bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential activation of GABAA and GABAB receptors by spontaneously released transmitter
Authors: Otis T. S. , Mody I.
Published: December 2017

1. Whole-cell patch-clamp techniques were used to record from dentate gyrus granule cells in adult rat brain slices when N-methyl-D-aspartate (NMDA) and non-NMDA type glutamate receptors were blocked by D-2-amino-5-phosphonovaleric acid (D-AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), respectively. Spontaneous inhibitory postsynaptic currents (sIPSCs), each presumably due to vesicular release of gamma-aminobutyric acid (GABA), selectively activated GABAA-type receptors. None of the individual sIPSCs showed a slow-onset potassium current characteristic of GABAB receptor activation. 2. In contrast, stimulation in the molecular layer with a bipolar stimulating electrode or bath application of the convulsant drug 4-aminopyridine (4-AP, 10-30 microM) elicited fast GABAA IPSCs followed by slower outward currents that were sensitive to the selective GABAB antagonist CGP 35348 (0.1-1 mM) and that reversed polarity near the potassium equilibrium potential. 3. CGP 35348 (0.5-1 mM) or the GABAB agonist (-)baclofen (1 microM) had no significant effect on the frequency or average amplitude of sIPSCs. However, either bath application of (-)baclofen (1 microM) or a preceding conditioning stimulus caused large reductions in the amplitude of stimulus-evoked IPSCs, suggesting a strong GABAB-mediated presynaptic inhibition of stimulus-evoked GABA release. 4. We conclude that under normal conditions spontaneous transmitter release does not activate GABAB receptors in dentate gyrus slices. These findings are consistent with either of two general possibilities. Separate groups of interneurons with different basal firing rates may selectively form GABAA and GABAB synapses.(ABSTRACT TRUNCATED AT 250 WORDS)
Relationship between repetitive firing and afterhyperpolarizations in human neocortical neurons
Authors: Lorenzon N. M. , Foehring R. C.
Published: December 2017

1. Human neocortical neurons fire repetitively in response to long depolarizing current injections. The slope of the relationship between average firing frequency and injected current (f-I slope) was linear or bilinear in these cells. The mean steady-state f-I slope (average of the last 500 ms of a 1-s firing episode) was 57.8 Hz/nA. The instantaneous firing rate decreased with time during a 1-s constant-current injection (spike frequency adaptation). Also, human neurons exhibited habituation in response to a 1-s current stimulus repeated every 2 s. 2. Afterhyperpolarizations (AHPs) reflect the active ionic conductances after action potentials. We studied AHPs with the use of intracellular recordings and pharmacological manipulations in the in vitro slice preparation to 1) gain insight into the ionic mechanisms underlying the AHPs and 2) elucidate the role that the underlying currents play in the functional behavior of human cortical neurons. 3. We have classified three AHPs in human neocortical neurons on the basis of their time courses: fast, medium, and slow. The amplitude of the AHPs was dependent on stimulus intensity and duration, number and frequency of spikes, and membrane potential. 4. The fast AHP had a reversal potential of -65 mV and was eliminated in extracellular Co2+, tetraethylammonium (TEA) or 4-aminopyridine, and intracellular TEA or CsCl. These manipulations also caused an increase in spike width. 5. The medium AHP had a reversal potential of -90 to -93 mV (22-24 mV hyperpolarized from mean resting potential). This AHP was reduced by Co2+, apamin, tubocurare, muscarine, norepinephrine (NE), and serotonin (5-HT). Pharmacological manipulations suggest that the medium AHP is produced in part by 1) a Ca-dependent K+ current and 2) a time-dependent anomalous rectifier (IH). 6. The slow AHP reversed at -83 to -87 mV (14-18 mV hyperpolarized from mean resting potential). This AHP was diminished by Co2+, muscarine, NE, and 5-HT. The pharmacology of the slow AHP suggests that a Ca-dependent K+ current with slow kinetics contributes to this AHP. 7. The currents involved in the fast AHP are important in spike repolarization, control of interspike interval during repetitive firing, and prevention of burst firing. Currents underlying the medium and slow AHPs influence the interspike interval during repetitive firing and produce spike frequency adaptation and habituation.
Comparison of the effects of flickering and steady light on dopamine release and horizontal cell coupling in the mudpuppy retina
Authors: Dong C. J. , McReynolds J. S.
Published: December 2017

1. The effects of flickering adapting illumination (repetitive flashes) on horizontal cell responses to illumination of the center and surround portions of the receptive field were compared with those of steady adapting illumination in dark-adapted mudpuppy retinas. 2. Exposure to flickering adapting light caused an increase in amplitude of responses to small spots in the receptive-field center and a decrease in the response to a concentric annulus. This is interpreted as due to an increase in coupling resistance between horizontal cells. 3. The uncoupling effect of flickering adapting light was no greater than that of the same quantity of steady adapting light at the same intensity, even when the rate of flickering was varied by a factor of 10. 4. The uncoupling effect of flickering light was blocked by the dopamine antagonists fluphenazine and SCH23390, indicating that it is mediated by dopamine release. 5. The uncoupling effect of flickering light was also blocked in the presence of 2-amino-4-phosphonobutyrate (APB), which prevents light responses of on-center but not off-center bipolar cells, suggesting that flickering light increases dopamine release via the on-pathway. 6. The gamma-aminobutyric acid (GABA) antagonist bicuculline had an uncoupling effect similar to that of adapting illumination. This effect was blocked by dopamine antagonists, indicating that there is tonic GABA-mediated inhibition of dopamine release in mudpuppy retina similar to that previously reported by others in fish and turtle retinas. 7. The uncoupling effect of bicuculline was not reversed by APB. However, APB alone caused an increase in coupling that was rapidly reversed by bicuculline.(ABSTRACT TRUNCATED AT 250 WORDS)
Response dynamics and receptive-field organization of catfish amacrine cells
Authors: Sakai H. M. , Naka K.
Published: December 2017

1. We have applied Wiener analysis to a study of response dynamics of N (sustained) and C (transient) amacrine cells. Stimuli were a spot and an annulus of light, the luminance of which was modulated by two independent white-noise signals. First- and second-order Wiener kernels were computed for each spot and annulus input. The analysis allowed us to separate a modulation response into its linear and nonlinear components, and into responses generated by a receptive-field center and its surround. 2. Organization of the receptive field of N amacrine cells consists of both linear and nonlinear components. The receptive field of linear components was center-surround concentric and opposite in polarity, whereas that of second-order nonlinear components was monotonic. 3. In NA (center-depolarizing) amacrine cells, the membrane DC potentials brought about by the mean luminance of a white-noise spot or a steady spot were depolarizations, whereas those brought about by the mean luminance of a white-noise annulus or a steady annulus were hyperpolarizations. In NB (center-hyperpolarizing) amacrine cells, this relationship was reversed. If both receptive-field center and surround were stimulated by a spot and annulus, membrane DC potentials became close to the dark level and the amplitude of modulation responses became larger. 4. The linear responses of a receptive-field center of an N amacrine cell, measured in terms of the first-order Wiener kernel, were facilitated if the surround was stimulated simultaneously. The amplitude of the kernel became larger, and its peak response time became shorter. The same facilitation occurred in the linear responses of a receptive-field surround if the center was stimulated simultaneously. 5. The second-order nonlinear responses were not usually generated in N amacrine cells if the stimulus was either a white-noise spot or a white-noise annulus alone. Significant second-order nonlinearity appeared if the other region of the receptive field was also stimulated. 6. Membrane DC potentials of C amacrine cells remained at the dark level with either a white-noise spot or a white-noise annulus. The cell responded only to modulations. 7. The major characteristics of center and surround responses of C amacrine cells could be approximated by second-order Wiener kernels of the same structure. The receptive field of second-order nonlinear components of C amacrine cells was monotonic.(ABSTRACT TRUNCATED AT 400 WORDS)
Identified proprioceptive afferents and motor rhythm entrainment in the crayfish walking system
Authors: Elson R. C. , Sillar K. T. , Bush B. M.
Published: December 2017

1. In crayfish, Pacifastacus leniusculus, remotion of a walking leg stretches the thoraco-coxal (TC) muscle receptor organ (TCMRO), located at the leg's articulation with the thorax. In vitro, alternate stretch and release of the fourth leg's TCMRO entrained the centrally generated rhythmic motor output to that leg, with the remotor phase of the rhythm entraining to TCMRO stretch, the promoter phase to release. This coordination of motor bursts to afferent input corresponds to that of active, rhythmic movements in vivo. 2. Entrainment was rapid in onset (stable coordination resulting within the first or second stimulus cycle) and was relatively phase-constant (whatever the stimulus frequency, during 1:1 entrainment, remotor bursts began near the onset of stretch and promotor bursts began near the onset of release). Outside the range of 1:1 entrainment, 2:1, 1:2, and 1:3 coordination ratios (rhythm:stimulus) were encountered. Resetting by phasic stimulation of the TCMRO was complete and probabilistic: effective stimuli triggered rapid transitions between the two burst phases. 3. The TCMRO is innervated by two afferents, the nonspiking S and T fibers, which generate graded depolarizing receptor potentials in response to stretch. During proprioceptive entrainment, the more phasic T fiber depolarized and hyperpolarized more rapidly or in advance of the more tonic S fiber. These receptor potentials were modified differently in the two afferents by interaction with central synaptic inputs that were phase-locked to the entrained motor rhythm. 4. Injecting slow sinusoidal current into either afferent alone could entrain motor rhythms: promoter phase bursts were entrained to depolarization of the S fiber or hyperpolarization of the T fiber, whereas the converse response was obtained for remotor phase bursts. 5. During proprioceptive entrainment, tonic hyperpolarization of the S fiber weakened entrained promotor bursts and allowed remotor burst durations to increase. Hyperpolarizing the T fiber weakened entrained remotor bursts and allowed promotor bursts to occur during stretch. These results suggest that the staggered receptor potentials of the two afferents alternately excite opposite burst phases of the rhythm during proprioceptive entrainment. 6. Injecting brief current pulses into either afferent perturbed the timing of entrained bursts in opposite ways, suggesting that, during proprioceptive entrainment, the membrane potential trajectories of the two afferents have reciprocal triggering effects on burst transitions. 7. We infer that entrainment results from 1) complete resetting of burst transitions in a two-phase central oscillator, 2) opposing feedback pathways mediated by a phasic and a tonic afferent, 3) temporally staggered afferent receptor potentials, and 4) the ability of afferent receptor potentials to trigger burst transitions.
Functional properties of single neurons in the face primary motor cortex of the primate. I. Input and output features of tongue motor cortex
Authors: Murray G. M. , Sessle B. J.
Published: December 2017

1. We have recently demonstrated that reversible, cooling-induced inactivation of the face motor cortex results in a severe impairment in the ability of monkeys (Macaca fascicularis) to perform a tongue-protrusion task but produces only relatively minor effects on the performance of a biting task by the same monkeys. To establish a neuronal correlate for these different behavioral relations, the present study has detailed the afferent input and intracortical microstimulation (ICMS)-defined output features of a population of face motor cortical neurons, and in a subsequent study we have documented the activities of the same population of neurons during the performance of the tongue-protrusion and biting tasks. 2. Of the 231 single neurons recorded within the face motor cortex, 163 were located at sites from which ICMS (less than or equal to 20 microA) could evoke tongue movements (i.e., "tongue-MI" sites) at the lowest threshold for eliciting orofacial movements. The remainder were located at sites from which ICMS evoked jaw movements ("jaw-MI" sites), face movements ("face-MI" sites), or at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 3. We confirmed the general organizational features of the face motor cortex that have been defined in previous studies, but we documented in detail the organizational features for tongue-MI. Thus we found that tongue movements were well represented, whereas jaw-closing movements were poorly represented; the representations for face, jaw, and tongue movements were overlapped; the same ICMS-evoked tongue movement could be multiply represented within tongue-MI; tongue-MI was characterized by a prominent input from superficial mechanosensory afferents, whereas there was little evidence for deep input; a close spatial match was found between ICMS-defined motor output and somatosensory afferent input for tongue-MI. 4. A variety of tongue movements could be evoked by ICMS at tongue-MI sites and were categorized into protrusion, retrusion, laterally directed, and other types of tongue movement. Low-threshold (i.e., less than or equal to 5 microA) ICMS-defined tongue-MI sites, which were considered to represent "efferent zones" projecting relatively directly to motoneurons, were reconstructed three dimensionally to provide insights into the spatial organization of tongue-MI. Examples of each of the four low-threshold efferent-zone categories were usually found throughout the ICMS-defined tongue-MI without any apparent preferential distribution. Furthermore, different low-threshold efferent-zone categories had close spatial relationships to each other in cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
How the frontal eye field can impose a saccade goal on superior colliculus neurons
Authors: Schlag-Rey M. , Schlag J. , Dassonville P.
Published: December 2017

Saccades were electrically evoked from the frontal eye field (FEF) of two trained monkeys while saccade-cells were recorded from the intermediate layers of the superior colliculus (SC). We found that FEF microstimulation, eliciting saccades of a given vector, excited SC saccade-cells encoding the same vector and inhibited all others. Such a mechanism can prevent competing commands from arising simultaneously in different structures.
Hypoxia-induced functional alterations in adult rat neocortex
Authors: Luhmann H. J. , Heinemann U.
Published: December 2017

1. Brief periods of hypoxia (2-7 min) were induced in rat neocortical slices maintained in an interface-type recording chamber at 34-35 degrees C by changing the aerating gas from 95% O2-5% CO2 to 95% N2-5% CO2. Field potential (FP) and intracellular recordings were obtained in layers II/III of primary somatosensory cortex. Intracellular injection of biocytin revealed the characteristic morphology of supragranular spiny pyramidal neurons. 2. Excitatory synaptic transmission reversibly decreased by 45% as estimated from FP responses to orthodromic stimulation of the underlying white matter/layer VI. Excitatory postsynaptic potentials (EPSPs) were suppressed by 36% in amplitude and recovered within 2-3 min after reoxygenation. During the recovery period, EPSPs showed a reversible increase in duration by 72%. 3. Inhibitory synaptic transmission was completely blocked as determined in FP responses with a paired-pulse inhibition protocol. The fast inhibitory postsynaptic potential (IPSP) declined by 58% during hypoxia. The long-lasting IPSP was suppressed by 75% and showed incomplete recovery. During hypoxia, the amplitude of both IPSPs was significantly more strongly suppressed than the EPSP. 4. In 40% of the cells, hypoxia induced an early anoxic hyperpolarization with a reversal potential of E = -80.8 mV, followed by a postanoxic hyperpolarization (E = -89.4 mV). In a second group of cells (37%), a gradual anoxic depolarization with E = -57.5 mV was observed instead of an early hyperpolarization. In both groups of cells, the anoxic response was associated with a marked decrease in input resistance, by 42 and 31%, respectively. 5. The spike discharge frequency was reversibly suppressed by 71% during hypoxia. A transient hyperexcitability accompanied with a rise in input resistance and discharge rate was observed in 38% of the cells on reoxygenation. 6. The reversal potential of the anoxic hyperpolarization was unaffected by tetrodotoxin (TTX) but was significantly altered by application of the ATP-sensitive K+ channel (KATP) blocker gliquidone. Application of gliquidone additionally resulted in a significantly smaller hypoxia-induced decline in paired-pulse inhibition. 7. Increases in tissue high-energy phosphates induced by preincubating the slices in 25 mM creatine for greater than 2 h had a pronounced protective effect on excitatory and inhibitory synaptic transmission. 8. These data suggest a selective vulnerability of the neocortical inhibitory system during hypoxia. Our results further indicate that hypoxia activates a pre- and postsynaptic KATP conductance because of the decline in intracellular ATP.
Cortical oscillations and temporal interactions in a computer simulation of piriform cortex
Authors: Wilson M. , Bower J. M.
Published: December 2017

1. A large-scale computer model of the piriform cortex was constructed on the basis of the known anatomic and physiological organization of this region. 2. The oscillatory field potential and electroencephalographic (EEG) activity generated by the model was compared with actual physiological results. The model was able to produce patterns of activity similar to those recorded physiologically in response to both weak and strong electrical shocks to the afferent input. The model also generated activity patterns similar to EEGs recorded in behaving animals. 3. In addition to replicating known physiological responses, it has been possible to use the simulations to explore the interactions of network components that might underlie these responses. This analysis suggests that the physiological properties of the cortex are dependent on the complex interaction of both network and cellular properties. In particular, we have found that the relationship between conduction velocities in intrinsic cortical fiber systems and the time constants of excitatory and inhibitory effects are critical for replicating physiological results. 4. Analysis of the model also suggests a correspondence between the 40-Hz oscillatory patterns of activity induced by low levels of odor-like stimulation and oscillatory patterns seen in lightly anesthetized cortex in response to weak electrical shocks to the afferent fiber system. 5. The specific relationships we have found between the different components of the model also support several speculations on their functional significance. The simulations suggest that during each 40-Hz cycle of EEG activity there is a convergence in rostral cortex of afferent information from the olfactory bulb and recurrent association fiber information from caudal cortex. This convergence could underlie an iterative process central to the recognition of complex olfactory stimuli.
Frequency discrimination training engaging a restricted skin surface results in an emergence of a cutaneous response zone in cortical area 3a
Authors: Recanzone G. H. , Merzenich M. M. , Jenkins W. M.
Published: December 2017

1. The responses of cortical neurons evoked by cutaneous stimulation were investigated in the hand representation of cortical area 3a in adult owl monkeys that had been trained in a tactile frequency discrimination task. Cortical representations of the hands in these experimental hemispheres were compared with those representing the opposite, untrained hand, as well as with those representing a passively stimulated hand in a second class of control monkeys. 2. A large cutaneous representation of the hairy and glabrous skin surfaces of the hand emerged in area 3a in each trained hemisphere. 3. With the emergence of cutaneous responses recorded for neurons at many area 3a locations, the normally recorded deep receptor inputs were no longer evident at most of these locations. 4. There was a greater territory of representation of the small area of skin that was stimulated in the behavioral task in trained monkeys, when compared with the representations of corresponding skin sites in the opposite hemisphere of the same monkeys, or to the representations of equivalent skin sites stimulated in passively stimulated control monkeys. 5. There was great variability in the receptive-field properties of neurons responsive to cutaneous inputs among trained monkeys. In most recording sites within the representations of the behaviorally engaged hands, the cutaneous receptive fields were large, extending over a significant part of the glabrous or hairy surfaces of the hand. However, in one monkey, very small, topographically ordered cutaneous receptive fields were recorded over a wide zone of area 3a. 6. The physiologically defined borders between areas 3a and 3b were in register with the cytoarchitectonically defined borders between these two cortical areas in trained and in control monkeys. 7. This study demonstrates that there is a reorganization of the cutaneous and "deep" representation of hand in cortical area 3a, with the main change being an emergence of a large cutaneous representation and the parallel disappearance of a large part of the normal deep representation in this field. These changes are discussed in light of the possible functional roles of cortical area 3a.
Properties of amino acid neurotransmitter receptors of embryonic cortical neurons when activated by exogenous and endogenous agonists
Authors: Blanton M. G. , Kriegstein A. R.
Published: December 2017

1. The properties of receptors for amino acid neurotransmitters expressed by developing cortical neurons were studied with the use of whole-cell recording in the intact cerebral cortex of embryonic turtles in vitro. The inhibitory agonist gamma-aminobutyric acid (GABA) and the excitatory agonist glutamate were focally applied to single cells under voltage clamp, and the ionic dependence, voltage dependence, and pharmacological sensitivity of the responses were characterized. The responses mediated by a glutamate receptor subtype, the N-methyl-D-aspartate (NMDA) receptor, produced by glutamate and by evoked release of an endogenous excitatory agonist, were compared further. Fluctuation analysis was used to characterize the properties of the NMDA channels and the mechanism of action of receptor antagonists. 2. When postmitotic neurons first appeared at stage 15, all neurons tested responded to GABA with a current that reversed at the equilibrium potential for chloride ions and that was sensitive to the GABAA receptor antagonist bicuculline methiodide (BMI). As development proceeded, an increasing proportion of neurons also responded with a BMI-insensitive current that reversed near the equilibrium potential for potassium ions. This current was blocked by the GABAB receptor antagonist 3-amino-2-propyl phosponic acid (phaclofen). The GABAB agonist baclofen, however, failed to produce a detectable postsynaptic current. 3. Neurons at stage 15 showed a biphasic response to glutamate that reversed at the equilibrium potential for cations. All neurons tested showed a slow, sustained response associated with an increase in current variance compared with background, and, as development proceeded, an increasing proportion also exhibited a fast, transient response. Both fast and slow responses varied linearly with voltage in the absence of Mg2+ ions, but the addition of Mg2+ ions to the bathing medium attenuated the slow response at hyperpolarized potentials. As a result, the current-voltage relation of the slow response in the presence of Mg2+ ions exhibited a region of negative slope conductance, like that of currents mediated by NMDA receptors. 4. The fast and slow responses to glutamate differed in their pharmacological sensitivity. The fast responses were sensitive to the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), whereas the slow responses were sensitive to the NMDA receptor antagonist D(-)-2-amino-5-phosphonovalerate (D-APV). 5. When cells were held at -70 mV, glutamate evoked a fluctuating current consisting of channel currents with a mean open time, tau, of 4.42 +/- 0.47 (SE) ms in early postmitotic neurons at stage 15 and 4.99 +/- 0.38 ms at stages 17-20.(ABSTRACT TRUNCATED AT 400 WORDS)
Intercellular signaling in Necturus taste buds: chemical excitation of receptor cells elicits responses in basal cells
Authors: Ewald D. A. , Roper S. D.
Published: December 2017

1. Taste cells in intact taste buds in slices of Necturus lingual epithelium were impaled with microelectrodes for intracellular recording. Two types of cells were investigated: taste receptor cells and basal cells. 2. Impaling cells in the apical end of taste buds resulted in intracellular records from taste receptor cells. Applying short pulses (100- to 200-ms duration) of 140 mM KCl solution to the apical pore elicited receptor potentials in the taste receptor cells. 3. Impaling cells in the base of the taste bud resulted in intracellular records from taste receptor cells and basal cells. KCl applied to the taste pore elicited responses in the basal region that varied greatly in both magnitude and time of onset. The latency of these responses (time of onset compared with the onset of the receptor potential) ranged from 0 to hundreds of milliseconds. 4. Impaled cells were identified by injecting Lucifer yellow after recording KCl responses for 21 cells. KCl responses recorded from identified basal cells all had latencies of greater than 75 ms. KCl responses from identified receptor cells all had latencies of less than 75 ms. 5. One explanation for the long latency of KCl responses recorded in basal cells is that the responses represent postsynaptic potentials. In agreement with this interpretation, long-latency responses, but not short-latency responses, were reversibly reduced by the Ca antagonist Cd (1 mM, 10- to 20-min bath exposure). 6. Long-latency responses also differed from short-latency responses in their voltage dependence. Short-latency responses had the same voltage dependence as apically recorded receptor potentials, increasing with hyperpolarization from resting potential with an extrapolated reversal potential near 0 mV. Long-latency responses were much less dependent on voltage in this range. 7. We measured the spread of exogenously applied KCl with potassium-sensitive electrodes. Long-latency responses were not generated by diffusion of applied KCl to the basal region of the taste bud. A small transient increase in extracellular potassium occurred at the base of the taste bud after chemostimulation at the apical pore. This increase was due to depolarization-evoked release of potassium from taste cells and did not cause the long-latency responses in basal cells. 8. We conclude that short-latency (less than 75 ms) responses recorded from cells situated in the bases of taste buds are electrotonically conducted receptor potentials generated at the apical region. Long-latency (greater than 75 ms) responses are consistent with recording postsynaptic responses in basal cells.
Innervation ratio is an important determinant of force in normal and reinnervated rat tibialis anterior muscles
Authors: Totosy de Zepetnek J. E. , Zung H. V. , Erdebil S. , Gordon T.
Published: December 2017

1. The technique of glycogen depletion and periodic acid-Schiff (PAS) staining, which identifies glycogen-free muscle fibers, was used to directly count the number (N) and measure the cross-sectional area (CSA) of muscle fibers in single motor units (MUs) from normal and reinnervated tibialis anterior (TA) muscles. Indirect estimates, derived from the proportions of muscle fiber types to MU types, were also made, and force per unit area (or specific force, SF) was calculated. Previous results using direct and indirect approaches have been contradictory. To shed more light on this issue, the relative contributions of N, mean fiber area (A), and SF to muscle-unit force were determined by the use of both methods. 2. TA muscles were examined in experimental rats 3.5-10 mo after cutting and resuturing the common peroneal nerve in one hindlimb and in muscles in age-matched control rats. Ventral roots were dissected to isolate and characterize single MUs according to contraction speed, sag, and fatigability. One unit per muscle was selected for repetitive tetanic stimulation designed to deplete muscle fiber glycogen stores. Muscles were removed for identification of the unit with the PAS reaction and histochemical fiber typing by the use of modified standard techniques. 3. In the total population of MUs sampled, isometric tetanic force ranged from 5 to 441 mN in normal muscles and from 5 to 498 mN in reinnervated muscles, and the mean values were not significantly different. In the smaller sample of glycogen-depleted units from normal muscle, for a force range of 14-217 mN, N varied from 57 to 202, and A varied from 1,135 +/- 45 to 6,706 +/- 172 (SE) microns2. Within each unit the variation in fiber area is broad. After reinnervation, for a force range of 30-278 mN, N varied from 70 to 374, and A varied from 1,694 +/- 81 to 5,425 +/- 93 microns2. Mean fiber number was 153 +/- 18 in reinnervated muscle, which is significantly higher (P less than 0.01) than the normal value of 121 +/- 9. 4. The contribution of N and A to MU tetanic force was assessed by plotting each factor as a function of force on a log-log scale. N accounts for 39% and A for 49% of the variation in force in normal muscle. The contributions are changed after reinnervation where N, accounting for 65% of force, appears to compensate for the reduced range in A, which accounts for only 19% of the variation in force.(ABSTRACT TRUNCATED AT 400 WORDS)
Connections between utricular nerve and dorsal neck motoneurons of the decerebrate cat
Authors: Bolton P. S. , Endo K. , Goto T. , Imagawa M. , Sasaki M. , Uchino Y. , Wilson V. J.
Published: December 2017

1. We studied connections between the utricular (UT) nerve and dorsal neck motoneurons in decerebrate cats. Electrodes were fixed in place on the UT nerve under visual observation; the other branches of the vestibular nerve were transected. 2. The N1 field potential evoked by UT nerve stimulation was recorded in the vestibular nuclei at the start of each experiment. The potential typically grew until it reached a plateau. Stimulus spread (if any) to the central ends of other nerve branches was revealed by an additional increase in N1 amplitude after the plateau was reached. 3. We recorded intracellularly from 55 motoneurons in C1-C3. Some were identified as having axons in the dorsal rami, which innervate dorsal neck muscles. Others projected in nerves that were not available for stimulation. 4. UT nerve stimulation evoked synaptic potentials in essentially all motoneurons studied. The predominant pattern consisted of disynaptic excitatory postsynaptic potentials in ipsilateral motoneurons and inhibitory postsynaptic potentials that were at least trisynaptic in contralateral motoneurons. 5. The results demonstrate the presence of short-latency connections between the utricular nerve and dorsal neck motoneurons. The functional role of this pathway remains to be investigated.
Modulation of excitatory amino acid responses in rat dorsal horn neurons by tachykinins
Authors: Rusin K. I. , Ryu P. D. , Randic M.
Published: December 2017

1. In freshly isolated spinal dorsal horn (DH) neurons (laminae I-III) of the young rat, the effects of tachykinins (substance P, neurokinin A) on inward current induced by excitatory amino acids were studied under whole-cell voltage-clamp conditions. 2. When the cells were clamped to a holding potential of -60 mV, a simultaneous application of N-methyl-D-aspartate (NMDA) (10(-4) M) and substance P (SP) (2 x 10(-9)-10(-7) M) for 10 s reversibly enhanced (by 129.6 +/- 8.2%, mean +/- SE) the peak amplitude of the initial transient component of the NMDA-induced current in approximately 60% of the examined cells and reduced it (to 83.3 +/- 2.7%) in 27% of the cells. In addition, SP produced an increase (by 133.6 +/- 11.7%) or a small decrease (to 85.9 +/- 1.4%) in the steady-state component of the NMDA response. In difference to SP, a simultaneous application of NMDA (10(-4) M) and neurokinin A (NKA) (10(-10)-10(-7) M) reversibly suppressed (to 86.8 +/- 2.1%) the peak amplitude of the NMDA-induced current in 75% of the examined cells. 3. The NMDA-induced currents were modulated by tachykinins not only during the coadministration but up to 20 min after the removal of the peptide. SP potentiated the initial peak NMDA current by 147.9 +/- 8.1% in 78% of examined cells and decreased it (76.3 +/- 5.7%) in 11% of cells. The potentiating effect was concentration-dependent (range: 10(-11)-10(-8) M) and reversible, but it was reduced with repeated applications. In addition, SP increased (by 125.4 +/- 3.6%) or reduced (to 86.0 +/- 1.8%) the steady-state component of the NMDA response. 4. When the single DH neurons were exposed to SP or NKA for 30 s-7 min before the testing of the NMDA responses, tachykinins had two distinct effects on the peak amplitude of the transient component of the NMDA-induced current, consisting of an initial depression (SP: to 64.8 +/- 2.1%; NKA: to 76.3 +/- 4.4%) followed by a potentiation (SP: by 146.6 +/- 6.8%; NKA: by 178.4 +/- 35.2%). The enhancing effect in some cells lasted less than or equal to 1 h. 5. A claimed novel nonselective tachykinin antagonist, spantide II (10(-8) M) coadministered with NMDA (10(-4) M), slightly depressed the peak component of NMDA-induced current. In addition, it effectively blocked the SP-induced potentiation of the responses of DH neurons to NMDA.(ABSTRACT TRUNCATED AT 400 WORDS)
PII component of the toad electroretinogram
Authors: Katz B. J. , Xu Z. , Zheng J. , Oakley B.
Published: December 2017

1. The PII component of the electroretinogram (ERG) is comprised of the b-wave and the DC component and is thought to reflect bipolar cell activity. Although the b-wave is generated in large part by a K+/Muller cell mechanism, the origin of the DC component is unclear. In this paper we detail our investigation of the origin of the DC component. We hypothesize that the DC component is generated by a K+/Muller cell mechanism identical to that involved in b-wave generation. 2. We studied the ERG in the dark-adapted, isolated retina preparation of the toad, Bu fo marinus. We used K+ ion-sensitive microelectrodes (K+ISM), as well as conventional intra- and extracellular microelectrodes, to record [K+]o changes, the vitreal ERG, and Muller cell responses. 3. We used the excitatory amino acid receptor agonist N-methyl-DL-aspartate (NMDLA) to inhibit light responses of third-order neurons and thereby eliminate most of the ERG M-wave. In the absence of the M-wave, the ERG consisted of PII and PIII. We then superfused the retina with a solution containing both kynurenic acid (KYN) and 2-amino-4-phosphonobutyric acid (APB), which together inhibit all retinal responses proximal to the photoreceptors. In the presence of KYN and APB, the ERG consisted only of PIII. Using digital subtraction, we reconstructed PII. To our knowledge, this is the first report of the isolation of a PII component in the ERG of a nonmammalian species. 4. Using K+ISMs, we recorded the distal K+ changes in the outer plexiform layer (OPL).(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence for nitric oxide synthase inhibitor-sensitive and insensitive hippocampal synaptic potentiation
Authors: Gribkoff V. K. , Lum-Ragan J. T.
Published: December 2017

1. Nitric oxide (NO) has been proposed as a retrograde messenger, mediating the postsynaptic to presynaptic transfer of the effects of conditioning stimulation, responsible for the initiation of hippocampal long-term potentiation (LTP). To further test this hypothesis, we inhibited nitric oxide synthase (NOS) to determine whether synaptic potentiation produced by different conditioning stimulus patterns and intensities was differentially affected by reduction of stimulation-dependent NO production. 2. Synaptic potentiation was produced in hippocampal slices from young F-344 rats by two different conditioning stimulation protocols. Conditioning stimuli were delivered to the Schaffer-collateral commissural system, and moderate levels of potentiation of the population excitatory postsynaptic potential (EPSP) in area CA1 were produced by a single 100 Hz, 1-s conditioning train delivered at half-maximal stimulus intensity. Higher levels of potentiation of the population EPSP were obtained by delivering two 100 Hz, 1-s conditioning stimulus trains, with a 60-s intertrain interval, at high stimulus currents. 3. Application of the nitric oxide synthase inhibitors NG-nitro-L-arginine (NOARG; 0.1-200 microM) and NG-monomethyl-L-arginine (NMMA; 100 microM) produced no significant direct effects on synaptic responses. 4. In slices that received a single conditioning stimulus train, both NOARG and NMMA were ineffective in blocking or reducing potentiation at concentrations between 0.1 and 200 microM. In slices receiving the more intense pair of conditioning stimulus trains, levels of potentiation in control slices were higher, and there was a very significant reduction by both NOARG (50 and 100 microM) and NMMA (100 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of velocity and direction of surface-parallel cutaneous stimuli on responses of mechanoreceptors in feline hairy skin
Authors: Greenspan J. D.
Published: December 2017

1. The responses of cutaneous mechanoreceptors in feline hairy skin were examined in vivo with systematic variations in the velocity and direction of stimulus motion across the receptive fields (RF). The mechanoreceptor classes studied were guard hair afferents, field afferents, down hair afferents, and slowly adapting type I (SAI) mechanoreceptors. A camel's hair brush, moved by a high-precision motor, provided surface-parallel stimulation at velocities ranging from 0.4 to 100 cm/s. The stimulating device and protocols were similar to those previously used to evaluate human perception, thus allowing direct comparison of the two sets of data. 2. Each mechanoreceptor produced highly reliable mean firing rates with repeated stimulation. All mechanoreceptors showed a growth in evoked activity with increased stimulus velocity. With few exceptions, the relationship between brush velocity and mean firing rate was well described by a power function throughout the range of velocities tested. The exponents of these power functions, reflecting the degree of velocity dependency for each mechanoreceptor, were largest for the field type 1 units (F1) and guard hair type 1 units (G1). 3. The capacity of the mechanoreceptors to discriminate velocity was examined in the context of signal detection theory. For each unit, a velocity discriminability estimate (velocity delta'e) was calculated for responses to 5 versus 10 cm/s brushing and 10 versus 20 cm/s. The G1 and F1 units exhibited the largest velocity delta'e values, which were comparable to human velocity discriminability (d'e) values. Thus these data show the quantitative parallel between the velocity discriminability of G1 and F1 mechanoreceptors and of human perception similarly tested. 4. Most mechanoreceptors generated different response rates with stimuli moving in opposing directions (in the proximal-distal axis of the hindlimb). However, no mechanoreceptor class showed a consistently preferred direction of movement. A directional delta'e value was calculated for each mechanoreceptor at each stimulus velocity. These values were quite variable, even within a single mechanoreceptor class. In general, a mechanoreceptor's directional delta'e value either 1) decreased with increasing velocity or 2) remained constant across velocities. The way in which human directional discriminability varies with stimulus velocity did not parallel the way in which mechanoreceptor's directional delta'e values varied with the same range of stimulus velocities. 5. Some mechanoreceptors were tested with both the standardized brush, which was smaller than most mechanoreceptors' RFs, and a much larger brush, which was at least twice the size of the mechanoreceptors' RFs.(ABSTRACT TRUNCATED AT 400 WORDS)
Blockade of excitation reveals inhibition of dentate spiny hilar neurons recorded in rat hippocampal slices
Authors: Scharfman H. E.
Published: December 2017

1. Extracellular and intracellular recordings in rat hippocampal slices were used to compare the synaptic responses to perforant path stimulation of granule cells of the dentate gyrus, spiny “mossy” cells of the hilus, and area CA3c pyramidal cells of hippocampus. Specifically, we asked whether aspects of the local circuitry could explain the relative vulnerability of spiny hilar neurons to various insults to the hippocampus. 2. Spiny hilar cells demonstrated a surprising lack of inhibition after perforant path activation, despite robust paired-pulse inhibition and inhibitory postsynaptic potentials (IPSPs) in adjacent granule cells and area CA3c pyramidal cells in response to the same stimulus in the same slice. However, when the slice was perfused with excitatory amino acid antagonists [6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), or CNQX with 2-amino-5-phosphonovaleric acid (APV)], IPSPs could be observed in spiny hilar cells in response to perforant path stimulation. 3. The IPSPs evoked in spiny hilar cells in the presence of CNQX were similar in their reversal potentials and bicuculline sensitivity to IPSPs recorded in dentate granule cells or hippocampal pyramidal cells in the absence of CNQX. 4. These results demonstrate that, at least in slices, perforant path stimulation of spiny hilar cells is primarily excitatory and, when excitation is blocked, underlying inhibition can be revealed. This contrasts to the situation for dentate and hippocampal principal cells, which are ordinarily dominated by inhibition, and only when inhibition is compromised can the full extent of excitation be appreciated.(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence of input from lagged cells in the lateral geniculate nucleus to simple cells in cortical area 17 of the cat
Authors: Saul A. B. , Humphrey A. L.
Published: December 2017

1. The visual cortex receives several types of afferents from the lateral geniculate nucleus (LGN) of the thalamus. In the cat, previous work studied the ON/OFF and X/Y distinctions, investigating their convergence and segregation in cortex. Here we pursue the lagged/nonlagged dichotomy as it applies to simple cells in area 17. Lagged and nonlagged cells in the A-layers of the LGN can be distinguished by the timing of their responses to sinusoidally luminance-modulated stimuli. We therefore used similar stimuli in cortex to search for signs of lagged and nonlagged inputs to cortical cells. 2. Line-weighting functions were obtained from 37 simple cells. A bar was presented at a series of positions across the receptive field, with the luminance of the bar modulated sinusoidally at a series of temporal frequencies. First harmonic response amplitude and phase values for each position were plotted as a function of temporal frequency. Linear regression on the phase versus temporal frequency data provided estimates of latency (slope) and absolute phase (intercept) for each receptive-field position tested. These two parameters were previously shown to distinguish between lagged and nonlagged LGN cells. Lagged cells generally have latencies > 100 ms and absolute phase lags; nonlagged cells have latencies < 100 ms and absolute phase leads. With the use of these criteria, we classified responses at discrete positions inside cortical receptive fields as lagged-like and nonlagged-like. 3. Both lagged-like and nonlagged-like responses were observed. The majority of cortical cells had only or nearly only nonlagged-like zones. In 15 of the 37 cells, however, the receptive field consisted of > or = 20% lagged-like zones. For eight of these cells, lagged-like responses predominated. 4. The distribution of latency and absolute phase across the sample of cortical simple cell receptive fields resembled the distribution for LGN cells. The resemblance was especially striking when only cells in or adjacent to geniculate recipient layers were considered. Absolute phase lags were almost uniformly associated with long latencies. Absolute phase leads were generally associated with short latencies, although cortical cells responded with long latencies and absolute phase leads slightly more often than LGN cells. 5. Cells in which a high percentage of lagged-like responses were observed had a restricted laminar localization, with all but two being found in layer 4B or 5A. Cells with predominantly nonlagged-like responses were found in all layers. 6. Lagged-like zones can not be easily explained as a result of stimulating combinations of nonlagged inputs.(ABSTRACT TRUNCATED AT 400 WORDS)
Membrane properties of mesopontine cholinergic neurons studied with the whole-cell patch-clamp technique: implications for behavioral state control
Authors: Kamondi A. , Williams J. A. , Hutcheon B. , Reiner P. B.
Published: December 2017

1. The whole-cell patch-clamp technique was used to study the membrane properties of identified cholinergic and noncholinergic laterodorsal tegmental neurons in slices of rat brain maintained in vitro. 2. On the basis of their expression of the transient outward potassium current IA and the transient inward calcium current IT, three classes of neurons were observed: type I neurons exhibited a large IT; type II neurons exhibited a prominent IA; and type III neurons exhibited both IA and IT. 3. Combining intracellular deposition of biocytin with NADPH diaphorase histochemistry revealed that the vast majority of type III neurons were cholinergic, whereas only a minority of type I and type II neurons were cholinergic. Thus mesopontine cholinergic neurons possess intrinsic ionic currents capable of inducing burst firing. 4. Delineation of the intrinsic membrane properties of identified mesopontine cholinergic neurons, in concert with recent results regarding the responses of these neurons to neurotransmitter agents, has led us to present a unifying and mechanistic hypothesis of brain stem cholinergic function in the control of behavioral states.