Proceedings Correlation between ultrastructure and histochemistry of mammalian intrafusal muscle fibres (original) (raw)
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BEHAVIOR OF NEURONS IN THE ABDUCENS NUCLEUS OF THE ALERT CAT I. MOTONEURONS
Abstract The activity ol 53 antidromically identified abducens motoneurons was analyzed in alert cats during spontaneous and vestibular induced eye movements. Conduction velocities ranged from 13 to 70 m/s and all motoneurons increased their discharge rates with successive eye positions in the abducting direction. Motoneurons were recruited from-19' Io *7". Within the oculomotor range lrequency saturation was never observed lor any cell. The slope of rate-position (/e) relationships ranged lrom 2 to l7.7spikes/s/deg(n:40,mean8.7*2.5).Regressionanalysisshowedthattherate positionplotscould be fit by straight lines but in most cases exponential curves produced slightly better statistical fits. Steeper slopes suggest that successively larger increases in k are required for the lateral rectus muscle to maintain mo¡e eccentric fixations in the on direction. Interspike intervals for a constant eye position exhibited low variability (<3.5%) lor fixations shorter than 1 s. Over longer periods, variability increased in proportion to the duration of the fixation in exponential-like fashion up lo 14oA. Abducens motoneurons showed considerable variability in frequency during repeated fixations of the same eye position. Discharge rates were found to depend upon both the direction ol the previous eye movement and, more importantly, th"e animal's level ol alertness. The rate-position regression lines lor fixation periods after saccades in the on direction significantly differed in slopes (100%) and thresholds (20V,) from those in the offdirection. The observed static hysteresis in abducens motoneuron behavior was in opposite direction to that previously described for the mechanical properties ofthe lateral rectus. This suggests both neural and mechanical factors are significantly involved in determining final eye position. The animal's level ol alertness was evaluated in this study by counting the number of saccadic movements/s occurring in "alert" (l + 0.2 saccades/s), and "drowsy" (0.5 + 0.2 saccades/s) circumstances. Comparison of the rate-position regression lines between the two conditions showed a significant decrease in slopes (100%) and elevation ol thresholds (70%). Discharge rate ol abducens motoneurons increased abruptly 8.9 + 2.8 ms prior to saccades in the horizontal on direction, and decreased 14.8 + 4.05 m before saccades in the ofldirection. During purely vertical saccades the firing frequency of abducens motoneurons did not change. Burst frequency did not saturate during saccades, but increased with saccadic velocity in a linear fashion. Slopes (r") of rate-velocity regression lines ranged from 0.64 to 2.2 spikes/s/deg ls (n : 14, mean l. 1 3 + 0.45). During saccades in the off direction, discharge lrequency always decreased, but it was not necessarily extinguished. Rate velocity regression lines measured after spontaneous saccades (r") and during the last phase of vestibular nystagmus (r,, : 1.1 I + 0.40 spikes/s/deg/s) showed no significant differences. However, r, and r." values were significantly different lrom slow phase velocity during vestibular stimulation (r":1.31 +0.34 spikes/s/deg/s) in 4/14 motoneurons. These data suggest that in a minority of motoneurons a different source and/or pattern ol synaptic innervation produces the two types of eye movements. Firing rate showed a continuously changing profile during saccades. Maximum intra-burst frequency was reached before peak velocity and decayed in exponential-like fashion with time constants ranging from l0 to 150ms. For saccades in the offdirection the opposite relationship held. During lowered states of alertness the sharp increase in frequency during saccades was less noticeable and in many cases occurred after onset of eye movement. Wide variations in burst onset and intra-burst frequency including the absence ol saturation largely explains the observation that saccades in the cat are generally 600/o slower than in monkey. Sinusoidal head rotation in the dark produced a phase lead of abducens motoneu¡ons with respect to eye position. Time constants (70) calculated from phase leads between firing rate profiles and eye position duringthesinusoidalrotationrangedlrom90.0to l9Tmswithameanof 143.1 +35.l.Therangesand means were not significantly different lrom time constants calculated from individual T,:y,¡¡, (126.6+ 58.0), r""-r",lk (123.0 + 51.7) and T,:r"lk (143.4+ 32.2) quotients. Qualitatively and quantitatively, every motoneuron participated in all types ofhorizontal conjugate eye movements. A significant correlation was found between the eye position threshold at which a motoneuron began to fire and the slope ofits rate-position regression line (k). The slope for the linear regression was 0.3. In addition, there was a correlation between the proportionality constant (k) and conduction velocity. The above relationships suggest a basis for relating the lunctional characteristics ol abducens motoneurons to their electrophysiological properties. As such these data underline the advantages of evaluating the individual role of motoneurons in eye movement lrom the perspective of a continuous structure-function entity centered around, but not dependent on, features attributed to the size principle.r3.sa Knowledge about the electrophysiology and morphology ol neurons in the cat abducens nucleus is the most extensive in the mammalian extraocular system.
Statistics of the maintained discharge of cat retinal ganglion cells
The Journal of physiology, 1983
Action potentials were recorded from single fibres in the optic tracts of anaesthetized cats. Continuous records were obtained at various levels of scotopic and mesopic retinal illumination. In some cases, the light intensity was modulated by a pseudorandom Gaussian white-noise signal. The maintained discharge of on-centre neurones increased while the maintained discharge of off-centre neurons decreased with increased illumination of the receptive field centre. For both cell types, the coefficient of variation declined with increased rate of discharge. There was minimal short-term dependency in the firing patterns, and it was unaffected by the level of retinal illumination. Virtually all of the structure revealed by the normalized autocovariance functions could be attributed to the shape of the interval distributions. The first few coefficients of the serial correlogram were slightly negative. The magnitude of this negativity was not related to illumination. Long-term dependency in ...
BEHAVIOR OF NEURONS IN THE ABDUCENS NUCLEUS OF THE ALERT CAT-II. INTERNUCLEAR NEURONS
The activity of 43 antidromically identified abducens internuclear neurons with conduction velocities ranging from 14 to 54 m/s was analyzed in alert cats during spontaneous and vestibular induced eye movements. The discharge rate of internuclear neurons significantly increased with successive adducting positions of the contralateral eye. Slopes of rate-position (ft) relationships ranged from 3.1 to 17.9 spikes/deg (mean 12.01 * 3.1). Threshold ranged from-19'to f3". Frequency saturation was never observed for any internuclear neuron within the oculomotor range. Although straight lines were selected to illustrate the rate position relationships, exponential curves always provided the best statistical fit demonstrating that an enhancement in frequency potentiation (É) must accompany more eccentric fixations in the on direction. Internuclear neurons showed a low variability in firing rate (<3.0%) for fixations less than 1s. Variability increased with both longer and repeated fixations of the same eye position. Discharge rates were found to depend upon both the direction of the preceding eye movement and the animal's level of alertness. Separate regression lines ol rate position relations following saccades in the on and off directions differed significantly in slope (100%), but not threshold. The observed static hysteresis in an identified non-motoneuron shows this property to be in a central neural circuit prior to the extraocular motoneuron. The slopes (k) of rate-position plots for all internuclear neurons decreased significantly (100%) when level of alertness changed from "alert" (l +0.2 saccades/s) to "drowsy" (0.5 + 0.2 saccades/s). Thresholds, however, were not significantly altered. Discharge rate of abducens internuclear neurons increased abruptly 10.4 + 2.5 ms preceding saccades 'in'ihe on direction, and decreased 20.5 + 7.8 ms before saccades in the offdirection. Internuclear neuronal activity was not affected by pure vertical saccades. During on direction saccades, firing lrequency did not saturate, but increased with velocity in a linear fashion. Exponential lunctions often fit the data better due to the difference in slopes ol rate-velocity plots for on vs off direction saccades. Slopes (r.) of rate-velocity regression lines during spontaneous saccades ranged from 0.99 to 4.10 spikes/s/deg/s (mean 2.16+0.93). During saccades in the off direction activity always decreased, but it seldom ceased. Rate velocity regression lines measured during the fast phase of vestitrular nystagmus (r"":2.09 + 0.88) showed no significant differences from r" slopes in 82%o ofthe cases. However, both r" and r.u values were significantly different from slow phase velocity during vestibular nystagmus (r":2.52 + l.l) in six out of l0 neurons. The intraburst firing rate during saccades showed a continuously changing profile similar to that described for extraocular motoneurons in the cat and monkey. Exponential-like changes in firing rate were observed near the end of on and off direction saccades. Compared to abducens motoneurons, internuclear neurons showed a more irregular firing rate, higher k and r values (I .4 and I .9 times, respectively), lower thresholds for recruitment and higher firing freq uency at a given eye position. Given the increases in k and r, time constants (Z" : r,/k) were also 1.4 times higher for internuclear neurons than abducens motoneurons. Al1 parameters were predictably modified by the animal's level of alertness and exhibited a directional hysteresis. Discharge rate was correlated to vergence movements in 5/13 neurons. During monocular eye movements of the contralateral eye, internuclear neurons responded with fr and r values not significantly different from those during conjugate eye movement. There was, however, no response for monocular movements of the ipsilateral eye. These data suggest differences in synaptic organization between abducens and medial rectus motoneurons during vergence and conjugate gaze. Sinusoidal rotation in the dark at I Hz produced a phase lead of the instantaneous firing frequency envelope with respecl to eye position in the orbit of 42.6''. The time constant (2.) calculated from the transfer function between firing frequency of internuclear neurons and contralateral eye position was found to be 152.9*43.1ms. This value significantly differed from those calculated lrom individual T,:r"lk (174.9+66.6), 7",:r""lk (169.t +63.4) and T,:r"lk (201.2+ 67.0) quotients; but not from that described lor abducens motoneurons (143.1 + 35.1). Every internuclear neuron participated in all horizontal conjugate eye movements, except vergence. The relationship between eye position thresholds and the value (k) for rate position relationships showed the same slope of0.3 described for abducens motoneurons. These findings argue that the distribution ofcell sizes may be ordered alike in both populations. By contrast, the relation between the coefficient k and conduction velocity exhibited a higher slope for abducens internuclear neurons than for motoneurons. This difference suggests that internuclear neurons, as a pool, are more excitable than motoneurons which correlates well with their different roles in horizontal eye movement. Abbret¡iation: MLF, medial longitudinal fasciculus. 953
Journal of Neurophysiology, 1998
Taylor, A., P. H. Ellaway, and R. Durbaba. Physiological signs of the activation of bag2 and chain intrafusal muscle fibers of gastrocnemius muscle spindles in the cat. J. Neurophysiol. 80: 130–142, 1998. A method is described for identifying the effect of single gamma static (γs) axons on bag2 or chain intrafusal fibers using random (Poisson-distributed) stimuli. The cross-correlogram of the stimuli with the firing of spindle primary afferents took one of three forms. A large, simple, brief response was taken to indicate pure chain fiber activation and a small, prolonged response to indicate pure bag2 activation. A compound response with brief and prolonged components was taken to be a sign of mixed innervation. The correlogram components could be well fitted with lognormal curves. They could also be transformed into curves of gain as a function of frequency, which were convenient for estimating the strength of the effects. In 68 effects of γs axons on Ia afferents, 16 were pure ch...
Experimental Brain Research, 1987
The activity of cerebellar Purkinje cells and interpositus neurones was recorded during and after periods of high frequency (2.5-7.5 Hz) climbing fibre activation in barbiturate-anaesthetized cats. 1. During the high frequency conditioning stimulation, the Purkinje cell simple spike (SS) firing was initially silenced in all zones studied. After a few seconds, the SS reappeared and the frequency increased to well above that of the control level after approximately 10 s. Thereafter, the SS rate started to decline so that, after 15-20 s, the Purkinje cells fired no more SS. This SS silence lasted up to 60 s, whether or not the stimulation was continued. 2. The Purkinje cells responded with a complex spike (CS) to every stimulus. If the high-frequency stimulation lasted for at least 15 s, the spontaneous CS discharge of the Purkinje cells in the cl, c2, and c3 zones was suppressed after the conditioning stimulation had ended. This suppression lasted for approximately the same length of time as the SS silence. In the b zone, however, no CS suppression was observed. 3. Interpositus neurones displayed an increased discharge rate after periods of conditioning stimulation, thus displaying a mirror image of the Purkinje cell SS firing. 4. The behaviour of the neurones agrees well with the behaviour predicted by an hypothesis of the olivo-cerebello-otivary loop (Andersson and Hesslow 1987). 5. The results suggest that the cerebelloolivary projection is topographically organized and matches the microzonal organization in the olivocerebellar projection.
Exp Brain Res (1988) 77:278-222 Summary. The activity of pontomedullary reticular, vestibular, and prepositus neurons has been recorded in the alert cat during spontaneous and vestibular-induced eye movements. Neurons were identified by their antidromic activation from the abducens nucleus. Spikes of these neurons were used to trigger the recording of field potentials in the abducens nucleus-The analysis by post-spike averaging of the field potentials showed the presence of a trifold system of reciprocal (excitatory and inhibitory) direct projections that originated in the above nuclei and terminated in the abducens nucleus with a distinctly graded effectiveness. This trifold afferent system is involved in the generation of fast eye movements, slow compensatory movements of vestibular origin, and eye fixation, respectively.Alert cat-Spike-triggered averaging-Post-synaptic potentials As "the final brainstem site for the integration of horizontal conjugate eye movements" (Baker and Spencer 1981), abducens (ABD) motoneurons and internuclear neurons must receive the convergent activity of several supranuclear circuits, in which each contributes a different oculomotor command; e.g., signals related to positions of eye fixation, saccades and slow eye movements of either visual or vestibular origin. Neurons projecting directly to the ABD nucleus are located almost exclusively in the vestibular, prepositus and oculomotor nuclei, as well as in the pontomedullary reticular formation (Baker and Spencer 1981; Langer et al. 1986; Maciewicz et al. 7977). The distribution, density and termination sites of these projections have been quantified in the Exoerimental Brain Research O Springer-Verlag 1988 cat using electron microscopy (Baker and Spencer 1981; Destombes and Rouvidre 1981; Spencer and Sterling I977) and by combining intra-cellular recording and HRP labelling in acute or chronic preparations (Grantyn et al. 1987; Ishizuka et al. 1980; McCrea et al. 1980; Strassman et al. 1986; Yoshida et al. 1982). There have also been some elegant descriptions of the nature and relative synap-tic efficiency of these different monosynaptic inputs in acute physiological conditions (Hikosaka et al. 1978, 1980). However, the present work represents a first attempt to study this question using the spike-triggered averaging technique in alert cats (Mendell and Henneman 1971; Jankowska and Roberts 1972; Hikosaka et al. 1980). The latter preparation allows a more adequate measure of the contribution of individual neurons to eye velocity and, specially, to eye position. Experiments were carried out in 7 adult cats. Under general anesthesia (sodium pentobarbital, 35 mg/kg, i.p.) cats were chronically implanted with a bipolar stimulating electrode on the left VIth nerve and with monopolar tungsten microelectrodes in the ipsilateral ABD nucleus and in the contralateral MLF. Eye movements were recorded with the scle-ral search-coil technique. A holding system was implanted to allow the extracellular recording of neuronal activity. Special care was taken to minimize discomfort in the animals during recording sessions. Single (or double) unit recording was carried out with glass microelectrodes filled with a 2M NaCl solution saturated with fast green (2-5 MQ of impedance). Recording areas were reached using a transcerebellar approach (Fig. 1). Neuronal activity and eye position records were stored on magnetic tape for subsequent analysis. Recorded units were identified by: i) their location in the brainstem in relation to the ABD nucleus chronic microelectrode (Fig. 1A); ii) their antidromic activation by microstimulation (< 10 Offprint requests /o: J.M. Delgado-García (address see above)
Background firing activity in guinea-pig neocortex in vitro
Neuroscience, 1992
The background firing activity was recorded extracellularly in experiments on guinea-pig neocortical slices maintained in vitro. The following types of background firing activity were revealed: (i) high regular single spikes (48%), (ii) irregular single spikes (lS%), (iii) bursts (7%), (iv) groups (7%), (v) mixed activity where single spikes alternated with bursts or groups (28%). The specific interspike interval distribution and the specific shape of autocorrelogram corresponded to each of these background firing activity types. Furie analysis of autocorrelograms showed periodic components in spike sequences with the maxima at 3, 12, and 28 Hz. When blocking synaptic transmission with 100 mM adenosine, about 70% of the background active cells "fell silent" and the remaining 30% of neurons continued to generate action potentials. The latter seem to be actual spontaneously active neurons, i.e. they were capable of autonomous spike generation. We failed to find any correlation between the type of neuronal firing and the ability of neurons to be spontaneously active. The selective blockade of inhibitory synapses with 100 mM picrotoxine did not practically change the character of background firing activity though the responses to stimulation became epileptic. An important conclusion to emerge from this study is that the background firing activity in cortical slices can include the actual spontaneous discharges related to intrinsic cell properties as well as those concerned with synaptic actions. Furthermore, a small number of spontaneously active neurons seem to he able to synaptically activate twice the number of cells. The inhibitory intemeurons did not significantly influence the propagation of excitation with the absence of stimulation.