bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurons in monkey parietal area LIP are tuned for eye-movement parameters in three-dimensional space
Authors: Gnadt J. W. , Mays L. E.
Published: December 2017

1. A functional class of neurons in area LIP on the lateral bank of the intraparietal sulcus were shown previously (Gnadt and Andersen 1988) to be related to the metrics of saccadic eye movements. In this study, we tested LIP neurons at different depths with respect to the plane of fixation. 2. Sixty-one neurons were identified for their increased activity before saccadic eye movements. While holding the location of the target constant at the center of the frontoparallel (saccadic) response field, the neurons were tested systematically during eye movements to target positions proximal (near) to the plane of fixation, at the plane of fixation, and distal (far) to the plane of fixation. By necessity, the movements of these targets required a combination of saccadic and vergence movements. 3. Seventy-two percent of the neurons were found to change their activity as a function of target depth relative to the plane of fixation. The neurons had broad tuning curves for depth. Some cells preferred "near" target positions, some preferred "far" positions, and others responded best in the frontoparallel plane of fixation. 4. The location of a neuron's response field in the frontoparallel plane remained constant regardless of target depth. However, the magnitude of the neuron's response increased when the target was positioned at the preferred depth and it decreased for targets positioned at nonpreferred depths. This indicated that the neurons always were related to the same frontoparallel coordinates, but responded more vigorously when the target was positioned at its preferred depth. 5. The visual display apparatus allowed independent presentation of two stimulus cues for depth: binocular disparity and accommodative demand whereas other cues were held constant. For many neurons, either cue was sufficient to tune the activity in depth, though most neurons responded best for the geometrically appropriate combination of the two cues. 6. Comparison of the binocular tuning for depth with the individual monocular responses showed that the tuning for depth was not produced by simple linear combination of two monocular response fields. 7. We tested a subset of the neurons in a double-movement task that dissociated the retinal coordinates of the visual stimuli from the eye-movement coordinates of the second movement. These tests confirmed earlier findings that this functional class of neurons are active when the eye-movement coordinates matched the neurons' response field. It was not necessary for a visual stimulus to fall within the neurons' response field for them to become active.(ABSTRACT TRUNCATED AT 400 WORDS)
Passive and synaptic properties of hippocampal neurons grown in microcultures and in mass cultures
Authors: Mennerick S. , Que J. , Benz A. , Zorumski C. F.
Published: December 2017

1. We used whole cell recordings to compare passive membrane properties and synaptic properties of postnatal rat hippocampal neurons grown for 7-15 days in either conventional mass cultures or on physically restricted microisland cultures. Despite matching microisland and mass culture cell across several variables, there were significant differences between neurons in the two groups regarding passive membrane characteristics and synaptic properties. 2. Microisland neurons displayed significantly faster charging of the membrane capacitance than mass culture counterparts matched with microisland neurons for age, somal diameter, and transmitter phenotype. When we used a two-compartment equivalent circuit model to quantify this result, microisland neurons displayed approximately half the distal capacitance of mass culture neurons. These data suggest that microisland neurons elaborate less extensive neuritic arborizations than mass culture neurons. 3. Evoked synaptic responses were enhanced on microislands compared with mass cultures. Excitatory and inhibitory autaptic currents were more frequent and displayed larger amplitudes on single-neuron microislands than in matched mass culture neurons. 4. In recordings from pairs of neurons in the two environments, we observed a significantly higher probability of obtaining a monosynaptic response on two-neuron microislands than in matched mass culture pairs (85% vs. 42%). Evoked excitatory postsynaptic currents were also significantly larger in the microisland environment, with evoked excitatory synaptic currents from two-neuron microislands exhibiting a mean amplitude 20-fold larger than mass culture monosynaptic responses. 5. The differences in evoked synaptic responses were not reflected in differences in the amplitude or frequency of spontaneous miniature excitatory postsynaptic currents (mEPSCs). Analysis of mEPSC rise times, decay times, and peak amplitudes within individual cells suggests that electrotonic filtering is not an important contributor to the variability of peak amplitudes and decay times of synaptic currents in cells of either culture environment. However, composite data across neurons in both cultures reveal a significant correlation between mEPSC rise and decay times. 6. Out results suggest that the microisland preparation may be a useful tool for exploring factors that influence synapse formation and development. Additionally, the preparation is a particularly convenient model for the study of single-neuron-mediated synaptic events.
Calcium-dependent inactivation of synaptic NMDA receptors in hippocampal neurons
Authors: Rosenmund C. , Feltz A. , Westbrook G. L.
Published: December 2017

1. We examined whether synaptically activated N-methyl-D-aspartate (NMDA) receptors are regulated by intracellular calcium in cultured hippocampal neurons by comparing excitatory postsynaptic currents (EPSCs) to the previously described calcium-dependent regulation of whole cell NMDA currents. Standard whole cell recording and fast application methods were used. 2. Low-frequency (0.2 Hz) stimulation of EPSCs in the presence of 2-amino-5-phosphonovalerate (AP5) evoked a constant amplitude alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated EPSC. On removal of AP5 in Ca(2+)-containing solutions, the amplitude of the slow NMDA receptor-mediated EPSC decreased by approximately 50% during the next 10 stimuli. The decrease in the EPSC was dependent on the extracellular calcium concentration and stimulus frequency, consistent with Ca(2+)-dependent desensitization/inactivation of postsynaptic NMDA receptors. A whole cell prepulse of NMDA (10 microM, 10 s) in Ca(2+)-containing solutions inhibited the slow EPSC to a similar degree. A series of slow EPSCs also produced Ca(2+)-dependent inactivation of whole cell NMDA currents evoked in low calcium solutions. 3. These results demonstrate that synaptic NMDA receptors are inactivated by intracellular calcium and that calcium entry through synaptically activated NMDA receptors is sufficient to provide feedback inhibition of the slow EPSC.
Properties of networks controlling locomotion and significance of voltage dependency of NMDA channels: stimulation study of rhythm generation sustained by positive feedback
Authors: Roberts A. , Tunstall M. J. , Wolf E.
Published: December 2017

1. We have built a realistic 24-neuron model based on data from the spinal pattern generator for swimming in Xenopus embryos with the use of the SWIM programs. The neurons have dendrite, soma, and axon compartments with voltage-gated Na+ and K+ channels. Dendritic synapses were modeled as modulated ionic conductances with currents that have different reversal levels. One of these conductances was voltage dependent to model N-methyl-D-aspartate ("NMDA") synapses in the presence of Mg2+. 2. In this model, rhythm generation is initiated by a brief excitation, depends on rebound from reciprocal inhibition, and is sustained by long-duration "NMDA-dependent" feedback excitation. 3. Without NMDA voltage dependency, rhythmic activity is stable over a wide range of synaptic conductances. Its frequency decreases with more inhibition and increases with more excitation. The introduction of normally distributed variation in soma size or excitatory synaptic conductance extends the lower stable frequency range. Without such variation the frequency of the 24-neuron model is the same as a 4-neuron model provided that the synaptic conductances for each neuron are the same. 4. The effect of introducing NMDA voltage dependency on rebound after negative current injections or synaptic inhibition was investigated in single depolarized model neurons. With NMDA voltage dependency, hyperpolarizations and rebound spike responses were increased. 5. Network activity with NMDA voltage dependency was similar to that without it, but inhibitory postsynaptic potentials (IPSPs) and spikes were larger, and frequencies were lower and more sensitive to changes in excitatory and inhibitory conductance. 6. We conclude that in the model, mutual reexcitation among excitatory spinal interneurons can sustain rhythm generation by positive feedback and that NMDA voltage dependency can enhance postinhibitory rebound, stabilize swimming activity and extend its lower frequency range, and steepen the dependency of frequency on synaptic drive.
Suppression of a Ca2+ current by NMDA and intracellular Ca2+ in acutely isolated hippocampal neurons
Authors: Chen Q. X. , Wong R. K.
Published: December 2017

1. Ca2+ current was examined in acutely isolated hippocampal cells with the use of whole cell voltage-clamp recording and under continuous intracellular perfusion. A persistent Ca2+ current was activated by depolarization to -10 mV from a holding potential of -50 mV. 2. The persistent Ca2+ current was suppressed upon a wash out of the intracellular Mg(2+)-ATP. Adenosine 3',5'-cyclic monophosphate (cAMP) introduced intracellularly potentiated the Ca2+ current, and kinase A inhibitor blocked the current. 3. Reversible suppression of the persistent Ca2+ current was also observed by elevating intracellular Ca2+. This Ca(2+)-dependent suppression was retarded by the addition of a phosphatase inhibitor, okadaic acid, to the intracellular solution. 4. N-methyl-D-aspartate (NMDA) elicited inward current (NMDA response) in the isolated cells. The persistent Ca2+ current was transiently suppressed after the NMDA response. Suppression of the Ca2+ current by NMDA was reduced when intracellular Ca2+ buffering capacity was increased by increasing the concentration of bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) from a concentration of 1-10 mM. 5. Substitution of ATP in the intracellular solution with ATP-gamma-S or the addition of okadaic acid to the intracellular solution reduced the suppressive effect of NMDA on the Ca2+ current. 6. The results suggest that the persistent Ca2+ current in the hippocampal cells is maintained by a kinase A-mediated phosphorylation. Increases in the intracellular Ca2+ concentration suppressed the Ca2+ current via a mechanism involving a phosphatase. Ca2+ entry through the NMDA receptor channel suppressed the Ca2+ channel by activating the phosphatase.
Cholinergic synaptic transmission between proprioceptive afferents and a hind leg motor neuron in the locust
Authors: Parker D. , Newland P. L.
Published: December 2017

1. The physiology and pharmacology of the connections made by stress-sensitive campaniform sensilla on the proximal dorsal tibia of a locust hind leg with a fast extensor tibiae motor neuron (FETi) have been examined. 2. Mechanical stimulation of a campaniform sensillum on the anterior surface of the tibia elicited bursts of spikes in its afferent and a depolarization in FETi. Each afferent spike was followed at short and constant latency by an excitatory postsynaptic potential (EPSP) in FETi, even at high-frequency stimulation. Electrical stimulation of the extensor tibiae muscle with the tibia fixed elicited an antidromic spike in FETi followed by a compound potential which resulted from the activation of the campaniform sensillum afferent. The connections between the campaniform sensillum and FETi was monosynaptic and chemically mediated. 3. Ionophoresis of ACh into the neuropil depolarized FETi, as did the application of the cholinesterase inhibitor physostigmine. Bath application of the cholinergic agonists, nicotine and muscarine, also depolarized FETi, with nicotine causing a reduction in input resistance, while muscarine caused no detectable change in input resistance. Muscarine and the muscarinic agonist oxotremorine also caused rhythmic depolarizations and bursts of spikes in FETi. These effects were seen in low calcium/high magnesium saline to block synaptic transmission and are therefore due to direct effects on FETi. FETi therefore appears to have both nicotinic and muscarinic receptors. 4. The compound potential in FETi, caused by activation of the campaniform sensillum, was reduced by bath application of nicotinic cholinergic antagonists. However, the muscarinic antagonist scopolamine increased the amplitude of the compound potential.(ABSTRACT TRUNCATED AT 250 WORDS)
Properties of regenerated primary afferents and their functional connections
Authors: Koerber H. R. , Mirnics K. , Mendell L. M.
Published: December 2017

1. The tibial and sural nerves in cats were cut, anastomosed to their distal stumps, and allowed to regenerate for 3-17.5 mo. In the terminal acute experiment, individual afferents were impaled in the dorsal root ganglion to study their receptive field properties, somatic spike parameters, and spinal projections using cord dorsum potential (CDP) measurements. Properties of the CDPs provided evidence on whether the afferent fibers were originally proprioceptive or cutaneous (rapidly or slowly adapting). 2. Fibers with the largest conduction velocity were selectively slowly adapting, suggesting that large muscle afferents maintained their adaptation properties regardless of the peripheral structure innervated. Similarly, the relationship of somatic spike configuration to mechanical threshold was largely normal. Cells with narrow spikes innervated low-threshold mechanoreceptors, whereas cells with broad spikes and an inflection on the descending limb innervated high-threshold mechanoreceptors. 3. Spikes with intermediate properties were observed in some cells that innervated low-threshold mechanoreceptors in the periphery. These were classified as "hybrid" spikes. 4. The largest CDPs were evoked by afferents classified as having originally been cutaneous fibers, regardless of whether they had reinnervated cutaneous or subcutaneous receptors. Fibers classified as has having originally been proprioceptive afferents produced much smaller CDPs; however, these afferents never produce CDPs in intact preparations. Afferents nonresponsive to peripheral stimulation, classified putatively as having been cutaneous, also evoked small CDPs. 5. Fibers classified as putatively cutaneous or proprioceptive could reinnervate foreign target tissue (subcutaneous tissue or skin, respectively), but a propensity to reinnervate the original target tissue was observed. 6. Among putative cutaneous afferents, those with rostrocaudal CDP distributions somatotopically correct for the location of their receptive fields evoked the largest CDPs regardless of the peripheral tissue innervated. 7. We conclude that receptive field properties (adaptation, mechanical threshold) of regenerated afferents are well matched with the electrophysiological properties of the soma and axon. The properties of the central projections of these afferents are not as well matched with their peripheral receptor properties. This is discussed in terms of the plasticity of the central projections of axotomized afferents.
Neural and behavioral effects of early eye rotation on the optokinetic system in the wallaby, Macropus eugenii
Authors: Hoffmann K. P. , Distler C. , Mark R. F. , Marotte L. R. , Henry G. H. , Ibbotson M. R.
Published: December 2017

1. Total optokinetic responses measured by electro-oculography and single unit recordings from the nucleus of the optic tract and dorsal terminal nucleus (NOT-DTN) of the accessory optic system were taken from young adult wallabies, whose one eye had been rotated about the optic axis at birth, and were compared with those from normal controls. 2. The velocities of the horizontal component of the slow phases of optokinetic nystagmus were measured in the horizontal plane as a function of the direction of stimulus motion. In normal animals the overall gain during monocular stimulation was greatest for horizontal temporonasal movement, with a lesser response to movement in the opposite, nasotemporal, direction. Upward or downward vertical stimulus motion did not elicit horizontal responses. In animals where one eye was removed at birth and the other eye was normal, the characteristic bidirectional response was retained; the response was identical with that elicited from one eye of a normal animal. 3. After surgical rotation (extorsion) of the left eye by approximately 90 degrees on or within a few days of birth, the animals were grown to adulthood. The visual streak of the retina of the operated eye was then found, in individual cases, to be between 30-100 degrees from horizontal with the head held in the standard resting position. This angle was taken as the definitive degree of cyclotorsion resulting from the operation in each animal. The extraocular muscles connected with regions of the eye adjacent to the location of their outgrowth in the orbit and not with the normal point of attachment on the globe.(ABSTRACT TRUNCATED AT 250 WORDS)
In vitro brain slice studies of the rat's dorsal nucleus of the lateral lemniscus. II. Physiological properties of biocytin-labeled neurons
Authors: Wu S. H. , Kelly J. B.
Published: December 2017

1. We made intracellular recordings from neurons in rat dorsal nucleus of the lateral lemniscus (DNLL), determined intrinsic and synaptic physiological properties, and labeled the cells by intracellular injection of biocytin. Biocytin-labeled neurons were reconstructed and classified according to their somatic and dendritic morphology. 2. We identified a diversity of morphological cell types in DNLL. Five main groups of neurons were recognized: multipolar; elongate I, II, and III; and round. The multipolar cells were characterized by several large dendrites with multiple branches that spread over large areas within the DNLL. The dendrites radiated equally in all directions. 3. Elongate cells were characterized by extended cell bodies with polar dendrites. In the case of elongate I and II cells, the dendrites were preferentially oriented in the horizontal plane and the dendritic branches extended across most of the cytoarchitectonic breadth of DNLL from the medial to lateral borders. The classification of elongate II was reserved for a single neuron with profuse dendritic branching that fanned out dorsoventrally along the margins of DNLL. This neuron was unique in our sample and was distinguished from the more common elongate I cells, which had less profuse dorsoventral dendritic branching. Elongate III cells had extended cell bodies, but their dendrites did not extend across the DNLL and showed no preferential orientation. 4. Round neurons had relatively small, round cell bodies and radial dendrites that extended over large areas within DNLL. These cells were quite common in our sample and are almost certainly not the same as the infrequently encountered small round cells found in Nissl-stained sections. Some biocytin-labeled neurons were difficult to classify as either multipolar, elongate I, II, or III, or round. These neurons had properties that most closely resembled elongate III cells, but they were treated separately here to minimize heterogeneity within morphological categories. 5. The intrinsic physiological properties measured in this study were uncorrelated with the morphological class of DNLL neurons. All DNLL neurons had similar current-voltage curves regardless of their anatomic category. Intracellular injection of positive current produced a sustained series of action potentials, the number of which was related to the magnitude of current injection. The interspike intervals were regular, although some cells had a tendency toward an increase or decrease in the length of the interval with prolonged current injection. The interspike intervals were regular, although some cells had a tendency toward an increase or decrease in the length of the interval with prolonged current injection. Injection of negative current produced a hyperpolarization that was proportional to the current strength.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanisms of selective long-term potentiation of excitatory synapses in stratum oriens/alveus interneurons of rat hippocampal slices
Authors: Ouardouz M. , Lacaille J. C.
Published: December 2017

1. We investigated long-term potentiation (LTP) of synaptic transmission in different populations of interneurons in the CA1 region of rat hippocampal slices using whole cell recordings. We elicited excitatory postsynaptic currents (EPSCs) in interneurons located in stratum oriens near the alveus (O/A) or in stratum lacunosum-moleculare near the stratum radiatum border (L-M) by electrical stimulation of nearby axons in stratum oriens and radiatum, respectively. 2. High-frequency stimulation (100 Hz, 1 s) of axons in conjunction with postsynaptic depolarization (to -20 mV) increased the peak amplitude of test EPSCs elicited at -80 mV in O/A interneurons. The mean peak amplitude of EPSCs was significantly potentiated relative to the control period at 10 min (39 +/- 7% increase, mean +/- SE; n = 11 cells) and 30 min (30 +/- 1% increase; n = 5 cells) after tetanization. Similar stimulation did not produce potentiation of EPSCs in L-M interneurons (n = 7 cells). 3. This selective LTP in O/A interneurons was reversibly blocked by the N-methyl-D-aspartate receptor antagonist (+/-)2-amino-5-phosphonopentanoic acid (AP-5). Tetanization in the presence of 25 microM AP-5 did not increase the amplitude of EPSCs (8 cells). After washout of AP-5 (4 cells), a second tetanization resulted in long-term potentiation of EPSCs. 4. LTP was dependent on the activation of metabotropic glutamate receptors. The peak amplitude of EPSCs was not increased 5-10 or 15-20 min after tetanization during bath application of the metabotropic glutamate receptor antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (500 microM) (n = 5 cells). 5. Inclusion of the Ca2+ chelator 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA; 25 mM) in the patch pipette blocked LTP in O/A interneurons. In five cells recorded with BAPTA-containing electrodes, the mean peak amplitude was not significantly increased after tetanization. Thus a rise in postsynaptic intracellular Ca2+ appeared necessary for the induction of LTP in these interneurons. 6. Incubation of slices with the inhibitor of nitric oxide synthase N omega-nitro-L-arginine methyl ester (100 microM) before and throughout the recording session also blocked the increase in EPSC amplitude at 5-10 min (5 cells) and 15-20 min (3 cells) after tetanization. NO synthesis may therefore be necessary for LTP in O/A interneurons. 7. These results suggest that LTP of excitatory synapses is selectively produced in O/A but not L-M interneurons, and that this LTP shares similar characteristics with LTP in hippocampal CA1 pyramidal cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic feedback excitation has hypothalamic neural networks generate quasirhythmic burst activity
Authors: Muller W. , Swandulla D.
Published: December 2017

1. Dissociated neurons from embryonic rat hypothalamus form synaptically coupled networks when cultured for several weeks. When synaptic inhibition is suppressed by the gamma-aminobutyric acid-A (GABAA) antagonist picrotoxin, neurons exhibit "rhythmic" burst activity that is blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 2. We have examined whether this type of activity is generated by pacemaker cells driving follower cells synaptically or whether it is generated by a neuronal network through feedback excitation by Ca2+ imaging of Fura-2/AM-loaded neurons and single-cell recording. 3. IN the presence of the GABAA antagonist picrotoxin (20 microM), a large majority of neurons (> 85%) displayed quasirhythmic increases in intracellular concentration of Ca2+ ([Ca2+]i). Single-cell recording revealed that these increases in [Ca2+]i correspond to burst discharges in individual neurons. When excitatory synaptic transmission was blocked by CNQX (20 microM), none of the imaged neurons exhibited significant oscillations in [Ca2+]i. 4. Investigation of the intervals between bursts from single-cell recording revealed a random distribution over a range of 400% from the minimum interval. Poincare maps of burst intervals, i.e., graphs of all burst intervals versus their preceding burst interval, revealed that a burst interval is unpredictable from its predecessor. 5. When synaptic coupling was attenuated by low concentrations of CNQX (50-500 nM), the mean burst interval was considerably increased without a change in the random character of burst activity. 4-Aminopyridine (1 mM), known to increase synaptic efficiency, reduced the mean burst interval.(ABSTRACT TRUNCATED AT 250 WORDS)
InsP3 causes an increase in apical [Ca2+]i by activating two distinct current components in vertebrate olfactory receptor cells
Authors: Schild D. , Lischka F. W. , Restrepo D.
Published: December 2017

1. Effects of inositol-1,4,5-trisphosphate (InsP3) applied through a patch pipette to Xenopus laevis olfactory receptor cells (ORCs) were studied using the patch-clamp technique in conjunction with calcium imaging with fura-2. 2. InsP3 activated, first, a novel voltage-independent Ca2+ current (ICa) and, second, a nonselective cation current (Icat). 3. The activation of these currents occurred at different intracellular calcium concentrations, and the activation of either current led to a marked increase of [Ca2+]i in the dendritic knob. 4. The results suggest that InsP3 might act as a second messenger in vertebrate olfactory receptor cells by activating, through different mechanisms, a plasma membrane Ca2+ conductance (ICa) and a nonselective cation conductance (Icat).
Preferential suppression of the ON pathway by GABAC receptors in the amphibian retina
Authors: Zhang J. , Slaughter M. M.
Published: December 2017

1. Electrophysiological recordings were obtained from neurons in the amphibian intact retina and retinal slice preparations. The effects of gamma-aminobutyric acid (GABA) were evaluated in the presence of bicuculline or SR95531, which block the GABAA receptor, and baclofen, which saturates the GABAB receptor. 2. Under these conditions, GABA preferentially reduced ON light responses in amacrine and ganglion cells, apparently through a presynaptic mechanism that reduced bipolar cell input. GABA also produced a small hyperpolarization in the resting membrane potential of ganglion cells. 3. Picrotoxin blocked these effects of GABA. The action of GABA was duplicated by muscimol and by trans-aminocrotonic acid. Cis-aminocrotonic acid was neither a potent nor selective agonist. This pharmacology is indicative of the GABAC receptor. 4. In voltage-clamp recordings of ganglion cells in the slice preparation, GABA produced a large chloride conductance that was blocked by bicuculline or SR95531, and a smaller chloride conductance that was not blocked by these GABAA receptor antagonists, but was blocked by picrotoxin. This indicates that ganglion cells possess both GABAA and GABAC receptors. 5. The GABAC receptor current was relatively nondesensitized. Consequently, whereas the peak GABAA receptor current was more than fivefold larger than the GABAC receptor current, after desensitization the latter current was larger. Both currents reversed near the chloride equilibrium potential.
Neurotransmitter regulation of the heart in the nudibranch Archidoris montereyensis
Authors: Wiens B. L. , Brownell P. H.
Published: December 2017

1. The heart of the nudibranch mollusc Archidoris montereyensis is uniquely responsive to regulation by identifiable cardiac motor neurons. The neurotransmitters mediating the strong excitatory and inhibitory actions of the neurons are unknown. 2. In this study we developed an infused, in vitro preparation of the Archidoris heart to determine which of several cardioactive transmitters described in mollusks could affect changes in the rate, amplitude, or tonus of cardiac contractions. Several neurotransmitters we tested increased the rate and amplitude of heart contractions, including serotonin (threshold < 10 nM), dopamine (100 nM), and the neuropeptides R15 alpha 2 (3 nM), small cardioactive peptide B (10 nM), and FMRFamide (20 microM). Myomodulin also excited the heart (0.8 microM) and potentiated the cardioexcitatory action of serotonin at subthreshold concentrations. 3. Only acetylcholine (10 nM) inhibited the heart, decreasing the rate, amplitude, and tonus of contraction. Glycine and the peptides substance P and R15 alpha 1 had no effect on the heart. 4. Antisera against the active neurotransmitters labeled central neurons and nerves innervating the heart in a pattern consistent with their putative cardioregulatory functions. 5. Thus, despite the simplicity of the cardiac motor circuit in Archidoris, contractile activity of the heart appears to be regulated by several neurotransmitters, each with subtly different modes and thresholds of action.
Learning of sequential movements in the monkey: process of learning and retention of memory
Authors: Hikosaka O. , Rand M. K. , Miyachi S. , Miyashita K.
Published: December 2017

1. To characterize procedural learning and memory, we devised a behavioral paradigm that allows us to examine the process of learning of new procedures, repeatedly and without serious difficulties for primate subjects. We trained two monkeys to perform a sequential button press task. Upon pressing of a home key, 2 of 16 (4 x 4 matrix) light-emitting diode (LED) buttons (called “set”) were illuminated simultaneously, and the monkey had to press them in a predetermined order that he had to find out by trial-and-error. A total of five sets (called “hyperset”) was presented in a fixed order for completion of a trial; an error at any set aborted the trial. A given hyperset was repeated as a block of experiment until 20 successful trials were performed. Monkeys PI and BO experienced 313 and 92 hypersets, respectively. Most of these hypersets were experienced only once (1 block of experiment); the others (28 hypersets for monkey PI and 14 hypersets for monkey BO) were chosen for extensive practice. 2. The learning, indicated as the decrease in the number of trials to criterion and the decrease in the performance time, proceeded at three levels: 1) short-term and sequence-selective learning that occurred by repeating a particular hyperset during a block of experiment; our monkeys learned, to some degree, to perform a new hyperset within a short period (< 5 min); 2) long-term and sequence-selective learning that took place for each hyperset across days; by daily practice, they further improved their skills for performing the particular hyperset; and 3) long-term and sequence-unselective learning that was indicated by the improvement of performance for new hypersets; the monkeys were required to learn many hypersets, each just once (a block of trials), in which they performed gradually better with more experiences in the 2 x 5 task. 3. To examine whether the memory was retained for a long period, we had the monkey learn 12 hypersets sufficiently, then we stopped the training and retested them after 1 or 6 mo. After the 1-mo interruption the performance was significantly better than that for new hypersets. After the 6-mo interruption the performance was not different from new hypersets in terms of the number of trials but was significantly better than new hypersets in terms of the performance time. The results suggest that motor memory (measured by performance time) can be retained longer than procedural memory (measured by the number of trials).
Activity-dependent response depression in rat hippocampal CA1 pyramidal neurons in vitro
Authors: Borde M. , Cazalets J. R. , Buno W.
Published: December 2017

1. A gradual and prolonged decrease of the response, termed here “depression”, evoked by repeated activation with transmembrane current stimuli was analyzed in rat CA1 hippocampal pyramidal cells under single-electrode current clamp by the use of the in vitro slice technique. 2. Depression was induced by 2-s duration 0.3- to 0.7-nA current pulses presented as a sequence of 12 stimuli at 3- to 60-s intervals. Sinusoidal currents (0.5-1.0 nA) at 5-Hz or 200-ms pulses repeated at 0.3-0.5/s, which may be more natural stimulations, also induced depression. 3. Depression outlasted stimulation up to 170 s in all cells tested. The initial high rate spike burst changed little (< 20%), whereas the lower rate adapted response decreased markedly (> 40%). Thus neurons increased their rate of adaptation. The afterhyperpolarizations following pulse-evoked responses increased in duration and amplitude with depression. There were input resistance (Rin) reductions at depolarized membrane potentials and during pulses. However, Rin reductions were considerably smaller or altogether absent late during interpulse intervals. Sub-threshold current stimuli were ineffective, indicating that spike activity was necessary to elicit depression. 4. Depression was 1) insensitive to the toxin omega-Agatoxin-IVA (omega-Aga-IVA; 0.5 microM), which blocked synaptic transmission, revealing a key involvement of intrinsic properties and little if any synaptic participation; 2) insensitive to 4-aminopyrydine (2.00-4.00 mM), which greatly enhanced excitatory and inhibitory synaptic efficacy, again suggesting little synaptic involvement and a principal postsynaptic participation, and no participation of the K(+)-mediated currents IA and ID; 3) abolished by carbamalcholine (5.0-20.0 microM)- an effect blocked by atropine (1.0-10.0 microM)- and reduced by Ca(2+)-free solutions, and by intracellular injection of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), suggesting that Ca(2+)-dependent K(+)-mediated currents are key factors, with a less important participation of the K(+)-mediated IM current. 5. We conclude that depression was due to activity-dependent modifications in intrinsic properties, with little if any synaptic participation. Depression may be functionally significant because it was induced by potentially natural stimulations. A model is proposed that accounts for the main traits of depression. In the model, depression was induced by a gradual decline of the speed at which Ca2+ was buffered intracellularly; an increase in the IK(Ca)S activation rate constant also simulated depression.
Odorant-specific spatial patterns in mucosal activity predict perceptual differences among odorants
Authors: Kent P. F. , Youngentob S. L. , Sheehe P. R.
Published: December 2017

1. Using operant techniques, rats were trained to differentially report (i.e., identify) the odorants propanol, carvone, citral, propyl acetate, and ethylacetoacetate. After acquisition training, the animals were tested using a 5 x 5 confusion matrix design. The results of the behavioral tests were used to measure the degree of perceptual dissimilarity between any pair of odorants. These dissimilarity measures were then subjected to multidimensional scaling analysis to establish a two-dimensional perceptual odor space for each rat. 2. At the completion of behavioral testing, the fluorescence changes in the dye di-4-ANEPPS were monitored on the rat's nasal septum and medial surface of the turbinates in response to the same odorants. For each mucosal surface a 6.0 x 6.0 mm area was sampled at 100 contiguous sites with a 10 x 10 photodiode array. 3. Formal statistical analysis indicated a highly significant predictive relationship between the relative position of an odorant's mucosal loci of maximal activity or “hot spot” and the relative position of the same odorant in a psychophysically determined perceptual odor space (F = 15.6, P < 0.001). 4. The results of this study suggest for the first time that odorant-induced mucosal activity patterns serve as the substrate for the perception of odorant quality.
Stimulation at 1-5 Hz does not produce long-term depression or depotentiation in the hippocampus of the adult rat in vivo
Authors: Errington M. L. , Bliss T. V. , Richter-Levin G. , Yenk K. , Doyere V. , Laroche S.
Published: December 2017

1. We examined the efficacy of low-frequency trains (1-5 Hz) in producing long-term depression (LTD) or depotentiation in the hippocampus of the awake adult rat and in anesthetized rats aged from 10 days to 3 mo. 2. In the dentate gyrus we found no evidence that low-frequency trains produce either depotentiation or LTD in the awake, adult animal or in the anesthetized animal at any age tested (10 days-adult). 3. In area CA1 of both awake and anesthetized adult rats, we also found no evidence that low-frequency trains induced either LTD or depotentiation. Only in area CA1 of very young rats (10-11 days) was clear evidence for LTD and depotentiation obtained; at this age experiments were only possible in anesthetized animals. By 16 days, the ability to display both LTD and depotentiation was lost. 4. These experiments suggest that repetitive low-frequency stimulation evokes a developmentally regulated form of activity-dependent depression that in the hippocampus is limited to specific pathways in the young animal. Our results leave open the question of whether alternative patterns of activity can induce LTD and/or depotentiation in the adult awake rat.
Neurons of the anterior mesial cortex related to faciovocal activity in the awake monkey
Authors: West R. A. , Larson C. R.
Published: December 2017

1. The anterior mesial cortex, including the cingulate region, is thought to be involved in the voluntary control of vocalization. Previous recording studies have demonstrated that anterior mesial neurons discharge before conditioned and spontaneous vocalizations, but questions remain regarding the location and functional properties of these neurons. The present study was performed to provide a more complete description of the location and discharge properties of anterior mesial neurons involved in faciovocal behaviors. 2. Single-unit activity was recorded from neurons in the anterior mesial cortex of monkeys during performance of self-paced vocalizations and jaw openings. Cells were also tested for responsiveness to acoustic stimulation, and attempts were made to elicit vocalization through stimulation of the cortex surrounding related cells. Discharge properties of the cells were statistically analyzed, and correlation analysis was performed between measure of cell discharge and vocalization. 3. A total of 145 neurons were observed to modulate their discharge in association with vocalization or jaw opening. Four general classes of neurons were observed: neurons related only to vocalization, neurons related only to jaw opening, neurons related to both vocalization and jaw opening, and neurons related to other oromotor activities such as lip movements or reinforcement consumption. 4. Vocalization-related cells typically discharged tonically at a low frequency (mean 22 Hz), and many instances of long-lead activity (lead time > 500 ms) were noted. No neurons responded to acoustic stimulation, and electrical stimulation failed to elicit vocalization. Neural activity was not correlated with any measure of vocalization. 5. Neurons related to faciovocal behavior were located in the anterior cingulate sulcus and adjacent cortex of the mesial wall at a level just rostral to the genu of the arcuate sulcus. This region roughly corresponds to the rostral cingulate motor area and is located caudal to the traditionally described cingulate vocalization region. 6. In the present study we demonstrate the existence of an additional region in the medial wall that is involved in a variety of faciovocal behaviors such as vocalization, jaw opening, lip movements, and reinforcement consumption. The neurons do not appear to be strongly coupled to the execution of these acts. These results suggest that the activity of neurons in the anterior mesial cortex may relate to faciovocal behavior in a more global way than the activity of neurons in other motor areas.
Quantitative analysis of dorsal horn cell receptive fields following limited deafferentation
Authors: Koerber H. R. , Brown P. B.
Published: December 2017

1. To test the hypothesis that subtotal deafferentation of dorsal horn cells can stimulate plastic changes in their receptive fields (RFs), diffuse deafferentation of the cat hindlimb dorsal horn was produced by transection of L7 or L6 and L7 dorsal roots. The following single-unit cutaneous low-threshold mechanoreceptor RF properties were compared between operated and control dorsal horns: 1) distance of RF center from tips of toes, 2) RF length-width ratio; and 3) RF area. 2. In both L7 and L6-L7 rhizotomized animals there was an increased incidence of silent electrode tracks in the most deafferented portion of the hindlimb map (the foot and toe representation). In the rhizotomized L6-L7 animals, there was also an increased incidence of symmetrically placed tracks in deafferented and control dorsal horns, in which cell RFs had no mirror-symmetrical components. In addition, cells in the lateral half of the L6 and L7 dorsal horns exhibited a proximal shift in the location of their RFs. In the rhizotomized L7 animals there was a distal shift of RFs in the L5 segment at long survival times. RFs had lower length-width ratios in L5 and L6 at short survival times and in L6 at long survival times. 3. In intact preparations, dorsal horn cells normally respond to inputs via single or small numbers of low-threshold cutaneous mechanoreceptors. Because these rhizotomies do not remove all inputs from any given area of skin, the deafferentations would produce only patchy loss of input from individual receptors. Therefore observed changes cannot be accounted for entirely by loss of afferent input, suggesting that some reorganization of dorsal horn cell RFs occurred. We conclude that the threshold stimulus for plastic change is less than total deafferentation of dorsal horn cells. At least some of the mechanisms underlying these changes may be active in normal animals in the maintenance of the somatotopic map or in conditioning.
Properties of motor units after self-reinnervation of the cat superior oblique muscle
Authors: Waldeck R. F. , Murphy E. H. , Pinter M. J.
Published: December 2017

1. The mechanical properties of motor units of the cat superior oblique muscle and axonal conduction velocities of trochlear motoneurons have been studied at several postoperative times after intracranial axotomy of the trochlear nerve. 2. Whole muscle twitch forces were generally within the normal range by approximately 4 mo postoperative, indicating that reinnervation is complete at this time. 3. Among animals studied 3.5-4.5 months after trochlear axotomy, average motor-unit tetanic forces were increased by a factor of approximately 2.5 compared with units studied in normal superior oblique muscle. Average motor-unit tetanic forces in animals studied 14.5-23 mo after axotomy were also increased relative to normal, but the difference was not significant. Among all reinnervated motor units, there was a tendency for increased twitch time-to-peak relative to control. Reinnervated motor-unit fatigue properties were similar to normal. 4. Average trochlear motoneuron conduction velocities for animals at all postoperative intervals remained significantly lower than the average conduction velocities from three of four normal animals. 5. Counts of Nissl-stained cell bodies in axotomized and control, contralateral trochlear nuclei showed that some cell loss had occurred, averaging approximately 17% 3.5-4.5 mo postoperative and 24% 14.5-23 mo postoperative. Associated with this loss was an increase (10%) of axotomized motoneuron soma cross-sectional area. 6. Muscle fiber cross-sectional areas (CSA) were measured in reinnervated superior oblique muscles and compared with CSAs from contralateral, control muscles. Average CSA was significantly decreased in all reinnervated muscles, with the relative decreases ranging from approximately 10 to 28%. 7. The results are discussed in terms of factors that determine motor-unit force; muscle fiber CSA, specific force, and innervation ratio. We conclude that the increases of average motor-unit force in short-term reinnervated superior oblique muscles are most likely related to polyneuronal innervation of muscle fibers and that the return of these forces to normal levels in long-term muscles is related to synapse elimination. Our results are compared with those of other self-reinnervation studies, and the potential role played by the time muscle remains denervated in determining the persistence of polyneuronal innervation after reinnervation is considered.
Passive compliance and active force generation in the guinea pig outer hair cell
Authors: Hallworth R.
Published: December 2017

1. Cochlear outer hair cells 20-80 microns in length were compressed axially in vitro using calibrated glass fibers mounted on a piezoelectric actuator. 2. When driven by rectangular pulses in the compression direction, the motion of the fiber tip consisted of a rapid initial compression that was complete in 10-20 ms followed by a smaller compression of slower time course. 3. The initial fiber deflections were found to be linear in amplitude for compressions up to 400 nm. The axial compliances of outer hair cells were calculated from the difference between the fiber tip motions when unattached and when in contact with a cell. Axial compliances were found to be in the range of 0.04-1.2 km/N for 149 cells. The axial compliance was an increasing function of cell length. 4. The peak forces generated by electrically stimulated outer hair cells were measured from the deflection of a glass fiber when the cells were stimulated by sinusoidal voltage commands. The slope gains of force generation (force generated per mV of command at the cell membrane) were estimated to range from 0.01 to 100 pN/mV. Most of the results fell in the range of 0.1-20 pN/mV. 5. When the apparent stiffness of the fiber was increased by moving the cell closer to the fiber base, the peak amplitude of the fiber deflection generated by the cell decreased and the peak force increased, for the same sinusoidal voltage command. 6. The results of the previous experiment were interpreted in the light of a model of outer hair cell motility in which an ideal extension generating element is in series with an internal stiffness element. This internal stiffness was then calculated for 13 cells. 7. The internal stiffnesses of cells calculated by the above procedure were found to be positively correlated with the axial stiffness measurements obtained for the same cells. 8. The implications of the above results for the effectiveness of outer hair cell motility in vivo are discussed.