Journal of Neurophysiology

Feldman, J. L.; Gautier, H.

doi: N/Apmid: 1249602

Abstract The interaction between the pulmonary afferents (PA) and the pneumotaxic center (PC) in control of respiratory pattern was studied in lightly anesthetized paralyzed cats before and after bivagotomy or lesions of the PC using inflations controlled by the onset or cessation of phrenic nerve discharge, i.e., cycle-triggered inflations. This interaction was also studied using electrical stimulation of the central stumps of cut vagi. Introduction of a delay between inspiratory onset and the commencement of an inflation at constant flow and duration resulted in increases of the durations of inspiration (T1) and expiration (TE) and amplitude of the integrated phrenic nerve discharge (A). The lung volume at inspiratory cutoff, i.e., the volume threshold, increased markedly as T1 increased. There were linear relationships between T1 and TE and between T1 and A. At constant alveolar CO2 and tidal volume, the quantitative effects of delay were dependent on the rate of inflation; i.e., when the flow increased, the volume threshold for a given T1 decreased. Bilateral vagotomy abolished the effects of delay and flow. PC lesions, which resulted in apneusis when the cycle-triggered inflations were stopped, produced the following changes compared to the delay effects seen in intact cats: a) the volume threshold for zero delay doubled and its rate of decrease with increased T1 was significantly smaller, and b) the change in TE for a given change in T1 was reduced markedly. Introduction of a delay between inspiratory onset and the start of electrical stimulation of the afferent vagi resulted in effects similar to those seen for delays in cycle-triggered inflations. The T1-TE relationship remained linear when the stimulus trains ended with inspiratory cessation. These results suggest that: a) the inspiratory cutoff mechanism is responsive to the rate, as well as the level, of lung inflation; b) all of the lung volume information affecting inspiratory cutoff in paralyzed cats is carried via the vagi; c) an intact PC is necessary for the generation of a normal time dependence of the volume threshold for inspiratory cutoff; d) the PC plays an important role in matching TE to T1 when the latter changes. For inflations and vagal stimulations applied during expiration, with introduction of a delay between inspiratory cessation and the start of cycle-triggered inflation or vagal stimulation, the results indicated that the expiratory cutoff mechanism has an irrevocable phase of 300-450 ms. Copyright © 1976 the American Physiological Society

Sherk, H.; Stryker, M. P.

doi: N/Apmid: 1249604

Abstract 1. Extracellular recordings were made from single units in the visual cortices of six kittens deprived of experience with pattern vision by binocular lid suture. 2. Selectivity for stimulus orientation was quantitatively assessed in 98 units; 90 responded selectively to the orientation of a moving bar stimulus, the remainder responding nonselectively or too poorly to classify. Cells in these visually inexperienced kittens were similar in their degree of selectivity for orientation to cells tested in adult cats. However, responses tended to be weaker and somewhat more erratic. 3. About half the cells in this simple responded to both directions of stimulus motion at the optimal orientation. Most of those responding to only one direction of motion were considered orientation rather than direction selective because they responded more strongly or more selectively to a moving bar than to a moving spot. 4. Cells appeared to be organized within the cortex in a pattern similar to that found in adult cats, with cells in one column selective for the same orientation, and adjacent column having similar preferred orientations. 5. It is concluded that selectivity for stimulus orientation in the cat's visual cortex is innately determined. Copyright © 1976 the American Physiological Society

Thompson, S. H.; Smith, S. J.

doi: N/Apmid: 1249599

Abstract 1. Spikes in molluscan bursting cells are followed by depolarizing afterpotentials (DAPs) which are not seen in nonbursting cells in the same ganglia. DAPs from successive spikes sum to provide a depolarizing drive capable of sustaining multiple discharge. 2. Subthreshold depolarization activates a DAP-like process in bursters. 3. DAP amplitude increases as the cell is hyperpolarized beyond the potassium equilibrium potential. The amplitude is not changed by intracellular iontophoresis of TEA-Cl. DAP amplitude is reduced by 39% after a 10-min exposure to CA++-free saline, and by 66% after 10 min in 4% Na+ (Tris substituted) saline. The amplitude is unchanged by exposure to K+-free saline. 4. During repetitive stimulation the amplitude of the summed DAP declines. 5. It is concluded that DAP results from a slowly decaying component of Ca++ and Na+ permeability. Copyright © 1976 the American Physiological Society

Britt, R.; Starr, A.

doi: N/Apmid: 1249600

Abstract Unitary discharge patterns (peristimulus time histograms or PSTH) and synaptic events were studies with intracellular recording techniques in 164 cat cochlear nucleus cells to steady-frequency tone bursts 250 ms in duration. There were four response types defined on the basis of the shape of the discharge patterns to tones at the characteristic or best frequency. Primarylike units resemble eighth nerve fibres and have a maximum discharge at tone onset, followed by a smooth decline to a steady level of activity. Buildup units have a transient response at tone onset, followed a period of little or not activity before gradually increasing their discharge rate for the remainder of the tone burst. Onset units have an initial burst of spikes at the onset, with little or no activity for the remainder of the tone burst. Pause units have a long latency (10-30 ms) between tone onset and the appearance of low levels of unit activity, which then gradually increase in rate for the remainder of the tone burst. Changes in signal frequency or intensity within the excitatory response area did not modify response patterns of primarylike and onset units, but could evoke primarylike patterns in buildup and pause units. Inhibition manifested by suppression of spontaneous activity and membrane hyperpolarization were of three kinds: 1) in response to signals at the edges of the excitatory response area (i.e., the inhibitory surround) and detected in onset buildup, and pause units but not in primarylike units; 2) occurring at the offset of tones in the excitatory response area and detected in all four types of cochlear nucleus cells; 3) during excitatory tone bursts in onset and buildup units associated with the periods of suppressed unit activity. Membrane hyperpolarization did not accompany the delay in unit activity after tone onset in pause units. Inhibitory events in cochlear nucleus cells provide mechanisms for producing diversity in the temporal pattern of discharges to acoustic signals which may underly the encoding of complex features of sounds. Copyright © 1976 the American Physiological Society

Georgopoulos, A. P.

doi: N/Apmid: 814209

Abstract High-threshold primary afferent units were selected from the population of axons functionally isolated in fine filaments dissected from the median and ulnar nerves of macaque monkeys. In 47 experiments, 536 such units were studied. They comprised 345 A-delta and 191 C fiber units; 90 low-threshold mechanoreceptive afferents were also studied for comparison. The high-threshold units were categorized by observing their responses to mechanical and thermal (53 and 8 degrees C) stimuli applied to their receptive fiblds in the glabrous skin of the hand. Copyright © 1976 the American Physiological Society

Drager, U. C.; Hubel, D. H.

doi: N/Apmid: 1249606

Abstract In adult mice of the C57BL/6J strain the projection of the visual field was systematically mapped under direct vision. As in other vertebrate species the nasal (anterior) field projected anterolaterally, and the inferior field posterolaterally. Values of magnification-1 (m-1, or degrees of visual field per millimeter tectal surface) were calculated over most of the tectum, for measurements in the coronal and sagittal planes. Whereas m-1 was fairly constant for measurement pairs in sagittal planes, for coronal planes there was a rather large, elongated, horizontally oriented area in the upper field of vision within which m-1 was smaller than elsewhere. In this area m-1 was anisotropic, with a ratio of almost 2:1 between sagittal and coronal planes. In a previously study we had observed that many cells recorded in deeper tectal layers responded to somatosensory stimulation, with whiskers especially conspicuous. In a given penetration perpendicular to the tectal surface, somatosensory receptive fields recorded in the deeper tectum were always concerned with that group of whiskers or with those parts of the body that crossed the regions of visual field represented in the superficial layers directly above. Given this information on the visual coordinates associated with certain somatosensory fields, the detailed mapping of the visual field onto the tectum made it possible to prepare a map of the somatosensory projection on the tectum. The resulting representation differed markedly from maps described for the classic somatosensory pathway. In the tectum the somatosensory map was dictated by the visual-field projection rather than by the peripheral tactile innervation density. Whiskers were thus featured much more prominently in the tectum, and structures close to the eye, such as the pinna and cheek, receive more representation than the tail or hindpaws. Copyright © 1976 the American Physiological Society

Cheney, P. D.; Preston, J. B.

doi: N/Apmid: 129543

Abstract The effects of stimulation of single static and dynamic fusimotor fibers on the dynamic sensitivity and position sensitivity of primary and secondary spindle afferents have been studied in the soleus muscle of the baboon. Static fusimotor fibers decreased the mean dynamic sensitivity of primary afferents at all rates of stretch and stimulation. The magnitude of the decrease in dynamic sensitivity increased as the rate of fusimotor stimulation was increased. Qualitatively similar effects were observed in secondary afferents. Static fusimotor stimulation had a strong excitatory effect on spindle afferent resting discharge and greatly increased the mean position sensitivity of both primary and secondary afferents. Dynamic fusimotor fibers increased the mean dynamic index of primary afferents at all rates of stretch and stimulation. The effect of dynamic fusimotor fibers on the mean dynamic sensitivity, however, was dependent on the rate of muscle stretch; at rates below 15 mm/s the dynamic sensitivity was substantially increased, whereas at rates greater than 15 mm/s it was either unchanged or decreased. Dynamic fusimotor fibers slightly decreased the mean position sensitivity of primary afferents. Copyright © 1976 the American Physiological Society

Nichols, T. R.; Houk, J. C.

doi: N/Apmid: 1249597

Abstract We studied stretch reflexes of soleus muscles of intercollicularly decerebrated cats using a new technique for estimating the component of a stretch reflex that results from the purely mechanical properties of the active muscle (mechanical response). The difference between a net stretch reflex and its underlying mechanical response provided a direct measure of reflex action. 1. The relative contributions of reflex action and the mechanical response are different for stretch and release. With stretch, reflex action is generally large and the mechanical response small. The opposite is true with release. The property that remains relatively constant, when stretch and release are compared, is the net stiffness in opposition to length change. We concluded that reflex action compensates for variations in the inherent stiffness of the muscle. 2. Compensation is effective over a range of intermediate values of initial force, but it fails whenever the reflex force approaches zero or the maximal force at that length. 3. Reflex action is capable of modifying muscular force within 22 ms of the onset of length change. This indicates that even during a fast gallop, there is sufficient time for reflex action. 4. The mechanical properties of the active soleus muscle are highly nonlinear; e.g., muscular stiffness becomes negative transiently during stretch. In stable decerebrate preparations we found that reflex action resulted in a considerable improvement in linearity. 5. Our results support two complementary hypotheses: a) stiffness may be the regulated property of the stretch reflex, and b) the main function of autogenetic reflexes may be to conpensate for variations in the properties of skeletal muscle rather than to oppose changes in load. Copyright © 1976 the American Physiological Society

Eccles, J. C.; Nicoll, R. A.; Schwarz, D. W.; Taborkova, H.; Willey, T. J.

doi: N/Apmid: 1249595

Abstract Almost 10% of neurons in the medial reticular nucleus or adjacent thereto were invaded antidromically in response to stimulation of the fastigial and interpositus nuclei. The fraction was 77/835 for the bulbar and caudal pontine levels, but 0/167 for rostral pontine levels. The mahority, 49, of the neurons projecting to the cerebellum were superficially located in the region of the perihypoglossal nucleus, but 23 were scattered through the medial reticular nucleus, being 2.5-5.0 mm below the bulbopontine dorsum. Both classes of cerebellopetal neurons had a similar range of antidromic latencies, usually from 0.8 to 2.0 ms, but some were ober 3 ms. Both classes responded to volleys from limb nerves and inputs from cutaneous mechanoreceptors, with ranges of excitatory and inhibitory latencies that were similar to those for other medial reticular neurons. It is conjectured that the axonal projection is primarily to the cerebellar cortex and that the branches to the nuclei are often slender, hence the long antidromic latencies; 31 of 59 neurons tested projected to cerebellar nuclei on both sides, often with a considerable latency differential. Rarely, there were also axonal branches projecting up the central tegmental tract. The experimental findings are in very good accord with the anatomical descriptions of Brodal and associates (4, 5, 8, 19). It is suggested that the paramedian reticular and the perihypoglossal nuclei may provide a background excitatory input to the interpositus nuclei. Copyright © 1976 the American Physiological Society

Coulter, J. D.; Mergner, T.; Pompeiano, O.

doi: N/Apmid: 1249603

Abstract The activity of axons located mainly in the ventral part of the lateral funiculi of the cervical segments C2-C3 were recorded in precollicular decerebrate cats and their responses to lateral tilt of the whole animal studied. Units were identified according to their antidromic and/or transynaptic responses to stimulation of the ipsilateral lateral reticular nucleus (NRL) as well as their responses to ipsilateral and/or contralateral forelimb nerve stimulation. In most respects, those units which could be antidromically identified as cervical ascending tract axons showed properties similar to those described for neurons of the spinoreticular pathway, the bVFRT. Among the 106 recorded units, 42 responded to 15 degrees tilts in the median plane. Steady changes in unit discharge frequency were evoked by tilting, which lasted as long as the position of the cat was maintained. The response of the units to tilting consisted of increased in discharge rate during tilt in one direction, while tilt in the opposite direction resulted in a decrease in discharge rate. The magnitude of the responses was clearly related to the degree of tilt. All the units affected by tilt, except one, received inputs from both ipsilateral and contralateral forelimb nerves and some of them also from high-threshold neck muscle afferents. Furthermore, 12 of these units could be orthodromically excited at short latency from the ipsilateral brain stem, suggesting a possible monosynaptic input perhaps transmitted via the lateral vestibulospinal tract. The responses of the cervical ascending spinal tract units to tilt did not appear to depend on peripheral proprioceptive or cutaneous feedback since a number of precautions were taken to eliminate such influences, while control experiments in animals submitted to partial or complete bilateral VIIth nerve section showed the number of neurons responsive to tilt to be profoundly reduced or eliminated. It appeared also that the average spontaneous discharge rate of the ascending units was much lower following bilateral VIIth nerve section than that obtained from the corresponding units recorded in preparations with the VIIth nerves intact. These findings suggested that the responses of the cervical ascending neurons to tilt as well as their spontaneous background activity depended on influences arising from the macular labyrinthine receptors. The observation that the responses of these ascending neurons to peripheral nerve stimulation are modified by tilt further suggested that the macular system may interact with the somatosensory system originating from the forelimb and the neck musculature, thus being able to produce the fine adjustments that cerebellar and brain stem structures exert in the control of posture and movements. Copyright © 1976 the American Physiological Society