bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage behavior along the irregular dendritic structure of morphologically and physiologically characterized vagal motoneurons in the guinea pig
Authors: Nitzan R. , Segev I. , Yarom Y.
Published: December 2017

1. Intracellular recordings from neurons in the dorsal motor nucleus of the vagus (vagal motoneurons, VMs) obtained in the guinea pig brain stem slice preparation were used for both horseradish peroxidase (HRP) labeling of the neurons and for measurements of their input resistance (RN) and time constant (tau 0). Based on the physiological data and on the morphological reconstruction of the labeled cells, detailed steady-state and compartmental models of VM were built and utilized to estimate the range of membrane resistivity, membrane capacitance, and cytoplasm resistivity values (Rm, Cm, and Ri, respectively) and to explore the integrative properties of these cells. 2. VMs are relatively small cells with a simple dendritic structure. Each cell has an average of 5.3 smooth (nonspiny), short (251 microns) dendrites with a low order (2) of branching. The average soma-dendritic surface area of VMs is 9,876 microns 2. 3. Electrically, VMs show remarkably linear membrane properties in the hyperpolarizing direction; they have an average RN of 67 +/- 23 (SD) M omega and a tau 0 of 9.4 +/- 4.1 ms. Several unfavorable experimental conditions precluded the possibility of faithfully recovering ("peeling") the first equalizing time constant (tau 1) and, thereby, of estimating the electrotonic length (Lpeel) of VMs. 4. Reconciling VM morphology with the measured RN and tau 0 through the models, assuming an Ri of 70 omega.cm and a spatially uniform Rm, yielded an Rm estimate of 5,250 omega.cm2 and a Cm of 1.8 microF/cm2. Peeling theoretical transients produced by these models result in an Lpeel of 1.35. Because of marked differences in the length of dendrites within a single cell, this value is larger than the maximal cable length of the dendrites and is twice as long as their average cable length. 5. The morphological and physiological data could be matched indistinguishably well if a possible soma shunt (i.e., Rm, soma less than Rm, dend) was included in the model. Although there is no unique solution for the exact model Rm, a general conclusion regarding the integrative capabilities of VM could be drawn. As long as the model is consistent with the experimental data, the average input resistance at the dendritic terminals (RT) and the steady-state central (AFT----S) and peripheral (AFS----T) attenuation factors are essentially the same in the different models. With Ri = 70 omega.cm, we calculated RT, AFS----T, and AFT----S to be, on the average, 580 M omega, 1.1, and 13, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation by a moving texture of cat area 18 neuron responses to moving bars
Authors: Gulyas B. , Spileers W. , Orban G. A.
Published: December 2017

1. The influence of a moving texture on neuronal responses to a moving bar was tested in 103 area 18 neurons of anesthetized and paralyzed cats. The texture was a two-dimensional noise pattern, the bar moved at optimal speed, and its contrast was adjusted to yield 50% of the maximum response. 2. The moving texture exerted two different but related effects: it suppressed the response of area 18 neurons to the moving bar, and it modulated the direction selectivity of parastriate neurons. These effects were strongest when the texture moved at the same speed or faster than the bar. 3. Genuine suppressive effects of the moving texture were distinguished from lack of summation between bar and texture responses. Suppressive effects of either type were observed in 75% of the area 18 cells and occurred more frequently among C family cells, velocity tuned cells, and in layer 5 than in other groups of cells. 4. The modulation of direction selectivity was distinguished from pseudomodulation because of lack of summation of bar and texture responses. The direction selectivity of 35% of the area 18 cells was modulated by the moving texture. Six different relative direction selectivity (RDS) types were observed in area 18. 5. The neurons of which direction selectivity was modulated by the moving texture occurred predominantly in layers 2-3 and 6, suggesting that they represent a further stage of processing within area 18. 6. Many (75%) area 18 cells responded to the texture moving on its own. Most of these cells respond to isolated features ("grains") in the patterns rather than to the movement of the whole pattern. Cells responding to the movement of the whole pattern were generally C family cells, and their direction selectivity was not modulated by the moving texture. 7. These results are compared with those obtained under identical experimental conditions in area 17. Although suppressive effects are similar in both areas, RDS types are differently distributed in the two areas. 8. The possible origins of the interactions and their functional significance are discussed.
Transient potassium currents in avian sensory neurons
Authors: Florio S. K. , Westbrook C. D. , Vasko M. R. , Bauer R. J. , Kenyon J. L.
Published: December 2017

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.
The 15-lipoxygenase product, 8R,15S-diHETE, stereospecifically sensitizes C-fiber mechanoheat nociceptors in hairy skin of rat
Authors: White D. M. , Basbaum A. I. , Goetzl E. J. , Levine J. D.
Published: December 2017

1. This study examined the effects of the 15-lipoxygenase product of arachidonic acid metabolism, (8R,15S)-dihydroxyicosa-(5E-9,11,13Z)tetraenoic acid (8R,15S-diHETE), on mechanical thresholds and thermal responses of saphenous nerve cutaneous C-fiber nociceptors that innervate the hairy skin of the rat hindpaw. Single C-fiber mechanoheat nociceptors (C-MH) that had von Frey hair (VFH) thresholds greater than 5 g and were activated by a noxious heat stimulus were chosen for study. We also studied the effects of prostaglandin E2 (PGE2), a cyclooxygenase product of arachidonic acid metabolism, on these nociceptors. 2. The 63 C-MHs studied had a conduction velocity of 0.82 +/- 0.03 m/s (mean +/- SE) and a mechanical threshold of 13.4 +/- 2.4 g. In a subgroup of these (n = 24), the thermal threshold was measured as (44 +/- 1 degree C) (mean +/- SE). 3. 8R,15S-diHETE produced a significant decrease in mechanical threshold of C-MHs (n = 33). The 8R,15S-diHETE-induced sensitization of C-MHs to mechanical stimuli was completely antagonized by coadministration with a stereoisomer, 8S,15S-diHETE (n = 10). 4. The mechanical threshold of C-MHs (n = 10), previously injected with the combination of 8R,15S-diHETE and 8S,15S-diHETE, was significantly reduced by a subsequent injection of PGE2. In a separate group of C-MHs (n = 7), PGE2 was co-injected with 8S,15S-diHETE, which failed to antagonize the sensitizing effect of PGE2 on mechanical threshold. 5. 8R,15S-diHETE also sensitized C-MHs (n = 9) to a thermal stimulus consisting of 37 degrees C for 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)
Neurotransmitter receptors mediating excitatory input to cells in the cat lateral geniculate nucleus. II. Nonlagged cells
Authors: Hartveit E. , Heggelund P.
Published: December 2017

1. We studied the type of receptor for excitatory amino acids (EAA) that mediates visual responses of nonlagged cells in the dorsal lateral geniculate nucleus (LGN) by recording the visual response of single cells to a stationary flashing spot before, during, and after iontophoretical application of antagonists and agonists to EAA receptors. 2. The visual response of the nonlagged cells was strongly suppressed, in a dose-dependent manner, by the specific quisqualate/kainate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). The average degree of suppression was 74%. Quisqualate enhanced the visual response. 3. Specific antagonists to the N-methyl-D-aspartate (NMDA) receptor had a weak suppressing effect on most nonlagged cells. The average degree of suppression was 22%. Measurement of such weak effects was complicated by the considerable spontaneous fluctuations of responsivity in the LGN cells. In the majority of cells where the visual response was suppressed by NMDA antagonists, the tonic response component was more strongly suppressed than the initial transient response component. The visual response was enhanced by NMDA, and this enhancement was antagonized by NMDA antagonists. 4. These findings suggest that the excitatory input from the retina to nonlagged LGN cells is mainly mediated by non-NMDA receptors. The non-NMDA receptors mediate fast EPSPs, and this can explain the fast onset and offset of the visual response of the nonlagged cells. 5. The generally small contribution from NMDA receptors to the visual response of the nonlagged cells might reflect a minor involvement of these receptors in the retinal input, or it could be related to the excitatory input to LGN from the visual cortex. 6. To study whether the expression of NMDA receptors was related to modulatory brain stem input to LGN, we examined the effects of the NMDA antagonists when the visual response was enhanced with gamma-aminobutyric acid (GABA) antagonists or acetylcholine (ACh). Neither of these pharmacologic manipulations consistently increased the relative contribution of NMDA receptors to the visual response. 7. No pharmacologic difference was found between nonlagged X- and Y-cells, or between ON- and OFF-center cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Structure-function relationships in rat brain stem subnucleus interpolaris. IX. Inputs from subnucleus caudalis
Authors: Hallas B. H. , Jacquin M. F.
Published: December 2017

1. In an accompanying paper, Jacquin et al. (1990) described the effects of cortical ablation on the receptive-field (RF) properties of neurons in spinal trigeminal (SpV) subnucleus interpolaris (SpVi). A similar ablation paradigm was used here to clarify the role of an additional source of SpVi RF modulation, the extensive projection from caudally adjacent subnucleus caudalis (SpVc). 2. Intra- and extracellular recording, electrical stimulation, and RF mapping techniques were used to study the responses and projections of 356 SpVi cells in 11 rats 58-141 days after surgical isolation of SpVc from SpVi. This was achieved by a transverse knife cut through the lateral one-half of the left medulla just caudal to the obex. Because this lesion severs trigeminal (V) primary afferents caudal to SpVi, as well as postsynaptic intersubnuclear axons traversing to and from SpVi, kainic acid was used in other animals to selectively lesion SpVc inputs to SpVi. Seven rats received kainic acid injections into SpVc 5-28 days before providing similar electrophysiological data on 300 SpVi cells. Results were compared with that of 330 cells from 9 normal adult rats. 3. Knife-cut or kainic-acid lesions did not alter the topography of SpVi cells or the RF properties of 71 ipsilateral V primary afferents. However, both types of lesions produced the same profound changes in the response character of SpVi cells. Statistically reliable increases were found in the relative percentages of cells that 1) expressed convergence from multiple receptor organs, 2) were unresponsive to mechanical stimulation of orofacial regions, 3) responded tonically to a maintained peripheral stimulus, 4) were spontaneously active, 5) were directionally sensitive, 6) responded to stimulation of body surfaces innervated by cervical primary afferents, and 7) had split RFs. 4. RFs were also reliably larger for whisker-activated local circuit and projection neurons after both types of lesions. Over one-third of this local circuit group responded to more than one whisker in both experimental groups, whereas in normals all responded to one whisker. 5. All other SpVi response indices were unchanged by SpVc lesions. The most notable negative result was a normally low percentage of cells that were responsive to nociceptive stimuli. 6. To assess whether these RF changes reflected altered collateral morphology of V primary afferents in SpVi, whisker (n = 11) and guard-hair- (n = 7) activated axons were stained with horseradish peroxidase rostral to knife-cut or kainic-acid lesions.(ABSTRACT TRUNCATED AT 400 WORDS)
Structure-function relationships in rat brain stem subnucleus interpolaris. VIII. Cortical inputs
Authors: Jacquin M. F. , Wiegand M. R. , Renehan W. E.
Published: December 2017

1. Spinal trigeminal (SpV) subnucleus interpolaris (SpVi) receives inputs from trigeminal (V) first- and second-order neurons, monoamine-containing brain stem nuclei, and somatosensory cortex. Prior studies suggest that SpVi receptive-field (RF) properties cannot be predicted solely on the basis of primary afferent inputs. To assess the cortico-V projection and its role in SpVi RFs, anatomic and electrophysiological experiments were conducted. 2. Phaseolus vulgaris leucoagglutinin (PHA-L) or wheat-germ-agglutinized horseradish peroxidase (WGA-HRP) were used as anterograde tracers to study cortico-V axons in 24 normal adult rats. Injections into SI barrel cortex-labeled pyramidal fibers that decussated at all levels of the V brain stem complex, though crossing fibers were most numerous in the pyramidal decussation and pons. A small number of axons projected to ipsilateral V brain stem subnuclei. PHA-L-labeled pyramidal fibers did not give rise to collaterals in their descent through the pons and medulla. 3. Heaviest terminal labeling occurred contralaterally and in the maxillary portion of caudalis laminae III-V. Moderately dense reaction product was seen in ventral portions of all other contralateral V brain stem subnuclei, as well as in laminae I and II of caudalis. Subnucleus oralis contained the least amount of label contralateral to the injection site. Ipsilateral projections were weak and most dense in principalis. 4. Cortico-V projections were topographic between matching whisker representations. Axons most commonly had longitudinal orientations and stringy shapes. Terminal boutons occurred at the ends of short collateral branches. Many of these collaterals were derived from axons that ascended through caudal V brian stem subnuclei after crossing in the lower medulla. 5. Cortico-V labeling was heavier in septal regions between single whisker representations. This “honeycomb-like” termination pattern was most pronounced in contralateral caudalis and SpVi and ipsilateral principalis. 6. In 13 other adult rats, right SI cortex was aspirated followed by single-unit recordings in left SpVi under pentobarbital sodium anesthesia. In 9 of these, chronic effects were evaluated by recording the responses of 346 left SpVi cells 4-55 days after the lesion. In the remaining four rats, acute effects were analyzed by recording the responses of 190 SpVi cells on the day of the lesion.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of NH4+ on reflexes in cat spinal cord
Authors: Raabe W.
Published: December 2017

1. In deeply barbiturate-anesthetized animals. NH4+ decreases spinal excitatory synaptic transmission by neuronal depolarization and subsequent block of conduction of action potentials into presynaptic terminals of low-threshold (presumably Ia-) afferents. Because barbiturates by themselves depress excitatory synaptic transmission and may have modified the effects of NH4+, this study examines the effect of NH4+ on excitatory synaptic transmission in the unanesthetized animal. 2. The effects of NH4+ on monosynaptic and polysynaptic excitatory reflexes as well as di- and polysynaptic inhibition were investigated in the spinal cord of the decerebrate and unanesthetized cat in vivo. 3. The monosynaptic excitatory reflex (MSR) elicited by muscle nerve stimulation and polysynaptic excitatory reflexes elicited by muscle (MSR-PSR) or cutaneous nerve stimulation (Cut-PSR) were recorded from the ventral roots L7 or S1. The P-wave was recorded from the cord dorsum. Di- and polysynaptic inhibition was elicited by muscle nerve stimulation and measured as decrease of the MSR. 4. Intravenous infusion of ammonium acetate (AA) decreased MSR and the monosynaptic motoneuron pool excitatory postsynaptic potential (EPSP) recorded from the ventral root (VR-EPSP). Decrease of MSR and VR-EPSP was accompanied by an increase of the intraspinal conduction time in presynaptic terminals. The maximal decrease of the MSR was preceded by a period of transient increase of the MSR and reflex discharges from previously subthreshold VR-EPSPs. 5. The effects of NH4+ on MSR and VR-EPSP are consistent with those in barbiturate-anesthetized animals and suggest that NH4+ also decreases monosynaptic excitation in unanesthetized animals by depolarization and subsequent conduction block for action potentials in presynaptic terminals. 6. Decrease of the MSR was accompanied by a decrease of the P-wave, indicating that NH4+ simultaneously decreases mono- and oligosynaptic excitatory synaptic transmission as well as presynaptic inhibition. 7. Decrease of the MSR was accompanied by increases of MSR-PSR and Cut-PSR and decreases of di- and polysynaptic postsynaptic inhibition. 8. The neuronal circuits underlying MSR-PSR and Cut-PSR include presynaptic inhibition of group I and II afferents as well as postsynaptic inhibition of motoneurons. It is suggested that increases of MSR-PSR and Cut-PSR are contributed to by decreases of pre- and postsynaptic inhibition and neuronal depolarization by NH4+. These effects increase afferent input to motoneurons, permit uncontrolled discharge of motoneurons, and initiate reflex discharges by previously subthreshold excitatory postsynaptic potentials.
Role of EPSPs in initiation of spontaneous synchronized burst firing in rat hippocampal neurons bathed in high potassium
Authors: Chamberlin N. L. , Traub R. D. , Dingledine R.
Published: December 2017

1. Spontaneous discharges that resemble interictal spikes arise in area CA3 b/c of rat hippocampal slices bathed in 8.5 mM [K+]o. Excitatory postsynaptic potentials (EPSPs) also appear at irregular intervals in these cells. The role of local synaptic excitation in burst initiation was examined with intracellular and extracellular recordings from CA3 pyramidal neurons. 2. Most (70%) EPSPs were small (less than 2 mV in amplitude), suggesting that they were the product of quantal release or were evoked by a single presynaptic action potential in another cell. It is unlikely that most EPSPs were evoked by a presynaptic burst of action potentials. Indeed, intrinsic burst firing was not prominent in CA3 b/c pyramidal cells perfused in 8.5 mM [K+]o. 3. The likelihood of occurrence and the amplitude of EPSPs were higher in the 50-ms interval just before the onset of each burst than during a similar interval 250 ms before the burst. This likely reflects increased firing probability of CA3 neurons as they emerge from the afterhyperpolarization (AHP) and conductance shunt associated with the previous burst. 4. Perfusion with 2 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a potent quisqualate receptor antagonist, decreased the frequency of EPSPs in CA3 b/c neurons from 3.6 +/- 0.9 to 0.9 +/- 0.3 (SE) Hz. Likewise, CNQX reversibly reduced the amplitude of evoked EPSPs in CA3 b/c cells. 5. Spontaneous burst firing in 8.5 mM [K+]o was abolished in 11 of 31 slices perfused with 2 microM CNQX.(ABSTRACT TRUNCATED AT 250 WORDS)
Motoneuron and muscle-unit properties after long-term direct innervation of soleus muscle by medial gastrocnemius nerve in cat
Authors: Foehring R. C. , Munson J. B.
Published: December 2017

1. This study addresses the following questions. 1) In a previous experiment, when the combined lateral gastrocnemius-soleus nerve was cross-innervated by the medial gastrocnemius (MG) nerve, was the predominance of slow muscle units in soleus muscle a result of selective routing of slow motor axons into soleus? 2) Is MG-nerve-induced conversion of soleus muscle fibers from slow to fast more complete at very long (18 mo vs. 9-11 mo) postoperative times? 3) Do MG motoneurons that cross-innervate soleus muscle recover their normal membrane electrical properties at very long postoperative times? 2. The proximal portion of approximately one-third of the MG nerve was coapted directly with the distally isolated soleus nerve. The MG muscle remained innervated by the unoperated portion of the MG nerve. At 6, 10, or 18 mos postoperative, motoneuron and/or muscle-unit properties were determined for MG motoneurons innervating MG, soleus, or neither muscle, and for axotomized soleus motoneurons. 3. In the partially denervated MG muscle, the proportions of motor units of each type were normal. This suggests that the population of MG motor axons that had been directed to the soleus nerve also contained a representative distribution of MG motoneuron types. 4. Most motor units (74%) in cross-innervated soleus (Xsoleus) were type S (based on muscle-unit contractile properties), in spite of the soleus nerve's having been cross-connected by approximately 75% fast MG motoneurons. Thus, even at very long postoperative times, slow soleus muscle units resisted conversion by fast MG motoneurons. 5. Thirty-two percent of MG motoneurons that had been cross-connected to soleus nerve elicited no measurable muscle contraction, compared with approximately 10% in previous reinnervation experiments in which the MG nerve was coapted with the MG or lateral gastrocnemius-soleus nerve. Thus MG motoneurons may be disadvantaged in their ability to innervate soleus muscle fibers. 6. It appears that at long postoperative times, those fast MG motoneurons tha had innervated large soleus muscle units had failed to convert those muscle fibers to fast types and had failed also to recover their normal motoneuron electrical properties. Conversion and recovery did occur for fast MG motoneurons that innervated small soleus muscle units and for slow MG motoneurons.
Long-term persistence of enlarged motor units in partially denervated hindlimb muscles of cats
Authors: Luff A. R. , Torkko K.
Published: December 2017

1. It was the aim of this study to determine the effect that regenerating motor axons would have on enlarged or sprouted motor units that had been established for a relatively long time. 2. The fast-twitch flexor digitorum longus (FDL) and slow-twitch soleus were partially denervated by unilateral section of the L7 ventral root in 12-wk-old kittens. After 200+ days single motor units were isolated, and their isometric contractile properties were determined. FDL units were also tested for their resistance to fatigue and categorized as fast-twitch-fatigable (FF), fast-twitch-fatigue-resistant (FR), and slow-twitch-fatigue-resistant (S). 3. It had been established previously that regenerating motor axons via L7 returned to the experimental muscles by approximately 100 days. Therefore from 100 to 200 days it was assumed that the sprouted units would be in competition with the regenerating axons. The extent of the original denervations was variable and was estimated from the contralateral side. In soleus most denervations ranged from 83 to 99%; in FDL, from 37 to 81%. 4. In both soleus and FDL there was no evidence that the motor units had sprouted to any less extent than found previously. Within some soleus muscles the largest motor units were developing substantially more force than was expected. However, determination of mean fiber cross-sectional area from muscles frozen, sectioned, and prepared for histochemical analysis showed that this was attributable to increased mean cross-sectional area of the type I fibers.(ABSTRACT TRUNCATED AT 250 WORDS)
Excitatory postsynaptic potentials in rat neocortical neurons in vitro. III. Effects of a quinoxalinedione non-NMDA receptor antagonist
Authors: Hablitz J. J. , Sutor B.
Published: December 2017

1. Intracellular microelectrodes were used to obtain recordings from neurons in layer II/III of rat frontal cortex. A bipolar electrode positioned in layer IV of the neocortex was used to evoke postsynaptic potentials. Graded series of stimulation were employed to selectively activate different classes of postsynaptic responses. The sensitivity of postsynaptic potentials and iontophoretically applied neurotransmitters to the non-N-methyl-D-asparate (NMDA) antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) was examined. 2. As reported previously, low-intensity electrical stimulation of cortical layer IV evoked short-latency early excitatory postsynaptic potentials (eEPSPs) in layer II/III neurons. CNQX reversibly antagonized eEPSPs in a dose-dependent manner. Stimulation at intensities just subthreshold for activation of inhibitory postsynaptic potentials (IPSPs) produced long-latency (10 to 40-ms) EPSPs (late EPSPs or 1EPSPs). CNQX was effective in blocking 1EPSPs. 3. With the use of stimulus intensities at or just below threshold for evoking an action potential, complex synaptic potentials consisting of EPSP-IPSP sequences were observed. Both early, Cl(-)-dependent and late, K(+)-dependent IPSPs were reduced by CNQX. This effect was reversible on washing. This disinhibition could lead to enhanced excitability in the presence of CNQX. 4. Iontophoretic application of quisqualate produced a membrane depolarization with superimposed action potentials, whereas NMDA depolarized the membrane potential and evoked bursts of action potentials. At concentrations up to 5 microM, CNQX selectively antagonized quisqualate responses. NMDA responses were reduced by 10 microM CNQX. D-Serine (0.5-2 mM), an agonist at the glycine regulatory site on the NMDA receptor, reversed the CNQX depression of NMDA responses.(ABSTRACT TRUNCATED AT 250 WORDS)
Neural mechanisms underlying the clasp-knife reflex in the cat. I. Characteristics of the reflex
Authors: Cleland C. L. , Rymer W. Z.
Published: December 2017

1. The goal of this study was to characterize the clasp-knife reflex by the use of stretch and isometric contraction of ankle extensor and flexor muscles in decerebrated cats with bilateral dorsal hemisections of their spinal cords at segment T12. 2. Stretch of an extensor muscle evoked inhibition in both homonymous and synergistic extensor muscles. The similarities between homonymous and synergistic inhibition suggest that similar neural mechanisms were responsible. 3. Homonymous and synergistic clasp-knife inhibition showed several characteristic features: 1) inhibition was evoked only by large stretches that produced significant muscle force. Short stretches that did not produce large forces evoked only excitation; 2) the magnitude of clasp-knife inhibition increased with increasing initial motor output, as reflected in the level of rectified EMG; 3) the time course of reflex inhibition evoked by ramp-and-hold stretch was characterized by segmentation of EMG during ramp stretch, dynamic overshoot of inhibition at the end-of-ramp stretch, and slow but usually complete decay of inhibition during maintained stretch; 4) inhibition persisted beyond the termination of stretch, and 5) inhibition showed adaptation to repeated stretch. 4. Isometric contraction of the soleus or medial gastrocnemius, produced by electrical stimulation of the muscle nerve, also evoked powerful synergistic-reflex inhibition via similar mechanisms as stretch-evoked, clasp-knife inhibition. Stretch evoked a greater degree of inhibition than did contraction, indicating that receptors responsive to both stretch and contraction contribute to clasp-knife inhibition. 5. The reflex effects produced by stretching the soleus or medial gastrocnemius were not confined to the homonymous and close synergistic muscles. Extensor muscles were inhibited and flexor muscles were excited throughout the hindlimb, which paralleled the pattern of a flexion-withdrawal reflex evoked by cutaneous stimulation. 6. Stretch of a flexor muscle, the tibialis anterior, evoked the same spatial pattern and time course of reflex action as stretch of an extensor muscle--inhibition of extensor muscles and excitation of flexor muscles throughout the hindlimb, including homonymous excitation of the tibialis anterior. 7. We conclude that neither Golgi tendon organs nor secondary spindle afferents are likely to contribute significantly to clasp-knife inhibition because their responses to stretch and isometric contraction differ from the reflex actions evoked by stretch and contraction.(ABSTRACT TRUNCATED AT 400 WORDS)
Epileptiform activity in microcultures containing small numbers of hippocampal neurons
Authors: Segal M. M. , Furshpan E. J.
Published: December 2017

1. Microcultures were grown containing small numbers of hippocampal neurons. The neurons grew on glial cells attached to patches of either collagen or palladium. A layer of agarose underlying the microcultures prevented connections from forming between nearby microcultures. 2. Neurons formed strong chemical synaptic connections within each microculture, with monosynaptic fast-excitatory, fast-inhibitory, and slow-inhibitory synaptic actions. 3. Small networks with as few as two neurons generated epileptiform activity that closely resembled the epileptiform activity seen in mass cultures containing thousands of neurons. The epileptiform activity was observed when microcultures that were grown for weeks in blockers of synaptic activity (kynurenate and elevated Mg2+) were washed free of these blockers. 4. Such a microculture technique allows study of epileptiform activity in a simplified system and facilitates analysis of the synaptic actions underlying the epileptiform activity.
Ionic currents in crustacean neurosecretory cells
Authors: Onetti C. G. , Garcia U. , Valdiosera R. F. , Arechiga H.
Published: December 2017

1. The patterns of electrical activity and membrane characteristics of a population of neurosecretory-cell somata in the X-organ of the crayfish were investigated with microelectrodes and whole-cell, voltage-clamp techniques. Some neurons (56%) were silent but could be excited by intracellular current injection: other cells showed spontaneous tonic activity (35%), and some had spontaneous bursting activity (9%). The spiking activity was abolished by tetrodotoxin (TTX) exposure and by severing the axon near the cell body. After axotomy, only a small, slow, regenerative depolarization remained that could be blocked by Cd2+. 2. Under voltage clamp the steady-state I-V curve in low [Ca2+]i (9 X 10(-9) M) showed a slope conductance of 16.7 +/- 3.9 (SD) nS (n = 10) at -50 mV and zero current potential of -50.1 +/- 7.7 mV. In current-clamp mode these neurons were either silent or fired tonically. With high [Ca2+]i (1.7 X 10(-6) M) both the slope conductance and inward and outward currents were reduced. In some neurons high [Ca2+]i reveals a negative slope resistance in the range of -46 to -41 mV. It could be supressed by removing [Na+]o, but it was TTX insensitive. These are the neurons that under current clamp showed bursting activity. 3. The main inward current in cell somata was a Ca2+ current of 2 +/- 0.6 nA (n = 18), activated at -40 mV and peaking at 20 mV. It showed relaxation with prolonged pulses. No Na(+)-dependent, TTX-sensitive inward currents were recorded with short (100-ms) pulses in axotomized neurons. 4. Two outward currents could be distinguished.(ABSTRACT TRUNCATED AT 250 WORDS)
Cross-correlation analysis of inhibitory interactions in dorsal cochlear nucleus
Authors: Voigt H. F. , Young E. D.
Published: December 2017

1. Cross-correlation analysis was used to study the organization of inhibitory connections between type II or type III units and type IV principal cells in cat dorsal cochlear nucleus (DCN). Pairs of units were isolated using two microelectrodes so that information about the distance over which connections are made could be analyzed. Data were obtained from 51 pairs consisting of a type II and a type IV unit and from 22 pairs consisting of a type III and a type IV unit. The analyses in this paper concentrate on type II-type IV pairs. 2. Inhibitory troughs (ITs) are observed in the cross-correlograms of type II-type IV pairs (21/51 cases). An IT is a transient decrease in discharge probability in the postsynaptic (type IV) unit immediately after spikes in the presynaptic unit (type II). The average latency to the start of ITs is 0.73 ms, and the troughs are asymmetric with a faster leading phase. Small excitatory peaks accompany the ITs in type II units, but these are probably secondary effects associated with the IT. ITs are consistent with a monosynaptic, inhibitory connection between type II and type IV units. A variety of evidence suggests that type II responses are recorded from vertical cells, an interneuron in the deep layer of the DCN that may be glycinergic. 3. The cross-correlograms of type III-type IV pairs are more complex and variable than those of type II-type IV pairs--ITs are seen in 4/22 cases, and peaks of correlation that are symmetrically located around the origin (central mound or CM) are seen in 4/22 cases; two cases have both an IT and a CM. CMs result from shared sources of input. Whereas type II-type IV correlogram features change primarily in amplitude as stimulus conditions change, correlogram features in some type III-type IV pairs change qualitatively with stimulus conditions; correlograms are flat for some stimuli and show ITs or CMs or mixtures of the two for others. This variability suggests that the circuitry associated with type III-type IV pairs is more complex than a monosynaptic connection, and further analysis of type III-type IV pairs was not done. 4. The strength of inhibition for an IT is measured as the area under the IT (effectiveness) and as effectiveness divided by the postsynaptic discharge rate (association index).(ABSTRACT TRUNCATED AT 400 WORDS)
Sustained and transient potassium currents of cultured horizontal cells isolated from white bass retina
Authors: Sullivan J. M. , Lasater E. M.
Published: December 2017

1. Horizontal cells (HCs) are second-order neurons in the retina that receive direct photoreceptor input. They rest at around -20 mV in the dark, because of the continuous release of neurotransmitter from photoreceptors. HCs respond to light with graded hyperpolarizations, which can reach -70 to -80 mV in the presence of very bright stimuli. 2. HCs from the retinas of white bass were isolated and maintained in culture. Potassium currents in three morphological types of HCs--H1, H2, and H4--were studied in culture with whole-cell, patch-clamp techniques, when sodium and calcium currents were blocked. 3. A transient outward potassium current (IA), with many characteristics of the A-current, was found in all H2s and H4s but only occasionally in H1s. The threshold for activation of this current was around -40 mV, a value more depolarized than usual for the A-current. The peak IA was typically smaller than 300 pA when the membrane was stepped from a holding potential of -70 mV to a command potential of -10 mV, the upper limit of the in vivo range of HC membrane potentials. Steady-state inactivation is expected to reduce the magnitude of IA in vivo. 4. A sustained outward potassium current (IK) was found in all types of HCs. This sustained potassium current did not activate until the membrane was stepped to potentials above -10 mV, a value much more depolarized than those reported for the delayed rectifier current in other neurons. As a result, IK is absent over the in vivo operating range of these cells. 5. No calcium-dependent potassium current was found in any cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Temperature dependence of extracellular ionic changes evoked by anoxia in hippocampal slices
Authors: Morris M. E. , Leblond J. , Agopyan N. , Krnjevic K.
Published: December 2017

1. Extracellular [K] and [Ca] were measured with ion-selective microelectrodes in CA1 pyramidal cell layer of rat hippocampal slices in an interface chamber. 2. Near room temperature (21-22 degrees C), brief periods of anoxia (3- to 4-min substitution of 95% N2-5% CO2 for 95% O2-5% CO2) produced very small changes in [K]o [-0.022 +/- 0.10 (SE) mM] or [Ca]o (-0.030 +/- 0.0029 mM) and were associated with only minor depression of population spikes (-22.5 +/- 11%). 3. Stratum radiatum (SR) stimulation (0.2-5 Hz) could evoke substantial increases in [K]o (by 0.2-2 mM); although variable, they were consistent in any one slice. The same stimulation regularly caused only small depressions of [Ca]o (by less than 0.1 mM, typically). 4. Also at 21-22 degrees neither stimulation nor anoxia generated more than minimal reductions in extracellular space [by 2.3 +/- 0.94%, as measured by the tetramethylammonium (TMA) method], and spreading depression (SD) occurred in only 1 out of 20 slices. 5. At 33-34 degrees C, anoxia (also for 3-4 min) consistently produced more substantial increases in [K]o (0.83 +/- 0.18 mM); but the apparent changes in [Ca]o at 33 degrees C (0.058 +/- 0.12 mM) could not with certainty be distinguished from thermoelectric artifacts. There was a severe depression of population spikes (-76 +/- 10%). 6. Although electrical stimulation evoked greater reductions in [Ca]o, increases in [K]o were 50% smaller. 7. During anoxia at 33-34 degrees C, the extracellular space was significantly reduced, by 6.1 +/- 0.9%. Moreover, in 37% of the slices, either stimulation or anoxia triggered massive increases in [K]o (greater than 10 mM) and large reductions in [Ca]o (less than 1 mM), associated with SD-like swings in focal potential. 8. It is concluded that the extracellular ionic changes evoked by brief anoxia do not contribute in a major way to the depression of synaptic transmission.
Contrasting properties of monkey somatosensory and motor cortex neurons activated during the control of force in precision grip
Authors: Wannier T. M. , Maier M. A. , Hepp-Reymond M. C.
Published: December 2017

1. Single cell activity was investigated in the precentral motor (MI) and postcentral somatosensory (SI) cortex of the monkey to compare the neuronal activity related to the control of isometric force in the precision grip and to assess the participation of SI in motor control. 2. Three monkeys (Macaca fascicularis) were trained in a visual step-tracking paradigm to generate and precisely maintain force on a transducer held between thumb and index finger. Great care was taken to have the monkeys use only their fingers without moving the wrist or proximal joints. In two monkeys electromyographic (EMG) activity was checked in 23 muscles over several sessions. 3. Five similar classes of task-related firing patterns were found in both SI and MI cortical hand and finger representations, but their relative proportions differed. The majority of the SI neurons were phasically or phasic-tonically active (61%), whereas in MI the neurons that decreased their firing rate with force were most frequent (42%). 4. The timing of activity changes related to the onset of force increase from low to higher levels strongly differed in the two neuronal populations. In SI, only 14% of the task-related neurons increased or decreased their firing rate before the onset of force increase, in contrast to 56% in MI. Only 3% of the SI neurons showed changes before the earliest EMG activation. 5. In both SI and MI neurons with tonic and phasic-tonic, increasing or decreasing discharge patterns disclosed a relationship between neuronal activity and static force. Distinction was made between neurons modulating their activity in a monotonic way and those that were active only at one force level and had a kind of recruitment or deactivation threshold. The latter ones were more frequent in MI than in SI, and in the neuron population with decreasing firing patterns. For the neurons with increases in activity, statistically significant linear correlations between firing rate and force were found more frequently in MI than in SI, where the proportion of nonsignificant correlations was relatively high (35% vs. 15% in MI). In SI the indexes of force sensitivity, calculated from the slopes of the regression lines, covered a wider range than in MI; and their distribution was bimodal, with one mean of 30 Hz/N and the other of 155 Hz/N. In contrast, the mean rate-force slope in MI was 69 Hz/N.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium ion levels in resting and depolarized goldfish retinal ganglion cell somata and growth cones
Authors: Ishida A. T. , Bindokas V. P. , Nuccitelli R.
Published: December 2017

1. We have estimated free, intracellular calcium ion concentrations ([Ca]i) in isolated retinal ganglion cells of adult goldfish by ratio-imaging fura-2 emission intensity at two excitation wavelengths. Here we describe [Ca]i in these cells, both at rest and during depolarization by elevated levels of extracellular potassium ions ([K]o). 2. [K]o was varied between 5 and 60 mM in sodium-free, tetrodotoxin-containing salines. Ganglion cell membrane potential, measured with patch electrodes, fell with each increment of [K]o used, from approximately -70 mV in 5 mM K+ to approximately -20 mV in 60 mM K+. 3. In control saline, [Ca]i was roughly 120 nM in cell somata and at least twofold higher in their growth cones. [Ca]i increased in both somata and growth cones to as high as 1.5 microM in salines containing 60 mM K+. [Ca]i exceeded 1.5 microM in some cells in high-K+ salines, although these levels could not be quantified accurately with fura-2. 4. Increases in [Ca]i elicited by elevated [K]o persisted for the duration of the exposure to high-K+ saline and were blocked by replacement of most of the bath Ca2+ by Co2+. These increases in [Ca]i were also sensitive to dihydropyridine calcium-channel ligands, viz., enhanced by BAY K 8644 (3 microM) and antagonized by nifedipine (10 microM). 5. Partial recovery of control [Ca]i occurred when [K]o was reduced to 5 mM after exposure to high-K+ saline and in high-K+ saline when nifedipine was included. These results show that goldfish retinal ganglion cells can partially buffer intracellular Ca2+ in the absence of extracellular Na+ ions. 6. These results provide measurements of the changes in [Ca]i brought about by depolarization of goldfish retinal ganglion cells in Na(+)-free salines. In these salines, at least part of the increase in [Ca]i appears to result from Ca2+ influx through a voltage-activated, noninactivating calcium conductance in the somata and growth cones of these cells. These measurements complement whole-cell patch-clamp and vibrating microprobe recordings from the somata and neurites of these cells and also immunocytochemical studies and patch-clamp measurements in amphibian, reptilian, and mammalian retinal ganglion cells.
Mechanical and electromyographic responses to stretch of the human ankle extensors
Authors: Toft E. , Sinkjaer T. , Andreassen S. , Larsen K.
Published: December 2017

1. During maintained ankle extension with background torques ranging from 0 to 70 N.m, the ankle extensors were stretched by a 5 degree rotation of the ankle joint. Maximal stretch velocity was 170 degrees/s. Regression analysis of simultaneous measurements of total torque and needle and surface electromyograms (EMG) from the soleus and gastrocnemius muscles showed that the soleus muscle generates about two-thirds of the maximal torque (approximately 120 Nm) with the subjects in sitting position. In addition, it was found that there is considerable cross talk between the soleus and gastrocnemius muscles when EMGs are recorded by surface electrodes. 2. The soleus EMG response to stretch began with a "phasic" response (latency 41 +/- 4 ms, mean +/- SD), consisting of two peaks, labeled M1 and M2. The phasic response ended 120-140 ms after stretch onset and was followed by a period of reduced EMG activity, ending at 170-210 ms. After this "silent period," a smaller "tonic" response was seen. The phasic responses of the soleus muscle were much larger than the corresponding responses in the anterior tibial muscle. In contrast, the tonic responses were comparable in the soleus and anterior tibial muscles. 3. The amplitudes of the phasic M1 and M2 responses were independent of the level of the background contraction. This disagrees with the "automatic gain principle," according to which the amplitudes of M1 and M2 should increase proportionally with the background EMG. In contrast to the phasic responses, the amplitude of the tonic EMG response, measured 200-400 ms after stretch onset, followed the automatic gain principle.(ABSTRACT TRUNCATED AT 250 WORDS)
Long-term potentiation of thalamic input to the motor cortex induced by coactivation of thalamocortical and corticocortical afferents
Authors: Iriki A. , Pavlides C. , Keller A. , Asanuma H.
Published: December 2017

1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.