bluuebunny/crossref_metadata_2025 huggingface dataset:
A Slow Transient Potassium Current Expressed in a Subset of Neurosecretory Neurons of the Hypothalamic Paraventricular Nucleus
Authors: Luther Jason A. , Halmos Katalin Cs. , Tasker Jeffrey G.
Published: December 2017

Type I putative magnocellular neurosecretory cells of the hypothalamic paraventricular nucleus (PVN) express a prominent transient outward rectification generated by an A-type potassium current. Described here is a slow transient outward current that alters cell excitability and firing frequency in a subset of type I PVN neurons (38%). Unlike most of the type I neurons (62%), the transient outward current in these cells was composed of two kinetically separable current components, a fast activating, fast inactivating component, resembling an A-type potassium current, and a slowly activating [10–90% rise time: 20.4 ± 12.8 (SE) ms], slowly inactivating component (time constant of inactivation: τ = 239.0 ± 66.1 ms). The voltage dependence of activation and inactivation and the sensitivity to block by 4-aminopyridine (5 mM) and tetraethylammonium chloride (10 mM) of the fast and slow components were similar. Compared to the other type I neurons, the neurons that expressed the slow transient outward current were less excitable when hyperpolarized, requiring larger current injections to elicit an action potential (58.5 ± 13.2 vs. 15.4 ± 2.4 pA; 250-ms duration; P < 0.01), displaying a longer delay to the first spike (184.9 ± 15.7 vs. 89.7 ± 8.8 ms with 250- to 1,000-ms, 50-pA current pulses; P < 0.01), and firing at a lower frequency (18.7 ± 4.6 vs. 37.0 ± 5.5 Hz with 100-pA current injections; P < 0.05). These data suggest that a distinct subset of type I PVN neurons express a novel slow transient outward current that leads to a lower excitability. Based on double labeling following retrograde transport of systemically administered fluoro-gold and intracellular injection of biocytin, these cells are neurosecretory and are similar morphologically to magnocellular neurosecretory cells, although it remains to be determined whether they are magnocellular neurons.
GABA-Mediated Inhibition Between Amacrine Cells in the Goldfish Retina
Authors: Watanabe Shu-Ichi , Koizumi Amane , Matsunaga Shinya , Stocker Jonathan W. , Kaneko Akimichi
Published: December 2017

Retinal amacrine cells have abundant dendro-dendritic synapses between neighboring amacrine cells. Therefore an amacrine cell has both presynaptic and postsynaptic aspects. To understand these synaptic interactions in the amacrine cell, we recorded from amacrine cells in the goldfish retinal slice preparation with perforated- and whole cell-patch clamp techniques. As the presynaptic element, 19% of the cells recorded (15 of 78 cells) showed spontaneous tetrodotoxin (TTX)-sensitive action potentials. As the postsynaptic element, all amacrine cells ( n = 9) were found to have GABA-evoked responses and, under perforated patch clamp, 50 μM GABA hyperpolarized amacrine cells by activating a Cl− conductance. Bicuculline-sensitive spontaneous postsynaptic currents, carried by Cl−, were observed in 82% of the cells (64 of 78 cells). Since the source of GABA in the inner plexiform layer is amacrine cells alone, these events are likely to be inhibitory postsynaptic currents (IPSCs) caused by GABA spontaneously released from neighboring amacrine cells. IPSCs were classified into three groups. Large amplitude IPSCs were suppressed by TTX (1 μM), indicating that presynaptic action potentials triggered GABA release. Medium amplitude IPSCs were also TTX sensitive. Small amplitude IPSCs were TTX insensitive (miniature IPSCs; n = 26). All of spike-induced, medium amplitude, and miniature IPSCs were Ca2+ dependent and blocked by Co2+. Blocking of glutamatergic inputs bydl-2-amino-phosphonoheptanoate (AP7; 30 μM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 2 μM) had almost no effect on spontaneous GABA release from presynaptic amacrine cells. We suggest that these dendro-dendrotic inhibitory networks contribute to receptive field spatiotemporal properties.
Cerebellar Flocculus and Ventral Paraflocculus Purkinje Cell Activity During Predictive and Visually Driven Pursuit in Monkey
Authors: Suh M. , Leung H.-C. , Kettner R. E.
Published: December 2017

Purkinje cells in the flocculus and ventral paraflocculus were studied in tasks designed to distinguish predictive versus visually guided mechanisms of smooth pursuit. A sum-of-sines task allowed studies of complex predictive pursuit. A perturbation task examined visually driven pursuit during unpredictable right-angle changes in target direction. A gap task examined pursuit that was maintained when the target was turned off. Neural activity patterns were quantified using multi-linear models with sensitivities to the position, velocity, and acceleration of both motor output (eye motion) and visual input (retinal slip). During the sum-of-sines task, neural responses led eye motion by an average of 12 ms, a value larger than the 9-ms transmission delay between flocculus stimulation and eye motion. This suggests that flocculus/paraflocculus neurons drove pursuit along predictable sum-of-sines trajectories. In contrast, neural responses led eye motion by an average of only 2 ms during the perturbation task and by 6 ms during the gap task. These values suggest a follow-up role during tasks more heavily dependent on visual processing. Activity in all three tasks was explained primarily by sensitivities to eye position and velocity. Eye acceleration played a minor role during ongoing pursuit, although its influence on firing rate increased during the high accelerations following unexpected changes in target motion. Retinal slip had a relatively small influence on responses during pursuit. This was particularly true for the sum-of-sines and gap tasks where predictive control eliminated any consistent retinal-slip signals that might have been used to drive the eye. Surprisingly, the influence of retinal slip did not increase appreciably during unpredictable perturbations in target direction that generated large amounts of retinal slip. Thus although visual control signals are needed in varying amounts during the three pursuit tasks, they have been converted to motor control signals by the time they leave the flocculus/paraflocculus system. Individual neurons showed a remarkable constancy in eye-sensitivity direction across tasks that indicated direct links to oculomotor neurons. However, some neurons showed changes in sensitivity magnitude that suggested changes in control strategy for different tasks. Magnitude differences were largest for the perturbation task. We conclude that the flocculus/paraflocculus system plays a major role in driving predictive pursuit. It also processes visually driven control signals that originate in other brain regions after a slight delay.
Oscillations and Long-Lasting Correlations in a Model of the Lateral Geniculate Nucleus and Visual Cortex
Authors: Kirkland Kyle L. , Sillito Adam M. , Jones Helen E. , West David C. , Gerstein George L.
Published: December 2017

We have previously developed a model of the corticogeniculate system to explore cortically induced synchronization of lateral geniculate nucleus (LGN) neurons. Our model was based on the experiments of Sillito et al. Recently Brody discovered that the LGN events found by Sillito et al. correlate over a much longer period of time than expected from the stimulus-driven responses and proposed a cortically induced slow covariation in LGN cell membrane potentials to account for this phenomenon. We have examined the data from our model, and we found, to our surprise, that the model shows the same long-term correlation. The model's behavior was the result of a previously unsuspected oscillatory effect, not a slow covariation. The oscillations were in the same frequency range as the well-known spindle oscillations of the thalamocortical system. In the model, the strength of feedback inhibition from the cortex and the presence of low-threshold calcium channels in LGN cells were important. We also found that by making the oscillations more pronounced, we could get a better fit to the experimental data.
Role of Potassium Conductances in Determining Input Resistance of Developing Brain Stem Motoneurons
Authors: Cameron William E. , Núñez-Abades Pedro A. , Kerman Ilan A. , Hodgson Tracy M.
Published: December 2017

The role of potassium conductances in determining input resistance was studied in 166 genioglossal (GG) motoneurons using sharp electrode recording in brain stem slices of the rats aged 5–7 days, 13–15 days, and 19–24 days postnatal ( P). A high magnesium (Mg2+; 6 mM) perfusate was used to block calcium-mediated synaptic release while intracellular or extracellular cesium (Cs+) and/or extracellular tetraethylammonium (TEA) or barium (Ba2+) were used to block potassium conductances. In all cases, the addition of TEA to the high Mg2+ perfusate generated a larger increase in both input resistance ( R n) and the first membrane time constant (τ0) than did high Mg2+ alone indicating a substantial nonsynaptic contribution to input resistance. With intracellular injection of Cs+, GG motoneurons with lower resistance (<40 MΩ), on the average, showed a larger percent increase in R n than cells with higher resistance (>40 MΩ). There was also a significant increase in the effect of internal Cs+ on R n and τ0 with age. The largest percent increase (67%) in the τ0 due to intracellular Cs+ occurred at P13–15, a developmental stage characterized by a large reduction in specific membrane resistance. Addition of external Cs+blocked conductances (further increasing R n and τ0) beyond those blocked by the TEA perfusate. Substitution of external calcium with 2 mM barium chloride produced a significant increase in both R n and τ0at all ages studied. The addition of either intracellular Cs+ or extracellular Ba2+created a depolarization shift of the membrane potential. The amount of injected current required to maintain the membrane potential was negatively correlated with the control R n of the cell at most ages. Thus low resistance cells had, on the average, more Cs+- and Ba2+-sensitive channels than their high resistance counterparts. There was also a disproportionately larger percent increase in τ0 as compared with R n for both internal Cs+ and external Ba2+. Based on a model by Redman and colleagues, it might be suggested that the majority of these potassium conductances underlying membrane resistance are initially located in the distal dendrites but become more uniformly distributed over the motoneuron surface in the oldest animals.
Specificity of Internal Representations Underlying Grasping
Authors: Salimi Iran , Hollender Ian , Frazier Wendy , Gordon Andrew M.
Published: December 2017

The present study examines anticipatory control of fingertip forces during grasping based on the center of mass (CM) of a manipulated object. Subjects lifted an object using a precision grip while the fingertip forces and the angle about the vertical axis (roll) were measured. The object's CM could be shifted to the left or right of the object's center parallel to the grip axis without changing it's visual appearance. Subjects performed 20 lifts with the CM in the center, left, and right side of the object, respectively. Subjects were instructed to lift the object while preventing it from tilting. Within three to five lifts, subjects were able to asymmetrically partition the load force development before lift-off such that it was higher in the digit opposing the CM. This anticipatory load force partitioning prevented the object from rolling sideways at lift-off. To determine whether the internal representation underlying the anticipatory control is specific to the effectors used to form it, subjects performed five lifts with the right hand with the CM on one side. Following these lifts, they rotated the object 180° around the vertical axis and performed one lift with the same hand or they translated the object to the left side of the body (with or without rotating it) and performed one lift with the left hand. Despite subjects' explicit knowledge of the new weight distribution, they were unable to appropriately scale the load forces at each digit, resulting in a subsequent large roll of the object. The findings suggest that within a few lifts subjects achieve a stable internal representation which accounts for the object's CM and is used to scale the fingertip forces in advance. They also suggest that this representation, which is used for anticipatory control of fingertip forces, is specific to the effectors used to form it. We propose that multiple internal representations may be used during the anticipatory control of grasping.
Activation of Protein Kinase C by Oxytocin-Related Conopressin Underlies Pacemaker Current inLymnaeaCentral Neurons
Authors: Van Soest Paul F. , Lodder Johannes C. , Kits Karel S.
Published: December 2017

The vasopressin/oxytocin-related neuropeptide Lys-conopressin activates two pacemaker currents in central neurons of the mollusk Lymnaea stagnalis. A high-voltage–activated current ( I-HVA) is activated at potentials greater than −40 mV and resembles pacemaker currents found in many molluscan neurons. A low-voltage–activated current ( I-LVA) activates throughout the range of −90 to 0 mV. Based on sequence homologies, Lymnaea conopressin receptors are thought to couple to Q-type G proteins and protein kinase C (PKC). Alternatively, agonist-induced pacemaker currents in molluscan neurons have traditionally been attributed to cAMP-dependent protein kinase (PKA) activation. Accordingly, this study aimed at resolving possible involvement of cAMP/PKA and diacylglycerol/PKC in the conopressin response. Injection of cAMP into anterior lobe neurons induced a slow inward current with a voltage dependence resembling that of ILVA(and not IHVA). However, lack of effect of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and the absence of cross-desensitization between cAMP and conopressin suggest that neither current is dependent on intracellular cAMP. The PKC-activating phorbol ester 12- O-tetradecanoylphorbol 13-acetate (but not inactive phorbol 12-myristate 13-acetate) mimicked activation of IHVA, but not ILVA, and occluded subsequent responses to conopressin. Activation of IHVAwas blocked by general protein kinase inhibitors and the PKC-inhibitor GF-109203X. Modulation of the calcium buffering capacity of the pipette medium did not affect the conopressin response, suggesting that calcium dynamics are not of major importance. We conclude that conopressin activates the ion channels carrying ILVAand IHVAthrough different second-messenger cascades and that PKC-dependent phosphorylation underlies activation of IHVA.
Supplementary Eye Field: Representation of Saccades and Relationship Between Neural Response Fields and Elicited Eye Movements
Authors: Russo Gary S. , Bruce Charles J.
Published: December 2017

The functional organization of the low-threshold supplementary eye field (SEF) was studied by analyzing presaccadic activity, electrically elicited saccades, and the relationship between them. Response-field optimal vectors, defined as the visual field coordinates or saccadic eye-movement dimensions evoking the highest neural discharge, were quantitatively estimated for 160 SEF neurons by systematically varying peripheral target location relative to a central fixation point and then fitting the responses to Gaussian functions. Saccades were electrically elicited at 109 SEF sites by microstimulation (70 ms, 10–100 μA) during central fixation. The distribution of response fields and elicited saccades indicated a complete representation of all contralateral saccades in SEF. Elicited saccade polar directions ranged between 97 and 262° (data from left hemispheres were transformed to a right-hemisphere convention), and amplitudes ranged between 1.8 and 26.9°. Response-field optimal vectors (right hemisphere transformed) were nearly all contralateral as well; the directions of 115/119 visual response fields and 80/84 movement response fields ranged between 90 and 279°, and response-field eccentricities ranged between 5 and 50°. Response-field directions for the visual and movement activity of visuomovement neurons were strongly correlated ( r = 0.95). When neural activity and elicited saccades obtained at exactly the same sites were compared, response fields were highly predictive of elicited saccade dimensions. Response-field direction was highly correlated with the direction of saccades elicited at the recording site ( r = 0.92, n = 77). Similarly, response-field eccentricity predicted the size of subsequent electrically elicited saccades ( r = 0.49, n = 60). However, elicited saccades were generally smaller than response-field eccentricities and consistently more horizontal when response fields were nearly vertical. The polar direction of response fields and elicited saccades remained constant perpendicular to the cortical surface, indicating a columnar organization of saccade direction. Saccade direction progressively shifted across SEF; however, these orderly shifts were more indicative of a hypercolumnar organization rather than a single global topography. No systematic organization for saccade amplitude was evident. We conclude that saccades are represented in SEF by congruent visual receptive fields, presaccadic movement fields, and efferent mappings. Thus SEF specifies saccade vectors as bursts of activity by local groups of neurons with appropriate projections to downstream oculomotor structures. In this respect, SEF is organized like the superior colliculus and the frontal eye field even though SEF lacks an overall global saccade topography. We contend that all specialized oculomotor functions of SEF must operate within the context of this fundamental organization.
Aδ and C Primary Afferents Convey Dorsal Root Reflexes After Intradermal Injection of Capsaicin in Rats
Authors: Lin Qing , Zou Xiaoju , Willis William D.
Published: December 2017

Antidromic activity was recorded in anesthetized rats from single afferent fibers in the proximal ends of cut dorsal root filaments at the L4–6 level and tested for responses to acute cutaneous inflammation produced by intradermal injection of capsaicin. This antidromic activity included low-frequency spontaneous firing and dorsal root reflex (DRR) discharges evoked by applying von Frey hairs to the skin of the foot. DRRs could be recorded from both small myelinated (Aδ) and unmyelinated (C) afferent fibers, as well as from large myelinated (Aβ) fibers. After capsaicin was injected intradermally into the plantar skin of the foot, a significant enhancement of DRR activity was seen in Aδ and C fibers but not in Aβ fibers, and this increase lasted for ∼1 h. This study supports the hypothesis that centrally mediated antidromic activity in Aδ and C primary afferent fibers contributes to the development of neurogenic inflammation, presumably by release of inflammatory substances in the periphery.
Task-Dependent Modulation of the Sensorimotor Transformation for Smooth Pursuit Eye Movements
Authors: Ferrera Vincent P.
Published: December 2017

To investigate the transformation of retinal image velocity into smooth pursuit eye velocity, eye movements were measured in the presence of two moving targets. In the first experiment, the targets were identical in all respects except for direction of motion, and the monkey was not cued to attend to either target. In this experiment, smooth pursuit eye velocity elicited by two targets was the vector average of the response evoked by each target alone. In subsequent experiments, we examined the effects of stimulus and task parameters on the selectivity of pursuit. When the targets were made different colors and monkeys were cued for the color of the rewarded target, their pursuit eye movements were biased in the direction of the rewarded target, but still showed a substantial influence of the nonrewarded target (distractor). It did not matter whether the same target color was used for an entire session or whether the color was randomized from trial to trial. Reducing uncertainty about the axis of motion of the rewarded target also had little effect. However, the pattern of image motion appeared to have a substantial effect; radial image motion favored averaging, and winner-take-all pursuit was found only with nonradial image motion. We conclude that the sensorimotor interface for pursuit uses a flexible decision rule that can vary continuously from vector averaging to winner-take-all. We present a simple recurrent network model that reflects this range of behavior. The model has allowed us to identify three computational elements (selection bias, competitive inhibition, and response normalization) that should be taken into consideration in future models of smooth pursuit.
Serotonergic and Peptidergic Modulation of the Buccal Mass Protractor Muscle (I2) inAplysia
Authors: Hurwitz I. , Cropper E. C. , Vilim F. S. , Alexeeva V. , Susswein A. J. , Kupfermann I. , Weiss K. R.
Published: December 2017

Plasticity of Aplysia feeding has largely been measured by noting changes in radula protraction. On the basis of previous work, it has been suggested that peripheral modulation may contribute to behavioral plasticity. However, peripheral plasticity has not been demonstrated in the neuromuscular systems that participate in radula protraction. Therefore in this study we investigated whether contractions of a major radula protraction muscle (I2) are subject to modulation. We demonstrate, first, that an increase in the firing frequency of the cholinergic I2 motoneurons will increase the amplitude of the resulting muscle contraction but will not modulate its relaxation rate. We show, second, that neuronal processes on the I2 muscle are immunoreactive to myomodulin (MM), RFamide, and serotonin (5-HT), but not to small cardioactive peptide (SCP) or buccalin. The I2 motoneurons B31, B32, B61, and B62 are not immunoreactive to RFamide, 5-HT, SCP, or buccalin. However, all four cells are MM immunoreactive and are capable of synthesizing MMa. Third, we show that the bioactivity of the different modulators is somewhat different; while the MMs (i.e., MMa and MMb) and 5-HT increase I2 muscle relaxation rate, and potentiate muscle contraction amplitude, MMa, at high concentrations, depresses muscle contractions. Fourth, our data suggest that cAMP at least partially mediates effects of modulators on contraction amplitude and relaxation rate.
Effects of Repeated Cold Stress on Activity of Hypothalamic Neurons in Rats During Performance of Operant Licking Task
Authors: Tamura Ryoi , Kondoh Takashi , Ono Taketoshi , Nishijo Hisao , Torii Kunio
Published: December 2017

The present study investigated the effects of repeated cold stress on single neuron activity in the lateral hypothalamic area (LHA) and medial hypothalamic area (MHA) of behaving rats. The rats were trained to lick a protruding spout in response to one of several cue-tone stimuli (CTSs) to ingest water, or amino acid, NaCl or glucose solution. Following this training, the rats were raised under either stressed (repeated temperature changes between −3 and 24°C) or control (24°C) condition for 2 mo. During this period, neuronal activity was recorded in the LHA and MHA. For rats raised under the stressed condition, mean spontaneous firing rate of LHA neurons was significantly greater than for rats under the control condition. More LHA neurons in the stressed rats responded, with an accompanying decrease in activity (inhibitory response), to CTSs than in the control rats. During extinction learning, some LHA neurons enhanced or reversed the responses to CTSs in the stressed rats, whereas no LHA neurons showed such response changes in the control rats. In contrast to the effects of the stressed condition on LHA neuron activity, mean spontaneous firing rate of MHA neurons in the stressed rats was significantly smaller than in the control rats. Fewer MHA neurons in the stressed rats responded to CTSs and/or ingestion of sapid solutions. The preceding results suggested that repeated cold stress produces a specific pattern of changes in spontaneous activity and responses to sensory stimuli in LHA and MHA neurons; this could underlie the behavioral changes induced by repeated cold stress such as hyperphagia and hyper-reactivity to sensory stimuli.
Developmental Regulation of Calcium Channel-Mediated Currents in Retinal Glial (Müller) Cells
Authors: Bringmann A. , Schopf S. , Reichenbach A.
Published: December 2017

Whole cell voltage-clamp recordings of freshly isolated cells were used to study changes in the currents through voltage-gated Ca2+ channels during the postnatal development of immature radial glial cells into Müller cells of the rabbit retina. Using Ba2+ or Ca2+ ions as charge carriers, currents through transient low-voltage-activated (LVA) Ca2+ channels were recorded in cells from early postnatal stages, with an activation threshold at −60 mV and a peak current at −25 mV. To increase the amplitude of currents through Ca2+ channels, Na+ ions were used as the main charge carriers, and currents were recorded in divalent cation-free bath solutions. Currents through transient LVA Ca2+ channels were found in all radial glial cells from retinae between postnatal days 2 and 37. The currents activated at potentials positive to −80 mV and displayed a maximum at −40 mV. The amplitude of LVA currents increased during the first postnatal week; after postnatal day 6, the amplitude remained virtually constant. The density of LVA currents was highest at early postnatal days (days 2–5: 13 pA/pF) and decreased to a stable, moderate level within the first three postnatal weeks (3 pA/pF). A significant expression of currents through sustained, high-voltage-activated Ca2+ channels was found after the third postnatal week in ∼25% of the investigated cells. The early and sole expression of transient currents at high-density may suggest that LVA Ca2+ channels are involved in early developmental processes of rabbit Müller cells.
Comparison of Odor Receptive Field Plasticity in the Rat Olfactory Bulb and Anterior Piriform Cortex
Authors: Wilson Donald A.
Published: December 2017

Recent work in the anterior piriform cortex (aPCX) has demonstrated that cortical odor receptive fields are highly dynamic, showing rapid changes of both firing rate and temporal patterning within relatively few inhalations of an odor, despite relatively maintained, patterned input from olfactory bulb mitral/tufted cells. The present experiment examined the precision (odor-specificity) of this receptive field plasticity and compared it with the primary cortical afferent, olfactory bulb mitral/tufted cells. Adult Long-Evans hooded rats, urethan anesthetized and freely breathing, were used for single-unit recording from mitral/tufted and aPCX layer II/III neurons. Partial mapping of receptive fields to alkane odors (pentane, heptane, and nonane) was performed before and immediately after habituation (50-s exposure) to one of the alkanes. The results demonstrated that odor habituation of aPCX responses was odor specific, with minimal cross-habituation between alkanes differing by as few as two carbons. Mitral/tufted cells, however, showed strong cross-habituation within the odor set with the most profound cross effects to carbon chains shorter than the habituating stimulus. The results suggest that although mitral/tufted cells and aPCX neurons have roughly similar odor receptive fields, aPCX neurons have significantly better odor discrimination within their receptive field. The results have important implications for understanding the underlying bases of receptive fields in olfactory system neurons and the mechanisms of odor discrimination and memory.
Hippocampal Place-Cell Firing During Movement in Three-Dimensional Space
Authors: Knierim James J. , McNaughton Bruce L.
Published: December 2017

“Place” cells of the rat hippocampus are coupled to “head direction” cells of the thalamus and limbic cortex. Head direction cells are sensitive to head direction in the horizontal plane only, which leads to the question of whether place cells similarly encode locations in the horizontal plane only, ignoring the z axis, or whether they encode locations in three dimensions. This question was addressed by recording from ensembles of CA1 pyramidal cells while rats traversed a rectangular track that could be tilted and rotated to different three-dimensional orientations. Cells were analyzed to determine whether their firing was bound to the external, three-dimensional cues of the environment, to the two-dimensional rectangular surface, or to some combination of these cues. Tilting the track 45° generally provoked a partial remapping of the rectangular surface in that some cells maintained their place fields, whereas other cells either gained new place fields, lost existing fields, or changed their firing locations arbitrarily. When the tilted track was rotated relative to the distal landmarks, most place fields remapped, but a number of cells maintained the same place field relative to the x-y coordinate frame of the laboratory, ignoring the z axis. No more cells were bound to the local reference frame of the recording apparatus than would be predicted by chance. The partial remapping demonstrated that the place cell system was sensitive to the three-dimensional manipulations of the recording apparatus. Nonetheless the results were not consistent with an explicit three-dimensional tuning of individual hippocampal neurons nor were they consistent with a model in which different sets of cells are tightly coupled to different sets of environmental cues. The results are most consistent with the statement that hippocampal neurons can change their “tuning functions” in arbitrary ways when features of the sensory input or behavioral context are altered. Understanding the rules that govern the remapping phenomenon holds promise for deciphering the neural circuitry underlying hippocampal function.
Does Anoxia Induce Cell Swelling in Carp Brains? In Vivo MRI Measurements in Crucian Carp and Common Carp
Authors: Linden Annemie Van der , Verhoye Marleen , Nilsson Göran E.
Published: December 2017

Although both common and crucian carp survived 2 h of anoxia at 18°C, the response of their brains to anoxia was quite different and indicative of the fact that the crucian carp is anoxia tolerant while the common carp is not. Using in vivo T2and diffusion-weighted magnetic resonance imaging (MRI), we studied anoxia induced changes in brain volume, free water content (T2), and water homeostasis (water diffusion coefficient). The anoxic crucian carp showed no signs of brain swelling or changes in brain water homeostasis even after 24 h except for the optic lobes, where cellular edema was indicated. The entire common carp brain suffered from cellular edema, net water gain, and a volume increase (by 6.5%) that proceeded during 100 min normoxic recovery (by 10%). The common carp recovered from this insult, proving that the changes were reversible and suggesting that the oversized brain cavity allows brain swelling during energy deficiency without a resultant increase in intracranial pressure and global ischemia. It is tempting to suggest that this is a function of the large brain cavity seen in many ectothermic vertebrates.
Postsynaptic Currents in Deep Cerebellar Nuclei
Authors: Anchisi Davide , Scelfo Bibiana , Tempia Filippo
Published: December 2017

Postsynaptic currents were studied by whole cell recordings in visually identified large neurons of the deep cerebellar nuclei (DCN) in slices of 4- to 11-day-old mice. Spontaneous postsynaptic currents were abolished by the GABAAreceptor antagonist bicuculline and had a single-exponential decay with a mean time constant of 13.6 ± 3.2 (SD) ms. Excitatory postsynaptic currents (EPSCs) were evoked in 48/56 neurons recorded. The addition of AMPA and N-methyl-d-aspartate (NMDA) receptor antagonists together completely abolished all synaptic responses. In 1 mM [Mg2+]oand at a holding potential of −60 mV, the peak amplitude of the NMDA component of the EPSC (NMDA-EPSC) was 83.2 ± 21.2% of the AMPA component (AMPA-EPSC). This indicates that in DCN neurons, at a physiological [Mg2+]oand at the resting membrane potential, NMDA receptors contribute to the synaptic signal. AMPA-EPSCs had a linear current-voltage relationship with a reversal potential of +2.3 ± 0.4 mV and a single-exponential decay with a voltage-dependent time constant that at −60 mV was 7.1 ± 3.3 ms. In 10 μM glycine and 1 mM [Mg2+]o, the I-V relationship of NMDA-EPSCs had a reversal potential of −0.5 ± 3.3 mV and a maximal inward current at −33.4 ± 5.8 mV. The apparent dissociation constant ( KD) of Mg2+for the NMDA receptor-channel at −60 mV, measured by varying [Mg2+]o, was 135.5 ± 55.3 μM, and when measured by fitting the I-V curves with a theoretical function, it was 169.9 ± 119.5 μM. Thus in the DCN, NMDA receptors have a sensitivity to Mg2+that corresponds to subunits that are weakly blocked by this ion (ε3 and ε4) of which the DCN express ε4. NMDA-EPSCs had a double-exponential decay with voltage-dependent time constants that at −60 mV were 20.2 ± 8.9 and 136.4 ± 62.8 ms. At positive voltages, the time constants were slower and their contributions were about equal, while in the negative slope conductance region of the I-V curve, the faster time constant became predominant, conferring faster kinetics to the EPSC. The weak sensitivity to Mg2+of NMDA receptors, together with a relatively fast kinetics, provide DCN neurons with strong excitatory inputs in which fast dynamic signals are relatively well preserved.
cAMP-Dependent Presynaptic Regulation of Spontaneous Glycinergic IPSCs in Mechanically Dissociated Rat Spinal Cord Neurons
Authors: Katsurabayashi Shutaro , Kubota Hisahiko , Wang Zhi Ming , Rhee Jeong Seop , Akaike Norio
Published: December 2017

Spontaneous miniature glycinergic inhibitory postsynaptic currents (mIPSCs) in mechanically dissociated rat sacral dorsal commissural nucleus (SDCN) neurons attached with intact glycinergic presynaptic nerve terminals and evoked IPSCs (eIPSCs) in the slice preparation were investigated using nystatin-perforated patch and conventional whole cell recording modes under the voltage-clamp conditions. Trans-ACPD (tACPD) reversibly reduced the mIPSC frequency without affecting the mean amplitude. The effect was mimicked by a specific metabotropic glutamate receptor (mGluR) II subtype agonist, (2S, 1′S, 2′S)-2-(carboxycyclo propyl) glycine (L-CCG-I), and a specific mGluRIII subtype agonist, 2-amino-4-phosphonobutyrate (L-AP4). These inhibitory effects on mIPSC frequency were blocked by the specific antagonists for mGluRII, α-methyl-1-(2S, 1′S, 2′S)-2-(carboxycyclo propyl) glycine and (RS)-α-cyclopropyl-4-phosphonophenylglycine. In the slice preparation, eIPSC amplitude and mIPSC frequency were decreased reversibly by L-CCG-I (10−6M) and L-AP4 (10−6M). In K+-free or K+-free external solution with Ba2+and Cs+, Ca2+-free or Cd2+external solution, the inhibitory effect of tACPD on mIPSC frequency was unaltered. Forskolin and 8-Br-cAMP significantly increased presynaptic glycine release, and prevented the inhibitory action of tACPD on mIPSC frequency. Sp-cAMP, however, did not prevent the inhibitory action of tACPD on mIPSC frequency. It was concluded that the activation of mGluRs inhibits glycine release by reducing the action of cAMP/PKA pathway.
GABA, Not Glutamate, a Primary Transmitter Driving Action Potentials in Developing Hypothalamic Neurons
Authors: Gao Xiao-Bing , Van Den Pol Anthony N.
Published: December 2017

Neuronal activity is critical for many aspects of brain development. It has often been assumed that the primary excitatory transmitter driving this activity is glutamate. In contrast, we report that during early development, synaptic release of GABA, the primary inhibitory neurotransmitter in the mature brain, is not only excitatory but in addition plays a more robust role than glutamate in generating spike activity in mouse hypothalamic neurons. Based on gramicidin perforated whole cell and extracellular recording, which leave intracellular Cl−unperturbed in brain slices and cultures, the GABAAreceptor antagonist bicuculline induced a dramatic decrease in spike frequency (83% decrease) in developing neurons, three times greater than that generated by glutamate receptor antagonists 2-amino-5-phosphono-pentanoic acid and 6-cyano-7-nitroquinoxalene-2,3-dione. Thus a number of factors related to spike-dependent stabilization of neuronal connections, including Hebbian mechanisms, that are generally applied to glutamate transmission may also participate in stabilization of GABA circuits.
Early Coding of Visuomanual Coordination During Reaching in Parietal Area PEc
Authors: Ferraina Stefano , Battaglia-Mayer Alexandra , Genovesio Aldo , Marconi Barbara , Onorati Paolo , Caminiti Roberto
Published: December 2017

The parietal mechanisms of eye-hand coordination during reaching were studied by recording neural activity in area PEc while monkeys performed different tasks, aimed at assessing the influence of retinal, hand-, and eye-related signals on neural activity. The tasks used consisted of 1) reaching to foveated and 2) to extra-foveal targets, with constant eye position; and 3) saccadic eye movement toward, and holding of eye position on peripheral targets, the same as those of the reaching tasks. In all tasks, hand and/or eye movements were made from a central position to eight peripheral targets. A conventional visual fixation paradigm was used as a control task, to assess location and extent of visual receptive field of neurons. A large proportion of cells in area PEc displayed significant relationships to hand movement direction and position. Many of them were also related to the eye's position. Relationships to saccadic eye movements were found for a smaller proportion of cells. Most neurons were tuned to different combination of hand- and eye-related signals; some of them were also influenced by visual information. This combination of signals can be an expression of the early stages of the composition of motor commands for different forms of visuomotor coordination that depend on the integration of hand- and eye-related information. These results assign to area PEc, classically considered as a somatosensory association cortex, a new visuomotor role.
Number of KCa Channels Underlying Spontaneous Miniature Outward Currents (SMOCs) in Mudpuppy Cardiac Neurons
Authors: Scornik Fabiana S. , Merriam Laura A. , Parsons Rodney L.
Published: December 2017

Spontaneous miniature outward currents (SMOCs) in parasympathetic neurons from mudpuppy cardiac ganglia are caused by activation of TEA- and iberiotoxin-sensitive, Ca2+-dependent K+(BK) channels. Previously we reported that SMOCs are activated by Ca2+-induced Ca2+ release (CICR) from caffeine- and ryanodine-sensitive intracellular Ca2+ stores. In the present study, we analyzed the single channel currents that contribute to SMOC generation in mudpuppy cardiac neurons. The slope conductance of BK channels, determined from the I-V relationship of single-channel currents recorded with cell-attached patches in physiological K+ concentrations, was 84 pS. The evidence supporting the identity of this channel as the channel involved in SMOC generation was its sensitivity to internal Ca2+, external TEA, and caffeine. In cell-attached patch recordings, 166 μM TEA applied in the pipette reduced single-channel current amplitude by 32%, and bath-applied caffeine increased BK channel activity. The ratio between the averaged SMOC amplitude and the single-channel current amplitude was used to estimate the average number of channels involved in SMOC generation. The estimated number of channels involved in generation of an averaged SMOC ranged from 18 to 23 channels. We also determined that the Po of the BK channels at the peak of a SMOC remains constant at voltages more positive than −20 mV, suggesting that the transient rise in intracellular Ca2+from ryanodine-sensitive intracellular stores in the vicinity of the BK channel reached concentrations most likely exceeding 40 μM.
Spatial Attention Modulates Sound Localization in Barn Owls
Authors: Johnen Anja , Wagner Hermann , Gaese Bernhard H.
Published: December 2017

Attentional influence on sound-localization behavior of barn owls was investigated in a cross-modal spatial cuing paradigm. After being cued to the most probable target side with a visual cuing stimulus, owls localized upcoming auditory target stimuli with a head turn toward the position of the sound source. In 80% of the trials, cuing stimuli pointed toward the side of the upcoming target stimulus (valid configuration), and in 20% they pointed toward the opposite side (invalid configuration). We found that owls initiated the head turns by a mean of 37.4 ms earlier in valid trials, i.e., mean response latencies of head turns were reduced by 16% after a valid cuing stimulus. Thus auditory stimuli appearing at the cued side were processed faster than stimuli appearing at the uncued side, indicating the influence of a spatial-selective attention mechanism. Turning angles were not different when owls turned their head toward a cued or an uncued location. Other types of attention influencing sound localization, e.g., a reduction of response latency as a function of the duration of cue-target delay, could not be observed. This study is the first attempt to investigate attentional influences on sound localization in an animal model.
A Physiologically Based Model of Discharge Pattern Regulation by Transient K+Currents in Cochlear Nucleus Pyramidal Cells
Authors: Kanold Patrick O. , Manis Paul B.
Published: December 2017

Pyramidal cells in the dorsal cochlear nucleus (DCN) show three characteristic discharge patterns in response tones: pauser, buildup, and regular firing. Experimental evidence suggests that a rapidly inactivating K+-current ( IKIF) plays a critical role in generating these discharge patterns. To explore the role of IKIF, we used a computational model based on the biophysical data. The model replicated the dependence of the discharge pattern on the magnitude and duration of hyperpolarizing prepulses, and IKIFwas necessary to convey this dependence. Phase-plane and perturbation analyses show that responses to depolarization are critically controlled by the amount of inactivation of IKIF. Experimentally, half-inactivation voltage and kinetics of IKIFshow wide variability. Varying these parameters in the model revealed that half-inactivation voltage, and activation and inactivation rates, controls the voltage and time dependence of the model cell discharge. This suggests that pyramidal cells can adjust their sensitivity to different temporal patterns of inhibition and excitation by modulating the kinetics of IKIF. Overall, IKIFis a critical conductance controlling the excitability of DCN pyramidal cells.
Binocular Contributions to Optic Flow Processing in the Fly Visual System
Authors: Krapp Holger G. , Hengstenberg Roland , Egelhaaf Martin
Published: December 2017

Integrating binocular motion information tunes wide-field direction-selective neurons in the fly optic lobe to respond preferentially to specific optic flow fields. This is shown by measuring the local preferred directions (LPDs) and local motion sensitivities (LMSs) at many positions within the receptive fields of three types of anatomically identifiable lobula plate tangential neurons: the three horizontal system (HS) neurons, the two centrifugal horizontal (CH) neurons, and three heterolateral connecting elements. The latter impart to two of the HS and to both CH neurons a sensitivity to motion from the contralateral visual field. Thus in two HS neurons and both CH neurons, the response field comprises part of the ipsi- and contralateral visual hemispheres. The distributions of LPDs within the binocular response fields of each neuron show marked similarities to the optic flow fields created by particular types of self-movements of the fly. Based on the characteristic distributions of local preferred directions and motion sensitivities within the response fields, the functional role of the respective neurons in the context of behaviorally relevant processing of visual wide-field motion is discussed.
Temporal and Spatial Dynamics of Human Forebrain Activity During Heat Pain: Analysis by Positron Emission Tomography
Authors: Casey Kenneth L. , Morrow Thomas J. , Lorenz Jürgen , Minoshima Satoshi
Published: December 2017

To learn about the sequence of brain activation patterns during heat pain, we acquired positron emission tomographic (PET) brain scans at different times during repetitive heat stimulation (40 or 50°C; 5-s contact) of each subject's left forearm. Early scans began at the onset of 60 s of stimulation; late scans began after 40 s of stimulation, which continued throughout the 60-s scan period (total stimulus duration 100 s). Each subject (14 normal, right-handed subjects; 10 male, 4 female; ages 18–42) used a visual analog scale to rate the perceived stimulus intensity (0 = no heat, 7 = pain threshold, 10 = barely tolerable pain) after each scan. The 40°C stimulation received an average intensity rating of 2.19 ± 1.22 (mean ± SD) and the 50°C an average rating of 8.93 ± 1.33. During the scan sessions, subjects did not report a difference between early and late scans. To examine the effect of the duration of stimulation specifically, 8 of these subjects rated the perceived intensity of each of 20 sequential 5-s duration contact heat stimuli (40 or 50°C; 100 s of stimulation). We used a graphical method to detect changes in perceived unpleasantness. There was no difference in perceived intensity or unpleasantness during the 40°C stimulation. However, during 50°C stimulation, perceived unpleasantness increased and subjects perceived the last five, but not the second five, stimuli as more intense than the first five stimuli. These psychophysical changes could be mediated by brain structures with increasing activity from early to late PET scans or that are active only during late scans. These structures include the contralateral M1/S1 cortex, bilateral S2 and mid-insular cortex, contralateral VP thalamus, medial ipsilateral thalamus, and the vermis and paravermis of the cerebellum. Structures that are equally active throughout stimulation (contralateral mid-anterior cingulate and premotor cortex) are less likely to mediate these psychophysical changes. Some cortical, but not subcortical, structures showed significant or borderline activation only during the early scans (ipsilateral premotor cortex, contralateral perigenual anterior cingulate, lateral prefrontal, and anterior insular cortex); they may mediate pain-related attentive or anticipatory functions. Overall, the results reveal that 1) the pattern of brain activation and the perception of heat pain both change during repetitive noxious heat stimulation, 2) cortical activity can be detected before subcortical responses appear, and 3) timing the stimulation with respect to the scan period can, together with psychophysical measurements, identify brain structures that are likely to participate in the perception of pain.