bluuebunny/crossref_metadata_2025 huggingface dataset:
Afterdepolarization mechanism in the in vitro, cesium-loaded, sympathetic preganglionic neuron of the cat
Authors: Yoshimura M. , Polosa C. , Nishi S.
Published: December 2017

Intracellular recordings were performed in Cs-loaded sympathetic preganglionic neurons (SPNs) of the intermediolateral nucleus, identified by antidromic stimulation, in the slice of the T2 or T3 segment of the cat spinal cord. Loading the neurons with Cs resulted in broadening of the action potential, depression of the fast component of the afterhyperpolarization (AHP), and appearance of an afterdepolarization (ADP). A typical ADP in a Cs-loaded neuron had time to peak of 45-110 ms, half-decay time of 70-250 ms, and amplitude of 2-10 mV at membrane potentials between -60 and -70 mV and at a Ca and K concentration of 2.5 and 3.6 mM, respectively, in the superfusion medium. The ADP was associated with a decrease in neuron input resistance and increased in magnitude with hyperpolarization of the cell membrane. The relation between peak ADP amplitude and membrane potential was linear within the range of membrane potentials from -60 to -100 mV. The ADP was reversibly suppressed by the Ca-channel blocker cobalt (2 mM) or by low Ca Krebs solution (0.25 mM). Superfusion with BaCl2 (1.0 mM) or tetraethylammonium (TEA) (10-20 mM) caused an increase in amplitude of the ADP and an increase in action potential duration. Hyperpolarizing pulses, delivered during the course of the spike shoulder, resulted in a decrease of spike duration and ADP amplitude. The ADP was not affected by tetrodotoxin, at a dose blocking the Na-spike, and was enhanced, in association with an increase in action potential duration, when NaCl in the Krebs solution was replaced with choline chloride. Increasing intracellular Cl concentration or decreasing extracellular Cl concentration had no effect on the ADP. Changes in external K concentration from 3.6 to 10 or 0.36 mM increased and decreased, respectively, the amplitude of the ADP. In the absence of Cs, and ADP, with similar time course to that recorded in Cs-loaded SPNs, was recorded when CaCl2 was replaced by BaCl or NaCl was replaced by TEAC1. It is concluded that the SPN afterpotential includes a Ca-dependent inward current, in addition to the already described fast and slow outward K currents of the AHP.
Lateral tegmental field neurons of cat medulla: a source of basal activity of ventrolateral medullospinal sympathoexcitatory neurons
Authors: Barman S. M. , Gebber G. L.
Published: December 2017

We tested the hypothesis that neurons of the lateral tegmental field (LTF) of the cat medulla exert their sympathoexcitatory actions over a pathway that includes rostral ventrolateral medullospinal neurons innervating the spinal intermediolateral nucleus (IML). Thirty-one LTF neurons with sympathetic nerve-related activity [as demonstrated with spike-triggered averaging of inferior cardiac postganglionic sympathetic nerve discharge (SND)] were antidromically activated by microstimulation of the rostral ventrolateral medulla (VLM). The threshold current required to elicit the longest latency antidromic response was increased when the stimulating microelectrode was moved to more dorsal or medial sites in the rostral medulla. This observation suggests that the axons of LTF neurons projected to the rostral VLM. The firing rate of LTF neurons with sympathetic nerve-related activity was decreased during baroreceptor reflex activation. This observation is consistent with the view that these neurons subserved a sympathoexcitatory function. Twenty-five VLM neurons with sympathetic nerve-related activity were synaptically activated by microstimulation of the LTF. The modal onset latency of synaptic excitation (25.6 +/- 2.6 ms) compared favorably with the difference (31 ms on the average) between the firing times of LTF and VLM neurons relative to the peak of the cardiac-related sympathetic nerve slow wave. The firing rate of these VLM neurons decreased during baroreceptor reflex activation. Of nine VLM neurons tested, seven were antidromically activated by microstimulation of the second thoracic (T2) IML. These data are consistent with the view that LTF neurons are a source of the basal discharge of VLM-spinal sympathoexcitatory neurons. Sixteen VLM neurons with sympathetic nerve-related activity were antidromically activated by microstimulation of both the LTF and the T2 IML. In some cases, LTF stimulation activated an axonal branch rather than the main axon. This was demonstrated using time-controlled collision of the VLM neuronal action potentials initiated by LTF and T2 IML stimulation. These data raise the possibility that individual VLM neurons influence SND by actions mediated at both spinal and supraspinal levels.
Vestibular nuclear neuron activity during active and passive head movement in the alert rhesus monkey
Authors: Khalsa S. B. , Tomlinson R. D. , Schwarz D. W. , Landolt J. P.
Published: December 2017

Responses of single neurons were recorded in the medial and descending vestibular nuclei (MVN and DVN) and in the deep cerebellar nuclei of three juvenile rhesus monkeys (Macaca mulatta). Neuronal activity was measured during both passive sinusoidal and nonsinusoidal whole body rotation (peak velocities were under 90 degrees/s) and during active head movements. Although the active head movements occasionally exceeded 300 degrees/s, most exhibited peak velocities of less than 200 degrees/s. A total of 133 units sensitive to horizontal head rotation were recorded, and of these, 38 were held for sufficient time to obtain both passive and active head movement data. Comparison of the neuronal firing patterns obtained during active and passive head movements revealed no apparent differences. Thus neurons that were observed to burst or pause during saccades with the head fixed continued to do so when the head was free. Both the sensitivity to head velocity and the "inferred" spontaneous firing rate were compared during active and passive head movements by plotting rate-velocity curves for both conditions. When the data points were fitted with linear regression lines, no statistically significant differences in either sensitivity or spontaneous rate were found. The present study provides no evidence that efferent vestibular activity alters the properties of afferent vestibular neurons during active head movements, as has previously been suggested (21). Furthermore, neurons in the rostral portions of the vestibular nuclei in primates encode head velocity based entirely on labyrinthine information. Neither neck proprioceptors nor an efference copy of the head movement motor program seem to contribute significantly to the firing patterns observed.
In vitro characterization of neurons in the ventral part of the nucleus tractus solitarius. II. Ionic basis for repetitive firing patterns
Authors: Dekin M. S. , Getting P. A.
Published: December 2017

1. The ventral part of the nucleus tractus solitarius in guinea pigs comprises the dorsal respiratory group and is composed of three classes of neurons. These have been termed types I, II, and III. Each cell type possesses a unique set of repetitive firing properties. An in vitro brain stem slice preparation was used to study the ionic basis for these repetitive firing properties. 2. Three different membrane currents were shown to contribute to the repetitive firing properties. These were: a slow calcium current (ICa), an early, transient potassium current (IKA), and a calcium-activated potassium current (IKC). Type I and II neurons displayed physiologically significant amounts of these currents; type III neurons did not. 3. During depolarization from potential levels between -50 and -60 mV, the repetitive firing properties of type I and II neurons were determined primarily by ICa and IKC. IKA was inactivated in this potential range. The expression of IKC was greater in type I neurons than in type II neurons, and as a result, type I neurons exhibited a self-terminating burst of spike activity early in depolarization, whereas type II neurons displayed a gradual decline in spike frequency throughout depolarization. 4. The properties of IKA in type I and II neurons were studied using the single-electrode voltage-clamp technique. The kinetics of IKA in type I neurons was approximately twice as slow as those of type II neurons. In addition, the voltage dependence of activation and the removal of inactivation for IKA in type I neurons were shifted by about -10 mV with respect to type II neurons. 5. Depolarization of type I neurons from membrane potential levels where inactivation of IKA was removed caused a decrease in the frequency of the initial burst of spikes. This decrease in spike frequency was result of the coactivation of IKA with ICa. 6. Depolarization of type II neurons from membrane potentials where inactivation of IKA was removed caused a long delay between the onset of depolarization and the beginning of spike activity. The delay in excitation was modulated by both the magnitude and duration of the prestimulus hyperpolarization. This modulation of delayed excitation paralleled the time and voltage dependence for the removal of IKA inactivation in type II neurons.
Evidence that periodontal pressoreceptors provide positive feedback to jaw closing muscles during mastication
Authors: Lavigne G. , Kim J. S. , Valiquette C. , Lund J. P.
Published: December 2017

1. Mastication was produced by stimulation of the right motor-sensory cortex of urethan-anesthetized rabbits with 15-s trains of shocks (1-ms duration) at 50 Hz. Movements of the lower jaw and jaw muscle electromyograms (EMGs) were recorded on magnetic tape for later computer analysis. 2. The stimulus site was chosen, and stimulus intensity adjusted, so that stereotyped movements were produced that included a wide swing of the mandible to the left side during jaw closure. 3. Control trials were alternated with trials in which a steel ball (2 mm diam) was thrust between the anterior molar teeth on the left side and left in place for several seconds. 4. When the obstruction was first introduced, a jaw opening reflex was sometimes evoked if the ball struck the buccal surface of the advancing mandibular molar teeth. Thereafter, when the ball was crushed between the occlusal surfaces of the teeth, no jaw opening reflex was seen. 5. Instead, the amplitude and duration of all the jaw closing EMGs increased, beginning at least 12 ms after contact with the ball. This caused a prolongation of the slow closing (SC) phase of the cycle that, coupled with a delay in the start of activity in the digastric muscle (jaw opener), prolonged the cycle by more than 60 ms. 6. During the SC phase of the obstructed trials, the medially directed grinding stroke was exaggerated because of an increase in the contraction of the contralateral zygomaticomandibular and anterior temporal muscles. 7. After collecting data, the sensory nerves to the maxillary and mandibular anterior molar teeth were cut to eliminate feedback from the periodontal pressoreceptors. Control and obstructed trials were repeated. 8. Following denervation, the obstructed cycles were of shorter duration. The mandible still moved to the right during SC in some animals, but the increase in closer muscle EMG activity was much reduced. 9. We conclude that periodontal receptors provide positive feedback to the jaw closing muscles during mastication. This is supplemented by input from other receptors, probably muscle spindles. In addition, an increase in periodontal feedback prolongs the SC phase and the early phases of the opening stroke.
The role of the posterior vermis of monkey cerebellum in smooth-pursuit eye movement control. II. Target velocity-related Purkinje cell activity
Authors: Suzuki D. A. , Keller E. L.
Published: December 2017

1. Purkinje cell activity was recorded from lobules VI and VII of the cerebellar vermis during the performance of visuooculomotor tasks designed to dissociate the signals related to head, smooth-pursuit eye, and retinal image movements. Task-related modulations in the simple spike discharge rates of 157 cells were observed in three alert monkeys. 2. Of 65 Purkinje cells that were completely tested for all three signals, all exhibited smooth-pursuit eye movement-related activity. An additional vestibular or visual response was observed in 17 and 11% of the cells, respectively. Eye, head, and retinal image velocity signals were all recorded in the same unit in 52% of the Purkinje cells. The responses of 5% of the fully tested cells were associated with changes in the direction of eye, head, and retinal image movement. 3. The observed sensorioculomotor responses were direction selective in 98% of the Purkinje cells. For the Purkinje cells that were fully tested, 60% of the cells exhibited peak discharge rates for ipsilateral and 40% for contralateral eye velocity. Of these Purkinje cells, 45% exhibited eye, head, and retinal image velocity signals with equivalent direction preferences. 4. Of 42 Purkinje cells tested, 88% demonstrated some kinds of interactive responses during combined eye and sensory stimulation. The interaction of eye and head velocity signals has been discussed in a companion paper (38). The modulation in discharge rate observed during tracking in the presence of a random dot background pattern could be predicted from the dissociated responses to smooth pursuit in the dark and to movements of the background pattern during suppression of eye movements. 5. The sensitivity to smooth-pursuit eye velocity averaged 1.4 times the sensitivity to head velocity. In 80% of the Purkinje cells, however, the sensitivity to eye velocity exceeded the sensitivity to head velocity by an average of only 10%. The sensitivity to smooth-pursuit eye velocity averaged 1.6 times the sensitivity to retinal image velocity. 6. An increase in Purkinje cell discharge rate was observed during the open-loop period of the initiation of smooth-pursuit eye movements. This open-loop response was consistent with the presence of a visual signal during ocular pursuit, since these cells were also shown to be responsive to a dissociated retinal image velocity signal. Furthermore, the magnitude of the open-loop response indicated an enhancement of the sensitivity to retinal image velocity when visual information became behaviorally significant.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity during mastication of periodontal mechanosensitive neurons of the trigeminal subnucleus oralis of the rabbit
Authors: Olsson K. A. , Lund J. P. , Valiquette C. , Veilleux D.
Published: December 2017

1. The activity of mechanosensitive neurons was examined before and during mastication. One hundred and seventy-eight neurons were recorded in the rostral parts of the trigeminal sensory nuclei of 20 rabbits anesthetized with urethan. Twenty-eight neurons received inputs from the periodontal mechanoreceptors, all on the ipsilateral side. Nineteen had receptive fields that were restricted to one tooth; 2 could be activated from more than 1 tooth, and 6 included parts of the mucosa. Only the latter were spontaneously active. 2. All periodontal neurons with a mandibular input responded to graded electrical stimulation of the inferior alveolar nerve at minimum latencies of less than or equal to 3.4 ms, and approximately half had inputs from the sensorimotor cortex. 3. Almost all periodontal units recorded were found to lie in, or just outside, the dorsal part of the most rostral subdivision of the spinal trigeminal nucleus (subnucleus oralis, pars gamma). None projected to the ipsi- or contralateral thalamus. 4. All periodontal neurons fired during mastication. Those without mucosal receptive fields fired during jaw closure, with almost all activity confined to the slow-closing phase when pressure is applied to the teeth. Injections of local anesthetic showed that input from mucosal fields was responsible for activating neurons in other phases of the cycle. 5. Possible roles in the control of mastication for these periodontal interneurons were discussed.
Membrane potential modulates the activation of GABA-gated channels
Authors: Weiss D. S.
Published: December 2017

1. The activity of single gamma-aminobutyric acid (GABA)-gated Cl- channels (GABA = 0.5-2.0 microM) was recorded in inside-out patches of membrane from cultured chick cerebral neurons. 2. The distribution of open intervals of the GABA channel was described by the sum of two exponentials, which suggests the presence of at least two open states of the channel. The time constants of these two components were 0.39 +/- 0.1 and 2.1 +/- 0.9 ms (+/- SD, n = 9). 3. The distribution of shut intervals was described by the sum of either three (n = 5) or four (n = 3) exponentials. This suggests the presence of at least three or four shut states. 4. At all GABA concentrations examined, the activity of the GABA channel decreased over time. This decline in activity was most likely the result of desensitization of the GABA channels. 5. The distribution of open intervals was unchanged during desensitization of the GABA channel. Thus desensitization is not associated with an alteration in either the mean lifetime of the two open states or the relative number of transitions to these two states. Rather, desensitization results from a decrease in the probability of channel opening. 6. There was an e-fold increase in the probability of finding a GABA channel open for every 80 +/- 43 mV (n = 4) of depolarization. The degree of voltage dependence decreased as the GABA channels desensitized. 7. The depolarization-induced increase in open channel probability was not associated with any change in the distribution of open intervals. Thus depolarization does not affect the mean open time of the channel but rather increases the likelihood that it will open. 8. A simple model with three or four shut and two open states is considered for the gating of the GABA channel by the agonist. Possible sites for the voltage dependence within this proposed model are discussed.
Neural correlations in the dorsal cochlear nucleus: pairs of units with similar response properties
Authors: Voigt H. F. , Young E. D.
Published: December 2017

1. Cross-correlation analysis of simultaneously recorded spike trains can be used to gain insight into functional interactions among neurons. In this paper, we report on cross-correlation analysis of neuron pairs in the dorsal cochlear nucleus (DCN) of the cat. Neuron pairs were isolated with two independent electrodes, which allow systematic study of the effects on correlation of distances between units and differences in their best frequencies (BFs). The data in this paper were obtained from 51 pairs consisting of two neurons of the same type. 2. Cross-correlograms were obtained for 35 pairs composed of type IV units, which are recorded from the principal cells of the DCN. Pairs of type IV units with correlated activities give cross-correlograms with increased correlation near zero delay. This feature is called a central mound (CM) and most likely results from shared excitatory or shared inhibitory inputs. 3. Records of spontaneous activity were obtained from 31 pairs of type IV units. Six of these pairs have correlated spontaneous activities. All six pairs have BFs that differ by less than 0.2 octaves. The shared input inducing these correlations must be a spontaneously active and tonotopically organized projection, like the auditory nerve. Type II units, thought to be DCN inhibitory interneurons that project to type IV units, are not spontaneously active, and thus cannot be the cause of correlated spontaneous activity. Similarly, cochlear granule cells, whose axons project orthogonally to the tonotopic sheets of DCN, cannot be the cause of correlated spontaneous activity because their projection is not confined tonotopically. 4. Stimulus-driven activities were studied for 12 type IV pairs that have uncorrelated spontaneous activities. Five of these pairs have correlated driven activities, with CMs whose sizes depend on the frequency and sound level of the acoustic stimulus. A frequency vs. sound level correlation response map shows the V-shaped tuning properties of the correlation-inducing mechanism. The properties of stimulus-driven correlation in these type IV pairs are consistent with the hypothesis that the correlation is induced by shared input from DCN type II units, although this is not the only possibility. 5. All six type IV pairs with correlated spontaneous activities have correlated driven activities. In five of these pairs, the degree of correlation decreases from its value with spontaneous activity when a low-level acoustic stimulus is applied. Three of these five pairs were tested at higher stimulus levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of pontomedullary reticular formation stimulation on the neuronal networks responsible for rhythmical jaw movements in the guinea pig
Authors: Chandler S. H. , Goldberg L. J.
Published: December 2017

1. In the ketamine-anesthetized guinea pig, electromyographic (EMG) responses of the digastric muscle and vertical and horizontal movements of the mandible were studied when loci within the caudal pontine and rostral medullary reticular formation were stimulated during rhythmic jaw movements (RJMs) evoked by stimulation of the masticatory area of the cortex. 2. Within these regions electrical brain stem stimulation of the pontis nucleus caudalis and nucleus gigantocellularis (PnC-Gi) of the reticular formation completely blocked RJMs at stimulus intensities as low as 10 microA while suppressing the short-latency digastric EMG response that was time locked to each cortical stimulus in the train. PnC-Gi stimulation did not, however, reduce the excitability of the short-latency corticotrigeminal excitatory pathway to digastric motoneurons when tested by short pulse train stimulation at 2 Hz (3 pulses, 500 Hz, 0.3 ms) in the absence of RJMs. 3. Short trains (80 ms) of PnC-Gi stimuli delivered at various phases of the RJM cycle produced a permanent phase shift of the RJM rhythm. If the stimulus train was delivered at an early phase of the cycle (8-40%) the next cycle onset was advanced; if the train was delivered later in the cycle (60-80%) the next cycle onset was delayed. Long trains of PnC-Gi stimuli (100, 200, 300, and 400 ms) increased the time of onset of the next cycle by an amount directly proportional to the duration of the stimulus train. 4. Digastric EMG activity occurring during cortically evoked RJMs occupied nearly 50% of the cycle. If a short train of PnC-Gi stimuli was delivered between approximately 5 and 125 ms after the onset of the burst, the duration of the burst was significantly shortened. 5. These results demonstrate that the suppression of cortically evoked RJMs resulting from PnC-Gi stimulation is due to direct effects on central circuits responsible for the production of the RJM behavior and not on the motoneurons themselves. The evidence presented is consistent with our previously presented hypothesis that the neurons involved in mediating the short-latency corticotrigeminal pathway to digastric motoneurons are separate and distinct from those neurons comprising the central networks responsible for the production of the fundamental jaw oscillation during RJMs.
Primate nucleus gracilis neurons: responses to innocuous and noxious stimuli
Authors: Ferrington D. G. , Downie J. W. , Willis W. D.
Published: December 2017

1. Recordings were made from 67 neurons in the nucleus gracilis (NG) of anesthetized macaque monkeys. All of the cells were activated antidromically from the ventral posterior lateral (VPL) nucleus of the contralateral thalamus. Stimuli used to activate the cells orthodromically were graded innocuous and noxious mechanical stimuli, including sinusoidal vibration and thermal pulses. 2. The latencies of antidromic action potentials following stimulation in the VPL nucleus were significantly shorter for cells in the caudal compared with the rostral NG. The mean minimum afferent conduction velocity of the afferent conduction velocity of the afferent fibers exciting the NG cells was 52 m/s, as judged from the latencies of the cells to orthodromic volleys evoked by electrical stimulation of peripheral nerves. The overall conduction velocity of the pathway from peripheral nerve to thalamus was approximately 40 m/s. 3. Cutaneous receptive fields on the distal hindlimb usually occupied an area equivalent to much less than a single digit. However, a few cells had receptive fields up to or exceeding the area of the foot. 4. NG cells were classified by their responses to graded mechanical stimulation of the skin as low threshold (LT) or wide dynamic range (WDR). No high-threshold NG cells were found. A special subcategory of pressure-sensitive LT (SA) neurons was recognized. Many of these cells were maximally responsive to maintained indentation of the skin. The sample of NG cells differed from the population of primate spinothalamic and spinocervicothalamic pathways so far examined, in having a larger proportion of LT neurons and a smaller proportion of WDR cells. A few NG cells responded best to manipulation of subcutaneous tissue. 5. Discriminant analysis permitted the NG cells to be assigned to classes determined by a k-means cluster analysis of the responses of a reference set of 318 primate spinothalamic tract (STT) cells. There were four classes of cells based on normalized responses of individual neurons and another four classes based upon responses compared across the population of cells. The NG cells were allocated to the various categories in different proportions than either primate STT cells or spinocervicothalamic neurons, consistent with the view that the functional roles of these somatosensory pathways differ. 6. Some of the pressure-sensitive NG cells were excited when the skin was stretched, suggesting an input from type II slowly adapting (Ruffini) mechanoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Identification of the physical stimulus and the neural basis of fabric-evoked prickle
Authors: Garnsworthy R. K. , Gully R. L. , Kenins P. , Mayfield R. J. , Westerman R. A.
Published: December 2017

1. The neurophysiological basis for the sensation of prickle evoked by contact of some fabrics with the skin is reported. 2. Single-unit sensory nerve recordings from the rabbit saphenous nerve were used to identify the receptors responsible for fabric-evoked prickle. These recordings showed that all low-threshold mechanoreceptors were activated by fabric, but they did not show differential response to prickly and nonprickly fabrics. 3. However, the response of some nociceptors, both A delta and polymodal C, differed according to the prickliness of fabrics. Some of these receptors responded to fine von Frey hairs with buckling loads of at least 75 mgf. This suggested that the prickle stimuli on the fabric surface were protruding fiber ends that exerted loads of 75 mgf, or more, against the skin. 4. A Teflon replication technique was devised for estimating the density of these fiber ends. Estimates of the sensation magnitude of prickle from graded fabric sets by a panel of 55 subjects correlated (coefficient 0.91) with this measure of fiber end density. 5. We conclude from these results that fabric-evoked prickle is the result of low-grade activity in nociceptors and that the stimuli are protruding fiber ends exerting loads of approximately 75 mgf or more against the skin.
Effect of tone-pulse rise time on rate-level functions of cat auditory cortex neurons: excitatory and inhibitory processes shaping responses to tone onset
Authors: Phillips D. P.
Published: December 2017

1. The responses of cat auditory cortex neurons are largely dominated by transient stimulus events, including tone-pulse onset. In addition, these neurons often receive sensitive inhibitory inputs in tone frequency-intensity domains flanking the excitatory one centered at characteristic frequency (CF). These observations suggest that auditory cortex neurons might be sensitive to the spectral splatter that occurs at tone onset due to the tone-pulse envelope shape. 2. To investigate this hypothesis, single neurons in the primary auditory cortex of anesthetized cats were studied for the form of their spike-rate versus tone-level functions using CF tone pulses of different rise times. Stimuli were presented to the contralateral ear using a calibrated, sealed stimulus delivery system. 3. Some neurons with monotonic rate-level functions for conventional (5-10 ms) rise-time tones were relatively insensitive to variations in tone-pulse rise time. Other monotonic neurons showed rate-level functions that became increasingly bell shaped for shorter rise-time stimuli. All neurons with bell-shaped, nonmonotonic rate-level functions for conventional rise-time tones became increasingly nonmonotonic for shorter rise-time signals. In the same neurons, lengthening of tone rise times typically reduced the slope of the high-intensity, descending limb of the rate-level function, in some cases to zero. 4. This pattern of rise-time effects is consistent with previous evidence on the association between rate-level function shape and the presence of inhibitory tone response areas flanking the excitatory one at CF. The present data suggest that cortical neurons are sensitive to the gross shape of the short-term stimulus spectrum at tone onset, and that for many neurons, the nonmonotonic form of CF tone rate level functions may be configured as much by the rate of tone onset as by the plateau amplitude of a tone pulse.
Comparison of physiological and histochemical properties of motor units after cross-reinnervation of antagonistic muscles in the cat hindlimb
Authors: Gordon T. , Thomas C. K. , Stein R. B. , Erdebil S.
Published: December 2017

1. Physiological and histochemical properties of the cat ankle extensor muscles, the lateral and medial gastrocnemius, and the soleus were studied after cross-reinnervation by flexor motoneurons. 2. Tibial and common peroneal nerves were cut and cross-united in the popliteal fossa of 2- to 6-mo-old cats. Eighteen to 24 mo later, single motor units were isolated by dissection and stimulation of ventral root filaments and classified into four types: fast-twitch, fatigable (FF), fast-twitch with intermediate fatigue resistance (FI), fast-twitch, fatigue-resistant (FR), and slow, fatigue-resistant (S). Muscle fibers were classified as fast glycolytic (FG), fast, oxidative glycolytic (FOG), and slow oxidative (SO) on the basis of histochemical staining. 3. Although motor-unit force was normally well correlated with the size of the innervating motor axon in the cross-reinnervated muscles, the force of different unit types overlapped considerably. The reinnervated motor units also showed a higher than normal degree of fatigability. 4. The range of muscle unit forces in cross-reinnervated triceps surae muscles was the same as in the normally innervated triceps surae muscles. This range is 2-3 times greater than the flexor muscles, which the common peroneal nerve normally supplies. The range of contraction speed of units in the cross-reinnervated extensor muscles was comparable to that in the flexor muscles, consistent with a motoneuron-specific determination of muscle speed (28). 5. SO and FOG muscle fibers were found in all reinnervated triceps surae muscles, but FG fibers were only found in reinnervated medial gastrocnemius (MG) and lateral gastrocnemius (LG) muscles, consistent with previous findings of the resistance of soleus muscles to complete conversion (10, 16, 20, 21). Type grouping of muscle fibers was characteristic of the reinnervated muscles. 6. Reinnervated SO muscle fibers were larger than the corresponding fibers in normally innervated muscles as were the estimated number of muscle fibers innervated by slow motor axons. Nonetheless, the force generated by the S motor units remained relatively smaller than FR and FF units. The relative contributions of the number, cross-sectional area and specific tension to the force generation of reinnervated motor units are discussed.
Bipolar origin of synaptic inputs to sustained OFF-ganglion cells in the mudpuppy retina
Authors: Arkin M. S. , Miller R. F.
Published: December 2017

1. The synaptic inputs to sustained OFF-center ganglion cells of the mudpuppy retina were studied using a superfused retina-eye-cup preparation. Intra- and extracellular electrophysiological recording techniques were carried out during bath application of 2-amino-4-phosphonobutyrate (APB), a glutamate analog that selectively blocks the light responses of ON-bipolars but has minor effects on OFF-bipolar or horizontal cells. 2. The use of APB reduced ganglion cell inputs to those arising from the OFF-bipolar channel. In this way, the existence and polarity (depolarizing vs. hyperpolarizing) of direct or indirect bipolar connections to ganglion cells was determined. 3. Cobalt application was used to block synaptic transmission and demonstrate that APB does not have a direct excitatory action on ganglion cells. 4. Intracellular recording experiments included the use of pulsatile and sustained current injection to evaluate the input resistance changes associated with light, the action of APB, and the excitatory, inhibitory, or disafacilitory nature of the postsynaptic potentials. 5. Some intracellularly recorded cells were stained with horseradish peroxidase (HRP) to verify the ganglion cell origin of the recordings. 6. The OFF-ganglion cell population of the mudpuppy appears to be a heterogeneous group of cells. Sustained OFF-ganglion cells can receive dominant inputs through either the ON- or OFF-bipolar cell pathway or through a mixture of the two. 7. Based on the analysis of this study, we divided sustained OFF-ganglion cells into three subclasses. For one class, light causes the removal of a sustained excitatory input which originates from the OFF-bipolar channel (i.e., a light-evoked disfacilitation); a second class of cells is almost entirely driven by the ON-bipolar channel through a sustained light-evoked inhibitory input; and a third class receives both a light-evoked sustained disfacilitory input from the OFF-bipolar channel and a sustained inhibitory input through the ON-bipolar pathway. Thus the retina appears to use a variety of mechanisms that result in a common response to flashing light stimuli. 8. The results of this study show that APB can be a powerful tool for pharmacologically deciphering the functional connections that exist between outer and inner retinal neurons.
Response properties and topography of vibrissa-sensitive VPM neurons in the rat
Authors: Ito M.
Published: December 2017

1. Extracellular responses to whisker deflections were recorded in the rat ventrobasal thalamic complex (VB) under urethan anesthesia. One-hundred eighty neurons were collected from 107 animals. 2. VB was sharply demarcated in sections reacted for cytochrome oxidase (CO) activity. Referring to 33 dye spots identified in coronal sections, the localization of 45 neurons could be mapped out. Whisker-sensitive thalamic neurons were confined to the ventral posteromedial nucleus (VPM). VPM points responding to caudal vibrissae were localized in the dorsal aspect of the nucleus, and rostral vibrissae were found to project to deeper points. Dorsal whisker rows tended to be represented by caudal VPM points while ventral whiskers were associated with more rostral points. 3. Of 134 neurons that were noted as either sustained or transient based on the response to a maintained whisker deflection, 50 were sustained-type neurons and 84 were transient-type neurons. The number of whiskers eliciting a response (receptive-field size) varied among neurons; from 1 to 5 (median = 1) among the sustained neurons and from 1 to 12 (median = 4) among the transient neurons. 4. A calibrated, controlled mechanical stimulator was used to deflect individual whiskers. The threshold velocity was measured at 10 mm from the follicle of the most effective whisker when it was deflected in the most preferred direction. Sustained cells (n = 33) had low threshold values, mostly less than 10 mm/s (58 degrees/s in terms of angular velocity) whereas transient cells (n = 62) displayed widely distributed values ranging from 1 to 100 mm/s (5.8-580 degrees/s). The median of velocity threshold values (and angular velocity threshold) was 3 mm/s (17.4 degrees/s) for the sustained type and 8.5 mm/s (50 degrees/s) for the transient type. 5. The response latency was determined using a supramaximal deflection. Sustained cells (n = 29) had slightly but significantly shorter latencies than transient cells (n = 64) (median, 7 vs. 8 ms). 6. Exponential ramp-and-hold deflection was applied to construct a tuning curve to determine the degree of contribution of amplitude and velocity components of a mechanical stimulus under threshold stimulus conditions. Sustained neurons (n = 13) were more dependent on amplitude than on velocity, whereas transient neurons (n = 20) were more dependent on velocity than on amplitude. 7. Fine rostral whiskers were represented exclusively by sustained-type neurons that had small receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of neurons responsive to noxious colorectal distension in the T13-L2 spinal cord of the rat
Authors: Ness T. J. , Gebhart G. F.
Published: December 2017

1. One-hundred thirty-two neurons responsive to colorectal distension in the dorsal horn of the T13-L2 spinal segments of 35 spinalized and 7 intact, deeply pentobarbital-sodium-anesthetized rats were characterized for convergent cutaneous receptive fields, long ascending projections and responses to the intra-arterial administration of the algesic peptide bradykinin. All but 9 neurons had an identifiable excitatory cutaneous receptive field; all receptive fields were located on the lower abdomen, flank, and dorsal body surface. Electrical stimulation in the cutaneous fields of 28 neurons demonstrated that neurons responsive to colorectal distension receive afferent information carried by A- and C-fibers. Stimulus-response functions (SRFs) of 52 neurons excited by graded colorectal distension (20-100 mmHg, 20 s) were monotonic and accelerating, allowing extrapolation of threshold distending pressures to neuronal response. Neurons were subdivided into four classes based upon their response to an 80-mmHg, 20-s colorectal distension search stimulus. 2. Short-latency abrupt [SL-A] neurons (spinalized, n = 46; intact, n = 9) were excited at short latency; activity abruptly returned to base line on termination of distension. Six of 9 neurons in intact rats had long ascending projections as demonstrated by antidromic invasion from the contralateral, ventrolateral caudal medulla. Responses of SL-A neurons to colorectal distension were significantly greater in spinalized than in intact rats. Fifty-three of 55 SL-A neurons had convergent excitatory cutaneous receptive fields and most were responsive to both noxious and nonnoxious stimuli. Ten of 13 neurons tested were excited by intra-arterial bradykinin. The threshold distending pressure, determined from the SRFs of 29 neurons in both the spinalized and intact states, extrapolated to near 0 mmHg. 3. Short-latency sustained (SL-S) neurons (spinalized, n = 31; intact, n = 11) were also excited at short latency in response to colorectal distension, but responses were sustained for 4-50 s following termination of the distending stimulus. Nine of 11 SL-S neurons in intact rats had long ascending projections. All 42 SL-S neurons were spontaneously active and 41 of 42 had convergent excitatory cutaneous receptive fields, excited exclusively by noxious stimuli (n = 29) or excited by both noxious and nonnoxious stimuli (n = 12). Responses to colorectal distension and spontaneous activity were significantly greater in spinalized rats. Twelve of 12 neurons tested were excited by intra-arterial bradykinin.(ABSTRACT TRUNCATED AT 400 WORDS)
Response of vestibular neurons to head rotations in vertical planes. II. Response to neck stimulation and vestibular-neck interaction
Authors: Kasper J. , Schor R. H. , Wilson V. J.
Published: December 2017

1. We have studied the responses of neurons in the lateral and descending vestibular nuclei of decerebrate cats to stimulation of neck receptors, produced by rotating the body in vertical planes with the head stationary. The responses to such neck stimulation were compared with the responses to vestibular stimulation produced by whole-body tilt, described in the preceding paper. 2. After determining the optimal vertical plane of neck rotation (response vector orientation), the dynamics of the neck response were studied over a frequency range of 0.02-1 Hz. The majority of the neurons were excited by neck rotations that brought the chin toward the ipsilateral side; most neurons responded better to roll than to pitch rotations. The typical neck response showed a low-frequency phase lead of 30 degrees, increasing to 60 degrees at higher frequencies, and a gain that increased about threefold per decade. 3. Neck input was found in about one-half of the vestibular-responsive neurons tested with vertical rotations. The presence of a neck response was correlated with the predominant vestibular input to these neurons; neck input was most prevalent on neurons with vestibular vector orientations near roll and receiving convergent vestibular input, either input from both ipsilateral vertical semicircular canals, or from canals plus the otolith organs. 4. Neurons with both vestibular and neck responses tend to have the respective orientation vectors pointing in opposite directions, i.e., a head tilt that produces an excitatory vestibular response would produce an inhibitory neck response. In addition, the gain components of these responses were similar. These results suggest that during head movements on a stationary body, these opposing neck and vestibular inputs will cancel each other. 5. Cancellation was observed in 12 out of 27 neurons tested with head rotation in the mid-frequency range. For most of the remaining neurons, the response to such a combined stimulus was greatly attenuated: the vestibular and neck interaction was largely antagonistic. 6. Neck response dynamics were similar to those of the vestibular input in many neurons, permitting cancellation to take place over a wide range of stimulus frequencies. Another pattern of interaction, observed in some neurons with canal input, produced responses to head rotation that had a relatively constant gain and remained in phase with position over the entire frequency range; such neurons possibly code head position in space.
Renal and somatic input to spinal neurons antidromically activated from the ventrolateral medulla
Authors: Ammons W. S.
Published: December 2017

1. Studies were done to characterize responses of spinal neurons backfired from the ventrolateral medulla to renal and somatic stimuli. Experiments were performed on 31 cats that were anesthetized with alpha-chloralose. Sixty-six spinal neurons were antidromically activated from the area of the lateral reticular nucleus or the ventrolateral reticular formation just rostral to the lateral reticular nucleus contralateral to the recording site. These cells could not be backfired from the medial reticular formation or from the spinothalamic tract just caudal to the thalamus. 2. Cells were located in laminae I, V, and VII of the T12-L2 segments. Antidromic conduction velocities averaged 35.9 +/- 7.2 m/s. Conduction velocities were unrelated to the projection site or laminar location of the cells. Termination sites of 21 cells were located in antidromic mapping experiments. Terminals were localized to the ventrolateral reticular formation, including the lateral reticular nucleus. 3. Responses to electrical stimulation of the renal nerves were always excitatory. Stimulation of renal A-delta-fibers excited 33 cells. These cells failed to respond to stimulation of renal C-fibers. The other 33 cells responded to both A-delta- and C-fiber stimulation. Latencies to A-delta-fiber stimulation averaged 9 +/- 2 ms, whereas latencies to C-fiber stimulation averaged 57 +/- 10 ms. 4. Renal mechanoreceptors were activated by occlusion of the renal vein or upper portion of the ureter. Renal vein occlusion excited 14 of 32 cells tested. Activity increased from 6 +/- 2 to 14 +/- 4 spike/s. Ureteral occlusion increased activity of 19 of 32 cells from 7 +/- 2 to 16 +/- 5 spikes/s. Cells responding to one of the mechanical stimuli were significantly more likely to receive A-delta-and C-fiber input compared with nonresponding cells. Nonresponders were more likely than responders to receive only A-delta input. 5. All cells received somatic input in addition to renal input. Twelve cells were classified as wide dynamic range, 46 as high threshold, and 8 as Deep. Somatic receptive fields most often included skin and muscle of the left flank and abdomen. Thirty-two cells had bilateral receptive fields, and 22 had inhibitory fields in addition to excitatory fields. 6. These data show that spinal neurons projecting to the ventrolateral medulla receive convergent inputs from the kidney and somatic structures. These cells may participate in a variety of functions including autonomic reflexes of renal origin.
The development of transmission at an identified molluscan synapse. II. A quantal analysis of transmission
Authors: Pawson P. A. , Chase R.
Published: December 2017

1. A quantal analysis of transmission at the identified molluscan synapse, V2-RPr1, was performed during development. The study was intended to determine the pre- and postsynaptic contributions to the marked changes in transmitter release described in the previous report. 2. The success of the quantal analysis was predicated on overcoming the problems associated with extending the quantal analysis technique to central synapses. This involved adopting the following strategies: 1) using a low-noise recording system coupled with electrical filtering; 2) establishing objective criteria for failures recognition; and 3) using three methods to determine the quantal content: amplitude histograms, failures analysis, and the coefficient of variation. 3. The correlation of the results obtained from an analysis of amplitude histograms and from failures analysis were highly significant (P less than 0.01) at all times studied. A similar significant correlation was observed between the failures method and the coefficient of variation methods. 4. The amplitude of the quantal unit declined progressively during development (range: 131-25 microV), in parallel with the decrease in the postsynaptic input resistance (range: 103-5 M omega). 5. At both frequencies of stimulation (0.02 and 0.2 Hz), there is an approximately 20-fold increase in quantal content over the period of the study. Frequency facilitation at the synapse is due to an increase in quantal content. 6. Possible structural correlates for the developmental increase in quantal content were discussed.