Long-lasting cycles in formal neural nets.
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Animals↗
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Fictive motor activity in rat after 14 days of hindlimb unloading.
The goal of the present study was to examine the effects of chronic hindlimb unloading on fictive motor patterns which can be developed in hindlimb nerves of adult rats. The animals were divided into two groups. The first group was submitted to hindlimb unloading for 2 weeks by tail suspension. The second group served as controls. After this initial phase, the animals of both groups were acutely decorticated, paralysed and electroneurographic efferent activity was recorded from hindlimb muscle nerves under conditions of "fictive locomotion" in order to evaluate variations in central locomotor command. Fictive rhythmic motor episodes were either spontaneous or evoked by electrical stimulation of the mesencephalic locomotor region. Only the second ones were recognised as locomotor-like activities. The motor pattern was not fundamentally affected by unloading except that, after the unloading period, extensor muscle nerves were significantly more frequently activated and their burst durations were increased compared to activity in control animals, despite the fact that the phasic sensory afferent inputs were suppressed. This suggests that unloading induces plastic modifications of the central networks of neurons implicated in the locomotor command. The origin of this extensor hyperactivity is discussed. It is proposed that it could be the consequence of either changes in motoneuronal properties or of an increase in afferent input to motoneurones.
Action Potentials↗
Immunocytochemical localization of GABA neurons and dopamine neurons in the rat main and accessory olfactory bulbs.
Immunocytochemical localization of GABA neurons and dopamine neurons in the rat olfactory bulb was obtained with sheep antiserum to glutamate decarboxylase (GAD) and rabbit antiserum to tyrosine hydroxylase (TH). GAD-positive neurons include periglomerular cells, granule cells, superficial and deep short axon cells. TH-positive neurons represent periglomerular cells. Two-color immunocytochemistry shows that GABA and dopamine periglomerular cells are separate populations. The accessory olfactory bulb has rare dopamine cells and few superficial short axon cells. Radial gradients of GAD-immunostaining are evident in the main but not in the accessory olfactory bulb.
Animals↗
Polyvagal Theory and developmental psychopathology: emotion dysregulation and conduct problems from preschool to adolescence.
In science, theories lend coherence to vast amounts of descriptive information. However, current diagnostic approaches in psychopathology are primarily atheoretical, emphasizing description over etiological mechanisms. We describe the importance of Polyvagal Theory toward understanding the etiology of emotion dysregulation, a hallmark of psychopathology. When combined with theories of social reinforcement and motivation, Polyvagal Theory specifies etiological mechanisms through which distinct patterns of psychopathology emerge. In this paper, we summarize three studies evaluating autonomic nervous system functioning in children with conduct problems, ages 4-18. At all age ranges, these children exhibit attenuated sympathetic nervous system responses to reward, suggesting deficiencies in approach motivation. By middle school, this reward insensitivity is met with inadequate vagal modulation of cardiac output, suggesting additional deficiencies in emotion regulation. We propose a biosocial developmental model of conduct problems in which inherited impulsivity is amplified through social reinforcement of emotional lability. Implications for early intervention are discussed.
Adaptation, Physiological↗
Obesity: should treatments target visceral afferents?
The fact that obesity is a chronic disorder has traditionally focused experimental attention on the long-term controls of energy balance. Searches for therapeutic targets tend to concentrate on central integrative mechanisms and to largely ignore the visceral afferents and other peripheral mechanisms providing short-term controls of energy balance. Investigations of central mechanisms have yet to yield, however, any practical and effective treatments for correcting obesity. In this review, we survey some of the arguments for considering peripheral visceral afferent mechanisms as promising targets for future research on obesity. These arguments include (1) the observation that visceral afferents have the specializations, complexities, heterogeneities, and extensive distributions at key sites to provide exhaustive and dynamic feedback to control energy handling, (2) the fact that the most effective treatments yet developed for achieving long-term or permanent weight loss, namely gastroplasty and similar bariatric surgical procedures, clearly alter visceral afferent feedback from the gastrointestinal tract, and (3) experimental observations that suggest loss of visceral negative feedback can lead to overeating, positive energy balance, and obesity. Furthermore, even though excess adiposity is a disturbance in long-term energy regulation, it is instructive that obesity in the final analysis is developed, is maintained, and ultimately needs to be treated one meal at a time. When these considerations are taken in conjunction with concerns about side effects and risks that can be expected to accompany pharmacological therapies directed at central nervous system circuits, it would seem prudent to assess ways in which the feedback of visceral afferents might be enhanced or manipulated to support or synergize with other therapeutic strategies used in the management of excess energy intake.
Afferent Pathways↗
The anatomic and physiologic basis of local, referred and radiating lumbosacral pain syndromes related to disease of the spine.
Conscious perception and unconscious effects originating from the vertebral column and its neural structures, although complex, have definite pathways represented in a network of peripheral and central nervous system (CNS) ramifications. These neural relationships consequently result in superimposed focal and diffuse, local and remote conscious perceptions and unconscious effects. Any one or combination of somatic and autonomic signs and symptoms may potentially be observed in a particular patient. This variety and inconsistency may mislead or confuse both the patient and the physician. A clear understanding of the basic anatomic and physiologic concepts underlying this complexity should accompany clinical considerations of the potential significance of spondylogenic and neurogenic syndromes in any disease process affecting the spine.
Autonomic Nervous System↗
Chemical stimulation of vagal afferent neurons and sympathetic vasomotor tone.
Vagal afferents innervate a diverse range of structures of the thoracic and abdominal viscera. While a proportion of these afferents function as mechanoreceptors and respond to changes in intramural tension within the structures that they innervate, many also sense a broad range of chemical substances ranging from peptides, sugars and lipids present in the intraluminal contents of the gastrointestinal tract, as well as tissue prostanoids, cytokines and monoamines in the cardiopulmonary circulation. This review examines the effects of chemical stimulation of vagal afferents on circulatory and sympathetic vasomotor function. Notably, the von Bezold-Jarisch reflex is a cardiorespiratory reflex produced by chemical activation of cardiopulmonary vagal afferents. Classical stimulants of the von Bezold-Jarisch reflex include the Veratrum alkaloids and 5-HT(3) receptor agonists. Atrial natriuretic peptides are agents which also produce a von Bezold-Jarisch reflex-like response or a sensitisation of this reflex via an action on vagal afferents. Cholecystokinin (CCK) activates abdominal visceral vagal afferents, which apart from a clear role in mediation of satiety, also produces selective sympathetic vasomotor inhibition probably by inhibition of sub-groups of presympathetic vasomotor neurons of the rostral ventrolateral medulla. These actions of CCK may constitute a novel gastrointestinal-cardiovascular reflex. The afferent vagus transmits a diverse array of signals to the central nervous system, influencing sympathetic vasomotor and cardiomotor function, gastrointestinal function, neuroimmune function and endocrine function.
Animals↗
Coherent sympathetic nerve activity in different postganglionic nerves after spinal cord transection in the cat.
In this study, simultaneous discharges were recorded in three nerves originating from different levels of the spinal cord and the correlation between them was analyzed in the absence of the synchronizing input from the brainstem. In acute spinal cats, significant coherence (up to 0.3) was found at low frequencies (<4 Hz) between the vertebral and cardiac nerves and between the vertebral and renal nerves. Coherent discharges were, however, unstable, intermittent, and occurred rarely. In most experiments, it took several hours of observation to capture such an episode. Intrathecal glutamate injections facilitated the occurrence of rhythmic slow waves, which were, however, not correlated. We conclude that spinal sympathetic networks are capable of low frequency synchronization of the activity in different sympathetic outputs.
Animals↗
The polysynaptic spine-stem reflex in clinical neurology.
Data from 25 years of studies of the spinobulbospinal (SBS) reflex in normal conditions and in a variety of nervous system diseases with lesions of the afferent and efferent systems, subcortical brain formations, and musculature (contracture of the expressive muscles, myofascial pain syndrome) are presented. The instability of many characteristics of the reflex (latency, amplitude, duration of response, presence) is shown to characterize this reflex in normal conditions. These measures become more stable in central nervous system pathology, which is evidence for impairment of programs which construct and execute movements. Lesions of the peripheral neuromotor apparatus produced no significant changes in the characteristics of the SBS reflex.
Electromyography↗
Origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats.
STUDY DESIGN: The authors studied the origin of nerves supplying the posterior portion of lumbar intervertebral discs in rats by resection of the sympathetic trunks. OBJECTIVE: To understand discogenic low back pain from the innervation of the lumbar intervertebral discs. SUMMARY OF BACKGROUND DATA: The afferent pathways of discogenic low back pain have not been studied thoroughly. It has been reported that stimulation of an inflamed lower spinal nerve root elicits leg pain but not low back pain and that stimulation of the posterior portion of lumbar intervertebral discs evokes only low back pain. These facts suggest that pain sensation from the posterior portion of lumbar discs is not transmitted via the lower spinal nerve roots. METHODS: Forty-five Wistar rats were used. Seven days after the resection of sympathetic trunks with ganglia at different levels, the whole lumbar spine was stained by an acetylcholinesterase histochemical method. The posterior portions of lumbar intervertebral discs were observed. RESULTS: The dense nerve network on the posterior portion of lumbar intervertebral discs had disappeared almost completely after total resection of bilateral sympathetic trunks at L2-L6. However, there was a slight decrease in the network after bilateral single-level resection or unilateral multisegmental resection. CONCLUSIONS: The results showed that the posterior portion of lumbar intervertebral discs was innervated by the sympathetic nerves multisegmentally and bilaterally.
Afferent Pathways↗
Computer simulation of brainstem respiratory activity.
A mathematical model of the medullary respiratory oscillator, composed of two mutually inhibiting populations (inspiratory and expiratory) of computer-simulated neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons. Neuronal coupling is such that either the inspiratory or expiratory population alone is capable of cyclic activity. Weak inhibitory connections between inspiratory and expiratory populations provide satisfactory reciprocating activity independent of the natural frequency of either population alone. Initiation and persistence of rhythmic activity is dependent on a diffused noncyclic excitatory input. Vagal discharge, simulated by phasic inhibition of inspiratory neurons, results in increased respiratory frequency with decreased inspiratory activity. In the absence of simulated vagal discharge, uniform facilitation of synaptic connections increases averaged activities of inspiratory and expiratory populations, with minor effect on frequency. In the presence of simulated vagal discharge, facilitation of synaptic connections increases both frequency and amplitude. The simulated effects of synaptic facilitation, with and without vagal discharge, mimic the physiological response to CO2 in the intact and vagotimized animal.
Computers↗
Simulation of motion on the skin. V. Effect of stimulus temporal frequency on the representation of moving bar patterns in primary somatosensory cortex of monkeys.
1. To assess the mechanisms used by cortical neurons to sense motion across the skin, we applied pulsatile stimuli to a series of adjacent positions on the glabrous skin of the hand using a computer-controlled OPTACON stimulator. We describe responses of 129 single neurons in primary somatosensory cortex of alert monkeys to a horizontal bar pattern that was displaced proximally or distally in 1.2-mm steps at 10-, 20-, and 40-ms intervals (100, 50, and 25 Hz, respectively). These frequencies span the range in which apparent motion is transformed perceptually in humans from a smooth uninterrupted sweep into a series of distinct pulses that are resolved as separate events. The experiments are thus designed to decipher the neural correlates distinguishing continuous motion from discrete taps. 2. Cortical receptive fields mapped with moving bar patterns spanned 5-24 rows on the tactile array (16.2 +/- 5.4, mean +/- SD). Over 40% of the fields encompassed 18 or more rows (greater than or equal to 21.6 mm), allowing these neurons to integrate spatial information from an entire image displayed on the OPTACON. Cortical receptive fields are considerably larger than those of mechanoreceptors mapped with the same moving bar patterns (4.2 +/- 2.3 rows, mean +/- SD), reflecting convergent inputs in subcortical and cortical relays. Responses were either relatively uniform across the field or strongest at the initial point of entry, depending on the frequency of stimulation. A sharply defined field center was absent from most of the cells recorded in this study. 3. Temporal frequency of stimulation appears to be a major determinant of cortical firing patterns. Low-frequency stimuli are more effective in activating cortical neurons, producing more spikes per sweep and greater phase-locking to individual stimuli than do high frequencies. The total spike output of cortical neurons is proportional to the pulse interval over the range 10-40 ms, increasing linearly by an average of 5.9 spikes/10-ms increase in pulse period. Peak firing rates and modulation amplitude are also highest when pulses are presented at long intervals, falling significantly as the stimulation frequency rises. The reduction in firing at high pulse rates is apparently due to central mechanisms, as both rapidly adapting and Pacinian corpuscle afferents display nearly constant spike outputs and uniform sensitivity within the field when tested with identical bar patterns. Central networks thus behave as low-pass filters, reducing cortical responses to rapidly applied sequential stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Possible network interactions indicated by bilaterally coherent fast rhythms in expiratory recurrent laryngeal nerve discharges.
1. In a search for correlated fast rhythms in recurrent laryngeal (RL) expiratory (E) activities, we performed spectral and coherence analysis on bilateral RL nerve discharges in 54 midcollicular decerebrate, paralyzed cats. 2. Inspiratory (I) RL activities showed in almost all cases high-frequency oscillations (HFO, range 50-100 Hz) that were bilaterally coherent and also coherent to HFOs in phrenic (PHR) activities. In contrast, bilaterally coherent rhythms (range 24-54 Hz) in RLE discharges were found in only a fraction of the cats (6/54); in the other cats (48/54) such coherences were absent even though the auto-spectra showed the presence of similar fast rhythms on the two sides. The bilateral RLE coherences were associated with increased amplitude and prolonged duration of RLE activity, such as occurred following removal of phasic pulmonary stretch receptor inputs by vagotomy or by no-inflation. 3. Thus, although coherent fast rhythms are uncommon in RLE discharges, their occurrence under some conditions indicates the presence of short-time-scale interactions between neurons involved in this activity. This suggests that such rhythms are a general feature of neural networks.
Afferent Pathways↗
Neural analogue of long-term sensitization training produces long-term (24 and 48 h) facilitation of the sensory-to-motor neuron connection in Aplysia.
1. An in vitro analogue of long-term sensitization training was used to gain insights into the mechanisms and time course of the memory for long-term sensitization in Aplysia. The analogue, consisting of four blocks of shocks, was delivered to peripheral nerves of the isolated pleural-pedal ganglia, which contain the sensory neurons and motor neurons that mediate the tail withdrawal reflex. 2. Long-term facilitation of the connections between the sensory neurons and motor neurons was produced by the conjoint stimulation of two peripheral nerves, P8 and P9. Long-term facilitation, however, was not observed after conjoint stimulation of three nerves, P7, P8, and P9. 3. The preparation was viable and stable (no changes in the amplitudes of excitatory postsynaptic potentials (EPSPs) and membrane properties in controls) for at least 48 h. Moreover, the long-term facilitation persisted for at least 48 h. 4. We observed no significant long-term changes in the resting membrane potentials of the sensory and motor neurons or in the input resistance of the motor neurons 24 and 48 h after the conjoint stimulation of nerves P8 and P9. Thus changes in these biophysical properties do not appear to contribute to the expression of long-term facilitation. 5. The finding that conjoint stimulation of three nerves, P7, P8, and P9, produced no long-term facilitation raised the possibility that stimulation of nerve P7 alone might produce long-term inhibition that opposes the facilitatory effects induced by conjoint stimulation of nerves P8 and P9. Stimulation of nerve P7 alone, however, had no long-term inhibitory effect on the EPSPs.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Pattern formation of the sensible nerves in the hand of mouse embryos with special reference to the posterior-anterior developmental gradient.
The development of the sensible innervation of the hand was investigated. For this reason normal forelimbs and limb bud cultures from 12- to 14-day-old mouse embryos were stained in toto using the cholinesterase technique. The dorsal side of the hand is mainly innervated by sensible branches of the radial and the musculocutaneous nerve, which penetrate the fascia in the region of the elbow. From here they grow in a distal direction forming the dorsal digital nerves. On the ventral side the median nerve grows in a subfascial compartment towards the palmar side of the hand. While passing the wrist the median nerve exhibits a frayed appearance. A net of branching and anastomosing small nerve fibre bundles is visible. This implies that on the palmar side of the metacarpal region of the hand-plate no specific highways for the growing nerve fibres exist. From late day 12 to early day 14 of embryonic development this diffuse nerve net is organized. In a posterior-anterior (ulnoradial) developmental gradient the common palmar digital nerves were formed, and these nerves divide at their tip into the proper digital nerves. However, the proper digital nerves again follow special pathways during their outgrowth.
Animals↗
Inhibitory effect of a SALMFamide neuropeptide on secretion of gonad-stimulating substance from radial nerves in the starfish Asterina pectinifera.
In starfish, the peptide hormone gonad-stimulating substance (GSS) secreted from nervous tissue stimulates oocyte maturation to induce 1-methyladenine (1-MeAde) production by ovarian follicle cells. The SALMFamide family is also known to an echinoderm neuropeptide. The present study examined effect of SALMFamide 1 (S1) on oocyte maturation of starfish Asterina pectinifera. Unlike GSS, S1 did not induce spawning in starfish ovary. In contrast, S1 was found to inhibit GSS secretion from radial nerves by treatment with high K+ concentration. Fifty percent inhibition was obtained by 0.1 mM S1. S1 did not have any effect on GSS- and 1-MeAde-induced oocyte maturation. Following incubation with a S1 antibody and subsequently with rhodamine-conjugated second antibody, neural networks were observed in ovaries. The networks were restricted mainly to their surface with little evidence of immunoreactivity inside the basement membranes. This indicates that neural networks are distributed in the ovarian wall. The result further suggests that S1 plays a role in oocyte maturation to regulate GSS secretion from the nervous system.
Animals↗
Innervation densities of the cochlea.
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Animals↗
On lateral inhibition in the auditory system.
Suga (1994) has presented arguments supporting the existence of lateral inhibition in the auditory system. We developed a computational model of a lateral inhibition neural network possibly taking part in auditory stimulus processing. The behavior of the model under several hypothetical auditory stimuli matches experimental results. We have shown that lateral inhibition can be the cause of tinnitus in some conditions. 95% of subjects have phantom perceptions in the absence of auditory stimulation (acoustically shielded chambers). We suggest that the spontaneous activity in the auditory nerve (a Poisson-like neural noise), processed by lateral inhibition, is responsible for this phenomenon. Activity is generated in the output layer of the network under stimulation with a Poisson-like noise. In the presence of acoustic stimulation this neural noise is masked by the stimulus or the ambient wideband acoustic noise. The wideband noise is effectively suppressed in lateral inhibition. The shape of the probability density function of the noise determines whether it will be effectively suppressed. The edge effect has been demonstrated to be also a possible consequence of lateral inhibition.
Acoustic Stimulation↗