Increase In Discharge Frequency Research Articles

Effects of Irradiation of Aplysia Pacemaker Neurons with 20-MeV Electrons

Aplysia pacemaker neurons are excited by irradiation with 20-MeV electrons. The response is an increase in discharge frequency occurring immediately after exposure and decaying within a few seconds to minutes except at very high exposures. The threshold is on the order of 1000 rad, and cell inactivation occurs acutely only at doses on the order of 20,000 rad. Within these limits the excitatory effect is more or less linear with dose. The acute effect is not associated with dramatic resistance changes, although the resulting depolarization indicates an increase in Na/sup +/ permeability. Synaptic transmission in this preparation does not appear to be more sensitive than impulse propagation. At very high doses, spike generation is blocked. Neurons recorded for a number of hours following irradiation show a hyperpolarization prior to final depolarization, which suggests that one terminal event may be an accumulation of intracellular Ca/sup 2 +/ leading to increased K/sup +/ conductance. These studies confirm and extend previous observations on the relative radioresistance of Aplysia neurons. With respect to mammalian studies on nervous system susceptibility to high doses of radiation, no events were found which correlate in time with early transient incapacitation. However, the depressed excitability occurring several hours aftermore » exposure may correlate with the occurrence of death due to the central nervous system syndrome which is seen in higher aminals.« less

Thermo-sensitive neurons in preoptic and anterior hypothalamic tissue cultures in vitro

Preoptic and anterior hypothalamic tissues of newborn mice were cultured in a Maximow double coverslip assembly. Neuron discharges were recorded extracellularly from 32 explants while medium temperature was changed between 30° and 42°C. Warm-sensitive response, an increased discharge frequency in response to a rise in temperature, was exhibited by 33 neurons and cold-sensitive response by 5 neurons. The temperature coefficients of these thermo-sensitive neurons were comparable to those reported in vivo.

Unitary activity of ventrolateral nucleus during placing movement and associated postural adjustment

The activity of neurons in the ventrolateral nucleus of the thalamus (VL) was analyzed in the cat during placing movements of both the right and left forelimbs. The purpose was to determine if thalamic neuron discharge patterns could be related to movement and/or to postural changes. Placing tests were conducted on animals maintained in a standing position and partially restrained by a hammock. Each of the forelimbs rested on a flat surface containing a strain gauge which allowed the stance forces to be measured. Two mobile plates, one on the left and one on the right, were used to elicit a contact placing reaction. The response was composed of an isometric phase, during which the body weight was shifted from the stimulated limb to the opposite forelimb while the stimulated limb was gently pushed backwards, and a movement phase during which the stimulated paw actually accomplished the placing reaction. (1) About half the recorded neurons ( 4786) in the VL region demonstrated a change in activity, generally an increase of discharge frequency, during placing of the right or left forelimb. (2) Almost all the reactive units ( 4547) responded to contralateral placing. Two units changed their activity with ipsilateral placing only, whereas 18 units were active during placing of both forelimbs. The discharge pattern of cells activated during ipsilateral placing was considered as related to the isometric postural adjustment of the contralateral limbs. (3) Cells reactive during contralateral tests were located preferentially in the ventrolateral part of VL. Units reactive during ipsilateral tests (postural units) were also clustered in the ventrolateral half of VL which is the zone controlling limb musculature. Some of the ‘postural units’ were identified as receiving afferents from cerebellar nuclei and projecting to motor cortex. (4) Changes in discharge frequency were observed during either the isometric phase, the movement phase, or both. The same type of patterns were observed during contralateral and ipsilateral placing. About half of the cells responding during the contralateral placing movement did so throughout the entire duration of the movement, and were not specifically related to either the flexion or the extension phase of the placing. (5) The timing of the discharge of VL units with respect to the isometric phase and to the movement phase of the motor sequence varied from cell to cell. No topographic arrangement of neurons with the same pattern of discharge could be found within the nucleus.

The transduction properties of tracheal stretch receptors in vitro

Extrathoracic trachea! stretch receptors and trachea! tension were recorded in rilru when the trachea was stretched. The receptors responded to an increase in tension produced by displacement in the longitudinal or transverse axis of the trachea. They were sensitive to the rate of change of tension as well as the tension level itself, i.e. there was a dynamic component in the response. A fall in temperature decreased discharge frequency but the receptors were not affected by changes in p co2 and pH of the perfusion fluid. Contraction of tracheal muscle, induced by acetylcholine. increased discharge frequency showing that the receptors studied were effectively in series with the muscle.

Response of medullary respiratory neurons to hypercapnia and isocapnic hypoxia.

Single-unit activity was monitored extracellularly from medullary respiratory neurons and nonspecified neurons of decerebrate cats which were paralyzed, vagotomized, and artificially ventilated. Hypercapnia consistently resulted in increased discharge frequencies and decreased modal interspike intervals for respiratory units; peak integrated phrenic discharge heights increased concomitantly. Although isocapnic hypoxia usually resulted in comparable changes, the firing frequency of some respiratory units was depressed. Moreover, this depression was frequently observed simultaneously with a hypoxia-induced increase in phrenic discharge. Nonrespiratory unit discharge was mainly unaltered by hypercapnia or hypoxia. Following bilateral carotid sinus nerve section, hypercapnia-induced increases in respiratory neuronal and phrenic activities were still obtained; hypoxia depressed these activities. It is concluded that central chemoreceptor afferent influences are ubiquitously distributed to the medullary respiratory complex whereas peripheral chemoreceptor afferents produce only a discrete and unequal excitation of respiratory units. Hypoxia-induced ventilatory changes are further concluded to be the net result of peripheral chemoreceptor excitation of respiratory units and a direct depression of the brain stem respiratory complex by hypoxia.

Presynaptic impulses in the abducens nucleus and their relation to postsynaptic potentials in motoneurons during vestibular nystagmus.

1. Unit spikes of axons projecting to the abducens nucleus and responding to horizontal rotation of the head were recorded within the cat abducens nucleus. Their discharge pattern related to vestibular nystagmus was investigated with reference to PSP changes of abducens motoneurons as monitored by the field potentials in the nucleus. There were four groups of presynaptic axons whose activity was tightly related to motoneuronal PSPs. 2. The first and second groups of axons were activated mono- and disynaptically from the contralateral labyrinth, respectively, and fired in phase with abducens nerve discharges. Their tonic activity during the slow excitatory phase of motoneurons was abruptly suppressed at the onset of positive field potential (motoneuronal hyperpolarization). The disynaptically activated axons exhibited burst-tonic discharges at the quick excitatory phase and steep increases in their discharge frequency were synchronous with the onset of negative field potential (motoneuronal depolarization). 3. The third group was activated monosynaptically from the ipsilateral labyrinth and fired in phase with the silent period of the abducens nerve. Their tonic activity during the slow inhibitory phase of motoneurons was abruptly silenced at the onset of negative field potential. At the quick inhibitory phase they tended to begin firing slightly later than the onset of positive field potential. 4. The fourth group exhibited high frequency burst discharges at the quick inhibitory phase of motoneurons. Steep increases in discharge frequency occurred synchronously with the onset of the positive field potential. These axons were silent during the slow inhibitory phase of motoneurons. 5. The characteristic time course of PSPs in abducens motoneurons during vestibular nystagmus was well explained by synaptic actions of these four groups of presynaptic axon on motoneurons. The origin of each group of axon was discussed in view of their responses to electric stimulation of the vestibular nerve.

Intrapulmonary receptors in the tegu lizard: I. Sensitivity to CO 2

Single unit vagal recordings from intrapulmonary receptors were obtained in decerebrate, paralyzed lizards both during pump ventilation and during unidirectional ventilation of the cannulated, sack-shaped lung. Two types of receptors were identified: (1) CO 2-receptors , which increased their discharge frequency as intrapulmonary CO 2 concentration decreased but were not sensitive to stretch of the lung. (2) Mechanoreceptors, which rapidly increased discharge frequency when the lung was stretched. These receptors' CO 2 sensitivity varied. Lungs of lizards thus appear to possess both CO 2 receptors, which have functional characteristics similar to those in birds, and mechanoreceptors with properties similar to stretch receptors in mammals.

Reflex changes in discharge activities of gamma efferents to varying skin temperatures in cats.

Changes in spontaneous discharges of single γ-efferents dissected from the lumbrosacral ventral root of spinal cats were observed during cooling of warming of a small area of the foot pad skin of the ipsilateral hind limb. In a certain range of skin temperature, varying from 34°C to 38°C from preparation to preparation, temperature changes resulted in either an increase or decrease in discharge frequency, whereas above this temperature range, heating produced an increase in discharge frequency. By contrast, all γ-efferents examined responded with a negative temperature coefficient to a change in skin temperature below the respective temperature. The thermal activation of these efferents elicited by a small temperature change of the skin was affected considerably by the velocity rather than by the degree of temperature changes but the effect of both variables differed according to the skin temperature at which the temperature change occurred. Ratios of increment or decrement in discharge frequency (±Δ imp./s) to degree (±Δ °C) and velocity of temperature change (±Δ °C/s) respectively were plotted as a function of skin temperature, and indicated a directional relationship between stimulus and response by attaching to each ratio either a positive or negative temperature coefficient. The maximum activity response in the range of 20–30°C was −19 imp./s per °C at 22°C and the average was −8.33±4.77 imp./s per °C. In the warmer range, the coefficients were positive and the average was 23.79±12.21 imp./s per °C in the range of 40–44°C. The steady state activity at a constant temperature showed no sign of dependency on skin temperature. On the basis of these results, the possible mechanisms for thermal inflow contributing to a thermally-induced reflex of the γ-motoneurons and the functional implications of these reflexes for the thermoregulatory system are discussed.

Evidence for Mechanoreceptors in the Muscular Stomach of the Chicken

Single-fiber, vagal recordings were made from mechanoreceptors in the muscular stomach of the chicken. These receptors increased discharge frequency (i) during gentle compression of the wall of this organ and (ii) when coordinated contractions of the organ were induced pharmacologically.

Metabolic regulations of the rhythmic activity in pacemaker neurons. III. Neutralization of the pentylenetetrazol effect in regularly beating Aplysia neurons by metabolic modifiers

In regular beating pacemaker neurons isolated from the sea hare Aplysia californica, 30-50 mM pentylenetetrazol (PTZ) induces spike doublets and triplets, multi-spike bursts, and paroxysmal depolarizing shifts. The development of the characteristic PTZ-induced changes in impluse pattern is preceded by a transient increase in discharge frequency and a reduction in after-hyperpolarization. According to earlier findings, the rhythmic spike activity of pacemaker neurons is governed by a phosphofructokinase-fructose-1,6-diphosphatase-mediated substrate cycle, the activation of which leads to the appearance of spike bursts. Inhibitory modifiers of this neuronal substrate cycle, such as citrate, ATP, and 3-phosphoglycerate, are able to neutralize the changes in the impluse characteristics occurring as the result of PTZ action. Since the reinitiated single-spike trains reverted again to the PTZ pattern following the further addition of activating modifiers, such as fructose-1,6-diphosphate or fructose-6-phosphate, it appears likely that PTZ exerts an influence on the metabolic reactions driving the rhythmic spike activity. In contrast to the reversible effects of the metabolic modifiers the conventional anti-convulsants, phenobarbital and pentobarbital, merely block all spike activity.

Recruitment and discharge frequency of phrenic motoneurones during inspiration

The discharges of 107 phrenic motor axons were recorded from cats under chloralose-urethane anaesthesia with spinal cords transected at T 1 or with intact neuraxis. During inspiratory occlusions in spinal cats, each motoneurone was recruited at a mouth pressure constant at a given end tidal CO 2; no motoneurone was recruited at a pressure greater than 70% of maximum. In eupnoea (32.3 torr CO 2) 73% of motoneurones were recruited during the first 30% of inspiration; during CO 2 rebreathing (60.8 torr CO 2), 89% were recruited in the first 30% of inspiration. Neurones recruited earlier in inspiration had a lower onset frequency than later recruited units; all increased instantaneous frequency in a linear relation to pressure. Early recruited units showed a smaller increase in frequency per unit change in pressure than did later recruited units. During CO 2 rebreathing, mean and peak frequencies increased on average 0.92 and 1.78 spikes · sec −(% CO 2 −, respectively, these increases being significantly less for early than for late recruited neurones. The data show that a stable order of recruitment of phrenic motoneurones exists during inspiration, the excitability of each motoneurone likely determining its time of recruitment. Above threshold, later recruited motoneurones are more ‘sensitive’ to a change in input. Recruitment of motoneurones is responsible for pressure generation at the start of inspiration and increase in discharge frequency (rate coding) is the dominant mechanism in the second half of inspiration.

Synchronization of respiratory frequency by somatic afferent stimulation.

In cats anesthetized with chloralose-urethan, vagotomized, paralyzed, and artifically ventilated, superficial radial (cutaneous) and hamstring (muscle) nerve afferents were stimulated while phrenic nerve electrical activity was recorded. The results obtained with both types of nerves were similar. Stimulation in mid and late expiration advanced the onset of the next inspiration, shortening its duration. Stimulation in early inspiration advanced, while that in late inspiration delayed, the onset of the next expiration. These effects were often accompanied by changes in phrenic motoneuron firing patterns (earlier recruitment, increased discharge frequency, increased slope of integrated phrenic neurogram). Repetitive somatic afferent stimulation produced sustained increases in respiratory frequency in all cats and in half of them entrainment of respiratory frequency to the frequency of stimulation occurred at ratios such as 4:3, 4:5, 1:2, 1:3, 1:4, and 1:7. The lowest stimulus intensity required for evoking these phase shifts was between 5 and 10T (threshold of most excitable fibers) for muscle afferents and between 1 and 2T for cutaneous afferents. These results demonstrate the existence of a reflex mechanism capable of locking respiratory frequency to that of a periodic somatic afferent input. They also provide an experimental basis for the hypothesis that reflexes are resposible for the observed locking between step or pedal frequency and respiratory rate during exercise in man.

Microelectrophoretic study of unit responses of the rabbit amygdaloid nucleus to acetylcholine and noradrenaline

Responses of 152 neurons of the basal and lateral nuclei of the amygdala and of the anterior amygdaloid field to microelectrophoretic application of acetylcholine and noradrenalin, in the case of 115 neurons to both substances, were investigated in immobilized, unanesthetized rabbit. In the basal nucleus 35% of neurons tested responded to acetylcholine, most often by an increase in discharge frequency (34%), and 63% of cells responded to noradrenalin, most of them giving inhibitory responses (53%). A response to only one of the two substances applied in turn was given by 45% of neurons. Among neurons responding to both acetylcholine and noradrenalin, 23% of cells did so in the opposite direction and only 11% in the same direction.

Methods to differentiate electrically induced afferent and sympathetic C unit responses in human cutaneous nerves.

AbstractC unit responses to intradermal electrical stimulation were recorded with tungsten micro‐electrodes inserted percutaneously into intact human cutaneous nerves. An increase in discharge frequency was associated with a decrease in conduction velocity in unmyelinated fibres, and this phenomenon was used to identify afferent C units which responded to both electrical and natural stimuli in the skin. Antidromic impulses in efferent, sympathetic fibres were also elicited by electrical stimulation in the skin as judged by latency changes or signs of collisions in the C responses associated with activity in sympathetic fibres. In this way, conduction velocities in distal segments of both afferent and sympathetic C fibres can be estimated. Furthermore, the possibility to differentiate afferent and sympathetic C units is of obvious importance for the study of their respective discharge characteristics and in psychophysiological studies in alert man.

Firing pattern of neurons in the rostral and ventral part of nucleus reticularis thalami during EEG spindles

The firing pattern of neurons in the rostral and ventral part of nucleus reticularis thalami during cortical EEG spindles was investigated in unanesthetized encéphale isolé cats. Spontaneous spindles as well as those induced by a single thalamic shock were accompanied by an increase in discharge frequency in 97% of the neurons in the rostral pole of the nucleus. In most cases the enhanced firing rate was tonically sustained throughout the duration of the spindles, although phasic bursts at EEG wave frequency were sometimes superimposed on the tonic cellular activation. Suppression of triggered spindles by conditioning fast-frequency stimulation in the mesencephalic reticular formation also abolished the rostral reticularis response. Intracellular recordings revealed a depolarizing shift of small amplitude which was sustained throughout the duration of triggered spindies. The majority of neurons in the ventral part of nucleus reticularis, in contrast, underwent a prolonged hyperpolarizing shift in membrane potential during cortical spindles, sustained for as long as 2 sec and interrupted by depolarizing waves. Both the prolonged membrane hyperpolarization and the depolarizing waves were reduced during the intracellular passage of polarizing currents, suggesting that the former was an inhibitory postsynaptic potential and the latter were disinhibitory potentials. Since neurons in dorsal thalamic nuclei, to which the reticularis axons project, are hyperpolarized concomitantly with cortical spindles, the results are viewed as being in agreement with the hypothesis that, during EEG spindles, neurons in the rostral pole but not in the ventral part of nucleus reticularis exert a tonic inhibitory influence on cells throughout the thalamus.

Electric Communication: Functions in the Social Behavior of Eigenmannia Virescens

Eigenmannia virescens was observed in aquaria in Guyana, South America, during the non-breeding and breeding seasons. Agonistic behavior was described and correlated with electrical activity. Variations in the electric discharges play important roles in agonistic behavior as displays given during attack and retreat. Although descriptions of sexual behavior are not complete, certain electrical signals also appear to be used in courtship. The role of electrical signals in agonistic behavior of Eigemnannia were studied by (1) an analysis of the behavior of fish in dominant and subordinate roles, (2) an analysis of the simultaneous occurrence of electrical displays and motor actions, (3) an analysis of preceding actions of one fish and following actions of the other fish, and (4) analysis of responses to artificial electrical stimuli. These studies indicate that at least three classes of electric signals are important in communication among Eigenmannia: the normal discharge, Interruptions, and Rises. The normal discharge. The normal discharge of Eigenmannia virescens is species-distinctive in the area where this study was conducted. Playback of recorded signals and presentation of sinusoidal electrical stimuli, indicates that the normal discharge particularly the fundamental frequency of the normal discharge (240 to 600 Hz)- is used in species recognition. Males and females overlap extensively in their discharge frequency, and males do not appear to distinguish the electric discharges of males from those of females. Interruptions. Interruptions are brief cessations of the electric discharge. They are most often 20 to 40 msec in duration during agonistic interactions whereas they are often 60 to 80 msec when given by males during interactions with females during the breeding season. Interruptions are usually given in bouts where a bout is any group of Interruptions separated by less than 1.5 seconds. Interruptions are given almost exclusively by dominant fish. They are given at the same time as Attacks, Threats, and No Action, but rarely during Retreat. Bouts with many Interruptions are more likely to be associated with Attacks, and less likely with No Action, than are bouts containing only a few Interruptions. Interruptions correlate with motivation to Attack, and the number of Interruptions in a bout correlates with the probability of attack. Interruptions in one fish are followed by Retreat and No Action in the other fish, thus they appear to be an effective threat display. Interruptions with long durations are given at high repetition rates by male Eigenmannia in the presence of females during the breeding season, thus they may play a role in courtship. Rises. A Rise is an increase in discharge frequency followed by a decrease to the resting frequency. Rises lasting less than two seconds (Short Rises) are often given by dominant fish in agonistic interactions, most often at the same time as Attacks or Threats. They are given rarely. Long Rises (longer than two seconds) are given predominantly by subordinate fish in agonistic interactions. They are given simultaneous with Retreat and No Action and are thus an indicator of submissive behavior. Long Rises in one fish are followed by Attacks, Threats, Approaches, and by No Action in the other. During the breeding season, females, in the presence of males, often give long series of frequency modulations of unknown significance.

The activity of lung afferent nerves during tracheal occlusion

We have recorded the activity of 72 pulmonary stretch receptors isolated from 34 rabbits and 19 receptors isolated from 3 cats both with the animal breathing through an open tracheal tube and against a closed airway. In the first breath during airway occlusion done at FRC 36.1% of the receptors showed an increase of firing during the inspiratory effort compared with the expiratory pause (inspiratory modulation). 47.2% of the receptors showed no change in firing frequency between the two phases of the respiratory effort and 16.7% increased their firing during the expiratory phase (expiratory modulation). However, the average modulation during the first occluded breath was only 7% of that observed in control breathing in rabbits and 2% in cats so the overall frequency of stretch receptors discharge ascending the vagus nerves hardly varied from inspiration to expiration. During the first occluded breath some of the stretch receptors normally silent at FRC became active while others increased their activity. This departure from FRC activity amounts to 6% of the increase in frequency of discharge observed in control breathing. We interpret the behaviour of pulmonary stretch receptors during occluded breathing as due to some re-distribution of air within the lung or some deformation of the airway. We have also studied 8 irritant receptors: 6 in rabbits and 2 in cats. All were active during the control breathing and their activity diminished when the airway was occluded. When the airway was re-opened these receptors showed a greatly augmented activity. This last observation could explain the augmented breath observed after a period of airway occlusion.

An electrophysiological investigation of the receptor apparatus of the duck's bill.

1. The properties of receptors in the duck's bill have been studied by recording from units isolated by dissecting fine filaments from the maxillary and ophthalmic nerves.2. The units studied were divisible into three groups, phasic mechanoreceptors responsive to vibration, thermoreceptive units, and high threshold mechanoreceptors.3. Vibration-sensitive mechanoreceptors (113 units) had small receptive fields, showed a rapidly adapting discharge to mechanical stimulation of the bill, were sensitive to vibratory but not to thermal stimuli and showed no background discharge.4. Temperature receptors (twenty-one units) were insensitive to mechanical stimulation and showed a temperature-dependent background discharge. Sudden cooling produced a transient increase in discharge frequency.5. High threshold mechanosensitive units (eight units) gave a slowly adapting discharge to strong mechanical stimulation and were insensitive to vibratory and thermal stimulation.6. It is concluded that the low-threshold, vibration-sensitive responses come from Herbst corpuscles. No specific function can yet be assigned to the Grandry corpuscles.

Baroreceptor sensitive neurones in the anterior hypothalamus of the cat.

1. The activity of 372 neurones, located within or close to the hypothalamic depressor area, was recorded on raising the pressure within a vascularly isolated carotid sinus.2. When the intrasinusal pressure was raised abruptly to 200 mm Hg the activity of fifteen neurones was enhanced and of six inhibited.3. The neurones exhibiting excitation on baroreceptor afferent stimulation were broadly divisible into two groups. Nine neurones responded with a marked increase in discharge frequency, the other six responded with a ;burst-on' discharge with a minimum latency of 90 msec. Excitation in both cases was always within 500 msec of the presentation of the stimulus. No functional distinction has been drawn from these responses.4. Evidence has been obtained suggesting that the responses of both types of neurone showing excitation may be potentiated using a pulsatile rather than static stimulus.5. The role of the neurones in the integration of the carotid sinus baroreceptor reflex is discussed. It is suggested that the hypothalamic depressor area represents the rostral extension of the integrative centre for the reflex.

Activity pattern of visceral cortex neurons during asphyxia

Upon stimulation of the vagus nerve, evoked responses and single unit activity were recorded from the orbital cortex of anesthetized and artificially ventilated rabbits. The neurons, based on single unit activity during asphyxia, could be separated into two groups: one whose activity disappeared with asphyxia in 54.6 sec; and the other, in 213.4 sec. In both cases, they fired in bursts during asphyxia and their recovery was characterized by a transient increase in discharge frequency.