bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of discharge rate on sound pressure level in cochlear nerve fibers of the alligator lizard: implications for cochlear mechanisms
Authors: Eatock R. A. , Weiss T. F. , Otto K. L.
Published: December 2017

1. Rate-level functions for individual cochlear nerve fibers of the alligator lizard, Gerrhonotus multicarinatus, were generated by measuring a fiber's driven discharge rate (the difference between the average discharge rates in the presence and absence of a tone burst) as a function of sound pressure level. 2. When plotted in double logarithmic coordinates, the rate-level function approaches a straight line at low sound pressure levels and saturates at high levels. Thus the rate-level function is a saturating power function of sound pressure. We developed an algorithm to estimate the exponent of the straight-line portion of the function. When tested on simulated data with known parameters, the algorithm provided unbiased estimates of the exponent. 3. Nerve fibers innervating two distinct regions of the alligator lizard's auditory organ, the free-standing region and the tectorial region, have differing rate-level functions. 4. The mean exponent estimate of the rate-level functions of fibers innervating the free-standing region is approximately 2 at all frequencies. For stimulus frequencies at the characteristic frequency (CF), the mean value was 2.1 +/- 0.10 (SE, n = 131). For stimulus frequencies above and below CF, the mean exponent estimates were 2.1 +/- 0.13 (n = 49) and 2.1 +/- 0.11 (n = 34), respectively. A value of 2 is expected for a broad class of nonlinear systems. 5. The mean exponent estimates of the rate-level functions of fibers innervating the tectorial region were 3.0 +/- 0.30 (n = 32) for stimulus frequencies at CF, 2.5 +/- 0.33 (n = 3) for stimulus frequencies below CF, and 1.0 +/- 0.21 (n = 16) for stimulus frequencies above CF. Both the deviation from square-law behavior at CF and the frequency dependence of the exponent imply that nonlinear processing in the tectorial region differs intrinsically from that in the free-standing region. 6. For free-standing fibers, the saturation rate of the rate-level function (the maximum driven rate) is independent of stimulus frequency. This suggests that, in the free-standing region, 1) the alternating (AC) component of the receptor potential makes no significant contribution to the average rate of discharge and 2) neural saturation results from a process that occurs after the narrow-band frequency-selective process(es). 7. In tectorial fibers, the saturation rate is a bandpass function of sound frequency, with a broad peak between 150 and 300 Hz. This function appears to be common to all tectorial fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
Cortical somatosensory evoked potentials. I. Recordings in the monkey Macaca fascicularis
Authors: McCarthy G. , Wood C. C. , Allison T.
Published: December 2017

1. The anatomic generators of somatosensory evoked potentials (SEPs) to median nerve stimulation in the 10- to 30-ms latency range were investigated in monkeys (Macaca fascicularis) by means of cortical-surface and laminar recordings. 2. Three groups of SEPs evoked by stimulation of the contralateral median nerve were recorded from the hand representation area of sensorimotor cortex: P10-N20, recorded anterior to the central sulcus (CS); N10-P20, recorded posterior to the CS; and P12-N25, recorded near the CS. These potentials were similar in morphology and surface distribution whether the animal was awake or anesthetized. 3. P10-N20 exhibited a polarity inversion to N10-P20 across the CS, both in cortical-surface recordings and in laminar recordings within cortex and white matter of motor and somatosensory cortex. In contrast, P10-N20 and N10-P20 did not exhibit polarity inversion in recordings from the surface and white matter of the crowns of motor and somatosensory cortex, respectively. These results strongly suggest that these potentials are produced by a tangential generator located in the posterior wall of the CS, primarily in area 3b of somatosensory cortex. 4. P12-N25 was largest over the hand area of somatosensory cortex and showed polarity inversion across the crown of somatosensory cortex but not across the crown of motor cortex or across the walls of the CS, suggesting that P12-N25 is due to a radially oriented generator located in areas 1 and 2 of somatosensory cortex. 5. P10-N20 and P12-N25 are thought to be equivalent to the “primary evoked response” recorded from somatosensory cortex of other mammals. 6. These results are very similar to those obtained in human cortical-surface recordings and demonstrate that the monkey P10-N20, N10-P20, and P12-N25 potentials correspond to the human P20-N30, N20-P30, and P25-N35 potentials, respectively. The only appreciable difference in human and monkey SEPs is that the monkey P12-N25 appears to be generated in areas 1 and 2, whereas the human P25-N35 appears to be generated only in area 1. 7. There was no evidence of locally generated activity in areas 3a and 4.
Reorganization of somatosensory area 3b representations in adult owl monkeys after digital syndactyly
Authors: Allard T. , Clark S. A. , Jenkins W. M. , Merzenich M. M.
Published: December 2017

1. These experiments were designed to test the hypothesis that temporally correlated afferent input activity plays a lifelong role in the establishment and modification of receptive fields (RFs) and representational topographies in the primary somatosensory cortex of adult monkeys. They were based in part on the finding that adjacent digits of the hand are represented discontinuously in area 3b of the adult owl monkey. If cortical receptive fields and the details of cortical topographic representations are shaped by the weights of the temporal correlations among afferent inputs, then representational discontinuities between digits would be expected to arise because inputs from the skin surfaces of adjacent digits are largely independent in the critical time domain. 2. In the present experiments, the skin of adjacent digits 3 and 4 of the monkey hand was surgically connected to create an artificial syndactyly, or webbed-finger condition. Highly detailed microelectrode maps of the cortical representation of the syndactyl digits were obtained 3-7.5 mo later. This experimental manipulation greatly increased the amount of simultaneous or nearly simultaneous input from the normally separated, now fused, surfaces of adjacent fingers. 3. Cortical maps of the representations of finger surfaces were highly modified from the normal after a several-month-long period of digital fusion. Specifically, the normal discontinuity between the cortical representations of adjacent fingers was abolished. Within a wide cortical zone, RFs were defined that extended across the line of syndactyly onto the surgically joined skin of both fused digits. The representational topography of the fused digits was similar to any normal single digit and was characterized by a continuous progression of partially overlapping RFs. 4. Control observations revealed that these reorganizational changes cannot be accounted for by any changes in cutaneous innervation induced by the surgery. They must arise from representational changes in the central somatosensory system. 5. These findings reveal that cortical maps can be altered in detail in adult monkeys by modifying the distributed temporal structure of afferent inputs. They support the longstanding hypothesis that the temporal coincidence of inputs plays a role in the grouping of input subsets into specific cortical RFs and, consequently, in the shaping of selected effective cortical inputs and representational topographies throughout life.
The terminations of single, physiologically identified, somatosensory, corticospinal tract axons in the lumbar spinal cord of the cat
Authors: Casale E. J. , Light A. R.
Published: December 2017

1. Two hundred and twelve corticospinal axons were identified by stimulation in the hindlimb representation in area 3b of the somatosensory cortex and were recorded in the left dorsolateral funiculus of the spinal cord of the cat. The mean conduction velocity was 38 m/s, range 9-113 m/s. 2. Electrical stimulation of the receptive field evoked discharge in corticospinal axons with a mean latency of 36 ms (range 9-100 ms). 3. One hundred nine of the 212 recorded axons were successfully intra-axonally labeled by iontophoretic injection of horseradish peroxidase, with the mean length of labeled axon being 4.8 mm. Seventy-three of the labeled axons issued no collaterals, and 36 issued at least one labeled collateral into the spinal gray matter along the labeled portion of the parent axon. 4. Most labeled axons issued only one labeled collateral per spinal cord segment. Fourteen collaterals from 10 units were labeled well enough to permit reconstruction of their terminal arborizations. 5. Most terminal collaterals were oriented rostrocaudally and terminated in laminae V, VI, and VII. Most collaterals terminated within large mediolateral extents of the gray matter with no apparent topographic organization. 6. No collaterals terminated in laminae I or II or within the motoneuron pools, and no apparent correlation was found between their anatomic and physiological characteristics.
State-related modulation of thalamic somatosensory responses in the awake monkey
Authors: Morrow T. J. , Casey K. L.
Published: December 2017

1. These experiments were performed to assess the nature and extent of the modulation of somatosensory transmission through the thalamus of the awake primate brain. We investigated physiologically induced modulation occurring during changes in state of arousal within the waking state. Changes in thalamic responsiveness during the sleep-waking cycle were not studied. 2. We recorded from single units in several nuclei within the ventral posterior region of the thalamus (VP) of awake squirrel monkeys (Saimiri sciureus). Recording sites included the ventral posterior lateral, ventral posterior medial, ventral posterior inferior, ventral lateral, and thalamic reticular nuclei. Four hundred twenty-seven thalamic units were tested for responsiveness to innocuous and noxious somatic stimulation of cutaneous (hair and skin) and deep (muscle and tendon) structures and to innocuous electrical stimulation of the spinal lemniscus (SL). Noxious stimuli were just sufficient to evoke withdrawal and did not cause tissue damage. 3. All neurons were spontaneously active in the absence of intentional stimulation. Only 260 (60.9%) of the neurons recorded in VP responded to somatic or SL stimulation. Based on their responsiveness to somatic stimuli, we classified neurons as cutaneous (67.7% or 176/260) if responsive to hair and/or skin stimulation or as deep (18.8% or 49/260) if responsive only to manipulation of joints or palpation of muscles or tendons. Thirty-five other cells (13.5%) responded best to brisk innocuous taps applied to the somatic receptive field and were placed in a separate group. Cutaneous units were subclassified as low-threshold (LT, 86.9% or 153/176) if responding maximally to innocuous stimuli only or as wide dynamic range (WDR, 13.1% or 23/176) if responding preferentially to noxious stimuli. No neurons responded exclusively to noxious stimuli. Single-pulse SL stimulation evoked discharges at an average latency of 3.3 +/- 4.8 (SD) ms in 51/132 (38.6%) LT neurons tested and similarly affected 7 of 12 WDR cells tested at an average latency of 1.54 +/- 0.39 ms. 4. We tested 88 neurons for changes in activity as the monkey's state of arousal shifted between quiet waking (QW), waking movement (WM), and drowsy (D) states as defined by behavioral and electroencephalographic criteria. The responses of 42% of the 88 somatically activated cells tested (n = 37) showed arousal-related response modulation (ARM). ARM produced a mean change in evoked activity of 40.1% (+/- 23.5 SD) relative to that cell's maximal response and the specific state of arousal during which the maximal response occurred. Neurons classified as WDR were equally likely to exhibit ARM as LT neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of ethanol and other drugs on excitatory and inhibitory neurotransmission in the crayfish
Authors: Blundon J. A. , Bittner G. D.
Published: December 2017

1. Crayfish exposed to 434 mM ethanol (EtOH) showed signs of hyperactivity within 0.5-2 h, at which times crayfish hemolymph EtOH concentration had reached 60-90 mM. 2. A 10-min exposure to 60-90 mM EtOH reduced presynaptic inhibition of excitatory postsynaptic currents (EPSCs) at the crayfish opener neuromuscular junction (NMJ) in vitro but did not significantly alter excitatory neurotransmission. The same concentrations of EtOH did not alter other potentials or currents associated with inhibition at this synapse, such as presynaptic inhibitory potentials (PIPs), inhibitory postsynaptic potentials (IPSPs), and inhibitory postsynaptic currents (IPSCs). 3. Intermediate EtOH concentrations (120-180 mM) applied for 10 min in vitro reduced the amplitude of excitatory postsynaptic potentials (EPSPs) by decreasing the membrane resistance of opener muscle fibers and by reducing the amplitude of EPSCs. 4. High EtOH concentrations (434 mM) applied for 10 min in vitro had yet greater depressive effects on measures of postsynaptic properties described above. The time course of EPSCs was also significantly reduced. In addition, presynaptic properties such as action-potential (AP) amplitude and frequency of spontaneous release of neurotransmitter were reduced by 434 mM EtOH. 5. Presynaptic inhibition, gamma-aminobutyric acid (GABA; 250-500 microM), muscimol (50 microM), and baclofen (75 microM) all reduced the depolarizing afterpotential of APs in the excitor axon and reduced EPSPs in opener muscle fibers. GABA (500 microM) and baclofen (75 microM) significantly reduced presynaptic AP amplitudes, whereas presynaptic inhibition, GABA (250 microM), and muscimol (50 microM) had no effect on AP amplitude. Bicuculline (250-500 microM), a GABAA antagonist, did not entirely eliminate presynaptic inhibition, whereas picrotoxin (50 microM), another GABAA antagonist, completely removed presynaptic inhibition. Thus presynaptic inhibitory mechanisms may involve both GABAA and GABAB receptors on the opener excitor axon. 6. Our data suggest that the behavioral hyperactivity seen at hemolymph EtOH concentrations of 60-90 mM is not accompanied by a change in excitatory synaptic transmission observed at the opener NMJ. Rather, crayfish hyperactivity may be due to depressive effects of EtOH on inhibitory synapses in the CNS similar to the disinhibition evoked by EtOH at the opener NMJ.
Properties of reach-related neuronal activity in cortical area 7A
Authors: MacKay W. A.
Published: December 2017

1. In protocol 1, two macaque monkeys were trained to reach to illuminated buttons with the right arm as reach-related unit activity was monitored in area 7a of the left hemisphere. 2. Of 402 neurons recorded in area 7a, 109 changed their discharge rates during the reach task. The change could occur early or late in the trajectory, or during the return movement of the arm to the rest plate. Spatial preferences were seen in 59/109 reach-related cells, usually for the right or center buttons. 3. In protocol 2, another monkey was trained to reach with either arm to targets displayed on a touch-sensitive video monitor. Of 273 neurons sampled in area 7a (both hemispheres) during the bilateral task performance, 84 were reach-related: 33 responded similarly to reaches of either arm. Most of the rest had a contralateral arm preference. When bilateral reach-related cells had a spatial preference, that preference was the same for both arms. 4. With the use of two target sequences in either protocol, it was found that spatial preferences were observable only for primary reaches from the side of the body up to the target. Relatively few cells responded to other trajectories, and those that did usually failed to discriminate movement direction. Movement extent did not influence discharge rates. 5. Although a total of 125/270 reach cells had observable visual responses, only 4 out of 18 cells tested in both dark and light conditions showed a significant drop in reach-related activity in the dark. Thus visual input from the moving hand probably is responsible for only part of the reach activity in area 7a. 6. Reach-related activity in area 7a appears to signal specific phases of the motor performance and is often restricted to distinct spatial regions. As such, it could be used by the frontal lobe to facilitate upcoming elements of a motor sequence, including terminal corrections.
Hypoxia decreases intracellular calcium in adult rat carotid body glomus cells
Authors: Donnelly D. F. , Kholwadwala D.
Published: December 2017

1. Carotid body chemoreceptors were removed intact from adult rats and subjected to protease and collagenase enzymatic digestion of connective tissue. 2. Recordings from the sinus nerve demonstrated that chemotransduction remains intact for at least 2-3 h after isolation, enzyme exposure, and suspension in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered saline at room PO2. 3. After mechanical dissociation, the interrelationship between changes in extracellular PO2 and pH and relative changes in intracellular calcium (Ca2+i) were observed in glomus cells with the use of fluo-3 and confocal microscopy. 4. Brief (60-s) decreases in PO2 from 150 mmHg to near 0 mmHg, at nadir, caused a marked reduction in Ca2+i (peak delta F/F0 = -32 +/- 3%, mean +/- SE, n = 43), which rapidly recovered after reoxygenation. The decrease was reproducible from trial to trial and was also observed in HCO3(-)-buffered Ringer solution. 5. Superfusion with Ca(2+)-free HEPES saline with 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) blocked the hypoxia-induced increase in afferent chemoreceptor activity in vitro. Superfusion of the same solution over isolated cells for 15 min caused a large decrease in Ca2+i (-34 +/- 7%, n = 16). 6. In the presence of Ca(2+)-free HEPES, reoxygenation caused calcium fluorescence to increase. This suggests that the Ca2+ decrease during hypoxia is due, at least partially, to binding to an intracellular site. 7. Extracellular cobalt (1 mM, 15 min) also reversibly blocked the chemoreceptor response to hypoxia, in vitro, and caused a reduction in Ca2+i (delta F/F0 = -37 +/- 8%, n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)
Extracellular alkaline shifts in rat hippocampal slice are mediated by NMDA and non-NMDA receptors
Authors: Chen J. C. , Chesler M.
Published: December 2017

1. The pharmacology of synaptically evoked extracellular alkaline shifts was studied in the CA1 area of rat hippocampal slices. 2. Stimulus-evoked alkalinizations were unaffected by 2-amino-5-phosphonovalerate (APV) (20 microM). 3. 6-Cyano-7-nitro-nitroquinoxaline-2,3-dione (CNQX) (10 microM) inhibited the alkalinizations. In the continued presence of CNQX, an APV-sensitive, picrotoxin-insensitive, alkaline shift was elicited in low Mg2+ media. 4. Antidromic stimulation produced small alkaline shifts in comparison with orthodromic activation. 5. Our results demonstrate that in the hippocampal CA1 region, synaptically evoked alkalinizations can arise through both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors. These responses cannot be explained by cell firing per se.
Ion channels in spinal cord astrocytes in vitro. I. Transient expression of high levels of Na+ and K+ channels
Authors: Sontheimer H. , Black J. A. , Ransom B. R. , Waxman S. G.
Published: December 2017

1. Na+ and K+ channel expression was studied in cultured astrocytes derived from P--0 rat spinal cord using whole cell patch-clamp recording techniques. Two subtypes of astrocytes, pancake and stellate, were differentiated morphologically. Both astrocyte types showed Na+ channels and up to three forms of K+ channels at certain stages of in vitro development. 2. Both astrocyte types showed pronounced K+ currents immediately after plating. Stellate but not pancake astrocytes additionally showed tetrodotoxin (TTX)-sensitive inward Na+ currents, which displayed properties similar to neuronal Na+ currents. 3. Within 4-5 days in vitro (DIV), pancake astrocytes lost K(+)-current expression almost completely, but acquired Na+ currents in high densities (estimated channel density approximately 2-8 channels/microns2). Na+ channel expression in these astrocytes is approximately 10- to 100-fold higher than previously reported for glial cells. Concomitant with the loss of K+ channels, pancake astrocytes showed significantly depolarized membrane potentials (-28.1 +/- 15.4 mV, mean +/- SD), compared with stellate astrocytes (-62.5 +/- 11.9 mV, mean +/- SD). 4. Pancake astrocytes were capable of generating action-potential (AP)-like responses under current clamp, when clamp potential was more negative than resting potential. Both depolarizing and hyperpolarizing current injections elicited overshooting responses, provided that cells were current clamped to membrane potentials more negative than -70 mV. Anode-break spikes were evoked by large hyperpolarizations (less than -150 mV). AP-like responses in these hyperpolarized astrocytes showed a time course similar to neuronal APs under conditions of low K+ conductance. 5. In stellate astrocytes, AP-like responses were not observed, because the K+ conductance always exceeded Na+ conductance by at least a factor of 3. Thus stellate spinal cord astrocyte membranes are stabilized close to EK as previously reported for hippocampal astrocytes. 6. It is concluded that spinal cord pancake astrocytes are capable of synthesizing Na+ channels at densities that can, under some conditions, support electrogenesis. In vivo, however, AP-like responses are unlikely to occur because the cells' resting potential is too depolarized to allow current activation. Thus the absence of electrogenesis in astrocytes may be explained by two mechanisms: 1) a low Na-to-K conductance ratio, as in stellate spinal cord astrocytes and in other previously studied astrocyte preparations; or, 2) as described in detail in the companion paper, a mismatch between the h infinity curve and resting potential, which results in Na+ current inactivation in spinal cord pancake astrocytes.
Effects of stationary textured backgrounds on the initiation of pursuit eye movements in monkeys
Authors: Kimmig H. G. , Miles F. A. , Schwarz U.
Published: December 2017

1. The initial ocular pursuit of small target spots (0.25 degrees diam) that suddenly start to move at constant speed (ramps) was recorded in four rhesus monkeys with the electromagnetic search coil technique. All target motions were horizontal, and both eyes were monitored. 2. In agreement with the observations of Keller and Khan, stationary textured backgrounds substantially reduced the initial eye acceleration achieved during pursuit but did not affect its latency. Correlation techniques were used to assess the changes in the eye speed profiles and indicated that the reduction in eye acceleration due to the background was a linear function of the logarithm of target speed over the range investigated (5-40 degrees/s), averaging 60% with the fastest targets. 3. Selectively excluding the background texture from the path of the target with a horizontal strip of card (vertical width, 4 degrees) reduced the impact of the background only slightly, and, even when the vertical width of the card was increased to 60 degrees, the effect of the background was not entirely eliminated. Thus the effect involves regions of the visual field well beyond the target and is not due simply to the reduced physical salience (contrast) of the target spot. Such spatially remote interactions suggest that the neurons decoding the target's motion have very extensive visual receptive fields. 4. Textured backgrounds also caused similar reductions in the eye acceleration during initial pursuit when, before the ramps, the fixated target spots stepped forward, i.e., stepped in the direction of the subsequent ramps (step ramps). In this situation, as with no steps, initial target ramps were foveofugal. When the fixated target spots were stepped back before moving forward so that initial target ramps were foveopetal, textured backgrounds now also delayed the onset of pursuit, and the reductions in eye acceleration were not seen until some time later when tracking resulted from foveofugal target-ramp motion. Selectively excluding the texture from the path of the target with a narrow strip of card eliminated any delays in the onset of pursuit to step ramps, but the later reductions in eye acceleration were still evident. These step-ramp data indicate that the mechanisms decoding foveofugal and foveopetal target ramps differ markedly in their sensitivity to textured backgrounds. That backgrounds can influence the latency and the initial eye acceleration independently is consistent with the idea that there are independent trigger and drive mechanisms for the decoding of target motions.(ABSTRACT TRUNCATED AT 400 WORDS)
Site of synaptic depression during hypoxia: a patch-clamp analysis
Authors: Hershkowitz N. , Katchman A. N. , Veregge S.
Published: December 2017

1. The effect of hypoxia on synaptic physiology was investigated in hippocampal slices from 16- to 23-day-old rats. CA1 pyramidal cells were examined by whole cell patch-clamp recording, and hypoxia was induced by switching perfusion of the slice from oxygenated artificial cerebrospinal fluid (ACSF) to ACSF saturated with 95% N2-5%CO2. Synaptic responses were assessed by stimulating the Schaffer collateral-commissural projection with an electrode in the stratum radiatum every 20 s. 2. Within 100-200 s of the onset of hypoxia, the orthrodromically elicited synaptic response of the CA1 cells was largely inhibited. In addition, a slow inward current was observed after the onset of hypoxia. A transient outward current, preceding the inward current, was observed in only 2 of 17 cells examined. The slow inward current culminated in an irreversible rapid inward current at approximately 140 s after hypoxia. This rapid inward current occurred simultaneously with spreading depression as measured by field potentials. Tetrodotoxin (TTX) had no effect on the onset of this current, whereas kynurenic acid significantly delayed its occurrence. 3. Before the onset of hypoxia, spontaneous transient inward currents were apparent. The frequency of these events increased by three- to fourfold after hypoxia. The transient inward currents persisted in slices incubated in TTX, but were almost completely inhibited in slices incubated with the mixed N-methyl-D-aspartate (NMDA)/non-NMDA antagonist kynurenic acid. This identified the spontaneous events that were increased in frequency by hypoxia as glutamatergic miniature excitatory postsynaptic currents (mEPSCs). 4. The mean amplitude of the mEPSCs was not affected by hypoxia at a time at which the orthodromically elicited synaptic response was almost completely inhibited by hypoxia. In addition, the response of the postsynaptic cell to pressure ejection of glutamate was not inhibited under conditions of nearly complete blocked the synaptic response. Thus, by two measures, the postsynaptic response was not affected by hypoxia, indicating that the site of hypoxia-induced synaptic failure was at the presynaptic terminal. 5. The orthodromically elicited synaptic response consisted of an EPSC followed closely by an inhibitory postsynaptic current (IPSC). The IPSC portion of the elicited postsynaptic response was more sensitive to inhibition by hypoxia than was the EPSC. In some cells the EPSC exhibited a monophasic decline in amplitude during hypoxia. However, in a majority of cells, an initial decline in the amplitude of the EPSC was followed by a transient increase and subsequent depression.(ABSTRACT TRUNCATED AT 400 WORDS)
Thalamic VPM nucleus in the behaving monkey. I. Multimodal and discriminative properties of thermosensitive neurons
Authors: Bushnell M. C. , Duncan G. H. , Tremblay N.
Published: December 2017

1. The role of the thalamic ventroposterior medial (VPM) nucleus in the discriminative aspects of nociception and thermoreception was evaluated in alert, trained rhesus monkeys. Single-unit responses were recorded from VPM while the monkeys performed a battery of tasks involving noxious heat, innocuous cool, and air-puff stimuli presented to the face. The discriminative ability of the monkey was compared directly with the responses of single neurons, to determine whether the neuronal response could subserve the monkey's discriminative behavior. 2. Most thermally sensitive neurons exhibited multimodal properties. Only 18% responded exclusively to heat (HT-Heat neurons), whereas 27% responded to innocuous mechanical, as well as noxious mechanical and heat stimuli (WDR-Heat). Twenty-three percent responded to innocuous mechanical stimuli and innocuous skin cooling (Mechano-Cool), and 32% responded to mechanical, innocuous cool, and noxious heat stimuli (WDR-Heat-Cool). 3. Almost all mechanical receptive fields were confined to one division of the trigeminal nerve. This was true for all of the above categories of VPM neurons, even those showing highly convergent properties (WDR-Heat-Cool). 4. Heat-activated neurons produced graded responses to noxious skin heating in the 46 to 49 degrees C range. Stimulus-response functions of neurons that responded to both heat and cool did not differ from those of neurons that responded exclusively to skin heating. 5. When the monkeys were detecting small changes in the intensity of a noxious heat stimulus (e.g., from 47 to 47.1–47.8 degrees C), heat-activated neurons responded to the smallest temperature changes that could be detected by the monkeys. Further, there was a high correlation between the monkey's success in detecting the stimulus changes and the magnitude of the neuronal responses to those changes. 6. Although the responsiveness of VPM cool-activated neurons was not compared with the monkeys' threshold for detecting cooling changes, larger stimulus changes (2 degrees C) that the monkey reliably detected produced significant neuronal responses. Further studies are needed to determine whether VPM neurons respond to the smallest detectable changes in skin cooling. 7. Several thermally sensitive VPM neurons were tested under two attentional conditions: 1) while the monkey was required to attend to a visual stimulus, and 2) while it was required to attend to the thermal stimulus to obtain reward. None showed a significant difference in heat- or cool-evoked activity in the two attentional states.(ABSTRACT TRUNCATED AT 400 WORDS)
Potassium currents and their modulation by muscarine and substance P in neuronal cultures from adult guinea pig celiac ganglia
Authors: Vanner S. , Evans R. J. , Matsumoto S. G. , Surprenant A.
Published: December 2017

1. Intracellular microelectrode and whole-cell patch-clamp recordings were obtained from adult guinea pig celiac ganglion neurons grown in tissue culture for 7-14 days. Over 90% of neurons showed phasic-type action-potential discharge with the use of either type of recording electrode; they stained immunohistochemically for catecholamines, tyrosine hydroxylase, and neuropeptide Y. Input resistance (140 M omega) and action-potential amplitude (103 mV) were significantly greater with whole-cell than with microelectrode recordings, but other passive electrical properties were similar. 2. Five potassium currents were characterized: an apamin-sensitive after hyperpolarizing current (IAHP), an apamin and tetraethylammonium-insensitive slow IAHP, an M-like current, a transient outward IA current, and a delayed rectifier IK current. A hyperpolarization-activated cationic Ih current was also present. The first three currents were not observed with whole-cell recordings. 3. Cadmium (200 microM), cobalt (1 mM), lanthanum (30 microM), or a low calcium/high magnesium solution blocked both IAHPS and the M-like current; barium (1 mM) also blocked these currents. 4. Kinetics of the M-like current were best described by a double exponential fit to deactivating tail currents with time constants of 50 and 390 ms at -50 mV. The apamin-sensitive and slow IAHP decayed exponentially with time constants of 145 ms and 3.5 s, respectively. There was no correlation between occurrence of M-like current (95% of neurons) and slow IAHP (40% of neurons), nor any correlation between magnitude of M-like current and IAHP in those cells exhibiting both currents. 5. Muscarine and substance P (SP) caused depolarizations or inward currents (under voltage clamp) at the resting potential (-55 mV) associated with a decreased membrane conductance. The slow IAHP and the M-like current, but not the apamin-sensitive IAHP nor the IA, were blocked by muscarine and SP (IC50 3 microM and 100 nM, respectively). Muscarine and SP also decreased a "leak" potassium current. 6. We conclude that celiac neurons express two calcium-dependent IAHP currents and a calcium-dependent M-current; these are seen by fine-tipped intracellular microelectrodes but not by whole-cell patch electrodes. These currents are not required for spike frequency accommodation. Muscarine and SP reduce these currents, as well as voltage-independent leakage potassium current.
Neuronal activity in the second somatosensory cortex of monkeys (Macaca mulatta) during active touch of gratings
Authors: Sinclair R. J. , Burton H.
Published: December 2017

1. In penetrations made into the upper bank of the lateral sulcus in two monkeys (Macaca mulatta), cells were isolated from the second somatosensory cortex (SII). During single-cell recordings, animals performed an active touch task in which they rubbed their fingertips over pairs of gratings differing in groove width and indicated which was the smoother surface. Hand motion and downward applied force were measured and recorded during these strokes. 2. In this survey, 151 penetrations provided observations on 352 cells that responded to passive stimulation of the digits or during performance of the active touch task. Consistent with previous reports, receptive fields (RFs) in SII were large, often multi-digit, and frequently included a portion or all of the hand and occasionally the arm. Modality was determined for 92 of 127 fully characterized cells, and included 70 cutaneous, 5 deep, 11 Pacinian corpuscle, and 6 joint cells. Characteristic of SII, modality could not be defined in 35 cells that were unresponsive to passive stimulation or whose responses varied widely over time. 3. Response properties of a subgroup of 79 cells in SII resembled those previously studied in the primary somatosensory cortex (SI) and ventroposterior lateral nucleus of the thalamus (VPL) using identical procedures. Correlation analysis revealed that 29 of these cells, like a portion of cells in SI, responded to changes in groove width independent of force or velocity. This selectivity could be considered a form of feature specificity. 4. In contrast to SI and VPL, transient responses to the fingertips contacting small elevated metal bars, which demarcated the beginning, middle, and end of strokes across the gratings, were seen in a majority of SII cells (109/127). During contact with bars, 89 cells displayed excitatory responses and 20 cells showed suppressed activity. Twelve cells, which responded to bars in isolation from gratings, provided a possible example of increased stimulus selectivity. 5. Passive stimulation failed to activate 16 cells that responded, in some cases differentially to gratings or force, during the task. Responses of nine other cells demonstrated task-dependent modulation in the form of response reduction or enhancement during selected portions of the stroke. In these same cells, response changes did not occur under comparable stimulus conditions in other portions of the stroke that differed only in behavioral context. These types of selective response modulations, not noted in our previous studies of VPL or SI, suggest that mechanisms regulating sensory inputs may affect SII.(ABSTRACT TRUNCATED AT 400 WORDS)
The location and mechanism of electromotility in guinea pig outer hair cells
Authors: Hallworth R. , Evans B. N. , Dallos P.
Published: December 2017

1. The microchamber method was used to examine the motile responses of isolated guinea pig outer hair cells to electrical stimulation. In the microchamber method, an isolated cell is drawn partway into a suction pipette and stimulated transcellularly. The relative position of the cell in the microchamber is referred to as the exclusion fraction. 2. The length changes of the included and excluded segments were compared for constant sinusoidal stimulus amplitude as functions of the exclusion fraction. Both included and excluded segments showed maximal responses when the cell was excluded approximately halfway. Both segments showed smaller or absent responses when the cell was almost fully excluded or almost fully included. 3. When the cell was near to, but not at, the maximum exclusion, the included segment response amplitude was zero, whereas the excluded segment response amplitude was nonzero. In contrast, when the cell was nearly fully included, the excluded segment response amplitude was zero, but the included segment response amplitude was still detectable. A simple model of outer hair cell motility based on these results suggests that the cell has finite-resistance terminations and that the motors are restricted to a region above the nucleus and below its ciliated apex (cuticular plate). 4. The function describing length change as a function of command voltage was measured for each segment as the exclusion fraction was varied. The functions were similar at midrange exclusions (i.e., when the segments were about equal length), showing nonlinearity and saturability. The functions were strikingly different when the segment lengths were different. The effects of exclusion on the voltage to length-change functions suggested that the nonlinearity and saturability are local properties of the motility mechanism. 5. The diameter changes of both segments were examined. The segment diameter changes were always antiphasic to the length changes. This finding implies that the motility mechanism has an active antiphasic diameter component. The diameter change amplitude was a monotonically increasing function of exclusion for the included segment, and a decreasing function for the excluded segment. 6. The voltage to length-change and voltage to diameter-change functions were measured for the same cell and exclusion fraction. The voltage to diameter-change function was smaller in amplitude than the voltage to length-change function. The functions were of opposite polarity to each other, but were otherwise similar in character. Thus it is likely that the same motor mechanism is responsible for both axial and diameter deformations.
Functional grouping of the cortico-pretectal projection
Authors: Ilg U. J. , Hoffmann K. P.
Published: December 2017

The ascendency of the cerebral cortex in mammals naturally raises questions about the role of the archetypal subcortical centers we share in common with other phyla. Here we report a situation in which an ancient oculomotor control center, the nucleus of the optic tract, is not so much dominated by the cerebral cortex as served by it. We suggest that the organization of cortical output to subcortical centers may be helpful in understanding the function of the cerebral cortex.
Cutaneous stimulation fails to alter motor unit recruitment in the decerebrate cat
Authors: Clark B. D. , Dacko S. M. , Cope T. C.
Published: December 2017

1. An attempt was made to repeat the observation that cutaneous input to the cat medial gastrocnemius (MG) muscle sometimes had the differential effect of inhibiting motoneurons with slow axonal conduction velocity while simultaneously exciting others with fast conduction velocity. Dual microelectrode recording from intact ventral root filaments was used to study the effects of cutaneous inputs on recruitment order and on firing frequency of physiologically characterized MG motor units in decerebrate cats. Motor responses to pinch of the skin over the lateral surface of the ankle as well as electrical stimulation of the caudal cutaneous sural (CCS) nerve were contrasted with the responses to static muscle stretch as well as muscle vibration. 2. In contrast to the prediction, recruitment order in pairwise tests was the same for skin pinch or CCS stimulation as it was for MG stretch or vibration in all 32 tested pairs of motor units. This sample included seven pairs comprising one slow-twitch (S) and one fast-twitch motor unit, where the predicted reversal of recruitment should have been most apparent. Regardless of the source of excitation, recruitment of motor units of the MG was consistent with Henneman's size principle in approximately 90% of trials. 3. Skin pinch increased the firing rate of 30 of 32 individual motor units previously activated by stretch or vibration, including 7 slow-twitch units. In the remaining two units, skin pinch transiently (100-400 ms) slowed the firing of an S unit in 11 of 13 vibration + pinch trials. The other unit (type unknown) showed one or two retarded spikes in each of four vibration + pinch trials. In three S units, including the lone inhibitable unit and two others that were only excited by skin pinch, there was a significant positive rank correlation between change in unit firing frequency and change in soleus integrated electromyographic activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Alteration of bursting properties in interneurons during locust flight
Authors: Ramirez J. M. , Pearson K. G.
Published: December 2017

1. The contribution of bursting properties to the generation of the flight motor pattern was examined for two identified interneurons (interneurons 566 and 567) in the flight system of the locust Locusta migratoria by means of intracellular recording and stimulation techniques. These interneurons are important elements in transmitting proprioceptive information from the hindwing tegula to wing elevator motoneurons. 2. Offset currents injected into these neurons revealed that bursts are triggered in the intact flying animal by synaptic input from tegula afferents (n = 10). These bursts lead to an amplification of proprioceptive input that is crucial for the generation of the intact flight motor pattern. In the absence of afferent input the activity of these neurons remained subthreshold for triggering a burst. This explains why these neurons exhibit only weak rhythmic oscillations in deafferented animals. 3. The property of interneuron 566 to burst was conditional, always being expressed during flight (n = 14) and occurring only occasionally in the quiescent animal. In the absence of flight, stimulation of tegula afferents never evoked bursts in interneuron 566 (n = 7) and depolarizing current pulses evoked weak bursts in only three of nine preparations. In 2 of 14 animals, bursting property of interneuron 566 was enhanced just after the termination of flight. 4. Variability in the bursting property was also found for interneuron 567. In the quiescent animal, tegula-evoked compound excitatory postsynaptic potentials were not sufficient to trigger bursts (n = 3) but depolarizing current pulses evoked always weak rhythmic bursting activity (n = 4). This bursting property was also variable and in one animal we found long-lasting plateau potentials that could be evoked by current injection after flight was elicited several times. 5. The data presented demonstrate that the capacity to burst is conditional in the interneurons 566 and 567. Bursting properties are always induced during flight and function to amplify proprioceptive pathways that are important for the generation of the intact flight motor pattern.
Protoporphyrins modulate voltage-gated Ca current in AtT-20 pituitary cells
Authors: Linden D. J. , Narasimhan K. , Gurfel D.
Published: December 2017

1. Zinc-protoporphyrin-IX (ZnPP-IX) is an inhibitor of the enzyme heme-oxygenase-2 (HO-2) and consequently has been used to examine the role of carbon monoxide production in neural tissues. We have measured voltage-gated Ca current in AtT-20 pituitary cells using the whole-cell patch-clamp technique and have assessed the effects of extracellularly applied ZnPP-IX and related compounds. 2. Ca currents evoked by depolarizing steps from a holding potential of -90 mV were of the high-threshold, slowly inactivating type. Fifty-six percent of this current was blocked by 10 microM nifedipine and 16% by 3 microM omega-conotoxin with the remainder resistant to both drugs in combination, suggesting that the total Ca current was a mixture of L, N, and possibly P-type conductances. 3. Bath application of ZnPP-IX resulted in an irreversible, dose-dependent attenuation of Ca current. Five micromolar ZnPP-IX produced a 62% reduction of peak current amplitude with no shift in the current-voltage relation, 0.5 microM produced a 19% reduction, and 0.05 microM produced a variable response, either a small transient attenuation or potentiation. 4. The attenuation of Ca current by 5 microM ZnPP-IX could be nearly completely blocked by co-application of superoxide dismutase in the bath (90 U/ml) but not by addition of an inhibitor of cGMP-dependent protein kinase to the internal saline (KT5823, 1 microM). 5. Other inhibitors of heme-oxygenase with similar potency such as tin-protoporphyrin-IX (Sn-PP-IX) and Zn-deuteroporphyrin-bis-glycol (ZnBG) did not attenuate Ca current when applied at 5microM.(ABSTRACT TRUNCATED AT 400 WORDS)
Glycine exerts potent inhibitory actions on mammalian olfactory bulb neurons
Authors: Trombley P. Q. , Shepherd G. M.
Published: December 2017

1. It is generally presumed that gamma-aminobutyric acid (GABA) mediates inhibition in the mammalian brain, whereas glycine is restricted to the brain stem and spinal cord. Recent immunocytochemical and molecular biological studies have demonstrated, however, a widespread distribution of glycine receptors through-out the CNS, including the olfactory bulb. To explore the functional significance of glycine receptors in the olfactory bulb we have used primary culture and whole-cell voltage-clamp recording techniques to test the hypothesis that glycine, as well as GABA, exerts inhibitory actions on olfactory bulb neurons. 2. Cultures of olfactory bulb neurons contain two primary populations of morphologically distinct neurons, mitral/tufted cells and interneurons (granule and periglomerular cells). In all mitral/tufted cells and interneurons examined, both glycine and GABA evoked concentration-dependent desensitizing currents mediated by chloride, similar to those seen in mammalian neurons elsewhere in the brain and spinal cord. 3. The median effective concentration (EC50) for glycine was 125 microM, with a Hill coefficient of 1.7, whereas the EC50 and Hill coefficient for GABA were 52 microM and 1.8, respectively. These values are similar to values previously reported for other central neurons. 4. At moderate concentrations (> 1 microM) strychnine nonselectively antagonized both glycine- and GABA-evoked currents. At low concentrations (< or = 1 microM) strychnine blocked glycine-mediated currents but had little effect on GABA-mediated currents. Similarly, picrotoxin was a nonselective antagonist for glycine- and GABA-mediated currents at high concentrations (100 microM), but was selective for GABA at low concentrations (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)