bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of presynaptic and postsynaptic events during establishment of long-term facilitation at crayfish neuromuscular junction
Authors: Wojtowicz J. M. , Atwood H. L.
Published: December 2017

Repetitive stimulation (10-20 Hz) of the motor axon supplying the opener muscle in the crayfish leg produces long-lasting enhancement of excitatory postsynaptic potentials. This long-term facilitation (LTF) was investigated by recording simultaneously from the presynaptic nerve terminal and from the innervated muscle fiber with intracellular microelectrodes. On cessation of stimulation, the facilitated postsynaptic potential declines in amplitude when monitored with low-frequency test stimuli. A rapid decline (phase I) occurs over the first 30 s and is succeeded by a more gradual decline lasting several minutes (phase II). Finally, a residual potentiation with a very slow decay (phase III) persists for several hours. Simultaneous pre- and postsynaptic recordings were made during induction of LTF with stimuli delivered at 20 Hz for 10 min. During the tetanus, excitatory postsynaptic potentials were enhanced 20-fold, while action potentials in the presynaptic terminal declined in amplitude from 108.6 to 97.2 mV, and the presynaptic membrane became hyperpolarized by 6.4 mV. The Na+ pump inhibitor ouabain (0.5-1.0 mM) abolished the hyperpolarization, indicating that the latter resulted from activation of an electrogenic Na+ pump. The reduction in amplitude of the presynaptic action potential was consistent with a reduced transmembrane concentration gradient for Na+. Thus, it is suggested that a significant accumulation of Na+ occurs during repetitive stimulation of crayfish motor axons. Decay of phase II of LTF, but not of phases I or III, had approximately the same time course as the decay of Na+ accumulation in the terminals, monitored by changes in the presynaptic action potential. Thus it is probable that in crayfish this phase of LTF is linked to an increased intraterminal Na+ concentration. Injection of Na+ from a microelectrode into the presynaptic terminal produced enhancement of the excitatory postsynaptic potential lasting for many minutes, as well as changes in presynaptic membrane potential and action potential similar to those seen during repetitive stimulation. The results provide the first direct measurements of electrical and ionic changes in axonal terminals during prolonged periods of activity leading to LTF, and support the hypothesis that accumulation of intraterminal Na+ is associated with one phase of LTF.
The ionic mechanism of the slow outward current in Aplysia neurons
Authors: Huguenard J. R. , Zbicz K. L. , Lewis D. V. , Evans G. J. , Wilson W. A.
Published: December 2017

A slow outward current associated with spike frequency adaptation has been studied in the giant Aplysia neurons R2 and LP1. The current was observed during 60-s voltage clamp commands to potentials just below spike threshold. The slow outward current shows a marked voltage dependence at membrane potential less negative than -40 mV. The slow outward current is associated with increased membrane conductance. The K+ sensitivity of the slow outward current was studied by varying the extracellular K+ concentration and also by measuring potassium efflux with a K+-sensitive electrode. Both procedures indicated that the slow outward current was K+ dependent. Tail currents following the activation of the slow outward current were examined. They were shown to have a similar potassium sensitivity as the slow outward current and had a reversal potential near the potassium equilibrium potential for these cells. The sensitivity of the slow outward current to known blockers of K+ currents, tetraethylammonium and 4-aminopyridine, was tested. The sensitivity was much less than that reported for other K+ currents. The sensitivity of the slow outward current to changes of the extracellular concentrations of Na+ and Cl- ions, as well as electrogenic pump inhibitors, was tested. The results indicate that the slow outward current is much less sensitive to these changes than to the manipulations of the extracellular K+ ion concentration. We tested the sensitivity of this current to manipulations of intracellular and extracellular Ca2+ ion concentrations. We found that the current persisted at a slightly reduced level in the absence of extracellular calcium or in the presence of calcium blocking agents, cobalt and lanthanum. Intracellular injection of the calcium chelator EGTA at a concentration sufficient to block the Ca2+-dependent K+ current, seen after a brief (1.4-s) burst of action potentials, had minimal effects on the slow outward current. Procedures thought to increase intracellular Ca2+ were tested. We found that exposure of the cell to solutions containing elevated Ca2+ concentrations for prolonged periods increased the slow outward current. Also, treatment with drugs thought to elevate intracellular Ca2+ increased the slow outward current. In conclusion, the slow outward current results from an increased K+ conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
The monkey vertical vestibuloocular response: a frequency domain study
Authors: Correia M. J. , Perachio A. A. , Eden A. R.
Published: December 2017

We studied the vertical vestibuloocular response (VVOR) in seven cynomolgus monkeys. Eye movements were measured by the search coil method. We tested the monkeys by rotating them about their interaural axis, which was colinear with gravity. Each monkey was tested by using a standard rotational paradigm that consisted of discrete sinusoidal oscillations at three frequencies (0.01, 0.1, and 1.0 Hz) and six peak velocities (5, 10, 30, 60, 100, and 150 degrees/S). The standard rotational paradigm was applied twice for each of two conditions. The first condition (EOD) consisted of rotations with the animal's vision occluded; the second condition (EOL) consisted of rotations during which the animal was allowed to view a well-lighted room. Using various statistics, we tested the linearity of the sinusoidal slow-phase velocity component of the VVOR. The largest nonlinearity found was a skewness of approximately 14% in the waveform of f = 0.01 Hz. We did not find an amplitude asymmetry between slow-phase eye velocity upward (SPVU) and slow-phase eye velocity downward (SPVD) greater than 6% for any oscillation. Nonlinearities present in the VVOR during testing with vision occluded (EOD condition) disappeared with the addition of vision (EOL condition). Intensity function plots [peak slow-phase eye velocity vs. peak rotator (head) velocity] revealed that at f = 0.01, 0.1, and 1.0 Hz over the intensity range from +/-30 degrees/s to +/-150 degrees/s, the VVOR is highly linear. The lowest correlation coefficient associated with linear regressions of the intensity function data at each frequency was 0.99. Analyses of frequency response functions for the bandwidth f = 0.01 to 1.0 Hz, revealed the following: 1) mean amplitude ratio (AR) and phase overlap for four different stimulus intensities (30, 60, 100, and 150 degrees/s); 2) no significant differences (Mann-Whitney U test, P greater than 0.05) between any AR or phase value for mean peak SPVU and mean peak SPVD re appropriately directed head velocity; 3) no significant differences (Mann-Whitney U test, P greater than 0.05) between AR and phase values for animals tested and then retested 1 mo later with five intervening standard rotational paradigms; 4) a large effect of vision in producing a VVOR with near-unity gain and near-perfect phase compensation.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity of spindle afferents from cat anterior thigh muscles. II. Effects of fusimotor blockade
Authors: Loeb G. E. , Hoffer J. A.
Published: December 2017

Chronically implanted electrodes and nerve cuff catheters were used to record the activity of individual muscle spindle afferents during treadmill walking as low doses of lidocaine were infused around the femoral nerve to progressively block gamma motoneuron activity. Both primary and secondary endings from both the monarticular knee extensors and the biarticular hip/knee muscles of the anterior thigh showed large decreases in afferent activity, usually well before changes in the electromyographic activity, force output, or length and velocity were seen in the parent muscles. This decline in the proprioceptive signal feeding back onto the spinal cord, which we presume to have involved most of the spindles supplied by the femoral nerve, did not cause noticeable irregularities or instability of the walking gait. At the peak of the fusimotor blockade, spindle afferents from knee extensor muscles lost about half of their usually brisk activity during the near-isometric contraction of the stance phase. Significant decreases in the response to passive stretch during the flexion phase also occurred. At the peak of the fusimotor blockade, spindle afferents from the biarticular muscles lost all of their activity during the rapidly shortening swing phase and about half of their activity during the rapidly lengthening stance phase. For both monarticular and biarticular muscle spindles, the activity decreases in stance and swing phase often occurred at distinctly different stages of the progressive fusimotor blockade, indicating several different sources of fusimotor control. From these data, we infer that the sensitivity of most spindle afferents is substantially influenced by fusimotor activity during phases of both extrafusal activity and extrafusal silence. At least some of this influence appears to come from fusimotor neurons whose recruitment is independent of the extrafusal recruitment. The extent and type of fusimotor effects on spindle afferent sensitivity (dynamic or static) appear to be specialized for the mechanical events that tend to occur during those phases.
Central compensation of vestibular deficits. IV. Responses of lateral vestibular neurons to neck rotation after labyrinth deafferentation
Authors: Xerri C. , Gianni S. , Manzoni D. , Pompeiano O.
Published: December 2017

The response characteristics of neurons located in the lateral vestibular nucleus (LVN) to neck rotation at 0.026 Hz, 10 degrees peak displacement, have been investigated in precollicular decerebrate cats submitted to ipsilateral acute (aVN) or chronic vestibular neurectomy (cVN). On the whole, 105 units were tested after aVN (i.e., during the first postoperative hours) and 132 units after cVN (i.e., after full compensation of the postural and locomotor deficits). The neurons were histologically located either in the rostroventral (rvLVN) or the dorsocaudal part (dcLVN) of Deiters' nucleus, which are known to project mainly to the cervical and the lumbosacral cord, respectively. Moreover, 55 units in the former group and 66 units in the latter group were identified as vestibulospinal neurons projecting to lumbosacral segments of the spinal cord. The responses of these 237 LVN neurons to the neck input were then compared with those of 120 LVN neurons recorded previously in decerebrate cats with intact labyrinths. Whereas 58.3% of the LVN units recorded in control experiments were responsive to neck rotation, 69.5% of the units were affected by this stimulation at the acute stage of the neurectomy and 74.2% at the chronic stage. This increase in responsive units after aVN and cVN with respect to the controls was found exclusively in the dcLVN. The mean discharge rate of the responsive LVN neurons decreased from 40.7 +/- 48.9 (SD) imp/s in control experiments to 22.1 +/- 15.8 (SD) imp/s after a VN. Similar value was also obtained after cVN [25.0 +/- 17.2 (SD) imp/s], suggesting that compensation of the postural deficits elicited by the vestibular neurectomy results from a redistribution of the excitatory drive within different populations of LVN neurons. Indeed, the relation found in control experiments, i.e., that the faster the conduction velocity of vestibulospinal axons the lower was the unit discharge at rest, was lost after aVN, due to a decrease in resting discharge of the slow units. The mean discharge rate of the slow units, however, recovered after cVN, so that the negative correlation between resting discharge rate and axonal conduction velocity was reestablished. The average gain and sensitivity of the first harmonic response of the LVN neurons to neck rotation recorded after aVN and cVN were comparable to those obtained in preparations with the vestibular nerves intact.(ABSTRACT TRUNCATED AT 400 WORDS)
Determinants of sound location selectivity in bat inferior colliculus: a combined dichotic and free-field stimulation study
Authors: Fuzessery Z. M. , Pollak G. D.
Published: December 2017

This study of the neural representation of sound location in the bat Pteronotus parnellii describes how the peripheral and central components of its auditory system shape the horizontal and vertical spatial selectivity of single neurons in the inferior colliculus. Pteronotus extracts spatial information from the echoes of an emitted pulse composed of four constant-frequency harmonics (30, 60, 90, and 120 kHz), each terminated by a downward frequency sweep. To quantify the intensity cues available in the echo, cochlear microphonic response thresholds were used to measure the directional selectivity of the ear and the interaural intensity level disparities (IIDs) created between ears at standardized speaker positions in the bat's frontal sound field, at frequencies in the pulse spectrum. Speaker positions where thresholds were lowest were termed the sensitive area (SA) of the ear. Positions where IID values were greater than 10 dB were termed the difference area (DA). Ear directionality exhibited a pronounced frequency dependence, both in terms of the degree of directional selectivity and the position of the SA. At the 30-kHz harmonic of the pulse, the ear was broadly directional; the SA covered most of the lower half of the ipsilateral field. The ear was highly directional at the 60- and 90-kHz harmonics. Also, the vertical position of the SA changed dramatically between 60 and 90 kHz, from the horizontal midline at 60 kHz to 40 degrees below the midline at 90 kHz. The positions of the DAs also showed a pronounced frequency dependence. The 30-kHz DA was restricted to the extreme lateral part of the frontal sound field. The 60- and 90-kHz DAs were located in the same positions as the equivalent SAs and exhibited the same difference in vertical position. The DAs of the pulse harmonics differ in both their horizontal and vertical positions; the ears thus generate pronounced binaural spectral cues, which provide two-dimensional spatial information. In the inferior colliculus, a combined paradigm of closed-field dichotic stimulation, followed by free-field stimulation, was used to document the frequency tuning and binaural response properties of single neurons and to correlate these properties with the neuron's horizontal and vertical spatial selectivity in the frontal sound field. Where a neuron responded to free-field stimulation at the lowest intensity is termed its SA. A neuron's frequency tuning primarily influenced its degree of spatial selectivity and its sensitivity in the vertical plane, reflecting the directional properties of the external ears at the neuron's best frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Tonic neck reflex of the decerebrate cat: a role for propriospinal neurons
Authors: Brink E. E. , Suzuki I. , Timerick S. J. , Wilson V. J.
Published: December 2017

In decerebrate, acutely labyrinthectomized cats we used neck rotation to study the role of direct upper cervical afferents to the cervical enlargement and of cervical and lumbar propriospinal neurons in the tonic neck reflex. Interruption of the dorsal columns between C4 and C5 had no qualitative effect on the dynamics of the reflex although gain usually increased. Direct upper cervical afferents to the cervical enlargement therefore have no unique role in producing the reflex. Many medially located propriospinal neurons in C4 were modulated by neck rotation. About 40% had axons, mostly crossed, that terminated in the cervical enlargement. The others projected more caudally, some as far as L3-L4 or even the lumbar enlargement. For a population of C4 neurons, including propriospinal neurons, we measured the response vector with combinations of roll and pitch stimuli. These vectors ranged from pitch to roll. Many propriospinal neurons in L3-L4, projecting to the lumbosacral enlargement, were also modulated by neck rotation with a variety of response vectors. Some of these neurons had an ascending projection. As in previous experiments, C4 neurons were modulated by neck rotation after spinal transection rostral to the C1 dorsal root entry zone; a wide variety of response vectors was observed. In contrast, almost no modulated L3-L4 neurons were found in the same experiments. The results suggest a role for propriospinal neurons in the tonic neck reflex. They also demonstrate that responses of lumbar neurons to neck rotation are much more dependent on supraspinal pathways than are those of cervical neurons.
Motoneuron input-resistance changes during fictive locomotion produced by stimulation of the mesencephalic locomotor region
Authors: Shefchyk S. J. , Jordan L. M.
Published: December 2017

Input-resistance changes during fictive locomotion were monitored in a variety of extensor and flexor hindlimb alpha-motoneurons in precollicular, postmammillary decerebrate cats induced to "walk" by electrical stimulation of the mesencephalic locomotor region (MLR). Using intracellular recording techniques and injected hyperpolarizing current pulses, the changes in the motoneuron input resistance recorded at the motoneuron soma were examined during nonlocomoting control periods as well as during the depolarized and hyperpolarized phases of the membrane potential oscillations (locomotor drive potentials, or LDPs) of fictive locomotion. In 28 of the 52 motoneurons examined, no change in the input resistance between the control and locomotor periods was observed. The remainder of the cells displayed a decrease (less than 20%) in input resistance when fictive stepping commenced. Over 80% of all the motoneurons depolarized (mean depolarization 4 mV), whereas only one LG motoneuron hyperpolarized (2 mV) with the onset of stimulation of the MLR. The remaining motoneurons did not display such changes. In 43 out of 52 motoneurons examined, no significant change in the input resistance could be observed between the depolarized and hyperpolarized phases of the step cycle. A decrease in the input resistance during the depolarized phase of the LDP was observed in four LG motoneurons, whereas five other motoneurons (2 LG, 1 TA, 1 PB, and 1 ST) displayed an increased input resistance during the depolarized phase compared with the hyperpolarized phase of locomotion. The data are consistent with the presence of an excitatory synaptic input alternating with an inhibitory input to the motoneuron during the fictive step cycle.(ABSTRACT TRUNCATED AT 250 WORDS)
Interactions of the slow oscillator interneuron with feeding pattern-generating interneurons in Lymnaea stagnalis
Authors: Elliott C. J. , Benjamin P. R.
Published: December 2017

We have used intracellular recording from groups of interneurons in the feeding system of the pond snail, Lymnaea stagnalis, to examine the connections of a modulatory interneuron, the slow oscillator (SO), with the network of pattern-generating interneurons (N1, N2, and N3). The SO is an interneuron whose axon branches solely within the buccal ganglia. There is only one such cell in each snail. In half the snails the cell body is in the right buccal ganglion and in the other half in the left buccal ganglion. Stimulation of either the SO or one of the N1 pattern-generating interneurons elicits the feeding rhythm, but of all the buccal neurons, only the SO can drive the feeding rhythm at the frequency seen in the intact snail. The SO makes reciprocal excitatory synapses with the N1 interneurons that drive the protraction of the radula. This ensures strong activation of the feeding system. The SO inhibits the N2 interneurons. Postsynaptic potentials evoked by stimulation of the SO facilitate without spike broadening in the SO. The SO is strongly inhibited by N2 and N3 interneurons, which are active during the retraction phase. This gates any excitatory inputs to the SO, probably preventing protraction of the radula while retraction is underway. The results support the idea of a single interneuron capable of driving a hierarchically organized motor system.
Activation of a nonspecific cation conductance by intracellular Ca2+ elevation in bursting pacemaker neurons of Helix pomatia
Authors: Swandulla D. , Lux H. D.
Published: December 2017

The pacemaker current of a bursting neuron of Helix pomatia was investigated using voltage-clamp and pressure-injection techniques. In the steady state the net membrane current was zero near threshold of the action potential at -45 mV. Negative to this potential the membrane current was inward and steady. During burst activity a long-lasting inward current instantaneously appeared with voltage steps to membrane potentials below -20 mV. This inward current was already present when the clamp step fell into the rising phase of the first spike and became larger during the depolarizing phase of the spike. The repolarization phase and the interspike interval did not add much current. As the spike duration became longer in the course of the burst discharge the inward current grew in amplitude, but its increase was not proportional to that of the spike duration. This was observed with clamp steps to the potassium equilibrium potential (EK = -70 mV). The inward current decayed during a hyperpolarizing step with a half time of approximately 400 ms, which was invariant to voltage as measured between -40 and -100 mV. It decreased linearly from -100 to -40 mV with an extrapolated zero potential of about -20 mV. The inward current was not generated by spikes if the Ca2+ conductance was blocked by Ni2+. At membrane potentials positive to EK the development of an outward current, probably carried by K+, could be observed during the burst. It overlasted the inward current and decayed with time constants of 6-7 s. This current grew successively in amplitude in the course of the burst discharge and finally nullified the inward-current component at potentials around spike threshold, thus terminating the burst. An inward current with properties similar to the spike-induced inward current was produced by pressure injecting CaCl2 into the neurons. This current was unselectively carried by cations as shown by both ion-substitution experiments and measurements with ion-selective microelectrodes. Large cations such as choline, TEA, and Tris passed through the channels nearly as well as Na+. Changes in the H+ or Cl- concentration were not seen to affect the inward current. Spike as well as the injection-induced currents were largest in bursting pacemaker cells compared with other cells of similar size. Both currents were found to be small or absent in nonbursting but regularly firing pacemaker cells, albeit these cells reveal a larger Ca2+ current density than the bursting pacemaker cell.(ABSTRACT TRUNCATED AT 400 WORDS)
Potentiation of transmission at Ia-motoneuron connections induced by repeated short bursts of afferent activity
Authors: Davis B. M. , Collins W. F. , Mendell L. M.
Published: December 2017

Single medial gastrocnemius Ia-afferent fibers and motoneurons to which they projected were simultaneously impaled in anesthetized cats. Each Ia-afferent fiber was electrically stimulated once every 2 s with short high-frequency bursts (32 shocks at 167 Hz) followed by 1-11 test shocks. The resulting motoneuron excitatory postsynaptic potentials (EPSPs) were recorded and averaged in register. The interval between the end of one burst and the beginning of the next was 2 s; therefore, the amplitude of the first EPSP in the burst was considered to be a measure of efficacy of transmission 2 s after the burst. At most connections (23/29) the mean amplitude of the first EPSP in the burst was equal to or larger than the mean amplitude of control EPSPs produced by low-frequency (18-Hz) stimulation. Enhancement of transmission was maximum 50-100 ms after the burst, and the amplitude of the test EPSP delivered at this time was always greater than that of the control. The period of enhanced transmission appeared to decay more rapidly at connections with small EPSPs. The greatest amount of EPSP amplitude enhancement at 50 or 100 ms after the burst was observed at connections at which EPSP amplitude increased during the burst. The shape (rise time, half width) of potentiated EPSPs was the same as control EPSPs averaged during low-frequency (18-Hz) stimulation. Multiple shocks delivered at low frequency between bursts revealed that enhanced transmission following the high-frequency burst is very sensitive to the effects of low-frequency test stimulation. Furthermore, increasing the number of shocks during the interval between bursts reduced the enhancement of the first EPSP in the burst. We suggest that modulation of synaptic transmission after high-frequency bursts differs across Ia-motoneuron connections. These time-dependent changes associated with short bursts of firing (which are similar in frequency to those observed in Ia-fibers supplying hind-limb muscles during stepping) emphasize the necessity to consider the history of the discharge pattern of the group Ia fiber in assessing efficacy at individual Ia-motoneuron connections.
Morphological observations of motor units connected in-series to Golgi tendon organs
Authors: Spielmann J. M. , Stauffer E. K.
Published: December 2017

The glycogen-depletion technique (17, 32) has been used to examine the functional and morphological relationships between single isolated motor units (MUs) and single isolated Golgi tendon organs (GTOs) that were excited by the MUs in the soleus muscle of the cat. All MUs whose twitch contraction generated a brisk discharge from the GTOs during the rising and plateau phase of force development had a muscle fiber attached specifically to the proximal end of the GTOs. A significant (P less than 0.05) linear relationship was found between GTO discharge rate and the cross-sectional area of the muscle fibers that connected to a receptor. This was true when the correlation was calculated between firing rate and 1) the cross-sectional area of the entire collection of muscle fibers that connected in series to the GTOs; and 2) for the cross-sectional areas of the individually depleted muscle fibers that inserted on the GTO sample. These findings support the notion that the most physiologically relevant input for GTOs arises from the MUs that are attached directly in-series with the receptor.
Lateral hypothalamus neuron involvement in integration of natural and artificial rewards and cue signals
Authors: Nakamura K. , Ono T.
Published: December 2017

Involvement of rat lateral hypothalamus (LHA) neurons in integration of motivation, reward, and learning processes was studied by recording single-neuron activity during cuetone discrimination, learning behavior to obtain glucose, or electrical rewarding intracranial self-stimulation (ICSS) of the posterior LHA. To relate the activity of an LHA neuron to glucose, ICSS, and anticipatory cues, the same licking task was used to obtain both rewards. Each neuron was tested with rewards alone and then with rewards signaled by cuetone stimuli (CTS), CTS1+ = 1,200 Hz for glucose, CTS2+ = 4,300 Hz for ICSS, and CTS- = 2,800 Hz for no reward. The activity of 318 neurons in the LHA was analyzed. Of these, 212 (66.7%) responded to one or both rewarding stimuli (glucose, 115; ICSS, 193). Usually, both rewards affected the same neuron in the same direction. Of 96 neurons that responded to both rewards, the responses of 72 (75%) were similar, i.e., either both excitatory or both inhibitory. When a tone was associated with glucose or ICSS reward, 81 of the 212 neurons that responded to either or both rewards and none of 106 neurons that failed to respond to either reward acquired a response to the respective CTS. Usually, the response to a tone was in the same direction as the reward response. Of 45 neurons that responded to both glucose and CTS1+, 38 (84.4%) were similar, and of 66 that responded to both ICSS and CTS2+, 47 (71.2%) were similar. The neural response to a tone was acquired rapidly after licking behavior was learned and was extinguished equally rapidly before licking stopped in extinction. The latency of the neural response to CTS1+ was 10-150 ms (58.7 +/- 40.9 ms, mean +/- SE, n = 31), and that of the first lick was 100-370 ms (204.8 +/- 59.1 ms, n = 31). The latency of neural responses to CTS2+ was 10-230 ms (68.3 +/- 53.5 ms, n = 33), and that of the first lick was 90-370 ms (212.4 +/- 58.5 ms, n = 33). There was no significant difference between the neural response latencies for the two cue tones nor between the lick latencies for the different rewards. Neurons inhibited by glucose or ICSS reward were distributed widely in the LHA, whereas most excited neurons were in the posterodorsal subarea; fewer were in the anteroventral subarea. Neurons responding to the CTS for glucose or ICSS were found more frequently in the posterior region.(ABSTRACT TRUNCATED AT 400 WORDS)
Discharge patterns of reticulospinal and other reticular neurons in chronic, unrestrained cats walking on a treadmill
Authors: Drew T. , Dubuc R. , Rossignol S.
Published: December 2017

Recordings were made from single units in the medullary reticular formation (MRF) between AP-4.2 and AP-12.9 and from the midline to 3.7 mm lateral in chronically prepared, unrestrained cats walking on a treadmill. Recordings were made with rigid microelectrodes held in a microdrive, and reticulospinal neurons were identified by antidromic stimulation of their axons through microwires chronically implanted into the spinal cord at the L2 level. Electromyograms (EMGs) were recorded from flexor and extensor muscles of the fore- and hindlimbs as well as from back and neck muscles. In total, 295 cells were recorded from 40 penetrations in 4 cats; 252 of these cells were recorded from the more medial regions of the reticular formation encompassing the gigantocellular, magnocellular, and lateral tegmental fields; 38.5% of these (97/252) were antidromically identified from the spinal cord. The remaining 43 neurons (43/295) were recorded from a more lateral and ventral position. These medial and ventrolateral groups of neurons differed not only in position but also in aspects of their discharge during locomotion. Rank-ordered raster displays, triggered from the onset of each recorded muscle, were used to correlate neuronal and muscular activity. The discharge rate of 31% of the reticulospinal neurons (30/97) was modulated once or twice in each step cycle and was strictly related to one or more of the recorded EMGs (EMG-related neurons) on the basis of the pattern of discharge. The discharge of 33/97 (34%) of the neurons was modulated at the periodicity of the locomotor rhythm but could not be correlated with any of the recorded EMGs (locomotor-related cells), whereas the remaining 34/97 neurons (35%) were either silent, fired tonically, or were not related to the locomotor pattern (unrelated cells). Of the EMG-related neurons 27% were related to flexor muscles and the remaining 63% to extensor muscle activity. The discharge pattern of all except two of the flexor-related neurons was correlated with hindlimb muscle activity, whereas that of the extensor-related neurons was correlated almost equally with fore- and hindlimb muscles. Correlations were found with muscles lying both ipsilaterally and contralaterally to the site of the recordings. Although the locomotor-related neurons showed no preferential relation with any of the recorded EMGs, a comparison of the depth of modulation of their discharge measured from postevent histograms suggested that more of these cells were related to the forelimb than to the hindlimb.(ABSTRACT TRUNCATED AT 400 WORDS)
Phase-dependent reversal of reflexes mediated by the thoracocoxal muscle receptor organ in the crayfish, Pacifastacus leniusculus
Authors: Skorupski P. , Sillar K. T.
Published: December 2017

Both negative feedback, resistance reflexes and positive feedback, assistance reflexes are mediated by the thoracocoxal muscle receptor organ (TCMRO) in the crayfish, depending on the central excitability of the preparation. In this paper we present evidence that the velocity-sensitive afferent T fiber of the TCMRO may elicit either resistance or assistance reflexes in different preparations. In preparations displaying assistance reflexes, the S and T fibers of the TCMRO exert reciprocal effects on leg motor neurons (MNs). The S fiber excites promotor MNs (negative feedback) and inhibits remotor MNs, the T fiber excites remotor MNs (positive feedback) and inhibits promotor MNs. During reciprocal motor output of promotor and remotor MNs, reflexes mediated by the TCMRO are modulated in a phase-dependent manner. The TCMRO excites promotor MNs during their active phases (negative feedback) but inhibits them during their reciprocal phases. Remotor MNs are excited by the TCMRO during their active phases (positive feedback). It is proposed that depolarizing central inputs that occur in the S and T fibers at opposite phases of the motor output cycle (21) facilitate the output effects of each afferent in alternation, effectively mediating a phase-dependent shift between the effects of one afferent and the other. The implications of central modulation of reflex pathways and the possible functions of positive and negative feedback reflexes during locomotion are discussed.
Histamine decreases calcium-mediated potassium current in guinea pig hippocampal CA1 pyramidal cells
Authors: Pellmar T. C.
Published: December 2017

The action of histamine on CA1 pyramidal cells was studied in a hippocampal slice preparation. In the presence of tetrodotoxin (TTX) and tetraethylammonium (TEA), histamine had little effect on the calcium spikes. Using the single-electrode voltage-clamp technique, the actions of histamine on membrane currents were tested. In TTX, histamine (1 microM) decreased outward current only at potentials more depolarized than approximately -50 mV, where calcium-mediated potassium current is predominant. In the presence of manganese, histamine was without effect. Histamine (10 microM) did not affect the transient outward potassium current (A-current), the inward M-current resulting from small hyperpolarizing steps, or the inward Q-current elicited by larger hyperpolarizing steps. Blocking potassium currents with TEA or replacing calcium with barium revealed a slow inward current normally carried by calcium. With TTX present to block sodium currents, histamine (10 microM) did not reduce the inward current. The outward current reduced by a maximally effective concentration of histamine (10 microM) can be further decreased by manganese. The results support the conclusion that histamine selectively decreases the calcium-mediated potassium conductance in CA1 pyramidal cells of hippocampus. The possibility is raised that there is a component of calcium-mediated potassium current that is insensitive to histamine.
Role of corticobulbar projection neurons in cortically induced rhythmical masticatory jaw-opening movement in the guinea pig
Authors: Nozaki S. , Iriki A. , Nakamura Y.
Published: December 2017

The role of the pyramidal tract (PT) in the induction of the rhythmical masticatory activity (RMA) of the anterior digastric motoneurons by repetitive stimulation of the cortical masticatory area (CMA) was studied in the ketamine-anesthetized guinea pig. The coronal section of the medial brain stem at the pontine level did not show any effect on the cortically induced RMA in the digastric EMG, as long as the majority of the PT fibers was spared of the section. In contrast, unilateral section of the PT at the pontine level abolished the RMA in the digastric EMG induced by repetitive stimulation of the ipsilateral CMA, while that induced by the contralateral CMA stimulation was not affected by the PT section. The threshold of repetitive PT stimulation for induction of the RMA of the digastric EMG was much higher at the levels caudal to the facial nucleus than that at more rostral levels, and no RMA was induced by the PT stimulation at the caudal bulbar levels even at the supramaximal intensities for RMA induction of the PT stimulation at more rostral levels. Single shocks applied to the PT at the caudal bulbar levels did not evoke any antidromic field potential in the CMA. Single shocks applied to the CMA evoked a negative field potential in the medial bulbar reticular formation (MBRF) mainly on the contralateral side after a monosynaptic latency, which was largest in amplitude in the region including the most dorsal portion of the nucleus reticularis paragigantocellularis and the area dorsally adjacent to it (dPGC). Stimulation of the oral portion of the nucleus reticularis gigantocellularis (GC) evoked an antidromic negative field potential in the ipsilateral dPGC. Intracellular recording from neurons in the dPGC demonstrated that neurons were located in the dPGC that responded with EPSPs after a monosynaptic latency to single shocks applied to the contralateral CMA and with antidromic spike potentials to stimulation of the oral portion of the ipsilateral GC (GCo). Single shocks applied to the dPGC evoked antidromic field potential in the area in the contralateral cerebral cortex corresponding with the CMA. Injection of horseradish peroxidase (HRP) into the dPGC on one side retrogradely labeled the pyramidal cells with HRP bilaterally in the cerebral cortical area corresponding with the CMA. The number and density of the labeled cells on the contralateral side far exceeded those on the ipsilateral side.(ABSTRACT TRUNCATED AT 400 WORDS)
Interocular transfer of adaptation after effect in neurons of area 17 and 18 of split chiasm cats
Authors: Maffei L. , Berardi N. , Bisti S.
Published: December 2017

Responses to sinusoidal gratings for neurons in area 17 and 18 of split chiasm cats were recorded extracellularly, and the interocular transfer of the effect of adaptation to high-contrast gratings was studied. In area 17 all but one of the simple cells showed the phenomenon of adaptation and its interocular transfer; 60% of the complex cells showed the effect of adaptation, and of these cells 35% showed an interocular transfer of adaptation. The adaptation aftereffect was comparable both in strength and duration for the direct and the callosal pathway. The strength of the adaptation aftereffect through the callosal pathway was not related to the strength of the input from the contralateral eye. An interocular transfer of the adaptation aftereffect was found in several neurons with a very weak input from the contralateral eye and in five simple cells apparently responding only to the ipsilateral eye. Fifty-eight percent of the neurons in area 18 showed the effect of adaptation, and 55% of them showed interocular transfer. No interocular transfer of the adaptation aftereffect was found in those neurons where an input from the contralateral eye was undetectable. Interocular transfer of the adaptation was found in all the neurons recorded in area 17 of animals with section of the corpus callosum but intact chiasm. No interocular transfer was found in neurons recorded in area 17 of cats with both the optic chiasm and the corpus callosum sectioned. We conclude that callosal connections are sufficient for the transfer of the adaptation aftereffect, although they are not necessary.
Receptors for excitatory amino acids on neurons in rat pyriform cortex
Authors: ffrench-Mullen J. M. , Hori N. , Carpenter D. O.
Published: December 2017

The actions of a variety of agonists and antagonists of the excitatory amino acids on rat pyriform cortex pyramidal neurons were studied in a submerged, perfused brain slice. The order of potency for the agonists, applied by ionophoresis, was kainate greater than quisqualate greater than N-methyl-D-aspartate greater than aspartate = glutamate. The endogenous monosynaptic excitation of pyramidal neurons upon stimulation of the lateral olfactory tract was blocked post-synaptically by DL-2-amino-4-phosphonobutyric acid, although this drug did not consistently block any of the exogenous responses. The synaptic excitation was not blocked, however, by antagonists presumed specific for the quisqualate (glutamate diethyl ester), kainate, (gamma-D-glutamylglycine), or N-methyl-D-aspartate (DL-2-amino-5-phosphonovaleric acid, DL-2-amino-7-phosphonohetaonic acid) receptors. Several antagonists blocked N-methyl-D-aspartate responses at lower concentrations than those to aspartate, and other antagonists distinguished between kainate and quisqualate responses. These results suggest that 1) pyriform neurons have a variety of receptors that have properties somewhat different from those found in other preparations and 2) the endogenous transmitter activates a receptor distinct from those activated by kainate, quisqualate, and N-methyl-D-aspartate.
Cellular and synaptic properties of amygdala-kindled pyriform cortex in vitro
Authors: McIntyre D. C. , Wong R. K.
Published: December 2017

The evoked and spontaneous activity of neurons in the pyriform cortex of control and kindled rats was examined using a coronal slice preparation containing the amygdala-pyriform region. Electrical stimulation of the amygdala nuclei elicited synchronized burst responses in pyriform cells of slices from both control and kindled animals. The mean duration of the burst was greatly prolonged in cells from kindled preparations. The depolarizing synaptic events underlying the burst response in the kindled and control animals could be examined when Mg2+ was increased to suppress but not block synaptic transmission. Electrical stimulation evoked a short-latency graded synaptic depolarization, followed by a long-latency all-or-none depolarizing event, which appeared to be involved in generating the burst response. Norepinephrine (NE), in a 4-microM concentration, reversibly blocked the burst responses in the control preparation. Burst responses elicited from kindled preparations were also suppressed by NE. For the latter cases, higher concentrations of NE were required to produce this effect. The alpha-2-agonist clonidine mimicked the suppressive action of NE on the evoked events. In contrast the beta-agonist isoproterenol facilitated the occurrence of spontaneous synchronous bursts and prolonged evoked burst discharges in both the control and kindled preparations. NE and clonidine block the burst response by suppressing the underlying synaptic events. The facilitatory action of isoproterenol on spontaneous and evoked responses suggests that NE may also exert an excitatory effect.
Complex-spike activity of cerebellar Purkinje cells related to wrist tracking movement in monkey
Authors: Mano N. , Kanazawa I. , Yamamoto K.
Published: December 2017

Four rhesus monkeys were trained to perform visually guided wrist tracking movements (50). While they performed tasks by wrist flexion or extension from a neutral position, simple-spike (SS) and complex-spike (CS) discharges of a single Purkinje cell (P-cell) were recorded from intermediate and lateral parts of cerebellar hemispheres (lobules IV to VI) ipsilateral to the task-performing wrist. Of approximately 400 P-cells observed, 215 (54%) significantly increased or decreased their SS discharge rate during task performance (task-related P-cells). Of these, 161 were selected for analysis of CS activity; in these P-cells, we could reliably discriminate between CS and background SS by a spike discriminator. The 161 P-cells were further classified into response locked (n = 65) and poorly locked (n = 96) cells according to temporal coupling of the SS frequency modulation to the onset of wrist movements. About 60% of the response-locked P-cells showed a phasic increase (statistical significance level: P less than 0.01) of CS firing rate at the onset of wrist tracking movement. In a few P-cells, a phasic decrease (statistically insignificant) of CS firing rate was observed with the wrist movement. In most P-cells, an increase of CS firing rate was observed with both rapid- and slow-tracking wrist movements. The increase was larger with faster step-tracking movement than with slower ramp-tracking movement. In most P-cells, the CS activity increased with both wrist flexion and extension; in some cells, however, it increased only with either flexion or extension. In most of the response-locked P-cells, the increase of CS firing rate occurred during motor time, i.e., after the onset of the EMG change in prime movers and before the beginning of wrist tracking movement. The increase occurred phasically at the onset and/or at the recovery phase of SS frequency modulation. At neutral wrist position, the maintained frequency of the CS was 0.72 +/- 0.29 CS/s (mean and SD for 161 task-related P-cells). Compared with the frequency at neutral position, the CS frequency did not change tonically during maintained flexed or extended wrist position in any response-locked P-cells. There was no increase of CS firing rate when the monkey returned the handle to center position after completing the tracking task, even in P-cells that had shown a significant increase of CS activity during tracking.(ABSTRACT TRUNCATED AT 400 WORDS)
Simultaneous control of two rhythmical behaviors. II. Hindlimb walking with paw-shake response in spinal cat
Authors: Carter M. C. , Smith J. L.
Published: December 2017

The simultaneous control of the hindlimb paw-shake response and hindlimb walking at slow treadmill speeds (0.2-0.4 m/s) was examined in adult cats spinalized at the T12 level, 3-6 mo earlier. Paw shaking was elicited by either 1) application of adhesive tape or 2) water to the right hindpaw. To assess intralimb and interlimb coordination of the combined behaviors, activity from selected flexor and extensor muscles at the hip, knee, and ankle was recorded, and the kinematics of these joints were determined from high-speed cinefilm. When paw shaking was combined with hindlimb walking, the response in the stimulated limb was initiated during swing (F phase) of the step cycle. The onset of knee extensor activity provided the transition from the flexor synergy of swing to the mixed synergy of paw shake. At the end of the paw shake, an extensor synergy initiated the E-1 phase of swing, and the resultant joint motion was in-phase extension at the hip, knee, and ankle to lower the paw for contact with the treadmill belt. During the rapid (81 ms) paw-shake cycles, knee extensor and ankle flexor muscles exhibited single, coactive bursts that were reciprocal with coactive hip and ankle extensor bursts. This mixed synergy was reflected in the limb coordination, as knee flexion coincided with ankle extension and knee flexion coincided with ankle extension. Phasing of hip motions was variable, reflecting the role of the proximal in stabilization during paw shake (16). Although the number of paw-shake cycles combined during swing varied greatly from 2 to 14, average cycle periods, burst durations, and intralimb synergies were similar to those previously reported for spinal cats tested under conditions in which the trunk was suspended and hindlimbs were pendent (23, 27). For step cycles during which a long paw-shake response of 8-14 cycles occurred, swing duration of the shaking limb increased by 1 s, and during this prolonged interval, the contralateral hindlimb completed two support steps. Stance duration of the support steps was also prolonged. This adjustment maximized the duration of paw-contact and minimized any period of nonsupport by the contralateral hindlimb during paw shake. Completion of the paw-shake response was followed by either an alternating, or a nonalternating, gait pattern on the recovery steps. One spinal cat combined locomotion with short two-cycle paw-shake responses, and because the shortened response was limited primarily to the time ordinarily devoted to swing, interlimb adjustments were slight.(ABSTRACT TRUNCATED AT 400 WORDS)