bluuebunny/crossref_metadata_2025 huggingface dataset:
Basolateral membrane Cl- and K+ conductances of the dark-adapted chick retinal pigment epithelium
Authors: Gallemore R. P. , Hernandez E. , Tayyanipour R. , Fujii S. , Steinberg R. H.
Published: December 2017

1. We characterized the basolateral membrane Cl- and K+ conductances of the dark-adapted chick neural retina-retinal pigment epithelium (RPE)-choroid preparation. Conventional microelectrodes were used to measure apical (V(ap)) and basolateral (Vba) membrane voltage, and double-barreled Cl- and K+ selective microelectrodes were used to follow the time course and magnitude of ion concentration changes outside the basolateral (basal) membrane. 2. In response to a fivefold decrease in basal [Cl-]o, Vba rapidly depolarized by 6.4 +/- 0.7 (SE) mV, and the apparent resistance of the basolateral membrane (Rba) increased. The Cl- channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) suppressed the Vba depolarization by 40% and blocked the Rba increase. Estimates of the relative Cl- conductance (transference number, TCl) from the DIDS-sensitive component of the Cl- diffusion potential gave an average value for TCl of 0.22 +/- 0.03. 3. Further evidence for a Cl- conductance was obtained by measuring changes in intracellular Cl- activity (aCli) induced by transtissue current. Depolarizing Vba elevated aiCl, whereas hyperpolarizing Vba had the opposite effect, consistent with conductive Cl- movement across the basal membrane. TCl estimated from these data averaged 0.23 +/- 0.02. 4. In response to a sixfold increase in basal [K+]o, Vba depolarized 6.1 +/- 0.8 mV. The amplitude of this K+ diffusion potential was inhibited 44 and 67% by 5 and 10 mM Ba2+, respectively. TK was estimated to be 0.61 +/- 0.05. 5. The rapid c-wave membrane hyperpolarizations in response to the light-evoked decrease in subretinal [K+]o were used to calculate the equivalent resistances of the apical membrane (R(ap)), basolateral membrane (Rba), and the paracellular shunt pathway (Rs). They were 152 +/- 10, 615 +/- 38, and 138 +/- 7 omega.cm2 (n = 11 tissues), respectively. From these data the equivalent electromotive force for the basal (Eba) and apical (Eap) membranes were estimated to be -45 +/- 2 and -77 +/- 1 mV, respectively. This estimate of Eba is in the range of that predicted from our estimates of TCl and TK, indicating that, in the dark-adapted chick retina, the resting conductance of the basal membrane can largely be accounted for by the Cl- and K+ conductances described here.
Identification and characterization of a multifunction neuron contributing to defensive arousal in Aplysia
Authors: Cleary L. J. , Byrne J. H.
Published: December 2017

1. The tail withdrawal reflex is mediated by a monosynaptic circuit composed of tail sensory and motor neurons, but there appear to be additional neuronal elements that also contribute to the reflex. A newly identified interneuron, called LP117, was located in the pleural ganglion. This neuron formed a parallel excitatory pathway between sensory and motor neurons. The distinguishing feature of LP117 was its ability to elicit a long-lasting (5-100 s) excitatory postsynaptic potential (EPSP) in the motor neuron. 2. Intracellular labeling of LP117 revealed axons projecting to the cerebral and abdominal as well as the pedal ganglia. Simultaneous intracellular recordings confirmed the widely divergent output of LP117 to tentacle motor neurons in the cerebral ganglion, as well as to gill, siphon, and ink motor neurons in the abdominal ganglion. 3. Also receiving input were abdominal neurons L29, which excites LFs motor neurons and facilitates LE sensory neurons, and L25, which is part of the pattern-generating network underlying respiratory pumping. Thus LP117 appears to be a neural element important for the conduction of information about tail stimulation to ganglia that are not innervated by tail sensory neurons themselves. Moreover, the divergent outputs suggest that LP117 is an element of a neural circuit underlying defensive arousal. 4. LP117 produced slow EPSPs in several motor neurons. The long time course of the EPSP could prolong the burst in the motor neuron produced by LP117 itself as well as increase the effectiveness of coincident synaptic input. This suggests that an important function of this interneuron is to extend the duration of the response to tail stimulation in the motor neuron. This could account for the relatively long time course of the motor neuron response to tail stimulation compared with that of the sensory neuron. 5. Sensitization is a form of nonassociative learning that produces changes in the amplitude and duration of reflex responses. It seems unlikely that all of these changes can be attributed to enhanced amplitude of the sensory-motor synapse, however. Therefore LP117 may itself be a site of plasticity for reflexes elicited by tail stimulation.
The role of interneurons in controlling the tail-withdrawal reflex in Aplysia: a network model
Authors: White J. A. , Ziv I. , Cleary L. J. , Baxter D. A. , Byrne J. H.
Published: December 2017

1. The contributions of monosynaptic and polysynaptic circuitry to the tail-withdrawal reflex in the marine mollusk Aplysia californica were assessed by the use of physiologically based neural network models. Effects of monosynaptic circuitry were examined by the use of a two-layer network model with four sensory neurons in the input layer and one motor neuron in the output layer. Results of these simulations indicated that the monosynaptic circuit could not account fully for long-duration responses of tail motor neurons elicited by tail stimulation. 2. A three-layer network model was constructed by interposing a layer of two excitatory interneurons between the input and output layers of the two-layer network model. These interneurons had properties mimicking those of the recently described interneuron LP117, receiving excitatory input from pleural sensory neurons and evoking a biphasic excitatory postsynaptic potential (EPSP) in pedal motor neurons (Cleary and Byrne 1993). The three-layer model could account for long-duration responses in motor neurons. 3. Sensory neurons are a known site of plasticity in Aplysia. Synaptic plasticity was incorporated into the three-layer model by altering the magnitudes of conductance changes evoked in motor neurons and interneurons by presynaptic sensory neurons. In these simulations the excitatory interneurons converted an amplitude-coded input into an amplitude- and duration-coded output, allowing the three-layer network to support a large range of output amplitudes and durations. 4. Synaptic plasticity at more than one locus modified dramatically the input-output relationship of the three-layer network model. This feature gave the model redundancy in its plastic properties and points to the possibility of distributed memory in the circuitry mediating withdrawal reflexes in Aplysia. Multiple sites of control over the response of the network would likely allow a more diverse repertoire of responses.
NMDA receptor-mediated components of miniature excitatory synaptic currents in developing rat neocortex
Authors: Burgard E. C. , Hablitz J. J.
Published: December 2017

1. In vitro slices of frontal neocortex were prepared from rat pups at various ages after birth: postnatal days (PN) 3-5, 6-8, and 9-14. Using whole-cell patch-clamp techniques, both spontaneous and evoked excitatory postsynaptic currents (EPSCs) were recorded from voltage-clamped layer II-III pyramidal neurons. Developmental changes in EPSCs were examined. 2. Four properties of miniature EPSCs (mEPSCs) were studied: rise time, amplitude, decay time constant (tau), and frequency. These parameters were not tetrodotoxin sensitive and did not exhibit significant developmental changes during the first two postnatal weeks. 3. mEPSCs occurred approximately every 2-3 s and had peak amplitudes of 25-30 pA. Within each age group, certain parameters of mEPSCs were voltage dependent. mEPSC rise time and decay tau were significantly increased at depolarized potentials (-30 to -45 mV) relative to hyperpolarized (-75 to -90 mV) or resting membrane potential (RMP) (-60 to -70 mV). 4. At threshold stimulation intensity, EPSCs were evoked in an "all-or-none" manner. The amplitude and decay tau of evoked unitary EPSCs and mEPSCs were not significantly different. As stimulation intensity was increased, a late EPSC component appeared that was not seen in mEPSCs. At suprathreshold stimulus intensities, EPSC duration was significantly longer in PN 3-5 than in PN 9-14 neurons. 5. The N-methyl-D-aspartate (NMDA) receptor antagonist D(-)2-amino-5-phosphonovaleric acid (APV, 10 microM) significantly decreased mEPSC decay tau and frequency only at depolarized membrane potentials. Likewise, EPSCs were depressed by APV to a greater extent at depolarized potentials, and the depression was mainly of the late component. mEPSCs recorded at RMP were blocked by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline- 2,3-dione (5 microM). 6. Removal of extracellular Mg2+ reversibly increased the decay tau of mEPSCs at RMP but not at depolarized membrane potentials. The decay tau and duration of evoked EPSCs were also increased in zero Mg2+. These effects were reversible with application of APV. All effects of zero Mg2+ on mEPSCs and EPSCs were observed as early as PN 3-5. 7. These results indicate that the basic kinetic properties of mEPSCs are present by PN 3-5 and do not change significantly over the first two postnatal weeks. NMDA receptor activation contributes to mEPSCs and sensitivity to Mg2+ appears as early as PN 3-5. Unitary EPSCs resemble mEPSCs, but a late NMDA receptor-mediated component appears in EPSCs as stimulus intensity is increased.(ABSTRACT TRUNCATED AT 400 WORDS)
Modeling simple-cell direction selectivity with normalized, half-squared, linear operators
Authors: Heeger D. J.
Published: December 2017

1. A longstanding view of simple cells is that they sum their inputs linearly. However, the linear model falls short of a complete account of simple-cell direction selectivity. We have developed a nonlinear model of simple-cell responses (hereafter referred to as the normalization model) to explain a larger body of physiological data. 2. The normalization model consists of an underlying linear stage along with two additional nonlinear stages. The first is a half-squaring nonlinearity; half-squaring is half-wave rectification followed by squaring. The second is a divisive normalization non-linearity in which each model cell is suppressed by the pooled activity of a large number of cells. 3. By comparing responses with counterphase (flickering) gratings and drifting gratings, researchers have demonstrated that there is a nonlinear contribution to simple-cell responses. Specifically they found 1) that the linear prediction from counterphase grating responses underestimates a direction index computed from drifting grating responses, 2) that the linear prediction correctly estimates responses to gratings drifting in the preferred direction, and 3) that the linear prediction overestimates responses to gratings drifting in the nonpreferred direction. 4. We have simulated model cell responses and derived mathematical expressions to demonstrate that the normalization model accounts for this empirical data. Specifically the model behaves as follows. 1) The linear prediction from counterphase data underestimates the direction index computed from drifting grating responses. 2) The linear prediction from counterphase data overestimates the response to gratings drifting in the nonpreferred direction. The discrepancy between the linear prediction and the actual response is greater when using higher contrast stimuli. 3) For an appropriate choice of contrast, the linear prediction from counterphase data correctly estimates the response to gratings drifting in the preferred direction. For higher contrasts the linear prediction overestimates the actual response, and for lower contrasts the linear prediction underestimates the actual response. 5. In addition, the normalization model is qualitatively consistent with data on the dynamics of simple-cell responses. Tolhurst et al. found that simple cells respond with an initial transient burst of activity when a stimulus first appears. The normalization model behaves similarly; it takes some time after a stimulus first appears before the model cells are fully normalized. We derived the dynamics of the model and found that the transient burst of activity in model cells depends in a particular way on stimulus contrast. The burst is short for high-contrast stimuli and longer for low-contrast stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Tonotopic and functional organization in the auditory cortex of the big brown bat, Eptesicus fuscus
Authors: Dear S. P. , Fritz J. , Haresign T. , Ferragamo M. , Simmons J. A.
Published: December 2017

1. In Eptesicus the auditory cortex, as defined by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps, encompasses an average cortical surface area of 5.7 mm2. This area is large with respect to the total cortical surface area and reflects the importance of auditory processing to this species of bat. 2. The predominant pattern of organization in response to tone bursts observed in each cortex is tonotopic, with three discernible divisions revealed by our data. However, although cortical best-frequency (BF) maps from most of the individual bats are similar, no two maps are identical. The largest division contains an average of 84% of the auditory cortical surface area, with BF tonotopically mapped from high to low along the anteroposterior axis and is part of the primary auditory cortex. The medium division encompasses an average of 13% of the auditory cortical surface area, with highly variable BF organization across bats. The third region is the smallest, with an average of only 3% of auditory cortical surface area and is located at the anterolateral edge of the cortex. This region is marked by a reversal of the tonotopic axis and a restriction in the range of BFs as compared with the larger, tonotopically organized division. 3. A population of cortical neurons was found (n = 39) in which each neuron exhibited two BF threshold minima (BF1 and BF2) in response to tone bursts. These neurons thus have multipeaked frequency threshold tuning curves. In Eptesicus the majority of multipeaked frequency-tuned neurons (n = 27) have threshold minima at frequencies that correspond to a harmonic ratio of three-to-one. In contrast, the majority of multipeaked neurons in cats have threshold minima at frequencies in a ratio of three-to-two. A three-to-one harmonic ratio corresponds to the "spectral notches" produced by interference between overlapping echoes from multiple reflective surfaces in complex sonar targets. Behavioral experiments have demonstrated the ability of Eptesicus to use spectral interference notches for perceiving target shape, and this subpopulation of multipeaked frequency-tuned neurons may be involved in coding of spectral notches. 4. The auditory cortex contains delay-tuned neurons that encode target range (n = 99). Most delay-tuned neurons respond poorly to tones or individual FM sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned.(ABSTRACT TRUNCATED AT 400 WORDS)
Development of metabolic activity patterns in the somatosensory cortex of cats
Authors: Juliano S. L. , Code R. A. , Tommerdahl M. , Eslin D. E.
Published: December 2017

1. The development of cortical responses to somatic stimulation was studied in kittens 2-5 wk of age using the 2-deoxyglucose (2DG) technique. During the 2DG experiment each kitten received an innocuous intermittent vertical displacement stimulus to the forepaw. 2. The pattern of metabolic activity was substantially different in young animals compared with adults. In the individual autoradiographs of the 2-wk-old kittens stimulus-evoked 2DG uptake in primary somatosensory cortex was localized to a small spot in the upper portion of the cortex, whereas in the adult the label extended vertically through the cortical layers and appeared more column-like. Individual patches of label were substantially smaller and less dense in young animals. Over a period of several weeks the evoked activity evolved to the more extensive adult pattern. The 2DG uptake displayed a mature distribution by approximately 4-5 wk of age. During this period, the cortical architecture also evolved from an immature to a mature arrangement. 3. The evoked activity was reconstructed into two-dimensional maps; the distribution of label > or = 1.5 SD above background was considered to be stimulus related. In the adult, the pattern appeared as a strip or strips of increased metabolic activity that extended in the rostrocaudal direction for approximately 1 mm. In contrast, the activity pattern in animals 2-4 wk old was less discretely organized into "strips" and was more diffusely spread over several mms of somatosensory cortex. The two-dimensional pattern gradually coalesced into a more localized strip by approximately 4-5 wk of age. Although the pattern of label was more widespread in the young animals, the absolute distance of the spread of activity did not vary substantially, regardless of the age of the animal. 4. Other measurements regarding the distribution of activity at different ages indicate that the amount of cortex activated increases in absolute terms, although the percent of cortex activated by the stimulus decreases. The overall intensity of the 2DG uptake as measured on the two-dimensional maps increases with age, as does the variability of the 2DG uptake; a wider range of intensity values is seen in the adult. Plots created from the individual two-dimensional reconstructions allowed a measure of "patch strength" at different ages. These histograms relate the most intense region of uptake in a given map to the spatial distribution of activity spreading in the medial and lateral directions.(ABSTRACT TRUNCATED AT 400 WORDS)
Loss of proprioception produces deficits in interjoint coordination
Authors: Sainburg R. L. , Poizner H. , Ghez C.
Published: December 2017

1. We analyzed the performance of a simple pantomimed gesture in 2 patients with large-fiber sensory neuropathy and 11 control subjects to determine how proprioceptive deafferentation disrupts unconstrained multijoint movements. Both patients had near-total loss of joint position, vibration, and discriminative touch sensation in the upper extremities. Muscle strength remained intact. 2. Subjects performed a gesture similar to slicing a loaf of bread. In this gesture, the hand first moves outward from the body, reverses direction sharply, and then moves back toward the body. Accurate performance requires precise coordination between the shoulder and elbow joints during movement reversals. Movements were performed under two conditions: with eyes open and with eyes closed. Three dimensional shoulder, elbow, wrist, and hand trajectories were recorded on a WATSMART system. 3. When control subjects performed the gesture with their eyes closed, their wrist trajectories were relatively straight and individual cycles of motion were planar. Movements reversed direction sharply, such that outward and inward portions of the wrist path were closely aligned. Corresponding to this spatial profile, the reversals in movement direction at the shoulder joint, from flexion to extension, and at the elbow joint, from extension to flexion, were synchronous. 4. In contrast, when deafferented patients performed the gesture with their eyes closed, their wrist trajectories were highly curved and individual cycles were severely nonplanar. The wrist paths showed a characteristic anomaly during the reversal in movement direction, when elbow joint movement became transiently locked. Correspondingly, the movement reversals at the shoulder and elbow joints were severely temporally decoupled. 5. When patients were able to view their limbs during performance of this gesture there was significant improvement in the linearity and planarity of movements. However, the patients remained unable to synchronize the movements at the shoulder and elbow joints to produce spatially precise wrist paths. 6. We conclude that loss of proprioception disrupts interjoint coordination and discuss the hypothesis that this interjoint coordination deficit results from a failure to control the interaction forces that arise between limb segments during multijoint movements.
Activity of medial vestibulospinal tract cells during rotation and ocular movement in the alert squirrel monkey
Authors: Boyle R.
Published: December 2017

1. Chronic unit and eye movement recording and microstimulation techniques were used to study the discharge properties of identified medial vestibulospinal tract (MVST) cells in the alert squirrel monkey. MVST cells were antidromically activated from the ventromedial funiculus at C1 and responded to orthodromic stimulation of the ipsilateral VIIIth nerve (Vi) at mono- or disynaptic latencies. Cell discharges were examined during imposed sinusoidal yaw rotation to activate horizontal semicircular canal afferents and during voluntary ocular pursuit and fixation of visual targets with the head held stationary. 2. MVST cells represented 15% (22 of 147 cells) of the population of horizontal canal-related cells recorded in the vestibular nuclei. Twelve MVST cells were monosynaptically related to Vi; of these cells, 7 (58%) were characterized as ipsilateral eye and head velocity, having a discharge modulation related to the velocity of both ipsilaterally directed eye movement and yaw rotation, and 3 also had an ipsilateral eye position sensitivity. Most (8 of 10, 80%) MVST cells disynaptically related to Vi responded only to contralateral head velocity; the other 2 cells carried a combined contralateral head and ipsilateral eye movement signal. A pause or burst of discharge associated with fast or saccadic eye movements made in any direction was not present on the 22 MVST cells. 3. The MVST is an output pathway of the vestibular nuclei through which the labyrinth controls reflex head movements. The results show that MVST cells transmit the movement and position of eyes in orbit, with vestibular signals, to the cervical spinal cord and suggest that the MVST may play a dynamic role in voluntary gaze stabilization and eye/head tracking.
The uptake inhibitor L-trans-PDC enhances responses to glutamate but fails to alter the kinetics of excitatory synaptic currents in the hippocampus
Authors: Isaacson J. S. , Nicoll R. A.
Published: December 2017

1. We have used patch-clamp recording techniques to study the physiological properties of a recently described glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC), in the CA1 region of the guinea pig hippocampus. 2. L-trans-PDC markedly potentiated the action of exogenously applied glutamate and raised the ambient extracellular levels of glutamate in hippocampal slices. Despite these actions, L-trans-PDC did not affect the time course of either the N-methyl-D-aspartate (NMDA) or non-NMDA receptor-mediated synaptic currents evoked by the stimulation of a large number of neighboring synapses. 3. These findings are consistent with models of fast synaptic transmission in which transmitter is rapidly cleared from the synaptic cleft by diffusion. However, in marked contrast to fast gamma-aminobutyric acid A (GABAA) synapses in the hippocampus, uptake does not appear to play a role in regulating the "spill-over" of transmitter from neighboring, co-activated glutamatergic synapses. Therefore, either diffusion alone can effectively limit the temporal and spatial domain of synaptically released glutamate, or alternatively, L-trans-PDC like other currently available blockers is not sufficiently potent to reveal a role for transmitter uptake at glutamatergic synapses.
Responses of rat medullary dorsal horn neurons following intranasal noxious chemical stimulation: effects of stimulus intensity, duration, and interstimulus interval
Authors: Peppel P. , Anton F.
Published: December 2017

1. Most quantitative examinations of nociception are performed with thermal or mechanical stimuli. Because nociceptive processing mechanisms may depend on the modality of the stimuli, comparable studies on chemonociception are necessary. 2. We examined the activity of chemonociceptive medullary dorsal horn neurons in halothane-anesthetized rats. For controlled noxious chemical stimulation, defined CO2 pulses were applied to the nasal mucosa. The effects of stimulus intensity, duration, and interstimulus interval (ISI) were tested by performing three different CO2 stimulation protocols (see below). 3. The recorded neurons were characterized by intranasal and facial stimuli of different modalities. The cells received input from intranasal A delta- and/or C-fibers. All tested neurons also responded to other intranasally applied irritants, e.g., mustard oil. Furthermore, the units were sensitive to intranasal high-threshold mechanical stimulation and to facial mechanical stimulation. According to the properties of their facial mechanoreceptive fields, the units were classified as wide dynamic range (WDR) or nociceptive specific (NS) neurons. The majority of the cells also responded to facially applied noxious heat stimuli, so that most of the recorded neurons were found to be multimodal. Some of the neurons, in addition, had convergent input from primary afferents innervating the maxillary tooth pulps or the cornea and periorbital structures. 4. In the first stimulation protocol we presented four different CO2 concentrations (25, 50, 75, and 100%; stimulus duration 2 s). In total, each concentration was applied 10 times (2 trains of 5 stimuli). Stimulus response functions (SRFs) were computed with average responses to identical stimuli. All but 2 of the 23 tested neurons displayed enhanced responses after stimulation with increasing intensities. In general, WDR cells (n = 15) discharged more vigorously to the same CO2 concentration than NS cells (n = 8). WDR neurons discriminated more reliably between stimulus intensities in the low to moderate range (25–50% CO2) than NS cells. Both categories of neurons, however, discriminated equally well in the moderate- to high-intensity range (50–75% CO2). The discriminatory capacity of WDR and NS neurons was reduced in the highest concentration range (75–100% CO2). The proportion of NS neurons significantly discriminating between these intensities tended to be higher compared with WDR neurons when stimuli were applied with long ISIs (120 s). 5. To examine the effects of the duration of the ISI, identical test sequences were performed with ISIs of 30 and 120 s. (ABSTRACT TRUNCATED AT 400 WORDS)
Cholinergic modulation of the swimmeret motor system in crayfish
Authors: Braun G. , Mulloney B.
Published: December 2017

1. The muscarinic agonist pilocarpine induced the swimmeret motor pattern in resting isolated preparations of the crayfish abdominal nerve cord and modulated the burst frequency in a dose-dependent manner. 2. Nicotine did not elicit rhythmic activity in resting isolated preparations but increased the burst frequency in active preparations. Nicotine produced higher burst frequencies than pilocarpine. 3. The acetylcholine (ACh) analogue carbachol combined the effects of pilocarpine and nicotine. It activated isolated resting preparations and increased the burst frequency as effectively as nicotine. The ACh-esterase inhibitor eserine also increased the burst frequency in active preparations. 4. Neither muscarinic nor nicotinic antagonists disrupted the proctolin-induced motor pattern, suggesting that proctolin and cholinergic agonists affect two different pathways for the activation of the swimmeret system. 5. We conclude that cholinergic interneurons participate in initiation of the swimmeret motor pattern and can modulate its burst frequency.
Antimasking effects of the olivocochlear reflex. I. Enhancement of compound action potentials to masked tones
Authors: Kawase T. , Liberman M. C.
Published: December 2017

1. The effects of olivocochlear (OC) feedback on signal processing in the cochlea were studied by comparing responses seen with and without a contralateral noise or by comparing responses seen before and after cutting the OC bundle (OCB). Adding and subtracting a contralateral noise is a convenient, reversible way of changing the level of OC feedback; however, it fully reveals only the contribution of the contralaterally responsive efferent fibers. Cutting the OCB can reveal the full contribution of all fibers in the OCB; however, the manipulation can only be performed once per experiment. 2. The amplitude of the compound action potential (CAP), recorded from anesthetized or decerebrate cats in response to tone pips, could be increased by addition of contralateral noise at moderate sound pressure levels. These enhancement phenomena were most easily demonstrable when the tone pips were masked by ipsilateral broadband noise; however, in some animals CAP enhancement was seen in the absence of ipsilateral maskers. Enhancement-in-quiet may arise because of internal masking from animal-generated noise. All contralateral-noise enhancement disappeared when the OCB was cut. 3. Enhancement effects of contralateral noise could be seen in both simultaneous and forward-masking paradigms. Enhancement was largest for high-frequency tone pips (8-16 kHz) and could be demonstrated over a wide range of tone-pip levels and ipsilateral-masker levels. Suppression of CAP by the contralateral noise was often seen for lower tone-pip frequencies (2-8 kHz) and lower tone-pip intensities. These trends may be understood in the context of known properties of OC peripheral effects and known properties of physiological masking. 4. Cutting the OCB resulted in a decrease in CAP amplitudes to masked tone pips. When CAP was measured to tone pips presented in equilevel, binaural noise, OCB section resulted in a decrease in CAP amplitudes equivalent to at least a 6-dB decrease in signal-to-noise ratio. Such antimasking effects of an intact OCB were seen in both simultaneous and forward-masking paradigms. 5. Present evidence suggests that all these antimasking effects can be explained on the basis of activation of the medial OC fibers to the outer hair cells. By suppressing responses to continuous noise backgrounds, the OC reflex may enhance responses to transient masked stimuli by decreasing the level of adaptation in auditory nerve fibers. Such effects of the OC reflex should improve discrimination of transient signals presented in a continuous noise background.
Antimasking effects of the olivocochlear reflex. II. Enhancement of auditory-nerve response to masked tones
Authors: Kawase T. , Delgutte B. , Liberman M. C.
Published: December 2017

1. The antimasking effects of olivocochlear (OC) efferent feedback were studied in anesthetized or decerebrate cats by comparing responses of single auditory-nerve fibers (ANFs) to tone bursts in continuous masking noise seen with and without addition of a moderate-level contralateral noise known to activate the OC reflex. Responses were measured as a function of tone-burst intensity, tone-burst frequency, and masker intensity and were analyzed so as to allow quantitative estimates of the detectability of the tone bursts against the noise background. 2. Addition of the contralateral OC elicitor both increased the maximum discharge rates to the masked tone bursts and decreased the rates to the ipsilateral masker. The rate increases to the tone bursts could be explained on the basis of a decrease in adaptation caused by decreasing the steady response to the masker. The result is a steepening of the rate-versus-level function for masked tone bursts and a concomitant increase in the estimated discriminability of small increments of tone-burst intensity. 3. For tone bursts at the fiber's characteristic frequency (CF), the OC effects on detection threshold for the masked tone bursts depended on masker level, with small increases in threshold for low masker levels and somewhat larger decreases in threshold for higher masker levels. For tone bursts below CF, OC effects, when present, always decreased the detection threshold. 4. The largest antimasking effects were seen for fibers with CFs between 6 and 12 kHz and for masker levels within 20 dB of the fiber's threshold to the masker. These trends appeared to hold for fibers of all spontaneous rates (SRs). 5. Enhancement of the response to unmasked tone bursts and concomitant decrease in the “spontaneous rate” was elicited by OC activation in fibers if threshold sensitivity approached -10 dB SPL. This “enhancement-in-quiet” appears to arise when an animal-generated noise produces a continuous response (in the absence of purposely applied sound) that is suppressed by OC activity. This finding raises questions as to the range of “true” spontaneous rates in the cat. 6. The results highlight two important distinctions between the effects of OC feedback in quiet versus those in noise. In quiet, the effects are predominately suppressive and are restricted to stimuli at frequencies near a fiber's CF and at intensities within its dynamic range. In continuous background noise, the OC reflex can enhance the responses to transient stimuli. Such effects are seen throughout the fiber's response area.(ABSTRACT TRUNCATED AT 400 WORDS)
Flow and thermal responses of aortic baroreceptors
Authors: Munch P. A.
Published: December 2017

1. The aims of this study were 1) to determine whether the impulse activity in rabbit aortic baroreceptors (BRs) was influenced by changes in nonpulsatile flow through the aortic lumen and 2) to examine the BR and aortic arch responses to changes in temperature. 2. An in vitro aortic arch-aortic nerve preparation was used to record suprathreshold steady-state discharge in a total of 29 single-unit BRs from 12 New Zealand white rabbits. Changes in BR frequency were measured relative to control and were recorded simultaneously with aortic arch pressure, flow, temperature, diameter, and calculated wall shear stress (Sw). 3. With pressure held constant, stair-step increases in flow (3–18 ml/min) constricted the arch and evoked two types of BR responses: activation in most units (15 of 17 BRs tested) and inhibition in 2 units. The activation response appeared closely related to the changes in flow and Sw, but also appeared related to uncontrolled changes in perfusate temperature. 4. When the effects of temperature were examined more closely with pressure and flow held constant, controlled step increases in temperature (between 32 and 42 degrees C) constricted the arch and again evoked two BR responses: activation in 11 of 14 BRs tested and inhibition in 3 units. The Q10 for the activation response was 1.55 +/- 0.08 (mean +/- SE), which was not significantly different from the Q10 for activation when temperature varied with flow (1.65 +/- 0.1, P < 0.05). Thus the effect of temperature on most BRs was directionally and quantitatively similar in the presence and absence of changes in flow. 5. Last, when flow was examined over a wide range (15–515 ml/min) with temperature and pressure held constant, stair-step increases in flow failed to produce any change in BR frequency in each of 15 fibers tested (10 arches). The lack of response was not due to a functionally damaged preparation because the usual BR and aortic arch responses to pressure and to drug-evoked vasoconstriction (norepinephrine) and endothelial-mediated vasodilation (acetylcholine) were intact. 6. These results demonstrate that aortic BRs in rabbits are not sensitive to flow and thus are not likely influenced by fluctuations in cardiac output apart from associated changes in pressure. The aortic BRs are affected directly by variations in temperature and in some cases indirectly by temperature-related vasoconstriction. The effects of temperature may have important implications for neural control of the circulation when core temperature varies because of physiological and environmental stress.
Metabotropic glutamate receptors depress afferent excitatory transmission in the rat nucleus tractus solitarii
Authors: Glaum S. R. , Miller R. J.
Published: December 2017

1. We have previously demonstrated that the metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate [(1S;3R)-ACPD] presynaptically inhibits evoked glutamatergic excitatory postsynaptic currents (EPSCs) in patch-clamped rat nucleus tractus solitarius (NTS) neurons recorded in thin slices. The present study investigated the ability of endogenously released glutamate to modulate EPSCs in the NTS. 2. A low-frequency tetanus of the tractus solitarius (TS) resulted in either posttetanic potentiation (PTP) (8 of 21 cells) or depression (13 of 21 cells) of monosynaptic EPSCs recorded in the presence of D(-)2-amino-5-phosphonopentanoic acid (AP5) and bicuculline. 3. The amplitude of the EPSC was not significantly affected by the bath application of the mGluR antagonist (+) alpha-methyl-4-carboxyphenylglycine (MCPG). 4. In the presence of MCPG, a low-frequency tetanus resulted in PTP of the EPSC in all neurons. PTP was significantly enhanced in those cells previously exhibiting PTP. 5. The results suggest that presynaptic mGluRs on TS projections to the NTS may be activated by endogenously released glutamate at physiologically relevant stimulus frequencies and therefore play a role in the modulation of autonomic afferent transmission.
Autoactive peptides act at three distinct receptors to depolarize the bag cell neurons of Aplysia
Authors: Loechner K. J. , Kaczmarek L. K.
Published: December 2017

1. In response to brief stimulation of an afferent input the bag cell neurons of Aplysia depolarize by 15-20 mV and generate an afterdischarge that, in vitro, lasts for approximately 30 min. During the discharge these neurons secrete three small peptides [bag cell peptides (BCPs)], Ala-Pro-Arg-Leu-Arg-Phe-Tyr-Ser-Leu (alpha-BCP), Arg-Leu-Arg-Phe-His (beta-BCP), and Arg-Leu-Arg-Phe-Asp (gamma-BCP), that share a common core sequence and that have electrophysiological effects on the bag cell neurons themselves. We have now studied the action of these three peptides on bag cell neurons isolated in culture. All three peptides were found to be capable of producing a depolarization of these cells. 2. The ability of alpha-, beta-, and gamma-BCP to induce a depolarization in isolated bag cell neurons exhibits a seasonal variability. The response to the peptides is maximal from early summer through late fall and parallels the frequency of egg-laying in vivo. 3. The depolarization induced by alpha-, beta-, and gamma-BCP desensitizes with repeated application of peptide. Desensitization of the response to one peptide does not, however, prevent the response to application of one of the other two peptides. This suggests that separate autoreceptor populations exist for alpha-, beta-, and gamma-BCP. 4. As reported previously, desensitization of the depolarizing response to the peptides was also observed after preincubation of intact clusters of bag cell neurons with a high concentration of all three peptides.(ABSTRACT TRUNCATED AT 250 WORDS)
Variation in IH, IIR, and ILEAK between acutely isolated adult rat dorsal root ganglion neurons of different size
Authors: Scroggs R. S. , Todorovic S. M. , Anderson E. G. , Fox A. P.
Published: December 2017

1. The distribution of IH, IIR, and ILEAK was studied in different diameter rat dorsal root ganglion (DRG) neuron cell bodies (neurons). DRG neurons were studied in three diameter ranges: small (19–27 microns), medium (33–37 microns), and large (44-54 microns). IH was defined as a slowly activating inward current evoked by hyperpolarizing voltage steps from a holding potential (HP) of -60 mV, and blocked by 1 mM Cs2+ but not 1 mM Ba2+. Inward rectifier current (IIR) was defined as a rapidly activating current evoked by hyperpolarizations from HP -60 mV, which rectified inwardly around the reversal potential for potassium (EK), and was completely blocked by 100 microM Ba2+. ILEAK was defined as an outward resting current at HP -60 mV, which did not rectify and was blocked by 100 microM Ba2+ but not by 2 mM Cs+. 2. IH was observed in 23 of 23 large, 11 of 12 medium, and in 9 of 20 small diameter DRG neurons tested. Peak IH normalized to membrane surface area was significantly greater in large than in medium or small diameter DRG neurons expressing IH. All neurons exhibiting IH under voltage clamp conditions had short duration action potentials and exhibited time-dependent rectification under current clamp conditions, properties similar to A-type DRG neurons. The 11 small diameter neurons not expressing IH had long duration action potentials and did not exhibit time-dependent rectification, properties similar to C-type DRG neurons. 3. IIR was detected in 18 of 22 medium diameter neurons tested.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of activity in dorsal root ganglion neurons by sympathetic activation in nerve-injured rats
Authors: Devor M. , Janig W. , Michaelis M.
Published: December 2017

1. Teased-fiber recordings were made from the axons of dorsal root ganglion (DRG) neurons in rats that underwent transection of the sciatic nerve 4–22 days previously. Many of the neurons had spontaneous ectopic discharge originating from within the DRG. 2. When postganglionic sympathetic efferents ending in the DRG were activated by tetanic stimulation of the T13 and L1 ventral roots (VRs), the ongoing afferent discharge was altered in more than one-half of the DRG neurons sampled. In most of the responsive units (62%), activity was augmented by this sympathetic stimulation; in the remainder (38%), activity was suppressed. Single-pulse stimuli of sympathetic efferents had no effect. 3. Responses to sympathetic stimulation began after a substantial delay (mean 14.3 s), peaked after 10–20 s, and then returned toward baseline over an additional 20–30 s. 4. Both excitatory and suppressive responses to sympathetic stimulation, as well as corresponding responses to systemically applied adrenaline, were blocked by the alpha-adrenoreceptor antagonist phentolamine. 5. Most of the active DRG neurons that responded to sympathetic stimulation, as well as others that did not, were excited by tetanic stimulation of neighboring afferent neurons that share the same DRG. These “crossed afterdischarge” responses were not blocked by phentolamine. Single-pulse stimuli of neighboring afferents had no effect. 6. Sympathetic-sensory coupling in DRGs of nerve-injured animals provides a previously unsuspected substrate for sympathetic involvement in neuropathic sensory dysfunction.
Multiple high-threshold calcium currents in acutely isolated rat amygdaloid pyramidal cells
Authors: Foehring R. C. , Scroggs R. S.
Published: December 2017

1. High-threshold Ca2+ currents were studied in large pyramidal cells acutely dissociated from the rat amygdaloid complex. L-, N-, and P-type currents were present in about equal proportions in these cells and accounted for most of the whole-cell current.
The role of D1-dopamine receptor in working memory: local injections of dopamine antagonists into the prefrontal cortex of rhesus monkeys performing an oculomotor delayed-response task
Authors: Sawaguchi T. , Goldman-Rakic P. S.
Published: December 2017

1. To examine the role of dopamine receptors in the prefrontal cortex (PFC) on working memory, we injected dopamine antagonists (SCH23390, SCH39166, haloperidol, sulpiride, and raclopride) locally into the dorsolateral PFC in two monkeys trained to perform an oculomotor delayed-response (ODR) task. In the ODR task, monkeys fixate a central spot on a cathode ray tube (CRT) monitor while a visual cue is briefly (300 ms) presented in one of several peripheral locations in the visual field. After a delay of 1.5-6 s, the fixation spot is turned off, instructing the monkey to move its eyes to the target location that had been indicated by the visuospatial cue before the delay. Each monkey also performed a control task in which the cue remained on during the delay period. In this task the monkey's response was sensory rather than memory guided. 2. Local intracerebral injection of the selective dopamine antagonists SCH23390 (10-80 micrograms) and SCH39166 (1-5 micrograms) and/or the nonselective dopamine antagonist haloperidol (10-100 micrograms) induced deficits in ODR task performance at a total of 22 sites in the dorsolateral PFC. The deficit was characterized by a decrease in the accuracy of the memory-guided saccade as well as an increase in the latency of the response. The deficit usually appeared within 1-3 min after the injection, reached a peak at 20-40 min, and recovered at 60-90 min. 3. Performance change was restricted to a few specific target locations, which varied with the injection site and were most often contralateral to the injection site. 4. The degree of impairment in the ODR task occasioned by the injection of the dopamine antagonists was sensitive to the duration of delay; longer delays were associated with larger decreases in the accuracy and delayed onset of the memory-guided saccade. 5. The deficit was dose dependent; higher doses induced larger errors and increases in the onset of the memory-guided saccade. 6. Dopamine antagonists did not affect performance on the control task, which required the same eye movements but was sensory guided. Thus, in the same experimental session in which ODR performance was impaired, the accuracy and the latency of the sensory-guided saccades were normal for every target location.(ABSTRACT TRUNCATED AT 400 WORDS)
A simulation of action potentials in synaptic boutons during presynaptic inhibition
Authors: Graham B. , Redman S.
Published: December 2017

1. During presynaptic inhibition, an increased conductance in the membrane of the presynaptic bouton is presumed to reduce the action potential, thereby reducing transmitter release. The object of the simulation has been to determine the magnitude of a chloride conductance required to reduce transmitter release, for various diameters of synaptic boutons, connected to axons with diameters in the range 0.1-1.0 microns. 2. A propagating action potential was simulated in axons connected to either side of a hemispherical bouton. The axons could be myelinated or unmyelinated, while the bouton membrane could be passive, a node of the myelinated nerve, or have the same active properties as the attached unmyelinated nerve. Membrane properties of the axons were derived from mammalian data and scaled to 37 degrees C. 3. A steady-state chloride conductance was included in the bouton membrane, with ECl = -40 mV. The amplitude of the action potential in the bouton was calculated for different diameters of axon and bouton and for different magnitudes of chloride conductance. 4. Using published data on the relationship between the amplitude of a presynaptic action potential and the resulting postsynaptic potential, the relationship between the chloride conductance and the postsynaptic response was calculated for different geometries. Transmitter release was reduced when an action potential was 90 mV or smaller, with no transmission for action potentials smaller than 50 mV. 5. Conductance increases in the range 3 to 10 nS were required to reduce the action potential to 90 mV, depending on the diameter of the axon (0.5-1.0 microns), diameter of the bouton (3-6 microns), whether the bouton had passive or active membrane, and whether the axon was myelinated or unmyelinated. A 3 microns passive bouton connected to a 0.5 micron myelinated axon was most sensitive to the effects of a chloride conductance, while a 6 microns active bouton connected to a 1 micron myelinated nerve was least sensitive to the effects of a chloride conductance. 6. The reduction in the action potential was compared when ECl = -40 mV and when ECl = E(rest) = -80 mV. Inactivation of the sodium conductance by terminal depolarization was the dominant influence on the amplitude of the action potential. 7. Conductances that were sufficient to completely block synaptic transmission at a bouton were insufficient to prevent the spread of the action potential away from that bouton.(ABSTRACT TRUNCATED AT 400 WORDS)