bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlational analysis of fictive swimming in the lamprey reveals strong functional intersegmental coupling
Authors: Mellen N. , Kiemel T. , Cohen A. H.
Published: December 2017

1. Cycle-to-cycle fluctuations in cycle periods and intersegmental burst delays of ventral root activity were studied during stable fictive swimming in the adult lamprey spinal cord. High spatial resolution was obtained by recording from 16 ventral roots, 1/2 on each side of the spinal cord. For ipsilateral ventral roots, correlations between cycle periods on the same cycle were high (0.50 +/- 0.16, mean +/- SD), and autocorrelations of intersegmental delays with a shift of one cycle were low (0.03 +/- 0.06). Correlations between cycle periods tended to decrease with intersegmental spacing but remained positive over the range of spacings tested (1-47 segments). 2. Sinusoidal movement imposed on the caudal end of the spinal cord/notochord was used to entrain the fictive swimming rhythm. When the phase between the movement and the rhythm was perturbed, several cycles were required for the phase to return to its preferred value, indicating that in these experiments the effect of the movement was weak. In the absence of external perturbations, autocorrelations of delays between the movement and ventral root bursts with a shift of one cycle were high. 3. Numerical simulations with a simple stochastic phase model of the lamprey central pattern generator (CPG) were conducted. High correlations of periods and low autocorrelations of delays, the pattern observed experimentally, emerged as intersegmental connection strengths were increased. Coupling including both long and short connections produced this pattern of correlations with an average connection strength less than that required by short connections alone. 4. It is concluded that functional intersegmental coupling in the lamprey CPG during stable fictive swimming is strong. Specifically, the low autocorrelations of intersegmental delays indicate that intersegmental coupling is sufficiently strong to ensure that perturbations are almost completely corrected within one cycle.
Envelope coding in the lateral superior olive. I. Sensitivity to interaural time differences
Authors: Joris P. X. , Yin T. C.
Published: December 2017

1. Interaural level differences (ILDs), created by the head and pinna, have long been known to be the dominant acoustic cue for azimuthal localization of high-frequency tones. However, psychophysical experiments have demonstrated that human subjects can also lateralize complex high-frequency sounds on the basis of interaural time differences (ITDs) of the signal envelope. The lateral superior olive (LSO) is one of two pairs of binaural nuclei where the primary extraction of binaural cues for sound source location occurs. "IE" cells in LSO are inhibited by stimuli to the contralateral and excited by stimuli to the ipsilateral ear, and their response rate is therefore dependent on ILD. Anatomic specializations in the afferent pathways to the LSO suggest that this circuit also has a function in the detection of timing cues. We hypothesized that, besides ILD sensitivity, the IE property also conveys a sensitivity to ITDs of amplitude-modulated (AM) tones and could provide the physiological substrate for the psychophysical effect mentioned above. 2. In extracellular recordings from binaural LSO cells in barbiturate-anesthetized cats, response rate was a periodic function of ITDs of AM stimuli, i.e., all cells displayed ITD sensitivity. Binaural responses were smaller than responses to stimulation of the ipsilateral ear alone and were minimal when the envelopes in both ears were in-phase or nearly so. There was good correspondence between responses to ITDs and to dynamic interaural phase differences (IPDs), created by a difference in the envelope frequency to the two ears. Qualitatively, the responses were consistent with the outcome of an IE operation on temporally structured inputs. 3. To compare the relative importance of ILD and ITD, responses to combinations of the two cues were obtained. Despite robust ITD sensitivity in all binaural LSO cells encountered, the changes in response rate that would occur in response to naturally occurring ITDs were small in comparison with the changes expected for naturally occurring ILDs. The main limitation on ITD sensitivity was a steep decline in average discharge rate as the modulation frequency exceeded several hundred Hertz. 4. ITD sensitivity was also present to broadband stimuli, again with minimal rates occurring near 0 ITD. The sensitivity depended in a predictable fashion on the passband of filtered noise and was absent to binaurally uncorrelated noise bands. In response to clicks, ILDs interacted with ITD in a complicated fashion involving amplitude and latency effects. 5. Three low-characteristic frequency (CF) LSO cells were encountered that were IE and showed ITD sensitivity to the fine structure of low-frequency stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Metabotropic glutamate receptor-mediated presynaptic depression at corticostriatal synapses involves mGLuR2 or 3
Authors: Lovinger D. M. , McCool B. A.
Published: December 2017

1. The pharmacology of the metabotropic glutamate receptor (mGluR) that mediates synaptic depression at corticostriatal synapses was investigated with the use of field potential and whole cell patch-clamp recording from striatal slices and whole cell recordings from isolated striatal neurons. 2. The mGluR2,3-selective agonists (R,S)-4-carboxy-3-hydroxyphenylglycine (CHPG), (2S, 1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl) glycine (DCG-IV), and (2S, 3S, 4S)-alpha-(carboxycyclopropyl) glycine (L-CCG-I) inhibited the synaptically driven population spike (PS) evoked by afferent stimulation during field potential recording in striatal slices. These agonists also inhibited excitatory postsynaptic potentials (EPSPs) evoked by afferent stimulation during whole cell recordings. The metabotropic receptor antagonist R,S-alpha-methyl-4-carboxyphenylglycine (MCPG) blocked the synaptic depressant actions of DCG-IV and trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD). 3. The mGluR4,6,7-selective agonist L-serine-O-phosphate (L-SOP) did not alter corticostriatal synaptic transmission, but both this agonist and the mGluR4,6,7 agonist D,L-2-amino-4-phosphonobutyric acid (AP4) reduced the amplitude of the population EPSP and PS evoked in the dentate gyrus (DG) by stimulation of the lateral perforant path (LPP). These data are consistent with earlier observations that AP4 does not inhibit corticostriatal transmission, but produces presynaptic depression at LPP-DG synapses. 4. Application of mGluR agonists that inhibited transmission did not alter the input resistance or excitability of striatal neurons and did not inhibit responses evoked by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor activation.(ABSTRACT TRUNCATED AT 250 WORDS)
Delay-tuned neurons in the midbrain of the big brown bat
Authors: Dear S. P. , Suga N.
Published: December 2017

1. The auditory midbrain in Eptesicus contains delay-tuned neurons that encode target range. Most delay-tuned neurons respond poorly to tones or individual frequency-modulated (FM) sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned. The index of facilitation (IF), a coefficient measuring combination sensitivity for individual delay-tuned neurons, ranged from 0.14 to 1.0, with an average of 0.64 +/- 0.24 (mean +/- SD). Of the 33 facilitated responses from 29 neurons, 23 (70%) exhibited IFs > 0.5, which corresponds to a facilitated response 3 times greater than the sum of the responses to individual pulse and echoes. Thus the responses of midbrain delay-tuned neurons are highly combination sensitive. 2. The response of midbrain delay-tuned neurons is phasic, with an average of 0.7 +/- 0.4 action potentials elicited per optimal pulse-echo pair. Thus midbrain delay-tuned neurons in Eptesicus act as probability encoders. 3. The distribution of best echo delays (BDs) of midbrain delay-tuned neurons ranged from 8 to 30 ms. As an ensemble, midbrain delay-tuned neurons encode target ranges of 138-516 cm. There is a basic correspondence between the physiologically determined span of midbrain BDs between 8 and 30 ms and the behaviorally determined borders of the approach (8- to 17-ms echo delay) and search stages (17- to 30-ms echo delay) of the insect pursuit sequence. Midbrain delay-tuned neurons can be separated into two subpopulations on the basis of the difference in distributions of the echo best amplitude (EBA) tuning at BD. The BDs of one subpopulation correspond to the span of search stage echo delays, and the BDs of the other subpopulation correspond to the span of approach stage echo delays. 4. EBAs of neurons in each subpopulation are tailored to the specific perceptual requirements of the corresponding behavioral stage. EBAs of midbrain neurons tuned to echo delays between 17 and 30 ms (N = 12) correspond to the search stage and are suited to the requirements of target detection. EBAs of midbrain neurons tuned to echo delays between 17 and 30 ms (N = 21) correspond to the approach stage and are suited to the requirements of target size discrimination. 5. The best FM sweeps for the pulse (PFM) and echo (EFM) were determined for each midbrain neuron. PFMs appear to cluster at frequencies corresponding to the three harmonic peaks in the emitted pulse power spectra.(ABSTRACT TRUNCATED AT 400 WORDS)
Bilateral labyrinthectomy in the cat: effects on the postural response to translation
Authors: Inglis J. T. , Macpherson J. M.
Published: December 2017

1. This study examined the role of vestibular afferent information on the postural responses of four cats, evoked by movements of the support surface during stance. Animals were exposed to linear translations of the supporting surface in eight evenly spaced directions in the horizontal plane, before and after bilateral labyrinthectomy. Postural responses were quantified in terms of the ground reaction forces under each paw and the evoked activity in selected muscles. 2. The cats were able to stand on the platform within 1-3 days after labyrinthectomy and were able to maintain balance during all perturbations of stance, even when they stood in total darkness, completely deprived of visual information. After lesion, postural responses were characterized by normal latency and normal spatial and temporal patterning of electromyographic (EMG) response. The pattern of force response showed the force constraint strategy that characterizes postural responses in the intact animal. 3. The only deficit in the postural response after lesion was a hypermetria, or active over-response that caused the animals to overbalance somewhat but did not impair their ability to remain upright. Analysis of the trajectory of the animal's center of mass during the trials indicated that the hypermetria was due to an abnormally large, active response on the part of the animal and could not be attributed to changes in the passive stiffness of the musculoskeletal system. The hypermetria was transient, and response amplitude returned to control levels after the rapid compensation phase of 10-15 days. 4. It is concluded that vestibular information is not essential for triggering the rapid, automatic postural response to translations of the support surface, nor is it necessary for the selection or shaping of the evoked response. Instead, somatosensory information appears to predominate in these postural adjustments. However, vestibular afferent input does influence the scaling of the postural response.
Pancreatic polypeptide inhibits calcium channels in rat sympathetic neurons via two signaling pathways
Authors: Wollmuth L. P. , Shapiro M. S. , Hille B.
Published: December 2017

1. We studied modulation of N-type Ca2+ channels in adult rat superior cervical ganglion (SCG) neurons by pancreatic polypeptide (PP) using whole cell clamp. In large (> 20 pF) SCG neurons, PP inhibited ICa (35 +/- 2%, mean +/- SE) in a concentration-dependent fashion, with one-half maximal inhibition at 19 nM. 2. One-third of the inhibition was blocked by pertussis toxin, about one-half was blocked by N-ethylmaleimide (NEM) treatments, and about one-half was voltage dependent. The NEM-insensitive component of the PP inhibition was voltage independent and not significantly blocked by intracellular Ca2+ chelators. 3. The NEM-insensitive component was only weakly attenuated by GDP-beta-S, and moderately reversible with guanosine 5'-triphosphate (GTP)-gamma-S, in the whole cell pipette, leaving open the possibility that it is not mediated by a G protein. 4. Hence, PP inhibits ICa via two mechanisms: one G-protein-mediated and the other possibly G-protein independent. The former pathway is sensitive to pertussis toxin (PTX) and NEM, voltage dependent, and shared by several other transmitters in these cells. The latter pathway is PTX-and NEM-insensitive, not voltage dependent, and not affected by the presence of intracellular Ca2+ chelators.
An identified glutamatergic interneuron patterns feeding motor activity via both excitation and inhibition
Authors: Quinlan E. M. , Gregory K. , Murphy A. D.
Published: December 2017

1. Previously we demonstrated that glutamate is an important neurotransmitter in the CNS of Helisoma. Exogenous glutamate applied to the buccal ganglia mimicked both the excitatory and inhibitory effects of subunit 2 (S2) of the tripartite central pattern generator (CPG) on S2 postsynaptic motor neurons. Here we identify buccal interneuron B2 as an S2 interneuron by utilizing a combination of electrophysiology, pharmacology, and intracellular staining. In addition, neurons that were electrophysiologically and morphologically characterized as neuron B2 demonstrated antiglutamate immunoreactivity, suggesting that neuron B2 is a source of endogenous glutamate in the buccal ganglia. 2. Depolarization of neuron B2 evoked excitatory postsynaptic potentials in motor neurons excited by S2. The excitatory effects of B2 depolarization and S2 activation were reversibly antagonized by the ionotropic glutamate receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione, similar to the antagonism shown previously for application of exogenous glutamate. Depolarization of neuron B2 also evoked inhibitory postsynaptic potentials in motor neurons inhibited by S2. When such motor neurons were maintained in isolated cell culture, application of exogenous glutamate produced a direct hyperpolarization of the membrane potential. 3. The activity of neuron B2 is necessary for the production of the standard pattern of buccal motor neuron activity, which underlies functional feeding movements. The subunits of the tripartite buccal CPG must be active in the temporal sequence S1-S2-S3 to produce the standard feeding pattern. Rhythmic inhibition from neuron B2 terminated activity in S1 postsynaptic motor neurons and entrained the frequency of activity in S3 postsynaptic motor neurons. Hyperpolarization of neuron B2 disrupted the production of the standard motor pattern by eliminating S2 postsynaptic potentials in identified buccal motor neurons, thereby prolonging S1 activity and disrupting S3 bursting. 4. These data support the hypothesis that S2 neuron B2 is glutamatergic and demonstrate that glutamatergic transmission, and especially inhibition, is fundamental to the production of behaviorally critical motor neuron activity patterns in Helisoma.
Receptors underlying excitatory synaptic transmission in slices of the rat anteroventral cochlear nucleus
Authors: Isaacson J. S. , Walmsley B.
Published: December 2017

1. The anteroventral cochlear nucleus (AVCN) contains two principal cell types that receive input from the auditory nerve. Stellate cells receive conventional synapses on their dendrites, and bushy cells of the AVCN receive axosomatic input via large, calyceal terminals (the end bulbs of Held). We have used whole cell patch-clamp recording techniques to study excitatory postsynaptic currents (EPSCs) in these two principal cells of the rat AVCN. 2. EPSCs evoked in stellate cells by stimulation of the auditory nerve were graded with stimulus strength, indicating a high degree of convergence of input to these cells. At depolarized membrane potentials, EPSCs evoked in stellate neurons had a dual-component time course. The slow component was blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV), and the fast component was abolished by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 3. EPSCs evoked in bushy cells by auditory nerve stimulation were large (50 nS average conductance) and all-or-none at the threshold stimulus level. At -70 mV, the time course of the EPSC was very brief (average time constant of decay 700 microseconds at room temperature). Membrane depolarization revealed a slow component to the EPSC. The fast and slow components were mediated by non-NMDA and NMDA receptors, respectively. The switch-off of end bulb NMDA EPSCs by voltage jumps to the EPSC reversal potential was very rapid, suggesting that the NMDA component arises from sites on or close to the soma. 4. Miniature EPSCs, recorded in the presence of tetrodotoxin (TTX) at depolarized potentials, also had a dual-component time course. The fast and slow components of the miniature EPSCs were blocked by CNQX and APV, respectively. This result indicates that NMDA and non-NMDA receptors can be co-localized at the same, presumably end bulb, release sites. 5. The relative contribution of the slow, NMDA component to the end bulb EPSC declined significantly with age (postnatal days 11-22). 6. These results indicate that both NMDA and non-NMDA receptors underlie excitatory synaptic transmission in the AVCN of young rats. The end bulb synapse onto bushy cells generates a non-NMDA receptor-mediated EPSC with very fast kinetics. NMDA receptors can also mediate synaptic transmission at the end bulb synapse, but their contribution becomes less as the auditory system matures. This finding suggests that NMDA receptors may play an important role in the development of this synapse.
Developmental increase in CA3-CA1 presynaptic function in the hippocampal slice
Authors: Dumas T. C. , Foster T. C.
Published: December 2017

1. We recorded extracellular and intracellular CA3-CA1 synaptic responses in hippocampal slices from neonatal rats [postnatal day (P) 15-21 and P29-35]. Presynaptic function was examined by measuring input-output relationships and paired-pulse facilitation and by quantal analysis of minimally evoked responses. 2. Extracellular recording revealed no difference in excitatory postsynaptic potential (EPSP) threshold or the fiber potential response for a given stimulus intensity between the two age groups. However, the slope of the field EPSP was consistently larger in older animals. The increase in EPSP slope was associated with a decrease in paired-pulse facilitation, suggesting an increase in presynaptic function with postnatal development. 3. Extracellular results were confirmed by intracellular recordings that revealed no difference in the minimal stimulation intensity needed to evoke a response, an increase in mean EPSP amplitude with development, and a decrease in paired-pulse facilitation. Quantal parameters were extracted by three separate methods including method of failures, coefficient of variance, and parameter optimization through noise deconvolution. All methods supported presynaptic mediation of facilitation. Comparison of quantal parameters during development indicated an increase in mean quantal content. 4. The results demonstrate that synaptic strength is altered over the course of development because of, at least in part, changes in presynaptic release mechanisms. Developmental differences in presynaptic function provide an explanation of differences in mechanisms for expression of long-term potentiation. The lower initial probability of transmitter release in neonates may permit increased presynaptic change.
Long-term potentiation at the apical and basal dendritic synapses of CA1 after local stimulation in behaving rats
Authors: Leung L. S. , Shen B.
Published: December 2017

1. We recorded the extracellular excitatory postsynaptic potentials (EPSPs) in CA1 in the freely behaving rats after stimulation of the apical dendritic and basal dendritic afferents. The apical dendritic population EPSP was negative at the apical dendritic layers and positive at stratum oriens and alveus. The basal dendritic population EPSP was negative at basal dendritic layer (stratum oriens) and positive at the cell body and apical dendritic layers. 2. We delivered various tetanic stimulus patterns in an attempt to elicit long-term potentiation (LTP) at the apical dendritic synapse of CA1 pyramidal cells. A 200-Hz high-frequency train (HF) 1 s in duration was more successful than theta-frequency primed bursts (PBs; 1 or 4 priming pulses followed by 10 or 4 pulses at 100 Hz) in eliciting LTP of the apical dendritic population EPSP, recorded either ipsilaterally or contralaterally. 3. Tetanus applied to the apical dendritic afferents occasionally elicited long-term depression (LTD) at an intensity lower than the LTP threshold. LTD persisted to > or = 1 day after a tetanus. 4. High-intensity tetanic stimulations often elicited hippocampal afterdischarges (ADs). If the AD duration was brief (< 15 s), apical dendritic LTP could follow the AD. However, if the AD duration was long, no apical dendritic LTP was observed. Tetanus that evoked an apical dendritic LTP typically evoked a short hippocampal AD < 15 s in duration. 5. LTP of the basal dendritic population EPSP was readily elicited either after an HF or a PB tetanus of low (1.5-2 times threshold) stimulus intensity.(ABSTRACT TRUNCATED AT 250 WORDS)
High extracellular potassium, and not extracellular glutamate, is required for the propagation of spreading depression
Authors: Obrenovitch T. P. , Zilkha E.
Published: December 2017

1. Cortical spreading depression (SD) is a propagating transient suppression of electrical activity associated with depolarization, which may contribute to the pathophysiology of important neurological disorders, including cerebral ischemia and migraine. The purpose of this study is to ascertain whether SD propagation depends on local accumulation of extracellular K+ or glutamate. 2. Propagating SD recorded through microdialysis probes perfused with artificial cerebrospinal fluid (ACSF) was much smaller than that recorded with conventional glass microelectrodes, presumably because some SD-induced transient changes in the extracellular fluid composition were buffered by ACSF. We have exploited this effect to determine whether perfusion with a medium containing increasing amounts of K+ and/or glutamate favors SD propagation. 3. Increasing the concentration of K+ (15-60 mmol/l) in the perfusion medium dose-dependently restored SD propagation, whereas application of 100-250 mumol/l glutamate through the microdialysis probe had no effect. Superimposing 200 mumol/l glutamate onto 15 and 30 mmol/l K+ did not further improve the restoration of SD propagation by K+. 4. Because potent uptake mechanisms may efficiently clear exogenous glutamate from the extracellular space, the effect of local inhibition of high-affinity glutamate uptake was also studied. Perfusion of the recording microdialysis probe with 1 mmol/l L-trans-pyrrolidine-2,4-dicarboxylate (L-trans-PDC), either alone or together with 200 mumol/l glutamate, had no effect. In addition, L-trans-PDC did not potentiate the positive effect of 30 mmol/l K+ on SD propagation. 5. These results strongly suggest that high extracellular K+, and not extracellular glutamate, is the driving force sustaining SD propagation.(ABSTRACT TRUNCATED AT 250 WORDS)
Acetylcholine excites GABAergic neurons of the ferret perigeniculate nucleus through nicotinic receptors
Authors: Lee K. H. , McCormick D. A.
Published: December 2017

1. The actions of acetylcholine (ACh) on the GABAergic neurons of the perigeniculate nucleus (PGN) were investigated with the use of extra- and intracellular recording techniques in spontaneously spindling ferret thalamic slices maintained in vitro. 2. Local application of ACh to PGN neurons resulted in rapid depolarization followed by a longer lasting hyperpolarization. Neither of these responses were abolished by blockade of synaptic transmission with tetrodotoxin (TTX) nor with low Ca2+ and elevated Mg2+ solution, indicating that they are direct postsynaptic actions of ACh on PGN cells. Functionally, the rapid depolarizing response could activate both single spike activity, as well as low-threshold Ca2+ spike-mediated bursts. 3. The fast depolarizing response to ACh was selectively blocked by application of the nicotinic antagonist hexamethonium, whereas the slow hyperpolarizing response to ACh was selectively blocked by application of the muscarinic antagonist (-)scopolamine. Application of both hexamethonium and (-)scopolamine blocked the modulation of PGN action-potential firing by ACh. 4. Local application of the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) resulted in a depolarizing response and an increase in membrane conductance, whereas application of the muscarinic agonist DL-muscarine chloride resulted in a hyperpolarizing response and an increase in membrane conductance. When applied to spontaneously spindling PGN cells, both DMPP and DL-muscarine blocked the occurrence of spindle oscillations. However, only DMPP was associated with depolarization and the generation of single spike activity. 5. These results indicate that the GABAergic cells of the PGN possess postsynaptic nicotinic as well as muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of brain stem parabrachial activation on receptive field properties of cells in the cat's lateral geniculate nucleus
Authors: Uhlrich D. J. , Tamamaki N. , Murphy P. C. , Sherman S. M.
Published: December 2017

1. The lateral geniculate nucleus is the primary thalamic relay for the transfer of retinal signals to the visual cortex. Geniculate cells are heavily innervated from nonretinal sources, and these modify retinogeniculate transmission. A major ascending projection to the lateral geniculate nucleus arises from cholinergic cells in the parabrachial region of the brain stem. This is an important pathway in the ascending control of arousal. In an in vivo preparation, we used extracellular recordings to study the effects of electrical activation of the parabrachial region on the spontaneous activity and visual responses of X and Y cells in the lateral geniculate nucleus of the cat. 2. We studied the effects of two patterns of parabrachial activation on the spontaneous activity of geniculate cells. Burst stimulation consisted of a short pulse at high frequency (16 ms at 250 Hz). Train stimulation was of longer duration at lower frequency (e.g., 1 s at 50 Hz). The firing rate of almost all geniculate cells was enhanced by either pattern of stimulation. However, the burst pattern of stimulation elicited a short, modulated response with excitatory and inhibitory epochs. We found that the different epochs could differentially modulate the visual responses to drifting gratings. Thus the temporal alignment of the brain stem and visual stimuli was critical with burst stimulation, and varied alignments could dramatically confound the results. In comparison, the train pattern of stimulation consistently produced a relatively flat plateau of increased firing, after a short initial period of more variable effects. We used the less confounding pattern of train stimuli to study the effects of parabrachial activation on visual responses. 3. Our main emphasis was to examine the parabrachial effects on the visual responses of geniculate cells. For most visual stimuli, we used drifting sine wave gratings that varied in spatial frequency; these evoked modulated responses from the geniculate cells. Parabrachial activation enhanced the visual responses of almost all geniculate cells, and this enhancement included both increased depth of modulation and greater response rates. 4. Our results were incorporated quantitatively into a difference-of-Gaussians model of visual receptive fields in order to study the parabrachial effects on the spatial structure of the receptive field. This model fit our data well and provided measures of the response amplitude and radius of the receptive field center (Kc and Rc, respectively) and the response amplitude and radius of the receptive field surround (Ks and Rs, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)
Different Ca2+ channels in soma and dendrites of hippocampal pyramidal neurons mediate spike-induced Ca2+ influx
Authors: Christie B. R. , Eliot L. S. , Ito K. , Miyakawa H. , Johnston D.
Published: December 2017

1. Intracellular recordings, in conjunction with fura-2 fluorescence imaging, were used to evaluate the contribution of the different Ca2+ channel subtypes to the Ca2+ influx induced by back-propagating trains of action potentials. High-threshold channels contributed mainly to Ca2+ influx in pyramidal cell somata and proximal dendrites, whereas low-threshold and other Ni(2+)-sensitive channels played a greater role in more distal dendritic signaling. These data suggest that the different Ca2+ channel types participate in distinct physiological functions; low-threshold channels likely play a greater role in dendritic integration, whereas high-threshold channels are more important for somatic Ca(2+)-dependent processes.
Long-term depression of naive synapses in adult hippocampus induced by asynchronous synaptic activity
Authors: Otani S. , Connor J. A.
Published: December 2017

1. Two independent Schaffer collateral pathways converging to the same pyramidal cell were alternately stimulated by 2-Hz trains (900 pulses) offset by a 150-ms interval in adult rat hippocampal slices. The second input underwent an immediate and persistent long-term depression (LTD). Depression in the first input was smaller than the second input. A narrower interpulse interval (20 ms) failed to induce LTD in either input. 2. Neither the N-methyl-D-aspartate receptor antagonist DL-2-amino-5-phosphonovaleric acid nor the metabotropic glutamate receptor antagonist (+)-alpha-methyl-4-carboxylphenyl-glycine blocked this associative LTD. However, coapplication of these two antagonists blocked LTD. 3. Associative LTD was blocked by prior injection of the Ca2+ chelator bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid into the postsynaptic cell and by bath-applied L-NG-nitroarginine, a nitric oxide synthesis inhibitor. 4. We propose that temporally confined, asynchronous synaptic activity weakens the efficacy of naive synapses in slices from the adult hippocampus.
Motor neuronal control of tail-directed and head-directed siphon responses in Aplysia californica
Authors: Hickie C. , Walters E. T.
Published: December 2017

1. Cutaneous stimulation of opposite ends of the body causes qualitatively different siphon responses: tail stimulation causes flaring and backward bending (the siphon T response), whereas head stimulation causes constriction and slight anterior bending (the siphon H response). This paper characterizes the motor neuronal control of siphon T and siphon H responses. 2. The siphon response to tail nerve (p9) shock in a semi-intact preparation was indistinguishable from the siphon T response in intact or parapodectomized animals. Similarly, the siphon response to head nerve (c2) shock in this preparation was indistinguishable from the siphon H response in intact or parapodectomized animals. 3. Central siphon motor neurons (SMNs) were found to cause a wider variety of movements than previously reported. The movements produced by the LFSB cells strongly resemble the flaring response of the siphon to tail or tail nerve stimulation. The movements produced by RDS and LDS1 resemble components of the constricting response of the siphon to head or head nerve stimulation. 4. Among central SMNs, the LFSB cells show the strongest activation by posterior stimulation, whereas RDS and LDS1 show the strongest activation by anterior stimulation. The LFSA cells, which produce much weaker siphon constriction, are only activated slightly by posterior stimulation and are inhibited by anterior stimulation. Peripheral SMNs are inhibited by stimulation of head and tail nerves, and thus their activity does not directly contribute to siphon T and H responses. 5. Artificially activating central SMNs with the pattern of activity previously exhibited after tail or head nerve stimulation indicated the sufficiency of the LFSB cells for the siphon T response, and of RDS and LDS1 for the siphon H response. 6. Dramatic behavioral deficits produced by hyperpolarizing the LFSB cells during tail nerve stimulation, or by hyperpolarizing RDS and LDS1 during head nerve stimulation, indicated the necessity of these cells for the expression of directed siphon responses to tail or head stimulation, respectively. 7. Because of their apparent necessity and sufficiency for directional siphon responses to anterior and posterior stimulation, these few cells provide well-defined vantage points for studying neural mechanisms underlying the motor control and transformation of siphon responses. The four LFSB cells offer a special advantage for cellular analysis because they form a homogeneous functional unit in which any sampled LFSB cell can be used as a precise monitor of the total motor output underlying the siphon T response.(ABSTRACT TRUNCATED AT 400 WORDS)
Discharge patterns of hippocampal theta-related cells in the caudal diencephalon of the urethan-anesthetized rat
Authors: Bland B. H. , Konopacki J. , Kirk I. J. , Oddie S. D. , Dickson C. T.
Published: December 2017

1. Single-unit discharge patterns of cells in specific nuclei of the caudal diencephalon were characterized in relation to simultaneously recorded field activity from the stratum moleculare of the dentate gyrus according to the criteria that have been used previously to classify cells in the hippocampal formation (including entorhinal cortex), medial septum, and cingulate cortex. Theta (theta)-related cells were classified as 1) tonic theta-ON, if they discharged nonrhythmically and increased their discharge rates during hippocampal theta relative to large, irregular hippocampal field activity (LIA); 2) tonic theta-OFF, if they discharged nonrhythmically and decreased their discharge rates during theta relative to LIA; or 3) phasic theta-ON, if they discharged rhythmically and in phase with ongoing theta, but nonrhythmically during LIA. Cells not meeting any of the above criteria were classified as nonrelated. 2. Recordings were obtained in a total of 127 cells from the caudal diencephalon. Recordings were made in 54 cells from the posterior hypothalamic nucleus (PH), 16 from the supramammillary nucleus (SuM), 20 from the PH/SuM border, and 23 from the medial mammillary nucleus (MM). Recordings were also made from nine cells from the central medial nucleus of the thalamus (CM) and five from the dorsomedial hypothalamic nucleus (DMH). 3. Of the 54 PH cells, 43 (80%) were classified as tonic theta-ON and 11 (20%) as nonrelated. Tonic theta-ON cells in the PH discharged at significantly higher rates during theta, either occurring spontaneously (9.6 +/- 1.7 Hz, mean +/- SE) or elicited with a tail pinch (TP theta; 10.6 +/- 1.9 Hz), than during LIA (3.6 +/- 1.4 Hz). Of the nine CM cells, seven (78%) were tonic theta-ON and two (22%) were nonrelated. Tonic theta-ON cells discharged at significantly higher rates during theta (17.5 +/- 7.8 Hz) or TP theta (18.0 +/- 7.1 Hz) than during LIA (7.3 +/- 4.8 Hz). All DMH cells were nonrelated. 4. Of the 20 PH/SuM border cells, 15 (75%) were classified as tonic theta-OFF and discharged at significantly higher rates during LIA (5.3 +/- 1.5 Hz) than during theta (0.8 +/- 0.4 Hz) or TP theta (0.4 +/- 0.3 Hz). Five (25%) cells in the PH/SuM border were nonrelated. 5. All of the 16 cells (100%) recorded from the body of the SuM were phasic theta-ON. The discharge rates of these cells did not change significantly across hippocampal field states (LIA = 8.3 +/- 1.6; theta = 7.3 +/- 1.6; TP theta = 8.6 +/- 1.7 Hz).(ABSTRACT TRUNCATED AT 400 WORDS)
NMDA-induced burst discharge in guinea pig trigeminal motoneurons in vitro
Authors: Kim Y. I. , Chandler S. H.
Published: December 2017

1. The responses of guinea pig trigeminal motoneurons (TMNs) to N-methyl-D,L-aspartate (NMA) were studied using brain stem slice preparations and whole cell patch-clamp (n = 89) or conventional microelectrode (n = 22) recording techniques. The primary goals of this study were to determine whether N-methyl-D-aspartate (NMDA) receptor activation would produce spontaneous bursting activity in TMNs and, if so, the underlying mechanisms responsible for the generation of these bursts. 2. Bath-applied NMA (100-300 microM, n = 80) in standard perfusion medium elicited depolarization, increase in apparent input resistance (Rinp), and rhythmic burst discharges (1-90 s in duration) from TMNs. These effects were blocked by the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5, 30 microM, n = 6), but not by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5-10 microM, n = 10). Furthermore, the burst-inducing effect of NMA was not mimicked by the non-NMDA receptor agonists kainate (KA, 5-10 microM, n = 6) and (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA, 5-10 microM, n = 5). 3. In tetrodotoxin (TTX) treatment conditions (n = 13), NMA elicited depolarization, an increase in apparent Rinp, and rhythmic membrane potential oscillations without action potential bursts (i.e., plateau potentials), suggesting that the effects of NMA observed in the TTX-free condition resulted from activation of postsynaptic NMDA receptors. 4. Graded depolarization of neurons (n = 20) by intracellular direct current injection generally led to a graded increase in frequency and duration of the NMA-induced bursts and plateau potentials until these rhythmic events eventually became transformed into continuous spike discharge and maintained depolarization, respectively. Removal of Mg2+ from the perfusion medium (n = 11) also turned the bursts and plateau potentials into continuous spike discharge and maintained depolarization, respectively. 5. The effects of NMA on the current-voltage (I-V) curve after a depolarizing ramp voltage-clamp command (15-20 mV/s) were examined (n = 40). Under NMA (100-300 microM) conditions, the I-V relationship exhibited a region of negative slope conductance (NSC) between -60 and -35 mV, thus making the I-V relationship N-shaped. The NSC was abolished by AP5 (30 microM, n = 8), but not by CNQX (5-10 microM, n = 6). The I-V relationship in AMPA (3-10 microM, n = 5) or KA (3-10 microM, n = 5) was almost linear between -80 and -30 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Prolonged GABA responses in dentate granule cells in slices isolated from patients with temporal lobe sclerosis
Authors: Williamson A. , Telfeian A. E. , Spencer D. D.
Published: December 2017

1. Medial temporal lobe sclerosis is a common pathological finding in patients with medically intractable temporal lobe epilepsy. This disease is characterized by extensive cell loss in the hilus and the hippocampal CA1 and CA3 cell fields in addition to synaptic reorganization throughout the dentate gyrus. 2. The dentate granule cells from hippocampal slices of patients diagnosed with medial temporal lobe sclerosis exhibit reduced synaptic inhibition with concommitant hyperexcitability. These physiological changes were studied relative to the hippocampi of patients with temporal lobe tumors in which the cell loss and synaptic reorganization are not seen. 3. We attempted to determine if this disinhibition was because of changes in the postsynaptic sensitivity to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) by studying the responses to exogenously applied transmitter. As in rodents, the GABA responses in human dentate granule cells studied at the resting membrane potential were depolarizing and were mediated primarily by GABAA receptors. In many cases, these depolarizing GABA responses could trigger action potentials. Thus in some situations, GABA could act as an excitatory neurotransmitter. 4. We found that GABAA receptor-mediated responses in the sclerotic hippocampi were approximately 80% longer than in the comparison population. This difference was not because of changes in either the GABA reversal potential or the GABA-induced conductance change. The data support the hypothesis that the GABA transport system is impaired in sclerotic tissue: application of the GABA uptake inhibitor NNC711 (a tiagibine derivative) greatly prolonged the GABA responses in the tumor-related temporal lobe epilepsy tissue, but had little effect on the sclerotic tissue.
Distributed amine modulation of graded chemical transmission in the pyloric network of the lobster stomatogastric ganglion
Authors: Johnson B. R. , Peck J. H. , Harris-Warrick R. M.
Published: December 2017

1. In the pyloric network of the lobster stomatogastric ganglion, graded synapses organize the network output. The amines dopamine (DA), serotonin, and octopamine each elicit a distinctive motor pattern from a quiescent pyloric network. We have examined the effects of these amines on the graded synaptic strengths between the six major types of neurons of this network to understand how amine modulation of synaptic strength contributes to the amine-induced motor patterns. Here we tested amine affects at 10 different graded chemical synapses of the pyloric network. We show that each amine has a statistically different spectrum of distributed effects across the network synapses. 2. Under our control conditions (isolated pairs of neurons, removal of modulatory input), most of the graded chemical synapses were weak and some synapses were nonfunctional. The output synapses of the ventricular dilator (VD) neuron were significantly stronger than the other synapses. 3. DA altered the synaptic strength of every graded chemical synapse. This amine strengthened the weak chemical output synapses of the anterior burster (AB), lateral pyloric (LP), and pyloric constrictor (PY) neurons and weakened (and in some cases abolished) the strong chemical output synapses of the VD neuron. The AB-->inferior cardiac neuron (IC) and PY-->IC graded chemical synapses were nonfunctional under our control conditions; DA activated these silent synapses. 4. Serotonin enhanced the AB's output chemical synapses but weakened all the other graded chemical synapses examined. Octopamine's effects were much weaker than those of the other two amines. It enhanced the AB-->LP synapse and the LP's output synapses and weakly strengthened the AB-->PY, VD-->LP, and VD-->PY synapses. 5. The amines alter the input resistance of many of the pyloric neurons, and this could contribute to the observed changes in synaptic strength by altering passive current flow between input and output sites in the cells. However, the input resistance changes were relatively small compared with the changes in synaptic strength and cannot alone account for the synaptic modulation. In some cases the sign of the input resistance change was inconsistent with the change in synaptic strength. Thus the amines appear to modify synaptic transmission directly in this system. 6. This study completes our description of amine effects on all the graded synapses of the pyloric network. We summarize our present and earlier work to show that modulators can reconfigure the entire synaptic organization of a neural network by acting at many distributed synaptic sites.(ABSTRACT TRUNCATED AT 400 WORDS)
Directional variation of spatial and temporal characteristics of limb movements made by monkeys in a two-dimensional work space
Authors: Turner R. S. , Owens J. W. , Anderson M. E.
Published: December 2017

1. The directional variation of kinematic and electromyographic (EMG) characteristics of two-joint arm movements made to targets in a two-dimensional work space was studied in monkeys trained to make targeted arm movements under different behavioral conditions. 2. In each animal, kinematic measures of movement (movement amplitude, movement time, peak velocity, and trajectory curvature) and endpoint spatial position within the target zone varied as a function of the direction of the target from the starting position. Movements made toward the body into the ipsilateral hemispace generally had the smallest amplitude, lowest peak velocity, and longest movement time. 3. Although the directional variation in peak velocity could partially be accounted for by predicted anisotropies in the inertial load imposed by the arm, deviations from these predictions suggest that movement amplitude is controlled more rigorously by the CNS. Adjustments in movement time may be used to compensate for inertial anisotropies. 4. The spatial characteristics of movements (amplitude, trajectory curvature, or endpoint error) were influenced little by the visibility of the target during movement, the advanced knowledge of target location, or the presence or absence of an external trigger cue. However, temporal characteristics (movement time, peak velocity, and for some animals, reaction time) varied more as sensory cues were changed. 5. The time of initial EMG activity in muscles acting around the shoulder varied systematically as a function of target direction. A cosine model accounted for a large fraction of the variability in initial onset time, as determined in a trial-by-trial analysis. The amplitude of the EMG activity was more narrowly tuned, however. Muscles acting at the elbow showed less activity and more variable directional tuning. 6. We conclude that directional variations in the kinematic characteristics of movement, and thus, the dynamic force requirements of the task, must be taken into consideration as contributors to the apparent directional coding described for neuronal populations in different portions of the CNS.
Covert orienting of attention in macaques. III. Contributions of the superior colliculus
Authors: Robinson D. L. , Kertzman C.
Published: December 2017

1. The present experiments were conducted to study physiological mechanisms in the superior colliculus and their relation to visual spatial attention. We used a cued reaction time task studied in detail previously (Bowman et al. 1993; Posner 1980). Monkeys learned to fixate a spot of light and release a bar when a target light appeared. Cues on the same side as the target (valid cue) were associated with faster reaction times than those on the opposite side (invalid cue). The difference in reaction times is hypothesized to be a measure of attention. 2. A total of 79 neurons within the superficial layers of the superior colliculi of two monkeys were studied. When the cues and targets were positioned so that both were within the visual receptive field, the cues excited the cells, and this produced a refractoriness to the targets for the following 400 ms. Both the ON and OFF responses to the cue were constant under all conditions. 3. These neurons were also tested with the cue just outside of the visual receptive field. This was done to avoid refractory effects from the cue; there was no significant modulation of the response to the target under these conditions. The visual responses of neurons in the intermediate layers of the superior colliculus also responded equivalently under these conditions. 4. When the activity of cells within the foveal representation was compared during the performance of three tasks, there was differential activity. The appearance of the fixation point during the performance of the cued reaction time task led to a strong, transient discharge.(ABSTRACT TRUNCATED AT 250 WORDS)