Bulbar Reticular Formation Research Articles

Neurophysiological effects of experimental intracranial hypertension on three different structures of the brain stem in the cat. Rostrocaudal deterioration.

Modifications if multi-unit activity are analyzed during experimental intracranial hypertension in the cat at three levels of the brain stem red nucleus (NR), nucleus giganto-cellularis (Gc), and lateral geniculate body (GO). An initial increase of activity is observed in NR and Gc, which is followed by a fall of activity. This fall is sooner and more important for the rostral structures than for the caudal ones. In GO, activity decreases as soon as intracranial hypertension starts. These results are similar to those already recorded in the mesencephalic and bulbar reticular formation. They are discussed on the basis of monoamine levels and local CBF variations studied in the brain stem, following the same protocol. The higher sensitivity of rostral brain stem structures to intracranial hypertension is correlated to the clinical concept of rostro-caudal deterioration.

Nucleus raphe magnus modulation of response of rat dorsal horn neurons to unmyelinated fiber inputs: partial involvement of serotonergic pathways

1. In the rat under N2O-halothane anesthesia, stimulation of the nucleus raphe magnus (NRM) with stimulus parameters similar to those used to obtain analgesia in freely moving animals strongly inhibits the responses of dorsal horn convergent neurons due to A-delta- and C-afferents. 2. Responses to noxious radiant heat were also depressed, and pronounced post-effects were frequently observed. 3. Comparison between coupled sites of stimulation in NRM and in adjacent bulbar reticular formation (BRF) on responses to C-fibers revealed the preeminent effects of NRM; these were systematically encountered (93% of neurons), much more pronounced, and of longer duration. 4. The latency of these inhibitory effects (around 20 ms) suggests the participation of myelinated axons in such descending action and, consequently, we question the involvement of unmyelinated serotonergic fibers. 5. However, descending inhibitory influences from NRM on responses to C-fibers are reduced after 5-hydroxytryptamine (5-HT) depletion by p-chlorophenylalinine (pCPA), thus demonstrating the implication of both serotonergic and nonserotonergic pathways. 6. In addition, after pCPA pretreatment, long-lasting and sustained excitatory effects from NRM were observed in 35% of convergent neurons; their possible origin is discussed.

Location and properties of dorsal horn neurons at origin of spinoreticular tract in lumbar enlargement of the rat.

1. Spinoreticular tract neurons at the rat lumbar cord level were identified by antidromic activation following stimulation at mainly pontine and mesencephalic levels. These units, which were found in the dorsal half of the cord, could be separated into two groups according to their spinal location, electrophysiological properties, and their central projections. 2. Units in the dorsolateral funiculus nucleus projected mainly to the cuneiformis area and adjacent structures with frequent bilateral projections. They had the slowest conduction velocities, sometimes in the unmyelinated range. Generally, they were driven only by stimulation of subcutaneous and/or deep structures. 3. Neurons located in the dorsal horn mainly projected contralaterally to pontine and mesencephalic levels. their conduction velocities and the electrophysiological properties were identical to those observed for the rat spinothalamic tract (22). Almost all (86%) had clear cutaneous sensitivity and generally large receptive fields: 40% responded to nonnoxious and noxious mechanical cutaneous stimuli and frequently to noxious radiant heat, 26% were exclusively excited by light tactile stimuli, and 20% required noxious cutaneous mechanical stimulation for activation. There was a good correlation between responses to natural and transcutaneous electrical stimulation: units driven by noxious mechanical stimuli received A-delta- and/or C-fiber inputs. The remaining units (14%) had more complex receptive fields associated with both excitatory and inhibitory inputs originating from a single peripheral area. 4. The functional heterogeneity of the rat spinoreticular tract is reminiscent of that demonstrated for the rat and monkey spinothalamic tracts. Similarly, the rat spinoreticular neurons are under the influence of descending inhibitory controls originating from the nucleus raphe magnus and bulbar reticular formation. 5. Responses of the rat spinoreticular tract neurons are consistent with the involvement of this pathway in the transmission of messages of both innocuous and noxious origins.

Strychnine effects on the sensory response patterns of reticular formation neurons

Strychnine (ST) administration results in enhanced responses of reticular formation neurons of the cat to visual, auditory, or somatosensory stimuli. Neurons in the bulbar reticular formation (BRF) also exhibited ST-induced spike-bursting which coincides with the onset of 10–20 Hz high amplitude rhythmic discharge in the lower brain stem often obscuring sensory response enhancement. Mesencephalic reticular formation (MRF) neurons showed enhanced sensory responsiveness at higher doses of ST but rarely showed spike-bursting. The rhythmic discharge in the EEG of BRF and spike-bursting in BRF neurons was not observed in animals with spinal cord transection suggesting that this bursting activity is due to the action of ST on the spinal cord. The enhancement of sensory responses may be due in part to reversal of repetition-induced response attenuation (habituation) mechanisms in RF neurons. The ST-induced enhancement of RF neuronal responses to sensory stimuli is similar to that reported previously with pentylenetetrazol. These findings extend the concept that enhancement of RF responses to sensory stimuli may be indicative of a general neuronal action of convulsant agents which may be important in sensory-induced seizures.

Central inhibition of depressor reflex at spinal level

The classical concept that the central inhibition of the depressor reflex occurs entirely in the bulbar reticular formation has recently been challenged by several reports, which have indicated the existence of a descending sympathetic inhibitory pathway2,4, 7,9. In the present study direct evidence about this spinal inhibition will be presented. In 15 experiments performed in cats, surgical intervention was carried out under Nembutal 38 mg/kg, i.p. The left carotid blood pressure was continuously monitored by sphygmomanometry. The vagal nerve of either side was dissected and sectioned for stimulation purposes (Fig. 1Aa). The cervical cord was first hemi-sectioned at the C1level on the left side, and then mid-sectioned caudally by a 10 mm long incision. A pair of insulated fine steel electrodes were then placed into this 'isolated' lateral column (Fig. lAb). The left splanchnic nerve was dissected manually with fine watch forceps into bundles cut distally for the recording of sympathetic preganglionic efferent discharges. The recording electrodes consisted of a pair of platinum wires (diameter 27 pm; Fig. 1Ae). During observation the animal was paralyzed by tubocurarine at a dose of 1 mg/kg i.v. and maintained by artificial ventilation. Once single unit discharges were found on the screen of the CRO, they could be identified as the vasomotor neuron discharges by verifying whether they ceased to discharge under vagal stimulation or during the pressor response induced by i.v. adrenaline administration. The identified vasomotor unit discharges were then recorded spontaneously. Repetitive electrical stimulation of the lateral column (0.3 msec, 10 Hz, 5-12 V, for several sec) invariably elicited at the spinal level sustained accelerated discharges of the vasomotor neuron together with a remarkable pressor response. During this response, the application of vagal stimulation (0.1 msec, 50 Hz, 5-10 V, 3 sec) could either effectively inhibit these enhanced unit discharges (9 cases) or greatly reduce them (4 cases), always accom-

Morphological and functional evaluation of the superior salivatory nucleus in rabbits

Horseradish peroxidase (HRP) was applied to the submandibular ganglion of the rabbit to determine the locus of the parasympathetic preganglionic neurons in the medulla. Labeled cells were recognized in the ipsilateral bulbar reticular formation at the level between the caudal end of the facial genu and the caudal part of the root of the facial nerve. The size of the labeled cells were distributed from 150 to 1150 μm 2 with a variety of forms such as spindle shape, triangular, and polygonal. Moreover, these cells of different sizes and forms were evenly scattered in the superior salivatory nucleus. To evaluate the physiologic functions of the bulbar salivatory nucleus, electrical stimulation was applied to the medulla, and salivary secretion and thermal change of the submandibular gland were measured simultaneously after bilateral cervical sympathectomy. A very good parallelism between the volume of salivary secretion and the magnitude of temperature change at each stimulating point suggests that secretory and vasodilator cells are intermingled with each other in the salivatory nucleus.

Three types of reticular neurons involved in the spinobulbo-spinal reflex of cats

Reticular neuron activity was recorded in 28 chloralosed cats in order to analyze the reflex arc of the spino-bulbo-spinal (SBS) reflex. Three types of reticular neurons, types I (input), II (output) and III (relay), were identified by unit discharges in response to stimulation of the sural nerve. (1) Type I (input) neurons received spinal ascending volleys monosynaptically and responded to stimulation of the sural nerve with spikes of low amplitude and short latency. Unit spikes, however, were not produced by stimulation of the superficial radial nerve and the sensorimotor cortex. These input neurons were located in the dorsocaudal part of the medial bulbar reticular formation. (2) Type II (output) neurons were part of the reticulospinal tract, which sends axons to the spinal cord, since these neurons exhibited antidromic spikes following stimulation of the ventrolateral funiculus of the spinal cord. Unit spikes were evoked by stimulation either to the sural or superficial radial nerves. These neurons were located in the ventrocaudal part of the medial bulbar reticular formation. (3) Type III neurons included relay neurons. Unit spikes were evoked by stimulation of the sural nerve, superficial radial nerve and sensorimotor cortex. However, unit discharges were not obtained by antidromic stimulation to the reticulospinal tract. These neurons were distributed widely in the brain stem, both in the bulb and pons. (4) Latency difference of unit discharges between input and output neurons was 3.5–5 msec, indicating the presence of interneurons (relays) between input and output neurons. Spikes of output neurons with 3.8–4.2 msec latency were observed following stimulation of the region where input neuron activity was found. We may conclude that three kinds of reticular neurons, input, relay and output, were involved in pathways of the SBS reflex.

Excitatory effects of TRH on medullary reticular neurones

Thyrotropin releasing hormone (TRH) was applied iontophoretically to single neurones in the rat bulbar reticular formation. TRH excited 41 to 56 cells tested; none were inhibited. Excitation developed slowly and was prolonged, and desensitization often occurred. TRH effects were not correlated with effects of acetylcholine, noradrenaline, dopamine or serotonin on the same cells. Atropine applied to cells affected by both acetylcholine and TRH did not affect TRH responses although the acetylcholine actions were blocked. The results support a transmitter role for TRH in this brain area and may explain certain arousal effects of TRH mediated via the reticular formation.

Reticulospinal tracts involved in the spino-bulbo-spinal reflex in cats

Twenty-three chloralosed cats were used to examine the spinal descending pathways of the spino-bulbo-spinal (SBS) reflex. Transection of the ventrolateral funiculus in the spinal cord at the thoracic level abolished the SBS reflex of caudal spinal segments ipsilateral to the transection, but did not abolish the ascending propriospinal reflex and SBS reflex of rostral segments. Unit discharges elicited in axons of the ventrolateral funiculus at L 3 by sural nerve stimulation had the appropriate latency for mediating the SBS reflex. These axons originated in the medial bulbar reticular formation, since the responses had a consistent short latency and followed repetitive stimulation of the bulbar reticular formation (up to a rate of 300 Hz). Conduction velocities of reticulospinal axons ranged widely from 20 to 120 m/sec. There were two peaks, fast (95 m/sec) and slow (35 m/sec). The fast conducting fibers showed oligo-spikes, high amplitude and wide distribution of latency. Almost 90% of the axons with slow conduction exhibited multi-spikes, low amplitude and narrow distribution. Unitary responses of the ventral rootlet at L 7 were elicited by sural nerve stimulation and correlated with the latency of the SBS reflex. The unitary response was also evoked by train pulse stimulation of the ventrolateral funiculus in the spinal cord. Conduction velocities of descending spinal tracts ranged from 20 to 60 ( mean±S.D., 35 ± 8) m/sec. We may conclude that the descending spinal pathway of the SBS reflex is the slowly conducting reticulospinal tract which originates in the medial bulbar reticular formation and passes through the ventrolateral funiculus of the spinal cord.

Profound hypotension and abolition of the vasomotor component of the cerebral ischemic response produced by restricted lesions of medulla oblongata in rabbit. Relationship to the so-called tonic vasomotor center.

SUMMARY We studied the effect of bilateral electrolytic lesions in the medulla oblongata on the cerebral ischemic reflex in 24 anesthetized rabbits. In IS animals lesions were placed in areas from which the differentiated vasomotor component of the response was elicited by electrical stimulation. In four rabbits (group A) the lesions entirely abolished the vasomotor, but not cardiac responses to cerebral ischemia, and resulted in an irreversible fall, to 30-40 mm Hg, of the arterial pressure (AP). These lesions destroyed large portions of the nucleus reticularis parvocellularis, the dorsal part of the nucleus reticularis gigantocellularis, and the ventromedial portion of the medial vestibular nuclei at the level of the inferior olive (3 mm rostral to the obex). In four other rabbits (group B) the pressor response was reduced to 25-87% of control with a fall of AP not as marked as that in group A. These lesions were within the same areas or very close to those of group A but smaller. In the remaining seven rabbits (group C) the lesions did not alter the ischemic response or AP; they were either restricted to the nucleus reticularis gigantocellularis alone, were smaller than in group B, or if large, were located several millimeters more rostral to those of group A. In nine control rabbits lesions placed elsewhere in the medulla failed to alter the ischemic response or resting AP. We conclude that the vasomotor, but not the cardiac or respiratory, components of the cerebral ischemic response depend upon a restricted portion of the bulbar reticular formation. Moreover, the integrity of this region is essential for maintenance of normal resting levels of AP and, hence, appears to function as the so-called tonic vasomotor center of the brainstem. Ore Res 44: 63-70, 1979

The nucleus reticularis paragigantocellularis as a site of analgesic action of morphine and enkephalin

In a number of studies employing inlracerebral microinjection techniques, it has been pointed out that the site for the anlinociceptive action of morphine in the brain stem may be localized in the hypothalamus, the periaqueductal gray matter (PAG), the floor of the fourth ventricle (see Yaksh and Rudy’) and the raphe magnus’. It is becoming increasingly evident that the bulbar reticular formation consisting of the nucleus reticularis gigantocellularis (NRGC) and nucleus reticularis paragigantocellularis (NRPG), located ilrmediately ventral to the NRGC, are the most important sites for the production of andgesia by morphine and enkephalins. This hypothesis is supported by the following findings.

An autoradiographic analysis of the efferent connections from premotor and adjacent prefrontal regions (areas 6 and 9) in macaca fascicularis.

The efferent connections from area 6 and adjacent regions of area 9 were investigated in 9 adult monkeys (Macaca fascicularis) using the autoradiographic technique. Injection fields throughout these regions projected ipsilaterally to area 7 in the parietal lobe, n. caudatus, claustrum, n. ventralis anterior, n. parafascicularis, n. medialis dorsalis, n. reticularis thalami, colliculus superior, griseum centralis, griseum pontis and n. reticularis tegmenti pontis. The dorsolateral and medial aspects of areas 6 and 9 projected to the caudal cingulate gyrus, n. ventralis lateralis pars caudalis and n. interstitialis of Cajal. Axons originating in the ventrolateral cortex of areas 6 and 9 terminated in the orbital cortex. Projections arising from area 6 were traced to area 4, into the ventral bank of the rostral cingulate sulcus, to putamen, n. centralis superior lateralis, area X and its caudal continuation within n. ventralis posterior lateralis pars oralis, to n. ruber pars parvocellularis as well as the bulbar reticular formation. Adjacent prefrontal areas projected to the medial aspect of area 24, to areas 19, 20, 21 and 49/27 and to parts of the lateral thalamic nuclear group. This prefrontal projection pattern was in many respects also seen in cases injected into the dorsolateral portion of area 6, while its medial and ventrolateral subdivisions showed additional projections to n. ventralis medialis, the medial parts of centrum medianum as well as spinal and prorhinal projections, respectively.Furthermore, extensive bilateral connections were found within the frontal lobe, to basal ganglia, n. parafascicularis, n. centralis thalami, n. ruber, griseum pontis, n. reticularis tegmenti pontis, bulbar reticular formation and, more selectively, to colliculus superior and n. medialis dorsalis. Evidence was also presented for direct prefrontal connections to amygdala and corticonigral projections arising from areas 6 and 9. The results are discussed with respect to the intermediate position of area 6 between primary motor and prefrontal cortex as well as to differences of projection patterns within area 6 itself and, in particular, the supplementary motor area.

Functional Correlation between the Reflexogenic Afferent Pathways from the Upper and Lower Airways

In order to elucidate the relationship of respiratory neurons in the lateral part of the bulbar reticular formation to reflexogenic afferent inputs, responses of respiratory neurons to afferent stimulation of the vagus and internal branches of the superior laryngeal nerves were investigated under controlling evoked potentials of both nerves. Besides the respiratory neurons (type 1, 101 neurons in cats, 130 in rabbits), the unitary discharge pattern of which was changed by afferent stimulation, the other neurons (type 2=input respiratory neuron, 55 neurons in cats, 32 in rabbits) responded to afferent nerve stimulation with single orthodromic spike with latency ranging from 1.9 to 19 msec in cats, and 1.4 to 7.0 msec in rabbits. Three subtypes of input respiratory neurons could be differentiated with respect to their relation to the afferent pathways: neuron driven by vagal stimulation: one activated by stimulation given to another nerve; and cell which receives synaptic inputs mediated mainly by the Aα-γ fiber groups of both nerves. A striking difference in the proportion of the 3 subtypes between the two species was noted. The input respiratory neurons responded also to the adequate stimulus respectively, e. g., to lung inflation and/or to mechanical stimulation to the laryngeal mucosa. The specific neuronal organization found in the input respiratory neuron population may play an important role in the central integrative process in the brain stem for the reflexogenic afferent inputs of various modalities originating in the upper and lower airways.

Reticular activity and intracranial pressure. Acute and chronic intracranial hypertension (author's transl)

Modifications of mesencephalic and bulbar reticular formation activity were studied with microelectrodes during acute and chronic intracranial hypertension. In both cases, the mesencephalic reticular activity increased progressively until a pressure level of 70 to 90 cm of CSF was reached and then fell irreversibly to less than the base value. The bulbar reticular activity followed the same pattern but more slowly. Different hypotheses are advanced to explain these modifications and their meanings.

Temporal and spatial parameters of excitation and afferent inhibition in cuneothalamic relay neurons

ArticlesTemporal and spatial parameters of excitation and afferent inhibition in cuneothalamic relay neuronsW. Janig, T. Schoultz, and W. A. SpencerW. Janig, T. Schoultz, and W. A. SpencerPublished Online:01 Jul 1977https://doi.org/10.1152/jn.1977.40.4.822MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByResponse Properties of Neurons in Primary Somatosensory Cortex of Owl Monkeys Reflect Widespread Spatiotemporal IntegrationJamie L. Reed, Hui-Xin Qi, Zhiyi Zhou, Melanie R. Bernard, Mark J. Burish, A. B. Bonds, and Jon H. Kaas1 April 2010 | Journal of Neurophysiology, Vol. 103, No. 4Processing of Vibrotactile Inputs From Hairy Skin by Neurons of the Dorsal Column Nuclei in the CatV. Sahai, D. A. Mahns, L. Robinson, N. M. Perkins, G. T. Coleman, and M. J. Rowe1 March 2006 | Journal of Neurophysiology, Vol. 95, No. 3Spinal sensorimotor systems and their supraspinal controlNeuroscience Research, Vol. 7, No. 4Gamma-aminobutyric acid and afferent inhibition in the cat and rat ventrobasal thalamusNeuroscience, Vol. 28, No. 1Response characteristics of tooth pulp-driven postsynaptic neurons in the spinal trigeminal subnucleus interpolaris of the cat: comparison with primary afferent fiber, subnucleus caudalis, reflex, and sensory responsesBrain Research, Vol. 422, No. 2Characteristics of periodontal mechanosensitive neurons in the first somatosensory cortex of the catBrain Research, Vol. 409, No. 1Inhibition of jaw-closing muscle activity by tactile air-jet stimulation of peri- and intra-oral sites in manArchives of Oral Biology, Vol. 31, No. 5Diencephalic mechanisms of pain sensationBrain Research Reviews, Vol. 9, No. 3Mechanoreceptive submodality channel interactions: Psychophysical observations on differential activation of flutter and vibrationBrain Research, Vol. 327, No. 1-2Mechanoreceptive submodality channel interactions: single unit analysis of afferent inhibition in the primary somatosensory cortex of the catBrain Research, Vol. 327, No. 1-2Interhemispheric transfer of voluntary motor commands in manElectroencephalography and Clinical Neurophysiology, Vol. 57, No. 5Natural cutaneous stimulation induces late and long-lasting facilitation of extensor motoneurons in the catBrain Research, Vol. 293, No. 2Parallel processing of somatosensory information: A theoryBrain Research Reviews, Vol. 6, No. 1Facilitatory interaction between cutaneous afferents from low threshold mechanoreceptors and nociceptors in segmental reflex pathways to α-motoneuronsBrain Research, Vol. 260, No. 1Mesencephalic and bulbar reticular formation influences on somatosensory transmission through the thalamusElectroencephalography and Clinical Neurophysiology, Vol. 53, No. 3Afferent inhibition on various types of cat's cuneate neurons induced by dynamic and steady tactile stimuliBrain Research, Vol. 221, No. 2Properties of velocity-mechanosensitive neurons of the cat ventrobasal thalamic nucleus with special reference to the concept of convergenceBrain Research, Vol. 209, No. 2Spatio-temporal patterns of pre- and postsynaptic inhibition induced by primary afferent activation in the trigeminal sensory nucleus in cats1 September 1980 | Experimental Brain Research, Vol. 40, No. 2Frequency following and conduction speed as identifiers of major subsets among cuneothalamic neuronsExperimental Neurology, Vol. 64, No. 1 More from this issue > Volume 40Issue 4July 1977Pages 822-835 Copyright & PermissionsCopyright © 1977 the American Physiological Societyhttps://doi.org/10.1152/jn.1977.40.4.822PubMed196055History Published online 1 July 1977 Published in print 1 July 1977 Metrics

Excitatory responses of neurones in rat bulbar reticular formation to bulbar raphe stimulation and to iontophoretically applied 5-hydroxytryptamine, and their blockade by LSD 25.

1. The micro-iontophoretic technique has been used to study the responses of single neurones in the bulbar reticular formation to 5-hydroxytryptamine and to noradrenaline, ACh or glutamate, and to compare these with the responses to electrical stimulation in or near the bulbar raphe nuclei. 2. In the bulbar reticular formation, most neurones were excited by 5-hydroxytryptamine; forty-three of fifty-one neurones excited by 5-hydroxytryptamine were also excited by stimulation in nucleus raphe magnus, nucleus raphe pallidus or nucleus raphe obscurus. Most of these stimulation-induced excitations were of long latency: LSD reduced six of seven of these excitations tested, while 5-hydroxytryptamine excitations were blocked on all seven. 3. In contrast, stimulation of areas adjacent to the raphe nuclei excited only fifteen of forty-six neurones excited by 5-hydroxytryptamine. Most of these stimulation effects were of short latency and none of the three tested were reduced by LSD, although 5-hydroxytryptamine excitations were blocked. 4. The relationship of the long-latency excitatory effects of stimulation with the position of the stimulating electrode in the raphe nuclei indicates that these effects are probably mediated via the raphe neurones and this is supported by the correlation of the effects of raphe stimulation with the effects of 5-hydroxytryptamine applied iontophoretically and by the ability of LSD to block both effects. 5. The results provide a physiological basis for the excitatory effects of iontophoretically applied 5-hydroxytryptamine in the bulbar reticular formation.

Differential effect of morphine on trigeminal nucleus versus reticular aversive stimulation: Independence of negative effects from stimulation parameters

Electrodes were implanted in mesencephalic, pontine, and bulbar reticularformation, and in spinal trigeminal nucleus and tract of rats. Central and peripheral aversive response thresholds were studied under normal conditions and with morphine. Peripherally elicited aversive reactions were assessed with tail-flick, hot-plate, and footshock responses. Centrally elicited aversive reaction thresholds were in all cases based on unconditioned behavioral distress signs (non-stereotyped, escape-like movements, vocalization, freezing, excretion, etc.) and confirmed in some cases with avoidance learning. Morphine (10 mg/kg) elevated the unconditioned aversive reaction threshold for brain stimulation in the trigeminal complex and for peripheral aversive stimulation, but failed to affect the thresholds for reticular brain stimulation. The failure to affect reticular thresholds was independent of stimulation frequency. Thresholds for 5 and 200 Hz sinusoidal stimulation were both unaffected as were previously reported thresholds with 333 Hz pulsatile stimulation. Trigeminal nucleus and tract stimulation were affected in similar degrees. The data were discussed as supporting descending inhibitory models of opiate analgesia.

Possible inhibitory neurons in the bulbar reticular formation involved in the cortically evoked inhibition of the masseteric motoneuron of the cat

Possible inhibitory neurons in the bulbar reticular formation involved in the cortically evoked inhibition of the masseteric motoneuron of the cat

Peripheral nerve input and neuronal response in the medial bulbar reticular formation

Peripheral nerve input and neuronal response in the medial bulbar reticular formation

Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Efferent discharges in intercostal nerves and activity of reticulospinal fibres during stimulation of the brain stem reticular formation, intercostal splanchnic nerves were recorded in cats anesthetized with chloralose (50 mg/kg). It is found that the structures involved in the transmission of spino-bulbo-spinal activity are located in the medial bulbar and pontine reticular formation as well as in its lateral regions. The structures producing long-lasting (300-800 ms) inhibition of spino-bulbo-spinal reflexes are also wide distributed in the brain stem, especially in the pontine region. Recording of activity of single reticulospinal fibres in the ventral (conduction velocity 16-120 m/s) and lateral (17-100 m/s) funiculi during spino-bulbo-spinal reflexes showed that both medial and lateral reticulospinal tracts may be involved into this reflex mechanism. New evidence is obtained that the inhibition of spino-bulbo-spinal reflexes may be located at supraspinal level.