anesthetic Enflurane on Spontaneous Discharge Rate and GABAA-Mediated Inhibition of Purkinje Cells in Rat Cerebellar Slices
Authors: Antkowiak Bernd , Heck Detlef
Published: December 2017

Antkowiak, Bernd and Detlef Heck. Effects of the volatileanesthetic enflurane on spontaneous discharge rate and GABAA-mediated inhibition of Purkinje cells in rat cerebellar slices. J. Neurophysiol. 77: 2525–2538, 1997. The effects of the volatile anesthetic enflurane on the spontaneous action potential firing and on γ-aminobutyric acid-A (GABAA)-mediated synaptic inhibition of Purkinje cells were investigated in sagittal cerebellar slices. The anesthetic shifted the discharge patterns from continuous spiking toward burst firing and decreased the frequency of extracellularly recorded spontaneous action potentials in a concentration-dependent manner. Half-maximal reduction was observed at a concentration corresponding to 2 MAC (1 MAC induces general anesthesia in 50% of patients and rats). When the GABAA antagonist bicuculline was present, 2 MAC enflurane reduced action potential firing only by 13 ± 8% (mean ± SE). In further experiments, inhibitory postsynaptic currents (IPSCs) were monitored in the whole cell patch-clamp configuration from cells voltage clamped close to −80 mV. At 1 MAC, enflurane attenuated the mean amplitude of IPSCs by 54 ± 3% while simultaneously prolonging the time courses of monoexponential current decays by 413 ± 69%. These effects were similar when presynaptic action potentials were suppressed by 1 μM tetrodotoxin. At 1–2 MAC, enflurane increased GABAA-mediated inhibition of Purkinje cells by 97 ± 20% to 159 ± 38%. During current-clamp recordings, the anesthetic (2 MAC) hyperpolarized the membrane potential by 5.2 ± 1.1 mV in the absence, but only by 1.6 ± 1.2 mV in the presence, of bicuculline. These results suggest that enflurane-induced membrane hyperpolarizations, as well as the reduction of spike rates, were partly caused by an increase in synaptic inhibition. Induction of burst firing was related to other actions of the anesthetic, probably an accelerated activation of an inwardly directed cationic current and a depression of spike afterhyperpolarizations.
Lateral and Medial Olivocochlear Neurons Have Distinct Electrophysiological Properties in the Rat Brain Slice
Authors: Fujino Kiyohiro , Koyano Konomi , Ohmori Harunori
Published: December 2017

Fujino, Kiyohiro, Konomi Koyano, and Harunori Ohmori. Lateral and medial olivocochlear neurons have distinct electrophysiological properties in the rat brain slice. J. Neurophysiol. 77:2788–2804, 1997. Electrical properties of cochlear efferent (olivocochlear) neurons were investigated with the use of the whole cell patch recording technique in slice preparations of the neonatal rat (postnatal days 5–11). Lateral and medial olivocochlear (LOC and MOC, respectively) neurons were retrogradely labeled with a fluorescent tracer injected into the cochlea. Stained neurons were identified under a fluorescence microscope, and they were subjected to whole cell recording. LOC and MOC neurons showed different electrophysiological properties. Both showed spike trains of tonic pattern in response to injection of depolarizing current pulses at the resting membrane potential (−60 to −70 mV). However, when the membrane was slightly hyperpolarized (−72 to −76 mV), LOC neurons showed spike trains with a long first interspike interval (ISI), whereas MOC neurons showed spike trains with a long latency to the first spike. Extracellular application of 4-aminopyridine (4-AP; 0.5–2 mM) shortened these ISIs and latencies. In voltage-clamp experiments, two transient outward currents with different (fast and slow) decay kinetics were observed in LOC neurons. The fast outward current ( I A-LOC) was inactivated by the preceding depolarization, and decayed with a time constant (τ) of 86 ms (at 0 mV). The preceding potential, which reduced the current size to the half-maximum ( V 1/2), was −72 mV. The slow current ( I KD) decayed with a τ of 853 ms (at 0 mV). I A-LOC was sensitive to 4-AP (2 mM), and was less sensitive to tetraethylammonium chloride (TEA; 20 mM). I KD was partially blocked by TEA (20 mM), but was insensitive to 4-AP (2 mM). The recovery from inactivation of I A-LOC was time dependent with a time constant (τrec) of 32 ms at −90 mV. MOC neurons also showed a transient outward current that consisted of a single transient component ( I A-MOC) with a steady outward current. I A-MOC was inactivated by the preceding depolarization. Decay τ of I A-MOC was 33 ms (at 0 mV), and V 1/2 was −75 mV. I A-MOC was sensitive to 4-AP (0.5–1 mM). The time-dependent recovery from inactivation of I A-MOC was faster than that of I A-LOC, and τrec was 15 ms at −90 mV. The different kinetics of transient outward currents between LOC and MOC neurons seems to be responsible for the difference in firing properties of these two neurons.
Inhibitory Effects Evoked From the Anterior Hypothalamus Are Selective for the Nociceptive Responses of Dorsal Horn Neurons With High- and Low-Threshold Inputs
Authors: Workman B. J. , Lumb B. M.
Published: December 2017

Workman, B. J. and B. M. Lumb. Inhibitory effects evoked from the anterior hypothalamus are selective for the nociceptive responses of dorsal horn neurons with high- and low-threshold inputs. J. Neurophysiol. 77: 2831–2835, 1997. The aim of the present study was to examine the selectivity of descending control of nociceptive information in the spinal dorsal horn following neuronal activation at “pressor” sites in the anterior hypothalamus. Extracellular single-unit activity was recorded from 11 dorsal horn neurons in the lower lumbar spinal cord of anesthetized rats. Neurons selected for investigation were those that responded to noxious (pinch and radiant heat >46°C) and nonnoxious (prod, stroke, and/or brush) stimulation within their cutaneous receptive fields on the ipsilateral hind paw. These are referred to as Class 2 neurons. Micropipettes were inserted stereotaxically into the anterior hypothalamus at sites where injection of the excitatory amino acidl-homocysteic acid (l-HCA) evoked increases in arterial blood pressure. The effects of microinjection of l-HCA at “pressor” sites in the anterior hypothalamus were then tested on the responses of Class 2 neurons to noxious and nonnoxious stimulation of their excitatory receptive fields. The high-threshold (pinch and/or radiant heat) responses of 7/7 Class 2 neurons tested were inhibited by an average of 66.3 ± 8.8% (mean ± SE) by neuronal activation at hypothalamic pressor sites. The low-threshold (prod) responses of 10/10 Class 2 neurons tested were not inhibited by neuronal activation at hypothalamic pressor sites; in 6 of these cells the response to low-intensity stimulation was increased by between 4 and 20%. Control injections of the inhibitory amino acid γ-aminobutyric acid (GABA) at the same hypothalamic pressor sites had no significant effects on arterial blood pressure or neuronal activity. With regard to sensory processing in the spinal cord, these data suggest that descending inhibitory control that originates from neurons in pressor regions of the anterior hypothalamus is highly selective for nociceptive inputs to Class 2 neurons.
Distinct Patterns of Motor Unit Behavior During Muscle Spasms in Spinal Cord Injured Subjects
Authors: Thomas C. K. , Ross B. H.
Published: December 2017

Thomas, C. K. and B. H. Ross. Distinct patterns of motor unit behavior during muscle spasms in spinal cord injured subjects. J. Neurophysiol. 77: 2847–2850, 1997. Surface electromyograms (EMG) and force were recorded during repeated involuntary spasms of paralyzed triceps surae muscles of four men with chronic cervical spinal cord injury. The firing rates of 78 medial gastrocnemius (MG) motor units also were recorded intramuscularly with tungsten microelectrodes. Spasms typically involved a relatively rapid rise, then a more gradual fall in triceps surae EMG and torque. Motor unit firing rates either increased and then decreased with the spasm intensity (54%) or were relatively constant (26%), firing mainly at 2–10 Hz. The remaining units (20%) produced trains that included one or several doublets. Mean peak spasm firing rates were 18 ± 9 Hz (mean ± SD) for rate modulated units and 11 ± 10 Hz for units with little or no rate modulation. Some motor units fired at rates comparable with those recorded previously during maximum voluntary contractions performed by intact subjects. Others fired at rates below the minimum usually seen when normal units are first recruited (<6 Hz). Doublets (interspike interval <10 ms) often repeated every 123–333 ms, or were interspersed in trains firing at low steady rates (<11 Hz). This study shows that rate coding for many motor units appears to be similar whether descending motor input is intact or whether it has been reduced severely by spinal cord injury. In contrast, rate modulation in other units appears to depend mainly on voluntary motor commands.
Regularity of Firing of Neurons in the Inferior Colliculus
Authors: Rees Adrian , Sarbaz Ali , Malmierca Manuel S. , Le Beau Fiona E. N.
Published: December 2017

Rees, Adrian, Ali Sarbaz, Manuel S. Malmierca, and Fiona E. N. Le Beau. Regularity of firing of neurons in the inferior colliculus. J. Neurophysiol. 77: 2945–2965, 1997. The spike discharge regularity of 254 tonically firing units in the inferior colliculus (IC) of the anesthetized guinea pig was studied in response to tones presented at best frequency (BF) to the ear contralateral to the recorded IC. Regularity of firing was measured by calculating the coefficient of variation (CV) as a function of time over the course of a unit's response. Two hundred and fifteen units (56 under urethan and 159 under chloralose anesthesia) in the central nucleus of the IC (CNIC) were studied in detail. In response to tones at 15–25 dB above threshold, 80% of units in the urethan sample fired regularly (CV < 0.5) during their sustained response, and 46% were highly regular (CV ≤ 0.35). For chloralose the values were 68% and 23%, respectively. Units recorded under urethan were significantly more regular than those recorded under chloralose. For units in the sample with a measurable onset CV, 63% were regular and 44% highly regular under urethan, and 73% were regular and 54% highly regular under chloralose. The units' peristimulus time histogram (PSTH) patterns were classified into subdivisions of four categories: choppers [9%: chop-sustained (Cs), chop-onset (Co)]; pausers [42%: pauser-chop-sustained(P/Cs), pauser-chop-onset (P/Co), pauser-no-chop]; on-sustained(43%: primary-type, L-type, h-type); and sustained (6%). The presence of chopping was a reliable predictor of regularity: Cs and P/Cs units were highly regular throughout their response, whereas Co and P/Co units were highly regular at onset and became less regular. Some units in the other PSTH categories were highly regular despite the absence of chopping, and units with virtually identical PSTHs showed very different sustained CVs. Regularity was measured as a function of firing rate in 71 units. In 23%, regularity remained constant when firing rate changed with stimulus level. Forty-six percent fired more regularly as firing rate increased, 8% fired less regularly, and 23% of units showed no consistent relationship between CV and firing rate. Regularity did not correlate with the neurons' frequency response areas or BFs. Regular firing was also found in a smaller sample of units recorded in cortices surrounding the CNIC. We conclude that regular firing is a characteristic feature of most neurons in the IC. Regularity is a specific feature correlated with four PSTH types (Cs, Co, P/Cs, and P/Co). Other PSTH types may or may not exhibit regularity.
Warm-Sensitive Afferent Splanchnic C-Fiber Units In Vitro
Authors: Adelson David W. , Wei Jen Yu , Kruger Lawrence
Published: December 2017

Adelson, David W., Jen Yu Wei, and Lawrence Kruger. Warm-sensitive afferent splanchnic C-fiber units in vitro. J. Neurophysiol. 77: 2989–3002, 1997. Receptive fields of 41 slowly conducting sensory fibers were located using a thermal (warm) search stimulus in an in vitro splanchnic nerve-mesentery preparation. Warm-sensitive receptive fields were punctate and were densest in the region surrounding the prevertebral ganglia, an area with prominent deposits of brown adipose tissue, where the abdominal aorta branches into the major trunks supplying the abdominal viscera. Impulse activity was recorded while applying a warm stimulus to identified receptive fields (RFs). The warm stimulus consisted of a warming ramp (10–15°C in 1–2 s to a 42–49°C peak temperature) followed by a 10- to 30-s period during which the RF was maintained at this peak temperature (plateau phase). Eighty percent (33/41) of warm-sensitive units responded to warming with discharge comprising both a phasic and a tonic component (slowly adapting warm-sensitive, or SA-W, units). The remainder (8/41) responded with only phasic discharge (rapidly adapting warm-sensitive, or RA-W, units). Units' adaptation characteristics were consistent from trial to trial and when applying stimuli from different positions. Fifty percent of SA-W units (8/16) and 17% of RA-W units (1/6) were activated by transient exposure to 9–90 nM bradykinin (BK). Twenty-seven percent (9/33) of SA-W units and 12%(1/8) of RA-W units were activated by probing their RF with von Frey hairs with bending forces <10 mN (∼1 g equivalent mass). An additional five SA-W units tested were activated by strong mechanical stimuli (compression with a metal probe or firm stretching). No BK-responsive warm-sensitive units were activated by von Frey probing <10 mN, but two (both SA-W) responded to strong mechanical stimuli. In six SA-W units and one RA-W unit, the number of impulses evoked by warming ∼5 min after exposure to BK was >2 SD greater than the mean pre-BK response, indicating sensitization. This sensitization was transient, the response to warming returning to within one standard deviation of the pretrial mean or less over the course of the next 5–10 min. Changes in background activity, mechanical sensitivity, BK sensitivity, and BK-induced sensitization were noted in various splanchnic units over the course of prolonged observations, suggesting that these indices may not reliably distinguish unit type, but instead may indicate the functional state of the sense organ. Splanchnic neurons responsive to the intense warming used in the present in vitro experiments may participate in the cardiovascular responses observed in vivo in heat-stressed rats. The dense distribution of warm-receptive fields in the vicinity of the celiac-superior mesenteric ganglionic complex is consistent with the localization of splanchnic thermosensitive units previously noted in vivo in the rabbit.
Sacculocollic Reflex Arcs in Cats
Authors: Uchino Y. , Sato H. , Sasaki M. , Imagawa M. , Ikegami H. , Isu N. , Graf W.
Published: December 2017

Uchino, Y., H. Sato, M. Sasaki, M. Imagawa, H. Ikegami, N. Isu, and W. Graf. Sacculocollic reflex arcs in cats. J. Neurophysiol. 77: 3003–3012, 1997. Neuronal connections and pathways underlying sacculocollic reflexes were studied by intracellular recordings from neck extensor and flexor motoneurons in decerebrate cat. Bipolar electrodes were placed within the left saccular nerve, whereas other branches of the vestibular nerve were removed in the inner ear. To prevent spread of stimulus current to other branches of the vestibular nerve, the saccular nerve and the electrodes were covered with warm semisolid paraffin-Vaseline mixture. Saccular nerve stimulation evoked disynaptic (1.8–3.0 ms) excitatory postsynaptic potentials (EPSPs) in ipsilateral neck extensor motoneurons and di- or trisynaptic (1.8–4.0 ms) EPSPs in contralateral neck extensor motoneurons, and di- and trisynaptic (1.7–3.6 ms) inhibitory postsynaptic potentials (IPSPs) in ipsilateral neck flexor motoneurons and trisynaptic (2.7–4.0 ms) IPSPs in contralateral neck flexor motoneurons. Ipsilateral inputs were about twice as strong as contralateral ones to both extensor and flexor motoneurons. To determine the pathways mediating this connectivity, the lateral part of the spinal cord containing the ipsilateral lateral vestibulospinal tract (i-LVST) or the central part of the spinal cord containing the medial vestibulospinal tracts (MVSTs) and possibly reticulospinal fibers (RSTs) were transected at the caudal end of the C1segment. Subsequent renewed intracellular recordings following sacculus nerve stimulation indicated that the pathway from the saccular nerve to the ipsilateral neck extensor motoneurons projects though the i-LVST, whereas the pathways to the contralateral neck extensors and to the bilateral neck flexor motoneurons descend in the MVSTs/RSTs. Our data show that sacculo-neck reflex connections display a qualitatively bilaterally symmetrical innervation pattern with excitatory connections to both neck extensor motoneuron pools, and inhibitory connections to both neck flexor motoneuron pools. This bilateral organization contrasts with the unilateral innervation scheme of the utriculus system. These results suggest a different symmetry plane along which sacculus postural reflexes are organized, thus supplementing the reference planes of the utriculus system and allowing the gravistatic system to represent all three translational spatial degrees of freedom. We furthermore suggest that the sacculocollic reflex plays an important role in maintaining the relative position of the head and the body against the vertical linear acceleration of gravity.
Late Sodium Channel Openings Underlying Epileptiform Activity Are Preferentially Diminished by the Anticonvulsant Phenytoin
Authors: Segal Michael M. , Douglas Andrea F.
Published: December 2017

Segal, Michael M. and Andrea F. Douglas. Late sodium channel openings underlying epileptiform activity are preferentially diminished by the anticonvulsant phenytoin. J. Neurophysiol. 77: 3021–3034, 1997. Late openings of sodium channels were observed in outside-out patch recordings from hippocampal neurons in culture. In previous studies of such neurons, a persistent sodium current appeared to underlie the ictal epileptiform activity. All the channel currents were blocked by tetrodotoxin. In addition to the transient openings of sodium channels making up the peak sodium current, there were two types of late channel openings: brief late and burst openings. These late channel openings occurred throughout voltage pulses that lasted 750 ms, producing a persistent sodium current. At −30 mV, this current was 0.4% of the peak current. The late channel openings occurred throughout the physiological range of trans-membrane voltages. The anticonvulsant phenytoin reduced the late channel openings more than the peak currents. The effect on the persistent current was greatest at more depolarized voltages, whereas the effect on peak currents was not substantially voltage dependent. In the presence of 60 μM phenytoin, peak sodium currents at −30 mV were 40–41% of control, as calculated using different methods of analysis. Late currents were 22–24% of control. Phenytoin primarily decreased the number of channel openings, with less effect on the duration of channel openings and no effect on open channel current. This set of findings is consistent with models in which phenytoin binds to the inactivated state of the channel. The preferential effect of phenytoin on the persistent sodium current suggests that an important pharmacological mechanism for a sodium channel anticonvulsant is to reduce late openings of sodium channels, rather than reducing all sodium channel openings. We hypothesize that pharmacological interventions that are most selective in reducing late openings of sodium channels, while leaving early channel openings relatively intact, will be those that produce an anticonvulsant effect while interfering minimally with normal function.
Neuronal Encoding of Sound Direction in the Auditory Midbrain of the Rainbow Trout
Authors: Wubbels R. J. , Schellart N.A.M.
Published: December 2017

Wubbels, R. J. and N.A.M. Schellart. Neuronal encoding of sound direction in the auditory midbrain of the rainbow trout. J. Neurophysiol. 77: 3060–3074, 1997. Acoustical stimulation causes displacement of the sensory hair cells relative to the otoliths of the fish inner ear. The swimbladder, transforming the acoustical pressure component into displacement, also contributes to the displacement of the hair cells. Together, this (generally) yields elliptical displacement orbits. Alternative mechanisms of fish directional hearing are proposed by the phase model, which requires a temporal neuronal code, and by the orbit model, which requires a spike density code. We investigated whether the directional selective response of auditory neurons in the midbrain torus semicircularis (TS; homologous to the inferior colliculus) is based on spike density and/or temporal encoding. Rainbow trout were mounted on top of a vibrating table that was driven in the horizontal plane to simulate sound source direction. Rectilinear and elliptical (or circular) motion was applied at 172 Hz. Generally, responses to rectilinear and elliptical/circular stimuli (irrespective of direction of revolution) were the same. The response of auditory neurons was either directionally selective (DS units, n = 85) or not (non-DS units, n = 106). The average spontaneous discharge rate of DS units was less than that of non-DS units. Most DS units (70%) had spontaneous activities <1 spike per second. Response latencies (mode at 18 ms) were similar for both types of units. The response of DS units is transient (19%), sustained (34%), or mixed (47%). The response of 75% of the DS units synchronized to stimulus frequency, whereas just 23% of the non-DS responses did. Synchronized responses were measured at stimulus amplitudes as low as 0.5 nm (at 172 Hz), which is much lower than for auditory neurons in the medulla of the trout, suggesting strong convergence of VIIIth nerve input. The instant of firing of 42% of the units was independent of stimulus direction (shift <15°), but for the other units, a direction dependent phase shift was observed. In the medial TS spatial tuning of DS units is in the rostrocaudal direction, whereas in the lateral TS all preferred directions are present. On average, medial DS units have a broader directional selectivity range, are less often synchronized, and show a smaller shift of the instant of firing as a function of stimulus direction than lateral DS units. DS response characteristics are discussed in relation to different hypotheses. We conclude that the results are more in favor of the phase model.
Ionic Currents of Isolated Retinal Pacemaker Neurons: Projected Daily Phase Differences and Selective Enhancement by a Phase-Shifting Neurotransmitter
Authors: Barnes Steven , Jacklet Jon W.
Published: December 2017

Barnes, Steven and Jon W. Jacklet. Ionic currents of isolated retinal pacemaker neurons: projected daily phase differences and selective enhancement by a phase-shifting neurotransmitter. J. Neurophysiol. 77: 3075–3084, 1997. The eye of Aplysia expresses a robust circadian rhythm of neuronal activity. We dissociated the retinal cells in primary culture and studied isolated pacemaker neurons to identify ionic currents that may have roles in the circadian clock mechanism. Individual neurons were studied with perforated-patch whole cell recording techniques in current- and voltage-clamp modes. Pacemaker neurons had resting potentials near −40 mV and, if neurites had grown out, produced spontaneous action potentials in darkness at <1 Hz. Depolarizing current injections increased the rate of action potential firing. Hyperpolarizing current injections were followed by slowly decaying (1–3 s) afterhyperpolarizations. Four ionic currents were characterized under voltage-clamp, including a Ca current ( ICa), a voltage-gated potassium current ( IKV), an A current ( IA), and a hyperpolarization-activated Cl current ( ICl). IClwas only seen using Cl−-filled electrodes when high concentrations of Cl−diffused from the electrode and is therefore unlikely to be important under physiological conditions. The magnitude of IKVwas significantly larger during the projected zeitgeber predawn phase than during the postdawn phase, whereas the magnitude of IAwas constant at these circadian phases, suggesting that only IKVis controlled by the circadian clock. Serotonin increased IKVby 29%, consistent with reports that serotonin suppresses optic nerve activity and phase shifts the circadian rhythm recorded from the intact eye. The enhancement of IKVlikely contributes to membrane hyperpolarization, and it may be required for phase shifting. The phase-dependent changes in IKVprovide evidence that each retinal pacemaker neuron contains a circadian clock, but confirmation must await further recordings made from individual pacemaker neurons that are isolated completely from all other cells in primary culture. From the present experiments, it appears that IKVis controlled by the circadian clock, in part, and it may be a required element in the pathway that is activated during serotonin-induced phase shifts.
Responses of Neurons in the Inferior Colliculus to Binaural Masking Level Difference Stimuli Measured by Rate-Versus-Level Functions
Authors: Jiang Dan , McAlpine David , Palmer Alan R.
Published: December 2017

Jiang, Dan, David McAlpine, and Alan R. Palmer. Responses of neurons in the inferior colliculus to binaural masking level difference stimuli measured by rate-versus-level functions. J. Neurophysiol. 77: 3085–3106, 1997. The psychophysical detection threshold of a low-frequency tone masked by broadband noise is reduced by ≤15 dB by inversion of the tone in one ear (called the binaural masking level difference: BMLD). The contribution of 120 low-frequency neurons (best frequencies 168–2,090 Hz) in the inferior colliculus (ICC) of the guinea pig to binaural unmasking of 500-Hz tones masked by broadband noise was examined. We measured rate-level functions of the responses to identical signals (So) and noise (No) at the two ears (NoSo) and to identical noise but with the signal inverted at one ear (NoSπ): the noise was 7–15 dB suprathreshold. The masked threshold was estimated by the standard separation, “D”. The neural BMLD was estimated as the difference between the masked thresholds for NoSo and NoSπ. The presence of So and Sπ tones was indicated by discharge rate increases in 55.3% of neurons. In 36.4% of neurons, the presence of So tones was indicated by an increase in discharge rate and Sπ tones by a decrease. In 6.8% of neurons, both So and Sπ tones caused a decrease in discharge rate. In only 1.5% of neurons was So indicated by a decrease and Sπ by an increase in discharge rate. Responses to the binaural configurations were consistent with the neuron's interaural delay sensitivities; 34.4% of neurons showing increases in discharge rate to both So and Sπ tones gave positive BMLDs ≥3 dB (Sπ tones were detected at lower levels than So), whereas 37.3% gave negative BMLDs ≥3 dB. For neurons in which So signals caused an increase in the discharge rate and Sπ a decrease, 72.7% gave positive BMLDs ≥3 dB and only 4.5% gave negative BMLDs ≥3 dB. The results suggest that the responses of single ICC neurons are consistent with the psychophysical BMLDs for NoSo versus NoSπ at 500 Hz, and with current binaural interaction models based on coincidence detection. The neurons likely to contribute to the psychophysical BMLD are those with BFs near 500 Hz, but detection of So and Sπ tones may depend on different populations of neurons.
Regulation of Masticatory Force During Cortically Induced Rhythmic Jaw Movements in the Anesthetized Rabbit
Authors: Hidaka O. , Morimoto T. , Masuda Y. , Kato T. , Matsuo R. , Inoue T. , Kobayashi M. , Takada K.
Published: December 2017

Hidaka, O., T. Morimoto, Y. Masuda, T. Kato, R. Matsuo, T. Inoue, M. Kobayashi, and K. Takada. Regulation of masticatory force during cortically induced rhythmic jaw movements in the anesthetized rabbit. J. Neurophysiol. 77: 3168–3179, 1997. To examine the relationships between masticatory force, electromyogram (EMG) of masticatory muscles, and jaw movement pattern, we quantitatively evaluated the effects of changing hardness of a chewing substance on these three variables. Cortically induced rhythmic jaw movements of a crescent-shaped pattern were induced by electrical stimulation of the cerebral cortical masticatory area in the anesthetized rabbit. The axially directed masticatory force was recorded with a small force-displacement transducer mounted on the ground surface of the lower molars. EMGs were recorded from the masseter and digastric muscles simultaneously with jaw movements. Five test strips of polyurethane foam of different hardness were prepared and inserted between the upper molar and the transducer during the movements. The peak, impulse, and buildup speed of the masticatory force increased with strip hardness, whereas duration of the exerted force did not vary with strip hardness. The integrated activity and duration of the masseteric EMG bursts also increased with strip hardness. The integrated EMG activity of the digastric bursts was weakly related to strip hardness, whereas the duration was not. The minimum gape increased with strip hardness, but the maximum gape did not. The horizontal excursion of the jaw did not vary in a hardness-dependent manner, although it was greater in the cycles with strip application than in the cycles without strip application. Deprivation of periodontal sensation by cutting the nerves to the teeth reduced the buildup speed of the force, maximum gape, net gape, and horizontal jaw movements. The denervation also elongated the force duration and that of masseteric EMG bursts. However, the rate of the hardness-dependent changes in the above parameters did not alter after denervation. The latency of the masseteric EMG response to strip application was evaluated before and after denervation. In both conditions, it was ⩾6 ms in ∼70% of the cycles and <6 ms in the remaining ∼30%, which cannot be explained by a simple reflex mechanism. On the basis of the analysis of correlation coefficients, the masseteric integrated EMG seemed to be a good indicator of the peak and impulse of the masticatory force both before and after denervation. We conclude that periodontal afferents would be responsible for a quick buildup of masticatory force and that afferents other than those from periodontal tissue would contribute to the hardness-dependent change of masticatory force during cortically induced rhythmic jaw movements.
Synaptic Connectivity in Cultured Hypothalamic Neuronal Networks
Authors: Müller Thomas H. , Swandulla D. , Zeilhofer H. U.
Published: December 2017

Müller, Thomas H., D. Swandulla, and H. U. Zeilhofer. Synaptic connectivity in cultured hypothalamic neuronal networks. J. Neurophysiol. 77: 3218–3225, 1997. We have developed a novel approach to analyze the synaptic connectivity of spontaneously active networks of hypothalamic neurons in culture. Synaptic connections were identified by recording simultaneously from pairs of neurons using the whole cell configuration of the patch-clamp technique and testing for evoked postsynaptic current responses to electrical stimulation of one of the neurons. Excitatory and inhibitory responses were distinguished on the basis of their voltage and time dependence. The distribution of latencies between presynaptic stimulation and postsynaptic response showed multiple peaks at regular intervals, suggesting that responses via both monosynaptic and polysynaptic paths were recorded. The probability that an excitatory event is transmitted to another excitatory neuron and results in an above-threshold stimulation was found to be only one in three to four. This low value indicates that in addition to evoked synaptic responses other sources of excitatory drive must contribute to the spontaneous activity observed in these networks. The various types of synaptic connections (excitatory and inhibitory, monosynaptic, and polysynaptic) were counted, and the observations analyzed using a probabilistic model of the network structure. This analysis provides estimates for the ratio of inhibitory to excitatory neurons in the network (1:1.5) and for the ratio of postsynaptic cells receiving input from a single GABAergic or glutamatergic neuron (3:1). The total number of inhibitory synaptic connections was twice that of excitatory connections. Cell pairs mutually connected by an excitatory and an inhibitory synapse occurred significantly more often than predicted by a random process. These results suggests that the formation of neuronal networks in vitro is controlled by cellular mechanisms that favor inhibitory connections in general and specifically enhance the formation of reciprocal connections between pairs of excitatory and inhibitory neurons. These mechanisms may contribute to network formation and function in vivo.
Invariant Visual Responses From Attentional Gain Fields
Authors: Salinas Emilio , Abbott L. F.
Published: December 2017

Salinas, Emilio and L. F. Abbott. Invariant visual responses from attentional gain fields. J. Neurophysiol. 77: 3267–3272, 1997. Inferotemporal (IT) neurons exhibit a substantial degree of invariance with respect to translation of images used as visual stimuli. Through theoretical and computer-modeling methods, we show how translation-invariant receptive fields, like those of IT neurons, can be generated from the responses of V4 neurons if the effects of attention are taken into account. The model incorporates a recently reported form of attention-dependent gain modulation in V4 and produces IT receptive fields that shift so they are centered at the point where attention is directed. Receptive fields of variable, attention-controlled spatial scale are obtained when the mechanism is extended to scale-dependent attentional gain fields. The results indicate that gain modulation may play analogous roles in the dorsal and ventral visual pathways, generating transformations from retinal coordinates to body- and object-centered systems, respectively.
Cutaneous Reflexes During Human Gait: Electromyographic and Kinematic Responses to Electrical Stimulation
Authors: Zehr E. P. , Komiyama T. , Stein R. B.
Published: December 2017

Zehr, E. P., T. Komiyama, and R. B. Stein. Cutaneous reflexes during human gait: electromyographic and kinematic responses to electrical stimulation. J. Neurophysiol. 77: 3311–3325, 1997. The functions of ipsilateral cutaneous reflexes were studied with short trains of stimuli presented pseudorandomly to the superficial peroneal (SP) and tibial nerves during human gait. Electromyograms (EMGs) of tibialis anterior (TA), soleus, lateral and medial gastrocnemius, vastus lateralis (VL), and biceps femoris (BF) muscle were recorded, together with ankle and knee joint angles. Net reflex EMG responses were quantified in each of the 16 parts of the step cycle according to a recently developed technique. After SP nerve stimulation, TA muscle showed a significant suppression during swing phase that was highly correlated to ankle plantarflexion. BF and VL muscles were both excited throughout swing and significantly correlated to knee flexion during early swing. Tibial nerve stimulation caused dorsiflexion during late stance, but plantarflexion during late swing. We argue that SP nerve reflexes are indicative of a stumbling corrective response to nonnoxious electrical stimulation in humans. The correlated kinematic responses after tibial nerve stimulation may allow smooth movement of the swing leg so as to prevent tripping during swing and to assist placing and weight acceptance at the beginning of stance.
Mg2+Inhibition of ATP-Activated Current in Rat Nodose Ganglion Neurons: Evidence That Mg2+Decreases the Agonist Affinity of the Receptor
Authors: Li Chaoying , Peoples Robert W. , Weight Forrest F.
Published: December 2017

Li, Chaoying, Robert W. Peoples, and Forrest F. Weight. Mg2+inhibition of ATP-activated current in rat nodose ganglion neurons: evidence that Mg2+decreases the agonist affinity of the receptor. J. Neurophysiol. 77: 3391–3395, 1997. The effect of Mg2+on ATP-activated current in rat nodose ganglion neurons was investigated with the use of the whole cell patch-clamp technique. Mg2+decreased the amplitude of ATP-activated current in a concentration-dependent manner over the concentration range of 0.25–8 mM, with a 50% inhibitory concentration value of 1.5 mM for current activated by 10 μM ATP. Mg2+shifted the ATP concentration-response curve to the right in a parallel manner, increasing the 50% effective concentration value for ATP from 9.2 μM in the absence of added Mg2+to 25 μM in the presence of 1 mM Mg2+. Mg2+increased the deactivation rate of ATP-activated current without changing its activation rate. The observations are consistent with an action of Mg2+to inhibit ATP-gated ion channel function by decreasing the affinity of the agonist binding site on these receptors.
Human Thalamic Nucleus Mediating Taste and Multiple Other Sensations Related to Ingestive Behavior
Authors: Lenz F. A. , Gracely R. H. , Zirh T. A. , Leopold D. A. , Rowland L. H. , Dougherty P. M.
Published: December 2017

Lenz, F. A., R. H. Gracely, T. A. Zirh, D. A. Leopold, L. H. Rowland, and P. M. Dougherty. Human thalamic nucleus mediating taste and multiple other sensations related to ingestive behavior. J. Neurophysiol. 77: 3406–3409, 1997. Until now, taste was the only primary sensory modality for which the human central nervous system pathways were unknown. We report sensations evoked by stimulation at microampere current levels in the region of the human thalamic nucleus (ventralis caudalis parvocellularis internis) corresponding to the monkey taste relay nucleus. Stimulation in this region during awake neurosurgical procedures evoked special visceral/somatic (taste/pungent smell), general visceral (fullness of a hollow viscus), as well as painful and nonpainful general somatic sensations. General somatic or visceral sensation was evoked by stimulation at 80% of sites where special visceral/somatic sensation was evoked. These results suggest that primate taste relay mediates multiple sensations in addition to taste.
Pulmonary Afferents Are Not Necessary for the Reflex Inhibition of Human Inspiratory Muscles Produced by Airway Occlusion
Authors: Butler Jane E. , McKenzie D. K. , Glanville A. R. , Gandevia S. C.
Published: December 2017

Butler, Jane E., D. K. McKenzie, A. R. Glanville, and S. C. Gandevia. Pulmonary afferents are not necessary for the reflex inhibition of human inspiratory muscles produced by airway occlusion. J. Neurophysiol. 78: 170–176, 1997. In contrast to limb muscles, the usual response of human inspiratory muscles to sudden loading consists of an initial marked reduction of electromyographic activity (EMG) followed by a subsequent increase in EMG. To determine definitively whether pulmonary receptors are necessary for this short-latency reflex inhibition produced by airway occlusion, we studied five subjects with complete pulmonary denervation due to bilateral transplantation of the lungs and five matched control subjects. Subjects with pulmonary denervation were studied between 10 and 50 days after transplantation (median 21 days). Brief airway occlusion during inspiration (i.e., loading; duration 250 ms) produced short-latency reduction in EMG in the inspiratory muscles of all subjects with acute pulmonary denervation (scalenes and parasternal intercostal muscles; mean onset of inhibition 27 and 29 ms, respectively). The ongoing EMG was reduced by an average of 50% in scalenes and 36% in parasternal intercostal muscles. The size and the magnitude of the initial response did not differ significantly from those in control subjects. After the occlusion (i.e., unloading), activity of the inspiratory muscles was transiently reduced in control subjects and patients after bilateral lung transplantation. Given that the initial responses to airway loading and unloading were preserved after bilateral lung transplantation, we conclude that these reflex responses are not critically dependent on the discharge of intrapulmonary receptors. The results support the view that the short-latency inspiratory responses to loading and unloading can be mediated by inspiratory muscle afferents. They suggest a functionally different organization of the reflex pathways for inspiratory compared with limb muscles.
Low-Frequency Depression of the Monosynaptic Reflex Is Not Altered by Tetrodotoxin-Induced Nerve Conduction Blockade
Authors: Seburn Kevin L. , Cope Timothy C.
Published: December 2017

Seburn, Kevin L. and Timothy C. Cope. Low-frequency depression of the monosynaptic reflex is not altered by tetrodotoxin-induced nerve conduction blockade. J. Neurophysiol. 78: 19–23, 1997. The present study is part of ongoing investigations into activity-related synaptic plasticity in the intact animal. In this investigation we sought to determine whether the previously reported increase in synaptic efficacy at the Ia-motoneuron connection following nerve conduction blockade could be attributed to changes in circuitry external to the monosynaptic pathway. Specifically, we used the phenomena of low-frequency depression of the extracellularly recorded group I monosynaptic reflex (MSR) as an indirect measure of presynaptic inhibition. Tibial nerve conduction blockade was achieved by superfusion of the sodium channel blocker tetrodotoxin (TTX). An osmotic pump delivered the TTX to the tibial branch of the sciatic nerve for a period of either 3 or 10 days. Control rats were either unoperated or received implants of pumps not containing TTX. Data collection consisted of tibial nerve stimulation (0.1–20 Hz) with bilateral recordings of the MSR from the L5 ventral roots. The extent of low-frequency depression was compared between treated and untreated sides of TTX-treated animals and between treated and untreated animals. Results showed that the extent of low-frequency depression was unchanged by either 3 or 10 days of complete blockade of tibial afferents. On the basis of this finding, it is concluded that the previously reported TTX-induced increase in Ia excitatory postsynaptic potential amplitude is unlikely to be due to changes in presynaptic inhibitory pathways.
Descending Control of Turning Locomotor Activity in Larval Lamprey: Neurophysiology and Computer Modeling
Authors: McClellan Andrew D. , Hagevik André
Published: December 2017

McClellan, Andrew D. and André Hagevik. Descending control of turning locomotor activity in larval lamprey: neurophysiology and computer modeling. J. Neurophysiol. 78: 214–228, 1997. The purpose of the present study was to examine the mechanisms that produce natural spontaneous turning maneuvers in larval lamprey. During swimming, spontaneous turning movements began with a larger-than-normal bending of the head to one side. Subsequently, undulations propagated down the body with greater amplitude on the side ipsilateral to the turn. During turning to one side, which usually occurred within one cycle, the amplitude and duration of ipsilateral muscle burst activity as well as overall cycle time increased significantly with increasing turn angle. In in vitro brain/spinal cord preparations, brief electrical stimulation applied to the left side of the oral hood at the onset of locomotor burst activity on the right side of the spinal cord produced turninglike motor activity. During the perturbed cycle, the duration and amplitude of the burst on the right as well as cycle time were significantly larger than during preceding control cycles. In several lower vertebrates, unilateral stimulation in brain stem locomotor regions elicits asymmetric, turninglike locomotor activity. In the lamprey, unilateral chemical microstimulation in brain stem locomotor regions elicited continuous asymmetric locomotor activity, but there was little change in cycle time, as occurs during the single turning cycles in whole animals. The descending mechanisms responsible for producing turning locomotor activity were examined with the use of a computer model consisting of left and right phase oscillators in the spinal cord that were coupled by net reciprocal inhibition. With relatively weak reciprocal coupling, a brief unilateral descending excitatory input to one oscillator produced effects ipsilaterally, but there was little effect on the contralateral oscillator. Turninglike patterns could be produced by each of the following modifications of the model: 1) unilateral descending input and relatively strong reciprocal coupling; 2) unilateral descending input that phase shifted as well as increased the amplitude of the waveform generated by an oscillator on one side; and 3) brief descending modulatory inputs that excited the oscillator on one side and inhibited the contralateral oscillator. In all three cases, there was an increase in “burst” duration ipsilateral to the excitatory input and an increase in cycle time, similar to turning locomotor activity in whole animals. It is likely that turning maneuvers are mediated by descending modulatory inputs primarily to the spinal oscillator networks, which control the timing of burst activity, but perhaps also to motoneurons for axial musculature.