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Results for “Reticular Formation”

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PubMed1990

Convergence of heterotopic nociceptive information onto neurons of caudal medullary reticular formation in monkey (Macaca fascicularis).

1. Recordings were made in anesthetized monkeys from neurons in the medullary reticular formation (MRF) caudal to the obex. Responses of 19 MRF neurons to mechanical, thermal, and/or electrical stimulation were examined. MRF neurons exhibited convergence of nociceptive cutaneous inputs from widespread areas of the body and face. 2. MRF neurons exhibited low levels of background activity. Background activity increased after periods of intense cutaneous mechanical or thermal stimulation. Nearly all MRF neurons tested failed to respond to heterosensory stimuli (flashes, whistle sounds), and none responded to joint movements. 3. MRF neurons were excited by and encoded the intensity of noxious mechanical stimulation. Responses to stimuli on contralateral limbs were greater than those to stimuli on ipsilateral limbs. Responses were greater to stimuli on the forelimbs than to stimuli on the hindlimbs. 4. MRF neurons responded to noxious thermal stimulation (51 degrees C) of widespread areas of the body. Mean responses from stimulation at different locations were generally parallel to those for noxious mechanical stimulation. Responses increased with intensity of noxious thermal stimulation (45-50 degrees C). 5. MRF neurons responded with one or two peaks of activation to percutaneous electrical stimulation applied to the limbs, the face, or the tail. The differences in latency of responses to stimulating two locations along the tail suggested that activity was elicited by activation of peripheral fibers with a mean conduction velocity in the A delta range. Stimulation of the contralateral hindlimb elicited greater responses, with lower thresholds and shorter latencies, than did stimulation of the ipsilateral hindlimb. 6. Electrophysiological properties of monkey MRF neurons resembled those of neurons in the medullary subnucleus reticularis dorsalis (SRD) in the rat. Neurons in the caudal medullary reticular formation could play a role in processing nociceptive information. Convergence of nociceptive cutaneous input from widespread areas of the body suggests that MRF neurons may contribute to autonomic, affective, attentional, and/or sensory-motor processes related to pain.

Action Potentials↗

PubMed1983

The possible role of opiates in habituation of responses recorded in the reticular formation of the frog, to peripheral stimulation.

Repeated stimulation can lead to a decrement in the amplitude of a response, or its disappearance. This is known as habituation. Responses recorded in the reticular formation of the brain to peripherally applied stimuli tend to habituate. Decerebration considerably reduces the occurrence of this habituation and naloxone reverses the effect. In decerebrate animals in which such responses rarely habituate, habituation can be induced by administration of D-Ala2,Met5-enkephalinamide and then reversed by a subsequent administration of naloxone. This would suggest that opiates are involved in habituation of responses recorded in the reticular formation of the frog.

Animals↗

PubMed1998

Tectal projections to the parvicellular reticular formation and the upper cervical spinal cord in the rat, with special reference to axon collateral innervation.

After Phaseolus vulgaris leucoagglutinin injection into the lateral part of the superior colliculus (SC) in the rat, labeled fibers and axon terminals in the lower brainstem were distributed not only in the medial reticular formation but also in the lateral tegmental field including the parvicellular reticular formation (RFp). More caudally, in the upper cervical spinal cord labeled fibers with bouton-like varicosities were distributed mainly in laminae V, VII and VIII, with relatively sparse distribution in lamina IX. These labeled axons were found bilaterally with a clear-cut contralateral dominance. After combined injections of rhodamine-dextranamine, Fluoro-ruby (FR) into the RFp and Fluoro-gold (FG) into the upper cervical spinal cord on the same side, SC neurons labeled with FR were intermingled with those labeled with FG in the lateral part of the SC contralateral to the injection sites. In the stratum griseum intermediale, some of them were double-labeled with both tracers. Our results suggest that SC neurons innervating both the RFp and the cervical spinal cord may be involved in the coordination of head and mouth movements.

Animals↗

PubMed1976

[Morpho-histochemical investigations about the connection of the mesencephalic reticular formation (Area cuneiformis) to the subcortical structures of the visual system (author's transl)].

There was investigated the connection of the mesencephalic reticular formation (Area cuneiformis) with subcortical structures of the visual system. After coagulation of the reticular formation we studied the connections by degeneration and enzymhistochemistric methods. Terminal degeneration in different intensity was observed in the ventral part of the lateral geniculate in the nucleus lateralis posterior, the pretectal region and in the lower laminae (IV ... VII) of the superior colliculus. The findings are mainly ipsilateral. A direct projection to the dorsal part of the lateral geniculate could not be observed. By enzymhistochemic methods we localized the AchE intracellular in the rostral part of the area cuneiformis. After destruction of this area there was observed a clear diminishing of the AchE activity in the ventral lateral geniculate and in the area pretectalis. These results were confirmed by biochemical methods.

Acetylcholinesterase↗

PubMed1986

[The role of brain-stem vasomotor centers on the neurogenic control of cerebrovascular tonus. Part 2: The effect of stimulation of the medullary reticular formation on cerebrovascular tonus].

Acute brain swelling has been proposed to be caused by vasomotor paralysis secondary to disruption of metabolic and/or neurogenic control of cerebrovascular tone. In previous experiments, acute brain swelling was produced by stimulation of the reticular formation of the medulla oblongata (MORF) with destruction of the dorsomedial nucleus of the hypothalamus (DM) and the reticular formation of the midbrain (MBRF) in 2 (out of 56) animals. The purpose of the present study is to clarify the effect of stimulation of the MORF on cerebrovascular tone. Using 32 cats, blood pressure (BP), intracranial pressure (ICP) and cerebral blood volume (CBV) were continuously measured. The animals were divided into 4 groups: those in which the ICP was normal (Group A), those in which the ICP increased after subarachnoid hemorrhage (Group B), those which underwent superior cervical ganglionectomy (Group C) and those in which the spinal cord was transected at the C2 level (Group D). In all animals, the MORF was stimulated after the DM and MBRF were destroyed. Thirty minutes after cessation of stimulation, the BP was increased again by injection of angiotensin II until it reached the same level as with MORF stimulation. The vasomotor index (VI), defined by delta ICP/delta BP, was calculated and compared between the two situations. BP, ICP and CBV increased simultaneously immediately after MORF stimulation. In 29 out of the 32 animals, ICP increased abruptly from 2 to 48 mmHg and after ten seconds or more decreased gradually. The BP rose about 50 mmHg more slowly than the ICP. After cessation of MORF stimulation, BP, ICP and CBV returned to the control value.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1975

Regulation of unit activity in nucleus reticularis thalami by the mesencephalic reticular formation and the frontal granular cortex.

Recruiting responses and related synchronous activities appear to be mediated by thalamic inhibition originating in nucleus reticularis thalami, a structure jointly regulated by an ascending projection from mesencephalic reticular formation and a descending influence from the frontal cortex. Extracellular unit activity was recorded in the anterior nucleus reticularis thalami (RVA) during recruiting responses, augmenting responses, stimulation of the mesencephalic reticular formation (MRF), and cryogenic blockade of the inferior thalamic peduncle (ITP). During recruiting responses, RVA units responded to medial thalamic (MT) stimulation with prolonged high frequency bursts. Analysis of the post-stimulus time histograms of these responses showed tham to have the same latency, duration, incrementing character, and envelope shape as the phasic thalamic inhibitory postsynaptic potentials (IPSPs) which appear to mediate recruiting responses. Brief stimulation of the MRF, which abolishes recruiting responses and thalamic IPSPs, prevented the response of RVA units to MT stimuli, and inhibited the spontaneous discharge of these units for 20 sec or more. We propose that the desynchronizing effect of MRF activation results from the abolition of thalamic inhibition originating in RVA. Cryogenic blockade of the ITP, which abolishes recruiting responses in the thalamus and cortex, also prevented R units from responding to MT stimuli. This result suggests that the MT activates R units via a thalamo-frontocortico-R pathway and explains the long latency of R bursts and thalamic IPSPs following MT stimulation. R cells that fired prolonged bursts during recruiting responses did not respond during augmenting responses. This result suggests that separate thalamic inhibitory mechanisms are involved in these two types of synchronization.

Animals↗

PubMed1991

The effect of procaine injection into the medullary reticular formation on forelimb muscle activity evoked by mesencephalic locomotor region and vestibular stimulation in the decerebrated guinea-pig.

The effect of procaine microinjection into the ventromedial portion of the medullary reticular formation on forelimb muscle activity evoked by electrical mesencephalic locomotor region and natural vestibular stimulation has been investigated in the decerebrated guinea-pig. This injection is followed by a reversible increase of the threshold of mesencephalic locomotor region stimulation necessary for the activation of muscle rhythmic activity. Procaine injection is accompanied by reduction of vestibular influence on flexor muscle activity evoked by electrical cutaneous and mesencephalic locomotor region stimulation. Vestibular influence on extensor muscle activity remains unchanged after the injection. The results indicate that medial medullary reticular formation is the site of the convergence of mesencephalic locomotor region and vestibular activity. It is suggested that the vestibular system contributes to the modulation of reticulospinal activity coupled with the initiation and control of locomotion.

Animals↗

PubMedDate not supplied

[Dependence of the spectrum of electrical activity of the neocortex and hippocampus in rabbits on the intensity of the stimulation of the midbrain reticular formation].

Study of dominating spectral maxima in delta-, theta- and alpha-ranges of the electrical activity of rabbits' neocortex and hippocampus showed that an increase of the frequency of the mesencephalic reticular formation stimulation from 60 to 200 imp/s led in both structures to an enhancement of the theta-rhythm (up to 130% in the neocortex and 147% in the hippocampus) and suppression of delta- and alpha-activity (correspondingly up to 67 and 34% in the neocortex and 37 and 48% in the hippocampus) with subsequent weakening of this effect at frequency increase up to 1000 imp/s. In the hippocampus, the reticular stimulation was more effective with respect to the theta- and delta-rhythms, and in the neocortex--with respect to the alpha-rhythm. In both structures the theta-rhythm amplitude changed less than the amplitude of the delta- and alpha-activities. Dependence of the amplitude of dominating rhythms on intensity of reticular formation stimulation differed from the analogous frequency dependence of the same rhythms.

Animals↗

PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary reticular formation of the cat: a quantitative retrograde tracing study.

Dextran-amines were used as retrograde tracers to investigate the organization of cortical projections to different cytoarchitectonic regions of the pontomedullary reticular formation of the cat. Injections into the nucleus reticularis pontis oralis resulted in labelling of neurones in the proreus cortex and area 6a beta of the premotor cortex, with little labelling in the motor cortex (area 4). This labelling was predominantly ipsilateral to the injection site. In contrast, injections into the nucleus reticularis pontis caudalis (NRPc), nucleus reticularis gigantocellularis (NRGc), and nucleus reticularis magnocellularis (NRMc) resulted in bilateral labelling--primarily in areas 6a beta, 6a gamma, and in the rostromedial region of area 4--with little labelling in the proreus cortex. In general, the cortical projections to the caudal NRGc and the NRMc were larger than those to the NRPc. More than 25% of the total projections to each of the latter three reticular regions arose from the medial part of area 4. Labelling in the hindlimb regions of area 4 was largest following the NRMc injections and smallest after injections in the NRPc. The projections to the NRPc originated from more medial parts of areas 4 and 6 than did the projections to the caudal region of the NRGc. These results suggest that areas 4 and 6 may be able to differentially activate different regions of the pontomedullary reticular formation depending on the movement that is made and perhaps also on the context of that movement.

Animals↗

PubMed2000

Effects of cholinomimetic injection into the brain stem reticular formation on halothane anesthesia and antinociception in rats.

The brain stem reticular formation plays an important role in determining consciousness and arousal. Modulation of cholinergic neurotransmission in this region alters the sleep-wake cycle. In the present study, we examined the effect of the direct application of cholinergic agents into the pontine reticular nucleus on anesthetic requirements and recovery and antinociception in rats. Sprague-Dawley rats were implanted with 24-gauge guide cannulas 1.0 mm above the oral portion of pontine reticular nucleus (PnO) while under pentobarbital anesthesia with the use of a stereotaxic apparatus. After recovery from surgery, animals were randomly assigned to one of the following protocols: minimum alveolar concentration (MAC), recovery time, tail-flick latency, or motor blockade. All measurements were performed after carbachol microinjection into the PnO after pretreatment with atropine or mecamylamine. Carbachol injection into the PnO significantly reduced MAC of halothane and prolonged recovery in a dose-dependent manner. Pretreatment with atropine reversed MAC reduction by carbachol, and both atropine and mecamylamine shortened recovery time under carbachol. In unanesthetized rats, carbachol produced antinociceptive effects as reflected by a change in tail-flick latency response. Atropine and mecamylamine inhibited antinociceptive effects of carbachol. These results suggest that cholinomimetic injection into the PnO modulates the anesthetic state produced by halothane, suggesting participation of this area in the mechanisms in the brain that generate the anesthetic state.

Analgesia↗

PubMed1997

Effects of stimulating the reticular formation during fictive locomotion in lampreys.

The effects of stimulating the reticular formation were studied during fictive locomotion in lampreys (Ichthyomyzon unicuspis). The in vitro isolated preparation of the brainstem and spinal cord was used and fictive locomotion was induced by bath application of N-methyl-D-aspartate (NMDA; 50-100 microM). During different phases of the locomotor cycle, short trains of stimuli (10 pulses at 80-100 Hz; 10 microA) were delivered through glass-coated tungsten microelectrodes positioned within the middle rhombencephalic reticular nucleus (MRRN) and their effects were studied on ipsi- and contralateral ventral root locomotor discharges. Irrespective of the locomotor phase during which the stimulation train was delivered, a resetting effect occurred. It was characterized by a re-synchronization of the locomotor discharges with a constant latency for each ventral root on the ipsilateral side. The latency increased as the recorded root was located further caudally. This increase in latency was in the range of the phase lag observed between roots during control bouts of locomotion. These results suggest that reticulospinal neurones exert strong resetting effects on spinal locomotor networks. These effects may play a significant role with respect to changes of direction during swimming.

Animals↗

PubMed1981

[Primary role of the midbrain reticular formation in mediating the preventive effects of a UHF electromagnetic field on excitation of emotion-producing centers in the hypothalamus].

A study was made of the role of different structures of the limbico-reticular complex (midbrain reticular formation, dorsal hippocampus and septum) in the mediation of UHF modulated electromagnetic field (frequency 40 MHz, modulation frequency 7 Hz, intensity 30--300 V/M) on the reactions evoked by electrical stimulation of the rabbit ventromedial hypothalamus. It was shown that the effect of UHF field on electrical stimulation of the ventromedial hypothalamus leads to the blockade of the hypertensive reaction in 33% of cases. Destruction of the midbrain reticular formation in the zone located laterally to the central grey matter and above the red nucleus eliminates the blocking effect of the UHF field on the hypothalamic responses.

Animals↗

PubMed1975

[Reticular formation nuclei and bioelectric activity in patients with ischemic brain stem strokes].

The study pertains to new approaches in the study of corrlations between the EEG data and the degree of lesions in the nuclei of the reticular formation in ischemic strokes due to occlusive processes in the vertebrobasillar system. In all cases, because of disorders of vital functions, the authors convened artificial lung ventilation which permitted to prolong the life of the patient and to study the dynamics of the EEG. In 10 lethal cases the brain stem was studied on a series of continuous preparations to determine the degree of lesions in the nuclei of the reticular formation in the pons Varoli and medulla oblongata in ischemic foci. It was not possible to establish significant differences in the indices of bioelectric brain activity in lesions of reticular nuclei of pons Varoli and medulla oblongata. The authors stress the necessitity of reconsidering the existing concepts of a dependence of EEG changed parameters upon the localization of the focus in the brain stem.

Adult↗

PubMed1985

The effects of decerebration and destruction of nucleus raphe magnus, periaqueductal grey matter and brainstem lateral reticular formation on the depression due to surgical trauma of the jaw-opening reflex evoked by tooth-pulp stimulation in the cat.

The effects on the jaw-opening reflex evoked by tooth-pulp stimulation of surgical trauma, decerebration and the destruction of a number of nuclei associated with descending inhibition of trigeminal or spinal neurones have been investigated in the cat. Surgical preparation caused a progressive elevation of the digastric reflex threshold. After decerebration, reflex thresholds remained elevated for 8-11 h before returning to close to pre-surgical control values. Destruction of the nucleus raphe magnus and of the periaqueductal grey matter did not affect the depressed reflex in decerebrate or anaesthetized cats. Variable effects were produced by bilateral ablation of the juxta-raphe reticular formation and destruction of the rostral ipsilateral lateral reticular formation of the brainstem.

Animals↗

PubMedDate not supplied

Participation of the medial reticular formation of the medulla oblongata in the supraspinal control of locomotor and postural activities in the guinea pig.

The influence of microinjections of novocaine (1.5 microliters of a 2% solution) into the ventromedial areas of the reticular formation of the medulla oblongata on the effects of electrical stimulation of the mesencephalic locomotor region, and of adequate stimulation of the vestibular apparatus, was investigated in experiments on decerebrate guinea pigs. It was demonstrated that such injections are accompanied by a reversible increase in the threshold of stimulation of the region indicated, necessary for the initiation of locomotor rhythmicity, as well as by the suppression of vestibular influences on the activity of the flexor muscles of the extremities. The role of the reticular formation of the brainstem in the supraspinal control of posture and locomotion is discussed.

Animals↗

PubMed1988

Interconnections between substantia nigra reticulata and medullary reticular formation.

Injections of wheat germ agglutinin-HRP into the medullary reticular formation (MRf) or the substantia nigra reticulata (SNr) revealed the presence of reciprocating fiber connections between the two areas. Large injections in the MRf demonstrated the existence of labeled neurons in the lateral portions of the SNr. Isolated injections into the parvocellular nuclei of the MRf resulted in the presence of terminal fields in the SNr particularly its lateral portions. Injections in the SNr resulted in the presence of labeled cells in the parvocellular nuclei. The significance of these findings is discussed in terms of oro-facial dyskinesias.

Animals↗

PubMed2006

On the role of the reticular formation in vocal pattern generation.

This review is an attempt to localize the brain region responsible for pattern generation of species-specific vocalizations. A catalogue is set up, listing the criteria considered to be essential for a vocal pattern generator. According to this catalogue, a vocal pattern generator should show vocalization-correlated activity, starting before vocal onset and reflecting specific acoustic features of the vocalization. Artificial activation by electrical or glutamatergic stimulation should produce artificially sounding vocalization. Lesioning is expected to have an inhibitory or deteriorating effect on vocalization. Anatomically, a vocal pattern generator can be assumed to have direct or, at least, oligosynaptic connections with all the motoneuron pools involved in phonation. A survey of the literature reveals that the only area meeting all these criteria is a region, reaching from the parvocellular pontine reticular formation just above the superior olive through the lateral reticular formation around the facial nucleus and nucleus ambiguus down to the caudalmost medulla, including the dorsal and ventral reticular nuclei and nucleus retroambiguus. It is proposed that vocal pattern generation takes place within this whole region.

Action Potentials↗

PubMed1996

Distributed gamma band responses in the brain studied in cortex, reticular formation, hippocampus and cerebellum.

The transient evoked responses of auditory cortex, reticular formation, hippocampus and cerebellar cortex to auditory stimulation have been analysed in the gamma frequency band on cats with chronically implanted electrodes. We found gamma band transient responses consisting of wave packets with 3-4 oscillations in all of the studied brain structures in the first 100 ms of the poststimulus period. The responses were strongly time-locked to the stimulation time point. The observation that the gamma band responses exist simultaneously in various brain structures supports the tentative proposal of our group on the "diffuse gamma response system" of the brain, which seems to be an important, universal operator in brain function. Furthermore, it shows that in search for generalized approaches to brain phenomena it is important to analyse the simultaneous behavior of different brain structures.

Animals↗