Bulbar Reticular Formation Research Articles

ASCENDING SPINAL TRACTS OF THE SPINOBULBO-SPINAL REFLEX IN CATS

Twenty-six chloralosed cats were employed in order to determine spinal ascending pathways of the spino-bulbo-spinal (SBS) reflex evoked by stimulation of the sural nerve. 1. Partial spinal transection of the dorsal part of the lateral funiculus abolished the SBS reflex ipsilateral to sural nerve stimulation. 2. By recording spinal cord potentials in response to sural nerve stimulation two pathways were established in the dorsolateral funiculus as the spinal ascending tracts of the SBS reflex; one is the direct pathway to the bulbar reticular-formation (direct spino-reticular tract) and the other one (indirect spino-reticular tract) is the relayed by the lateral cervical nucleus. Direct stimulation of the dorsolateral funiculus at the lumbar level elicited the SBS reflex. 3. Short-latency unit discharges were recorded from axons of the direct spino-reticular tract by sural nerve stimulation. These axons were discharged antidromically by stimulation of the bulbar reticular formation. 4. Intracellular recordings from the neurons of the lateral cervical nucleus revealed that spike potentials, riding on EPSPs, were induced by sural nerve stimulation and antidromic firings were obtained by stimulation of the bulbar reticular formation. 5. Neurons originating the spino-reticular tract, direct and indirect, were located in the Rexed V-VII laminae in the lower lumbar segments. They were fired monosynaptically by sural nerve stimulation and antidromically by stimulating the dorsolateral funiculus of the lumbar segments. Among them, some were activated antidromically by stimulating the bulbar reticular formation.

Pericruciate cortical neurons projecting to brain stem reticular formation, dorsal column nuclei and spinal cord in the cat

Cells of origin of the pericruciate cortical fibers to the bulbar medial reticular formation, the dorsal column nuclei and the pinal cord in the cat were identified by means of the retrograde axonal transport of horseradish peroxidase. After injection of the enzyme in the dorsal column nuclei or the spinal cord many layer V pyramidal neurons were labeled retrogradely in areas 2, 3 and 4 (see ref. 6), but area 4 giant Betz cells were only labeled after spinal cord injections. Medial bulbar reticular formation injections resulted in the labeling of pyramidal neurons mainly in area 6.

Effects of morphine, L-Dopa and tetrabenazine on the lamina V cells of spinal dorsal horn

Experiments were performed to clarify the adrenergic mechanism of morphine action in the spinal cord. Unit activity of lamina V cell of spinal dorsal horn (L 6−L 7) of the rabbit was recorded using microelectrode. An administration of bradykinin into the femoral artery markedly increased in frequency of the unit activity. Morphine or L-Dopa inhibited the bradykinin-induced response of lumina V cell. In contrast, tetrabenazine facilitated the bradykinin-induced response. Electrical stimuli of the bulbar reticular formation, particularly the nucleus reticularis gigantocellularis markedly inhibited the dorsal horn response induced by bradykinin injection. Effect of stimulation of the bulbar reticular formation was blocked by tetrabenazine and reversed by L-Dopa. These results support the hypothesis that the bulbospinal catecholaminergic neuron inhibits the pain transmission at the dorsal horn of the spinal cord and analgesic action of morphine is mainly mediated by activation of this neuron.

Monosynaptic reciprocal control of trigeminal motoneurons from the medial bulbar reticular formation

Monosynaptic reciprocal control of trigeminal motoneurons from the medial bulbar reticular formation

L'inhibition bulbaire de l'activite electrodermale

Skin potential responses (SPR) elicited by stimulation of the mesencephalic reticular formation are inhibited by simultaneous stimulation of the bulbar reticular formation. The mechanisms of this inhibition, its anatomical origin and its pathways were studied in the anaesthetized cat. The inhibitory points are located within the posterior gigantocellular nucleus, the paramedian reticular nucleus and the ventral reticular nucleus. Partial lesions of the spinal cord, ipsilateral to the stimulated bulbar area, suppress the inhibition of SPR recorded from the ipsilateral hind paw. Inhibition could thus result from the effect of lateral reticulo-spinal fibres on sympathetic spinal neurones. Since the effects on blood pressure of stimulating the bulbar inhibitory areas are variable, the hypothesis that SPR inhibition is a secondary consequence of circulatory variations can be rejected; it also confirms the functional heterogeneity of the bulbar inhibitory structures. Finally, the inhibition of SPR through bulbar stimulation is accompanied, in very lightly anaesthetized animals by strong cortical arousal; hence it can be concluded that SPR inhibition is not a result of diffuse depression of the mesencephalic activating system.

Modification of escape from noxious stimuli after bulbar reticular formation lesions

Quantitative behavioral tests showed that unilateral bulbar lesions made in anesthetized cats, damaging nucleus gigantocellularis (NGc), nucleus paragigantocellularis dorsalis (Pgd), and/or the magnocellular tegmental field (FTM), increased latency and threshold voltage for escape from electric shock to the feet. Motor function, visual orientation, and orientation to sound were normal. It is hypothesized that NGc, Pgd, and FTM may constitute a functional complex, operating such that adequate unilateral damage to this field significantly disrupts input into the midline thalamic area.

Efferent fibers of the deep cerebellar nuclei in hedgehogs.

AbstractThree main deep cerbellar nuclei are apparent in hedgehogs belonging to the genera Erinaceus and Hemiechinus; however, at various levels they exhibit a considerable continuity with one another. Electrolytic unilateral lesions were placed in the deep cerebellar nuclei of these hedgehogs, and additional animals were subjected to a midline incision of the cerebellum between the two fastigial nuclei. Degenerating axons were traced from the sites of lesions using the Nauta and Fink‐Heimer techniques.The typical mammalian pattern is evident in the distribution of the cerebellifugal fibers of the hedgehog. Crossed and uncrossed fastigial efferent fibers are directed primarily toward vestibular nuclei and the bulbar reticular formation except for a relatively small ascending limb of the uncinate fasciculus. The brachium conjunctivum originates from the nucleus interpositus and nucleus lateralis. The efferents of these nuclei are directed rostrally to the contralateral red nucleus. Fibers passing beyond the level of the red nucleus terminate in the thalamic nuclei. Fibers from the brachium conjunctivun also supply the inferior and superior colliculi. Axons forming the descending limb of the brachium conjunctivum are divided into medial and lateral fascicles.

Effects of intermittent electric stimulation of the medulla oblongata at different points of the respiratory cycle on respiration of rabbits

In urethane-anesthetized rabbits the bulbar reticular formation was stimulated with volleys of 120 msec duration at 100 pulses per sec, the pulse duration being 0.5 msec. When shifted along the inspiration, the volleys caused an increasingly stronger inhibition followed by a rebound activation of the inspiratory activity. Towards the end of the inspiration, the volleys stopped the latter phase and shortened the following expiration. When applied during the expiration, the volleys also caused an inhibition and shortened this phase. Results suggest that the stimulus-induced pause of the inspiratory activity delays the activation by the inspiratory centre of the central inhibitory feedback mechanism.

Modifications of the firing rate of bulbar reticular units (nucleus gigantocellularis) after intra-arterial injection of bradykinin into the limbs

To define the role of the nucleus gigantocellularis (NGC) of the bulbar reticular formation in the pain process, modifications of the firing rate of NGC cells were studied after nociceptive stimulation induced by intra-arterial injection of bradykinin into the limbs of cats. Eighty-two per cent of NGC cells were affected. Sixty-five per cent were excited; the mean increase in firing rate was 415%, the mean latency 14.5 sec and the mean duration 17 sec. Twelve per cent were inhibited and one-half of these cells were also inhibited by natural stimulation. Five per cent had a mixed response. Modifications of firing rate were reproducible in any given cell. The observed modifications of firing rate appeared to be independent of arousal mechanisms. The possible functional significance of these results is discussed.

Bulbar respiratory neurons participating in the sniff reflex in the cat

Activity of bulbar respiratory neurons was recorded extracellularly in anesthetized cats in which sniffs were induced by mechanical stimulation of the nasopharyngeal mucosa during the expiratory pause. Sniffs were indicated by brief, rapid activation of the diaphragmatic EMG which was followed by a sharp rise of tracheal inspiratory airflow (aspiration reflex of Tomori). In large sniffs, inspiratory neurons were activated in highfrequency bursts which preceded diaphragmatic activation. Other neurons in the bulbar reticular formation did not exhibit these properties. Inspiratory neurons located ipsilateral to the stimulated nasopharynx in the region ventrolateral to fasciculus solitarius exhibited low-threshold bursting and the earliest activation. The same neurons responded weakly and late to stimulation of the contralateral nasopharynx. Inspiratory neurons located in the environs of nucleus ambiguus frequently failed to participate in weaker sniffs, but a few always participated. Most neurons in this region were activated at nearly equal times before the diaphragm whether ipsilateral or contralateral nasopharynx was stimulated. Expiratory neurons located bilaterally near nucleus ambiguus were inhibited in numbers and in degree which matched the magnitude of the sniff. Weaker sniffs were accompanied by inhibition of late expiratory units alone, while stronger sniffs involved all expiratory neurons. Repeated stimulations could silence the expiratory units for long periods.

Unit activity of bulbar raphe nuclei and reticular formation in cats.

Spontaneous activity and single unit responses of the bulbar raphe nuclei (NR) and mesencephalic reticular formation (MRF) were studied in unanesthetized cats. In addition to the general features, a number of special features of the unit activity of these two structures were discovered: a) in most cases NR neurons respond predominantly or entirely to cutaneous stimulation of 3 to 4 limbs; b) spontaneous activity (SA) of NR neurons is more regular and less variable in time than that of MRF neurons. Under the influence of various peripheral stimulations the spontaneous activity of NR neurons briefly increases in frequency without any change in firing pattern, whereas the increase in frequency of MRF neurons occurs for much longer and is accompanied by marked changes in spontaneous activity c) NR neurons respond to all peripheral stimuli used by an absolutely uniform, short and compact volley of spikes, whereas MRF neurons respond differently to each stimulus, with various numbers of spikes and different firing patterns. These peculiarities of NR unit activity are evidently attributable to its simpler synaptic organization than that of MRF.

An extralemniscal projection to the centrum medianum and pulvinar of the thalamus.

Electrophysiologic studies in cats were undertaken to determine the possible pathways for somatosensory transmission to the centrum medianum and pulvinar nuclei of the thalamus. The effects of discrete lesions in the various thalamic nuclei, mesencephalic reticular formation and spinal cord on the evoked potentials of the centrum medianum and pulvinar were recorded. It was noted that the centrum medianum and pulvinar had a dual activation from both dorsal and ventrolateral columns of the cord. The ventrolateral column component was mediated by the bulbar reticular formation and is believed to transmit nociceptive stimuli. The findings were correlated with known information about the mediation of acute and chronic pain and are consistent with the concept of a paleospinothalamic system for pain transmission.

Control exerted during sleep by primary cortical areas upon different sensory afferents

1. 1. Eighteen cats with chronically implanted electrodes were studied during wakefulness and sleep, with somatic, visual and auditory stimulation; the responses were recorded in different convergent structures: marginalis anterior and suprasylvian gyri, centrum medianum, mesencephalic reticular formation, gigantocellularis nucleus of the bulbar reticular formation. Twenty-five consecutive responses were averaged in each stage of sleep and compared, before and after bilateral removal of the primary sensory areas. 2. 2. In intact animals, and at each level, all the stimuli evoke responses which are largest during drowsiness and slow sleep, smallest during fast sleep and wakefulness. 3. 3. After the removal of both primary cortical areas, the modifications of the corresponding responses during sleep are no longer observed. Each primary cortical area seems to control the associative afferents only within the same sensory system. 4. 4. When the bilateral lesion is incomplete, the normal evolution reappears 3–5 weeks after surgery. 5. 5. The enhancement of the descending control exerted upon the associative afferents by primary afferents during fast sleep, its specificity, its nature and its points of impact are discussed.

The effect of different descending systems on flexor and extensor activity during locomotion

The angles of the joints of the hindlimb and the electromyographical activity of the hindlimb muscles were recorded during locomotion in mesencephalic and thalamic cats. Electrical stimulation of the Deiters' nucleus, the bulbar reticular formation, the red nucleus and the pyramidal tract was carried out during locomotion. Short trains of impulses were applied at different phases of the animal's step. The strength of applied stimulus was so weak that it produced only slight motor effects when the cat was inactive. The timing of the locomotor cycle, i.e. the beginning and ending of muscular activity, is not affected by the stimulus, but the degree of muscular activity is. The extensors are active in the standing phase. This activity increases with stimulation of the Deiters' nucleus and decreases with stimulation of the bulbar reticular formation. The flexors are active at the end of the standing phase and in the phase of swinging the leg. This activity increases with stimulation of the bulbar reticular formation, the red nucleus and the pyramidal tract. Destruction of Deiters' nucleus results either in disappearance of the stepping movements of the ipsilateral limb, or in a decrease of the extensor activity during locomotion.

Resection of the facial nerve for blepharospasm.

ESSENTIAL blepharospasm is a focal disturbance of the central nervous system producing progressive involuntary, spasmodic closure of the eyes. As it progresses, the patient becomes visually crippled even though having normal visual pathways because the eyes are closed almost 25% of the time. In a thorough monograph, Henderson 1 postulates that the disorder is the result of a disturbance in the inhibitory apparatus between the pyramidal and extra pyramidal system, located in the suppressor strip 4-S of Hines or the bulbar reticular formation. Since cortical representation of the orbicularis oculi is bilateral and much greater than lower half facial muscles, a loss of 4-S fibers in this area has a greater effect on the eyes than other muscles of the face. 1 Essential blepharospasm typically begins in the sixth decade of life as a blinking in one or both eyes and progresses to bilateral involvement and functional blindness. Most patients

A comparison of the effects of monoamines on neurones of the bulbar reticular formation

A study was made of the actions of microelectrophoretically administered 5-HT, NA and DA on the spontaneous and amino acid-induced firing of bulbar reticular neurones in unanaesthetized, decerebrate cats. Some of these neurones were activated antidromically and/or synaptically by stimulation of the cervical spinal cord and sciatic nerve. 5-HT and NA excited approximately one-third, depressed one-quarter and had a dual action on a few of the neurones tested. DA affected about half the cells, causing mainly depression, although it excited some neurones. Almost all reticulospinal neurones were excited by 5-HT and NA, but usually depressed or unaffected by DA. The depressant actions of the monoamines were generally rapid in onset and recovery, whereas the excitant actions were of a slow time course and sometimes showed desensitization on repeated applications. Various combinations of excitation and depression were observed when the effects of the monoamines were compared on the same neurone. Monoamine-sensitive cells seemed to be diffusely scattered throughout the bulbar reticular formation. The monoamines were usually less effective than glutamate and glycine.

Place and modality analysis in caudal reticular formation.

1. Evoked potentials and unit responses were studied under chloralose anaesthesia in a restricted region of the caudal bulbar reticular formation of the cat which is known anatomically to receive a preferential spinal input.2. Responses were analysed in terms of place and sensory modality and show varying degrees of place and modality convergence, as well as preferential responses for certain loci of stimulation.3. Evidence is presented which suggests that some unit responses are generated in dendrites.4. The response properties of the whole population are compared with those obtained from other reticular regions in previous identical experimental series. It is shown that the integrated activity of the ascending reticular formation acting as a whole would enable the organism to discriminate, to a greater or lesser degree, place and modality from the convergent peripheral input to the reticular formation.

Essai de classification des structures centrales au moyen des variations d'amplitude de leurs réponses évoquées somatiques au cours des cycles veille-sommeil

1. 1. The evolution of the amplitude and shape of responses evoked at various cortical and sub-cortical levels during different phases of sleep and wakefulness were studied in thirty-eight cats. In addition to the cerebral recording electrodes. stimulating electrodes were placed on the superficial radial nerve. The means of groups of 25 responses were obtained, using an averaging computer. 2. 2. Three groups of structures could be recognized according to the evolution of their responses during sleep: (a) primary structures (VPL, somato-motor cortex, SII cortex) in which the responses were largest during “fast sleep”; (b) convergent structures (centrum medianum, bulbar reticular formation, caudate nucleus, pallidum, putamen, antero-inferior portion of VL, antero-lateral and suprasylvian gyri) in which the amplitude of responses was large during “slow sleep”, but small during fast sleep or wakefulness; (c) mixed structures (claustrum, red nucleus, postero-superior portion of VL) showed responses with several components which behaved like one or other of the preceding types. In addition new components appeared during fast sleep. 3. 3. The late components of responses from mixed structures were abolished by ablation of the somato-motor cortex but were unaffected by cerebellectomy. 4. 4. The occurrence of late components in the responses of mixed structures during fast sleep was attributed to an increase in the excitatory influence which the somato-motor cortex normally exerts on subcortical structures. Reinforcement of an inhibitory influence of somato-motor cortical origin is also believed to occur during fast sleep and will be the subject of a further paper.

Place and modality analysis in nucleus of posterior commissure.

1. Single units (157) responsive to somatic stimulation in the nucleus of the posterior commissure were examined in the cat under chloralose anaesthesia. 87.3% responded to stimulation of all four limbs, 2.4% to three limbs, 8.7% to two limbs and 2% to one limb.2. 44.7% of units could be activated by phasic hair movement; 52.4% responded additionally to auditory stimuli and 34.6% to visual stimuli, although there are marked differences in degree of heterosensory convergence between hair-sensitive units and others.3. Analysis by spike numbers and latencies show marked preference for contralateral limbs.4. Results are compared with those obtained under identical experimental conditions from units of the gigantocellular bulbar reticular formation, and show that anatomically discrete areas of the reticular formation are capable of differential analysis of afferent input.

The startle and orienting reactions in man. A study of their characteristics and habituation

(1) Electromyographic (EMG) responses induced by short bursts of white noise have been studied in 8 human subjects. The stimuli were either of a fixed intensity with the intervals varying randomly, or at fixed intervals with 3 different intensities in random succession. Each subject was submitted to several sequences of about 30 min each, consisting of a series of 50 to 150 stimuli. (2) EMG responses consisted of ‘early’ and ‘late’ components which can be considered as the EMG manifestation of the startle response and the orienting response, respectively. (3) The amplitude of the startle reaction shows a clear positive correlation with the intensity of the stimulus; no such correlation was found for the oreinting reaction. (4) A significant correlation seems to exist between the amplitude of the startle reaction and the ‘frequency’ of the EEG measured during the 1 sec period just preceding the tone stimulus. (5) The amplitude of the orienting reaction displays a fair correlation with that of the startle; however each component may be present at times independently of the other. (6) During some sequences of stimuli, it has been possible to observe a habituation of both the startle and the orienting responses. However the occurrence of habituation seems to be strongly correlated with the variability of the EEG recorded during the sequence: that is, habituation can be observed if the distribution of EEG ‘frequencies’ displays a small dispersion around its modal value. (7) It is suggested that startle and orienting reactions, while corresponding to 2 different psychomotor activities, may be engendered by a common neuronal structure, probably located in the bulbar reticular formation. (8) The results obtained would favor the hypothesis that habituation of the motor responses may be the manifestation of a decrementing process occurring principally in the lower nervous centers, including spinal neurons, implicated in the observed responses. Modulating influences, coming from higher structures, may interfere with this process by introducing superimposed ‘noise’.