bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-term potentiation in an isolated peripheral nerve-spinal cord preparation
Authors: Lozier A. P. , Kendig J. J.
Published: December 2017

1. Long-lasting increases in synaptic efficacy following repetitive stimulation have been demonstrated at several sites in the CNS, where they are collectively termed long-term potentiation (LTP). LTP is of interest with respect to its presumptive relationship to learning and memory in hippocampus. In the spinal cord in vivo, an LTP-like phenomenon is thought to underlie the allodynia and hyperalgesia that follows some peripheral injuries. 2. We investigated the capacity of the isolated neonatal rat spinal cord to sustain a long-lasting increase in a nociceptive-related slow ventral root potential (sVRP) recorded from a lumbar root after a tetanic train of stimuli to the peripheral cutaneous saphenous nerve. Stimuli were delivered at a low constant (0.02 s-1) frequency during a 30-min control period. A tetanic stimulus train (10 s-1 for 60 s) was then given followed by a resumption of low (0.02 s-1) frequency stimulation. Potentiation was defined as an increase in sVRP area > 2 SD above control mean. 3. Twenty of 20 preparations showed immediate posttetanic potentiation. In 13 of the 20, potentiation was maintained for > or = 1 h after the tetanic stimulus train. 4. Potentiation was dependent on activation of C fibers during the inducing train; stimuli below C-fiber threshold, activating only A fibers, were ineffective. Potentiation was selectively expressed by a long-latency component of the sVRP elicited by stimuli at a strength that evoked both A- and C-fiber responses in the nerve.(ABSTRACT TRUNCATED AT 250 WORDS)
Voltage-dependent calcium channels in rat midbrain dopamine neurons: modulation by dopamine and GABAB receptors
Authors: Cardozo D. L. , Bean B. P.
Published: December 2017

1. Voltage-dependent calcium channels were studied with whole cell voltage-clamp recordings from neurons enzymatically dispersed from the ventral mesencephalon of rat brains (postnatal days 3-10) and identified as dopamine neurons by 5,7-dihydroxytryptamine autofluorescence. 2. Dopamine neurons had large high-threshold calcium currents activated by depolarizations positive to -50 mV. Different components of calcium channel current were not readily distinguishable by voltage dependence or kinetics, but pharmacological experiments showed the existence of different channel types. The overall current had significant components blocked by nimodipine (28%), by omega-conotoxin GVIA (22%), and by omega-agatoxin-IVA (omega-Aga-IVA) (37%), and there was a significant amount of current (16%) remaining in saturating concentrations of all three blockers. 3. High-threshold calcium current was reversibly reduced by the gamma-aminobutyric acid-B (GABAB) receptor agonist baclofen and by dopamine and the D2 receptor agonist quinpirole. Inhibition by GABAB or dopamine agonists developed and reversed within seconds. 4. Quinpirole reduced both omega-conotoxin-sensitive and omega-Aga-IVA-sensitive components of calcium current. 5. With physiological ionic conditions, inward calcium currents were outweighed by outward currents, in part through calcium-activated potassium channels activated by omega-conotoxin-sensitive and omega-Aga-IVA-sensitive calcium entry.
Face-sensitive regions in human extrastriate cortex studied by functional MRI
Authors: Puce A. , Allison T. , Gore J. C. , McCarthy G.
Published: December 2017

1. We have previously identified face-selective areas in the mid-fusiform and inferior temporal gyri in electrophysiological recordings made from chronically implanted subdural electrodes in epilepsy patients. In this study, functional magnetic resonance imaging (fMRI) was used to study the anatomic extent of face-sensitive brain regions and to assess hemispheric laterality. 2. A time series of 128 gradient echo echoplanar images was acquired while subjects continuously viewed an alternating series of 10 unfamiliar faces followed by 10 equiluminant scrambled faces. Each cycle of this alternating sequence lasted 12 s and each experimental run consisted of 14 cycles. The time series of each voxel was transformed into the frequency domain using Fourier analysis. Activated voxels were defined by significant peaks in their power spectra at the frequency of stimulus alternation and by a 180 degrees phase shift that followed changes in stimulus alternation order. 3. Activated voxels to faces were obtained in the fusiform and inferior temporal gyri in 9 of 12 subjects and were approximately coextensive with previously identified face-selective regions. Nine subjects also showed activation in the left or right middle occipital gyri, or in the superior temporal or lateral occipital sulci. Cortical volumes activated in the left and right hemispheres were not significantly different. Activated voxels to scrambled faces were observed in six subjects at locations mainly in the lingual gyri and collateral sulci, medial to the regions activated by faces. 4. Face stimuli activated portions of the midfusiform and inferior temporal gyri, including adjacent cortex within occipitotemporal sulci.(ABSTRACT TRUNCATED AT 250 WORDS)
Existence in the nucleus incertus of the cat of horizontal-eye-movement-related neurons projecting to the cerebellar flocculus
Authors: Cheron G. , Saussez S. , Gerrits N. , Godaux E.
Published: December 2017

1. Properties of nucleus incertus (NIC) neurons projecting to the cerebellar flocculus were studied in alert cats by using chronic unit and eye movement recording and antidromic activation. Projection of these neurons onto the flocculus was verified with retrograde transport of horseradish peroxidase after injections in the flocculus. 2. Bipolar stimulation electrodes were implanted into the "middle" zone of each flocculus because this zone is known to be involved in the control of horizontal eye movements. The dorsomedial aspect of the pontine tegmentum was explored with microelectrodes during stimulation of both flocculi. The majority of neurons antidromically activated from the flocculus were found in the caudal part of the NIC. 3. Of the 69 neurons activated from the flocculus, 44 were classified as burst-tonic (BT) neurons; 34 discharged in relation with horizontal movements of the eye, 10 in relation with vertical movements. Of the 14 remaining neurons, 6 were not related to eye movements and 8 were classified as burst neurons. The BT neurons of the NIC displayed a great sensitivity to both horizontal eye position and horizontal eye velocity. 4. This study demonstrates the presence of a new group of horizontal eye movement related BT neurons situated in the NIC. The fact that they project to the horizontal floccular zone emphasizes the importance of the functional specialization of the different Purkinje cell zones.
Comparison of noise and tone azimuth tuning of neurons in cat primary auditory cortex and medical geniculate body
Authors: Clarey J. C. , Barone P. , Irons W. A. , Samson F. K. , Imig T. J.
Published: December 2017

1. A comparison of the azimuth tuning of single neurons to broadband noise and to best frequency (BF) tone bursts was made in primary auditory cortex (AI: n = 173) and the medial geniculate body (MGB: n = 52) of barbiturate-anesthetized cats. Observations were largely restricted to cells located within the tonotopically organized divisions of the MGB (i.e., the ventral nucleus and the lateral division of the posterior nuclear group) and the middle layers of AI. All cells studied had BFs > or = 4 kHz. 2. The responses of each cell to sounds presented from seven frontal azimuthal locations (-90 to +90 degrees in 30 degrees steps; 0 degree elevation) and at five sound pressure levels (SPLs: 0-80 dB or 5-85 dB in 20-dB steps) provided an azimuth-level data set. Responses were averaged over SPL to obtain an azimuth function, and a number of features of this function were used to describe azimuth tuning to noise and to tone stimulation. Azimuth function modulation was used to assess azimuth sensitivity, and cells were categorized as sensitive or insensitive depending on whether modulation was > or = 75% or < 75% of maximum, respectively. The majority (88%) of cells in the sample were azimuth sensitive to noise stimulation, and statistical analyses were restricted to these cells, which are presumably best suited to encode sound source azimuth. Azimuth selectivity was assessed by a preferred azimuth range (PAR) over which azimuth function values exceeded 75% (PAR75) or 50% of maximum response. Cells were categorized according to the location and extent of their noise PARs. Unbounded cells had laterally located PARs that extended to the lateral pole (+/- 90 degrees); bounded cells had PARs that were contained entirely within the frontal hemifield, and a subset of these had PARs centered on the midline (+/- 15 degrees). A final group of cells exhibited multipeaked azimuth functions to noise stimulation. 3. Azimuth functions to noise were generally more selective and/or more sensitive than those to tones. Statistical analyses showed that these differences were significant for cells in each azimuth function category, and for the thalamic and cortical samples. With the exception of multipeaked cells, responsiveness to noise was significantly lower than that to tones in all categories, and for the thalamic and cortical samples.(ABSTRACT TRUNCATED AT 400 WORDS)
Burst responses in thalamic relay cells of the awake behaving cat
Authors: Guido W. , Weyand T.
Published: December 2017

1. Relay cells of the dorsal lateral geniculate nucleus (LGN) respond in one of two modes: tonic or burst. The purpose of this study was to determine whether, and under what conditions, burst responses occur in LGN cells of an awake, behaving animal. 2. We recorded the extracellular responses of cells located in the A layers of LGN in two cats trained to perform a simple fixation task. In our paradigm, head position was fixed and gaze monitored with the use of the scleral search coil technique. They were trained to fixate on a small target light while we probed the receptive field of an isolated LGN cell with drifting gratings. 3. Many LGN cells (37/48; 77%) recorded in the awake cat showed some form of burst firing. However, the degree of burstiness a given cell displayed was relatively low. The probability of recording a burst response during any second within the fixation task was 0.09. This reflects the fact that during wakefulness, LGN cells are generally in a state of relative depolarization and the low-threshold Ca2+ conductance underlying burst firing is inactivated. 4. The majority of bursts occurred (262/377; 71%) during visual stimulation. These comprised the initial response to the grating and were confined to the early phase of fixation. As the cat continued to hold fixation and as subsequent cycles of the grating passed through the cell's receptive field, the response shifted from a burst to a tonic firing pattern. Some bursts (67/377, 18%) were related to eye movements. All of these were postsaccadic, and most occurred > 150 ms from the onset of the eye movement. Finally, some bursts were neither visually driven nor related to eye movements. However, these spontaneous bursts were infrequent (41/377; 11%) and never rhythmic. 5. Burst firing in LGN cells has a dual purpose. During quiescent states such as slow-wave sleep, they support the decoupling of retinal signals from LGN. During the waking state, bursts can facilitate signal transmission during target acquisition and early phases of fixation.
Changes in the electrophysiological properties of cat spinal motoneurons following the intramuscular injection of adriamycin compared with changes in the properties of motoneurons in aged cats
Authors: Liu R. H. , Yamuy J. , Xi M. C. , Morales F. R. , Chase M. H.
Published: December 2017

1. This study was undertaken to investigate the effects of adriamycin (ADM, Doxorubicin) on the basic electrophysiological properties of spinal cord motoneurons in the adult cat. ADM was injected into the biceps, gastrocnemius, semitendinosus, and semimembranosus muscles of the left hindlimb (1.2 mg per muscle). Intracellular recordings from motoneurons innervating these muscles were carried out 12, 20, or 40 days after ADM administration and from corresponding motoneurons in untreated control cats. 2. Twelve days after ADM injection, motoneurons innervating ADM-treated muscles (ADM MNs) exhibited statistically significant increases in input resistance, membrane time constant, and amplitude of the action potential's afterhyperpolarization (AHP). In addition, there was a statistically significant decrease in rheobase and in the delay between the action potential of the initial segment (IS) and that of the somadendritic (SD) portion of the motoneuron (IS-SD delay). There were no significant changes in the resting membrane potential, threshold depolarization, action potential amplitude, or axonal conduction velocity. 3. The changes in electrical properties of motoneurons at 20 and 40 days after ADM injection were qualitatively similar to those observed at 12 days. However, at 40 days after ADM injection there was a statistically significant decrease in the axonal conduction velocity of the ADM MNs. 4. The normal correlations that are present between the AHP duration and electrical properties of the control motoneurons were observed in the ADM MNs, e.g., AHP duration was positively correlated with the input resistance and time constant and negatively correlated with the axonal conduction velocity. The correlation coefficients, however, were reduced in comparison with the control data. 5. This study demonstrates that ADM exerts significant effects on the electrical properties of motoneurons when injected into their target muscles. The majority of the changes in motoneuron electrical properties caused by ADM resemble those observed in motoneurons of aged cats. Additional research is required to determine whether the specific changes induced in motoneurons by ADM and those that occur in motoneurons in old age are due to similar degradative mechanisms.
Axotomy induces a transient and localized elevation of the free intracellular calcium concentration to the millimolar range
Authors: Ziv N. E. , Spira M. E.
Published: December 2017

1. Axonal transection triggers a cascade of pathological processes that frequently lead to the degeneration of the injured neuron. It is generally believed that the degenerative process is triggered by an overwhelming influx of calcium through the cut end of the axon. 2. Theoretical considerations and indirect observations suggest that axotomy is followed by an increase in the free intracellular calcium concentration ([Ca2+]i) to the millimolar level. In contrast, only relatively modest and transient elevation in [Ca2+]i to the micromolar level was revealed by recent fura-2 studies. 3. In the current study we used the low-affinity Ca2+ indicator mag-fura-2 to reexamine the spatiotemporal distribution pattern of Ca2+ after axotomy and to map the free intracellular Mg2+ concentration gradients. 4. We report that axotomy elevates [Ca2+]i well beyond the "physiological" range of calcium concentrations, to levels > 1 mM near the tip of the cut axon and to hundreds of micromolars along the axon further away from the cut end. Nevertheless, [Ca2+]i recovers to the control levels within 2-3 min after the resealing of the cut end. 5. A comparison of the behavior of fura-2 and mag-fura-2 in the cytosol of the axotomized neurons reveals that the determination of [Ca2+]i by fura-2 largely underestimates the actual intracellular Ca2+ concentrations. 6. Experiments in which one branch of a bifurcated axon was transected revealed that the elevation in [Ca2+]i is confined to the transected axonal branch and does not spread beyond the bifurcation point. 7. After axotomy, the intracellular Mg2+ concentration equilibrates rapidly with the external concentration and then recovers at a rate somewhat slower than that of [Ca2+]i. 8. To the best of our knowledge, this study is the first direct demonstration that axotomy elevates [Ca2+]i to the millimolar range and that neurons are able to recover from these extreme calcium concentrations.
Light-dependent control of calcium in intact rods of the bullfrog Rana catesbeiana
Authors: Younger J. P. , McCarthy S. T. , Owen W. G.
Published: December 2017

1. Using Fura-2, we measured cytosolic free calcium concentrations in rod outer segments of the bullfrog (Rana catesbeiana) under a wide range of steady-state, adapting light intensities. We also measured rod circulating currents under the same adapting conditions. 2. Both the steady-state cytosolic free calcium concentration and the steady-state circulating current were halved by background lights that isomerized approximately 100 rhodopsin molecules per rod per second. A just-measurable reduction in calcium was evoked by a background 1/10 as bright. The steady-state calcium concentration and the steady-state circulating current were proportional to each other over the full range of intensities tested, the brightest of which suppresses the circulating current by 75% and reduces flash sensitivity by about two orders of magnitude relative to the rods' sensitivity in darkness. 3. Additional experiments, in which the Na+:Ca2+,K+ exchanger in the rod outer segment was inactivated while maintaining intracellular calcium at physiological levels, demonstrated that steady-state calcium concentrations in the outer segment are set only by the influx of calcium through the light-sensitive channels and its efflux via the Na+:Ca2+,K+ exchanger. We found no measurable light-induced release of calcium from internal stores and no evidence of any other calcium flux between the cytosol and intracellular compartments. 4. Taken together, these findings lead us to conclude that over the normal operating range of the rod, the selectivity of the cGMP-gated channels for calcium does not change as a result of background illumination. 5. Our data also suggest that a major role of calcium-dependent cGMP synthesis by guanylyl cyclase is to stabilize both the circulating current and the cytosolic free calcium concentration in darkness. This would minimize the dark noise of the rod and thereby increase the reliability with which dim stimuli can be detected in the dark-adapted state.
Classifying illusory contours by means of orientation discrimination
Authors: Westheimer G. , Li W.
Published: December 2017

1. Thresholds for discrimination of orientation were measured for solid and interrupted lines, and for illusory borders defined by offset abutting lines of a variety of configurations. 2. Illusory contours defined by orthogonal lines with a clear gap or overlap manifest excellent orientation discrimination even for very short exposure durations, and are robust to pattern motion and masking. The performance is almost as good as that for real lines. 3. When the contour is made up of abutting lines without gap or overlap, orientation discrimination is not nearly as good, and deteriorates further with short exposure duration, with target motion, and with masking. 4. The introduction of disparity in such illusory borders does not improve the discrimination of its orientation, so that concepts such as surface elaborations do not yet have to be invoked. 5. The results suggest that there is one class of illusory contour whose orientations can be discriminated by virtue of its delivering adequate stimuli to orientation-selective units in primary visual cortex. For contours with a uniform space-averaged luminance, the orientation discrimination is helped by the orthogonality of the generating lines, and this gives support to the concept that orthogonally oriented end-stopped neurons may participate in the orientation discrimination.
Spontaneous rhythmic bursts induced by pharmacological block of inhibition in lumbar motoneurons of the neonatal rat spinal cord
Authors: Bracci E. , Ballerini L. , Nistri A.
Published: December 2017

1. The effects of blocking gamma-aminobutyric acid- and glycine-mediated synaptic transmission by bicuculline and strychnine on the neonatal rat isolated spinal cord were investigated by intracellular recording from motoneurons with the use of current-clamp and voltage-clamp techniques and by extracellular recording from homologous ventral roots of the L5 segment. 2. Bicuculline per se evoked irregular bursts of motoneuron membrane potential, often comprising individual events fused together. Strychnine alone did not elicit spontaneous bursting in the large majority of preparations. Simultaneous application of bicuculline and strychnine consistently induced regular rhythmic bursts (frequency approximately 2 per min, duration approximately 7 s), comprising a rapid depolarization followed by large-amplitude oscillations. 3. Burst frequency, duration, and intraburst oscillation time course were independent of motoneuron membrane potential. Burst and oscillation amplitude decreased with membrane depolarization and, under voltage-clamp conditions, inverted polarity near 0 mV. 4. The regular bursts produced by bicuculline and strychnine were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione, tetrodotoxin, or Cd2+. 5. N-methyl-D-aspartate antagonists [R-5-aminophosphonovalerate or 3-((RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonate (CPP)] reversibly blocked or slowed down bursting induced by bicuculline and strychnine. Addition of cyclothiazide to the bicuculline and strychnine solution increased bursting frequency while preserving the regular burst structure; under these conditions bursts became insensitive to CPP. 6. In the presence of bicuculline and strychnine, 5-hydroxytryptamine (5-HT) increased burst frequency and decreased burst duration in a dose-dependent fashion. 7. In the presence of bicuculline and strychnine, L5 ventral roots developed synchronous rhythmic activity with a time course similar to that recorded from individual motoneurons. The rhythmic activity was accelerated by 5-HT on both roots, in accordance with observations on single motoneurons. 8. Rhythmic bursts thus appear to result from large, synchronous synaptic events generated by a network modulated by 5-HT and highly sensitive to variations in efficacy of glutamatergic synaptic transmission. These results show that in the rat spinal cord highly patterned motor output can occur despite block of inhibition.
Role of syringeal muscles in gating airflow and sound production in singing brown thrashers
Authors: Goller F. , Suthers R. A.
Published: December 2017

1. The role of syringeal muscles in song production, particularly in regulating airflow through the syrinx, was studied in singing brown thrashers (Toxostoma rufum). In nine individuals, muscle activity was recorded electromyographically together with bilateral syringeal airflow, subsyringeal air sac pressure, and vocal output. 2. Dorsal muscles, m. syringealis dorsalis (dS) and m. tracheolateral dorsalis (dTB), are consistently activated during ipsilateral closing of the syrinx or increasing syringeal resistance, suggesting that their main role is adduction. This interpretation is supported by the motor patterns accompanying syllables with rapid oscillations in the rate of airflow. Bursts of electrical activity (2-10 ms) in dorsal muscles are precisely synchronized with decreasing airflow. 3. Electrical activity in m. tracheobronchialis ventralis (vTB) and m. tracheolateralis (TL) is associated with active abduction. An important contribution of vTB is to open the syringeal lumen for short inspirations in between syllables. In syllables with oscillatory flow modulations, vTB bursts show variable alignment with the phase of increasing flow. From this and activity during other syllables, it appears that, during phonation, vTB activity fine tunes the syringeal configuration, which is set by action of the dorsal muscles into a partially constricted state. 4. Activity in the ventral portion of TL, an extrinsic muscle, is strikingly similar to that of vTB, an intrinsic muscle, suggesting that the two muscles have a similar functional role. This supports the notion that intrinsic syringeal muscles of songbirds evolved from extrinsic muscles of nonpasserines. 5. M. syringealis ventralis (vS) does not appear to contribute directly to gating of airflow. Its activity is not consistently correlated with active changes in syringeal resistance. 6. Activity in m. sternotrachealis (ST) is most prominent during rapid changes in the rate of airflow or when switching between expiratory and inspiratory flow, suggesting a role in stabilizing the syringeal framework.
Importance of NMDA receptors for multimodal integration in the deep layers of the cat superior colliculus
Authors: Binns K. E. , Salt T. E.
Published: December 2017

1. Many sensory events contain multimodal information, yet most sensory nuclei are devoted to the analysis of single-modality information. In the deep superior colliculus (DSC), visual, auditory, and somatosensory information converges on individual multimodal neurons. The responses of multimodal neurons are determined by the temporal and spatial correspondence properties of the converging inputs such that stimuli arising from the same event elicit a facilitated multimodal response. 2. N-methyl-D-aspartate (NMDA) receptors may underlie the detection of spatial and temporal coincidence and could be involved in the generation of multimodal facilitatory responses because of the nonlinear properties of NMDA-receptor-mediated events. To assess the role of NMDA receptors in multimodal integration, we made extracellular recordings from single multisensory neurons in the DSC of the cat. 3. The responses to visual, auditory, and somatosensory stimuli alone and to multimodal combinations of stimuli were challenged with iontophoretically applied D-2-amino-5-phosphonovalerate (AP5), an NMDA receptor antagonist. All responses to visual stimuli presented alone (n = 9) were greatly reduced. Somatosensory responses (n = 25) were usually decreased. In contrast, the responses to auditory stimulation were decreased (n = 9), unaffected (n = 3), or enhanced (n = 5). 4. Responses to multimodal stimulus presentations were consistently reduced during iontophoretic application of AP5, irrespective of the modalities that made up the stimulus. The reductions of multimodal responses were significantly greater than the sum of the reductions of responses to single-modality stimuli. 5. The data suggest that for unimodal stimuli, the importance of NMDA receptors in synaptic transmission of sensory responses in DSC may be dependent on the stimulus modality. Furthermore, NMDA receptors are of major importance in the integration of input from different modalities for the generation of multimodal responses.
Cellular short-term memory from a slow potassium conductance
Authors: Turrigiano G. G. , Marder E. , Abbott L. F.
Published: December 2017

1. We use the dynamic clamp to add the slowly inactivating and slowly recovering K+ conductance Kv1.3 to cultured stomatogastric ganglion neurons. 2. Introduction of Kv1.3 produced long delays to firing during depolarization. Additionally, the slow recovery from inactivation produced an increase in neuronal excitability after a depolarizing input that outlasted the input by many seconds. Finally, when introduced into bursting neurons, Kv1.3 produced a long-lasting depolarization-induced switch between tonic and burst firing. 3. These data demonstrate that the slow kinetics of a K+ conductance can produce a form of cellular short-term memory that is independent of any changes in synaptic efficacy.
Responses in area V4 depend on the spatial relationship between stimulus and attention
Authors: Connor C. E. , Gallant J. L. , Preddie D. C. , Van Essen D. C.
Published: December 2017

1. We studied the spatial interaction between stimulus and attention in macaque area V4. Monkeys were required to fixate a small spot while continuously attending to a ring-shaped target within a large array of identical rings. Meanwhile, the response of the V4 cell under study was tested by flashing behaviorally irrelevant bar stimuli in the cell's classical receptive field (CRF). The location of the attended ring was varied across four positions surrounding the CRF, and the location of the bar stimulus was varied across five positions spanning the CRF. 2. Response strength depended on two aspects of the spatial relationship between the stimulus driving the cell (the bar) and the position of attention (the target ring). First, for 49% of the cells studied, responses were greater for bar stimuli near the attended ring; i.e., the receptive field profile shifted toward the attentional focus. Second, for 84% of the cells, the overall response level depended on the direction in which attention lay relative to the stimulus in the CRF (e.g., to the left, right, above, or below). 3. This study confirms a key prediction of spatial models of attention, which postulate enhanced processing of all stimuli near the attentional focus. It also introduces the novel finding that responses are influenced by the relative direction of attention. This result indicates that area V4 carries information about the spatial relationship between visual stimuli and attention.
Conditions for the induction of long-term potentiation in layer II/III horizontal connections of the rat motor cortex
Authors: Hess G. , Aizenman C. D. , Donoghue J. P.
Published: December 2017

1. The present studies investigated conditions for the induction of long-term potentiation (LTP) in the local horizontal pathways of layers II/III in the primary motor cortex (MI) of the adult rat. Field potential and intracellular recordings demonstrated synaptic interactions across the superficial layers within MI that could be enhanced transiently by focal application of the gamma-aminobuturic acid-A receptor antagonist bicuculline methiodide (Bic) at the recording site. 2. Field potentials evoked in the superficial MI horizontal pathways increased in amplitude after tetanizing, theta burst stimulation (TBS), but only when Bic was applied transiently at the recording site immediately before TBS. In the absence of Bic, TBS failed to produce long-lasting increases in horizontally evoked field responses. By contrast, TBS delivery during focal Bic application increased field potential amplitudes by 25-35% when measured 25-30 min after stimulation. The amount of potentiation was greater when two converging horizontal inputs were stimulated together but was not increased with higher intensity stimulation. Persistent effects of Bic application alone were evident. However, these effects were small unless Bic application continued until evoked field potential amplitude increase exceeded 200% of baseline. 3. The synaptic nature of field potential increases were confirmed using intracellular recordings of layer II/III neurons located near field potential electrodes. 4. LTP also could be induced without Bic application by cotetanization of vertical pathways simultaneously with horizontal activation. Vertical conditioning alone at 2 Hz, which affects inhibitory efficacy, was shown to transiently relieve depression of successive responses that ordinarily occurs during a burst of three horizontal stimuli. These results suggest that LTP of horizontal pathways may be regulated by spatiotemporal interactions between horizontal and vertical pathways. 5. Horizontal LTP was blocked reversibly by bath application of the N-methyl-D-aspartate (NMDA) antagonist 2-amino-5-phosphonovaleric acid, thereby implicating NMDA-receptor activation in LTP induction for these pathways. 6. The results confirm and extend our previous finding that the potential for activity-dependent modification of synaptic connections exists within the intrinsic horizontal connections of the superficial cortical layers. Synaptic modification across horizontally connected neurons appears to be regulated both by the arrangement of intrinsic circuitry and by the availability of mechanisms for modification at individual synapses. The properties of horizontal connections indicate that they form a spatial substrate and provide an activity-dependent mechanism for plasticity of adult cortical representations.
Long-lasting potentiation and depression without presynaptic activity
Authors: Neveu D. , Zucker R. S.
Published: December 2017

1. Long-term potentiation (LTP) and long-term depression (LTD) require a rise in intracellular Ca2+ concentration ([Ca2+]i) in the postsynaptic CA1 pyramidal neuron to activate Ca-dependent biochemical processes. This rise in [Ca2+]i is a necessary trigger for the induction of LTP and LTD, but it is unclear if concurrent presynaptic activity is required for their induction or expression. 2. We used photolysis of the caged-Ca2+ compound nitr-5 to elevate postsynaptic [Ca2+]i. Long-lasting potentiation (LLP) and long-lasting depression (LLD) were obtained in the absence of presynaptic activity. 3. Because LLP and LLD share common features with LTP and LTD induced by presynaptic stimulation these results show that a rise in [Ca2+]i in the postsynaptic CA1 pyramidal neurons is necessary and sufficient for the induction and expression of LTP and LTD, and that concurrent presynaptic activity is not required.
Unitary excitatory synaptic currents in preganglionic neurons mediated by two distinct groups of interneurons in neonatal rat sacral parasympathetic nucleus
Authors: Araki I. , De Groat W. C.
Published: December 2017

1. Excitatory postsynaptic currents (EPSCs) in parasympathetic preganglionic neurons (PGNs) were examined by the use of the whole cell patch-clamp recording technique in slice preparations of the neonatal rat lumbosacral spinal cord. Synaptic responses were evoked in PGNs by extracellular stimulation of a neighboring interneuron. 2. Stimulation of interneurons medial to the sacral parasympathetic nucleus (SPN) elicited EPSCs or inhibitory postsynaptic currents in 58 and 11%, respectively, of PGNs. Stimulation of interneurons dorsal to the SPN evoked EPSCs in 70% of PGNs. 3. EPSCs occurred at short latency (2.1 ms) and were usually elicited in an all-or-none manner, indicating that they were monosynaptic and mediated by a single interneuron (i.e., unitary). 4. EPSCs were mediated by both non-N-methyl-D-aspartate (non-NMDA) and NMDA receptors. 5. Unitary excitatory postsynaptic potentials evoked by single stimuli did not induce action potentials in PGNs, but repetitive stimulation (> 20 Hz) of the single interneurons could evoke firing of PGNs. 2-Amino-5-phosphonovalerate, an NMDA receptor antagonist, reduced the synaptic depolarization induced in PGNs by high-frequency interneuronal impulses. 6. EPSCs mediated by dorsal interneurons were smaller in amplitude (36.3 +/- 15.7 pA, mean +/- SD) than EPSCs mediated by medial interneurons (88.4 +/- 45.7 pA). 7. Paired-pulse facilitation of EPSCs was observed in PGNs (147.2 +/- 26.2%). The degree of facilitation was higher in dorsal (174.6 +/- 10.3%) than in medial interneuronal pathways (120.9 +/- 3.6%). Within each of interneuronal pathways the degree of facilitation was independent of the magnitude of the unitary EPSC. 8. The results show that PGNs receive monosynaptic glutamatergic excitatory inputs from two distinct populations of interneurons in the dorsal and medial regions of the SPN. These two populations of interneurons are likely to have different functions in the regulation of the preganglionic outflow to the pelvic organs.
Neuronal activity in posterior parietal area 7a during the delay periods of a spatial memory task
Authors: Constantinidis C. , Steinmetz M. A.
Published: December 2017

1. Neuronal activity was recorded from area 7a of monkeys performing a delayed match-to-sample task requiring release of a behavioral key when a visual stimulus appeared at a remembered spatial location. 2. Activity in the delay periods was significantly elevated in 28% of 405 neurons studied and could be classified as either sustained or anticipatory in nature. 3. Sustained activity was characterized by maintained or slowly decreasing discharge rates that were typically greater when the preceding stimulus was at a location that evoked a strong response. Sustained activity was terminated when a subsequent stimulus appeared at another location. 4. Anticipatory activity was characterized by accelerating discharge rates that were ordinarily greater after a stimulus at a location that evoked a weak response. Anticipatory activity was often associated with facilitated responses to the next stimulus. 5. These data demonstrate that a population of neurons in area 7a is active during the delay periods of a spatial memory task that does not require a behavioral response directed toward the location of the stimulus. This activity could represent a short-term memory trace for the spatial location of the preceding stimulus.
Anticipatory saccades in sequential procedural learning in monkeys
Authors: Miyashita K. , Rand M. K. , Miyachi S. , Hikosaka O.
Published: December 2017

1. In a preceding paper we examined the short-term and long-term processes of learning of sequential procedures in monkeys. We now report that the pattern of eye movements changed along with the long-term learning. 2. The monkey's task was to press five consecutive pairs of target buttons (indicated by illumination) in the correct order for every pair, which the monkey had to find by trial and error (2 x 5 task). The whole sequence was called the "hyperset"; each pair was called the "set." 3. Initially, the saccade toward the correct target occurred after illumination of the targets (visually guided saccade). After sufficient learning, the saccade tended to occur before the target illumination (anticipatory saccade). This was true only for the hyperset that had been learned. 4. The likelihood of anticipatory saccade increased gradually over 20-30 days of practice of the particular hyperset. The time course was similar to how the hand learned (button press latency). 5. The monkeys were required to use the same hand for each hyperset throughout learning, except when we asked them to use the opposite hand. The nearly perfect performance due to the extensive practice was then deteriorated by the use of the opposite hand. We found, in addition, that anticipatory saccades became much less frequent. This finding suggests that critical for the skilled performance was the combination of the eyes and the side of the hand that was used for the practice of a given sequence.
Metabotropic glutamate receptors switch visual response mode of lateral geniculate nucleus cells from burst to tonic
Authors: Godwin D. W. , Vaughan J. W. , Sherman S. M.
Published: December 2017

1. Metabotropic glutamate receptors (mGluRs) on relay cells of the lateral geniculate nucleus appear to be activated exclusively by cortical inputs. We thus sought to manipulate these receptors in an effort to gain insight into the possible role of the corticogeniculate pathway. We used in vivo recording and pharmacological techniques in cats to activate or inactivate these receptors on geniculate neurons while analyzing their response properties. 2. Iontophoretic application of the mGluR agonist 1-amino-cyclopentane-1,3-dicarboxylic acid (ACPD) to X and Y cells in the geniculate A laminae diminished or abolished burst activity characteristic of low-threshold Ca2+ spikes. This was accompanied by pronounced changes in the visual response, including a decrease in signal detectability as measured with receiver operating characteristic curves. 3. ACPD effects appear specific to mGluRs, because a specific antagonist of ionotropic glutamate receptors (iGluRs) failed to affect the ACPD-evoked responses, and antagonists of ACPD failed to affect iGluR-mediated responses. We found that 3,5-dihydroxyphenylglycine, an agonist reported to be specific for phosphatidylinositol (PI)-linked mGluRs, had effects similar to those of ACPD, implying that these effects are mediated by PI-coupled mGluRs. Furthermore, antagonists reported to be effective against PI-linked mGluRs were effective in antagonizing the ACPD-mediated effects, and substances reported to be agonists to mGluRs coupled to the adenosine 3',5'-cyclic monophosphate cascade did not affect neuronal responses on their own. These data, when added to our preliminary anatomic data, indicate that the receptor responsible for the observed effects may be mGluR1, or a functionally equivalent mGluR. 4. Activation of mGluRs produces changes in geniculate relay cell activity consistent with depolarization of these cells seen during in vitro studies. Such membrane depolarization has been shown to control the activation state of a voltage-dependent Ca2+ conductance, and this, in turn, determines whether the relay cell fires in tonic or burst mode. Our data show that application of ACPD produces a shift in response mode from burst to tonic. Because response mode is an important characteristic of the geniculate relay and because the activation state of certain mGluRs, which helps determine response mode may be controlled by corticogeniculate input, we conclude that an important function of this input is to provide a visuotopically discrete transition from burst to tonic response mode.
Characterization of dopamine receptors mediating inhibition of excitatory synaptic transmission in the rat hippocampal slice
Authors: Hsu K. S.
Published: December 2017

1. The effect of dopamine (DA) on the excitatory synaptic transmission was studied in the CA1 neurons of rat hippocampal slices using intracellular recording technique. 2. Depolarizing excitatory postsynaptic potentials (EPSPs) were evoked by stimulation of the Schaffer collateral-commissural pathway. Superfusion of DA (0.03-1 microM) reversibly decreased the EPSP in a concentration-dependent manner and with an estimated IC50 of 0.3 microM. The sensitivity of postsynaptic neurons to the glutamate-receptor agonists, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid or N-methyl-D-aspartate was unchanged by DA (0.3 microM) pretreatment. In addition, DA (0.3 microM) increased the magnitude of paired-pulse facilitation, a phenomenon attributed to an increase in the amount of transmitter released in response to the second stimulus. 3. The reduction of DA (0.3 microM) on the EPSP was antagonized by sulpiride (1-10 nM), a selective D2-receptor antagonist. However, D1-receptor antagonist, SKF-83566 (1-10 microM), did not significantly affect the reduction of DA (0.3 microM) on the EPSP. 4. (+/-)-2-(N-Phenylethyl-N-propyl)amino-5-hydroxytetralin (1 microM), an agonist of D2 receptor, mimicked the inhibitory effect of DA on the EPSP. However, neither the D1-receptor agonist SKF-38393 (1 microM) nor the D3-receptor agonist (PD-128,907 (1 microM) affected the EPSP. 5. Incubation of hippocampal slices with pertussis toxin (PTX, 5 micrograms/ml) for 12 h prevented the reduction of EPSP induced by DA (0.3 microM). 6. Rp-adenosine-3',5'-cyclic monophosphothioate (25 microM), a potent inhibitor of protein kinase A (PKA), alone decreased the amplitude of EPSP below baseline values and prevented the subsequent reduction by DA (0.3 microM). 7. These results indicate that DA at a low concentration (< or = 0.3 microM) reduces the excitatory response of hippocampal CA1 neurons after synaptic stimulation via the activation of presynaptic D2 receptors. The presynaptic action of DA is mediated by a PTX-sensitive Gi-proteins-coupled to PKA pathway.
Receptive field of the retinal bipolar cell: a pharmacological study in the tiger salamander
Authors: Hare W. A. , Owen W. G.
Published: December 2017

1. It is widely believed that signals contributing to the receptive field surrounds of retinal bipolar cells pass from horizontal cells to bipolar cells via GABAergic synapses. To test this notion, we applied gamma-aminobutyric acid (GABA) agonists and antagonists to isolated, perfused retinas of the salamander Ambystoma tigrinum while recording intracellularly from bipolar cells, horizontal cells, and photoreceptors. 2. As we previously reported, administration of the GABA analogue D-aminovaleric acid in concert with picrotoxin did not block horizontal cell responses or the center responses of bipolar cells but blocked the surround responses of both on-center and off-center bipolar cells. 3. Surround responses were not blocked by the GABA, antagonists picrotoxin or bicuculline, the GABAB agonist baclofen or the GABAB antagonist phaclofen, and the GABAC antagonists picrotoxin or cis-4-aminocrotonic acid. Combinations of these drugs were similarly ineffective. 4. GABA itself activated a powerful GABA uptake mechanism in horizontal cells for which nipecotic acid is a competitive agonist. It also activated, both in horizontal cells and bipolar cells, large GABAA conductances that shunted light responses but that could be blocked by picrotoxin or bicuculline. 5. GABA, administered together with picrotoxin to block the shunting effect of GABAA activation, did not eliminate bipolar cell surround responses at concentrations sufficient to saturate the known types of GABA receptors. 6. Surround responses were not blocked by glycine or its antagonist strychnine, or by combinations of drugs designed to eliminate GABAergic and glycinergic pathways simultaneously. 7. Although we cannot fully discount the involvement of a novel GABAergic synapse, the simplest explanation of our findings is that the primary pathway mediating the bipolar cell's surround is neither GABAergic nor glycinergic.
Effects of single-pulse transcranial magnetic stimulation over the prefrontal and posterior parietal cortices during memory-guided saccades in humans
Authors: Muri R. M. , Vermersch A. I. , Rivaud S. , Gaymard B. , Pierrot-Deseilligny C.
Published: December 2017

1. We used single-pulse transcranial magnetic stimulation (TMS) to explore the temporal organization of the cortical control of memory-guided saccades in eight humans. The posterior parietal cortex (PPC) or the dorsolateral prefrontal cortex (DPFC), which are both known to be involved in the control of such saccades, were stimulated on the right side at different time intervals after the presentation of a flashed lateral visual target. The memorization delay was 2,000 ms. Single pulses were applied at 160, 260, and 360 ms after the flashed target, during the period of 700 and 1,500 ms, and finally at 2,100 ms, i.e., 100 ms after the extinguishing of the central fixation point. The effects of TMS were evaluated by calculating the percentage of error in amplitude (PEA) and latency of memory-guided saccades. The PEA was determined for the primary saccade (motor aspect) and the final eye position, i.e., after the end saccade (mnemonic aspect). Stimulation over the occipital cortex at the same time intervals served as control experiments. 2. After PPC stimulation, a significant increase in the PEA of the primary saccade and final eye position existed for contralateral saccades, compared with the PEA without stimulation, when stimulation was applied 260 ms after target presentation, but not at other time intervals. There was no significant effect on ipsilateral saccades. Latency was significantly increased bilaterally when stimulation was performed 2,100 ms after target presentation. 3. After prefrontal stimulation, a significant increase in the PEA of the primary saccade and final eye position existed for contralateral saccades, when stimulation was applied between 700 and 1,500 ms after target presentation, but not at other time intervals. There was no significant effect on ipsilateral saccades. Latency was not affected by prefrontal TMS at any stimulation times. 4. Occipital stimulation resulted in no significant effect on the PEA and latency of ipsilateral or contralateral saccades, in particular including the application at 260 ms after target presentation or during the memorization phase. 5. From these results it may be concluded that the observed effects of TMS on saccade accuracy were specific to the stimulated region and specific to the stimulation time. The PPC seems to be involved in the preparation of saccade amplitude, during the early phase of the paradigm, i.e., the sensorimotor processing period, whereas the DPFC could play a role during the later phase of the paradigm, i.e., the memorization period. Therefore in humans these results support the experimental findings suggesting that sensorimotor integration is controlled by the PPC and spatial memory by the DPFC. Furthermore, our results suggest that the PPC, although not the DPFC, plays a role in saccade triggering.