bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation and propagation of epileptiform discharges in a combined entorhinal cortex/hippocampal slice
Authors: Rafiq A. , DeLorenzo R. J. , Coulter D. A.
Published: December 2017

1. The development of epileptiform discharges in response to tetanic stimulation of the Schaeffer collaterals was studied by using extracellular field potential recordings in CA1, CA3, dentate gyrus, and entorhinal cortex and intracellular recordings in CA1 neurons in rat hippocampal-parahippocampal slices, which were cut so as to maintain reciprocal connections between entorhinal cortex and hippocampus in vitro. 2. The first type of epileptiform discharge to develop was an immediate afterdischarge, which grew in duration and amplitude with repeated stimulation trains at 10-min intervals, until it plateaued after five to nine trains at 40-s duration, on average. This afterdischarge, when fully developed, consisted of an early, high frequency tonic component, followed by a later, lower frequency clonic component. Fully developed primary afterdischarges were all-or-none, in that they had a definite threshold, and varied little in amplitude or duration when activated by threshold or suprathreshold stimulation. The primary discharge could be recorded simultaneously throughout the hippocampal-parahippocampal slice, providing evidence for the intact reciprocal connections between hippocampus and entorhinal cortex. Intracellular recordings in CA1 neurons revealed that during the tonic phase of the afterdischarge, neurons were depolarized by 15-30 mV and gradually repolarized during the clonic component. 3. After full development of the primary afterdischarge, a delayed secondary epileptiform discharge began to appear after five to nine stimulation trains. This late discharge began 2-5 min after the stimulation train and progressed in amplitude and duration with repeated stimulation, in some cases to 2-3 h long self-sustained epileptiform discharges. Like the primary afterdischarge, the secondary discharge could be recorded simultaneously throughout the hippocampal-parahippocampal slice, and individual bursts comprising the secondary discharge occurred at earliest latency in the dentate gyrus, followed by activation in CA3, CA1, and finally in the entorhinal cortex. Intracellular recordings in CA1 neurons established that the secondary discharge occurred without an accompanying depolarization. Rather, it appeared as synaptic bursts developing in an escalating frequency barrage, initiated 2-5 min after the primary afterdischarge. 4. Lesioning studies were conducted to begin determining the site of origin of the secondary epileptiform discharge. After appearance of the secondary discharge, the mossy fibers were cut. This lesion abolished the secondary discharge but did not block the primary afterdischarge. Moving the stimulating electrodes from the Schaeffer collaterals to the mossy fibers proximal to the cut reestablished a truncated secondary discharge. In a second lesioning experiment, a cut was made through the subicular region of the hippocampal-parahippocampal slice before the onset of stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of aging on the intrinsic membrane properties of medial NTS neurons of Fischer-344 rats
Authors: Johnson S. M. , Felder R. B.
Published: December 2017

1. Recent studies have demonstrated that the arterial baroreflex is imparied with aging and have implicated central components of the baroreflex arc in this autonomic dysfunction. Neurons in the medial portion of the nucleus tractus solitarius (mNTS) receive a major input from the arterial baroreceptors. The present study was undertaken to characterize the intrinsic membrane properties of mNTS neurons in young rats and to test the hypothesis that these properties are altered with aging. An in vitro brain stem slice preparation was used to record intracellularly from mNTS neurons; passive membrane properties, action potential characteristics, and repetitive firing properties were examined and compared. 2. Neurons in the mNTS of young (3-5 mo old) Fischer-344 rats (F-344; n = 35) had a resting membrane potential of -57 +/- 6.9 mV (mean +/- SD), a membrane time constant of 18 +/- 9.0 ms, and an input resistance of 110 +/- 60 m omega. Action potential amplitude was 81 +/- 7.5 mV with a duration at half-height of 0.83 +/- 0.15 ms. The spontaneous firing rate in 24 cells was 4.3 +/- 2.9 Hz. The amplitude and duration of the action potential afterhyperpolarization (AHP) were 6.6 +/- 3.0 mV and 64 +/- 34 ms, respectively. All neurons expressed spike frequency adaptation, action potential AHP, and posttetanic hyperpolarization. Delayed excitation and postinhibitory rebound were present in 34 and 14% of neurons tested, respectively. Neurons from adult (10-12 mo old) F-344 rats (n = 34) were similar to the young F-344 rats with respect to all of these variables. 3. Neurons from aged (21-24 mo old) F-344 (n = 32) were similar to those from young and adult rats, but there were two potentially important differences: the mean input resistance of the aged neurons was higher (170 +/- 150 M omega), with a larger proportion (46% of aged neurons vs. 20% of young neurons and 21% of adult neurons) having input resistances > 150 M omega; and there was a tendency for a smaller percentage of aged neurons (16% of aged neurons vs. 34% of young neurons and 29% of adult neurons) to express delayed excitation. 4. The potential significance of a high input resistance was tested by comparing the steady-state current-voltage (I-V) relationships and the frequency-current (f-I) relationships among low-resistance (1-100 M omega), medium-resistance (101-200 M omega).(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibitory action of muscarinic agonists on neurons in the rat laterodorsal tegmental nucleus in vitro
Authors: Luebke J. I. , McCarley R. W. , Greene R. W.
Published: December 2017

1. The effects of the mixed cholinergic agonist carbachol and the muscarinic agonist methacholine (MCh) on neurons of the laterodorsal tegmental nucleus (LDT) were studied with the use of intracellular and whole-cell patch-clamp recordings in a rat brain stem slice preparation. 2. Neurons were classified into one of two categories on the basis of their intrinsic membrane properties: those that displayed a prominent low-threshold calcium burst (LTB, 60%) and those that did not exhibit such a burst (non-LTB, 40%). 3. Neurons from which recordings were obtained were filled with biocytin, visualized with Texas-red avidin, and identified as cholinergic or noncholinergic with NADPH-diaphorase histochemistry. Eighty percent of the LTB neurons that were processed in this manner were cholinergic, and 60% of the non-LTB neurons were cholinergic. 4. Carbachol elicited a membrane hyperpolarization associated with a decrease in input resistance in 95% of the cells tested. Under voltage clamp this response was shown to be due to an outward current that reversed near the equilibrium potential for potassium and displayed marked inward rectification. The conductance/voltage relationship was fit to the Boltzmann equation with a mean V1/2 = -73 +/- 4 (SD) mV and a mean k value of 10 +/- 4. The carbachol-evoked current was fully blocked by extracellular barium. 5. There was no significant effect of carbachol on the transient currents IA or IT. 6. The carbachol-evoked current was mimicked by the specific muscarinic agonist methacholine and blocked by high concentrations of the muscarinic receptor antagonist pirenzepine (IC50 = 580 nM).(ABSTRACT TRUNCATED AT 250 WORDS)
Subthreshold oscillations of the membrane potential: a functional synchronizing and timing device
Authors: Lampl I. , Yarom Y.
Published: December 2017

1. Subthreshold membrane potential oscillations have been observed in different types of CNS neurons. In this in vitro study, we examined the possible role of these oscillations by analyzing the responses of neurons from the inferior olivary nucleus to a combined stimulation of sine wave and synaptic potentials. 2. A nonlinear summation of the sine wave and the synaptic potential occurred in olivary neurons; a superlinear summation occurred when the synaptic potential was elicited at the trough of the sine wave or during the rising phase. On the other hand, a less than linear summation occurred when the synaptic potentials were evoked during the falling phase of the wave. 3. Significant changes in the delay of the synaptic responses were observed. As a result of these changes, the maximum amplitude of the response occurred at the peak of the sine wave, regardless of the exact time of stimulation. The output of the neuron was therefore synchronized with the sine wave and depended only partly on the input phase. 4. These data demonstrate that neurons from the inferior olivary nucleus are capable of operating as accurate synchronizing devices. Moreover, by affecting the delay line, they act as a logic gate that ensures that the information will be added to the system only at given times.
Effects of temperature on synaptic potentials in the locust flight system
Authors: Robertson R. M.
Published: December 2017

1. Neuronal circuitry in the locust flight system operates normally within a temperature range of 24-42 degrees C. I investigated the effects of temperature on parameters of postsynaptic potentials generated in different neurons following action potentials of the forewing stretch receptor. 2. Increases in temperature reduced latency, time-to-peak and duration (Q10s = 0.51, 0.70, and 0.68, respectively; 24–34 degrees C) and increased the slope (Q10 = 1.13; 24-34 degrees) of the excitatory postsynaptic potential (EPSP). However, increases in temperature increased EPSP amplitude below room temperature (Q10 = 1.25; 14–24 degrees C) but decreased EPSP amplitude above room temperature (Q10 = 0.80; 24–34 degrees C). 3. I conclude that neuronal and synaptic function were affected by temperature in ways predictable by well-established thermal effects on channel conductance and kinetics and on membrane properties. Thus temperature compensation of the output of the flight system must be mediated in some way by the operation of the circuitry. 4. I propose that below room temperature EPSP amplitude was increased by predominant effects on channel conductance and membrane time constant, and above room temperature EPSP amplitude was decreased by a predominant effect on the amplitude and duration of the presynaptic action potential. Further, I suggest that the frequency of the output rhythm is unaffected by the amplitude of single EPSPs, within permissive limits.
Indirect inputs to ventral temporal cortex of monkey: the influence of unit activity of alerting auditory input, interhemispheric subcortical visual input, reward, and the behavioral response
Authors: Ringo J. L. , O'Neill S. G.
Published: December 2017

1. This study examined nonvisual and indirect inputs to 1,021 single units recorded in inferotemporal and parahippocampal cortex of behaving macaques. 2. To better isolate these influences, a fully split-brain, split-chiasm preparation was used. Extracellular single-unit activity was recorded while the ipsilateral eye was covered. During the recordings the monkeys worked on a visual discrimination task that consisted of a series of presentations of single images. 3. When the interval between presentations was varied randomly (usually between 4 and 15 s) about one-quarter of these cells responded to an alerting tone sounded 500 ms before the onset of the visual image. That this response is due to the warning value of the tone was shown by finding that an identical tone sounded at the end of each trial produced no response from these cells. Use of an exchange between pairs of light-emitting diodes as a warning signal (one turned on as the other was turned off, also 500 ms before the visual stimulus onset) produced a similar response in many units. This indicates a subcortical route for the alerting signal. In most cases, warning responses were inhibitory, often delayed with respect to the warning signal occurrence to more nearly match the image arrival time. 4. Surprisingly, and despite the monkeys' confirmed split-brain status, occasional cells (approximately 2%) showed a response from a visual presentation limited to the other hemisphere. Although this subcortical visual input was far weaker than direct visual input, it was nonetheless statistically reliable. Importantly, the indirect input was stimulus specific and could form the neural basis for a limited interhemispheric visual transfer of the sort seen in human split-brain patients. 5. Also rarely, cells showed activity time locked to the animal's behavioral response.
Excitation of lumbar motoneurons by the medial longitudinal fasciculus in the in vitro brain stem spinal cord preparation of the neonatal rat
Authors: Floeter M. K. , Lev-Tov A.
Published: December 2017

1. The excitation of lumbar motoneurons by reticulospinal axons traveling in the medial longitudinal fasciculus (MLF) was investigated in the newborn rat using intracellular recordings from lumbar motoneurons in an in vitro preparation of the brain stem and spinal cord. The tracer DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine) was introduced into the MLF of 6-day-old littermate rats that had been fixed with paraformaldehyde to evaluate the anatomic extent of this developing pathway. 2. Fibers labeled from the MLF by DiI were present in the cervical ventral and lateral white matter and a smaller number of labeled fibers extended to the lumbar enlargement. Patches of sparse terminal labeling were seen in the lumbar ventral gray. 3. In the in vitro preparation of the brain stem and spinal cord, MLF stimulation excited motoneurons through long-latency pathways in most motoneurons and through both short-(< 40 ms) and long-latency connections in 16 of 40 motoneurons studied. Short- and longer-latency components of the excitatory response were evaluated using mephenesin to reduce activity in polysynaptic pathways. 4. Paired-pulse stimulation of the MLF revealed a modest temporal facilitation of the short-latency excitatory postsynaptic potential (EPSP) at short interstimulus intervals (20–200 ms). Trains of stimulation at longer interstimulus intervals (1–30 s) resulted in a depression of EPSP amplitude. The time course of the synaptic depression was compared with that found in EPSPs resulting from paired-pulse stimulation of the dorsal root and found to be comparable. 5. The short-latency MLF EPSP was reversibly blocked by 6-cyano-7-nitroquinoxaline (CNQX), an antagonist of non-N-methyl-D-aspartate glutamate receptors, with a small CNQX-resistant component. Longer-latency components of the MLF EPSP were also blocked by CNQX, and some late components of the PSP were sensitive to strychnine. MLF activation of multiple polysynaptic pathways in the spinal cord is discussed.
Neural activity in the monkey anterior ventrolateral thalamus during trained, ballistic movements
Authors: Forlano L. M. , Horne M. K. , Butler E. G. , Finkelstein D.
Published: December 2017

1. To examine the role of the anterior ventrolateral thalamic nucleus (VLa) in motor control, extracellular single-cell recordings were made from the VLa nucleus in three conscious monkeys performing visually triggered, rapid movements requiring flexion and extension of the wrist joint. The movement paradigms consisted of three components: an initial hold period, a ballistic movement, and a final hold period. 2. Cerebellar nuclear stimulation was used to physiologically identify thalamic neurons receiving input from the cerebellum. Neurons subsequently confirmed histologically as lying within the VLa nucleus were located anterior to those “driven” by cerebellar stimulation. 3. The activities of 261 VLa neurons displaying movement-related behavior were examined. In the absence of movement, the activity of these neurons ranged from 5 to 80 spikes/s, the majority of cells (222/261; 85%) firing between 10 and 30 spikes/s. Neural activity was not influenced by afferent input from skin, joint, or muscle but altered markedly when the animal engaged in active movement. 4. The relationship between neural activity and movement at a specific joint was determined in 189 of the 261 neurons. The majority of these neurons (161/189; 85%) modulated their activity in response to movement confined to a single joint; the remaining neurons displayed multijoint motor responses, their activity being best related to a motor act, such as grasping, reaching, or feeding. There was no clear segregation in the representation of body parts in the VLa nucleus to suggest the presence of clearly defined somatotopy. 5. The activities of wrist-related neurons (45 of the 261) were examined to determine the motor characteristics of the VLa nucleus. Three distinctive activity patterns were exhibited by these neurons during the performance of the movement paradigms: 1) a phasic burst of < 300 ms in duration (34/45; 76%); 2) a sustained change in neural activity lasting > 300 ms (typically up to 1,000 ms; 4/45; 9%); and 3) both a phasic and a sustained response, the sustained response occurring either prior or subsequent to the phasic response (7/45; 15%). 6. The movement-related activity of the wrist-related neurons occurred late, 52% firing after the onset of the forearm electromyogram (EMG). In 47% of the neurons, discharge rate was related to movement direction and, in a smaller proportion (13%), joint position. No relationship was found between neural activity patterns and amplitude of movement or velocity of movement. (ABSTRACT TRUNCATED AT 400 WORDS)
Statistical analysis of neural organization
Authors: Erickson R. P. , Rodgers J. L. , Sarle W. S.
Published: December 2017

1. The responses of 32 taste neurons in the solitary nucleus of the rat to 12 stimuli were analyzed with multidimensional scaling (MDS) and cluster analysis (CA) procedures. These analyses of empirical taste data were compared with similar analyses of two model data sets of known configuration to help clarify the implications of these methods commonly used in forming conclusions about the organization of the taste system. 2. To relate to possible conclusions about groupings in taste, both model data sets were chosen as the best possible examples of ungrouped data, the first being completely regular (in the form of a checkerboard) across the taste space, the second randomly arranged. The analysis of the present empirical data appear to be similar to the present ungrouped models, more so the random than the regular model, in the sense that all are amenable to grouping. 3. Because of the similarity of these model MDS and CA solutions to the present empirical solutions and to most published analyses of this sort, the idea is suggested that the appearance of the plots per se for empirical data does not support the conclusion of grouping. And, technically, MDS and CA do not have the statistical power to provide conclusions about issues of neural organization. 4. MDS and CA analyses have two very powerful roles relating to their ability to disclose the hidden organization of complex data sets; they may lend support for or refute theories about the data sets developed from other considerations, and may help generate theories for further consideration. The question of groupings is only one of many such issues. 5. Because data in the present and other reports are quite adequately accounted by MDS solutions of low dimensionality, it is suggested that their organization is characterized as continuous (i.e., rather than belonging to several disjoint spaces). 6. The use of correlations as distance measures in MDS and CA procedures distorts the spatial solutions, making analysis by visual inspection misleading. For example, using correlations, the true or natural spatial arrangements of data sets are probably less circular or spherical than shown in published MDS solutions. Also they are probably more evenly distributed across the space in the sense that the points are actually more concentrated toward the centers of the spaces; this may have strong influences on interpretations of the general form of the solutions. CA solutions can be influenced in analogous fashion. These problems of distortion of the solutions can be avoided with use of direct, linear estimates of distances. (ABSTRACT TRUNCATED AT 400 WORDS)
Activity of neuromuscular compartments in lateral gastrocnemius evoked by postural corrections during stance
Authors: Dunbar D. C. , Macpherson J. M.
Published: December 2017

1. The electromyographic (EMG) activity of the four neuromuscular compartments in lateral gastrocnemius (LG) of cats was investigated to determine whether these intramuscular subdivisions could be activated differentially during automatic postural corrections. EMG electrodes were surgically implanted into each of the four compartments of left LG-LG1, LG2, LG3, and LGm--in two cats. Electrodes were also implanted into soleus and gluteus medius for comparative purposes. 2. Quiet quadrupedal stance was disturbed first by linearly translating the cats on a movable platform in each of 16 different horizontal directions. Mechanical events during corrections were characterized in terms of the three-dimensional forces exerted by each paw on the platform. EMG and force traces were quantified (area under the curve) and normalized, and tuning curves were constructed that relate muscle response and force change to direction of platform movement. 3. In a second series of trials, translations were presented along one direction only over a series of six velocities ranging from 5 to 16 cm/s. The third series of perturbations, termed the pop-up, consisted of a rapid upward displacement of the support under the left hindlimb only over a series of six amplitudes ranging from 1 to 10 mm. Evoked EMG activity and average change in force were normalized and regressions were computed onto velocity and amplitude, respectively. The slopes of the regressions were compared. 4. EMG tuning curves associated with the multidirectional horizontal translations revealed no differential activity across LG compartments. Similarly, there was no statistical difference among the slopes of the regressions within LG. In contrast, soleus exhibited significantly different slopes from LG for the regressions. Thus it is concluded that LG compartments are not differentially activated during automatic postural responses to perturbations of the support surface.
Morphology of A beta hair follicle afferent collaterals in dorsal horn of cats with neonatal chronic denervation of digits
Authors: Wilson P. , Snow P. J.
Published: December 2017

1. The effect of neonatal denervation of two adjacent hindpaw digits (digits 3 and 4) in the cat on the morphology of spinal collaterals of identified A beta hair follicle afferents (HFAs) with receptive fields (RFs) on the neighbouring digits has been investigated using intra-axonal injection of horseradish peroxidase. 2. The morphology of collaterals of HFAs innervating intact digits (digit 2 or digit 5) was examined within the neonatally and chronically deprived region of dorsal horn by selectively injecting the afferents directly over this region. 3. Of a total of nine injected axons, seven had RFs on the distal part of digit 2, whereas two had RFs on the distal part of digit 5. With the exception of one of the digit 5 afferents, all injected afferents gave rise to stained collaterals throughout the chronically deprived digit representation. 4. Many collaterals within the chronically deprived region of dorsal horn gave rise to arborizations having relatively large numbers of boutons when compared with previously described somatotopically inappropriate (SIA) collaterals in the normal adult cat. 5. It is suggested that neonatal denervation of digits in the cat may lead to collateral sprouting and bouton formation by SIA collaterals of A beta HFAs innervating adjacent intact digits. This morphological plasticity could explain the previously reported functional reorganization of the RFs of spinocervical tract neurons that occurs in these neonatally deafferented animals.
Differential activation and classification of cutaneous afferents in the rat
Authors: Leem J. W. , Willis W. D. , Weller S. C. , Chung J. M.
Published: December 2017

1. A total of 312 cutaneous afferent units identified in the rat foot as belonging to one of nine major types of sensory receptors were included in the present study. A natural stimulus set was defined to differentiate optimally among those receptor types according to the distinguishing response patterns that it produced. It included air puffs, 30- and 300-Hz sinusoids, 200-mN force indentation of the skin, 1.2- and 6-N compressions of a skin fold, cooling the skin by 5 and 20 degrees C, warming by 5 degrees C, and heating by 15 degrees C. 2. The responses to predefined stimuli of 188 units were subjected to multivariate statistical analyses. The responses of an individual unit were measured as the number of impulses evoked by 10 stimuli, each lasting 10 s. Additionally, the number of impulses occurring for 5 s after withdrawal of a 200-mN indentation (1 of the 10 stimuli) was counted. 3. In discriminant analysis, the 11 stimulus variables predicted fairly correctly the grouping of afferent units into nine predetermined receptor categories (175 of 188, 93.1%), indicating a powerful ability to discriminate among different receptor types. Using hierarchical cluster analysis, afferent unit data described by 11 variables were divided into clusters that well represented prior receptor categories (170 of 188, 90.4%), suggesting the reliable application of this procedure to the classification of newly recorded cutaneous sensory receptors. 4. Eleven variables were then reduced to 7 on the basis of the results of factor analysis (95% of variance accounted for). The seven variables corresponded to 1.2-N compression, heating the skin by 15 degrees C, cooling the skin by 20 degrees C, 30- and 300-Hz sinusoids, withdrawal of a 200-mN indentation, and air puffs. 5. The seven selected variables correctly assigned afferent units into five modality-based categories in the discriminant solution (177 of 188, 94.1%). In the cluster solution, afferent units described by the seven selected variables were divided into clusters, most of whose members were modality specific (176 of 188, 93.6%). 6. The results indicate that cutaneous receptors can be divided into modality-specific groups according to similarities in their responses to seven stimulus variables. It is proposed that the stimulus set developed here and multivariate statistical methods can be used as powerful tools for the functional classification of central somatosensory neurons.
Sensorimotor transformation in the cat's vestibuloocular reflex system. I. Neuronal signals coding spatial coordination of compensatory eye movements
Authors: Graf W. , Baker J. , Peterson B. W.
Published: December 2017

1. Coordinate transformation between vestibular and oculomotor reference frames is required to produce compensatory, vestibuloocular reflex (VOR) eye movements in view of the differing, although similar, peripheral three-dimensional geometry of the semicircular canals and the extraocular muscles. This transformation requires convergence of canal-specific signals at some level in the VOR arc. 2. To investigate the networks that underlie the transformation between oculomotor and vestibular reference frames for spatial coordination of compensatory eye movements, we recorded intracellularly in decerebrate cats from 93 identified second-order vestibulooculomotor and abducens internuclear neurons in the medial longitudinal fasciculus (MLF) between abducens and trochlear nuclei and characterized their spatial response properties. Neurons were classified according to whether they were activated from the labyrinth ipsi- or contralateral to the recording site and according to the canal from which they received their strongest input. Our data revealed neurons that carried single- and multiple-canal signals. 3. Twenty-two neurons received their primary input from the ipsi- or contralateral anterior canal (AC). Ten nonconvergent AC neurons responded maximally to rotation in a plane within 10 degrees of the AC plane, whereas 6 AC neurons received sufficient convergent input from the orthogonal vertical canals to shift their plane of maximum response > 10 degrees from the AC plane. Of 29 ipsi- and contralateral posterior canal (PC) neurons, 9 were non-convergent, whereas 13 received sufficient convergent input from the orthogonal vertical canals to shift their response plane > 10 degrees from the PC plane. The rotational responses of 6 AC and 12 PC neurons indicated that they received convergent input from the horizontal canals. However, when these responses were averaged, the horizontal responses tended to cancel, leaving little net population response to horizontal rotation. We also encountered 19 ascending axons of second-order neurons activated primarily from the horizontal canals. Nine of these received significant input from the vertical canals, but the mean population response was within 4 degrees of the horizontal canal plane. 4. Our results demonstrate single canal responses and specific canal-canal convergence within the population of vertical vestibulooculomotor neurons. This convergence is thought to participate in the coordinate transformation within the specific geometry of the VOR system. The data indicate response shifts of a population of AC neurons toward the plane of the inferior oblique muscle, and of a population of PC neurons toward the plane of the superior oblique muscle. Conspicuously absent are neurons that fall into the plane of either the superior rectus or the inferior rectus muscles. (ABSTRACT TRUNCATED AT 400 WORDS)
Spatial distribution of Ca2+ influx in turtle Purkinje cell dendrites in vitro: role of a transient outward current
Authors: Midtgaard J. , Lasser-Ross N. , Ross W. N.
Published: December 2017

1. Intracellular recordings were made from Purkinje cells in a slice preparation of the turtle cerebellum. Simultaneously, changes in [Ca2+]i in all regions of the cell were detected with high-speed fluorescence imaging of injected fura-2. Cells were stimulated either intrasomatically or synaptically. In addition, the cells were polarized locally with an external electrical field aligned parallel to the soma-dendritic axis. 2. The soma, smooth dendrites, and spiny dendrites displayed voltage-dependent changes in [Ca2+]i. Changes in the somatic region were correlated with Na+ spike firing and local depolarization. Small [Ca2+]i changes in the spiny dendrites were correlated with graded potentials and larger changes with Ca2+ action potentials. Individual Ca2+ spike transients sometimes occurred separately in different dendritic regions demonstrating localized firing. 3. The amplitude and spatial extent of spike-related [Ca2+]i transients were increased with intrasomatic depolarizing prestimulus membrane potentials and reduced by hyperpolarizing prestimulus potentials. This dependence and the latency to Ca2+ spike activation were strongly reduced by 4-aminopyridine (4-AP). These results suggest that a transient A-like current regulates the generation of Ca2+ spikes and the localization of Ca2+ influx in turtle Purkinje cell dendrites. 4. Both electric field depolarization and intrasomatic depolarization affected the generation of Ca2+ spikes and [Ca2+]i signals in a similar manner. Strong field stimulation could evoke focal depolarization at the tips of the spiny dendrites and cause local Ca2+ spike generation near the pial surface. When both stimuli were used, their effects were additive. 5. Climbing fiber (CF) or parallel fiber (PF) stimulation were associated with the generation of dendritic Ca2+ transients. In some experiments the PF-induced Ca2+ transients were confined to a small part of the spiny dendrites. The spatial distribution and the amplitude of these transients were influenced by somatic depolarization or field stimulation in a manner similar to their effect on directly evoked Ca2+ spikes and consistent with the involvement of a transient outward current in the control of the synaptically induced Ca2+ influx. 6. These results suggest that the intrinsic potassium conductances dynamically modulate spatial integration and influence the compartmentalization of Ca2+ spikes and [Ca2+]i changes in the dendrites.
Precision and variability of hindlimb representation in cat dorsal horn and implications for tactile localization
Authors: Koerber H. R. , Hobbs G. , Brown P. B.
Published: December 2017

1. One hundred fifty-eight cells were recorded extracellularly in rows of tracks spanning both left and right dorsal horns, at segmental boundaries and midsegment in segments L5-S1, in six anesthetized cats. For each cell the low-threshold cutaneous mechano-receptive field was determined with the use of hand-held probes, and the recording site was marked with a microlesion. Recording sites were reconstructed, and the mediolateral (ML) and rostrocaudal (RC) locations of each cell were recorded along with the location of the cell's receptive field, expressed as distance from tips of toes (D). 2. Ninety-five percent of pairs of cells recorded from bilaterally symmetric locations (+/- 10%) in the same animal had receptive fields on opposite legs that had components that were mirror symmetric. Only 42% of cell pairs deviating from bilateral symmetry by approximately +/- 240 microns had receptive fields with overlapping components. This indicated that there was a substantial bilateral symmetry that was not simply due to large receptive fields. 3. The trajectories of receptive fields of cells in a single row of tracks were plotted in order of mediolateral recording site, going from medial to lateral, combining both sides. These trajectories followed a distoproximal course on the leg. Of 144 adjacent cells used to plot these trajectories, with an average spacing of approximately 120 microns, only 6 reversals of the distoproximal gradient polarity were observed within animals. 4. Data from individual animals were shifted rostrally and caudally, to obtain best agreement of mediolateral somatotopic gradients with the combined data from the other animals in the sample. Best agreement was obtained with shifts ranging from 0.3 segment rostral to 0.4 segment caudal, with an average absolute value shift of 0.22 segment. 5. By comparing cell pairs within the same dorsal horn, on opposite sides of the same animal, and across animals, variability in cell placement given the average map and the receptive field could be calculated. Interanimal variability and bilateral asymmetry were approximately +/- 60 microns, and within-dorsal horn variability was approximately +/- 35 microns. The interanimal variability is equivalent to a variability of distoproximal receptive-field location on the leg of +/- 13 mm, with a smaller variability in areas of high magnification (e.g., the toes), and a larger variability in areas with small magnification (e.g., the thigh). This degree of variability is consistent with the ability of animals with transected dorsal columns to localize tactile stimuli with a normal degree of precision.
Role of synaptic excitation in the generation of bursting-induced epileptiform potentials in the endopiriform nucleus and piriform cortex
Authors: Hoffman W. H. , Haberly L. B.
Published: December 2017

1. The mechanism of generation of epileptiform excitatory postsynaptic potentials (e-EPSPs) induced by bursting activity in vitro was examined in slices of piriform cortex. 2. Previous study revealed that e-EPSPs in piriform cortex are generated in the subjacent endopiriform nucleus, perhaps with a contribution from the claustrum and deep part of layer III of piriform cortex. A puzzling feature of these e-EPSPs was their abrupt origin at long latency with little sign of preceding abnormal activity. 3. Systematic mapping revealed that within spatially restricted regions of the endopiriform nucleus there is an irregular buildup in extracellularly recorded multiunit activity and intracellularly recorded depolarization that precedes the onset of e-EPSPs. Analysis of latency revealed that these “slow-onset” e-EPSPs precede the more widely distributed “abrupt-onset” e-EPSPs, suggesting that they occur at sites of initiation. 4. The hypothesis was tested that the buildup associated with slow-onset e-EPSPs is dependent on synaptically mediated excitation. According to this hypothesis, all-or-none e-EPSPs originate when mutually excitatory (positive feedback) interactions within a population of cells in the endopiriform nucleus become self-regenerative. 5. Predictions from the regenerative positive feedback hypothesis that were successfully verified include the presence of excitatory synaptic connections between cells in the endopiriform nucleus; the consistent prediction of a subsequent e-EPSP from the occurrence of the accelerating buildup in population activity; the occurrence of inhibitory postsynaptic potentials (IPSPs) together with EPSPs during the buildup period; and the blockage of the buildup and e-EPSP by a low concentration of a specific excitatory amino acid antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). 6. Blockage of e-EPSPs by a concentration of DNQX that was much less than that required to block monosynaptic EPSPs in the endopiriform nucleus indicates that synaptic reverberation is mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) type excitatory amino acid receptors. 7. D-2-amino-5-phosphonovaleric acid (D-APV) reduced the duration and amplitude of e-EPSPs but did not block their occurrence, indicating that N-methyl-D-aspartate (NMDA) receptors have a boosting effect on e-EPSPs but are not required for their generation. This is in contrast to the induction of e-EPSPs by bursting activity for which NMDA receptor activation is required. 8. Outside the region of initiation e-EPSPs propagated through the endopiriform nucleus at a velocity of 0.1 m/s.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of pigeon vestibulocerebellar neurons to optokinetic stimulation. I. Functional organization of neurons discriminating between translational and rotational visual flow
Authors: Wylie D. R. , Kripalani T. , Frost B. J.
Published: December 2017

1. Extracellular recordings were made from 235 neurons in the vestibulocerebellum (VbC), including the flocculus (lateral VbC), nodulus (folium X), and ventral uvula (ventral folium IXc,d), of the anesthetized pigeon, in response to an optokinetic stimulus. 2. The optokinetic stimuli consisted of two black and white random-dot patterns that were back-projected onto two large tangent screens. The screens were oriented parallel to each other and placed on either side of the bird's head. The resultant stimulus covered the central 100 degrees x 100 degrees of each hemifield. The directional tuning characteristics of each unit were assessed by moving the largefield stimulus in 12 different directions, 30 degrees apart. The directional tuning curves were performed monocularly or binocularly. The binocular directional tuning curves were performed with the direction of motion the same in both eyes (in-phase; e.g., ipsi = upward, contra = upward) or with the direction of motion opposite in either eye (antiphase; e.g., ipsi = upward, contra = downward). 3. Mossy fiber units (n = 17) found throughout folia IXa,b and IXc,d had monocular receptive fields and exhibited direction selectivity in response to stimulation of either the ipsilateral (n = 12) or contralateral (n = 5) eye. None had binocular receptive fields. 4. The complex spike (CS) activity of 218 Purkinje cells in folia IXc,d and X exhibited direction selectivity in response to the large-field visual stimulus moving in one or both visual fields. Ninety-one percent of the cells had binocular receptive fields that could be classified into four groups: descent neurons (n = 112) preferred upward motion in both eyes; ascent neurons (n = 14) preferred downward motion in both eyes; roll neurons (n = 33) preferred upward and downward motion in the ipsilateral and contralateral eyes, respectively; and yaw neurons (n = 40) preferred forward and backward motion in the ipsilateral and contralateral eyes, respectively. Within all groups, most neurons (70%) showed an ipsilateral dominance. 5. For most binocular neurons (91%), the maximum depth of modulation occurred with simultaneous stimulation of both eyes, compared with monocular stimulation of the dominant eye alone. For the translation neurons (descent and ascent), binocular inphase stimulation produced the maximum depth of modulation, whereas for the rotation neurons (roll and yaw), binocular antiphase stimulation produced the maximum depth of modulation. 6. There was a clear functional segregation of the translation and rotation neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Characteristics and postnatal development of a hyperpolarization-activated inward current in rat hypoglossal motoneurons in vitro
Authors: Bayliss D. A. , Viana F. , Bellingham M. C. , Berger A. J.
Published: December 2017

1. Single-electrode voltage clamp recordings in a rat brain stem slice preparation were used to determine the characteristics and postnatal development of a hyperpolarization-activated inward current (Ih) in hypoglossal motoneurons (HMs). 2. In young adult HMs (> P21), a noninactivating, time- and voltage-dependent inward current was evident during hyperpolarizing voltage steps to membrane potentials negative to approximately -65 mV from depolarized holding potentials [Vh = -56.2 +/- 1.0 (SE) mV]. The averaged reversal potential (Erev) of the inward current, estimated using an extrapolation procedure, was -38.8 +/- 2.9 mV (n = 5), suggesting that a mixed cationic current underlies inward rectification in HMs. 3. The voltage dependence of Ih activation was determined from tail current relaxations that followed a family of voltage steps to different membrane potentials. Normalized tail current amplitudes were well-fitted with a single Boltzman function with a half-activation at -79.8 +/- 0.7 mV and slope factor = 5.3 +/- 0.3 (n = 8). 4. Time constants of Ih activation and deactivation were voltage-dependent. Activation proceeded more quickly with larger hyperpolarizing voltage steps; time constants averaged 389, 181, and 134 ms at -69, -82, and -95 mV, respectively (n = 6). Ih deactivated during depolarizing voltage steps from hyperpolarized holding potentials. Deactivation was faster with larger depolarizing steps; time constants averaged 321, 215, and 107 ms at -80, -71, and -62 mV, respectively (n = 4). 5. Ih was sensitive to extracellular cesium but relatively insensitive to extracellular barium. The current amplitude near half-activation (approximately -84 mV) was almost completely blocked (to 11% of control) by Cs+ (3 mM, n = 3) but was reduced to only 85 and 60% in 0.5 (n = 2) and 2 mM Ba2+ (n = 3), respectively. 6. There was a marked increase in the amplitude of Ih during postnatal development of HMs. Measured near half-activation, Ih was approximately 10-fold larger in adult (> or = P21; n = 20) than in neonatal HMs (< or = P8; n = 7). Input conductance (GN) was only threefold higher in the same sample of HMs. There were no apparent differences in the voltage dependence or Erev of Ih between neonatal and older HMs. These results suggest that the increased amplitude of Ih results from an increase in Ih current density.(ABSTRACT TRUNCATED AT 400 WORDS)
Topographic patterns of responsiveness to odorants in the rat olfactory epithelium
Authors: Mackay-Sim A. , Kesteven S.
Published: December 2017

1. Regional differences in odorant-induced responsiveness of the rat olfactory epithelium were measured via electrophysiological recordings [negative component of electro-olfactogram (Veog(-)) made from the surface of the olfactory epithelium on the nasal septum]. The nasal septum provided a flat surface from which multiple recordings could be made. 2. Veog(-)s were recorded from a standardized grid of 16 sites. This grid of recording sites extended over most of the surface of the olfactory epithelium on the nasal septum. 3. Twenty-one animals were tested for their responses to seven odorants. The animals were divided into three groups, each of which was tested with two different odorants plus amyl acetate, which provided a comparison between the groups. 4. For each odorant in each animal, topographic maps of relative responsiveness were derived to test whether odorants elicited different patterns of responses in the same individual. Topographic maps of responsiveness were derived also for the animal groups to test for the generality of the form of the maps for different odorants. Response latencies were also measured for each odorant at each recording site. 5. All individuals showed different topographic patterns of responses to the three test odorants. For most odorants, the location of the most responsive site was similar in all animals. In different animals the topographic maps for the same odorant were remarkably similar. Topographic maps for the odorants were all different from one another. 6. These results are consistent with the hypothesis that odorant quality is encoded in the differential spatial distribution of receptor cells whose differences in responsiveness appear to be distributed as a continuum across the epithelium. The results establish for a mammalian species what was previously reported in amphibians. These differences are presumed to be due to differential expression of odorant receptor proteins. 7. The mean response latency was 32 ms. This period was similar for all odorants, all animals, and all recording sites and was independent of Veog(-) amplitude. It is concluded that diffusion through the mucus contributed approximately 6 ms to the latency of onset of the responses to these odorants.