Effect of chronic acidosis on discharge frequency of intrapulmonary chemoreceptors in the chicken

Effects of electrical stimulation of sympathetic nerves to the carotid sinus on the discharge of single active baroreceptor fibers of the rabbit were examined in situ and in functionally isolated carotid sinus preparations with an intact sympathetic innervation under controlled conditions of pressure and temperature. Among 30 single units, 18 units responded to sympathetic stimulation of increasing discharge frequency. The excitatory effect of sympathetic stimulation on baroreceptor activity was not abolished by phentolamine (1 mg/kg iv or 10(-6) g/ml in perfusate). In isolated carotid sinus preparations perfused with Krebs-Henseleit solution, various pressure steps were applied to the sinus, and effects of norepinephrine (NE; 10(-9) and 10(-6) g/ml) on activity of nine single baroreceptor units were examined. In the presence of 10(-9) g/ml NE, discharge frequency of all units significantly increased at a given pressure step when compared with the control, whereas NE at a high concentration (10(-6) g/ml) did not produce significant changes in the discharge frequency. It is concluded that NE released by sympathetic nerve endings most likely acts directly on the baroreceptor nerve endings and sensitizes them.

Download Full-text

Cerebellar nuclear cell activity during antagonist cocontraction and reciprocal inhibition of forearm muscles

Journal of Neurophysiology ◽

10.1152/jn.1985.54.2.231 ◽

1985 ◽

Vol 54 (2) ◽

pp. 231-244 ◽

Cited By ~ 78

Author(s):

R. Wetts ◽

J. F. Kalaska ◽

A. M. Smith

Keyword(s):

Activity Patterns ◽

Cell Activity ◽

Reciprocal Inhibition ◽

Discharge Frequency ◽

Wrist Flexion ◽

Wrist Movement ◽

Forearm Muscles ◽

Flexion Extension ◽

Nuclear Cell ◽

Low Order

Monkeys were trained to exert a maintained isometric pinch with the thumb and forefinger. This task reliably elicited a simultaneous cocontraction of the forearm muscles. The same monkeys were also taught to insert the open hand into a manipulandum, flex and extend the wrist 35 and 15 degrees, respectively, and maintain an isometric wrist position against a mechanical stop for 1 s. This second task comprised two conditions: a dynamic or movement phase and a static or isometric phase. Movement always involved a wrist displacement of 50 degrees. Although some forearm muscles demonstrated bidirectional activity during the wrist displacement phase, all the wrist and finger muscles were alternatively active in isometric flexion or extension. Of the neurons in the dentate and interposed nuclei that consistently changed discharge during repeated isometric prehension, over 90% (61/67) of the neurons increased activity during this cocontraction of forearm muscles. About 70% (47/67) of these same nuclear cells discharged with a reciprocal pattern of firing during alternating wrist flexion-extension movements. Forty-six neurons had sustained and reciprocal discharge during the maintained isometric wrist postures. No differences were seen between the activity patterns of dentate and interposed cells with respect to either the prehension task or the reciprocal wrist-movement task. The discharge frequency of some dentate and interpositus neurons could be correlated with prehensile force as well as velocity of wrist movement and torque developed by wrist muscles. Correlation coefficients were calculated between nuclear cell discharge and the amplitude of the surface EMGs of the flexors and extensors of the wrist and fingers during the wrist-movement task. Sixteen nuclear cells showed low-order, but reliably positive, correlations with one of the two forearm muscle groups (mean r = 0.33). In contrast, a sample of seven Purkinje cells recorded during the same task demonstrated low-order correlations that were negative in sign (mean r = -0.30) between discharge frequency and one of the two forearm EMGs.

Download Full-text

Responses of primate SI cortical neurons to noxious stimuli

Journal of Neurophysiology ◽

10.1152/jn.1983.50.6.1479 ◽

1983 ◽

Vol 50 (6) ◽

pp. 1479-1496 ◽

Cited By ~ 261

Author(s):

D. R. Kenshalo ◽

O. Isensee

Keyword(s):

Receptive Field ◽

Cortical Neurons ◽

Receptive Fields ◽

The Body ◽

Thermal Stimulation ◽

Discharge Frequency ◽

Mechanical Stimuli ◽

Noxious Heat ◽

Nociceptive Neurons ◽

Heat Pulses

Recordings were made from single SI cortical neurons in the anesthetized macaque monkey. Each isolated cortical neuron was tested for responses to a standard series of mechanical stimuli. The stimuli included brushing the skin, pressure, and pinch. The majority of cortical neurons responded with the greatest discharge frequency to brushing the receptive field, but neurons were found in areas 3b and 1 that responded maximally to pinching the receptive field. A total of 68 cortical nociceptive neurons were examined in 10 animals. Cortical neurons that responded maximally to pinching the skin were also tested for responses to graded noxious heat pulses (from 35 to 43, 45, 47, and 50 degrees C). If the neuron failed to respond or only responded to 50 degrees C, the receptive field was also heated to temperatures of 53 and 55 degrees C. Fifty-six of the total population of nociceptive neurons were tested for responses to the complete series of noxious heat pulses: 46 (80%) exhibited a progressive increase in the discharge frequency as a function of stimulus intensity, and the spontaneous activity of two (4%) was inhibited. One population of cortical nociceptive neurons possessed restricted, contralateral receptive fields. These cells encoded the intensity of noxious mechanical and thermal stimulation. Sensitization of primary afferent nociceptors was reflected in the responses of SI cortical nociceptive neurons when the ascending series of noxious thermal stimulation was repeated. The population of cortical nociceptive neurons with restricted receptive fields exhibited no adaptation in the response during noxious heat pulses of 47 and 50 degrees C. At higher temperatures the response often continued to increase during the stimulus. The other population of cortical nociceptive neurons was found to have restricted, low-threshold receptive fields on the contralateral hindlimb and, in addition, could be activated only by intense pinching or noxious thermal stimuli delivered on any portion of the body. The stimulus-response functions obtained from noxious thermal stimulation of the contralateral hindlimb were not different from cortical nociceptive neurons with small receptive fields. However, nociceptive neurons with large receptive fields exhibited a consistent adaptation during a noxious heat pulse of 47 and 50 degrees C. Based on the response characteristics of these two populations of cortical nociceptive neurons, we conclude that neurons with small receptive fields possess the ability to provide information about the localization, the intensity, and the temporal attributes of a noxious stimulus.4+.

Download Full-text

Differing activities of medullary respiratory neurons in eupnea and gasping

Journal of Applied Physiology ◽

10.1152/jappl.1991.70.3.1265 ◽

1991 ◽

Vol 70 (3) ◽

pp. 1265-1270 ◽

Cited By ~ 16

Author(s):

D. Zhou ◽

M. J. Wasicko ◽

J. M. Hu ◽

W. M. St John

Keyword(s):

Carbon Monoxide ◽

Brain Stem ◽

Phrenic Nerve ◽

Peak Discharge ◽

Discharge Frequency ◽

Respiratory Neurons ◽

Ventilatory Pattern ◽

Medullary Respiratory Neurons ◽

Inspiratory Neurons ◽

Expiratory Neurons

Our purpose was to compare further eupneic ventilatory activity with that of gasping. Decerebrate, paralyzed, and ventilated cats were used; the vagi were sectioned within the thorax caudal to the laryngeal branches. Activities of the phrenic nerve and medullary respiratory neurons were recorded. Antidromic invasion was used to define bulbospinal, laryngeal, or not antidromically activated units. The ventilatory pattern was reversibly altered to gasping by exposure to 1% carbon monoxide in air. In eupnea, activities of inspiratory neurons commenced at various times during inspiration, and for most the discharge frequency gradually increased. In gasping, the peak discharge frequency of inspiratory neurons was unaltered. However, all commenced activities at the start of the phrenic burst and reached peak discharge almost immediately. The discharge frequencies of all groups of expiratory neurons fell in gasping, with many neurons ceasing activity entirely. These data are consistent with the hypothesis that brain stem mechanisms controlling eupnea and gasping differ fundamentally.

Download Full-text

Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats

Journal of Applied Physiology ◽

10.1152/jappl.1996.81.6.2428 ◽

1996 ◽

Vol 81 (6) ◽

pp. 2428-2435 ◽

Cited By ~ 15

Author(s):

J. H. Mateika ◽

E. Essif ◽

R. F. Fregosi

Keyword(s):

Motor Unit ◽

Unit Activity ◽

Motor Units ◽

Discharge Frequency ◽

Oblique Muscle ◽

Single Motor Unit ◽

Motor Unit Activity ◽

Rate Coding ◽

External Oblique ◽

Spontaneously Breathing

Mateika, J. H., E. Essif, and R. F. Fregosi. Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats. J. Appl. Physiol. 81(6): 2428–2435, 1996.—These experiments were designed to examine the behavior of external oblique motor units in spontaneously breathing cats during hypoxia and to estimate the contribution of recruitment and rate coding to changes in the integrated external oblique electromyogram (iEMG). Motor unit activities in the external oblique muscle were identified while the cats expired against a positive end-expiratory pressure (PEEP) of 1–2.5 cmH2O. After localization of unit activity, PEEP was removed, and recordings were made continuously for 3–4 min during hyperoxia, normoxia, and hypoxia. A total of 35 single motor unit activities were recorded from 10 cats. At each level of fractional concentration of end-tidal O2, the motor unit activity was characterized by an abrupt increase in mean discharge frequency, at ∼30% of expiratory time, which then continued to increase gradually or remained constant before declining abruptly at the end of expiration. The transition from hyperoxia to normoxia and hypoxia was accompanied by an increase in the number of active motor units (16 of 35, 20 of 35, and 29 of 35, respectively) and by an increase in the mean discharge frequency of those units active during hyperoxia. The changes in motor unit activity recorded during hypoxia were accompanied by a significant increase in the average peak amplitude of the abdominal iEMG. Linear regression analysis revealed that motor unit rate coding was responsible for close to 60% of the increase in peak iEMG amplitude. The changes in abdominal motor unit activity and the external oblique iEMG that occurred during hypoxia were abolished if the arterial [Formula: see text] was allowed to fall. We conclude that external oblique motor units are activated during the latter two-thirds of expiration and that rate coding and recruitment contribute almost equally to the increase in expiratory muscle activity that occurs with hypoxia. In addition, the excitation of abdominal motor units during hypoxia is critically dependent on changes in CO2 and/or tidal volume.

Download Full-text